Southern Saltmarsh Mosquito larvae found in Whangaparoa

Media Statement

30 May 2005

Southern Saltmarsh Mosquito larvae found in Whangaparoa

Three Southern Saltmarsh Mosquito larvae were detected during routine surveillance in Whangaparoa, 50 kilometres north of Auckland in the same place that larvae were also found in January last year.

The identification of the larvae has been confirmed and 0.42 hectares of swamp treated and further traps set.

The area was last treated a month ago and it was thought the area was free of the pest. The finding may necessitate the continuation of treatments, Ministry of Health Chief Technical Officer (Health) Sally Gilbert said.

New Zealand Biosecure experts identified the mosquito as Ochlerotatus camptorhynchus, or the Southern Saltmarsh Mosquito.

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 Southern Saltmarsh Mosquito is a known vector for Ross River Virus (RRV) in Australia.

Southern saltmarsh mosquitoes have previously been found in the Hawke's Bay, Tairawhiti, Kaipara (including Whangaparoa) and Wairau. The mosquito has been successfully eradicated from the east coast of the North Island, Whitford, and Mangawhai. Attempted eradication programmes are still underway in the Kaipara (including Whangaparoa) and Wairau.

For further information please contact:

Peter Abernethy
Communications Manager
ph: 04-496-2008
or 021-366-111
http://www.moh.govt.nz/media.html

Background

Where were the mosquitoes found?

Three larvae were found at Okoromai Bay, Whangaparoa. The specimens were all larvae - mosquitoes in the wriggler stage of the lifecycle when the mosquito lives in water.

How big is the initial infestation area (size of area)?

An area of 20 hectares will be treated to kill any other mosquitoes present. Larvae have been previously found on the same site in March 2004.

Why have the mosquitoes only been found now?

The life cycle of the Southern Saltmarsh Mosquito means that the mosquito can survive for lengthy periods as eggs outside water. It is only possible to identify breeding habitats when the site has been deluged with water and the eggs have hatched. Following treatment, infestation sites are often checked following rain or spring tides.

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

Ongoing monitoring since March 2004 has not detected the mosquito larvae prior to this find and no adults have been found at this site.

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, Mahia, Porangahau, Tairawhiti, Mangawhai and Whitford have been completed and there have been no further finds of the Southern Saltmarsh Mosquito in these areas.

The treatment phase of the Kaipara eradication programme has been completed and this area is in phase three (surveillance) of the eradication programme. No larvae have been detected since February 2004 and the last adult was last trapped at a surveillance site in Kaipara in September 2003. The Wairau eradication plan is being fully implemented over approximately 1200 hectares of saltmarsh in the Wairau lagoons and Grassmere areas, Marlborough.

The full treatment phase of the eradication programme commenced in December 2004 and it is anticipated it will continue until March or April 2006 when it will move into the surveillance phase of eradication.

A small site at Whangaparoa discovered in January 2004, with more mosquito larvae found this month, this site will continue to be treated.

	S-methoprene treatment started	Last adult detected	Last larvae detected	Treatment ceased	Eradication completed
Napier	Aug 1999	April 2000	August 2000	April 2001	July 2002
Mahia	Nov 2000	April 2001	August 2001	August 2002	August 2003
Tairawhiti	Nov 2000	Sept 2002	Sept 2002	June 2003	Sept 2004
Porangahau	Nov 2000	June 2002	August 2002	April 2003	Sept 2004
Kaipara	Oct 2002	Sept 2003	Feb 2004	June 2004	Due Feb 2006
Mangawhai	Oct 2002	Dec 2002	Nil	April 2003	Dec 2004
Whitford	Oct 2002	April 2002	Nov 2002	March 2004	Nov 2004
Whangaparoa	Jan 2004	Nil	May 2005	Ongoing	Est May 2007
Wairau	Dec 2004	TBA	TBA	Ongoing	Est April 2008

Related information

Ministry of Health media releases

Exotic mosquitoes