Mosquito investigation Wollogorang and Borroloola Dec 95 · The results of the container survey of...

MOSQUITO INVESTIGATION FOR A POSSIBLE AUSTRALIAN ENCEPHALITIS

CASE

WOLLOGORANG AND BORROLOOLA

7 DECEMBER 1995

Brian L. Montgomery and Ross A. Nowland

For more information contact: Department of Health and Community Services Medical Entomology Branch PO Box 40596 Casuarina NT 0811 Telephone: 08 8922 8901 Fax: 08 8922 8820 Email: [email protected]

MOSQUITO INVESTIGATION

FOR A POSSIBLE AUSTRALIAN ENCEPHALITIS CASE

WOLLOGORANG AND BORROLOOLA

7 DECEMBER 1995

Brian L. Montgomery and Ross A. Nowland Medical Entomology Branch

Territory Health Services

2 F:\ENTO\ento_files\public_information\branch_reports\katherine_region\1995_borroloola_wool\Mosquito Investigation Wollogorang & Borroloola.DOC

1.0 INTRODUCTION On 5 December 1995 the Medical Entomology Branch (MEB) of Territory Health Services (THS) was notified by the Disease Control Centre (THS) of the sudden and unexplained death of a pilot who had been working in the Wollogorang area. The clinical symptoms of the deceased were considered to be consistent with a viral illness. The pilot was one of a 6 member geological survey team that had been stationed at Wollogorang homestead between 15-30 November 1995. MEB was informed that the survey team had been withdrawn from the field on the possibility that the cause of death was Australian encephalitis. The deceased had previously been ill on several occasions after swimming in Africa. Wollogorang is a remote homestead situated approximately 225 km south east of Borroloola (Fig. 1) on an unsealed road that connects Borroloola to Hells Gate roadhouse and Burketown across the Queensland border. It is situated approximately 75 km from the coast and on the southern bank of Settlement Creek. The survey team had been operating in Georgetown and near Normanton, Queensland (west of Cairns) prior to operating in the Wollogorang area. On 7 December 1995 two officers of the MEB conducted an investigation of the Wollogorang area in response to the possibility that the cause of death was a mosquito borne virus. Efforts to involve the regional Environmental Health Officers (EHO) were unsuccessful. The confirmed vector of Australian encephalitis is the "common banded mosquito" Culex annulirostris (Mackenzie et al., 1994; Russell, 1995). Aedes normanensis has been identified as a potential vector of Australian encephalitis (Whelan and Weir, 1993). The vector capabilities of other mosquito species is as yet unknown. Several mosquito species including Aedes normanensis, Ae. pseudonormanensis and Cx. annulirostris have adapted to opportunistically utilise flooding of ephemeral habitats. Rainfall records from the Bureau of Meteorology indicated significant rainfall in the area before and during the previous three week period when the deceased was at Wollogorang. High numbers of mosquitoes were recalled by survey team members at Hells Gate, although it was reported that the deceased had seldom left an air conditioned room there or at Wollogorang. Initially the reported habits and movements of the deceased, reports of very few mosquitoes at Wollogorang and the unusual time of the year for Australian encephalitis transmission indicated that the transmission of Australian encephalitis was unlikely. However, the possibility that the deceased had the symptoms of Australian encephalitis indicated a need to investigate the mosquito vector situation in the Wollogorang area. Information provided by the survey team in May 1996 indicated that the exposure of the deceased to mosquitoes was considerably higher than first indicated and vindicated the need to conduct an entomological investigation. This and other relevant information has been included in this revised report. This report is detailed with respect to Aedes larval surveys and adult trapping because this Branch has very limited information on the Wollogorang area and Borroloola is a vulnerable point for the reintroduction of Ae. aegypti into the NT


2.0 MATERIALS AND METHODS 2.1 Ground survey of Borroloola A ground survey of Borroloola was conducted on 7 December 1995 to determine favourable mosquito trap positions for that night. The septic systems at the three Aboriginal camps (Garawa, Rumbarriya and Yanyula) were also inspected with a Borroloola community health worker (Ms Irene Thompson). 2.2 Ground survey of Wollogorang A brief ground survey of the Wollogorang roadhouse was conducted on 8 December 1995. The septics tanks for the roadhouse and tourist accommodation were also inspected. 2.3 Adult mosquito traps Access to Wollogorang was by a chartered plane from Borroloola. One MEB officer set four EVS type carbon dioxide baited mosquito traps (Rohe and Fall, 1979) at Borroloola (Fig. 2). The other MEB officer set a further four traps set at Wollogorang (Fig. 3) late on the afternoon of 7 December 1995. Traps were placed around Borroloola township and Wollogorang roadhouse to intercept potential vectors that may have been dispersing from flooded ephemeral creek lines and ground depressions. Traps were set before dusk and collected after dawn the following morning. 2.4 Container survey of Borroloola and Wollogorang Brief container surveys for mosquito breeding were conducted in Borroloola on 7-8 December 1995 and Wollogorang on 8 December 1995. The purpose of these surveys was to determine the vulnerability of each area to the reintroduction of Ae. aegypti. This species is the vector of Dengue fever and its distribution is currently restricted to Queensland. Containers were categorised using the methodology of Barker-Hudson et al. (1988, see Table 4). The survey methodology was that used previously in MEB surveys (see Hayes, 1992). Due to time restrictions the survey in Borroloola was confined to one residential street selected at random (Horney Street) and several other vulnerable points (e.g., caravan parks and hotel grounds). 2.4 Virus isolation from adult mosquitoes Virus isolation requires the collection of living mosquitoes. Mosquitoes were kept alive after collection in each of the trap containers by the use of wetted strips of "Wettex" (an absorbent material) stapled to the wall. The trap containers were wrapped in damp towels and the "Wettex" re-wetted to maintain a high humidity and enhance the survival of adults. Mosquitoes were then transported to the Darwin MEB laboratory for processing prior to virus isolation.


