A wet spring and summer means more mosquitoes, but now we also have the Japanese encephalitis virus.

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Mosquitoes are a problem every summer. But the recent arrival of the mosquito-borne Japanese encephalitis virus in eastern Australia raises more significant concerns.


  • Cameron Webb

    Cameron Webb is a Conversation Friend.

    Clinical Associate Professor and Principal Hospital Scientist, University of Sydney

There are hundreds of different mosquito species in Australia, but only a few pose a threat to public health. The activity of these mosquitoes varies from season to season with differences in rainfall and temperature.

A changing climate and extreme wet weather events can increase mosquito populations and bring additional hazards.

How can we reduce the risk of contracting mosquito-borne diseases, including Japanese encephalitis?

First, some mozzie basics

Mosquitoes need stagnant water to complete their life cycle. Immature mosquitoes hatch and complete their development under water until they pupate before emerging as adult mosquitoes.

Female mosquitoes need blood before they can lay eggs. They seek blood from different types of animals and can pick up the virus in addition to ingesting blood. This virus can then be passed to another animal or human when they need blood.

Mozzies make you sick by injecting a cocktail of saliva and viruses when they bite. “Mozzie spit” can leave you with an itchy red welt, as well as a dose of a potentially fatal disease.

What diseases can mosquitoes transmit?

Australia has always struggled with mosquito-borne diseases. Ross River virus infects thousands of people every year. Extreme weather events are increasing the number of events around our cities and growing coastal communities.

Murray Valley encephalitis virus is extremely rare but can be fatal. Significant outbreaks have been closely associated with flooding in the Murray-Darling Basin region.

Mosquito-borne diseases are more dangerous than humans. Horses can experience severe symptoms after being infected with Ross River virus or Kunjin virus.

There are also concerns about cattle ephedrine fever and bovine skin disease.

Even in our backyard, our dogs can be affected by parasites spread by mosquito bites.

What about Japanese encephalitis virus?

The discovery of the mosquito-borne Japanese encephalitis virus last summer changed the landscape of mosquito-borne disease in Australia.

The disease can be mild, with common symptoms being fever, joint pain and rash. In severe cases, people also experience headaches, neck stiffness, confusion, seizures, and sometimes coma and death. Less than 1% of those infected will develop encephalitis, a severe brain infection that can be fatal.

Japanese encephalitis virus is a serious health problem in Southeast Asia and the Western Pacific. The virus circulates among mosquitoes and waterfowl, but pigs can also be hosts.

The virus was first detected in commercial pig farms where reproductive losses were observed, and Australia declared it an “infectious disease event of national importance” in March.

The virus has been detected in humans, pigs (both commercial pig farms and wild populations) and mosquitoes in South Australia, Victoria, New South Wales, Queensland and the Northern Territory. There have been 40 cases of human illness, including six deaths.

A recent study of five regional communities in southern NSW found that almost 9% of the human population was exposed to the virus last summer.

What can happen this summer?

Thanks to the third consecutive season affected by La Nina, we are expecting a wetter summer. The floods have already started.

More rain not only means more mosquitoes, but also better breeding conditions for waterfowl. More water, more birds and more mosquitoes set the scene for potentially more activity of Japanese encephalitis and other mosquito-borne diseases.

The mosquito species of greatest concern is Culex annulirostris. This mosquito is the most responsible for the transmission of the virus between animals, as well as its spread to the human population.

This species is closely associated with freshwater habitats. With extensive flooding in many areas, there will be plenty of suitable habitat throughout the coming summer.

So how can we reduce the risk?

While officials are investigating ways to control mosquito populations, particularly spraying insecticides around piggeries and other high-risk areas, insecticides alone will not eliminate the risk of Japanese encephalitis this season. Other strategies are required.

A safe and effective vaccine is available, and authorities are developing strategies to ensure access to it for “at-risk” communities and individuals.

But there is not enough vaccine globally to vaccinate everyone at risk in Australia.

Monitoring will provide early warning of high risks. Authorities will monitor and test mosquito populations for the virus, as will various animal control networks. If detected, authorities can respond strategically through enhanced monitoring, surveillance, or education programs.

There are many ways we can reduce mosquito bites during the summer, whether it’s in the bush, spending time outdoors, or protecting against mosquitoes that carry these viruses.

Covering up with loose-fitting long sleeves, long pants, and covered shoes will prevent mosquito bites.

Application of topical insect repellents, particularly formulations containing diethyltoluamide, picaridin, or oil of lemon eucalyptus, will provide safe and effective long-term protection against mosquito bites.

Preventing mosquito bites is the best way to protect yourself and your family from mosquito-borne diseases.


Cameron Webb and the Department of Medical Entomology, NSW Health Pathology, were engaged by a wide range of repellent and insecticide manufacturers to provide product testing and provide expert advice on mosquito biology. Cameron also received funding from local, state and federal agencies to conduct research on mosquito-borne disease control and management.

/Courtesy of chat. This material from the creative organization/author(s) may be timely, edited for clarity, style and length. The views and opinions expressed are those of the author(s).

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