RRV infected soldiers may cause outbreaks of epidemic polyarthritis

Major outbreaks of epidemic polyarthritis may be triggered by soldiers infected with Ross Rover Virus (RRV) by mosquitos while on training exercises, infectious disease experts have warned.

Two outbreaks of EPA in Australian Defence Force personnel after training in remote areas of Queensland in 2016 and 2017 likely involved human-mosquito-human transmission without any intermediate host, an investigation has concluded.

The outbreaks showed the Ross River Virus had established its natural endemic cycle in the closed military area that has mosquito control programs, concluded scientists from the Australian Defence Force Malaria and Infectious Disease Institute in Queensland.

And more worryingly, if transmission of RRV is occurring between humans this could lead to major epidemics of polyarthritis in other geographical areas similar to ones such as occurred in Fiji in 1979, they warned.

In their analysis of the two Queensland outbreaks, they found that in each case groups of more than 40 soldiers reported symptoms such as polyarthritis and muscle pain (71-88%), arthralgia (67-88%), fatigue (71-88%), loss of appetite (52-75%), stiff neck (38-71%), fever (33-47%), rash (9.5-65%), headache (28-41%), and sore throat (14-24%) after completing a 12 day exercise in the Shoalwater Bay Training Area north of Rockhampton.

Ross River Virus was detected in about a third of those affected, all of whom reported being bitten by mosquitos despite limited avoidance measures such as use of repellent and sleeping under nets while outdoors.  Most recovered within 4–6 weeks but three remained unfit for work three months after illness onset.

The investigators said the first wave of polyarthritis cases were likely due to ‘spillover’ from the natural endemic animal-mosquito-animal transmission cycle in the area where there are large uncontrolled populations of native animals such as kangaroos that harbour RRV.

But some of the ADF members affected became ill three to five weeks after returning to barracks, suggesting there was a secondary human-mosquito-human infection cycle, possibly involving asymptomatic but viraemic individuals.

This created a potential risk for RRV to be exported by asymptomatic personnel to other areas of Australia and even to other countries, the researchers said.

“This risk is of particular concern for countries with mosquitoes known to be RRV vectors  …  The recent experience with Zika and chikungunya viruses underscores the serious threat posed to global health by the potential for previously obscure arboviruses to move from their historical cycles of transmission,” they wrote in Emerging Infectious Diseases.

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