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Treatment begins in Whitford following larvae find

Media Release

8 March 2002

Treatment begins in Whitford following discovery of larvae

Treatment to control the southern saltmarsh mosquito began today near Whitford following the discovery of more larvae there yesterday, the Ministry of Health announced today.

Associate Minister for Biosecurity Marian Hobbs this morning authorised the treatment to limit the spread of this unwanted insect, said Public Health Programmes Manager Graeme Gillespie.

The southern saltmarsh mosquito, Ochlerotatus camptorhynchus, is a potential vector for Ross River virus disease.

Three semi-rural creek-side sites covering approximately a hectare in area were treated with s-methoprene, an insect growth regulator that stops the mosquito pupae hatching into adults.

S-methoprene has been used against mosquitoes throughout the world. It has no long term residual effects. The product is being used successfully as part of the eradication programme in Hawke's Bay and Tairawhiti. It has undergone a full environmental and health impact assessment in New Zealand. Studies of its use in Napier have shown no adverse impact on any animals or insects on than southern saltmarsh mosquitoes.

"Applying control agents is necessary to attempt to stop this exotic pest. We've never had an outbreak of a mosquito-borne disease in New Zealand and we want it to stay that way."

Efforts were made to contact affected landowners and close neighbours before treatment began. Consultation has occurred with the Department of Conservation, Whitford Residents and Ratepayers' Association, Auckland Regional Council, and Manukau City Council environmental staff being notified of the treatment programme. Consultation with other interested groups is underway.

The larvae were first found at one site Monday March 4 near the eastern mouth of Turanga Creek during routine checks of likely mosquito habitat following last weekend's king tide. This is the first time exotic mosquitos have been identified in this area.

Ground teams yesterday carried out further checks around the original Whitford site.

"We think we've found some more suspect samples from the original site, which was something we expected as a female mosquito lays many eggs at the same time.

"We haven't heard back from Australia yet with a positive confirmation of the first two larvae found but this is really a formality. We have two top Australian mosquito experts visiting here at present, including Professor Brian Kaye who is head of the Queensland Institute of Mosquito Research. Professor Kaye is very confident that the Whitford larvae are southern saltmarsh mosquitoes," said Mr Gillespie.

Intensive surveillance is underway around the coastline in the Auckland region. Auckland public health staff and New Zealand Biosecure contractors spent seven hours in a helicopter yesterday visiting 22 sites from east of Howick, along the coast south to Miranda and also part of Waiheke Island.

"We also found some larvae at other sites, there is no indication at this stage they are southern saltmarsh mosquitos. They've been taken back to the lab and we've have two taxonimists working on identifying the samples. We probably won't know the full story until early next week."

"It's essential this survey is completed today so any larvae that hatched during last weekend's king tide can be found before they transform into pupae."

Today, the Waiheke Island survey is being completed by helicopter and the Tamaki Estuary has also been surveyed. So far there have not been any further positive samples of southern saltmarsh mosquito larvae collected from the region.

The southern saltmarsh mosquito lays its eggs on vegetation just above the waterline but wetting is vital for the eggs to hatch. High tides, heavy rain and wind that increases the size of waves can all encourage hatching.

No further evidence has been found of the mosquito in the area between Whitford and the Kaipara Harbour despite ongoing surveillance. The mosquito's natural flight range is estimated at five kilometres.

For more information contact: Anne-Marie Robinson, Media Advisor, ph: 04-496-2067 or 025-802 622 http://www.moh.govt.nz/media.html


Why is it important the initial survey is completed within 48 hours before any larvae that may have hatched following the recent king tide become pupae? The mosquito life cycle has four stages, these being The EGGS are laid in water. Southern saltmarsh mosquitos lay their eggs above the surface of the water and the eggs do not hatch until there is a king 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 pupa is difficult to detect The ADULT is the flying stage of the insects life cycle. Breeding and egg laying occur. An adult female southern saltmarsh mosquito requires a blood meal before laying eggs.

What is s-methoprene? S-methoprene is an insect growth regulator that stops the mosquito pupae hatching into adults. It is not a spray and does not drift. Sand granules are coated in the active ingredient. S-methoprene is used against mosquitoes throughout the world. It has undergone a full health impact assessment in New Zealand. S-methoprene breaks down quickly in the environment and is believed to be environmentally safe for use in New Zealand. Studies of the impact on non-target species where it has been applied in the Hawke's Bay have shown no impact.

What is Ross River virus (RRV) disease? Ross River virus disease is a viral infection which has been reported from Australia, as well as 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 recently discovered in Napier has been shown to transmit Ross River virus disease in Australia but there is no evidence that this has occurred yet, 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 check your home and garden for areas where mosquitoes can breed, such as garden rubbish or blocked gutters and drains which hold water and ensure that these are kept dry.

For further information concerning Ross River virus disease prevention contact your local public health service.

How much funding did the Government allocate to controlling and eradicating exotic mosquitos in 2001? There has been $5-million approved for spending over four years to eradicate the exotic mosquito in Napier, Gisborne, Mahia and Porangahau and to contain and control the spread of the mosquito in the Kaipara and Mangawhai areas, as phase one of a possible eradication programme.

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