Studies of the epidemiology of arthropod-borne virus infections at Mitchell River Mission, Cape York Peninsula, North Queensland. IV. Arbovirus infections of mosquitoes and mammals, 1967-1969

Complex transmission epidemiology of neglected Australian arboviruses: diverse non-human vertebrate hosts and competent arthropod invertebrate vectors

More than 75 arboviruses are indigenous to Australia, of which at least 13 are known to cause disease in humans. Alphaviruses are the most common arboviruses, notably including Ross River and Barmah Forest viruses, which contribute a significant public health and economic burden in Australia. Both can cause febrile illness with arthritic symptoms. Each circulates nationally across diverse climates and environments, and has multi-host, multi-vector dynamics. Several medically important flaviviruses also circulate in Australia. Infection with Murray Valley encephalitis or Kunjin viruses is less common but is associated with brain inflammation. Key research priorities for Australian arboviruses aim to understand clinical manifestations, develop timely diagnostics, and identify transmission cycles that permit the maintenance of arboviruses. While these can now be answered for a handful of notifiable alpha- and flaviviruses there are others for which non-human vertebrate hosts and competent arthropod invertebrate vectors are still to be identified and/or whose role in transmission is not well understood. One or more of these 'neglected' arboviruses may be the causative agent of a proportion of the many thousands of fever-related illnesses reported annually in Australia that at present remain undiagnosed. Here, what is known about enzootic cycling of viruses between arthropod vectors and mammalian and avian reservoir hosts is summarised. How and to what extent these interactions influence the epidemiology of arbovirus transmission and infection is discussed.

Animal board invited review: Risks of zoonotic disease emergence at the interface of wildlife and livestock systems

The ongoing coronavirus disease 19s pandemic has yet again demonstrated the importance of the human-animal interface in the emergence of zoonotic diseases, and in particular the role of wildlife and livestock species as potential hosts and virus reservoirs. As most diseases emerge out of the human-animal interface, a better understanding of the specific drivers and mechanisms involved is crucial to prepare for future disease outbreaks. Interactions between wildlife and livestock systems contribute to the emergence of zoonotic diseases, especially in the face of globalization, habitat fragmentation and destruction and climate change. As several groups of viruses and bacteria are more likely to emerge, we focus on pathogenic viruses of the Bunyavirales, Coronaviridae, Flaviviridae, Orthomyxoviridae, and Paramyxoviridae, as well as bacterial species including Mycobacterium sp., Brucella sp., Bacillus anthracis and Coxiella burnetii. Noteworthy, it was difficult to predict the drivers of disease emergence in the past, even for well-known pathogens. Thus, an improved surveillance in hotspot areas and the availability of fast, effective, and adaptable control measures would definitely contribute to preparedness. We here propose strategies to mitigate the risk of emergence and/or re-emergence of prioritized pathogens to prevent future epidemics.

Ross River Virus Infection: A Cross-Disciplinary Review with a Veterinary Perspective

Ross River virus (RRV) has recently been suggested to be a potential emerging infectious disease worldwide. RRV infection remains the most common human arboviral disease in Australia, with a yearly estimated economic cost of $4.3 billion. Infection in humans and horses can cause chronic, long-term debilitating arthritogenic illnesses. However, current knowledge of immunopathogenesis remains to be elucidated and is mainly inferred from a murine model that only partially resembles clinical signs and pathology in human and horses. The epidemiology of RRV transmission is complex and multifactorial and is further complicated by climate change, making predictive models difficult to design. Establishing an equine model for RRV may allow better characterization of RRV disease pathogenesis and immunology in humans and horses, and could potentially be used for other infectious diseases. While there are no approved therapeutics or registered vaccines to treat or prevent RRV infection, clinical trials of various potential drugs and vaccines are currently underway. In the future, the RRV disease dynamic is likely to shift into temperate areas of Australia with longer active months of infection. Here, we (1) review the current knowledge of RRV infection, epidemiology, diagnostics, and therapeutics in both humans and horses; (2) identify and discuss major research gaps that warrant further research.

