Bluetongue and Related Viruses in New South Wales: Isolations from, and Serological Tests on Samples from Sentinel Cattle

Abstract

Sentinel cattle at a number of localities in northern and central coastal New South Wales were sampled over the summer and autumn seasons of the years 1979, 1980 and 1981. A total of 118 orbiviruses were isolated; 99 were of the Palyam group, 15 were of the epizootic haemorrhagic disease (EHD) of deer group, and 4 of the bluetongue group. The Palyam group viruses were identified by serotype as 68 Bunyip Creek, 23 CSIRO Village, 7 D' Aguilar and one was not typed. The EHD viruses were identified as 13 type 5 and 2 type 6. All 4 bluetongue viruses were type 21. There was also convincing serological evidence that bluetongue type 1 infection occurred in 1980.Antibody to the bluetongue group, as demonstrated in a gel diffusion precipitin test, was often transient. It appeared to be mostly cross-reactive with, and induced by, other orbivirus infections, particularly those of the EHD group. Viruses of the Palyam group also seemed to be implicated in some circumstances. Where infections by viruses of the bluetongue group were demonstrated, the precipitating antibody responses to a bluetongue group antigen were not noticeably stronger than many which followed EHD virus infection.The results generally confirm previous conclusions, deduced from serological surveys, regarding the frequency of orbivirus infections, the presence of bluetongue viruses, and the transient nature of many bluetongue group antibody reactions.

Infection of cattle in Queensland with bluetongue viruses: 1. prevalence of antibodies

“…Infection of cattle with the latter serotypes is known to be widespread in Australia (St George 1985, 1992Gard and Melville 1989). Neutralising antibodies to these two serotypes have been detected in cattle from north-west Western Australia, the 'Top End' of the Northern Territory, and northeastern New South Wales (Coackleyetall980; Smithetall981; StGeorge 1982StGeorge ,1985Burton and Littlejohns 1988;Littlejohns and Burton 1988).…”

“…This test has been widely used in survey work on bluetongue virus infection, both in Australia and elsewhere (St George 1982; Della-Portaetal1983). However, alack of specificity caused by antibodies to orbiviruses is probably the most serious limitation of this test (Coackley eta1 1980;Littlejohns and Burton 1988;Littlejohns et a1 1988). Test reactions were classified as negative (negative and doubtful categories) or positive (l+, 2+, 3+ and > 3+ categories) (Della-Porta et a f 1983).…”

Epizootic haemorrhagic disease

“…It is assumed, therefore, that the epidemiological features of EHDV infection mirror those of BTV. Thus, although less well documented on a global basis, the distribution of EHDV infection likely is similar to that of BTV and includes tropical and temperate regions throughout the world between latitudes of approximately 40-50°N and 35°S (4,25,31,37,38,44,45,46,47,48,49,50,51,52). It is assumed, but not well proven, that the specific vector species differ throughout the world.…”

“…The high seroprevalence of EHDV infection among ruminants in endemic areas indicates that most ungulates survive infection with the virus and experience only subclinical infections (2,18,28,30,37,45,46,47,48,49,50,51). In Australia, for example, where six serotypes of EHDV have been recognised, and five of these for more than 30 years (54), clinical disease attributable to EHDV infection has not been recognised.…”

“…Since the initial description of EHD in the eastern United States, EHDV infection of wild and domestic ungulates has been identified elsewhere in the Americas (including the Caribbean islands and both Central and South America), Africa, Asia (including Eastern, Central and Southeast Asia), Australia, Indian Ocean islands such as Mauritius and Reunion, and the Middle East (4,14,16,25,30,(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55). Although infection of domestic livestock is prevalent in many endemic areas, EHDV only rarely causes overt disease in livestock species and apparently only in cattle and not small ruminants (4,23).…”