Neglected Australian arboviruses associated with undiagnosed undifferentiated febrile illness

Australia is home to over 75 arthropod-borne viruses, with least 13 associated with human infection. Ross River (RRV), Barmah Forest (BFV), Murray Valley encephalitis (MVEV) and Kunjin (KUNV) viruses commonly cause disease and are diagnosed in pathology laboratories. Following commercial ELISA development to diagnose RRV, in 2016 cases exceeded 9,000. However, other indigenous arboviruses, such as Alfuy (ALFV), Edge Hill (EHV), Kokobera (KOKV), Sindbis (SINV) and Stratford (STRV), are not routinely tested. Little is known of their role in human pathology, undifferentiated febrile illness (UFI) or serious diseases. This study aimed to determine prevalence of infection of humans with these neglected Australian arboviruses and whether any causes UFI. Screening of 1,000 age- and gender-stratified plasma samples from healthy Queensland-resident blood donors for antiviral IgG antibodies by indirect ELISA produced non-specific reactivity so a sub-sample was tested by plaque reduction neutralisation. 492 acute-phase samples from UFI patients in northern Australia were also screened by indirect immunofluorescence for virus-specific IgM antibodies. There was a linear increase in prevalence of neutralising antibodies with annual seroconversion rates ranging from RRV 1.3% to KOKV and STRV 0.05%. Among UFI patient samples 5.2% contained IgM against one or more of: RRV 0.8%; BFV 0.4%; ALF 1.4%; EHV 1.8%; KOKV 1.4%; KUNV 2.4%; MVEV 1.0%; STRV 1.2%. No age-dependent anti-ALFV antibodies prevalence was observed. A small proportion of UFI was attributable to infection; 2 ALFV, 4 EHV, 14 KOKV, 8 KUNV, 8 MVEV and 1 STRV identified cases per 1000 persons tested. These results indicate several neglected Australian arboviruses have been infecting humans for decades and some may be associated with UFI. A program of systematic testing of UFI patients is recommended to examine for recent infection to determine the significance of the burden of the disease that these neglected arboviruses cause

Neglected Australian arboviruses and undifferentiated febrile illness: Addressing public health challenges arising from the ‘Developing Northern Australia’ government policy

The Australian Government is currently promoting the development of Northern Australia, with an associated increase in the local population. Consequent to this is the public health threat posed by heightened human exposure to many previously neglected arboviruses that are indigenous to the region. This initiative to support economic activity in the tropical north of the continent is leading to the accelerated expansion of an infection-naïve human population into hitherto un-encountered ecosystems inhabited by reservoir animals and vectors for these arboviruses. Combined with an apparent rise in the number and impact of dramatic climate events, such as tropical cyclones and floods caused by torrential monsoonal rainfall, this heightens the potential for viral transmission to humans. More than 75 arboviruses have been identified in Australia, some of which are associated with human disease but for which routine tests are not available to diagnose infection. Here, we describe briefly the neglected Australian arboviruses that are most likely to emerge as significant agents of human disease in the coming decades. We also advocate the establishment of a thorough surveillance and diagnostic protocol, including developing new pan-viral rapid tests for primary care use to assist in the early diagnosis and correct treatment of affected patients. We propose that the implementation of these activities will enhance our understanding of the geographical range, prevalence, identification and control of neglected Australian arboviruses. This would minimise and limit the possibility of large-scale outbreaks with these agents as population and economic growth expands further into Australia’s tropical north

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. © 2017 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved

Australian arboviruses associated with undiagnosed undifferentiated febrile illness

There are at least 13 Australian arboviruses that have been associated with human infection but routine tests are not available to diagnose infection with most of these and their role in human pathology, undifferentiated febrile illness (UFI) or other serious diseases is unknown. Following the development of a commercial ELISA to diagnose Ross River virus infections, the number of cases in Australia rose from 20-50 per year to more than 9000 in 2016. The aim of this study was to determine how prevalent infection of humans with these “orphan” viruses was and whether any of them are the cause of UFI. Screening of 1000 age and gender stratified plasma samples from healthy blood donors for IgG antibodies against, Ross River, Barmah Forest, Alfuy, Kokobera, Stratford, Kunjin and Edge Hill viruses by indirect ELISA produced a large number of non-specific reactions so, an age and gender stratified sub-sample from the plasma panel was tested in plaque reduction neutralisation tests. Additionally, 492 UFIs samples from patients in northern Australia were screened by indirect immunofluorescence for the presence of IgM antibodies against these viruses. There was a linear increase in the prevalence of neutralising antibodies against these viruses with annual seroconversion rates of Ross River virus,1.4% (r2=0.7); Barmah Forest virus, 0.5% (r2=0.7); Kunjin virus, 0.4% (r2=0.7); Edge Hill virus, 0.4% (r2=0.5); Kokobera virus,0.3% (r2=0.9); Alfuy virus 0.2% (r2=0.5); Murray valley encephalitis virus, 0.1% (r2=0.3) and Stratford virus 0.6% (r2=0.9). Of the 492 samples from UFI patients 5.2% contained IgM antibodies against one or more of these Australian arboviruses: RRV (0.8%); BFV (0.4%); ALF (1.4%); EHV (1.8%); KOK (1.4%); KUNV (2.4%); MVE (1%); STRV (1.2%). These results suggest that a number of the “orphan” Australian arboviruses have been infecting humans at a regular rate for decades and some of them may be associated with UFIs. There should be ongoing, and systematic, testing of UFI patients for evidence of recent infection with these orphan arboviruses to determine how significant the burden of the disease they cause is