Mosquito-Borne Viruses and Non-Human Vertebrates in Australia: A Review

Mosquito-borne viruses are well recognized as a global public health burden amongst humans, but the effects on non-human vertebrates is rarely reported. Australia, houses a number of endemic mosquito-borne viruses, such as Ross River virus, Barmah Forest virus, and Murray Valley encephalitis virus. In this review, we synthesize the current state of mosquito-borne viruses impacting non-human vertebrates in Australia, including diseases that could be introduced due to local mosquito distribution. Given the unique island biogeography of Australia and the endemism of vertebrate species (including macropods and monotremes), Australia is highly susceptible to foreign mosquito species becoming established, and mosquito-borne viruses becoming endemic alongside novel reservoirs. For each virus, we summarize the known geographic distribution, mosquito vectors, vertebrate hosts, clinical signs and treatments, and highlight the importance of including non-human vertebrates in the assessment of future disease outbreaks. The mosquito-borne viruses discussed can impact wildlife, livestock, and companion animals, causing significant changes to Australian ecology and economy. The complex nature of mosquito-borne disease, and challenges in assessing the impacts to non-human vertebrate species, makes this an important topic to periodically review.

Infection of Western Gray Kangaroos (Macropus fuliginosus) with Australian Arboviruses Associated with Human Infection

More than 75 arboviruses (arthropod-borne viruses) have been identified in Australia. While Alfuy virus (ALFV), Barmah Forest virus (BFV), Edge Hill virus (EHV), Kokobera virus (KOKV), Murray Valley encephalitis virus (MVEV), Sindbis virus (SINV), Ross River virus (RRV), Stratford virus (STRV), and West Nile virus strain Kunjin (KUNV) have been associated with human infection, there remains a paucity of data regarding their respective transmission cycles and any potential nonhuman vertebrate hosts. It is likely that these viruses are maintained in zoonotic cycles involving native animals rather than solely by human-to-human transmission. A serosurvey (n = 100) was undertaken to determine the prevalence of neutralizing antibodies against a panel of Australian arboviruses in western gray kangaroos (Macropus fuliginosus) obtained from 11 locations in the midwest to southwest of Western Australia. Neutralizing antibodies against RRV were detected in 25%, against BFV in 14%, and antibodies to both viruses in 34% of serum samples. The prevalence of antibodies against these two viruses was the same in males and females, but higher in adult than in subadult kangaroos (p < 0.05). Twenty-one percent of samples had neutralizing antibodies against any one or more of the flaviviruses ALFV, EHV, KOKV, MVEV, and STRV. No neutralizing antibodies against SINV and KUNV were detected. If this sample of kangaroo sera was representative of the broader Australian population of macropods, it suggests that they are common hosts for RRV and BFV. The absence or low seroprevalence of antibodies against the remaining arboviruses suggests that they are not prevalent in the region or that kangaroos are not commonly infected with them. The detection of neutralizing antibodies to MVEV requires further investigation as this virus has not been identified previously so far south in Western Australia.

Can Bats Serve as Reservoirs for Arboviruses?

Bats are known to harbor and transmit many emerging and re-emerging viruses, many of which are extremely pathogenic in humans but do not cause overt pathology in their bat reservoir hosts: henipaviruses (Nipah and Hendra), filoviruses (Ebola and Marburg), and coronaviruses (SARS-CoV and MERS-CoV). Direct transmission cycles are often implicated in these outbreaks, with virus shed in bat feces, urine, and saliva. An additional mode of virus transmission between bats and humans requiring further exploration is the spread of disease via arthropod vectors. Despite the shared ecological niches that bats fill with many hematophagous arthropods (e.g. mosquitoes, ticks, biting midges, etc.) known to play a role in the transmission of medically important arboviruses, knowledge surrounding the potential for bats to act as reservoirs for arboviruses is limited. To this end, a comprehensive literature review was undertaken examining the current understanding and potential for bats to act as reservoirs for viruses transmitted by blood-feeding arthropods. Serosurveillance and viral isolation from either free-ranging or captive bats are described in relation to four arboviral groups (Bunyavirales, Flaviviridae, Reoviridae, Togaviridae). Further, ecological associations between bats and hematophagous viral vectors are characterized (e.g. bat bloodmeals in mosquitoes, ingestion of mosquitoes by bats, etc). Lastly, knowledge gaps related to hematophagous ectoparasites (bat bugs and bed bugs (Cimicidae) and bat flies (Nycteribiidae and Streblidae)), in addition to future directions for characterization of bat-vector-virus relationships are described.

