Understanding the Ecology of the Fasciola Parasite and the Snail Vector

to Know the Risk Factors Involved

CLARISSA YVONNE J. DOMINGOProfessor, CLSU-CVSM

Introduction• This study is a collation of research findings in the

Philippines and other Asian countries that describe the:

behavior adaptation of the parasite and the vector in their

natural habitat how these bionomics influence Fasciola

transmission to animals. • Understanding the parasite and vector bionomics

explains the rationale behind the strategies of fasciolosis control.

Modified from Gray GD, Copland RS and Copeman DB (eds) 2008. Overcoming liver fluke as a constraint to ruminant production in South-East Asia. ACIAR Monograph No. 133

SNAIL BIONOMICSSNAIL BIONOMICS

• Snail density in rivers may be negatively related to intense rainfall.

• Flooding… 1.disrupts the snail habitat 2.disperses the snails 3.cause them to float up to 70% of their time,

at the water surface

1. Stability of water level (flooding) (Widjajanti, 1989)

After flooding, water level stabilizes a few months•towards the end of the west season as seen in closed water bodies (rice paddies, lakes, water holes) •throughout the dry season in slow moving rivers

Thus, stable water level is favorable to snails for cercarial shedding and metacercarial encysting

1. Stability of water level (flooding) (Tembely et al., 1995)

2. Irrigated rice fields (Widjajanti, 1989)

• Availability of water in rice fields favors increase in snail density

• Lymnea spp. in areas with infected ruminants: rice fields, p value=0.05

(Domingo, 2012)

3. Season (Grigoryan, 1959)

• Towards the end of the wet season and throughout the duration of the dry season, the habitat is no longer suitable for snails.

• Hence, exposure of animals to infection with F. gigantica from rivers and lakes with infected snails may be restricted to only a few months each year.

4. Snail survival from previous cropping (Widjajanti, 1989)

Snails and their eggs surviving from the previous crop may: •colonize recently planted rice fields •may enter with water introduced to flood the field after planting. Their numbers then increase over the next few months before declining again a few weeks before harvest.

Snail Density

5.Number of rice cropping per year (Heytens, 1991)

• Irrigation enhances two crops per year and this maintains a high population of L. rubiginosa.

• In Indonesia, direct relationship between liver fluke infection in cattle and intensity of cropping of irrigated rice was found.

• Risks associated with the infection were: 1) rice cultivation, 2) cattle management and 3) irrigated rice fields as suitable habitat for L. rubiginosa.

5. Surface temperature of soil (Widjajanti, 1989)

• Cooler temperature in shaded soil allowed the snail hosts of the F. gigantica to survive dessication for some weeks.

• After one month, it was observed that the mean survival time of snails was reduced by about one-third.

• Snail egg masses were reduced by about one-half relative to hydrated controls but no adverse effect of dessication was observed for one month on subsequent hatchability of eggs.

Snail Density

PARASITE

BIONOMICS

EGG

MIRACIDIUM

REDIA

CERCARIA

METACERCARIA

Flukes

Optimum Range: 24-27oC water temp. for :1.Miracidia development1

2.Fast switching of rediae to cercaria2

3.Cercaria early shedding from snail3,4

4.Metacercaria 6 wks viability for encystment5

FAVORABLETEMPERATURE

1. TEMPERATURE

1Grigoryan, 19582Dinnick and Dinnick, 19643Al Kubaisee RY and Altaif KI. 19894Asanji, 19885Dreyfuss and Rondelaud, 1994

> 43oC ambient temp: miracidia dessication1

30-35oC water temp: metacercaria viable 5 to 2 wks only2

< 16oC water temp: reduces rediae development3

UNFAVORABLETEMPERATURE

5Grigoryan, 1958.6Dreyfuss and Rondelaud, 1994.9Dinnick and Dinnick, 1964.

1. TEMPERATURE

2. Sunlight exposure and humidity • Metacercaria – directly related to degree of

humidity; inversely related to sun exposure (Dreyfuss and Rondelaud, 1994)• Desiccated metacercariae exposed to direct

sunlight die within eight hours (Grigoryan, 1959)• Exposing fresh rice stalks to direct sunlight

before feeding them to livestock, reduce infection among animals

(Suhardono et al., 2006c)

3. Water level• Metacercaria – receding water levels cause drying of

contaminated aquatic forage or hay; they are no longer infectious after six weeks in the tropics but may survive up to about four months in cooler climates.

(Grigoryan, 1959)• Metacercaria immersed in water remain viable at most

5 wks than those allowed to dessicate (viable less than 2 wks).

(Suhardono et al., 2006c)

4. Behavior in WaterCERCARIA: encystment •Cercariae are shed off up to 15 waves, one to eight days apart, up to 50 days. (Dreyfuss and Rondelaud, 1994)•About two-thirds attach to various objects near the surface of the water to become metacercaria (Ueno and Yoshihara, 1974)•The remaining 1/3 of metacercariae become floating cysts. (Dreyfuss and Rondelaud, 1994)•These floating cysts may move with the flow of water to become a source of infection where the habitat is unsuitable for snails and presumed to be safe from infection. (Dreyfuss and Rondelaud, 1994)

5. Animal dung as fertilizer(Grigoryan, 1959)

• Infection is highest from fields fertilized with egg-laden animal manure.