Mosquitoes were identified and counted on a cold table on 9 December 1995. Aliquot's of individual species were stored in liquid nitrogen. Samples were then transferred to the Virology Laboratories of the Department of Primary Industries and Fisheries in Berrimah (Darwin) to undergo virus isolation procedures. 2.5 Water sample from Branch Creek (Qld) To determine if the cause of death was by Naegleria infection, a series of water samples were taken from the waterhole where the deceased was reported to have swum on two occasions. The waterhole was situated in Branch Creek, approximately 15 km east of Wollogorang across the Queensland border. Recent heavy rain had probably significantly increased the size and flushed out the original contents of the water hole. A sample was collected from the site where the deceased most likely swam (Fig. 4), a point approximately 1 km downstream and a point approximately 1 km upstream (immediately upstream of floodway on the highway). Approximately 50 ml of water sample was collected in a sterile specimen jar at each site. Water samples were kept at ambient temperature wherever possible. These jars were transferred to the MEB laboratory and subsequently forwarded by Environmental Health (THS) to Mr Brett Robertson for analysis (State Laboratories, South Australia) because of the small size of sample. 3.0 RESULTS 3.1 Ground surveys Table 1 shows the results of the ground survey for mosquito larvae in Borroloola and Wollogorang. 3.1.1 Borroloola The survey of Borroloola was conducted 2 days after isolated heavy rainfall. Rocky Creek runs through the approximate middle of town and discharges to the McArthur River. The McArthur River flows 500 m to the east of Borroloola and is tidal at this time of year. Ephemeral creek lines and ground depressions were holding water on 7 December 1995. The upper reaches of Rocky Creek to the north west of town were not connected to the McArthur River. The creek margins were clear of vegetation and fish were present. Mosquito larvae were not detected in the creek or an adjacent old borrow pit that was fringed with vegetation (Fig. 5). In the lower reaches of Rocky Creek the substrate is rock, with no fringing vegetation or cut off pools and muddy water (Fig. 6). Very low levels of Culex "Normanton species" mosquito larvae were detected and abundant biological control agents (aquatic beetles and bugs) were observed.


An inspection of the absorption trench at Garawa camp (east side of the McArthur River) indicated that the pit was saturated. The pit supported an extremely luxuriant growth of grass. The lids of the inspection pits had been removed (Fig. 7) and high densities of Cx. annulirostris larvae (all instars) and low levels of Cx. quinquefasciatus larvae (older instars) were present. High levels of Cx. annulirostris larvae (4th instar) and low level of An. amictus larvae were detected in seepage from the absorption trench. The seepage from this pit had flooded roadside drainage in which a moderate level of Cx. annulirostris larvae (second to fourth instar) were also detected. Yanyula aboriginal camp was briefly inspected. There was a large amount of domestic refuse (predominantly discarded aluminium beer cans) that may provide suitable mosquito breeding sites if not collected. There was no evidence of mosquito breeding from the absorption trench. The grounds of the caravan park and tourist accommodation on Robinson Rd were inspected. Ineffective disposal of excess effluent at the caravan park had created a long term breeding site for Cx. annulirostris (all instars) and Cx. quinquefasciatus (older instars) larvae. 3.1.2 Wollogorang Much of the surrounding area, including Settlement Creek (Fig. 8), was dry as the substrate is predominantly sand. The septic tanks at Wollogorang were adequately sealed. However an inspection pit for drainage to the absorption trench was not sealed and may provide mosquitoes access to breeding sites. A low level of An. amictus (fourth instar) was collected from a small flooded ground depression. 3.2 Adult traps 3.2.1 Wollogorang Mosquito numbers at Wollogorang were extremely low (Table 2) with a total of 19 mosquitoes. The most common species was a flood water species Aedes normanensis (56.6 %), followed by Ae. tremulus (15.8 %). The presence of Ae. normanensis and Ae. pseudonormanensis indicated flooding of breeding sites by rainfall in the previous 7-9 days. No mosquitoes were collected in the trap set on the bank of Settlement Creek. 3.2.2 Borroloola Moderate numbers of mosquitoes were trapped at Borroloola (Table 3). A total number of 333 mosquitoes were trapped. The most common species were the "salt marsh mosquito" Ae. vigilax (33.03 %), Cx. annulirostris (26.73 %) and Ae. (Mac) sp. 76 (22.8 %). Anopheles annulipes and Ae. normanensis were in relatively low numbers (8.4 % and 4.5 % respectively). 3.3 Container Survey


The results of the container survey of Borroloola and Wollogorang are summarised in Tables 4 and 5. 3.3.1 Borroloola A total of 9 premises were inspected, of which 5 were breeding mosquitoes (Table 6). A total of 96 containers capable of breeding mosquitoes were recorded. Of the 39 that contained water 7 were found with larvae. There was an average of 6.5 containers per residential premise capable of breeding mosquitoes. Of the 26 potential mosquito breeding receptacles, the most common were water storage containers (38.5 %) and building fixtures and materials (38.5 %). Two species were recorded from the container survey, Cx. quinquefasciatus (86.7 %) and Ae. tremulus (13.3 %). No Ae. aegpyti larvae were detected. Using the container classification of Barker-Hudson et al. (1988) the most common containers for mosquito breeding was categories 2 (water storage containers) and 4 (rubbish) . The majority of breeding (53.2 %) was detected in rubbish (category 4). The larvae in this category were Cx. quinquefasciatus. Mosquito breeding in category 2 (water storage containers) consisted of Cx. quinquefasciatus ( 74.4 %) and Ae. tremulus (25.6 %). 3.3.2 Wollogorang There were relatively few container breeding sites on the grounds of the roadhouse. A total of 15 containers capable of breeding mosquitoes were recorded (Table 7). The 2 potential mosquito breeding receptacles were water storage containers (category 2) and building fixtures and materials (category 7). High levels of Cx. annulirostris (particularly fourth instars) larvae were detected in a tap box (category 7) that was filled with leaf litter and runoff from irrigation. Low levels of An. amictus and Cx. quinquefasciatus larvae (fourth instar) were also in the sample from the tap box. No Ae. aegpyti larvae were detected. The proximity of Wollogorang to the Queensland border and potential increase in tourist traffic make it a potential source of introduction of Ae. aegypti into the Northern Territory. The manager is to be commended on the general lack of water holding containers. 3.4 Discussions with the manager of Wollogorang Roadhouse Mr Paul Zlotkowski provided the following information; 1. There had been significant rain 3 weeks previous to the MEB investigation and significant rainfall during November 1995 (Mr Zlotkowski provided daily rainfall readings for the Bureau of Meteorology).