Ecological and life history traits are associated with Ross River virus infection among sylvatic mammals in Australia

Background

Ross River virus (RRV) is Australia’s most important arbovirus given its annual burden of disease and the relatively large number of Australians at risk for infection. This mosquito-borne arbovirus is also a zoonosis, making its epidemiology and infection ecology complex and cryptic. Our grasp of enzootic, epizootic, and zoonotic RRV transmission dynamics is imprecise largely due to a poor understanding of the role of wild mammalian hosts in the RRV system.

Methods

The current study applied a piecewise structural equation model (PSEM) toward an interspecific comparison of sylvatic Australian mammals to characterize the ecological and life history profile of species with a history of RRV infection relative to those species with no such history among all wild mammalian species surveyed for RRV infection. The effects of species traits were assessed through multiple causal pathways within the PSEM framework.

Results

Sylvatic mammalian species with a history of RRV infection tended to express dietary specialization and smaller population density. These species were also characterized by a longer gestation length.

Conclusions

This study provides the first interspecific comparison of wild mammals for RRV infection and identifies some potential targets for future wildlife surveys into the infection ecology of this important arbovirus. An applied RRV macroecology may prove invaluable to the epidemiological modeling of RRV epidemics across diverse sylvatic landscapes, as well as to the development of human and animal health surveillance systems.

Electronic supplementary material

The online version of this article (10.1186/s12898-019-0220-5) contains supplementary material, which is available to authorized users.

Hydrological features and the ecological niches of mammalian hosts delineate elevated risk for Ross River virus epidemics in anthropogenic landscapes in Australia

Background

The current understanding of the landscape epidemiology of Ross River virus (RRV), Australia’s most common arthropod-borne pathogen, is fragmented due to gaps in surveillance programs and the relatively narrow focus of the research conducted to date. This leaves public health agencies with an incomplete understanding of the spectrum of infection risk across the diverse geography of the Australian continent. The current investigation sought to assess the risk of RRV epidemics based on abiotic and biotic landscape features in anthropogenic landscapes, with a particular focus on the influence of water and wildlife hosts.

Methods

Abiotic features, including hydrology, land cover and altitude, and biotic features, including the distribution of wild mammalian hosts, were interrogated using a Maxent model to discern the landscape suitability to RRV epidemics in anthropogenically impacted environments across Australia.

Results

Water-soil balance, proximity to controlled water reservoirs, and the ecological niches of four species (Perameles nasuta, Wallabia bicolor, Pseudomys novaehollandiae and Trichosurus vulpecula) were important features identifying high risk landscapes suitable for the occurrence of RRV epidemics.

Conclusions

These results help to delineate human infection risk and thus provide an important perspective for geographically targeted vector, wildlife, and syndromic surveillance within and across the boundaries of local health authorities. Importantly, our analysis highlights the importance of the hydrology, and the potential role of mammalian host species in shaping RRV epidemic risk in peri-urban space. This study offers novel insight into wildlife hosts and RRV infection ecology and identifies those species that may be beneficial to future targeted field surveillance particularly in ecosystems undergoing rapid change.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2776-x) contains supplementary material, which is available to authorized users.

The non-human reservoirs of Ross River virus: a systematic review of the evidence

Understanding the non-human reservoirs of zoonotic pathogens is critical for effective disease control, but identifying the relative contributions of the various reservoirs of multi-host pathogens is challenging. For Ross River virus (RRV), knowledge of the transmission dynamics, in particular the role of non-human species, is important. In Australia, RRV accounts for the highest number of human mosquito-borne virus infections. The long held dogma that marsupials are better reservoirs than placental mammals, which are better reservoirs than birds, deserves critical review. We present a review of 50 years of evidence on non-human reservoirs of RRV, which includes experimental infection studies, virus isolation studies and serosurveys. We find that whilst marsupials are competent reservoirs of RRV, there is potential for placental mammals and birds to contribute to transmission dynamics. However, the role of these animals as reservoirs of RRV remains unclear due to fragmented evidence and sampling bias. Future investigations of RRV reservoirs should focus on quantifying complex transmission dynamics across environments.

Neglected Australian arboviruses: quam gravis?

At least 75 arboviruses have been identified from Australia. Most have a zoonotic transmission cycle, maintained in the environment by cycling between arthropod vectors and susceptible mammalian or avian hosts. The primary arboviruses that cause human disease in Australia are Ross River, Barmah Forest, Murray Valley encephalitis, Kunjin and dengue. Several other arboviruses are associated with human disease but little is known about their clinical course and diagnostic testing is not routinely available. Given the significant prevalence of undifferentiated febrile illness in Australia, investigation of the potential threat to public health presented by these viruses is required.

