I’ve written previously about how livestock are just as vulnerable as people to emerging infectious diseases. Livestock are an essential part of global food security, contributing 40% of the global value of agricultural output. Now, a major outbreak of Japanese encephalitis in Australia is affecting both people and animals.
The outbreak in Australia was first detected in February 2022 on a pig farm in Queensland and rapidly spread. Within weeks, Japanese encephalitis had affected over 50 farms throughout the country. According to veterinary experts in Australia, by late May swine farm losses had exceeded AUD$350,000. Japanese encephalitis impacts the reproductive health of sows, and piglets may be stillborn or mummified. Another clinical sign is uncontrollable shaking in piglets who are then not able to suckle.
On March 4, 2022, the Australian Department of Health declared the outbreak to be a Communicable Disease of National Significance. And the Australian government intends to invest as much as AUD$69 million to control spread and minimize damages.
As of June 1, Japanese encephalitis had sickened over 40 people and killed 5 Australians who lived in different states. According to the World Health Organization, prior to the current outbreak, only 15 human cases had been confirmed in Australia in the previous decade.
Japanese encephalitis is a disease caused by Japanese encephalitis virus. Like most emerging viruses, Japanese encephalitis virus is zoonotic, meaning that it is primarily maintained in non-human animals.
Until now, Japanese encephalitis has primarily been restricted to Southeast Asia. Even though the majority of infections are asymptomatic, it is estimated that there are approximately 68,000 clinical cases every year. However, the number of people who are annually infected is probably much higher.
Japanese encephalitis virus is a flavivirus similar to West Nile virus, which was introduced to North America in 1999 and has subsequently become endemic in birds. Like West Nile virus, Japanese encephalitis virus is spread by mosquitoes in the genus Culex.
Various bird species, including herons and egrets are amplifying hosts for the virus, but so are domestic and wild pigs, as the Australia outbreak has shown. Other species, including domesticated animals like ducks, chickens, cattle, horses, buffalo, goats and dogs can also be infected, but these are not usually considered to be amplifying hosts.
Japanese encephalitis and the North America Pork Industry
The most pressing concern for now is controlling the current outbreak in Australia, but officials and industry experts are worried that widespread transmission in Australia could result in introduction to other parts of the world, including North America. Wild pigs are prevalent in many parts of North America, including most southern US states.
Should the virus be introduced and begin transmitting in wild animals it would be impossible to eradicate and would then represent a new and continuing threat to the North American pork industry. Domestic swine herds that are impacted by Japanese encephalitis outbreaks can experience production losses of 60% to 80%.
Given the state of Japanese encephalitis virus in Australia, it would be wise to begin surveillance in North America and elsewhere. Japanese encephalitis was described for the first time in 1871 in Japan. Today it is endemic in at least 24 countries. Unfortunately, it is probably a matter of time before it is introduced to the United States.