Detection of the European ‘field’ strain of bluetongue virus serotype 6 by real-time RT-PCR

African horse sickness: The potential for an outbreak in disease-free regions and current disease control and elimination techniques

African horse sickness (AHS) is an arboviral disease of equids transmitted by Culicoides biting midges. The virus is endemic in parts of sub-Saharan Africa and official AHS disease-free status can be obtained from the World Organization for Animal Health on fulfilment of a number of criteria. AHS is associated with case fatality rates of up to 95%, making an outbreak among naïve horses both a welfare and economic disaster. The worldwide distributions of similar vector-borne diseases (particularly bluetongue disease of ruminants) are changing rapidly, probably due to a combination of globalisation and climate change. There is extensive evidence that the requisite conditions for an AHS epizootic currently exist in disease-free countries. In particular, although the stringent regulations enforced upon competition horses make them extremely unlikely to redistribute the virus, there are great concerns over the effects of illegal equid movement. An outbreak of AHS in a disease free region would have catastrophic effects on equine welfare and industry, particularly for international events such as the Olympic Games. While many regions have contingency plans in place to manage an outbreak of AHS, further research is urgently required if the equine industry is to avoid or effectively contain an AHS epizootic in disease-free regions. This review describes the key aspects of AHS as a global issue and discusses the evidence supporting concerns that an epizootic may occur in AHS free countries, the planned government responses, and the roles and responsibilities of equine veterinarians.

Bluetongue virus serotype 6 in Europe in 2008-Emergence and disappearance of an unexpected non-virulent BTV

Bluetongue viruses (BTVs) could invade N-W Europe similar to BTV serotype 8 (BTV8/net06), since the source and route of introduction of this virus has not been solved. Therefore, the Dutch survey for Bluetongue by PCR testing was extended by further analysis of PCR positives to identify the involved BTV. In late August 2008, BTV was reported with 12 nucleotide differences in the S10 amplicon (S10 genotyping). This virus was identified as serotype 6, here named BTV6/net08. Promptly, serotype specific real-time PCR tests were developed for serotypes 1, 6, and 8 (S2 genotyping). Agreement was found between results by S10- and S2 genotyping. Further, BTV1 was identified by both S10- and S2 genotyping in one imported animal. After initial discovery of BTV6 in the Netherlands, animals from 18 holdings tested PCR positive for BTV6/net08 in 2008. Remarkably only one or two PCR positive animals per holding were found. Serum neutralization tests did not result in the discovery of more BTV6 infected animals. Retrospective studies indicated no evidence for infections by BTV6/net08 prior to the first discovery. Experimental infections with BTV6/net08 did not cause clinical disease in sheep, calves and cattle, except for a very short fever in some animals. This clearly showed that the vaccine-related BTV6/net08 is not virulent. BTV6/net08 was not found by passive and active surveys in the years after its discovery. Apparently, BTV6/net08 was not efficiently transmitted by endemic species of Culicoides in N-W Europe, and disappeared without the need of any control measure.

RT-PCR assays for seven serotypes of epizootic haemorrhagic disease virus & their use to type strains from the Mediterranean region and North America

Epizootic haemorrhagic disease virus (EHDV) infects wild ruminants, causing a frequently fatal haemorrhagic disease. However, it can also cause bluetongue-like disease in cattle, involving significant levels of morbidity and mortality, highlighting a need for more rapid and reliable diagnostic assays. EHDV outer-capsid protein VP2 (encoded by genome-segment 2 [Seg-2]) is highly variable and represents the primary target for neutralising antibodies generated by the mammalian host. Consequently VP2 is also the primary determinant of virus "serotype", as identified in virus neutralisation tests (VNT). Although previous reports have indicated eight to ten EHDV serotypes, recent serological comparisons and molecular analyses of Seg-2 indicate only seven EHDV "types". Oligonucleotide primers were developed targeting Seg-2, for use in conventional RT-PCR assays to detect and identify these seven types. These assays, which are more rapid and sensitive, still show complete agreement with VNT and were used to identify recent EHDV isolates from the Mediterranean region and North America.