Mosquito-borne diseases

Some mosquitoes carry viruses that can make humans sick. These viruses are spread to humans by the bite of an infected mosquito. Some viruses can be carried by mosquitoes in Tasmania, other viruses are only carried by mosquitoes in other states or territories, or overseas.  

It is important to take steps to protect yourself and your family from mosquito-borne diseases by avoiding mosquito bites and removing mosquito breeding sites. This is especially important in the warmer months in Tasmania and when travelling interstate or overseas. Ross River virus and Barmah Forest virus are present in Tasmania.

In recent years, people have contracted serious mosquito-borne diseases in parts of Australia where they don’t usually occur, such as Japanese encephalitis virus in South Eastern Australia. There have also been recent reports of Murray Valley encephalitis. 

Mosquito borne diseases are notifiable to the Tasmanian Department of Health and are on Australia’s National Notifiable Disease List. There is also a mosquito surveillance program underway in Tasmania.

Protect yourself

• Wear covered footwear and loose-fitting, light-coloured clothing that covers as much of your body as possible. Mosquitoes can bite through tight-fitting clothing.
• Use insect repellents containing DEET (Diethyl toluamide), Picaridin or oil of lemon eucalyptus (OLE) on exposed skin. Always read the manufacturer's instructions before applying.
• Take extra care when mosquitoes are more active, especially around dawn and dusk and when outdoors or camping.
• Use ‘knockdown’ fly sprays and plug-in repellent devices indoors.
• Use mosquito coils in outdoor areas where you gather to sit or eat.
• Remove potential mosquito breeding sites from around the home (for example containers that collect water). 
• Use insect screens on your house, caravan or tent. If this is not possible, use a mosquito net.

Reduce your risk

• Stay in rooms with insect screens or in air-conditioned rooms.
• Use a mosquito net over your bed if the area where you are sleeping is exposed to the outdoors. Nets are most effective when they are treated with a pyrethroid insecticide, such as permethrin. 
• Stay up-to-date with local health guidance on mosquito-borne diseases at your travel destination and consider getting travel vaccines if recommended. 

Mosquito-borne diseases that occur in Tasmania

Ross River virus and Barmah Forest virus

Ross River virus and Barmah Forest virus are infections spread by the bite of an infected mosquito.

These viruses are related and cause a similar illness.

Ross River virus is mostly acquired during the summer months when the weather is warmer and mosquitoes are more active. Outbreaks can occur when local conditions of rainfall, tides and temperature promote mosquito breeding.

Barmah Forest virus is relatively common in mainland states. It has only recently become present in Tasmania.

Symptoms

Many people will not develop symptoms.

However, if they do develop symptoms these can include:

• fever
• headache
• aches and pains in muscles and joints
• tiredness
• rash
• swollen or stiff joints

Symptoms usually develop three to nine (but up to 21) days after being bitten by an infected mosquito. Most people recover completely in a few weeks.

Diagnosis

These infections are diagnosed following clinical assessment by a doctor who may order a blood test. Two blood tests may be needed two weeks apart. Other illnesses with similar symptoms may need to be ruled out.

Treatment

There is no specific treatment or vaccine for either infection. Your doctor will advise you on medication to ease the discomfort of symptoms such as joint pain and fever.

As there is no treatment, prevention by avoiding mosquito bites is important.

How are Ross River virus and Barmah Forest virus spread?

Both Ross River and Barmah Forest virus infections are spread by certain types of mosquitoes. When a female mosquito feeds on the blood of an infected animal, the mosquito may become infected with the virus.

The virus may then be passed on to humans when the mosquito feeds again. The virus is not spread from person-to-person. A mosquito is always involved.

Where is Ross River virus and Barmah Forest virus found in Tasmania?

Ross River virus can be found in coastal regions extending from the North (including the islands of eastern Bass Strait), down to the south-eastern corner of Tasmania.

So far, Barmah Forest virus seems localised to the East Coast.

Mosquito-borne diseases that occur interstate or overseas

Japanese encephalitis

Japanese encephalitis is a rare but potentially serious infection of the brain caused by the Japanese encephalitis virus. It is a nationally notifiable disease.

Japanese encephalitis is spread by some types of mosquitoes and is more common in areas of increased mosquito activity. Pigs and certain water birds are hosts for the virus. There is no evidence of person-to-person transmission.

Most people infected with Japanese encephalitis virus have no symptoms. Very rarely, Japanese encephalitis virus can be serious and brain inflammation (encephalitis) can occur.

No cases have been detected in Tasmania.

The risk of being infected with Japanese encephalitis virus in Tasmania is currently very low.

