Australia declares Japanese encephalitis situation a “communicable disease incident of national significance”

On Friday, March 4, the Australian government issued a joint press release quoting the country’s acting chief medical officer and its chief veterinary officer that declared an outbreak of Japanese encephalitis virus in pigs across four states and at least one confirmed human case in Queensland for the first time since 1998. Importantly, they noted multiple states with human cases of encephalitis of unknown origin: “The Department of Health is aware of other cases, in multiple states, of encephalitis of unknown origin that are being investigated for arboviral diseases, including JEV.”

At least some of these human cases are in the four states with confirmed outbreaks in pigs: Queensland, New South Wales, Victoria and South Australia. For example, on March 7, in New South Wales two people were diagnosed with Japanese encephalitis virus, according to the Australian Broadcasting Corporation. To my knowledge, no human cases this far south in Australia have been reported previously.

Citing Mark Schipp, Australia’s chief veterinary officer, the Australian Broadcasting Corporation also reported on March 7 that “more than 12 people and animals at 21 piggeries have been infected.”

A licensed vaccine for Japanese encephalitis is available. This vaccine is being offered to workers at piggeries and other people at risk. This virus is transmitted by mosquitoes. No person-to-person transmission occurs. There are no licensed antiviral drugs or monoclonal antibodies. The majority of infections in humans have few or no symptom. Thus, there are many more humans infected than those hospitalized due to neurologic disease.

The exact cause of this outbreak of unprecedented geographic scope in Australia is uncertain.  Very likely a large and growing economic and trade impact will result. Testing of mosquitoes for the virus is likely ongoing. Genetic sequencing of this virus in pigs, mosquitoes and humans over time might offer some clues as to origin and spread. Movement of pigs, whether from outside Australia or within Australia, is also likely being investigated.

If the number of human cases rises sharply, then any investigational antiviral drugs or monoclonal antibodies might be studied under clinical protocols for treatment or possibly prophylaxis. More developments in the coming days and weeks should be anticipated.