Bluetongue Disease is historically a African disease. It is probably enzootic throughout Africa, but has not been reported in every country. This is probably becasue clinical recognition of the disease largely depends on the presence of highly susceptible European breeds of sheep as indigenous African breeds generally exhibit subclinical infeactions (Erasmus & Potgieter, 2009).
It was first described in the late 18th century as ‘tong-sikte’ by a French biologist Francois de Vaillant (Gutsche, 1979). Some of the clinical features of Bluetongue disease were recorded by the Chief Veterinary Officer of the Cape Colony (Duncan Hutcheon) in his annaul report for 1880. He later wrote about malarial catarrhal fever, suggesting that it was transmitted by insects (Hutcheon, 1902). At the begining of the 20th century Spruell published details of his experiments with malarial catarrhal fever describing clinical features and a typical case of the disease, and suggesting that the name of the disease be changed to Bluetongue (Spreull, 1902; Spreull, 1905)
The first recognised occurrence of Bluetongue in Europe (and the first outside of Africa) occurred in Cyprus in 1943. During this outbreak approximately 2500 sheep died, with mortality reaching 70% in some flocks. Though it is possible that unrecognised outbreaks had been occurring on the island since 1924 (Mellor et al., 2009b). Following this outbreak there were further outbreaks of Bluetongue in Palestine (1943), Turkey (1944, 1946 & 1947) and Israel (1949) (Gambles, 1949; Komarov and Goldsmit, 1951).
The next outbreak of Bluetongue in Europe was casued by BTV serotype 10 in Portugal in 1956. This outbreak quickly expanded into Spain during 1957 and continued until 1960. This outbreak in the Iberian Peninsular caused the death of almost 180,000 sheep (with a mortality rate in sheep of up to 75%) (Manso-Ribiero et al., 1957; Mellor et al., 2009b).
For the next 20 years Bluetongue appeared to be absent from Europe, with the exception of Cyprus (where Bluetongue was detected in 21 of the years between 1924 and 1973). In 1979 and 1980 an outbreak caused by Bluetongue virus serotype 4 occurred on the islands of Lesbos and Rhodes in the eastern Mediterranean (Vassalos,1980; Dragonas, 1981; Mellor et al., 2009b).
Bluetongue once again appeared to disappear from Europe, until 1998, when a series of outbreaks involving at least five different serotypes spread through the Mediterranean Basin (a more detailed description for this period, and more recent years, can be found here). By 2005 Bluetongue outbreaks had occurred in at least 12 European countries (many of which are usually free of Bluetongue), three north African countries and Israel. Over one million sheep died from the disease during these outbreaks or by being culled for welfare or control purposes (Purse et al., 2005).
The disease 'Soremuzzle' (Hardy and Price, 1952) was reported from 1948 onwards, affecting sheep in California and Texas in the USA. The causative agent was identified to be Bluetongue virus serotype 10 (McKercher et al., 1953). Over the next twenty years a further three serotypes (11, 13 and 17) were identified from a total of 13 US states (Hourrigan & Klingsporn, 1975). Serotype 2 was isolated from an outbreak in Florida in 1982 and investigations stretching over seven years from 1999 identified a further eight serotypes (1, 3, 5, 6, 14, 19, 22 and 24) in Florida, Mississippi, and Lousiana (Mellor et al., 2009a; Wilson et al., 2009).
Canada is considered free from Bluetongue disease. With the exception of occasional incursions of Bluetongue virus serotype 11 into the Okanagan Valley, British Columbia (Wilson et al., 2009).
Studies have indicated that Bluetongue disease is widespread throughout Central and South American and the Carribean, but with little or no clinical signs. It has been observed that >60% of livestock in some countries have antibodies to bluetongue virus (Gibbs et al., 1983). Serological surveys and virus isolations through Central America and the Carribean have identified the presence of Bluetongue virus serotypes 1, 3, 4, 6, 8, 10, 11, 12, 13, 14 and 17. In South America serotypes 4 and 12 have been isolated from Brazil and Argentina. While there is serological evidence for the presence of serotypes 4, 6, 12, 14, 17, 19, and 20 (Wilson et al., 2009).
The first occurance of Bluetongue disease (serotype 16) was recorded in vaccinated sheep imported from the USA in Mansehra District, North West Frontier Province of Pakistan in 1958 (Sarwar, 1962; Sapre,1964). This was followed by the first occurance in India was reported from Maharashtra state in 1963 (Sapre,1964). Since then Bluetongue has been identified in Northern (Haryana, Himachal Pradesh, Jammu and Kashmir, Punjab, Rajasthan and Uttar Pradesh), Central (Madhya Pradesh), Western (Gujarat and Maharashtra) and Southern areas (Andhra Pradesh, Karnataka, Kerala and Tamil Nadu) . By 2009 evidence for the presence of twenty-one of the twenty four known serotypes of Bluetongue virus had been found in India (Prasad et al., 2009).
While BTV is now considered endemic in India and Pakistan, there are few reports from other countries in the region (Prasad et al., 2009)
Australia and South-East Asia
Across Southeast Asia there is a pattern of limited pathogenicity of circulating Bluetongue virus strains, with indiginous animals showing resistance to the disease. Which means that Bluetongue disease is not a major animal health issue and outbreaks of the disease are rarely reported (Daniels et al., 2009).
BTV20 was isolated from Culicoides (captured in 1975) in the Northern Territory. Seven more serotypes 1,3,9,15,16,21 and 23 were subsequently identified, for a total of 8 identified serotypes by 1986 (Kirkland, 2004). However Bluetongue disease is rarely observed as sheep are rarely raised in the northern and eastern areas of Australia where Bluetongue virus occurs, and studies have shown that many Australian strains have limited virulence or are non-virulent (Daniels et al., 2009). BTV7 was identified in a sentinal herd of cattle in the Northern Territory in 2007. It is believed that this serotype had spread from affected countries to the north of Australia on the monsoonal winds (OIE, 2008).
Across Indonesia, Malaysia, China and Japan there is evidence for Blueotngue virus serotypes 1-4, 7, 9, 11-13, 15, 16, 20, 21 and 23 with an unconfirmed report of serotype 17 from China (Kirkland et al., 2002). The serotypes 1, 3, 9, 16 and 23 seem to be widely spread thorughout the region. While serotype 2 appears to be absent in the south and east of the region, and serotypes 8 and 18 (present in India) have not yet spread as far as Southeast Asia (Daniels et al., 2009).
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