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Exotic Mosquito Treatment begins in Whangaparaoa

Media Release

28 January 2004

Treatment begins in Whangaparaoa following discovery of exotic mosquito larvae

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

Associate Minister for Biosecurity Marian Hobbs today authorised the treatment to limit the spread of this unwanted insect, said Chief Technical Officer (Health), Sally Gilbert.

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

Three sites in an area covering approximately 22 hectares 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, Tairawhiti and Kaipara. 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" said Sally Gilbert

Efforts were made to contact affected landowners before treatment began. Consultation has occurred with the Auckland Regional Council and New Zealand Navy. Rodney District Council environmental staff are being notified of the treatment programme. Consultation with other interested groups is underway.

The larvae were first found at one site on Tuesday 27 January 2004 near the Shakespear Regional Park during routine checks of likely mosquito habitat following recent heavy rainfall. This is the first time exotic mosquitoes have been identified in this area.

Ground teams today carried out further checks around the original site. "We think we've found some more suspect larvae near 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 larvae found but this is really a formality. The scientists undertaking the mosquito identification are very experienced and we are very confident that the Whangaparaoa larvae are southern saltmarsh mosquitoes," said Sally Gilbert.

Intensive surveillance is underway around the coastline in the Whangaparaoa Peninsula region. Auckland public health staff and New Zealand Biosecure contractors are surveying all possible habitat and using aerial photographs, maps and helicopter surveillance to assist in identifying where habitat may be.

"It's essential this survey and treatment of any positive sites is completed quickly so any larvae that hatched after the heavy rain on 23 to 25 January can be found before they transform into pupae."

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.


Why is it important the initial survey is completed within 48 hours before any larvae that may have hatched following the recent water event 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.

How much funding has the Government allocated to controlling and eradicating southern saltmarsh mosquitoes?
There has been around $40million approved for spending over nearly ten years to eradicate the exotic mosquito in Napier, Haumoana, Tairawhiti, Mahia, Porangahau, and Kaipara including Whitford and Mangawhai).

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 eradication plan for the remaining Hawke’s Bay site (Porangahau) and for sites in Tairawhiti is being implemented. Applications of S-methoprene to sites in Porangahau and Tairawhiti were completed in April 2003 and June 2003 respectively, and surveillance is continuing. 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. Permanent sentinel surveillance sampling sites have been established at 31 locations including Mangawhai and Whitford, and sites are visited twice weekly and sampled for adults and larvae. Sites have been selected to represent known positive areas; intermittently positive areas and known negative sites and reports include community reports of unusual biting activity.
Small numbers of larvae are still being detected but to date, 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.


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