AKABANE  

Nature of the disease
Akabane is an arboviral infection caused by a virus from the Bunyaviridae family (Simbu serogroup) and transmitted by Culicoides. It affects cattle, sheep and goats that causes abortions, stillbirths and foetal deformities.
Classification
SPC List D disease
Susceptible species
Cattle, sheep and goats are the natural hosts.
Distribution
The distribution of Akabane disease is determined by that of its vectors (Culicoides spp.). The virus is believed to be distributed through two large north-south geographical bands — firstly from Japan through South East Asia to Australia, and secondly from the Middle East through Africa to South Africa.

Clinical Akabane disease tends to occur only near the northern and southern extremities of these geographical bands, or in susceptible stock introduced to the endemic areas.
Clinical signs 
Akabane manifests as a seasonal, sporadic epidemic of abortions, stillbirths, premature births and deformed foetuses or neonates in cattle, sheep and goats. The pregnant dam experiences no clinical symptoms at the time of infection. Infection in the first trimester produces foetal damage in utero.
Dystocia may occur at parturition due to badly deformed foetuses.
Badly deformed foetuses will be dead with limbs locked into flexed or extended position.
Live neonates frequently have central nervous system deficiencies manifested clinically as:
  • Blindness
  • Nystagmus
  • Deafness
  • Dullness
  • Slow suckling
  • Paralysis
  • Incoordination
Post-mortem findings 
Lesions are associated with damage to the musculature and central nervous system of the foetus:
  • Arthogryposis — affected joints cannot be straightened
  • Torticollis, scoliosis and brachygnathism may also be seen
  • Subcutaneous haemorrhages in foetus and placenta
  • Hypoplasia of the lungs and skeletal muscle
  • Opthalmia
  • Cataracts

Central nervous system lesions include:

  • Hydranencephaly
  • Hydrocephalus
  • Agenesis of the brain
  • Microencephaly
  • Porencephaly and cerebellar cavitation
  • Agenesis or hypoplasia of the spinal cord
Differential diagnosis 
A variety of nutritional, toxic and infectious diseases can produce foetal wastage and deformities. Bluetongue would present the greatest difficulty in differential diagnosis.

Two newly isolated arboviruses cause similar symptoms:

  • Aino virus, which belongs to the same serogroup than Akabane virus, was isolated in Japan and in Australia, and is spread by Culicoides and mosquitoes.
  • Chuzan virus, which is a reovirus, was isolated in Japan from Culicoides.
Specimens required for diagnosis 
A field diagnosis can be made on the basis of the clinical picture, gross lesions and epidemiology. 

Diagnosis can be confirmed by taking samples of placenta, foetal muscle and nervous tissue for virus isolation.

Foetal blood samples and blood samples from adult animals for serology.

Transmission   
Akabane is transmitted by biting mites and some miosquitoes, it is a biological vector and the virus replicates in insects. The most common vectors are Culicoides brevitarsis, Culicoides nebeculosus. There is no indication of transmission other than by vectors.
Risk of introduction   
Akabane could be introduced through importation of viraemic animals or by the introduction of infected insects. 

For the disease to establish, suitable vector species would need to be present. It is likely that many Pacific countries would have suitable vectors.

Control / vaccines  
Inactivated and attenuated vaccines for Akabane have been developed.
References
  • Akabane, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 451-452
  • Akabane, In Veterinary Medicine, Saunders, Eight ed, 1997, London p. 951-953
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