Akabane

Akabane is a disease causing deformities in the foetus of livestock. It primarily affects cattle, although deformities in lambs have been recorded on rare occasions.

Cause

An arbovirus in the Bunyavirus family.

Distribution in Queensland

Akabane virus occasionally causes disease in Queensland and is found in other areas of Australia.

It is also found in Japan, Korea, Israel and Central Africa.

Affected animals

cattle; sheep; buffalo; camels; horses; goats; dogs

Hosts

Culicoides brevitasis (midges)

Symptoms

No clinical signs are seen. Infection of animals results in a transient viraemia causing a rise in antibodies. It affects the nervous system of the foetus in pregnant females.

The disease appears in 3 forms in calves:

  • early infection of the foetus results in calves born with arthrogryposis (deficiency of cerebral cortex) and hydranencephaly (replacement of brain tissue by a fluid-filled sac)
  • infection at 3-4 months foetal age shows hydranencephaly only in calves
  • infection at an older foetal age (5-6 months) results in calves with arthrogryposis (fixation of joints in the limbs and spine due to the failure of muscle development). These skeletal deformities are the first seen in an outbreak.

There may be calving problems with arthrogryposis calves due to calf limb deformity. When born alive, their teeth, coat and hooves are fully mature but they are small, underweight, weak and often unable to stand.

Calves with hydranencephaly can rise and walk, but are blind, have no basic reflexes and lack intelligence.

How it is spread

The disease is transmitted by blood-feeding insects, mostly Culicoides brevitasis (midges), but other vectors could exist. Immunity in dams can occur before pregnancy in areas where midges are present, so no signs of the disease are seen.

When suitable weather conditions allow the midges to extend their normal range into areas with susceptible animals, and these animals have not previously been infected, clinical signs may be seen in the next calving season.

Monitoring and action

Diagnosis can often be made by clinical signs and can be confirmed by antibodies in the blood of the calf or dam.

Control measures

There are no options for treatment or control because of the nature of the lesions and the method of disease spread. If akabane is endemic in an area, breeding stock should be introduced to the area at an early age to gain immunity.