Performance Evaluation of VIDAS® Diagnostic Assays Detecting Anti-Chikungunya Virus IgM and IgG Antibodies: An International Study

Chikungunya (CHIK) is a debilitating mosquito-borne disease with an epidemiology and early clinical symptoms similar to those of other arboviruses-triggered diseases such as dengue or Zika. Accurate and rapid diagnosis of CHIK virus (CHIKV) infection is therefore challenging. This international study evaluated the performance of the automated VIDAS^® anti-CHIKV IgM and IgG assays compared to that of manual competitor IgM and IgG ELISA for the detection of anti-CHIKV IgM and IgG antibodies in 660 patients with suspected CHIKV infection. Positive and negative agreements of the VIDAS^® CHIKV assays with ELISA ranged from 97.5% to 100.0%. The sensitivity of the VIDAS^® CHIKV assays evaluated in patients with a proven CHIKV infection confirmed reported kinetics of anti-CHIKV IgM and IgG response, with a positive detection of 88.2-100.0% for IgM ≥ 5 days post symptom onset and of 100.0% for IgG ≥ 11 days post symptom onset. Our study also demonstrated the superiority of ELISA and VIDAS^® assays over rapid diagnostic IgM/IgG tests. The analytical performance of VIDAS^® anti-CHIKV IgM and IgG assays was excellent, with a high precision (coefficients of variation ≤ 7.4%) and high specificity (cross-reactivity rate ≤ 2.9%). This study demonstrates the suitability of the automated VIDAS^® anti-CHIKV IgM and IgG assays to diagnose CHIKV infections and supports its applicability for epidemiological surveillance and differential diagnosis in regions endemic for CHIKV.

Susceptibility of Aedes albopictus, Ae. aegypti and human populations to Ross River virus in Kuala Lumpur, Malaysia

BACKGROUND

Emerging arboviruses such as chikungunya and Zika viruses have unexpectedly caused widespread outbreaks in tropical and subtropical regions recently. Ross River virus (RRV) is endemic in Australia and has epidemic potential. In Malaysia, Aedes mosquitoes are abundant and drive dengue and chikungunya outbreaks. We assessed risk of an RRV outbreak in Kuala Lumpur, Malaysia by determining vector competence of local Aedes mosquitoes and local seroprevalence as a proxy of human population susceptibility.

METHODOLOGY/PRINCIPAL FINDINGS

We assessed oral susceptibility of Malaysian Ae. aegypti and Ae. albopictus by real-time PCR to an Australian RRV strain SW2089. Replication kinetics in midgut, head and saliva were determined at 3 and 10 days post-infection (dpi). With a 3 log10 PFU/ml blood meal, infection rate was higher in Ae. albopictus (60%) than Ae. aegypti (15%; p<0.05). Despite similar infection rates at 5 and 7 log10 PFU/ml blood meals, Ae. albopictus had significantly higher viral loads and required a significantly lower median oral infectious dose (2.7 log10 PFU/ml) than Ae. aegypti (4.2 log10 PFU/ml). Ae. albopictus showed higher vector competence, with higher viral loads in heads and saliva, and higher transmission rate (RRV present in saliva) of 100% at 10 dpi, than Ae. aegypti (41%). Ae. aegypti demonstrated greater barriers at either midgut escape or salivary gland infection, and salivary gland escape. We then assessed seropositivity against RRV among 240 Kuala Lumpur inpatients using plaque reduction neutralization, and found a low rate of 0.8%.

CONCLUSIONS/SIGNIFICANCE

Both Ae. aegypti and Ae. albopictus are susceptible to RRV, but Ae. albopictus displays greater vector competence. Extensive travel links with Australia, abundant Aedes vectors, and low population immunity places Kuala Lumpur, Malaysia at risk of an imported RRV outbreak. Surveillance and increased diagnostic awareness and capacity are imperative to prevent establishment of new arboviruses in Malaysia.

