Spread of vicious virus carrier puzzles experts

By MONIQUE DEVEREUX

Biosecurity experts are unable to tell if a ferocious Australian mosquito is spreading across New Zealand by itself or if each discovery of the pest is a new incursion.

The Government has given the Ministry of Health $40 million to combat the southern saltmarsh mosquito since it was first identified in 1998.

That money is supposed to last until 2006 but most of it has been spent.

So far the treatments have been deemed successful but the ministry is not sure the eradication is working because it does not know how the mosquito keeps reappearing.

The mosquito can carry the Ross River virus, a crippling disease not found in New Zealand. The ministry has conservatively estimated that an outbreak in Auckland alone would cost $38 million.

The pest has now been found in the South Island and a three-day investigation starts today in Wairau, near Blenheim, to determine how widely the population is spread.

The southern saltmarsh is a vicious insect, biting relentlessly in the day, unlike most mosquitoes, which attack at dusk and dawn.

Victims in Wairau report the insect biting through thick jerseys and long-sleeved shirts.

Eradication in two areas, Napier and Mahia, appears to have been successful, but there is no technology to determine if the mosquitoes in the various areas are related, and therefore spreading.

The ministry's chief technical officer, Sally Gilbert, said the ministry was watching closely for the development of such technology.

"Obviously how they [the mosquitoes] might move around New Zealand or how they might come across from Australia is one of our key questions.

"However, it doesn't seem likely that this new incursion could have come from the east coast of the North Island in recent times anyway because we have had no southern saltmarsh mosquitoes there now for nearly 18 months."

Ross River virus

People infected may suffer pain and tenderness in muscles and joints, particularly the wrists, knees and ankles. Flu-like symptoms, including fever, chills, sweating, headache and tiredness are common.

Symptoms surface from 3 days to 21 days (an average of 9 days) after being bitten and can last months or years. They subside with few or no side-effects.

Painkillers such as aspirin or paracetamol may relieve pain and swelling. Sometimes stronger medication is needed.

The disease, which can only be diagnosed with a special blood test, is usually milder and runs a shorter course in children.

The virus is not contagious and if people avoid being bitten by mosquitoes they cannot get infected.

(Source: Ministry of Health)