Vector-transmitted diseases are spread through the bites of infected arthropods (e.g. mosquitoes and ticks).
The main vector-transmitted diseases in cattle are three-day sickness (bovine ephemeral fever) and Akabane disease.
Equine infectious anaemia is a vector-disease affecting horses that can significantly increase after flooding.
There are 2 types of mosquito-borne viruses, namely Arboviruses (e.g. Ross River virus) and Flaviviruses (e.g. the Murray Valley encephalitis virus (MVEV) and Kunjin virus).
National Arbovirus Monitoring Program
The Australian National Arbovirus Monitoring Program (NAMP) is responsible for monitoring the distribution of insect-borne viruses.
Many arboviruses are present in Australia, especially in the tropical north. The main ones of concern are:
- orbiviruses (bluetongue, epizootic haemorrhagic disease)
- flaviviruses (Murray Valley encephalitis, Japanese encephalitis, Kunjin)
- alphaviruses (Ross River, Barmah forest)
- bunyaviruses (Akabane, Aino)
- rhabdoviruses (bovine ephemeral fever).
The program currently monitors the distribution of the 3 most economically important insect-borne viruses that affect livestock for trade:
The program's objectives are:
- Trade support: Facilitating the export of live sheep, cattle and goats to countries sensitive to bluetongue, Akabane and bovine ephemeral fever (BEF or three-day sickness) by providing scientific information for the development of export protocols and to meet export certification requirements.
- Bluetongue early warning: Detecting incursions of exotic strains of bluetongue virus into North Queensland through surveillance of the northern bluetongue virus endemic area.
- Risk management: Detecting seasonal changes in distribution of the 3 viruses and their vectors. Surveillance carried out under the program provides producers with early warning of movement by these endemic diseases into new areas where cattle that have not previously been exposed are likely to suffer severe symptoms, including abortion, fever, loss of coordination and, in some cases, death.
Data for the program is gathered by monitoring cattle located in sentinel herds – groups of cattle previously unexposed to arboviral infections. They are blood tested at regular intervals to detect the incidence of viral infection. New animals are selected each year to replace those that develop antibodies to the viruses. Insect traps near the animals in these herds show whether insect vectors are present.
Zones and maps
The distribution of arboviruses is determined by their insect vectors. Those carried by Culicoides midges (such as bluetongue and Akabane) are mainly confined to the north and east of Queensland. Those carried by mosquitoes (such as bovine ephemeral fever, Murray Valley encephalitis, Ross River and Kunjin) are more widely distributed.
A bluetongue-free zone has been established from surveillance data obtained by the monitoring program. This has given some Australian producers access to bluetongue-sensitive overseas markets that were not previously available to them.