bluetongue disease

Prepared by: MONOCLONAL ANTIBODY SECTION

July 25th, 2013 R&D meeting

by Debbra Marcel

• 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 the coronary 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)


Bluetongue disease @ catarrhal fever

http://en.wikipedia.org/wiki/Cyprus

• 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 isolated from 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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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

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)


Figure 5: Culicoides imicola., the major BTV vector in tropical regions.

Photo source: http://www.nature.com/nrmicro/journal

Figure 4: BTV Transmission cycle

Photo source: http:// bluetonguevirus.org


BT disease is caused by fever and vascular permeability Characterized by changes to the mucous linings of the mouth 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 have been 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.

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BT_clinical.pdf

BT_clinical signs.pdf



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


OIE Terrestrial Manual 2009 Chapter 2.1.3.- Bluetongue


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

bluetongue disease

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