2. There had been few mosquitoes noticed at Wollogorang after rainfall, although high numbers were reported at Hells Gate (Qld). 3. The deceased had remained in an air conditioned room for the majority of the stay in Hells Gate and Wollogorang, with the exception of 3 hours of flying at Wollogorang each morning. 4. The deceased had swum in a watering hole in Branch Creek (Qld) on approximately 2 occasions. 5. The deceased had left Wollogorang for Mt Isa due to technical problems associated with the geological survey. The pilot had flown the aircraft to South Australia for a routine overhaul before dying. 3.5 Diagnosis of cause of death On 22 December 1995 the MEB was notified by the Disease Control Centre (THS) that the cause of death was amoebic encephalitis. On 24 January 1996 the cause of death was confirmed as consistent with Naegleria fowleri infection. 3.6 Branch Creek water sample analysis MEB was notified by Environmental Health (THS) on 20 March 1996, after follow up enquiries, that the volume of water was inadequate to perform appropriate analysis. 3.7 Virus Isolation from adult mosquitoes All the aliquots of adult mosquitoes collected were negative for virus (7 May 1996). 3.8 Discussion with Survey Team Manager The following information on the habits of the deceased was provided by Mr Andrew Cole (survey team manager) in May 1996 after reading the original report. 1. The survey team had observed a lot of standing water on site, in creeks and near the airstrip. Two sources were identified; the raised water tank 30 m from the rear of the homestead was continually being filled, with large pools of runoff resulting. An unfinished swimming pool opposite the units had contained water for over 6 months. 2. Mosquitoes were noticed daily at Wollogorang by the survey crew, with increased numbers after rainfall. All crew members were exposed to mosquito bites almost daily unless protected by insect repellent, particularly when meals were taken in the outside dining area. 3. The deceased was an outdoor person, an avid astronomer who could always be found outdoors during the early evening and into the night pursuing his hobby. 4. The deceased swam at Branch Creek with at least one other team member on a regular basis, almost every day for long periods.


5. The deceased starting showing symptoms of illness 3 days prior to departure from Wollogorang. Symptoms included headaches, fever and vomiting which the deceased attributed to food poisoning. 6. The pilot flew to Mt Isa (Qld) and returned the same day to Adelaide via a commercial airline (30 November 1995). 7. The employer of the survey team had withdrawn staff from the general area following warnings of the possibility of arbovirus transmission and insisted that all survey team members have blood tested. 4.0 DISCUSSION 4.1 Mosquito species of medical importance The species of medical importance in Borroloola were determined by trap catches and a previous MEB baseline mosquito monitoring report prepared for the McArthur River Mine (Montgomery, 1995). The baseline report included a mosquito trap in Borroloola set once a month over a 12 month period. 4.1.1 Aedes normanensis "A floodwater Aedes mosquito" Aedes normanensis is a significant potential vector of epidemic polyarthritis (Mackenzie et al., 1994; Russell, 1995) and a potential vector of Australian encephalitis and Barmah Forest virus disease (Whelan and Weir, 1993). It can bite in significant numbers during the day in shaded areas and can be a major pest around sundown and for up to two hours after dark. Its persistent biting habits require significant self protection measures from mosquito bites for residents of Borroloola. This species breeds in newly flooded ephemeral ground pools or swampy areas in inland regions following heavy rain (Whelan and Kelton, 1992). During the latter part of the previous wet season the eggs are laid at the receding margins of ground pools. The eggs hatch soon after flooding by the first rains of the wet season. Adults will continue to lay eggs in suitable sites as the wet season continues to produce a peak in adult numbers in March. The highest numbers of Ae. normanensis were trapped at the site in the upper reaches of Rocky Creek at Borroloola. Numbers typically fall dramatically after the cessation of rain (see Montgomery, 1995), indicating that this species primarily exploits ephemeral pools and flooded depressions and does not utilise permanent pooling in the McArthur River or nearby creeks. The presence of Ae. normanensis at Wollogorang and Borroloola indicated that ephemeral creek lines and ground depressions had been flooded 7-9 days previously. The flight over Wollogorang indicated that the majority of Settlement Creek was dry, with the exception of a water hole to the west of the road house. This area was not surveyed due to the time constraints of the investigation. 4.1.2 Aedes vigilax "The salt marsh mosquito"


Aedes vigilax commonly breeds in salt water swamps and temporary pools that are filled by the highest spring tides and after episodes of significant rain (over 25 mm in a 24 hour period; Whelan and Kelton, 1992). Breeding sites may be created when sand dunes or mangrove boundaries have been disturbed so that natural drainage is impeded. Unlike many species of mosquito Ae. vigilax can be a significant pest during the day because it will bite during the day, particularly in shaded areas. The 60 Ae. vigilax trapped at the Borroloola boat ramp would have represented a significant pest problem for unprotected people at this site because of its painful bite and habit of biting during the morning, evening and early hours of the night. The approximate pest threshold for relatively unprotected Darwin residents is 20 Ae. vigilax per trap night. The presence of Ae. vigilax at Borroloola indicated that adults have dispersed from breeding sites in the tidally influenced sections of Mule, Batten and Bing Bong Creeks and McArthur River or other suitable breeding places around the coast. The source of these mosquitoes will be determined by the prevailing wind directions. At sites distant from the coast Ae. vigilax is generally present only in significant numbers for approximately a week after the high tides at the latter stage of the dry season. Aedes vigilax numbers will peak from December to January after spring tides. Adults will appear in C02 baited traps about 9-10 days after the first initiation tide. The threshold tide level for initiating large hatches of this species in coastal areas near Bing Bong (Fig. 1) is approximately the 1.5 m A.C.D. tide mark (Montgomery, 1995). The longevity of adults at this time of year is approximately 1-2 weeks. Aedes vigilax is a potential vector of epidemic polyarthritis (Mackenzie et al., 1994; Russell, 1995). The potential for epidemic polyarthritis transmission for personnel in Borroloola will be highest between December and April when Ae. vigilax numbers are high. 4.1.3 Culex annulirostris "The common banded mosquito" The low numbers of Cx. annulirostris adults recorded in adult traps (and during baseline mosquito monitoring at McArthur River Mine; Montgomery, 1995) indicated that the risk for Australian encephalitis, particularly in Borroloola, was relatively low. As this species bites primarily after sundown, self protection measures can be relatively easily employed to give a good degree of protection against mosquito bites. It is most likely to be prevalent from November to March during dry years and from November to June in the wetter years. Culex annulirostris breeds in open sunlit ground pools, often in association with vegetation such as grasses and semi aquatic sedges and reeds. This species will exploit poorly constructed water storage ponds, poorly cleared areas that contain depressions, and water retention structures that do not drain completely within 4 or 5 days of filling with water. Biological control agents in the McArthur River, Settlement Creek and associated creeks probably keep numbers low in the larger breeding sites once the monsoonal weather stops. The low numbers of Cx. annulirostris adults at Borroloola and Wollogorang indicated a paucity of extensive breeding sites at these locations at the time of the investigation. However, the larval survey located very productive localised sources. The high density of


