Aino virus

From Cow
Aino viral infection in a calf in utero resulting in limb deformities
A similar unrelated case of Aino-virus infection in a calv

Aino virus is an arthropod-borne viral disease that causes neurological symptoms in cattle. Clinical cases of Aino disease have been reported from Japan and rarely, Australia[1]. The disease agent that has been implicated in the syndrome of hydranencephaly and arthrogryposis in calves.

Hydranencephaly and arthrogryposis in newborn calves as a result of Aino virus infection cannot be distinguished clinically from that caused by Akabane virus infection.

Cause

Aino virus is a member of the Simbu serogroup of the genus Orthobunyavirus, family Bunyaviridae. It is closely related to the Akabane virus. Aino virus is transmitted between animals by insect vectors. It has been isolated from Culicoides spp mosquitoes.

Cattle in endemic regions are often exposed from a young age and develop long-lasting immunity. Disease is usually associated with the virus spreading to immunologically-naive cattle that have no prior exposure to the virus. In utero infections of pregnant cows is common during outbreaks.

Although laboratory-confirmed cases in Australia is rare, regular and significant outbreaks have been reported in Japan.

Clinical signs

Aino virus infection in adult animals is subclinical. Fetal defects caused by Aino virus are seen at term, or months after infection of the cow. Newborn calves infected with Aino virus during gestation can exhibit a range of skeletal and neurological abnormalities.

In naturally infected pregnant cattle, Aino virus has been associated with stillbirths, premature births, and birth defects including arthrogryposis, scoliosis, sunken eyes, cataracts, maxillary retraction, and dental irregularities. Some calves may have a domed head from hydranencephaly and cerebellar hypoplasia. Surviving calves may be weak and can have difficulty suckling or standing. They may also be blind or have poor eyesight. In addition, they may display a variety of neurologic signs including ataxia, torticollis, tetany, paresis, swimming movements, opisthotonus, and circular walking. The type of abnormality seen can be related to the time of infection of the foetus; early infection results in hydranencephaly, later infection results in arthrogryposis[2].

Postmortem changes observed in dead cattle include non-suppurative encephalomyelitis of the brain and spinal cord.

Diagnosis

Presumptive diagnosis can be made on clinical signs an supportive evidence found during postmortem of dead cattle.

Definitive diagnosis of an Aino virus infection is based on virus isolation from an animal or postmortem material or the demonstration of a four-fold rise in specific antibody titre or both. Both ELISA[3] and PCR tests are highly sensitive and specific prognosticators of infection[4].

Differential diagnosis would include other neurological disease processes such as Sporadic bovine encephalomyelitis, Bovine viral diarrhea virus (BVDV) as well as other arthropod-borne agents such as Akabane virus, Peaton virus and Chuzan virus.

Treatment

There is no specific treatment for affected animals. Measures should be directed at the prevention of infection of susceptible animals with Aino virus during pregnancy. Introduction of stock from non-endemic to endemic areas should be done well before first breeding.

Trivalent vaccines have been developed which are reportedly effective at minimizing outbreaks in cattle[5]. In calves, maternal antibodies against Akabane wane after 4 months and vaccinations are recommended at this age[6].

References

  1. Cave JG et al (2008) An extended outbreak of congenital chondrodysplasia in calves in South East Australia. Aust Vet J 86(4):130-135
  2. Gard GP et al (1988) Arboviruses recovered from sentinel cattle using several virus isolation methods. Vet Microbiol 18(2):119-125
  3. Kim HJ et al (2012) Competitive ELISA for the detection of antibodies to Rift Valley fever virus in goats and cattle. J Vet Med Sci 74(3):321-327
  4. Doherty RL et al (1972) Virus strains isolated from arthropods during an epizootic of bovine ephemeral fever in Queensland. Aust Vet J 48:81-86
  5. Kim YH et al (2011) Development of inactivated trivalent vaccine for the teratogenic Aino, Akabane and Chuzan viruses. Biologicals 39(3):152-157
  6. Tsutsui T et al (2009) Duration of maternally derived antibodies against Akabane virus in calves: survival analysis. J Vet Med Sci 71(7):913-918