Prevalence of Barmah Forest Virus, Chikungunya Virus and Ross River Virus Antibodies among Papua New Guinea Military Personnel before 2019

Barmah Forest virus (BFV), Chikungunya virus (CHIKV) and Ross River virus (RRV) belong to the Alphavirus genus of the family Togaviridae. All three virus infections have been reported in Papua New Guinea (PNG) previously, but the exact prevalence and distribution of these three alphaviruses in PNG has not been established. Sera collected from 204 PNG Military Personnel (PNGMP) study participants in April 2019 was tested for the presence of anti-BFV, anti-CHIKV and anti-RRV immunoglobulin G (IgG) antibodies using commercially available enzyme-linked immunosorbent assay (ELISA) IgG detection kits, as well as for specific neutralizing antibodies (NAb) against individual viruses. Overall, sero-positivity of the sera was anti-BFV IgG 12.3% (25/204), anti-BFV NAb 8.3% (17/204); anti-CHIKV IgG 47.1% (96/204), anti-CHIKV NAb 34.8% (71/204); and anti-RRV IgG 93.1% (190/204), anti-RRV NAb 56.4% (115/204), respectively. Of the 137/204 participants that were Nab-positive for at least one virus, we identified 4 BFV, 40 CHIKV and 73 RRV single infections, and 9 RRV+CHIKV and 11 BFV+RRV double infections. The lower proportion of NAb sero-positive compared to the ELISA IgG sero-positive assay samples suggests that the currently available commercial ELISA detection kits for these three alphaviruses may not be suitable for diagnostic/surveillance purposes in endemic areas such as PNG, due to serological cross-reactivity among these three alphaviruses. Laboratory testing using known positive control sera indicated no cross-neutralization between BFV and RRV; however, some RRV or BFV single infection human sera demonstrated low-level cross-neutralization against CHIKV (the ratio of RRV/CHIKV NAb titers or BFV/CHIKV ≥ 4). Our preliminary results indicate that the majority of PNGMP have previously been exposed to RRV, with mild exposure to CHIKV and low-level exposure to BFV, suggesting that multiple alphaviruses have been circulating among PNGMP. The transmission landscapes of these three alphaviruses across PNG should be prioritized for further investigation, including identification of specific vectors and hosts that mediate human spillover in order to mitigate future outbreaks. Ongoing education regarding precautionary and protective measures are needed to better protect individuals who travel to PNG.

Physiology and ecology combine to determine host and vector importance for Ross River virus

Identifying the key vector and host species that drive the transmission of zoonotic pathogens is notoriously difficult but critical for disease control. We present a nested approach for quantifying the importance of host and vectors that integrates species' physiological competence with their ecological traits. We apply this framework to a medically important arbovirus, Ross River virus (RRV), in Brisbane, Australia. We find that vertebrate hosts with high physiological competence are not the most important for community transmission; interactions between hosts and vectors largely underpin the importance of host species. For vectors, physiological competence is highly important. Our results identify primary and secondary vectors of RRV and suggest two potential transmission cycles in Brisbane: an enzootic cycle involving birds and an urban cycle involving humans. The framework accounts for uncertainty from each fitted statistical model in estimates of species' contributions to transmission and has has direct application to other zoonotic pathogens.

Persistent Joint Pain Following Arthropod Virus Infections

PURPOSE OF REVIEW

Persistent joint pain is a common manifestation of arthropod-borne viral infections and can cause long-term disability. We review the epidemiology, pathophysiology, diagnosis, and management of arthritogenic alphavirus infection.

RECENT FINDINGS

The global re-emergence of alphaviral outbreaks has led to an increase in virus-induced arthralgia and arthritis. Alphaviruses, including Chikungunya, O'nyong'nyong, Sindbis, Barmah Forest, Ross River, and Mayaro viruses, are associated with acute and/or chronic rheumatic symptoms. Identification of Mxra8 as a viral entry receptor in the alphaviral replication pathway creates opportunities for treatment and prevention. Recent evidence suggesting virus does not persist in synovial fluid during chronic chikungunya infection indicates that immunomodulators may be given safely. The etiology of persistent joint pain after alphavirus infection is still poorly understood. New diagnostic tools along and evidence-based treatment could significantly improve morbidity and long-term disability.

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.

