VICTORIAN doctors who treated a baby with Japanese encephalitis in one of the first cases in the state have shared their experience, urging fellow clinicians to consider differential diagnoses. The question is, is the mosquito-borne disease here to stay?
Doctors at the Royal Children’s Hospital in Melbourne described the case of a 4-month-old boy who had feverish seizures after a 2-day fever, reduced energy and diet, which progressed to aseptic meningoencephalitis. .
No pathogen was initially found in the cerebrospinal fluid (CSF) tests and the child was treated for sepsis and seizures.
It was not until a public health alert was issued for the Japanese mosquito-borne encephalitis (JEV) virus, which had not been seen before in the southern Australian states, that it was considered a potential cause of symptoms of the child.
The child’s CSF, taken on day 1, was tested for JEV and tested positive. Another story revealed that he had traveled to a town on the border between Victoria and New South Wales 15 days before the onset of symptoms, near where the virus had been detected 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 should be considered “now in all patients with meningoencephalitis in whom no alternative causative pathogen has been identified, especially when there are epidemiological risk factors,” they wrote.
They reported good results for their patient, who returned close to the initial neurological function with some residual weakness but improved limbs.
Why was JEV so surprised?
Since the first human case was reported in Queensland in March 2022, there have been 42 confirmed and probable cases of Japanese encephalitis in Australia, including four deaths. Two-thirds of the cases were reported in NSW and Victoria.
In an exclusive podcast, Dr. David Williams, leader of the Emergency Disease Laboratory Diagnostic Group at CSIRO’s Australian Center for Disease Preparedness, said this year’s discovery of Japanese encephalitis had been “without precedents “, so that the experts were” caught unawares “.
Dr Williams explained that VEV had not been seen in Australia since the outbreaks in the far north and Torres Strait in the 1990s.
“There was a certain complacency that Japanese encephalitis would not be transmitted further south,” Dr. Williams said. “I think everything has taken us by surprise, and it’s also under the radar.”
Surveillance activities in recent years had focused mainly on Ross River fever, Murray Valley encephalitis and West Nile / Kunjin virus, he said: “Many of the mosquito surveillance systems did not have encephalitis. Japanese in the target list “.
Dr. Williams said he was also surprised that the first case was detected in a Queensland pigsty (the virus causes dead and weak piglets and wild boar infertility) and that in the following days cases were found in NSW, Victoria and South. Australia too.
“It wasn’t in a single focused area,” he said. “It was everywhere.”
In addition, the disease had been in the country at least since early November 2021, as the sow infection must have occurred before 60-70 days of gestation to affect the piglets.
Associate Professor Cameron Webb, a medical entomologist at NSW Health Pathology, said the occurrence of JEV in a very large area of South Australia was “incredibly significant”.
“In particular, in NSW, this is the first time people have died from mosquito bites since the 1970s, when there was a severe outbreak of the Murray Valley encephalitis virus,” he said. to say.
Associate Professor Webb said the strain of JEV that was now circulating was different from that found in northern Australia in the 1990s.
“The best explanation is that the virus has reached Australia through infected birds, or potentially through wind-infected mosquitoes,” said Associate Professor Webb.
Will climate change make JEV more common?
Although extreme weather events associated with climate change are clearly part of the equation, predicting the impact of climate change on diseases such as Japanese encephalitis is not straightforward.
Associate Professor Webb explained that the virus probably made its way from northern Australia to the southern regions by a “cascade effect” through waterfowl and mosquito populations, enabled by the conditions. weather conditions associated with La Niña weather patterns.
“But if we return to an extreme drought in many parts of Australia, this virus could go away and we may not see it again for a decade or so,” he said.
“So while a change in climate may explain the emergence of JEVs in Australia in 2021-22, that doesn’t necessarily mean it will be an annual issue in many of these same areas.”
As the first day of winter approaches this week, Associate Professor Webb said there was little evidence that the JEV was actively circulating among the mosquitoes in the areas affected by the outbreak.
However, the virus could still persist in mosquito eggs during the winter, he said, paving the way for it to be reintroduced next summer.
Good news for next summer
Sentinel chickens will be waiting along the Riverina River.
Professor Dominic Dwyer, a virologist and NSW Health infectious disease physician, said labs will be testing their chicken sentinel herds for JEV next summer, in addition to the usual tests for Murray’s encephalitis. Valley and the Kunjin virus.
“Now that we know it’s there, finding it makes it easier and asking for the right evidence makes it easier,” he said.
Professor Dwyer said that for doctors, the most important red flag for JEV was encephalitis, along with anything in the patient’s history that might be relevant, such as being in an endemic area or working with pigs. .
“You can make a JEV [polymerase chain reaction (PCR) test] in cerebrospinal fluid, but it is often negative because the viremia period is short, so serological tests become important in both CSF and blood, “he said.
There are no antivirals for JEV, but there are two vaccines available in Australia: Imojev, a live attenuated vaccine, and JEspect, an inactivated vaccine, which is usually given to travelers to endemic Asian countries.
Given the limited supply of vaccines, the Australian government has given priority to populations at risk for local vaccination, including slaughterhouse workers and pig farmers and some entomologists and virologists.
Professor Dwyer said it was too early to say whether the vaccine should be given routinely in Australia as in some parts of Asia.
“We don’t know if this is a one-off raid on Australia or if it will happen next summer or next summer and if so, which parts of the country will be affected,” he said. “We need to know all this before launching a vaccine strategy.
“We’re lucky to have a breathing space to work on it before next summer,” he added.
Dr. Williams of the CSIRO said states and the federal government had responded quickly to the detection of JEVs, forming working groups to address various aspects of the response.
“There have been pretty good levels of communication between the animal health and human health sectors, but also with the participation of the pig industry,” he said.
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