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July 25 th
, 2013 R&D mee
ting
by Debbra Marcel
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• emerging non-zoonotic, insect-borne viral disease
• affects ruminant livestock and some wild ruminants, occurs almost worldwide.
• primarily affected animals: sheep, occasionally goats and deer and, very rarely,
cattle
•
characterized by changes to the mucous linings of the mouth and nose and thecoronary band of the foot.
• the virus recognized as important agent of disease in sheep in South Africa in early
20th century, and confined to Africa.
• the first confirmed outbreak outside of Africa occurred in Cyprus in 1943
• the disease has been identified in several countries worldwide including
Malaysia since henceforth• In 2006, reported for the first time in Germany, Belgium and The Netherlands and
other parts of European countries (emerging disease)
• Listed in OIE as one of the world’s economically important disease in sheep due to
its potential for rapid spread and socio-economic impact ( Pradeep et. al, Virol. Sin. 2010)
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Bluetongue disease @ catarrhal fever
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• Bluetongue (BT) is caused by a type of virus called Bluetongue Virus (BTV) which
belong to the family of Reoviridae, genus of Orbivirus
• 24 serotypes of BTV have been described internationally. While the viruses
are classified antigenically and taxonomically as BTV, each serotype is unique and
may not cause BT, the disease.
• Virus particles = composed of three protein layers.
• Genomes = dsRNA distributed amongst 10 segment (facilitate virus re-assortment)
• The presence of BTV in Malaysia was first indicated serologically in 1977 and clinical
bluetongue disease was reported in imported Australian sheep (Chiang et al., 1989;
Sharifah et al., 1995). Subsequently, serotypes 1, 2, 3, 9, 16 and 23 were isolatedfrom sentinel cattle and appeared to be endemic (Sharifah et al., 1995).
• This causative agent is spread through temperate and tropical regions of the world
by biting Culicoides midges.
• The pathogenesis of bluetongue disease is similar to that of zoonotic viral hemorrhagic
fevers such as EHD(Epizootic Hemorrhagic Disease) & AHS (African Horse Sickness)
• Ref: Biosafety in Microbiological & Biomedical Laboratories, 5th Edition – CDC & NIH
Figure 1. Schematic of the mature BTV particle.
Organization of the major structural proteins VP2, VP5,
VP3 and VP7 in the architecturally complex BTV particle.
On entry into cells the outer capsid proteins VP2 and VP5
are lost, releasing a transcriptionally active core particle.
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S o u r c e : m i c r o b e w i k i . k e n y o n
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Map courtesy of: Vet. Ital. , 40(3), 145-150
Multiple serotypes of BTV are apparently endemic in M’sia and in other countries world-wide,
located between latitudes 35◦S and 50◦N within their respective region. Recent study also shown that the
global distribution of BTV infection has recently altered, perhaps driven in part by climatic influences
on midge species resident in different regions. In short, the distribution patterns of this disease are
greatly influenced by these midges populations worldwide. Tabachnick W J ,2004, J. Med. Entomology
Figure 2: Worldwide distribution of the bluetongue viruses and the major Culicoides vectors
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BTV solely relies on vector to
spread from host to host.
The midges species & populations
vary according to :-
local environmental
topographical conditions
meteorological conditions seasonal variations
- also affect the spread of BTV
• In 1983, 5 new of culicoides
species of were described in West
Malaysia (Kitaoka S, Natl Inst Anim
Health Q (Tokyo)
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Figure 5: Culicoides imicola. ,the major BTV vector in tropical
regions.
Photo source: h ttp://www.nature.com/nrmicro/journal
Figure 4: BTV Transmission cycle
Photo source: http:// bluetonguevirus.org
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BT disease is caused by fever and vascular permeability
Characterized by changes to the mucous linings of themouth and nose and the coronary band of the foot
Ranged from mild to severe, vary by species, between
breeds and within the flock or herd.
Symptoms more severe in sheep, rarely in deer, goat &
cattle. However, relatively high number of cattle havebeen affected during the current outbreak in Northern
Europe.
The incubation period : 5 – 20 days & symptoms develop
within a month.
The clinical signs of BT : BT_clinical signs.pdf
Causing high morbidity and high mortality to susceptible
sheep (imported breed e.g Suffolk & Dorset)
Asymptomatic infected animals may spread the disease
into new areas without necessarily being noticed.
s u s c e p t i b l e a n i m a l s
deer
sheep
goat
cattle
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Virus isolation (in ECE, cell culture or sheep)
Immunological methods (serogrouping/serotyping)
RT-PCR (viral DNA extraction)
A) Identification of BTV agent
B) Serological Tests:-
Complement fixation test (CFT)
Agar gel immunodifussion (AGID)=
Competitive ELISA (C-ELISA)
OIE
GOLD
STANDARD
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OIE Terrestrial Manual 2009 Chapter 2.1.3.- Bluetongue
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Control strategy
challenging/complicated due to the plurality of virus serotypes and the ubiquity and
opportunistic feeding behavior of its midge vector.
Prevention
no efficient treatment found for the disease
quarantine & vaccination are the first line of defense for every farmer as and when
vaccine becomes available in their area.
simple husbandry changes and practical midge control measures helps break the
livestock infection cycle limiting the chances of the livestock being bitten by virus-carrying midges e.g:-
a) Keping animals inside during early morning and early evening to avoid the periods
of peak midge activity
b) Keep infected stock inside to prevent them being bitten by midges and hence
passing the disease on
Surveillance
report all cases of BT infection on the premises.
livestock keepers/farmers should remain vigilant and report any clinical signs of
disease including in animals that have previously been vaccinated against BT. This will
facilitated assessment of any new midge-transmission from the continent or re-
emergence of disease
Vigilant livestock
keeper
Risk reduction
Photo source: wikimedia.com
Photo source: mstar.online
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