Climate change and infectious diseases in Australia's Torres Strait Islands

OBJECTIVE

This research seeks to identify climate-sensitive infectious diseases of concern with a present and future likelihood of increased occurrence in the geographically vulnerable Torres Strait Islands, Australia. The objective is to contribute evidence to the need for adequate climate change responses.

METHODS

Case data of infectious diseases with proven, potential and speculative climate sensitivity were compiled.

RESULTS

Five climate-sensitive diseases in the Torres Strait and Cape York region were identified as of concern: tuberculosis, dengue, Ross River virus, melioidosis and nontuberculous mycobacterial infection. The region constitutes 0.52% of Queensland's population but has a disproportionately high proportion of the state's cases: 20.4% of melioidosis, 2.4% of tuberculosis and 2.1% of dengue.

CONCLUSIONS

The Indigenous Torres Strait Islander peoples intend to remain living on their traditional country long-term, yet climate change brings risks of both direct and indirect human health impacts. Implications for public health: Climate-sensitive infections pose a disproportionate burden and ongoing risk to Torres Strait Islander peoples. Addressing the causes of climate change is the responsibility of various agencies in parallel with direct action to minimise or prevent infections. All efforts should privilege Torres Strait Islander peoples' voices to self-determine response actions.

Animals as potential reservoirs for dengue transmission: A systematic review

Dengue is a rapidly spreading mosquito-borne flavivirus infection that is prevalent in tropical and sub-tropical regions. Humans are known to be the main reservoir host maintaining the epidemic cycles of dengue but it is unclear if dengue virus is also maintained in a similar enzootic cycle. The systematic review was conducted in accordance to Cochrane's PRISMA recommendations. A search was done on PubMed, EMBASE, Scopus and Cochrane Library. Key data on animal dengue positivity was extracted and classified according to animal type and diagnostic modes. Of the 3818 articles identified, 56 articles were used in this review. A total of 16,333 animals were tested, 1817 of which were positive for dengue virus by RT-PCR or serology. Dengue positivity was detected in bats (10.1%), non-human primates (27.3%), birds (11%), bovid (4.1%), dogs (1.6%), horses (5.1%), pigs (34.1%), rodents (3.5%), marsupials (13%) and other small animals (7.3%). While majority of dengue positivity via serology suggests potential enzootic transmission, but regular dengue virus spillback cannot be excluded. With the exception of bats, acute infection among animals is limited. Further investigation on animals is critically required to better understand their role as potential reservoir in dengue transmission.

Spatial and temporal patterns of Ross River virus in south east Queensland, Australia: identification of hot spots at the rural-urban interface

Background

Ross River virus (RRV) is responsible for the most common vector-borne disease of humans reported in Australia. The virus circulates in enzootic cycles between multiple species of mosquitoes, wildlife reservoir hosts and humans. Public health concern about RRV is increasing due to rising incidence rates in Australian urban centres, along with increased circulation in Pacific Island countries. Australia experienced its largest recorded outbreak of 9544 cases in 2015, with the majority reported from south east Queensland (SEQ). This study examined potential links between disease patterns and transmission pathways of RRV.

Methods

The spatial and temporal distribution of notified RRV cases, and associated epidemiological features in SEQ, were analysed for the period 2001–2016. This included fine-scale analysis of disease patterns across the suburbs of the capital city of Brisbane, and those of 8 adjacent Local Government Areas, and host spot analyses to identify locations with significantly high incidence.

Results

The mean annual incidence rate for the region was 41/100,000 with a consistent seasonal peak in cases between February and May. The highest RRV incidence was in adults aged from 30 to 64 years (mean incidence rate: 59/100,000), and females had higher incidence rates than males (mean incidence rates: 44/100,000 and 34/100,000, respectively). Spatial patterns of disease were heterogeneous between years, and there was a wide distribution of disease across both urban and rural areas of SEQ. Overall, the highest incidence rates were reported from predominantly rural suburbs to the north of Brisbane City, with significant hot spots located in peri-urban suburbs where residential, agricultural and conserved natural land use types intersect.

Conclusions

Although RRV is endemic across all of SEQ, transmission is most concentrated in areas where urban and peri-urban environments intersect. The drivers of RRV transmission across rural-urban landscapes should be prioritised for further investigation, including identification of specific vectors and hosts that mediate human spillover.

