Forty years continous monitoring for bluetongue virus at an Australian site of high arbovirus activity. What have we achieved?

The potential for bluetongue virus serotype 16 to cause disease in sheep in New South Wales, Australia

BLUETONGUE VIRUS SEROTYPE 16 DETECTION IN NSW: In coastal New South Wales (NSW), bluetongue virus (BTV) serotypes 1 and 21 are endemic and transmitted in most years without evidence of disease. However, serotype 16 (BTV-16) infection was detected for the first time in NSW in November 2016 in cattle undergoing testing for export. Retrospective testing of blood samples collected from sentinel cattle as part of the National Arbovirus Monitoring Program (NAMP) established that the first detected transmission of BTV-16 in NSW occurred in April 2016 in sentinel cattle on the NSW North Coast. Subsequently, until 2022, BTV-16 has been transmitted in most years and was the predominant serotype in the 2018-2019 transmission season. The data available suggests that BTV-16 may have become endemic in NSW. EXPERIMENTAL STUDIES: During experimental infection studies with BTV-16, all sheep were febrile, with the peak of viremia occurring 6-10 days after inoculation. There was nasal and oral hyperaemia in most sheep with several animals developing a nasal discharge and nasal oedema. All sheep developed coronitis of varying severity, with most also developing haemorrhages along the coronary band. There was a high incidence of haemorrhage in the pulmonary artery, epicardial petechiae, extensive pericardial haemorrhages and moderate body cavity effusions including pericardial effusions. CONCLUSION: Overall, experimental pathogenicity findings suggest moderate disease may occur in sheep in the field. These findings, when combined with climatic variability that could result in an expansion of the range of Culicoides brevitarsis into major sheep-producing areas of the state, suggest that there is an increasing risk of bluetongue disease in NSW.

Genome-scale molecular and phylogenetic characterization of Middle Point orbiviruses from Australia

Middle Point orbivirus (MPOV) is an Australian arbovirus, belongs to the Yunnan orbivirus species found in China. First detected and reported from Beatrice Hill, Northern Territory (NT), MPOV has to date, only been exclusively reported from the NT, Australia. Whilst genetic characterization of MPOV has been previously described, only restricted to sequence information for segments 2 and 3 coding core protein VP2 and outer capsid protein VP3, respectively. This study presents for the first time nearly full-length genome sequences of MPOV, which represent 24 isolates collected over a span of more than 20 years from 1997 to 2018. Whilst the majority of isolates were sampled at Beatrice Hill, NT where MPOV is most frequently isolated, this report also describes the first two isolations of MPOV from Queensland (QLD), Australia. One of which is the first non-bovine isolate obtained from the mosquito vector Aedes vittiger. We further compared these MPOV sequences with known sequences of the Yunnan orbivirus and other known orbivirus sequences of mosquito origin found in Australia. The phylogenetic analyses indicate the Australian MPOV sequences are more closely related to each other than other known sequences of Yunnan orbivirus. Furthermore, MPOV sequences are closely related to sequences from the Indonesian isolate JKT-8650. The clustering of Australian sequences in the phylogenetic tree suggests the monophyletic lineage of MPOV circulating in Australia. Further, ongoing surveillance is required to assess the existence and prevalence of this or other yet undetected lineages of MPOV and other orbiviruses in Australia.

The Ecology and Evolution of Japanese Encephalitis Virus

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus mainly spread by Culex mosquitoes that currently has a geographic distribution across most of Southeast Asia and the Western Pacific. Infection with JEV can cause Japanese encephalitis (JE), a severe disease with a high mortality rate, which also results in ongoing sequalae in many survivors. The natural reservoir of JEV is ardeid wading birds, such as egrets and herons, but pigs commonly play an important role as an amplifying host during outbreaks in human populations. Other domestic animals and wildlife have been detected as hosts for JEV, but their role in the ecology and epidemiology of JEV is uncertain. Safe and effective JEV vaccines are available, but unfortunately, their use remains low in most endemic countries where they are most needed. Increased surveillance and diagnosis of JE is required as climate change and social disruption are likely to facilitate further geographical expansion of Culex vectors and JE risk areas.

