Locals and not so locals

New Zealand has 12 native species of mosquito and four introduced species; these are at present harmless but have the potential to transmit disease if certain other disease-carrying species of mosquito slip into the country and become established. In such a scenario, the most likely potential diseases to be transmitted are arboviral diseases such as Ross River virus and dengue fever.

Potential threat is not being underestimated

A report to the Minister of Biosecurity in 1997 warned the risk of an outbreak of an arboviral disease or malaria in New Zealand is real and likely to increase with time. [An arboviral disease is a virus spread by arthropods such as mosquitoes or other biting insects. Malaria is caused by a parasitic infection that is transmitted by infected mosquitoes.] GPs have also been prompted to make themselves aware of the symptoms of mosquito-borne illnesses such as these (New Zealand Doctor, 11 February 2004).

"The likely consequences of a major outbreak of arboviral disease are so serious that all reasonable steps should be taken to prevent such an occurrence," the report Exclusion and Control of Exotic Mosquitoes of Public Health Significance reads.

It is important to also raise public awareness generally to dispel the misconception that mosquitoes present no risk to New Zealand. "The public should be made aware of the potential risk of mosquito-borne diseases, their cost and health implications and new environmentally friendly methods of control."

Arboviral diseases

Ross River fever
Ross River fever - also called epidemic polyarthritis - is caused by Ross River virus (RRV), which is transmitted by a variety of mosquitoes. The virus is present in many parts of Australia. Symptoms range from a mild flu-like illness to arthritis affecting all the joints. Arthritis onset is often followed by a rash, and sometimes fever may be present. At least 20% of affected persons get the arthritis form.

Symptoms include:

• sudden onset of aching in the muscles and joints;
• headaches followed by a rash of numerous slightly raised spots (40-78% of people);
• arthritis in numerous joints.

Most symptoms settle in a few days but the arthritis can be incapacitating for five or six weeks. Recovery may take still longer; in 1% of cases joint symptoms last more than five months, and relapses (eg, muscle aches, tiredness, arthritis) can occur much later on.

Barmah Forest virus
Infection characterised by fever, arthritis and rash - very similar to RRV.

Dengue fever
Dengue fever is caused by one of four 'Flaviviridae' arboviruses. Sometimes called breakbone fever, dengue fever is a short sudden illness, characterised by severe headaches, fever and severe joint and muscular pains.

Japanese encephalitis
This disease is caused by the Japanese encephalitis of the 'Flaviviridae' family - carried by a number of arthropods (eg, biting insects including mosquitoes). It causes inflammation of the brain, spinal cord and meninges (lining tissues of the brain). Headaches, fever, convulsions and coma are some of the more severe symptoms associated with this infection. 

NZ population not immune

According to the Ministry of Health's chief technical advisor [2004] Sally Gilbert, arboviruses pose a particular threat to New Zealand, as the human population is non-immune and susceptible. Susceptibility can be exacerbated by the fact the population knows little about mosquito-borne diseases and how to minimise the risks of infection.

Potentially the most significant mosquito-borne diseases to New Zealand are arboviral diseases - Ross River fever (epidemic polyarthritis), dengue fever, Barmah Forest virus and Japanese encephalitis (see above). Yellow fever, malaria and filariasis warrant consideration but are thought to present a much lower level of risk to this country. [Filariasis is a tropical disease caused by parasitic worms which are introduced to the blood by some biting flies and mosquitoes.]

The report says New Zealand has no or little risk of "becoming malarious", especially as we do not have the vector mosquitoes, but goes on to say exceptions occur and the risk must be continuously reassessed.

Photos

The Medical Entomology Department, University of Sydney has an extensive online collection of mosquito photos.

Related topics

See also Mosquitoes - how could a disease outbreak occur in NZ?

Mosquitoes - types that are a cause for concern

Original material provided by New Zealand Doctor magazine, February 2004. Reviewed and edited by everybody, November 2011.