Localized Outbreaks of Epidemic Polyarthritis among Military Personnel Caused by Different Sublineages of Ross River Virus, Northeastern Australia, 2016-2017

Two outbreaks of epidemic polyarthritis occurred among Australian Defence Force personnel during and following short military exercises in the Shoalwater Bay Training Area, northeastern Australia, in 2016 and 2017. Ross River virus (RRV) IgM was detected in acute-phase serum samples from most patients (28/28 in 2016 and 25/31 in 2017), and RRV was recovered from 4/38 serum samples assayed (1/21 in 2016 and 3/17 in 2017). Phylogenetic analyses of RRV envelope glycoprotein E2 and nonstructural protein nsP3 nucleotide sequences segregated the RRV isolates obtained in 2016 and 2017 outbreaks into 2 distinct sublineages, suggesting that each outbreak was caused by a different strain of RRV. The spatiotemporal characteristics of the 2016 outbreak suggested that some of the infections involved human-mosquito-human transmission without any intermediate host. These outbreaks highlight the importance of personal protective measures in preventing vectorborne diseases for which no vaccine or specific prophylaxis exists.

First evidence of concurrent enzootic and endemic transmission of Ross River virus in the absence of marsupial reservoirs in Fiji

BACKGROUND

Ross River virus (RRV) is a zoonotic alphavirus transmitted by several mosquito species. Until recently, endemic transmission was only considered possible in the presence of marsupial reservoirs.

METHODS

RRV seroprevalence was investigated in placental mammals (including horses, cows, goats, pigs, dogs, rats, and mice) in Fiji, where there are no marsupials. A total of 302 vertebrate serum samples were collected from 86 households from 10 communities in Western Fiji.

RESULTS

Neutralizing antibodies against RRV were detected in 28% to 100% of sera depending on the species, and neutralization was strong even at high dilutions.

CONCLUSIONS

These results are unlikely to be due to cross-reactions. Chikungunya is the only other alphavirus known to be present in the Pacific Islands, but it rarely spills over into non-humans, even during epidemics. The study findings, together with a recent report of high RRV seroprevalence in humans, strongly suggest that RRV is circulating in Fiji in the absence of marsupial reservoirs. Considering that all non-human vertebrates present in Fiji are pan-global in distribution, RRV has the potential to further expand its geographic range. Further surveillance of RRV and access to RRV diagnostics will be critical for the early detection of emergence and outbreaks.

The 2019 report of the MJA-Lancet Countdown on health and climate change: a turbulent year with mixed progress

The MJA-Lancet Countdown on health and climate change was established in 2017 and produced its first Australian national assessment in 2018. It examined 41 indicators across five broad domains: climate change impacts, exposures and vulnerability; adaptation, planning and resilience for health; mitigation actions and health co-benefits; economics and finance; and public and political engagement. It found that, overall, Australia is vulnerable to the impacts of climate change on health, and that policy inaction in this regard threatens Australian lives. In this report we present the 2019 update. We track progress on health and climate change in Australia across the same five broad domains and many of the same indicators as in 2018. A number of new indicators are introduced this year, including one focused on wildfire exposure, and another on engagement in health and climate change in the corporate sector. Several of the previously reported indicators are not included this year, either due to their discontinuation by the parent project, the Lancet Countdown, or because insufficient new data were available for us to meaningfully provide an update to the indicator. In a year marked by an Australian federal election in which climate change featured prominently, we find mixed progress on health and climate change in this country. There has been progress in renewable energy generation, including substantial employment increases in this sector. There has also been some progress at state and local government level. However, there continues to be no engagement on health and climate change in the Australian federal Parliament, and Australia performs poorly across many of the indicators in comparison to other developed countries; for example, it is one of the world's largest net exporters of coal and its electricity generation from low carbon sources is low. We also find significantly increasing exposure of Australians to heatwaves and, in most states and territories, continuing elevated suicide rates at higher temperatures. We conclude that Australia remains at significant risk of declines in health due to climate change, and that substantial and sustained national action is urgently required in order to prevent this.