In recent years, cases of Japanese Encephalitis occurred in south-eastern Australia, particularly along the Murray River at the NSW-VIC border. Most cases had extensive exposure to mosquitos or water-based activities prior to getting sick. Prior to this, in Australia, Japanese encephalitis virus had only been detected in the outer Torres Strait of Australia. 

Symptoms

Less than one per cent of people infected with Japanese encephalitis virus develop symptoms. 

Symptoms typically include fever, joint pain and rash.

More rarely, the infection can progress to brain inflammation (encephalitis). Symptoms of encephalitis may include:

• headache
• nausea and vomiting
• confusion or change in mental status
• generalised weakness
• weakness on one side of the body or face
• speech, visual or hearing problems
• loss of coordination
• seizures
• coma

Symptoms usually develop five to 15 days after a person has been bitten by an infected mosquito. If you experience these symptoms, seek medical attention immediately. Children under five years old and older adults are at higher risk of developing severe illness.

Diagnosis

Depending on the severity of the illness, Japanese encephalitis virus can be diagnosed either by a General Practitioner or in hospital.

Clinical history, examination and time spent in an area where Japanese encephalitis virus has been detected may lead a doctor to suspect Japanese encephalitis virus.

The diagnosis is confirmed by a laboratory testing of blood or cerebrospinal fluid (the fluid surrounding the brain and spinal cord) collected through a lumbar puncture procedure.

Other illnesses with similar symptoms may need to be ruled out.

Treatment

There is no specific treatment for Japanese encephalitis virus infection.

For people who experience symptoms, treatment aims to ease the discomfort of milder symptoms such as joint pain and fever.

If your symptoms are severe or you experience complications, you may need to be treated in hospital.

How is Japanese encephalitis spread?

Japanese encephalitis virus is spread by some types of mosquitoes.

There is no evidence of person-to-person transmission.

Pigs and certain water birds can also be infected with JEV. While they cannot directly transfer the virus to humans, indirect transmission can occur via mosquitoes.

Prevention

You can reduce your chances of becoming unwell with Japanese encephalitis virus by:

• Protecting yourself against mosquito bites
• Getting a Japanese encephalitis virus vaccine

Vaccination

Japanese encephalitis virus is a vaccine preventable disease. 

Two safe and effective vaccines are available in Australia (Imojev and JEspect). 

These vaccines have different recommendations depending on age, pregnancy, and whether a person has immunocompromise.

If you meet certain conditions, you may be eligible for a free vaccine.

Visit your General Practitioner, travel doctor or another immunisation provider for more information.

Japanese encephalitis virus vaccine information for health professionals

Imojev is a live attenuated vaccine given subcutaneously as a single dose. It is suitable for people aged nine months and older where there are no contraindications to its use. Imojev is contraindicated in those who are pregnant, planning pregnancy (avoid pregnancy for 28 days), and immunocompromised. It is not licensed for use in children less than nine months of age.

JEspect (branded Ixiaro) is an inactivated vaccine given intramuscularly in a two-dose schedule. It is the preferred JEV vaccine for those who are pregnant or breastfeeding, children aged two to nine months and immunocompromised individuals. The recommended doses vary with age. The dose interval is 28 days although can be reduced to seven days if there is a high risk of exposure.

Both vaccines can be co-administered with other vaccines if required. 

Adverse events are generally minor and short-lived, with most symptoms resolving within a few days.

More detailed information on the vaccines can be found in the Australian Immunisation Handbook.

Eligibility for the Department of Health, Tasmania Japanese encephalitis virus vaccination program

The Communicable Diseases Network of Australia has prioritised certain risk groups for Japanese encephalitis virus vaccination.

As the risk of Japanese encephalitis virus within Tasmania is assessed as very low, only people travelling to or residing on mainland Australia or the Torres Strait and Tiwi Islands and who meet one of the following criteria, are eligible for vaccination:

• work at or reside at a piggery, including but not limited to farm workers and their families (including children aged two months and older), transport workers, veterinarians and others involved in the care of pigs
• work at or reside at a pork abattoir or pork rendering plant
• work directly with mosquitoes through their surveillance (field or laboratory based) or control and management, and indirectly through management of vertebrate mosquito-borne disease surveillance systems (for example sentinel animals) such as environmental health officers and workers and entomologists
• diagnostic and research laboratory workers who may be exposed to the virus, such as persons working with Japanese encephalitis virus cultures or mosquitoes with the potential to transmit Japanese encephalitis virusV as per the Australian Immunisation Handbook
• living near a piggery with current or recent Japanese encephalitis virus activity
• feral pig hunters and doggers
• individuals living, working, or undertaking frequent recreational activities in regions, including aquatic habitats, determined to be at current or anticipated, near future Japanese encephalitis virus risk.
• Healthcare professionals who have patients that meet the above criteria should contact the Communicable Diseases Prevention Unit (CDPU) Immunisation team to discuss eligibility. CDPU will undertake a risk assessment based on the epidemiology of Japanese encephalitis virus in Australia.
• Healthcare professionals can contact the CDPU Immunisation team on 1800 671 738 (option 3 to speak to a Communicable Diseases Clinical Nurse Consultant) or via fax (6173 0821).
• Additionally, oversees travellers to endemic areas and those who live or work on the outer islands of the Torres Strait continue to be recommended to receive a private vaccine.

How much does it cost?

• The vaccine is free for eligible people.
• People who request Japanese encephalitis virus vaccine for domestic and international travel purposes are not eligible for a free vaccine under this public health program and instead should speak to their General Practitioner, travel doctor or another immunisation provider.

Murray Valley encephalitis

Murray Valley encephalitis is a potentially serious infection closely related to Japanese encephalitis. It is a nationally notifiable disease.

There have been recent cases of Murray Valley encephalitis infections in mainland Australia, some of these infections have resulted in serious illness and death. 

Murray Valley encephalitis is spread through the bite of infected mosquitoes. Water birds are the primary host for the virus. Person-to-person transmission does not occur. 

The incubation period is usually seven to 12 days but can be between five to 28 days. It is thought that once a person has been infected, they acquire long lasting immunity. 

Symptoms

People infected with Murray Valley encephalitis often don’t develop any symptoms or they develop mild symptoms such as fever, headache, nausea and vomiting. 

Rarely, meningitis or encephalitis (brain inflammation) can occur. People with severe infection may develop drowsiness, severe headaches, neck stiffness, photophobia, muscle weakness, neurological symptoms, seizures, or loss of consciousness. 

In severe cases, infection may result in permanent disability or death.

Who is at risk?

Everyone is at risk of mosquito bites and mosquito borne diseases. Everyone should take steps to protect themselves.

People who have more frequent exposure to infected mosquitos are at increased risk. This includes people participating in outdoor activities such as camping and water sports. 

Outcomes may be worse in the very young and people over 50 years old. It is also thought that immunosuppressed individuals have increased susceptibility to disease. 

Diagnosis

Clinical history, examination, and time spent in an area where Murray Valley Encephalitis virus has been detected may lead a doctor to suspect the infection.

The diagnosis can be confirmed by laboratory testing of blood or cerebrospinal fluid (the fluid surrounding the brain and spinal cord) collected through a lumbar puncture procedure.

Repeat testing may be required to confirm the diagnosis. 

Other illnesses with similar symptoms may need to be ruled out.

Treatment

It is important to seek medical attention if you think you have Murray Valley encephalitis virus. 

There is no specific treatment available for Murray Valley encephalitis. 

For people who experience symptoms, treatment aims to ease the discomfort of milder symptoms.

How is it spread?

Murray Valley encephalitis virus is spread through the bite of an infected mosquito. 

The main mosquito that spreads the virus is Culex annulirostris, however other mosquito species including other Culex and some Aedes species may also be involved. 

There is no evidence of person-to-person transmission. 

Water birds are the primary reservoir for the virus. 

Where is it found? 

Murray Valley encephalitis virus is endemic to northern Australia and Papua New Guinea, with single cases or small outbreaks every few years.

Less frequent outbreaks also occur in the south-easterly states (excluding Tasmania). In early 2023, the virus was detected in Victoria and south-eastern Australia for the first time since 1974.

Environmental conditions increase the circulation of the virus in some areas, for example when there has been higher than average rainfall and particularly following floods.

The mosquito primarily involved in transmitting Murray Valley encephalitis Virus is C. annulirostris. This mosquito is not currently found in Tasmania.

Prevention

Avoiding mosquito bites and taking care during travel are important to avoid getting Murray Valley encephalitis. 

There is no vaccine available for the Murray Valley encephalitis.

Other mosquito-borne diseases

• West Nile/Kunjin virus
• Chikungunya virus 
• Dengue fever
• Malaria
• Yellow Fever
• Zika virus 

Interstate travel

Where to get help

• In an emergency call 000 (triple zero) for an ambulance
• Visit your nearest hospital emergency department 
• Speak to your General Practitioner
• For other queries, contact the Communicable Diseases Prevention Unit on 1800 671 738 (option 3 to speak to a Communicable Diseases Clinical Nurse Consultant) or via fax (6173 0821).