larvae in a tap box at Wollogorang represented a potentially productive source of this species very near to tourists and residents. This and similar breeding sites near the roadhouse may have been responsible for the perception by the survey team that mosquito numbers were higher than that detected by the monitoring traps which were set away from the roadhouse (Fig. 3). The small but productive breeding site in one of several tap boxes at Wollogorang could be eliminated by keeping all tap boxes clear of leaf litter and ensuring that sprinkler use is rotated at intervals that will minimise the likelihood of water collecting in any given box for more than a week. The high levels of Cx. annulirostris larvae at the Garawa camp and the Borroloola caravan park were the result of artificially created breeding sites. These increase the risk of mosquito borne disease because of their proximity to human habitation. The Borroloola community health worker reported that on occasions polluted water from the Garawa camp absorption trench flooded across the road. Episodes of moderate rainfall are likely to result in flushing highly polluted water into the McArthur River, in contravention of the Public Health Act. 4.1.4 Culex quinquefasciatus "The brown house mosquito" Culex quinquefasciatus is a species associated with human settlement. Larvae are often found in septic tanks, polluted ground water and artificial containers. Breeding sites of Cx. quinquefasciatus may only be productive during, and for the few months following, the wet season. The high incidence of Cx. quinquefasciatus in Borroloola in water holding containers (disused tyres) and items of rubbish could be decreased by a public education program aimed at reducing these potential mosquito breeding containers in yards, particularly around domestic and tourist premises during and after the wet season. Unsealed septic tanks may be providing a perennial reservoir for this species from which they can rapidly exploit additional containers as they become available. The container survey indicated high numbers of mosquito larvae at the Borroloola caravan park which is of concern as this site is a vulnerable point for the introduction of Ae. aegypti into the NT as the result of tourist travel (e.g. drought resistant eggs in pots, tyres) from Queensland. Septic tanks are required to be installed such that they are completely mosquito proof. An inspection of any septic tanks by the regional EHO is recommended when first installed and then on an annual basis to ensure that they remain mosquito proof. 4.1.5 Aedes aegypti "The Dengue mosquito" The vector of Dengue Fever (Ae. aegypti) is no longer present in the Northern Territory (Whelan, 1990). However it has the potential to be imported from Queensland in tyres or other containers that may have held water that are sourced from areas where Ae. aegypti occurs (e.g., Mt Isa, Townsville, Cairns). The high number of potential mosquito breeding containers in Borroloola indicates that this species may quickly become established once introduced. It is therefore recommended that


all large water holding items e.g, old machinery tyres in particular, be either stored under cover, holed or filled with sand or soil to prevent the retention of rainwater. 4.1.6 Aedes tremulus "A container breeding Aedes mosquito" The natural breeding places of this species are holes in trees and stumps, especially narrow holes in eucalypts, paperbarks and mangroves that have been filled with rain water. However it is often found in artificial containers such as tins, tyres and pot plant bases that have been filled by rain or artificially flooded and therefore can act as an indicator of potential Ae. aegpyti breeding sites. As they do not travel far from their breeding sites high numbers in a trap indicates within the immediate vicinity. This species frequently bite at dawn and the later afternoon. It is not considered a vector of Australian encephalitis. 4.1.7 Anopheles amictus This species breeds in fresh water ground pools and swamp margins, either sunlit or shaded. Often the water is muddy (although usually not polluted) and larvae are sometimes found in running water Lee et al., 1987). The larvae often occur in shallow muddy pools formed by the drying out of larger temporary water bodies at the end of the wet season. They have also been collected in swamp margins, amongst green algae in fresh running water, rock pools, hoof marks at the edge of billabongs and soakage holes in dry river beds (Lee et al., 1987). Adult and larval numbers of An. amictus were low in the current survey. However, numbers previously trapped near the McArthur River, and to a much lesser extent in Borroloola, were shown to increase dramatically at certain times of the year after periods of heavy rainfall (Montgomery 1995). This and other Anopheles species are not considered as vectors of Australian encephalitis. The potential for malaria transmission in Borroloola will be relatively high, particularly in March and April when An. amictus numbers are high. The current potential for malaria transmission is possibly lower than more northern areas of the "Top End" where high numbers of Anopheles are extended over longer periods. 4.1.8 Anopheles annulipes "The common Australian Anopheline" This species breeds in open sunlit ephemeral and perennial fresh water ground pools, often in association with emergent vegetation or algae that offers some protection from aquatic predators. It is also highly responsive to newly created water bodies in earth without vegetation (Lee et al., 1987). It is a potential vector of malaria and can be a minor pest. The numbers of An. annulipes were low at Borroloola but have previously reached high numbers at the McArthur River Mine in April (late wet season) and had secondary peaks in the mid dry season (Montgomery, 1995). As was the case for An. amictus, large peaks in April probably corresponded to the period after when the McArthur River and associated creek banks had flooded and probably begun to recede, leaving large areas of isolated pools where biological control agents had not become established.


Anopheles species do not bite until after dusk and do not tend to fly more than a few kilometres from their breeding sites. As mentioned previously Anopheles species are not regarded as vectors of Australian encephalitis. The relatively low level of An. annulipes at Borroloola and absence from Wollogorang indicated that the potential for malaria transmission near accommodation was relatively low in this area compared with many areas in the "Top End". 4.2 Potential Breeding Sites at Borroloola and Wollogorang 4.2.1 Septic tanks and waste water Septic tanks and waste water from watering or wash down operations have the potential to breed a number of mosquito species including Cx. quinquefasciatus. Septic tanks in particular have an enormous capacity to breed mosquitoes because of the high organic content and the lack of any biological control organisms. All waste water should be correctly collected, stored and disposed of such that it can not breed mosquitoes. Precautionary measures, such as the elimination of containers holding water and the correct sealing of septic tanks, are recommended to minimise breeding sites for Cx. quinquefasciatus. The elevated water tank at Wollogorang identified by the survey team as the source of runoff was not inspected as an access ladder was not available. The observation by the survey team that it overflowed regularly may indicate that the tank itself was not a source of mosquitoes due to regular agitation of the water surface. The unfinished swimming pool at Wollogorang was not detected during the brief larval inspection. The observation by survey team members that it had been full of water for several months indicated that it also may not have been a source of mosquitoes because predators of mosquito larvae tend to exploit these sites. An examination of the aerial photograph taken on 7 December 1995 (Fig. 3) indicated that the pool was dry at the time of inspection and that the pool margins were free of vegetation and therefore unlikely to have provided a productive mosquito breeding site. From the limited inspection of Borroloola there may also be a high probability of other unsealed septic tanks in the township. The regional EHO had previously been notified and indicated that an inspection of Aboriginal community septic systems was conducted in October 1995. 4.2.2 Ephemeral creek lines Rocky Creek, Settlement Creek and other ephemeral creek lines are likely to include significant areas of poorly draining floodways during the wet season that will provide suitable and productive habitats for An. amictus, An. annulipes, Cx. annulirostris and Ae. normanensis. The rainfall episodes from November 1995 would have hatched Ae. normanensis eggs in ephemeral creek lines, flood plains or other depressions that retained water for a period of five days. Any depressions that subsequently retained water for an extended period of time would become breeding sites for Cx. annulirostris. However the presence of biological


