Mosquito larvae in tyres highlight NZ border risk

Mosquito larvae of a species capable of spreading illnesses such as Ross River virus in humans and heartworm in dogs have been intercepted in a cargo of tyres on a truck from Australia.

The striped mosquito, Ochlerotatus notoscriptus, was discovered by agriculture quarantine staff on Monday in tyres on a truck from Australia due to be shipped on to a Pacific island.

The truck has been fumigated and the cargo where the mosquitoes were found was also treated.

Ministry of Health chief technical officer for biosecurity Sally Gilbert said that although the species was established in New Zealand, the specimens originated from outside the border and demonstrated the risk of pest mosquitoes being imported.

But the mosquito, native to Australia and formerly known as Aedes notoscriptus, is already spreading through New Zealand from an initial incursion before World War I.

Fifty years later, it was still only established around sea ports, but during the next 20 years it spread inland. Its spread into rural areas was accelerated by the use of used tyres to hold covers on silage pits. It prefers to feed on cattle, but also attacks humans, possums, horses and dogs.

It is known to carry murray valley encephalitis, and in the 1994 Brisbane epidemic of ross river virus, the species was found to also spread that illness. If mosquitoes capable of carrying disease pick up a virus from a tourist or returning New Zealand traveller, they may trigger a "virgin soil epidemic".

According to Ms Gilbert, the Health Ministry's conservative estimate for a New Zealand epidemic of ross river virus disease - or epidemic polyarthritis - is case rates of 10,000 people per 100,000 population.

Ross River virus is not fatal, but it can cause chronic fatigue for up to a year, and the economic effect in 10 per cent of workers would be drastic.

Of the 3500 mosquito species recognised worldwide, New Zealand has only 16, four of them introduced, including the striped mosquito. Australia, which has about 200 mosquito species, has serious problems with the diseases they spread, including ross river virus, murray valley encephalitis and barmah forest disease (inflammation of the brain).

Ms Gilbert said exotic mosquitoes of "public health significance" had been intercepted on 22 previous occasions since January 1998.

- NZPA