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Japanese encephalitis, Murray Valley encephalitis are feared, but mosquito experts say death risk is low

Health officials have expressed concern over the resurgence of Japanese encephalitis (JE) and the detection of mosquito-borne Murray Valley encephalitis (MVE) this summer, but the likelihood of death remains low in both cases. .

There have been 7 deaths out of 45 cases of JE notified in Australia since 1 January 2021, with almost all cases from 2022.

Warnings against mosquito-borne viruses were issued after flooding in New South Wales, Victoria and South Australia, creating perfect conditions for insect populations to grow rapidly.

No one was infected with MVE this summer, but it was detected in mosquitoes during monitoring in 2012. Northern Victoria When Local NSWMenindee, Griffith, etc.

Multiple cases of Japanese encephalitis have been detected in recent months after the floods.

How likely is it to get worse?

Medical virologist Dominic Dwyer of NSW Health Pathology said MVE is similar to JE and most people don’t know which one they have.

“Both have encephalitis in their names, which means inflammation of the brain,” said Professor Dwyer.

“Both of them [brain inflammation] are relatively rare. Only one of the hundreds of infected people develops encephalitis. “

Professor Dwyer says Japanese encephalitis is a concern for medical professionals.(Courtesy: Dominic Dwyer, NSW Health Pathology)

However, Professor Dwyer said the fatality rate is substantial for the few people who become inflamed.

“A quarter or a third of people who develop either MVE or JE could die if they get encephalitis,” he said.

“Many of the survivors have fairly significant long-term brain damage.”

When MVE broke out in 1974, about one-third of those who developed encephalitis in Victoria died, one-third had permanent brain damage, and one-third made a full recovery.

Differences and Similarities

Professor Dwyer said MVE is of Australian origin, but JE is the most common cause of viral brain infections in Southeast Asia.

“They belong to the same virus family, but they are genetically different,” he said.

A man with glasses in the green grass.
Cameron Webb studies mosquitoes and the transmission cycle.(Courtesy: Cameron Webb, NSW Health Pathology)

Cameron Webb is a Medical Entomologist at the University of Sydney and NSW Health Pathology.

Webb said the mosquito species most likely to spread both MVE and JE are Culex pipienslove life in freshwater.

“All of these habitats across the environment will be flooded with rain, and as the floodwaters recede, pools and puddles will become ideal habitats,” he said.

Both viruses have similar symptoms such as fever, headache, and vomiting.

Symptoms of more serious infections include neck stiffness, coma, and seizures.

A hut in a caravan park, surrounded by a meter of water.
The recent floods have caused mosquito numbers to skyrocket.(ABC Riverina: Romy Stevens)

Why are viruses emerging now?

Dr Webb said it was not surprising that the mosquito population was “massive” this year, given the recent floods.

“Towards the end of summer, mosquito populations are generally expected to start peaking,” he said.

Dr. Webb said mosquitoes typically picked up MVE and JE from waterfowl, which also breed due to flooding and transmit the virus to humans.

He said the more mosquitoes bite, the more likely they are to be exposed to the virus.

“High mosquito populations don’t necessarily guarantee disease outbreaks,” says Dr. Webb.

“It certainly increases the chances of an infected mosquito biting someone.”

A mosquito trap hanging from a tree.
Surveillance can help detect mosquito-borne viruses early.(Courtesy: Cameron Webb, NSW Health Pathology)

Which viruses are health authorities more concerned about?

Professor Dwyer said MVE has been around for a long time, with occasional outbreaks such as in the 1970s.

There have been detections of Japanese encephalitis in Australia in the past, but it did not emerge properly until last year.

“Because Japanese encephalitis is a relatively new disease, people of all ages are at risk of infection,” said Professor Dwyer.

“It’s new, we don’t really know what the extent of it is, and whether it’s likely to continue to be part of our ecosystem now, so it’s cause concern.

“It’s entirely possible that Japanese encephalitis will persist as Murray Valley persisted.”

A man with a bucket-shaped mosquito trap.
Capture and sample mosquito populations to test for viruses.(By: NSW Health Pathology)

Dr. Webb said surveillance programs such as sampling of mosquito populations and sentinel chickens have played an important role in the early detection of mosquito-borne viruses.

He said mosquitoes don’t travel far, so people who have lived in or traveled to areas where the virus has been active should be vigilant.

“Some of the mosquitoes we know of can fly perhaps two to five kilometers away from swamps,” Dr. Webb said.

A man sprays repellent on his arm.
Mosquito repellents are considered the most effective protection.(Flickr: Miguel Garces)

how to protect yourself

There are no treatments available for either virus, and vaccines are only available for Japanese encephalitis, so personal protection is the best defense.

Japanese encephalitis vaccine is widely available across Australia, and eligibility requirements are determined by state and territory public health departments.

Dr. Webb said the most important form of defense is mosquito repellents, especially products containing diethyltoluamide. [DEET]picaridin, or oil of lemon eucalyptus.

“It doesn’t matter what formula you choose, whether it’s a roll-on, cream, gel, or spray, but choose a product that contains those active ingredients,” he said.

Other ways to avoid mosquito bites:

  • Cover your body—wear long, loose, light-colored clothing
  • Limit outdoor activities if there are a lot of mosquitoes
  • Removes stagnant water where mosquitoes can breed around your home or campsite
  • Please ensure your accommodation is equipped with mosquito nets or screens on holidays

https://www.abc.net.au/news/2023-01-15/japanese-encephatlitis-murray-valley-encephalitis-risks/101853404 Japanese encephalitis, Murray Valley encephalitis are feared, but mosquito experts say death risk is low

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