Establishment of an Alphavirus-Specific Neutralization Assay to Distinguish Infections with Different Members of the Semliki Forest complex

Background: Alphaviruses are transmitted by arthropod vectors and can be found worldwide. Alphaviruses of the Semliki Forest complex such as chikungunya virus (CHIKV), Mayaro virus (MAYV) or Ross River virus (RRV) cause acute febrile illness and long-lasting arthralgia in humans, which cannot be clinically discriminated from a dengue virus or Zika virus infection. Alphaviruses utilize a diverse array of mosquito vectors for transmission and spread. For instance, adaptation of CHIKV to transmission by Aedes albopictus has increased its spread and resulted in large outbreaks in the Indian Ocean islands. For many alphaviruses commercial diagnostic tests are not available or show cross-reactivity among alphaviruses. Climate change and globalization will increase the spread of alphaviruses and monitoring of infections is necessary and requires virus-specific methods. Method: We established an alphavirus neutralization assay in a 384-well format by using pseudotyped lentiviral vectors. Results: MAYV-specific reactivity could be discriminated from CHIKV reactivity. Human plasma from blood donors infected with RRV could be clearly identified and did not cross-react with other alphaviruses. Conclusion: This safe and easy to use multiplex assay allows the discrimination of alphavirus-specific reactivity within a single assay and has potential for epidemiological surveillance. It might also be useful for the development of a pan-alphavirus vaccine.

Temperature explains broad patterns of Ross River virus transmission

Thermal biology predicts that vector-borne disease transmission peaks at intermediate temperatures and declines at high and low temperatures. However, thermal optima and limits remain unknown for most vector-borne pathogens. We built a mechanistic model for the thermal response of Ross River virus, an important mosquito-borne pathogen in Australia, Pacific Islands, and potentially at risk of emerging worldwide. Transmission peaks at moderate temperatures (26.4°C) and declines to zero at thermal limits (17.0 and 31.5°C). The model accurately predicts that transmission is year-round endemic in the tropics but seasonal in temperate areas, resulting in the nationwide seasonal peak in human cases. Climate warming will likely increase transmission in temperate areas (where most Australians live) but decrease transmission in tropical areas where mean temperatures are already near the thermal optimum. These results illustrate the importance of nonlinear models for inferring the role of temperature in disease dynamics and predicting responses to climate change.

Mosquitoes cannot control their body temperature, so their survival and performance depend on the temperature where they live. As a result, outside temperatures can also affect the spread of diseases transmitted by mosquitoes. This has left scientists wondering how climate change may affect the spread of mosquito-borne diseases. Predicting the effects of climate change on such diseases is tricky, because many interacting factors, including temperatures and rainfall, affect mosquito populations. Also, rising temperatures do not always have a positive effect on mosquitoes – they may help mosquitoes initially, but it can get too warm even for these animals.

Climate change could affect the Ross River virus, the most common mosquito-borne disease in Australia. The virus infects 2,000 to 9,000 people each year and can cause long-term joint pain and disability. Currently, the virus spreads year-round in tropical, northern Australia and seasonally in temperate, southern Australia. Large outbreaks have occurred outside of Australia, and scientists are worried it could spread worldwide.

Now, Shocket et al. have built a model that predicts how the spread of Ross River virus changes with temperature. Shocket et al. used data from laboratory experiments that measured mosquito and virus performance across a broad range of temperatures. The experiments showed that ~26°C (80°F) is the optimal temperature for mosquitoes to spread the Ross River virus. Temperatures below 17°C (63°F) and above 32°C (89°F) hamper the spread of the virus. These temperature ranges match the current disease patterns in Australia where human cases peak in March. This is two months after the country’s average temperature reaches the optimal level and about how long it takes mosquito populations to grow, infect people, and for symptoms to develop.

Because northern Australia is already near the optimal temperature for mosquitos to spread the Ross River virus, any climate warming should decrease transmission there. But warming temperatures could increase the disease’s transmission in the southern part of the country, where most people live. The model Shocket et al. created may help the Australian government and mosquito control agencies better plan for the future.