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Southern Saltmarsh Mosquito found near Blenheim

Media Statement
11 May 2004

Southern Saltmarsh Mosquito found near Blenheim

The Southern Saltmarsh Mosquito has been found in lagoons in the Wairau estuarine area near Blenheim, the Ministry of Health said today.

The Southern Saltmarsh Mosquito (SSM) is an aggressive daytime biter and in Australia it is known to spread disease although there is no evidence to date of this happening in New Zealand.

The mosquito was found after duck shooters reported being bitten by aggressive mosquitoes on the opening day of the duck season.

An initial investigation of the area on the seaward side of the Wairau Valley by Nelson Marlborough District Health Board’s Public Health Service and New Zealand Biosecure found specimens at all stages of the mosquito’s lifecycle

New Zealand Biosecure experts identified the mosquito as Ochlerotatus camptorhynchus, or Southern Saltmarsh Mosquito. An overseas expert has also been asked to verify the identification.

“We are undertaking an investigation to determine the extent of the infestation in the initial site. We are also checking the mosquitoes in other potential sites in Marlborough region, “ said Acting Director of Public Health, Dr Doug Lush.

“At this point we do know that SSM have been found. The next step is look for other places that the mosquito could be living and then to determine the size and extent of the problem. Once we know that we can determine the appropriate response,” Dr Lush said.

“We will be talking with others that have an interest such as the Department of Conservation, Marlborough District Council, local iwi and landowners to discuss the extent of the problem.”

A helicopter is being used in the survey to identify habitat suitable for mosquito breeding and then teams will investigate each potential site to see if the mosquito is present. It is expected that this will take three days, and it is hoped to start on Friday, although this will depend on the weather.

“Public health services throughout New Zealand are also undertaking enhanced surveillance of saltmarsh habitat within their regions to identify if this mosquito is established anywhere else that we do not already know about” said Dr Lush.

“Once the information about the extent of the Wairau infestation, and nation-wide surveillance is available Health officials will discuss the information with scientific and technical experts and identify a full range of possible options to respond to the Wairau incursion.”
The Southern Saltmarsh Mosquito is a known vector for Ross River Virus (RRV) in Australia

“While most people will not experience serious health effects from RRV, it is a disease that may cause unpleasant and long lasting illness in some patients, with painful symptoms and lethargy which can last months or years,” Dr Lush said.

“People should avoid being bitten by mosquitoes where possible by using insect sprays or mosquito coils indoors, wearing long clothing and repellent when outdoors.

Southern saltmarsh mosquitoes have previously been found in Napier, Porongahau, Mahia, Tairawhiti and Kaipara (including Whitford, Mangawhai and Whangaparoa). The mosquito has been successfully eradicated from Napier and Mahia. Attempted eradication programmes are still underway in other areas and officials are cautiously optimistic that these programmes will also be successful



Where were the mosquitoes found?

They were found in several sites around the Wairau estuarine area. Specimens at all life stages of the mosquitoes lifecycle were found.

How big is the initial infestation area (size of area)
An initial survey is being conducted over 2500 hectares to determine the extent of the spread of the mosquito.

Why is it so important to do a survey of possible habitats?

It is only possible to identify breeding habitat when the site has been deluged with water. Some sites may need to be resurveyed following rain, rises in river levels or spring tides.

What monitoring has occurred in the area within the past two years?

Intermittent routine monitoring has not detected the mosquito prior to this find. To assist the public health staff, the national response unit is to go to Marlborough to assist with surveying.

What biosecurity efforts have been directed at preventing the spread?

At the moment efforts are being concentrated on determining the extent of the problems.

What should people do?

If people need to go into this area they should wear long loose clothing and use insect repellent to prevent getting bitten.

What is the lifeycle of the SSM

The mosquito life cycle has four stages, these being

Southern saltmarsh mosquitos lay their EGGS above the surface of the water and the eggs do not hatch until there is a water event such as spring tide or heavy rainfall to wet them.

The LARVAE hatch out and swim in water. The larval stage is when the mosquito is easiest to detect and is vulnerable to eradication measures

The PUPAE is the resting stage between LARVAE and ADULT.

The ADULT is the flying stage of the insects life cycle. Breeding and egg laying occur. An adult female SSM requires a blood meal before laying eggs. Adults can fly up to 5km from their breeding sites.

What is Ross River virus (RRV) disease?

Ross River virus disease is a viral infection that is endemic in Australia, and has affected people from Papua New Guinea, the Solomon Islands and some Pacific Islands. All cases that have so far been reported in New Zealand have acquired the infection from travel overseas.

What are the symptoms?

People infected by Ross River virus may develop a wide range of symptoms. Many people do not become ill but those who do may complain of pain and tenderness in muscles and joints. Joints most commonly affected are the wrists, knees and ankles. Flu like symptoms are also common and include fever, chills, sweating, a headache and tiredness. A rash may also occur on the trunk and limbs for a short time.

The symptoms may be similar to some rheumatic diseases and can only be diagnosed by a special blood test.

Symptoms occur three to 21 days (average nine days) after being bitten and may persist for months to years. The symptoms subside eventually and leave few or no after-effects.

Symptoms occur most commonly in adults. The disease is usually milder and runs a shorter course in children.

How is it spread?

The only way that people can catch Ross River virus is by being bitten by a virus-carrying mosquito. The virus cannot be spread from person to person.

A number of different mosquitoes can spread the virus to humans. The mosquito has been shown to transmit Ross River virus disease in Australia but there is no evidence that this has occurred in New Zealand.

How is Ross River virus treated?

Treatment is aimed at relieving symptoms. Your doctor may recommend rest and pain-killers, like aspirin or paracetamol to relieve the pain and swelling of joints. Sometimes stronger medications are required to ease the inflammation.
Most people fully recover within a month of the onset of symptoms but these can last for longer and be quite severe.

How can infection be prevented?

Ross River virus is not contagious. If people can avoid being bitten by mosquitoes, they cannot get infected.

There are a number of things people can do to avoid mosquito bites:
- wear loose fitting clothing that covers the skin as much as possible - mosquitoes can bite through tight clothing - and avoid dark colours which attract mosquitoes.
- use an effective insect repellent when outdoors. A repellent that contains the chemical DEET (diethyl toluamide) or DIMP (dimethyl phthalate) is recommended.
- doors and windows can be screened to stop mosquitoes from getting inside
- aerosol sprays and mosquito coils may be used indoors

How successful are the eradication programmes?

The eradication programmes in Napier, Haumoana and Mahia have been completed and there have been no further finds of the southern saltmarsh mosquito in these areas.

The last mosquito found in Porangahau was in August 2002. If no further larvae or adults are detected, eradication will be completed in September 2004. The last SSM was detected in Tairawhiti in September 2002. If no further mosquitoes are found, eradication will be completed in October 2004.

The Kaipara eradication programme is being fully implemented. No larvae have been detected since February 2004, the last adult was last trapped at a surveillance site in Kaipara was in September 2003.

The last SSM was trapped at Mangawhai in December 2002. If no further SSM are found, eradication will be completed in December 2004.

The last SSM detected in Whitford was in November 2002. If no further adults or larvae are found, eradication will be completed in November 2004.

A small site at Whangaparoa discovered in January 2004 will continue to be treated until April 2005.


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