Mosquito-borne diseases

Mosquitoes can carry many different diseases that can be passed on to humans through a mosquito bite.

In Australia, these include:

Murray Valley Encephalitis (MVE) virus:

MVE is a serious but rare infection. The majority of people infected by the virus don’t show symptoms. Others develop a mild illness and make a full recovery. A small proportion of people go on to develop encephalitis – a swelling of the brain tissue that can lead to brain damage or death.

Symptoms of the virus usually appear 7 to 12 days after being infected by a mosquito bite and can include fever, nausea and vomiting, headache and muscle aches. Encephalitis symptoms are serious and require urgent medical attention. They include severe headaches, neck stiffness, sensitivity to bright light, seizures or fits (especially in young children), drowsiness and confusion.

MVE virus cannot be spread directly from one person to another, only via a mosquito bite. The virus is present all year in northern Australia and can be present in Victoria during the summer months – especially during heavy rainfall or flooding.

Ross River and Barmah Forest virus:

Ross River and Barmah Forest viruses are very similar, especially in their symptoms – however, Barmah Forest virus symptoms tend to be milder.

Ross River virus and Barmah Forest virus can cause joint inflammation and pain, fatigue and muscle aches, and a rash. Recovery is generally between 3 and 6 months, although some people have intermittent symptoms for a year or more.

Dengue virus:

Dengue virus is also spread by mosquito bites and is an issue in tropical and subtropical parts of the world including Africa, Asia, South America and some parts of Northern Queensland in Australia. It is not a common virus. Cases generally occur when someone from an international location visits or returns to Australia and introduces the virus to the local mosquito population.

Dengue virus ranges in severity from mild to severe flu-like illness. There is no specific treatment or vaccine. Symptoms include fevers, headaches, pain in joints and muscles, lack of appetite, nausea and vomiting, and skin rash. These symptoms generally resolve within one to two weeks.

Japanese Encephalitis (JE) virus:

Japanese encephalitis is a rare but serious infection of the brain spread to humans through mosquito bites. The virus can be transmitted from pigs to humans via a mosquito bite. JE virus cannot be caught by eating pork or pig products. Those most at risk of JE are people who live near or work with pigs. Children under the age of 5 years and older people are at higher risk of developing severe illness when infected with the JE virus.

Symptoms of JE can range from very mild to severe illness including fever, headache, light sensitivity, neck stiffness, vomiting, confusion, convulsions and coma. Symptoms develop between 6-16 days after being bitten by an infected mosquito. There is no specific treatment.

Across Australia, JE virus vaccination is available for specific priority groups, including those who may have occupational exposure, free of charge. These groups include those who work or live at a piggery; personnel who work directly with mosquitoes; and, diagnostic and research laboratory workers who may be exposed to JE virus. GP clinics can provide the JE virus vaccination.

Farmers and agricultural workers should be aware that the JE virus can cause encephalitis in pigs and horses, leading to infertility and abortion; neurological symptoms in pigs; and, fever, lethargy, anorexia and neurological symptoms in horses.

JE virus is a notifiable exotic disease in animals throughout Australia. If you suspect an animal is showing signs of JE virus – you must report it, either by contacting your local veterinarian or call the national Emergency Animal Disease Watch Hotline on 1800 675 888.

Notification:

Murray Valley Encephalitis (MVE), Ross River, Barmah Forest, Dengue and Japanese Encephalitis viruses are all nationally notifiable diseases in humans.

• Notification to the Communicable Diseases Network Australia (CDNA) is made by health professionals after diagnosis through laboratory or clinical evidence.

How to avoid mosquito bites:

Prevention of mosquito bites is key to reducing the risk of infection from Murray Valley Encephalitis virus, Ross River and Barmah Forest virus, Dengue virus and Japanese Encephalitis virus. There are many ways you can protect yourself against mosquito bites, they include:

• Wearing long, loose-fitting clothing and covering up as much as possible
• Using an effective mosquito repellent on all exposed skin
• Preventing mosquito breeding around the home by:
  • Removing any uncovered areas where water can lie, including pet water bowls, underneath pot plants, bird baths, tyres, wheelbarrows and children’s toys
  • Keeping lawns and gardens trimmed to reduce the areas where mosquitoes can rest
• Preventing mosquitoes from entering the home by using intact and well-fitting fly screens on windows and doors.

Fast facts:

• Mosquitoes can carry a range of different viruses
• Many mosquito-borne viruses can cause flu-like symptoms ranging from very mild to severe
• Preventing mosquito bites and mosquito breeding are key to reducing risks associated with mosquito-borne disease.