control agents (e.g. fish, aquatic beetle and bugs, dragonfly and damselfly nymphs) would serve to dramatically reduce the larval population until the water sources dry out during the dry season. 4.2.3 McArthur River and associated creek lines The McArthur River near Borroloola is under tidal influence during the dry season. Water is retained further upstream in defined and deeper channels in the lower reaches of its tributaries. The lower reaches of these tributaries will continue to breed mosquitoes after the wet season at specific sites of thick marginal vegetation or isolated pools, but at decreasing levels as the dry season progresses. In the early dry season the upper and the lower reaches of the McArthur River and associated creek lines are likely to provide favourable harbouring and resting sites, as well as breeding sites for An. amictus and An. annulipes and to a much lesser extent Cx. annulirostris. This will increase the probability of survival of individual mosquitoes in these sites and these areas will give rise to potentially infected mosquitoes that could infect Borroloola residents. In the mid and late dry season, the river and creeks ares not likely to be contain significant mosquito breeding sites, either because they will be dry or contain only defined pools, with bare margins and numerous aquatic predators of mosquito larvae. Even minor numbers at deeper pools are not likely to cause a significant pest or public health problem for Borroloola residents because of the considerable distance between the persistent pools and the township over the majority of the dry season. 4.3 Assessment of risk of Australian encephalitis An assessment of the risk of Australian encephalitis transmission prior to diagnosis in this case may be inferred from; 4.3.1 The season of Australian encephalitis transmission The season of Australian encephalitis transmission has been established from previous confirmed cases (Whelan and Burrow, 1994). Australian encephalitis occurs in the first half of the year, especially in the months March to May. The peak time of transmission occurs when the major suspect mosquito vector population increases during the later part of the wet season and early dry season. Hence the timing of flooding of mosquito breeding habitats and the breeding patterns of the natural hosts (probably birds) probably accounts for the seasonal incidence of Australian encephalitis (Whelan and Burrow, 1994). The occurrence of this case in November provided circumstantial evidence that the cause of death was not from Australian encephalitis. 4.3.2 Exposure to mosquito bites The risk of Australian encephalitis transmission to humans is also related to the exposure to mosquito bites. Minimising exposure to vector mosquito bites will minimise the risk of virus transmission. Discussions with the Wollogorang manager (Mr Zlotkowski) indicated that the deceased had remained indoors for the majority of time in air conditioned accommodation


and he considered that the numbers of mosquitoes were always low at Wollogorang, despite recent episodes of significant rainfall. Information provided by the survey team however indicated that the deceased spent considerable time outdoors during dusk when mosquito activity would be highest. The survey team considered that exposure to themselves and the deceased was significant. It is not known whether the deceased used insect repellent. The discrepancy in the subjective assessment of the numbers of mosquitoes reported between Mr Zlotkowski and the survey team may be related to the difference in personal habits of the respective parties after dusk, e.g. eating indoors or outdoors. The levels of rainfall reported during November and observations by survey team members of flooded ground depressions was consistent with a probable higher number of flood water species being present prior to this investigation. An additional source of mosquitoes experienced by the survey team may have been from domestic breeding sites situated closer to the roadhouse (e.g. tap boxes). The mosquito traps may not have been detected adults from these sites as the traps were placed at some distance from the roadhouse. The very low number of mosquitoes trapped provided circumstantial evidence that the cause of death was not Australian encephalitis. However the number of Ae. normanensis may also have decreased rapidly a week after the emergence of adults. 4.3.3 Epidemiological details The time of first symptoms and the location and date of probable infection will provide an indication of the likelihood of Australian encephalitis transmission. The date of death was 4 December 1995. Details of the onset of first symptoms were not available at the time of inspection. Subsequent information indicated the onset of symptoms to be 27 November 1995. The location of infection can be based on a 2 week incubation period for MVE, placing the patient at Hells Gate or Wollogorang. The ability of the deceased to pilot an aircraft to Mt Isa 3 days after the onset of symptoms may not be consistent with the rapid onset of the debilitative symptoms characteristic of Australian encephalitis in adults, e.g. high fever, headache, confusion and tremors. The amount of resources invested in conducting a mosquito investigation for possible Australian encephalitis, especially in remote locations, indicate the need to have rapid blood testing, for at least the flavivirus infection group, to be conducted as soon as possible. 5.0 CONCLUSIONS 5.1 Wollogorang 1. The low numbers of adult mosquitoes trapped at Wollogorang indicated that there was a relatively small chance that the cause of death was Australian encephalitis. Observations by the survey team members however indicated that the numbers of mosquitoes were higher in previous weeks. 2. The majority of adult mosquitoes trapped at Wollogorang were Ae. normanensis and indicated that if numbers are high after episodes of significant rain there may be a potential


for Australian encephalitis and epidemic polyarthritis transmission for people not protected from mosquito bites. 3. There were few potential mosquito breeding containers at Wollogorang. The majority of mosquito larvae collected in the container breeding survey were Cx. annulirostris in tap boxes associated with landscape irrigation. 4. The diagnosis of amoebic encephalitis caused by Naegleria fowleri was consistent with the habit of the deceased to frequently swim in Branch Creek. 5.2 Borroloola 1. The majority of adult mosquitoes trapped at Borroloola were Ae. vigilax and Cx. annulirostris. Previous trapping have also recorded Ae. normanensis after significant episodes of rain. These species indicate that there is a potential for Australian encephalitis and epidemic polyarthritis transmission for people not protected from mosquito bites. 2. The majority of mosquito larvae collected in the ground survey of Borroloola were Cx. annulirostris associated with an absorption trench at the Garawa Aboriginal camp and a sewage system in a caravan park. 3. Rectification of the absorption trench at the Garawa camp should be investigated as it is creating mosquito breeding sites and probably periodically polluting the McArthur River. 4. The majority of mosquito larvae collected in the container breeding survey of Borroloola were Cx. quinquefasciatus in disused tyres. 5. The high proportion of residential areas in Borroloola with containers breeding or capable of breeding mosquitoes indicated that Borroloola is vulnerable to the reintroduction of Ae. aegypti, especially after rainfall. The results of the limited survey and the general impression derived by a drive through the residential areas indicated that many properties had a high number of containers in the yards that would be potential mosquito breeding sites. 6. The awareness of the potential impact of mosquitoes on public health was increased by distributing information pamphlets on epidemic polyarthritis, dengue fever and Australian encephalitis to Wollogorang management and the Borroloola Community Health Centre and the Borroloola General Practitioner. 6.0 RECOMMENDATIONS 1. The regional EHO has been notified of the probable high proportion of unsealed septic tanks in the Borroloola township. There should be a survey of all septics in the Borroloola area and action taken to have facilities repaired. 2. The appropriate authority should investigate rectification of the Garawa camp absorption trench to remove a significant mosquito breeding site.


