Murray Valley encephalitis and Kunjin viruses
Image © Richard C. Russell, 1999
What are Murray Valley encephalitis and Kunjin viruses?
Murray Valley encephalitis (MVE) is a rare but potentially fatal disease caused by the MVE virus which is carried by mosquitoes.
Kunjin virus is a related virus that is also carried by mosquitoes, but generally causes less severe symptoms.
There are no vaccines to prevent MVE or Kunjin diseases and no medical cures.
How do you catch these viruses?
In nature, these viruses move in cycles between birds (especially water birds) and mosquitoes. Humans can only catch MVE or Kunjin viruses after being bitten by an infected mosquito. These viruses cannot be caught directly from birds or other people.
Both MVE and Kunjin viruses are very rare. Approximately only 1 person in 1000 will develop MVE symptoms after being bitten by an infected mosquito.
People at greatest risk of these illnesses are those unlikely to have previously been exposed to the viruses, such as very young children or people new to an area where MVE and Kunjin viruses occur.
When do symptoms appear?
The time between being bitten and becoming sick (the incubation period) varies from 5 to 15 days. Symptoms usually appear 8 to 10 days after being bitten.
What are the symptoms?
Symptoms will vary from person to person. While many infected people will not develop any symptoms at all, children and adults who develop symptoms can become seriously ill.
MVE symptoms in young children include:
- drowsiness (excessive sleepiness)
In older children and adults MVE symptoms include:
- drowsiness or confusion
- bad headache and stiff neck
- nausea and vomiting
- muscle tremors
The symptoms for Kunjin disease can be similar to MVE but are generally milder. However, the most common symptoms for Kunjin virus include:
- swollen and aching joints
- muscle weakness
- enlarged lymph nodes.
A doctor who diagnoses a patient with MVE or Kunjin disease must notify the Department of Health immediately so more can be learnt about where the virus is active and public health action can be taken if necessary. These actions may include implementing mosquito control programs where possible and the issuing of public warnings.
How serious are these diseases?
Symptoms can vary from mild to severe or even fatal. Patients with the severe form of MVE become ill very quickly with confusion, worsening headaches, increasing drowsiness and possible fits.
There is no way of telling whether a person will get a mild or severe form of MVE or Kunjin disease. Early symptoms are the same in either case so it is important to seek urgent medical attention in suspected cases.
What is the recovery time?
Recovery time will vary depending on the severity of the disease. In mild cases, the patient will start to improve after a few days. People with more severe symptoms may take several months to recover and need physiotherapy, speech therapy and other forms of rehabilitation. Others will be left paralysed or with brain damage. Unfortunately, about a quarter of people who become ill with MVE will not survive.
What medical treatments are available?
There are no vaccines or medical cures for MVE or Kunjin viruses. People who are suspected to have these diseases should be taken to the nearest hospital for urgent medical treatment to manage symptoms. Often patients are transferred to major hospitals with intensive care facilities because they are seriously ill or because their doctor is concerned their condition may deteriorate.
Can I catch MVE or Kunjin viruses more than once?
No. Once you have been infected with MVE or Kunjin viruses (even if you did not develop any symptoms) you cannot be infected again.
Adults who have grown up in areas where MVE and Kunjin viruses occur naturally are often immune to these diseases following infection during childhood.
Unfortunately, people who have been infected with the MVE virus are not immune to the Kunjin virus and vice versa.
When and where are MVE and Kunjin viruses most active in Western Australia?
The main areas of risk in WA occur every wet season in the Kimberley and parts of the Pilbara, generally between December and June.
In the Gascoyne, Murchison, northern Goldfields and Midwest regions the virus is only active after very heavy summer and/or autumn rainfall.
People living, visiting or camping near swamps, floodplains, river systems, large irrigation areas or major dams may be at particular risk, especially during the evening and night. However, MVE and Kunjin viruses can also be active in other areas when mosquitoes are abundant.
Map of Western Australia, MVE and Kunjin activity
Annual wet season activity
Activity in very wet season
Rare activity after extreme flooding
How can I protect myself against these viruses?
The best protection against MVE and Kunjin viruses is to minimise your risk of being bitten by an infected mosquito. Simple tips to avoid mosquito bites include:
- Insect-proof houses by screening all doors and windows.
- Doors should be self-closing and open outwards.
- In high-risk areas build a fully screened outdoor area to protect yourself when outside.
Cover up and use repellents
- Avoid mosquitoes when they are most active, particularly around dawn and dusk. Some mosquitoes will also bite during the day. Reduce the risk of contracting RRV or BFV by timing outdoor activities to avoid periods of greatest mosquito activity.
- Cover up with long, loose-fitting and preferably light-coloured clothing. Mosquitoes can bite through fitted clothing, even denim jeans.
- Mosquito repellents are an important way of avoiding exposure to diseases transmitted by mosquitoes. When outdoors, carry an effective mosquito repellent for use if mosquitoes are active.
- The most effective repellents contain either diethyl toluamide (DEET) or picaridin.
- Lotion or gel repellents are the most effective. Always read the label. Apply and re-apply repellents in accordance with the manufacturer’s instructions.
- Natural or organic repellents are generally not as effective as DEET or picaridin and may need to be re-applied more frequently.
- The best protection for babies and young children is protective clothing, bed nets and other forms of insect screening. Only infant-strength repellents should be used on young children.
Travelling and camping
- If you are travelling, discuss with your GP how to protect yourself against diseases carried by mosquitoes.
- Screen caravans, tents, swags and other sleeping equipment or use a mosquito net.
- Recognise and avoid areas of mosquito activity such as swamps, salt marshes, billabongs and river floodplains.
Eliminate backyard breeding habitats
- Dispose of all containers that hold water.
- Stock ornamental ponds with mosquito-eating fish such as goldfish. Keep vegetation away from the water’s edge.
- Keep swimming pools well chlorinated, filtered and free of dead leaves.
- Level or drain depressions in the ground that hold water.
- Fit mosquito-proof covers to vent pipes on septic tank systems. Seal all gaps around the lid and ensure leach drains are completely covered.
- Screen rainwater tanks with insect-proof mesh, including inlet, overflow and inspection ports. Ensure guttering is not blocked and does not hold water.
- Empty pot plant drip trays once a week or fill with sand. Empty and clean animal and pet drinking water bowls once a week.
- Some plants (especially bromeliads) hold water in their leaf axils. These should also be emptied weekly.
Residual chemical sprays can be used to further reduce mosquitoes. This should not, however, replace the removal and prevention of backyard breeding sites which is a more effective control method. Always read the label and apply residual sprays in accordance with the manufacturer’s instructions.
What broader mosquito control measures are in place?
Effective mosquito control in natural environments is currently not achievable in most parts of WA where MVE and Kunjin viruses occur due to the large scale of areas that would require chemical treatment. In an effort to reduce mosquito numbers, some local governments use residual surface sprays or carry out fogging; however, these methods are only partially effective, so it is important to take personal measures to reduce the risk of catching a mosquito-borne disease.
For further information contact:
Where to get help
- See your doctor
- Visit a GP after hours
- Ring healthdirect on 1800 022 222
This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.