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

Neglected Australian arboviruses associated with undifferentiated febrile illnesses

Infections with commonly occurring Australian arthropod-borne arboviruses such as Ross River virus (RRV) and Barmah Forest virus (BFV) are diagnosed routinely by pathology laboratories in Australia. Others, such as Murray Valley encephalitis (MVEV) and Kunjin (KUNV) virus infections may be diagnosed by specialist reference laboratories. Although Alfuy (ALFV), Edge Hill (EHV), Kokobera (KOKV), Sindbis (SINV), and Stratford (STRV) viruses are known to infect humans in Australia, all are considered ‘neglected.’ The aetiologies of approximately half of all cases of undifferentiated febrile illnesses (UFI) in Australia are unknown and it is possible that some of these are caused by the neglected arboviruses. The aims of this study were to determine the seroprevalence of antibodies against several neglected Australian arboviruses among residents of Queensland, north-east Australia, and to ascertain whether any are associated with UFI. One hundred age- and sex-stratified human plasma samples from blood donors in Queensland were tested to determine the prevalence of neutralising antibodies against ALFV, BFV, EHV, KOKV, KUNV, MVEV, RRV, SINV, and STRV. The seroconversion rates for RRV and BFV infections were 1.3 and 0.3% per annum, respectively. The prevalence of antibodies against ALFV was too low to enable estimates of annual infection rates to be determined, but the values obtained for other neglected viruses, EHV (0.1%), KOKV (0.05%), and STRV (0.05%), indicated that the numbers of clinical infections occurring with these agents are likely to be extremely small. This was borne out by the observation that only 5.7% of a panel of 492 acute phase sera from UFI patients contained IgM against any of these arboviruses, as detected by an indirect immunofluorescence assay. While none of these neglected arboviruses appear to be a cause of a significant number of UFIs in Australia at this time, each has the potential to emerge as a significant human pathogen if there are changes to their ecological niches

Identification of the source of blood meals in mosquitoes collected from north-eastern Australia

Background: More than 70 arboviruses have been identified in Australia and the transmission cycles of most are poorly understood. While there is an extensive list of arthropods from which these viruses have been recovered, far less is known about the non-human hosts that may be involved in the transmission cycles of these viruses and the relative roles of different mosquito species in cycles of transmission involving different hosts. Some of the highest rates of human infection with zoonotic arboviruses, such as Ross River (RRV) and Barmah Forest viruses (BFV), occur in coastal regions of north-eastern Australia. Methods: Blood-engorged mosquitoes collected as a part of routine surveillance using CO2-baited light traps in the Rockhampton region and the adjoining Shire of Livingstone in central Queensland, north-eastern Australia, were analysed individually for the source of their blood meal. A 457 nucleotide region of the cytochrome b gene of blood in engorged mosquitoes was amplified by PCR and the amplicons sequenced. The origin of the blood were identified by comparing the sequences with those published in the GenBank. Results: The most common hosts for the mosquitoes sampled were domestic cattle (26/54) and wild birds (14/54). Humans (2/54) were an infrequent host for this range of mosquitoes that are known to transmit arboviruses causing human disease, and in an area where infections with human pathogens like RRV and BFV are commonly recorded. The blood meals identified in the most abundant vector analysed, Culex annulirostris, were from 10 different vertebrate hosts. The notable detection of chimpanzee blood in two mosquitoes, presumably obtained from a nearby zoo, extends the known range of hosts for this species. Culex quinquefasciatus and Cx. sitiens fed almost exclusively on a variety of bird species. Conclusions: While human-mosquito-human transmission of arboviruses like RRV can occur this study highlights the potential importance of zoonotic cycles of transmission including avian species, of arboviruses that are indigenous to Australia. Further work on larger samples of blood-engorged mosquitoes is required to validate the trends observed herein as well as to confirm the virus isolations from the various vertebrate hosts that have been identified in this study