3. A more focussed local awareness effort by a radio or television media campaign may be needed to create an awareness in the public of container breeding mosquitoes as there is no local newspaper in the Borroloola area circulation at present. 4. There should be a procedure in place for future suspected Australian encephalitis cases for at least group tests for flavivirus to be done as soon as possible. 7.0 ACKNOWLEDGMENTS The authors gratefully acknowledge Peter Whelan (Director of MEB) for guidance and comments on this investigation. Ms Gwenda Hayes assisted in the identification and preparation of specimens for virus isolation. A special thank you to the Borroloola Community Health Clinic staff for their cooperation at short notice. Sister Helen Collinson provided use of a vehicle for the ground survey and trap set and collection. We thank Sister Carolyn Bell for picking us up from the McArthur River airport. Irene Thompson (health worker) assisted in the ground survey. The flight to Wollogorang was chartered through Shaw Flight (Borroloola). A special thank you to Paul Zlotkowski, manager of Wollogorang road house for his hospitality, the provision of meteorological details and transport to Branch Creek for the collection of water samples. We also are indebted to Mr Andrew Cole for providing details on mosquito exposure of the survey team and relevant habits of the deceased. 8.0 REFERENCES Barker-Hudson, P. (1988). Categorisation of domestic breeding habitats of Aedes aegypti (Diptera:Culicidae) in Northern Queensland, Australia. Ent. Soc. America. Vol. 25 (3): 178-181. Hayes, G. (1992). Dengue vector survey of Darwin NT - March to April 1992. NT Department of Health and Community Services. Medical Entomology Branch report. Lee, D.J., Hicks, M.M., Griffiths, M., Debenham, M.L., Bryan J.H., Russell, R.C. and Geary, M. (1987). The Culicidae of the Australasian Region Vol. 5. Australian Government Publishing Service: Canberra. Mackenzie, J.S., Lindsay, M.D., Coelen, R.J., Broom, A.K., Hall, R.A. and Smith, D.W. (1994). Arboviruses causing human disease in the Australasian zoogeographic region. Arch. Virol. Vol. 136: 447-467. Montgomery, B.L. (1995). McArthur River Mine - baseline mosquito monitoring report, April 1995. Medical Entomology Branch report, Territory Health Services. 38 pp., Appendix 7 pp..


Russell, R.C. (1995). Arboviruses and their vectors in Australia: an update on the ecology and epidemiology of some mosquito-borne arboviruses. Review of Med. and Vet. Ent. Vol. 83 (4): 141-158. Rohe, D.L. and Fall, R.R. (1979). A miniature battery powered CO2 baited light trap for mosquito borne encephalitis virus surveillance. Bull. Soc. Vector Research. Vol. 4: 24-27. Whelan, P. (1982). Container breeding mosquito surveys. NT Department of Health and Community Services. Medical Entomology Branch report. Whelan, P. (1990). The Northern Territory remains free of Dengue fever. NT Department of Health and Community Services. Medical Entomology Branch report. Whelan, P.I., Merianos, A., Patel, M.S., Tai, K.S. and Currie, B. (1992). The epidemiology of arbovirus infection in the Northern Territory 1980-1992. In "Proceedings of the sixth Arbovirus Conference": Brisbane 1992. Whelan, P.I. and Burrow, J. (1994). Australian encephalitis in the NT. NT Comm. Diseases Bull. Vol. 2 (4): 21-23. Whelan, P.I. and Kelton, W. (1992). Common mosquitoes in the Northern Territory. Description of species, habitats and disease potential. NT Department of Health and Community Services. Medical Entomology Branch report. Whelan, P.I. and Weir, R.P. (1993). The isolation of alpha and flaviviruses from mosquitoes in the Northern Territory, 1982-1992. In: "Arbovirus research in Australia - Proceedings 6th Symposium. December 7-11, 1993". Brisbane, Australia. M.F. Uren and B.H. Kay (Eds) pp. 270-278.


Figure 1. Location of Borroloola and Wollogorang NT.



Figure 2. Borroloola township. The location of adult mosquito traps and areas surveyed for container breeding are indicated.

Figure 3. Wollogorang roadhouse showing the location of adult mosquito traps. The dry bed of Settlement Creek can be seen to the west. 7 December 1995.

Figure 4. Branch Creek, Queensland. The general location of the swimming hole that was subsequently flooded by rain. 8 December 1995.


Figure 5. Borrow pit adjacent to the Rocky Creek, N.W of Borroloola. No mosquito larvae were detected 7 December 1995.

Figure 6. Rocky Creek, South of Anyula St, Borroloola. No mosquito larvae were detected 7 December 1995.


Figure 7. Garawa Aboriginal Camp absorption trench, east side of the McArthur River from Borroloola. High levels of Cx. quinquefasciatus larvae in open inspection pits and in areas of seepage. 7 December 1995.

Figure 8. Settlement Creek, Wollogorang, west of roadhouse. 8 December 1995.


TABLE 1. MOSQUITO LARVAL SURVEYS OF BORROLOOLA AND WOLLOGORANG. 7 & 8 DECEMBER 1995.

LOCATION LARVAL SITE NO.

DATE SITE DESCRIPTION SPECIES INSTARS NUMBER OF DIPS

NO. OF LARVAE PER DIP

COMMENTS

FIRST SECOND THIRD FOURTH

BORROLOOLA 1 07-DecGarawa camp infiltration trenches. Open "inspection pits".

Culex (Cux) annulirostris 22 18 189 39 0.33 816

Culex (Cux) quinquefasciatus 1 3

2 07-DecGarawa camp ex-infiltration trenches. Roadside drain.

Culex (Cux.) annulirostris 5 3 1 1 9

Aboriginal health worker reported that water often covered the road.

3 07-DecGarawa camp infiltration trenches. In seepage pools.

Culex (Cux) annulirostris 18 1 19

Anopheles (Ano) amictus 1

4 07-DecUpper reaches of Rocky Creek. Access via end of Mulholland Rd.

