VICTORIAN doctors who treated a child with Japanese encephalitis in one of the state’s first cases have shared their experience and urge fellow medics to consider the differential diagnoses. It begs the question: Is the mosquito-borne disease here to stay?
Doctors from the Royal Children’s Hospital in Melbourne described the case from a previously healthy 4-month-old boy who presented with febrile seizures after a 2-day prodrome of fever, decreased energy and nutrition, which progressed to aseptic meningoencephalitis.
No causative pathogen was initially found in cerebrospinal fluid (CSF) tests and the boy was treated for sepsis and seizures.
It wasn’t until a public health warning was issued for the mosquito-borne Japanese encephalitis virus (JEV), previously unseen in the southern states of Australia, that it was considered a possible cause of the child’s symptoms.
The child’s CSF taken on day 1 was tested for JEV and found positive. Further history revealed that he had traveled 15 days before the onset of symptoms to a town on the Victoria/New South Wales border, close to where the virus was discovered in pigs.
dr. Andrea Zhu and colleagues said that while 99% of JEV infections were thought to be asymptomatic, the case described a typical symptomatic presentation.
Japanese encephalitis “must now be considered in all patients with meningoencephalitis in whom no alternative causative agent has been identified, especially when epidemiological risk factors are present,” they wrote.
They reported good results for their patient, who returned near baseline neurological function with some residual but improved limb weakness.
Why was JEV such a surprise?
Since the first human case was reported from Queensland in March 2022, there are 42 confirmed and probable cases of Japanese encephalitis in Australia, including four deaths† Two-thirds of cases have been reported in NSW and Victoria.
in a exclusive podcastsaid Dr. David Williams, leader of the emergency disease lab diagnosis group at CSIRO’s Australian Center for Disease Preparedness, said the discovery of Japanese encephalitis this year was “unprecedented”, leaving the experts “stunned”.
dr. Williams explained that JEV had not been seen in Australia since outbreaks in the far north of the country and Torres Strait in the 1990s.
“There was a certain sense of complacency that Japanese encephalitis wouldn’t be transmitted further south,” said Dr Williams. “It has surprised us all I think, and also comes under the radar.”
Surveillance activities in recent years have mainly focused on Ross River fever, Murray Valley encephalitis and West Nile/Kunjin virus, he said: “Many of the mosquito surveillance systems had no Japanese encephalitis on the list of targets.”
dr. Williams said it was also a surprise that the first case was discovered in a pigsty in Queensland (the virus causes stillbirths, weak piglets and infertility in swine) and that over the following days, cases were found in pigsties in NSW, Victoria and South Australia. also.
“It wasn’t in a single focused area,” he said. “It was everywhere.”
In addition, the disease had been in the country since at least the beginning of November 2021, as the infection in sows must have occurred before 60-70 days of gestation to affect piglets.
Associate Professor Cameron Webb, a medical entomologist with NSW Health Pathology, said the occurrence of JEV in a very large area of South Australia was “incredibly significant”.
“In NSW in particular, this is the first time people have died from mosquito bites since the 1970s, when there was a serious outbreak of the Murray Valley encephalitis virus,” he said.
Associate Professor Webb said the strain of JEV circulating now is different from the one in northern Australia in the 1990s.
“The best explanation is that the virus made its way to Australia through infected birds, or possibly through wind-blown infected mosquitoes,” said associate professor Webb.
Will climate change make JEV more common?
While the extreme weather events associated with climate change are clearly part of the equation, predicting the impact of climate change on diseases like Japanese encephalitis isn’t easy.
Associate Professor Webb explained that the virus most likely made its way from northern Australia to the southern regions through a “cascade effect” through waterfowl and mosquito populations, enabled by wet weather events linked to La Niña weather patterns.
“But if we were to return to extreme drought in many parts of Australia, this virus could disappear and we may not reappear for the next ten years,” he said.
“So, while a change in climate may explain the emergence of JEV in Australia in 2021-22, that doesn’t necessarily mean it will be an annual problem in many of the same areas.”
With the first day of winter approaching this week, associate professor Webb said there was little evidence that JEV was actively circulating among mosquitoes in areas affected by the outbreak.
However, the virus can still be present in mosquito eggs during the winter, he said, paving the way to reintroduce it next summer.
Good news for next summer
Tell-tale chickens await along the Riverina’s waterways.
Professor Dominic Dwyer, a medical virologist and infectious disease physician at NSW Health, said labs will test their sentinel flocks of chickens for JEV next summer, in addition to their usual tests for Murray Valley encephalitis and Kunjin virus.
“Now that we know it’s there, it will be easier to search for it and it will be easier to order the right tests,” he said.
Professor Dwyer said that for clinicians, the main red flag for JEV was encephalitis, along with anything in the patient’s history that might be relevant, such as having been in an endemic area or working with pigs.
“You can do a JEV [polymerase chain reaction (PCR) test] on the cerebrospinal fluid, but it’s often negative because the period of viremia is short, so serological testing becomes important on both the CSF and the blood,” he said.
There are no antivirals for JEV, but two vaccines are available in Australia: Imojeva live attenuated vaccine, and JEspectan inactivated vaccine – usually given to travelers to endemic countries in Asia.
Given the limited supply of vaccines, the Australian government has prioritized populations at risk for local vaccination, including slaughterhouse and pig workers and some entomologists and virologists.
Professor Dwyer said it was too early to say whether the vaccine should be given routinely in Australia, such as in parts of Asia.
“We don’t know if this is a one-off raid in Australia or if it will happen next summer or the summer after and if so, which parts of the country will be affected,” he said. “You need to know all that before you roll out a vaccine strategy.
“We’re lucky we have breathing room to work through this for next summer,” he added.
dr. Williams of the CSIRO said the states and federal government had responded quickly to the detection of JEV and formed working groups to address various aspects of the response.
“There has been pretty good communication between the animal health and human health sectors, as well as with the pork industry,” he said.
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