Akabane disease of cattle

AKABANA DISEASE OF CATTLE

Synonyms
  • Congenital Arthrogruposis Hydranencephaly Syndrome

Definition

  • Akabane disease caused by a bunyavirus termed Akabane virus is an arbovirus infections of cattle, which leads to disease of the foetus without systemic lesions in the pregnant cow.
  • The disease in newly born calves, lambs and kids is characterized by congenital arthrogryposis (fixed joints) causing deformities of the limbs and vertebral column, or by hydranencephaly (formation of a big space or cavity in the cerebrum)

Incidence

  • The disease has occurred in Japan, Australia, Israel and the Middle East.
  • No disease occurs in bulls
  • Natural disease also has been recently described in sheep and goats
  • New born calves are affected

Transmission

  • By mosquitoes (Culex and Aedes species), and the midges (small mosquito-like insects)

Pathogenesis

  • A viraemia occurs in the dam for 3-4 days
  • The virus passes from the dam, which is unaffected, to the foetus and causes arrest of differentiation in its growing neural tube
  • Which part of the tube is most affected depends on the stage of its development, and therefore on the age of the foetus
  • Usually three forms of the disease are observed
  • The first ones to appear are calves with arthrogryposis (infected at 105-174 days of pregnancy)
  • They are therefore at an older foetal age when infected than others
  • The next group is those with arthrogryposis accompanied by hydranencephaly
  • The third group is those with hydranencephaly only (infected between days 76 and 104 of pregnancy)

Clinical signs

  • The cow is unaffected.
  • The two syndromes, arthrogryposis and hydranencephaly, occur separately.
  • Arthrogryposis occurs in the early stage of the outbreak and hydranencephaly at the end.
  • Calves with both defects occur in the middle of the outbreak.
  • In some outbreaks, only one of the manifestations of the disease is seen.
  • Calves with arthrogryposis (fixed joins) are unable to rise, stand or walk.
  • One or more limbs are fixed at the joints.
  • There is a congenital articular rigidity.
  • The muscles of affected limbs are severely wasted.
  • Severe deformity of the vertebral column, such as kyphosis (abnormal dorsal curvature of the spine) or scoliosis (lateral curvature of the spine), or lordosis (abnormal ventral curvature of the spine), is common.
  • These abnormalities are believed to be of neurogenic origin.
  • Calves with hydranencephaly have no difficulty in rising or walking.
  • The major defects are blindness and a lack of intelligence.
  • They will such if put onto the teat, but if this is not done, they stand and bleat (utter a mournful cry).
  • They have no dam-seeking reflex.
  • A part from skeletal and neurological defects, cases of abortion, stillbirth and premature birth are also regarded as being caused by Akabane virus infection in cows.
  • They are usually observed at the beginning of the outbreak before neurological defects occur.

Gross and microscopic lesions

  • In the foetus, the virus invades the brain and skeletal muscle, producting encephalomyelitis and polymyositis (simultaneous inflammation of many muscles), Encephalitis occurs regardless of the age of the foetus when affected.
  • However, myositis occurs only when the foetus is infected during the first half of gestation.
  • The foetus may die and abort, be stillborn, or be born with deformities such as arthrogryposis in all four legs.
  • The non-suppurative encephalomyelitis is characterized by extensive necrosis and endothelial proliferation, leading to formation of cysts, porencephaly (occurrence of cavities in brain) and hydranencephaly (formation of cavities in cerebral hemispheres due to lack of proper development.
  • The cavities are filled with cerebrospinal fluid.
  • Hydranencephaly is a common manifestation.
  • There is loss of neurons in the ventral horn of the spinal cord.
  • Myositis is accompanied by swelling, necrosis and fragmentation of muscle fibres (myofibres).
  • At birth, muscles are smaller than normal and replaced by adipose tissue, giving rise to the names “Runt-Muscle Disease” and “Runt-Muscle Fibre”.
  • Microscopically, there is thinning and loss of myofibres.
  • Many lack transverse striations.
  • In differential diagnosis, Akabane disease must be differentiated from other forms of congenital arthrogryposis.
Last modified: Friday, 23 March 2012, 9:34 AM