The seroprevalence and factors associated with Ross river virus infection in western grey kangaroos (Macropus fuliginosus) in Western Australia

A serosurvey was undertaken in 15 locations in the midwest to southwest of Western Australia (WA) to investigate the seroprevalence of Ross River virus (RRV) neutralizing antibodies and factors associated with infection in western grey kangaroos (Macropus fuliginosus). The estimated seroprevalence in 2632 kangaroo samples, using a serum neutralization test, was 43.9% (95% CI 42.0, 45.8). Location was significantly associated with seroprevalence (p<0.001). There was a strong positive correlation between seroprevalence and the average log-transformed neutralizing antibody titer (r=0.98, p<0.001). The seroprevalence among adult kangaroos was significantly higher than in subadult kangaroos (p<0.05). No significant association was observed between seroprevalence and the sex of kangaroos (p>0.05). The results of this study indicate that kangaroos in WA are regularly infected with RRV and may be involved in the maintenance and transmission of RRV.

The phylogenetic and evolutionary history of Kokobera virus

OBJECTIVE

To estimate the genetic diversity of Kokobera virus, the date of origin and the spread among different viruses in the endemic regions of Australia.

METHODS

Two datasets were built. The first consisting of 29 sequences of the NS5/3' UTR region of Kokobera group downloaded from GenBank, the second including only 24 sequences of Kokobera viruses, focus is on this group.

RESULTS

Bayesian time analysis revealed two different entries in Australia of Kokobera virus in the 50s years with the dated ancestor in 1861 year. Clades A and B showed a clear separation of the Kokobera sequences according to the geographic region.

CONCLUSIONS

Data from the study showed as Kokobera virus, despite of its ancient origin and its circulation before the European colonization, remained limited to the Australian country and nowadays limited mostly to the regions were Australian marsupials are mostly found.

Complete coding sequences of three members of the kokobera group of flaviviruses

The Kokobera group of flaviviruses circulates in Australia and Papua, New Guinea, and has been associated with occasional human polyarticular disease. To facilitate future studies to identify virulence determinants, the complete coding regions of the Stratford virus, and isolates of the Bainyik virus and Torres virus were obtained.

Arbovirus models to provide practical management tools for mosquito control and disease prevention in the Northern Territory, Australia

Ross River virus (RRV) causes the most common human arbovirus disease in Australia. Although the disease is nonfatal, the associated arthritis and postinfection fatigue can be debilitating for many months, impacting on workforce participation. We sought to create an early-warning system to notify of approaching RRV disease outbreak conditions for major townships in the Northern Territory. By applying a logistic regression model to meteorologic factors, including rainfall, a postestimation analysis of sensitivity and specificity can create rainfall cut-points. These rainfall cut-points indicate the rainfall level above which previous epidemic conditions have occurred. Furthermore, rainfall cut-points indirectly adjust for vertebrate host data from the agile wallaby (Macropus agilis) as the life cycle of the agile wallaby is intricately meshed with the wet season. Once generated, cut-points can thus be used prospectively to allow timely implementation of larval survey and control measures and public health warnings to preemptively reduce RRV disease incidence. Cut-points are location specific and have the capacity to replace previously used models, which require data management and input, and rarely provide timely notification for vector control requirements and public health warnings. These methods can be adapted for use elsewhere.

Purification and crystallization of Kokobera virus helicase

Kokobera virus is a mosquito-borne flavivirus belonging, like West Nile virus, to the Japanese encephalitis virus serocomplex. The flavivirus genus is characterized by a positive-sense single-stranded RNA genome. The unique open reading frame of the viral RNA is transcribed and translated as a single polyprotein which is post-translationally cleaved to yield three structural and seven nonstructural proteins, one of which is the NS3 gene that encodes a C-terminal helicase domain consisting of 431 amino acids. Helicase inhibitors are potential antiviral drugs as the helicase is essential to viral replication. Crystals of the Kokobera virus helicase domain were obtained by the hanging-drop vapour-diffusion method. The crystals belong to space group P3(1)21 (or P3(2)21), with unit-cell parameters a = 88.6, c = 138.6 A, and exhibit a diffraction limit of 2.3 A.