Bluetongue and Epizootic Hemorrhagic Disease in the United States of America at the Wildlife-Livestock Interface

Bluetongue (BT) and epizootic hemorrhagic disease (EHD) cases have increased worldwide, causing significant economic loss to ruminant livestock production and detrimental effects to susceptible wildlife populations. In recent decades, hemorrhagic disease cases have been reported over expanding geographic areas in the United States. Effective BT and EHD prevention and control strategies for livestock and monitoring of these diseases in wildlife populations depend on an accurate understanding of the distribution of BT and EHD viruses in domestic and wild ruminants and their vectors, the Culicoides biting midges that transmit them. However, national maps showing the distribution of BT and EHD viruses and the presence of Culicoides vectors are incomplete or not available at all. Thus, efforts to accurately describe the potential risk of these viruses on ruminant populations are obstructed by the lack of systematic and routine surveillance of their hosts and vectors. In this review, we: (1) outline animal health impacts of BT and EHD in the USA; (2) describe current knowledge of the distribution and abundance of BT and EHD and their vectors in the USA; and (3) highlight the importance of disease (BT and EHD) and vector surveillance for ruminant populations.

Bluetongue virus serotype 12 enters Australia - a further incursion of novel western lineage genome segments

Bluetongue virus (BTV) is an arbovirus (genus: Orbivirus) that occurs worldwide. It infects domestic and wild ruminant species and can cause disease in livestock, producing high economic impact. Recently, it gained extra prominence throughout Europe, with disease occurring in regions traditionally free of BTV. BTV enters Australia from Southeast Asia via wind-borne infected Culicoides spp. The first Australian isolation was 1975 (BTV-20) and further serotypes were isolated between 1979-86 (BTV-1, -3, -9, -15, -16, -21, -23). Despite increased, more sensitive, monitoring, no more were detected in over two decades, implying a stable BTV episystem of eastern ancestry. Isolations of BTV-2, -7 and -5 then occurred between 2007-15, with the latter two possessing genome segments with high sequence identity to western isolates. We report on the first isolation and genomic characterization of BTV-12, which revealed that three more novel western topotype gene segments have entered northern Australia.

Bovine Ephemeral Fever in Asia: Recent Status and Research Gaps

Bovine ephemeral fever is an arthropod-borne viral disease affecting mainly domestic cattle and water buffalo. The etiological agent of this disease is bovine ephemeral fever virus, a member of the genus Ephemerovirus within the family Rhabdoviridae. Bovine ephemeral fever causes economic losses by a sudden drop in milk production in dairy cattle and loss of condition in beef cattle. Although mortality resulting from this disease is usually lower than 1%, it can reach 20% or even higher. Bovine ephemeral fever is distributed across many countries in Asia, Australia, the Middle East, and Africa. Prevention and control of the disease mainly relies on regular vaccination. The impact of bovine ephemeral fever on the cattle industry may be underestimated, and the introduction of bovine ephemeral fever into European countries is possible, similar to the spread of bluetongue virus and Schmallenberg virus. Research on bovine ephemeral fever remains limited and priority of investigation should be given to defining the biological vectors of this disease and identifying virulence determinants.

Genomic analysis of bluetongue virus episystems in Australia and Indonesia

The distribution of bluetongue viruses (BTV) in Australia is represented by two distinct and interconnected epidemiological systems (episystems)—one distributed primarily in the north and one in the east. The northern episystem is characterised by substantially greater antigenic diversity than the eastern episystem; yet the forces that act to limit the diversity present in the east remain unclear. Previous work has indicated that the northern episystem is linked to that of island South East Asia and Melanesia, and that BTV present in Indonesia, Papua New Guinea and East Timor, may act as source populations for new serotypes and genotypes of BTV to enter Australia’s north. In this study, the genomes of 49 bluetongue viruses from the eastern episystem and 13 from Indonesia were sequenced and analysed along with 27 previously published genome sequences from the northern Australian episystem. The results of this analysis confirm that the Australian BTV population has its origins in the South East Asian/Melanesian episystem, and that incursions into northern Australia occur with some regularity. In addition, the presence of limited genetic diversity in the eastern episystem relative to that found in the north supports the presence of substantial, but not complete, barriers to gene flow between the northern and eastern Australian episystems. Genetic bottlenecks between each successive episystem are evident, and appear to be responsible for the reduction in BTV genetic diversity observed in the north to south–east direction.