Ministry urges lift in mosquito attack

Health officials say the spraying they called for last week to fight the Gisborne infestation of southern saltmarsh mosquitoes is an urgent bid to contain the biosecurity breach.

Technical experts advising the ministry want all aircraft leaving Gisborne sprayed in a bid to stop the spread of the potential disease-carriers to the rest of New Zealand.

The experts also want 36ha of infested wetland around a local lagoon sprayed with the relatively benign bacillus thuringiensis israelensis (Bti), a biological bug-killer which targets mosquitoes and blackflies.

This would help contain the mosquito while a decision was made about its future management in the Gisborne area, said Health Ministry spokeswoman Dr Sally Gilbert.

At an earlier Napier infestation of the Australian mosquito, 200km to the south, the Government spent more than $2 million on a containment programme using Bti spray but then switched to a chemical spray known as S-methoprene.

Dr Gilbert said that while the containment programme was under way in Gisborne, surveys and sampling would continue north to Hicks Bay, as well as coastal lagoons as far south as Wairoa.

A full health-impact assessment and cost-benefit analysis would be needed before a recommendation was made to the Government on longer-term management around Gisborne, such as spraying with chemical pesticide.

The initial use of Bti will be around the Wherowhero Lagoon near Muriwai, 20km south of Gisborne, where alert health workers noticed the saltmarsh mosquito larvae during routine sampling.

It was not immediately clear what sprays would be used on up to 14 commercial aircraft a day departing Gisborne Airport.

And health officials have not said how they plan to disinfest the large numbers of light aircraft which operate from the airport.

The mosquito, known as aedes camptorhynchus, can spread the devastating Ross River virus.

The virus causes a disease known as epidemic polyarthritis, and in some patients can cause chronic fatigue and lethargy for up to a year.

The virus is not yet in New Zealand, but if the mosquitoes become established they could easily pick it up from an infected visitor, such as an Australian tourist.

The virus could then be transmitted to animal "reservoirs" such as feral possums or farm livestock, and become almost impossible to eradicate.

- NZPA