Weather variability, tides, and Barmah Forest virus disease in the Gladstone region, Australia

In this study we examined the impact of weather variability and tides on the transmission of Barmah Forest virus (BFV) disease and developed a weather-based forecasting model for BFV disease in the Gladstone region, Australia. We used seasonal autoregressive integrated moving-average (SARIMA) models to determine the contribution of weather variables to BFV transmission after the time-series data of response and explanatory variables were made stationary through seasonal differencing. We obtained data on the monthly counts of BFV cases, weather variables (e.g., mean minimum and maximum temperature, total rainfall, and mean relative humidity), high and low tides, and the population size in the Gladstone region between January 1992 and December 2001 from the Queensland Department of Health, Australian Bureau of Meteorology, Queensland Department of Transport, and Australian Bureau of Statistics, respectively. The SARIMA model shows that the 5-month moving average of minimum temperature (b=0.15, p-value<0.001) was statistically significantly and positively associated with BFV disease, whereas high tide in the current month (b=-1.03, p-value=0.04) was statistically significantly and inversely associated with it. However, no significant association was found for other variables. These results may be applied to forecast the occurrence of BFV disease and to use public health resources in BFV control and prevention.

Prevalence of neutralising antibodies to Barmah Forest, Sindbis and Trubanaman viruses in animals and humans in the south-west of Western Australia

A study was undertaken in the south-west of Western Australia to investigate potential vertebrate hosts of Barmah Forest virus (BFV), Sindbis virus (SINV) and Trubanaman virus (TRUV) following isolation of these viruses from mosquitoes collected during routine surveillance for arboviruses. Over 3000 animal and human sera collected between 1979 and 1995 were tested for the presence of neutralising antibodies to each of the viruses. The overall prevalence of antibodies to BFV, SINV and TRUV was 0.4%, 0.3% and 1.6%, respectively. Antibodies to BFV were detected only in quokkas (3.2%), horses (1.2%) and humans (0.9%). No definitive evidence of infection with BFV was detected in samples collected prior to 1992, supporting previous suggestions that BFV was introduced into the region after this time. Antibodies to SINV were detected in western native cats (16.7%), emus (4.5%), rabbits (0.8%) and horses (0.7%), and evidence of TRUV infection was most common in western grey kangaroos (21.1%), feral pigs (3.6%), rabbits (2.4%), foxes (2.3%), quokkas (1.6%) and horses (1.6%).

Identification of new flaviviruses in the Kokobera virus complex

Novel flavivirus isolates from mosquitoes collected in northern Australia were analysed by partial genomic sequencing, monoclonal antibody-binding assays and polyclonal cross-neutralization tests. Two isolates were found to be antigenically distinct from, but related to, viruses of the Kokobera virus complex, which currently contains Kokobera (KOKV) and Stratford (STRV) viruses. Nucleotide sequence comparison of two separate regions of the genome revealed that an isolate from Saibai Island in the Torres Strait in 2000 (TS5273) was related closely to KOKV and STRV, with 74–80 and 75–76 % nucleotide similarity, respectively. An isolate from mainland Cape York in 1998 (CY1014) was found to be more divergent from KOKV and STRV, with <70 % nucleotide sequence similarity to either virus. It is proposed that isolate TS5273 represents a new subtype of KOKV and that CY1014 be classified as a novel species within the Kokobera virus complex of flaviviruses, named New Mapoon virus.

Assessment of the potential of dogs and cats as urban reservoirs of Ross River and Barmah Forest viruses

OBJECTIVE

To determine whether dogs and cats are potential reservoirs of Ross River (RR) and Barmah Forest (BF) viruses

METHOD

Young seronegative female dogs and cats were experimentally exposed to the viruses using Ochlerotatus vigilax (Skuse) mosquitoes.

RESULTS

Only one of the 10 dogs and one of the 10 cats exposed to RR developed neutralising antibody. None of the animals developed detectable viraemia or clinical signs. One dog and three cats exposed to BF developed neutralising antibody. In addition, a serological survey of sera obtained from domestic dogs and cats residing in the Brisbane region indicated that 23.7% and 1.3% of dogs, and 14% and 2% of cats, had neutralising antibodies to RR and BF respectively.

CONCLUSIONS

Although dogs and cats are exposed naturally to these viruses, and can become infected, they are unlikely to be important urban reservoirs of either virus.

