Mosquito borne Murray Valley Encephalitis warnings for NSW and North Victoria

By Dr. Ananya Mandal, MDJan 1 2012

The NSW Health authorities are warning residents and visitors in southern and western NSW to take extra precautions and protect themselves against mosquitoes following the detection of the Murray Valley Encephalitis (or MVE) virus in NSW. Residents and visitors to North Victoria are also similarly warned.

MVE and other more common mosquito borne infection are prevalent in summer and autumn, everyone should take simple measures to avoid mosquito bites say authorities. The MVE virus has been detected in sentinel chickens located near Leeton, Hay and Moama in the south of the state, and also in the Macquarie Marshes, located in the west of the state approximately 100km from the townships of Brewarrina, Walgett, Nyngan and Coonamble. Sentinel chicken flocks act as a warning system for human infection by being regularly monitored for viruses that mosquitoes can transmit to people and cause illness.

NSW Health Director of Health Protection, Dr Jeremy McAnulty, said the latest detections should serve as an important reminder for people to protect themselves. “Positive MVE findings in chickens are relatively rare in NSW. The important message is to avoid mosquito bites and be alert to any symptoms,” Dr McAnulty said. “The current area of risk for MVE extends in regions west of the Great Dividing Range and is likely to be highest around rivers and wetlands, especially along the Murray, Darling, and Paroo rivers and their tributaries and in recently flooded areas in western NSW…The increased risk of human cases is related to increasing numbers of mosquitoes that carry the virus and can transmit it to birds and occasionally people. Mosquito numbers increase with warmer temperatures and rainfall,” he said.

“We saw MVE activity last summer and autumn in sentinel chickens and in mosquitoes, and two human cases of MVE infection were detected in NSW, but there have been no cases reported so far this summer. Both cases were in people who lived near the Macquarie Marshes and both recovered...While MVE is relatively rare, and most people will not develop symptoms, it is a serious mosquito-borne disease,” Dr McAnulty said.

“In mild cases, symptoms of MVE include fever, headache, nausea and vomiting and muscle aches. In more severe cases symptoms can include neck stiffness, lethargy, drowsiness, confusion, delirium, tremors, neurological problems and coma in severe cases. People with these symptoms should immediately seek medical assistance. In young children, fever might be the only early sign, so parents should see their doctor if concerned, and particularly if their child has convulsions, drowsiness, floppiness, irritability, poor feeding or general distress,” he warned.

Victoria's acting chief health officer Dr Rosemary Lester said, “There have been no confirmed cases of MVE in humans. The last confirmed human case of MVE in Victoria was in 1974.” Most people infected with the virus did not develop symptoms, but if they did occur, they included a severe headache, high fever, drowsiness, tremor and seizures, Dr Lester said. She urged people with these symptoms to seek urgent medical attention from their GP or local hospital.

Mosquitoes also carry other human diseases including Ross River virus, Barmah Forest virus and Kunjin viruses that can cause fever, rash and joint pains. The MVE virus is transmitted by infected mosquitoes which breed in flooded, grassy and swamp areas and around rivers and waterways. The mosquito is especially active around dawn and around sundown, with a peak in the first two hours of the night.

The authorities advise covering up as much as possible when outside in light-colored, loose-fitting clothing and covered footwear. They advise the use of an effective repellent on all exposed skin and reapplication within a few hours, as protection wears off from perspiration, particularly on hot nights. The best mosquito repellents contain Diethyl Toluamide (DEET) or Picaridin. Use of physical barriers such as netting of prams, cots and play areas is preferred for children especially below 3 months. Repellents containing less than 10% DEET or Picaridin are safe for older children if applied according instructions. Screens and nettings on windows and doors can help.