Culex (Cux) 'normanton' species 1 4 0.25

5 08-Dec"Croc. Spot" Caravan Park sewage system.

Culex (Cux) annulirostris 3 9 6 1 32

Source either a broken pipe or full infiltration trench.

Culex (Cux) quinquefasciatus 4 10

6 08-Dec"Croc. Spot" Caravan Park sewage system.

Culex (Cux) annulirostris 2 1 5 1 2 6.5Culex (Cux) quinquefasciatus 1

WOLLOGORANG 1 08-Dec Ground depression.Anopheles (Ano) amictus 1 2 0.5

F:/Ento/Ento_files/public information/branch reports/katherine region/1995_Borrolooa_Wool/Table 1

TABLE 2. WOLLOGORANG ADULT MOSQUITO MONITORING DATA

TOTAL NUMBER OF ADULT FEMALE MOSQUITOES CAUGHT USING CO2 BAITED EVS TRAPS.DECEMBER 8 1995

SITE TRAP LOCATION MOSQUITO SPECIES TOTALS % OFNO.

An. (

Cel

.) am

ictu

s

An. (

Cel

.) an

nulip

es

Ae. (

Cha

.) el

choe

nsis

Ae. (

Fin.

) bri

tteni

Ae. (

Mac

.) sp

. 121

Ae. (

Mac

.) sp

. 76

Ae. (

Mac

.) tr

emul

us

Ae. (

Och

.) no

rman

ensi

s

Ae. (

Och

.) ps

eudo

norm

anen

sis

Ae. (

Och

.) vi

gila

x

Cx.

(Cux

) ann

ulir

ostr

is

Cx.

(Cux

) qui

nque

fasc

iatu

s

TOTALS

1Settlement Creek - Behind (North) of the Roadhouse, half way down bank. NIL MOSQUITOES 0 0.00

2Large tree outside Roadhouse boundary, 100m East of tourist accommodation. 1 2 3 6 31.58

3

150 m South of tourist accomodation - Melaleuca beyond open gound of Roadhouse. 1 1 5 1 1 1 10 52.63

4200 m West of Roadhouse in stand of trees20 m above Settlement Creek bank. 1 2 3 15.79TOTALS 1 0 1 1 0 0 3 10 1 1 1 0 19 100.00% OF TOTALS 5.26 0.00 5.26 5.26 0.00 0.00 15.79 52.63 5.26 5.26 5.26 0.00 100.00


TABLE 3. BORROLOOLA ADULT MOSQUITO MONITORING DATA

TOTAL NUMBER OF ADULT FEMALE MOSQUITOES CAUGHT USING CO2 BAITED EVS TRAPS.DECEMBER 8 1995

SITE TRAP LOCATION MOSQUITO SPECIES TOTALS % OFNO.

An. (

Cel

.) am

ictu

s

An. (

Cel

.) an

nulip

es

Ae. (

Cha

.) el

choe

nsis

Ae. (

Fin.

) bri

tteni

Ae. (

Mac

.) sp

. 121

Ae. (

Mac

.) sp

. 76

Ae. (

Mac

.) tr

emul

us

Ae. (

Och

.) no

rman

ensi

s

Ae. (

Och

.) ps

eudo

norm

anen

sis

Ae. (

Och

.) vi

gila

x

Cx.

(Cux

) ann

ulir

ostr

is

Cx.

(Cux

) qui

nque

fasc

iatu

s

TOTALS

1NW of T&W 679 - Beside Rocky Ck. 400 - 500 m NW from Mulholland St 1 4 12 7 23 47 14.11

2East Borroloola - Between McArthur River and 50 - 100 m east of Searcy St. 3 2 1 23 13 42 12.61

3Upper Boat Ramp. 50 m West of the McArthur River. 15 2 60 23 1 101 30.33

4

Borroloola Airstrip - 100 m West of airstrip and approx. 1/4 of the length of the airstrip from the northern end. 1 11 76 20 30 5 143 42.94TOTALS 5 28 0 0 4 76 0 15 0 110 89 6 333 100.00% OF TOTALS 1.50 8.41 0.00 0.00 1.20 22.82 0.00 4.50 0.00 33.03 26.73 1.80 100.00


TABLE 4. Aedes aegypti CONTAINER BREEDING SURVEY. SUMMARY BY CATEGORY.

DATE OF SURVEY- 7 & 8 December 1995SUBURB/AREA Borroloola and WollogorangINSPECTED BY B. Montgomery & R. Nowland

CATEGORY CATEGORY DESCRIPTION

TOTAL POTENTIAL CONTAINERS

% OF TOTALS

NUMBER OF CONTAINERS WITH WATER

% OF CONTAINERS WITH WATER

NUMBER OF CONTAINERS BREEDING

% OF WET CONTAINERS BREEDING

SPECIES

An. a

mic

tus

Ae. t

rem

ulus

Cx.

ann

ulir

ostr

is

Cx.

qui

nque

fasc

iatu

s

1 Garden accoutrements 16 14.41 2 12.50 0 0.00

2 Water storage containers 20 18.02 10 50.00 3 30.00 20 58

3Discarded household items 18 16.22 8 44.44 0 0.00

4 Rubbish 23 20.72 7 30.43 3 42.86 92

5Domestic / commercial usage containers 8 7.21 4 50.00 1 25.00 3

6 Recreation items 0

7Building fixtures and materials 26 23.42 10 38.46 1 10.00 1 45 1

8 Natural habitats 0TOTALS 111 100.00 41 36.94 8 19.51 1 23 45 151% TOTALS 0.45 10.45 20.45 68.64


TABLE 5. Aedes aegypti CONTAINER BREEDING SURVEY. RESULTS LISTED BY ORDER OF CATEGORY.

