Arbovirus surveillance program

Arboviruses circulate in the environment between blood feeding insects (vector) and vertebrate animals (host). The term arbovirus is derived from arthropod-borne virus. Whilst a range of arthropods, including mosquitoes, ticks and biting midge, have been implicated in virus transmission in Australia, mosquitoes pose the biggest public health risk in Western Australia (WA). 

Mosquito-borne viruses are those arboviruses that are specifically transmitted by a mosquito vector. Transmission to people can only occur through the bite of an infected mosquito, and not exposure to the animal host. 

Medical Entomology (ME) monitors mosquito-borne virus activity throughout WA. There are three main components to the surveillance program:

  • Notified mosquito-borne disease case data surveillance 
  • South West arbovirus surveillance
  • Northern arbovirus surveillance
Notified mosquito-borne disease case data surveillance

ME monitors human cases of mosquito-borne disease notified to the Department of Health and recorded in the Western Australian Notifiable Infectious Disease Database (WANIDD). This data is used to identify patterns of disease throughout the State, inform mosquito management activities and ascertain the need to release a media statement regarding the risk to public health.

Locally acquired mosquito-borne disease cases

ME closely monitors mosquito-borne disease cases associated with the following four, locally transmitted viruses:

  • Ross River virus (RRV)
  • Barmah Forest virus (BFV)
  • Murray Valley encephalitis virus (MVEV)
  • West Nile virus strain Kunjin (WNVKUN)
A summary of case data related to mosquito-borne diseases acquired in WA can be accessed in Medical Entomology’s regional Quarterly Reports and Annual Report.

Exotic mosquito-borne disease cases

ME also monitors the incidence of exotic mosquito-borne diseases acquired overseas, but diagnosed in WA, in visitors or residents returning from travel outside of Australia. The following exotic mosquito-borne pathogens are of interest to the program:

  • chikungunya virus (CHIKV)
  • dengue viruses (DENV)
  • Japanese encephalitis virus (JEV)
  • malaria parasites (MAL)
  • Zika virus (ZIKV)

A summary of case data related to exotic mosquito-borne diseases acquired overseas, but diagnosed in WA, can be accessed in Medical Entomology’s Annual Report.

Practitioners involved in the diagnosis of the notifiable mosquito-borne diseases listed above, whether acquired within the State or elsewhere, have a legal obligation to report the diagnosis to the WA Department of Health.

South West arbovirus surveillance

The South West of WA is considered a high risk region for RRV and BFV disease outbreaks. Monitoring of mosquitoes and mosquito-borne virus activity commenced in the region in 1987, and continues on a regular basis throughout the year. Surveillance efforts help to determine when mosquito numbers are on the rise and virus is active within the environment. This information is used by both local government and the Department of Health to inform mosquito management activities and issue media statements regarding the increased risk to public health.

The surveillance program involves setting EVS/CO2 (encephalitis virus surveillance) traps to collect adult mosquitoes. These traps are set at strategic locations along the Swan Coastal Plain between Mandurah and Dunsborough, on a fortnightly basis from August to April. The traps are set at or before sunset and retrieved close to sunrise the following morning. The mosquitoes are then frozen on dry ice and transported to Perth. Mosquitoes are identified to species level and sent to PathWest to be tested for the presence of RRV and BFV. Upon detection of an arbovirus, the Department of Health issues a media statement advising the general public to take personal protection measures to prevent mosquito bites.

Between the months of May and July, trapping is undertaken on a monthly basis, as the risk of virus transmission is low. Mosquitoes are identified to species level, but not sent off for virus detection, at this time.

Northern arbovirus surveillance

Mosquitoes in the north of WA can transmit RRV, BFV, MVEV or WNVKUN. Murray Valley encephalitis is a mosquito-borne disease, caused by MVEV, that can result in severe neurological symptoms and may lead to coma, permanent brain damage and in some cases, death. Kunjin disease, caused by WNVKUN, causes milder symptoms than MVE, but can still result in encephalitis (inflammation of the brain). There is no vaccine or cure for either of these diseases. Regular monitoring of MVEV and WNVKUN activity is conducted across the northern two-thirds of WA. 

The northern arbovirus surveillance program has two distinct components:

  • sentinel chicken surveillance
  • northern mosquito surveillance 

Sentinel chicken surveillance

MVEV and WNVKUN viruses are maintained in a bird - mosquito - bird cycle throughout the north of WA. The Department of Health manages a sentinel chicken program, which provides an early warning for MVEV and WNVKUN activity within the State. Currently 23 sentinel chicken flocks are located in major towns and communities in the Kimberley, Pilbara, Gascoyne, Midwest and Wheatbelt regions of WA.

When a chicken is bitten by an infected mosquito, it develops antibodies to the virus but does not become sick. It makes an excellent sentinel species as it doesn't develop high levels of the virus and therefore cannot transmit the virus back to mosquitoes or people.

Chickens are bled by trained environmental health officers, vets or volunteers and the blood samples are sent to PathWest to be tested. When antibodies to MVEV and WNVKUN are detected, the information is used to issue a timely media statement, advising residents and travellers to affected regions of the increased risk of severe mosquito-borne diseases and the need to take personal protection measures to prevent being bitten by mosquitoes.

Northern mosquito surveillance

Annual mosquito collections are conducted towards the end of the wet season in the Pilbara and/or Kimberley regions of WA.

Adult mosquitoes are collected in EVS/COtraps in a similar manner to those collected in the South West. Mosquitoes are then transported to Perth, identified in the laboratory and sent to PathWest to test for arboviruses of local significance: RRV, BFV, MVE virus and WNVKUN.

Increased MVE detections are often seen in years when heavy wet season rains and flooding occur in the Kimberley/Pilbara regions. However, increased MVEV activity does not always lead to human cases of disease.

More information

Medical Entomology
Phone: (08) 9285 5500

Last reviewed: 21-08-2020