Ross River virus: ecology and distribution

Ross River virus is the most common mosquito-borne pathogen in Australia, and approximately 5000 human cases are reported annually. The infection is not fatal, but there is considerable morbidity associated with a debilitating polyarthritis that is the major symptom. The virus is annually active in most regions of Australia, but exists as strains that vary in virulence. Native macropods are thought to be the natural vertebrate hosts, although horses and humans may be involved during epidemic activity, and vertical transmission of the virus occurs in mosquitoes. Different mosquito species are involved as vectors in various regions and in different seasonal and environmental conditions. In coastal areas the saltmarsh mosquitoes Aedes camptorhynchus and Ae. vigilax are the most important vectors in southern and northern regions, respectively, whereas in inland areas Culex annulirostris is the most important vector, although various Aedes species can be involved depending on region and conditions, and the epidemiology of the disease and vector control imperatives vary with circumstance concomitantly.

Ross River virus transmission, infection, and disease: a cross-disciplinary review

Ross River virus (RRV) is a fascinating, important arbovirus that is endemic and enzootic in Australia and Papua New Guinea and was epidemic in the South Pacific in 1979 and 1980. Infection with RRV may cause disease in humans, typically presenting as peripheral polyarthralgia or arthritis, sometimes with fever and rash. RRV disease notifications in Australia average 5,000 per year. The first well-described outbreak occurred in 1928. During World War II there were more outbreaks, and the name epidemic polyarthritis was applied. During a 1956 outbreak, epidemic polyarthritis was linked serologically to a group A arbovirus (Alphavirus). The virus was subsequently isolated from Aedes vigilax mosquitoes in 1963 and then from epidemic polyarthritis patients. We review the literature on the evolutionary biology of RRV, immune response to infection, pathogenesis, serologic diagnosis, disease manifestations, the extraordinary variety of vertebrate hosts, mosquito vectors, and transmission cycles, antibody prevalence, epidemiology of asymptomatic and symptomatic human infection, infection risks, and public health impact. RRV arthritis is due to joint infection, and treatment is currently based on empirical anti-inflammatory regimens. Further research on pathogenesis may improve understanding of the natural history of this disease and lead to new treatment strategies. The burden of morbidity is considerable, and the virus could spread to other countries. To justify and design preventive programs, we need accurate data on economic costs and better understanding of transmission and behavioral and environmental risks.

Entomological investigations of an outbreak of Japanese encephalitis virus in the Torres Strait, Australia, in 1998

Japanese encephalitis (JE) virus first appeared in Australia in 1995, when three clinical cases (two fatal) were diagnosed in residents on Badu Island in the Torres Strait, northern Queensland. More recently, two confirmed human JE cases were reported in the Torres Strait Islands and Cape York Peninsula, in northern Queensland in 1998. Shortly after JE virus activity was detected in humans and sentinel pigs on Badu Island in 1998, adult mosquitoes were collected using CO2 and octenol-baited CDC light traps; 43 isolates of JE virus were recovered. Although Culex sitiens group mosquitoes yielded the majority of JE isolates (42), one isolate was also obtained from Ochlerotatus vigilax (Skuse). Four isolates of Ross River virus and nine isolates of Sindbis (SIN) virus were also recovered from members of the Culex sitiens group collected on Badu Island in 1998. In addition, 3,240 mosquitoes were speciated and pooled after being anesthetized with triethylamine (TEA). There was no significant difference in the minimum infection rate of mosquitoes anesthetized with TEA compared with those sorted on refrigerated tables (2.8 and 1.6 per 1,000 mosquitoes, respectively). Nucleotide analysis of the premembrane region and an overlapping region of the fifth nonstructural protein and 3' untranslated regions of representative 1998 Badu Island isolates of JE virus reveled they were identical to each other. Between 99.1% and 100% identity was observed between 1995 and 1998 isolates of JE from Badu Island, as well as isolates of JE from mosquitoes collected in Papua New Guinea (PNG) in 1997 and 1998. This suggests that the New Guinea mainland is the likely source of incursions of JE virus in Australia.