DATE OF SURVEY 7 & 8 December 1995SUBURB/AREA Borroloola and WollogorangINSPECTED BY B. Montgomery & R. Nowland

DESCRIPTION OF WATER BEARING CONTAINER

CATEGORY TOTAL POTENTIAL CONTAINERS

% OF TOTALS

NUMBER OF CONTAINERS WITH WATER

% OF CONTAINERS WITH WATER

NUMBER OF CONTAINERS BREEDING

% OF WET CONTAINERS BREEDING

SPECIES

An. a

mic

tus

Ae. t

rem

ulus

Cx.

ann

uliro

stris

Cx.

qui

nque

fasc

iatu

s

Pot plant base 1 13 11.71 1 7.69 0 0.00

Wheelbarrow 1 2 1.80 1 50.00 0 0.00

Watering can 1 1 0.90 0 0.00 0 0.00

Drum 2 5 4.50 0 0.00 0 0.00

Drum 20L 2 4 3.60 3 75.00 1 33.33 6

Drum 44gal 2 4 3.60 3 75.00 0 0.00

Bucket 4L 2 3 2.70 2 66.67 0 0.00

Beer keg 1/2 2 2 1.80 1 50.00 1 100.00 52

Drum 1/2 44 gal 2 1 0.90 1 100.00 1 100.00 20

Tank - rainwater 2 1 0.90 0 0.00 0 0.00

Bin lid 3 4 3.60 2 50.00 0 0.00

Bucket 3 4 3.60 1 25.00 0 0.00

Bucket 40L 3 2 1.80 1 50.00 0 0.00

Dust pan 3 2 1.80 2 100.00 0 0.00

Box - foam 3 1 0.90 0 0.00 0 0.00

Bucket 20L 3 1 0.90 0 0.00 0 0.00

Esky 3 1 0.90 0 0.00 0 0.00

pot - cooking 3 1 0.90 1 100.00 0 0.00

Tray - freezer 3 1 0.90 1 100.00 0 0.00

Tyre - pushbike 3 1 0.90 0 0.00 0 0.00

Tyre - car 4 19 17.12 4 21.05 3 75.00 92

Container 4L 4 4 3.60 3 75.00 0 0.00

Dog bowl 5 3 2.70 2 66.67 0 0.00

Bucket - feed 5 2 1.80 0 0.00 0 0.00

Trough 5 2 1.80 1 50.00 1 100.00 3

Chook feeder 5 1 0.90 1 100.00 0 0.00

Footing poles 7 12 10.81 8 66.67 0 0.00

Plumbing - disused 7 8 7.21 1 12.50 0 0.00

Tap box 7 6 5.41 1 16.67 1 100.00 1 45 1

TOTALS 111 100.00 41 36.94 8 19.51 1 23 45 151F:/Ento/Ento_files/public information/branch reports/katherine region/1995_Borrolooa_Wool/Table 5

TABLE 6. Aedes aegypti CONTAINER BREEDING SURVEY OF BORROLOOLA. 7 DECEMBER 1995.Categories

DATE OF SURVEY 07-Dec-95 1. Garden accoutrements 5. Domestic commercial usage containersSUBURB/AREA Borroloola 2. Water storage containers 6. Recreation itemsINSPECTED BY B. Montgomery & 3. Discarded Household items 7. Building Fixtures and materials

R. Nowland 4. Rubbish 8. Natural habitats

No. Address Closed Refused Inspected Description of water bearing container

Category Total potential containers

No. with water

No. breeding

Sample No

Species Other comments

An. a

mic

tus

Ae n

otos

crip

tus

Ae tr

emul

us

Cx

annu

liros

tris

Cx

halif

axii

Cx

pullu

s

Cx

quin

quef

asci

atus

Cx

(Lop

) sp.

1 1 Horney Crt yes Drum 44gal 2 3 3

Tyre - car 4 6 2 1 1 1

Drum 2 5

Bin lid 3 2

Dog bowl 5 1 1

Container 4L 4 1

2 2 Horney Crt yes Dog bowl 5 2 1

Drum 44 gal 2 1

3 3 Horney Crt yes Nil Guard dog. No obvious

Nil problem.

4 4 Horney Crt yes Nil No obvious containers





9 9A Horney Crt yes Drum 20L 2 1 1

10 9B Horney Crt yes Container 4L 4 1 1

Bin lid 3 2 2

Pot plant base 1 6

11 9C Horney Crt yes Container 4L 4 2 2

Pot plant base 1 3 1

Trough 5 1 1 1 2 3

Drum 1/2 44 gal 2 1 1 1 3 20

12 10 Horney Crt yes Nil

13 11 Horney Crt yes Tyre pushbike 3 1

Tyre car 4 6 1 1 4 8

14 12 Horney Crt yes Nil vacant property

F:/Ento/Ento_files/public information/branch reports/katherine region/1995_Borrolooa_Wool/Table 6 & 7

TABLE 6. (CONTINUED)Categories

DATE OF SURVEY 7 - 8/12/1995 1. Garden accoutrements 5. Domestic commercial usage containersSUBURB/AREA Borroloola 2. Water storage containers 6. Recreation itemsINSPECTED BY B. Montgomery & 3. Discarded Household items 7. Building Fixtures and materials

R. Nowland 4. Rubbish 8. Natural habitats



No. with water

No. breeding

Sample No.


An. a

mic

tus

Ae. n

otos

crip

tus

Ae. t

rem

ulus

Cx.

ann

uliro

stris

Cx.

hal

ifaxi

i

Cx.

pul

lus

Cx.

qui

nque

fasc

iatu

s

Cx.

(Lop

) sp.

15 13 Horney Crt yes Drum 20L 2 2 2 1 5 6

Wheelbarrow 1 1 1

Plumbing - disused 7 1 1Chook feeder 5 1 1pot - cooking 3 1 1Drum 20L 2 1 1

16 14 Horney Crt yes Nil17 "Croc Spot" caravan park yes Dust pan 3 2 2

Box - foam 3 1Wheelbarrow 1 1Bucket 3 4 1Beer keg 1/2 2 2 1 1 6 52Tyre - car 4 5 1 1 7 83Footing poles 7 12 8Plumbing - disused 7 7Bucket 4L 2 3 2Pot plant base 1 4Esky 3 1Can watering 1 1Tray - freezer 3 1 1

18 "HM Projects" accommodation yes Nil


TABLE 7. Aedes aegypti CONTAINER BREEDING SURVEY OF WOLLOGORANG. 8 DECEMBER 1995Categories

DATE OF SURVEY 08-Dec-95 1. Garden accoutrements 5. Domestic commercial usage containersSUBURB/AREA Wollogorang 2. Water storage containers 6. Recreation itemsINSPECTED BY B. Montgomery 3. Discarded Household items 7. Building Fixtures and materials

4. Rubbish 8. Natural habitats



No. with water

No. breeding

Sample No.


An. a

mic

tus

Ae. n

otos

crip

tus

Ae. t

rem

ulus

Cx.

ann

uliro

stris

Cx.

hal

ifaxi

i

Cx.

pul

lus

Cx.

qui

nque

fasc

iatu

s

Cx.

(Lop

) sp.

Stockyard yes Trough 5 1yes Bucket 20L 3 1yes Tyre - car 4 1yes Bucket - feed 5 2

Chicken coop yes Bucket 40L 3 2 1House yard yes Tank - rainwater 2 1

yes Tyre - car 4 1yes Tap box 7 6 1 1 2 1 45 1 Inspection pits in yards

(plate size) filled by irrigation.


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