• Exposure of animals to metacercaria from dung-fertilized irrigated rice fields occurs when animals graze infectious rice stubble after harvest or drink water flowing from the fields.

• Goat fasciolosis – affected by the presence of carabao as draft power (OR=6.14, p value=0.059)

(Domingo, 2012)

REFERENCE: Gray GD, Copland RS and Copeman DB (eds) 2008. Overcoming liver fluke as a constraint to ruminant production in South-East Asia. ACIAR Monograph No. 133

6. Continuous rice cropping

• Exposure to metacercaria occurs throughout the year in regions where rice

cropping is continuous in irrigated fields.• Fields most heavily contaminated are those

flooded again after harvest. (Suhardono, 2001)

• Exposure is only for a few weeks after harvest when rice cropping is seasonal (rain-fed)

(Grigoryan, 1959)

7. Metacercaria predilection site in plant stalks (Suhardono et al.,2006d)

• 98% of sheep fed with the lower 10 cm of the fresh rice stalks harbored flukes

• Rejection of the lower portion of rice stalk previously immersed in water would help control infection with F. gigantica in animals fed on fresh rice straw.

Lower 10 cm of fresh stalk

8. Grazing after harvest time

(Suhardono, 2001)

The most important risk factor for large ruminantsto become infected with F. gigantica are:•grazing in recently harvested contaminated rice fields. •feeding fresh herbage from such fields •allowing animals to drink from ditches surrounding rice fields and water from flooded rice fields

• Over 80% in infection was acquired from January to June by Ongole cattle in a rice-cropping environment in West Java which coincided with the period of harvest of irrigated rice.

• It is also concluded that the main source of infection with F. gigantica in cattle is fresh rice straw, especially that from fields within about 200 m. from a cattle pen.

Proof of infection after harvest time (Suhardono, 2001)

9. Feeding management (Domingo, 2015)

• Animals managed by “Cut and Carry” system are 5.33 times (p=0.01) and fed with kangkong are 4 times more likely to be sick (p=0.01)

• Animals fed with grasses gathered in the afternoon are 4 times more likely to be sick (p=0.0022)

• Animals allowed to eat grasses from pasture areas with occasional swamping of water are 1.86 times more likely to be sick (p=0.0244)

• Animals sharing common pasture are twice more likely to be sick (p=0.0002)

10. Presence of snails

• Irrigation and river waters are 7.3 times more likely to be associated with the Fasciola snail vector (p=0.002)

• Goats grazing in areas flooded with irrigation and river waters are 15.34 times more likely to be sick (p=0.004)

SUMMARYA. Controlling Infection from irrigated rice fields1.Avoid feeding rice stems, grazing or drinking from field fertilized with animal dung for 1.5 mos after the field dries out after harvest.2.Feed only the top two-thirds of fresh rice stalks

3. Expose rice stalks to the sun for three days or store dry for five weeks before feeding to stock

4. If dung is used as fertilizer in rice fields, store under the sun for at least one month before use or mix with herbage to promote fermentation and increase the temperature above 45oC which is lethal to fluke eggs.

B. Controlling infection from lakes, swamps or streams1. Avoid water consumption, grazing or harvesting of fringing herbage from water bodies when snails are shedding cercariae (2 mos. after the end of the wet season and persists for a couple of months)•The duration of the “infection period” depends on the persistence of emergent vegetation and snails in the water body.

2. Apply molluscicide:• 1 month after the rice crop is planted in

tropical areas to prevent cercarial shedding.

• 7 weeks or almost 2 months after planting in cooler regions where larval development in the snail is slower.

molluscicide

Single treatment with triclabendazole: (Suhardono, 2001)

•six weeks after the last of the seasonal rice harvest. •enables the generation of snails in the first seasonal rice crop to remain free from infection and thus break the annual cycle of transmission.

Schedule of deworming:

Single Treatment

1.5 mos afterharvest

Triclabendazole

In rice-growing areas, double treatment is necessary: (Srihakim and Pholpark, 1991)

•with triclabendazole or clorsulon that are effective against immature and mature flukes.•three months before rice crop planting so that stored and fresh feces used as fertilizer would be free from eggs of F. gigantica; safeguards snails from becoming infected.•six weeks after harvest if the field remains dry (this is sufficient time for metacercariae on stubble to die)

double treatment

1.5 mos afterharvest

TriclabendazoleTriclabendazole

In continuous or asynchronous rice cropping throughout the year, there is continuous exposure of animals to infection with F. gigantica. (Gray GD, Copland RS and Copeman DB (eds) 2008)•In the Philippines, treatment is done every three months if the available drug is only an adulticide (albendazole). •If all farmers share common grazing on their newly harvested rice fields, treatment is extended to four months with a flukicide that is effective against immature and adult flukes (Triclabendazole). •Treat all animals that share common grazing area.•If maintained for one year, it can reduce the level of infection in the common grazing animals to levels that could then be kept low with grazing management or other biological means.

Every 3 months treatment (asynchronous cropping system)

Albendazole TriclabendazoleAlbendazole

REFERENCES:

Domingo CYJ.2012. Epidemiology Of Fasciolosis In Nueva Ecija Province, Northern Philippines, Including An Assessment Of Ecological Factors and Recommended Control Measures. UN-FAO (EAHMI)

Thank you for your kind attention.