The molecular epidemiology of Kokobera virus

We describe herein the molecular epidemiology and phylogeny of Kokobera (KOK) virus, a flavivirus found in Australia and Papua New Guinea. We sequenced a region encompassing the 200 nucleotides of the 3' terminus of the NS5 gene, and the first 300 nucleotides of the 3' untranslated region (UTR). The study included 25 isolates of the virus, including an isolate from PNG, and several recent isolates from the south-west of Western Australia (WA), where the virus had not previously been detected. We found that the KOK isolates clustered according to geographic location and time of isolation into three distinct topotypes: one covering Queensland and New South Wales; another represented by the single isolate from PNG; and a third covering the Northern Territory and WA. This latter group was further subdivided into northern and south-west isolates. This molecular epidemiology is significantly different from other Australian flaviviruses, such as Murray Valley encephalitis (MVE) and Kunjin (KUN) viruses, which exist as single genetic types across the entire Australian continent. However, it is similar to the molecular epidemiology of the alphavirus Ross River (RR) virus. This may be explained by the fact that MVE and KUN viruses are known to have birds as their main vertebrate hosts, whereas RR virus utilises macropods, which have also been implicated as the vertebrate host for KOK virus. In addition, the south-west isolates exhibited a degree of sequence heterogeneity, including one isolate that has a nine nucleotide deletion in the 3'UTR. This suggests that KOK virus has been in the south-west of WA for some time, and was not recently introduced.

Australian X disease, Murray Valley encephalitis and the French connection

Epidemics of a severe encephalitis occurred in eastern Australia between 1917 and 1925, in which over 280 cases were reported with a fatality rate of 68%. The disease had not been described previously and was called Australian X disease. The next epidemic occurred in south-east Australia in the summer of 1950-51. The disease was given its name of Murray Valley encephalitis as this was the area from which most cases were reported. A virus was isolated by Eric French in Victoria, and about the same time by John Miles and colleagues in South Australia. The virus Murray Valley encephalitis (MVE) virus, was shown to be a Group B arbovirus (flavivirus) which was related to, but distinct from, Japanese encephalitis virus. Early seroepidemiological studies showed that the most likely vertebrate hosts were water birds. MVE virus was first isolated from Culex annulirostris mosquitoes in 1960. The most recent epidemic of Murray Valley encephalitis occurred in 1974, at which time it was renamed Australian encephalitis. Since 1974, however, all cases have been confined to northern Australia, particularly the north of Western Australia. Indeed, the Kimberley region of Western Australia contains the only confirmed enzootic foci of virus activity. A closely related flavivirus, Kunjin virus, has also been shown to be an aetiological agent of Australian encephalitis. Since the first isolation of MVE and Kunjin viruses, considerable information has been accumulated on their ecology and epidemiology, some aspects of which are briefly described.

Arboviruses causing human disease in the Australasian zoogeographic region

Over 65 arboviruses have been reported from countries in the Australasian zoogeographic region, but only a few have been implicated in human disease. These include the flaviviruses Murray Valley encephalitis (MVE), Kunjin (KUN), Kokobera (KOK), and dengue, particularly types 1 and 2; the alphaviruses Ross River (RR), Barmah Forest (BF), and Sindbis (SIN); and the bunyaviruses, Gan Gan and Trubanaman. In this paper recent epidemiological and clinical results pertaining to these viruses are reviewed, with major emphasis on MVE and RR viruses. The extensive early studies of Australian arboviruses have been reviewed by Doherty [49, 50], and their ecology and vectors more recently by Kay and Standfast [87]. In addition, the biology of MVE and KUN [113] and RR [87, 114] viruses have been the subjects of more detailed reviews. The Australasian zoogeographic region is defined as countries east of the Wallace and Weber lines, two hypothetical lines in the Indo-Australian archipelago where the fauna of the Australasian and Oriental regions meet. Seroepidemiological studies of human arboviral infections have suggested that the Japanese encephalitis flavivirus and the chikungunya alphavirus occur only in the Oriental region, whereas the related MVE and RR viruses, respectively, are restricted to the Australasian region [85, 148]. Serological results from Wallacea, the zone between the Wallace and Weber lines, are not so clear-cut [85]. This review is therefore restricted to countries east of Wallacea, specifically New Guinea and Australia.

Haemorrhagic manifestations with Sindbis infection. Case report

Sindbis infection in man occurs rarely in Australia. Most recorded cases are either asymptomatic or result in a fever sometimes accompanied by a macular or vesicular rash. This case is of particular interest because of the severe haemorrhagic vesicular rash and the repeated recurrence of symptoms over a 5 month period together with the persistence of IgM antibodies to Sindbis virus.