Media Release
18 November 2005
Treatment to start again in Kaipara following discovery of a Southern Saltmarsh Mosquito.
Treatment to control the southern saltmarsh mosquito will be re-started at Carters Bach in the Kaipara region following
the discovery of an adult southern saltmarsh mosquito there earlier this month, the Ministry of Health announced today.
Minister for Biosecurity Jim Anderton yesterday authorised the treatment to limit the potentially serious public health
risks linked with the introduction of mosquito-borne disease into this country, said JR Gardner, Ministry of Health
Deputy Chief Technical Officer (Health).
The southern saltmarsh mosquito, Ochlerotatus camptorhynchus, is a potential vector for Ross River virus disease.
Mr Gardner said the discovery of the adult was a disappointment but not a knockout blow to the eradication programme for
the Southern Saltmarsh Mosquito in the Kaipara. "The last adult mosquito had been detected in Kaipara in September 2003
and no larvae have been found since June 2004. " World Health Organisation protocols are that no mosquito biomass should
be detected in the eradication zone for two years before eradication can be declared.
Treatment of the habitat was completed in June 2004. "However, on November 14 2005, a lone female adult mosquito was
trapped at one of the 15 sentinel sites on the Kaipara Harbour," Mr Gardner said.
The site at Carters Bach was an area of initial heavy infestation when the programme began. The area in a five kilometre
radius around the Carters Bach site has been intensively searched and there have been no further findings of the
mosquito larvae or adults. Over 60 kilometres of surveillance has been walked by eight experienced field staff from
Southern Monitoring Services- New Zealand BioSecure (SMS-NZB) with some 200 potential sites sampled. All have been
negative for the SSM.
However, Mr Gardner said because the habitat was dry at the moment it now requires a significant water event (high tide
and rainfall) to occur. Such an event would hatch out any SSM eggs that might have been laid. "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," he said.
"It is understood the next significant king tide would not be until late January, so, unless there is some rain, there
could be some delay before we can know for sure the exact size of the infestation."
"Applying control agents is necessary to eradicate this exotic pest. We've never yet had an outbreak of a mosquito-borne
disease in New Zealand and we want it to stay that way."
The affected landowners have been contacted in person already so they know that further treatment of habitat on their
land will be occurring. Consultation has also occurred with the Department of Conservation, iwi, Residents and
Ratepayers Association, and Auckland Regional Council and other stakeholders. "At this point in time the initial
response from those contacted has been very supportive, " Mr Gardner said.
Background
Why is it important the delimiting survey is completed after rainfall or a king tide?
The mosquito life cycle has four stages, these being
The EGGS are laid in water. Southern saltmarsh mosquitoes 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. Eggs cannot be detected in the field.
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. Traps are used to attract adult mosquitoes as part of the surveillance programme.
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. It was used (with Bti) in the successful
eradication programmes on the east coast of the North Island (Hawke's Bay and Tairawhiti) and is being used at
Whangaparaoa and in the Wairau to attempt to eradicate the southern saltmarsh mosquito from those sites. Studies of the
impact on non-target species where it has been applied in the Hawke's Bay have shown no impact.
What other treatment agents are being used to eradicate the mosquito in Kaipara?
Sites are also being treated with the biological spray Bti. This product has been used extensively in control programmes
in Australia, Africa, the United States and Germany. It was used in the successful eradication programmes on the east
coast of the North Island (Hawke's Bay and Tairawhiti) and is being used at Whangaparaoa and in the Wairau to attempt to
eradicate the southern saltmarsh mosquito from those sites. Bti has undergone a full health impact assessment and is not
allergenic. It leaves no long-term residue but is not considered adequate to achieve eradication on its own.
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 3-21 days (average 9 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.
ENDS