Mosquitoes, cyclones and flooding

The risk of mosquito-borne disease activity may increase after a cyclone or flooding event. Please see the Department of Health's website on managing environmental health risks following cyclones and flooding.

Tidal storm surges and flooding associated with heavy rains, which often accompany cyclones, can produce extensive breeding habitat for mosquitoes. Residents of affected areas may be particularly vulnerable to mosquito, and mosquito-borne virus, exposure if their housing and insect screens have been damaged by a cyclone.

The mosquito breeding habitat created by cyclones can include vast areas of:
  • temporary ground pools
  • pools along receding river floodplains
  • tidal saltmarshes in low lying coastal areas
  • natural or man-made containers
  • overflow and pooling of storm and wastewater management infrastructure (such as sewage lagoons).

As well as being a nuisance, several species of mosquitoes that may breed in post-cyclonic conditions are also vectors of disease. A list of common mosquitoes found in Western Australia is available here

Mosquito-borne diseases of concern

Mosquito-borne diseases of concern in Western Australia (WA) include:

  • Ross River virus disease
  • Barmah Forest virus disease
  • Murray Valley encephalitis 
  • Kunjin disease
  • Japanese encephalitis 

The likelihood of a disease outbreak occurring post-cyclone will depend on a range of factors including presence of a vector species, availability of natural hosts (non-human animals) and time since the last disease outbreak. 

Pre-cyclone preparation measures

A number of things can be done ahead of the cyclone season to prepare for the possibility of increased mosquito numbers. 

Local government environmental health officers can:

  • monitor cyclone and rainfall activity through the Bureau of Meteorology (external)
  • purchase necessary mosquito management chemicals
  • ensure mosquito control equipment is available and in reliable working order
  • identify likely breeding sites and appropriate management options - this may include physical works to modify or remove the site, and/or chemical control of larval mosquitoes (larviciding) or adult mosquitoes (adulticiding)
  • inform the general public about health risks associated with mosquitoes and how to prevent being bitten - consider using Fight the Bite resources to promote community awareness. 

Communities can be advised to:

  • appropriately store, cover or discard any containers that may hold water (e.g. buckets, pot plant drip trays, toys, household rubbish and larger items, such as wheelbarrows, trailers, boats and kayaks)
  • purchase bed nets and effective personal mosquito repellents containing diethyltoluamide (DEET), picaridin or oil of lemon eucalyptus (OLE)
  • ensure insect screens are in good working order.
Post-cyclone management measures
The sheer extent and inaccessibility of mosquito breeding habitat after a cyclone is likely to overwhelm the resources of many individual jurisdictions. Therefore, it will be important to seek assistance and additional resources from neighbouring local governments and other local/State agencies.

Mosquitoes will not be an issue in the first few days after a cyclone, giving personnel time to address more urgent public health risks. However, in hot conditions some mosquito species will go through their life cycle and emerge as adults in as little as 5 days. This does not leave a large window of opportunity for control measures targeting larvae to be implemented.

Effective mosquito management is best achieved by integrating several different approaches, including physical, chemical and cultural control:

Physical control:

  • remove container breeding habitats, by discarding or burying rubbish and debris that may hold water around affected communities 
  • repair or modify damaged infrastructure (e.g. wastewater infrastructure) that may have created mosquito breeding habitat
  • undertake basic earthworks to prevent standing water, where appropriate - this may include filling in depressions or promoting better drainage, to prevent standing water
  • facilitate the regular cutting of grass/weeds, particularly in and around remote towns/communities, as overgrown vegetation can promote mosquito harbourage.

Chemical control:

  • monitor breeding sites for larvae to determine the timing and the priority of sites for chemical control
  • seek advice from Medical Entomology regarding mosquito management options and/or apply for access to emergency chemical supplies 
  • apply larvicide to manage contained mosquito breeding sites within close proximity to residential or temporary accommodation. Note, in most post-cyclone situations, breeding sites will be so extensive that it may not be logistically feasible to control the situation with larvicides alone
  • use adulticides to reduce mosquito populations through thermal or ULV fogging. Note, fogging is not target specific and should only be undertaken when there is an identified public health risk
  • apply residual surface sprays (adulticides) to the perimeter of affected residential areas and surrounding vegetation to limit mosquito exposure. 

Cultural control:

Proactive communication can increase the general public’s understanding of post-cyclone challenges faced by local government. It also plays a key role in minimising the public health risk associated with mosquitoes. This is best achieved by issuing a media statement and distributing information to affected residents through a range of mechanisms (e.g. posters/brochures, community displays, radio/print advertising etc). The Department of Health has produced a number of Fight the Bite resources for this purpose.

It is important to communicate the following information to the general public at this time: 
  • predicted mosquito-borne disease risk
  • likely duration of the problem
  • what the local government is doing
  • how to avoid bites using effective personal insect repellent, bed nets and protective clothing
  • empty, store or discard water holding containers around the home to prevent mosquitoes breeding
  • keep grass/weeds short to stop mosquitoes seeking shelter and hiding around the home.
Last reviewed: 20-05-2022
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Public Health