Akabane virus
| Akabane virus | |
|---|---|
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| Transmission electron micrograph of the Akabane virus | |
| Virus classification | |
| Group: | Group V ((−)ssRNA) |
| Family: | Bunyaviridae |
| Genus: | Orthobunyavirus |
| Species: | Akabane virus |
The Akabane virus is an insect-transmitted virus that causes congenital abnormalities of the central nervous systems in ruminants.
Two viruses, both arthropod borne, have been implicated in the cause of these congenital defects: Akabane virus, named after the district in Japan where it was first found, and Aino virus. Generally, both these viruses are referred to as Akabane virus.
Akabane virus does not, as far as is known, cause any overt sign of disease, in either young or adult animals. Its effect is on the fetus and the conditions which result in the disease in the fetus may be summarised as follows- 1. The pregnant dam has not previously had exposure to the virus and therefore has no specific immunity and becomes infected, and 2. The virus passes through the placenta and infects the , specifically the calf's central nervous system (CNS) where it may cause varying amounts of damage. Affected calves may be blind, have difficulty in suckling, walking or learning herd behaviour, etc. Other species may become infected. These include buffalo, camels, horses, sheep, goats and dogs. The disease in these hosts is not commonly observed and, apart from in buffalo, is probably not a particularly important infection.
Malformation of the joints, brain, spine and jaw are common in affected newborn animals. Abortion may also occur if damage to the fetus is severe.
As Akabane is an infectious disease, it is necessary to know how the virus is transmitted if the infection is to be combatted. It has been shown that animals that have been infected with Akabane virus are found mostly in those parts of Australia which have the blood sucking midge "Culicoides brevitarsis." This, and the fact that the Akabane virus has been isolated from this midge, has led to the supposition that it is C. brevitarsis which is responsible for the spread of the disease. Normally, in areas where the midge is prevalent, no signs of the disease is seen because the dams are immune. When suitable weather conditions (such as warm humid summers) prevail, the virus-carrying midge can extend its normal range into areas with susceptible animals. If these cattle have not previously been infected (often the younger animals) then it can be expected that the disease will make an appearance in the calving season.
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