Chuzan virus (SBV) is an arthropod-borne viral disease that causes neurological symptoms in cattle. Clinical cases of Schmallenberg disease have been diagnosed primarily in Aisa. The disease agent causes considerable economic losses and has been implicated in the syndrome of hydranencephaly and arthrogryposis in calves.
Hydranencephaly and arthrogryposis in newborn calves as a result of Chuzan virus infection cannot be distinguished clinically from that caused by Akabane virus, Peaton virus, Schmallenberg virus or Aino virus infections.
Chuzan virus is a member of the Simbu serogroup of the genus Orthobunyavirus, family Bunyaviridae. It is closely related to the Akabane virus and Aino virus. Chuzan 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.
Chuzan virus infection in adult animals is subclinical. Fetal defects caused by Chuzan virus are seen at term, or months after infection of the cow. Newborn calves infected with Chuzan virus during gestation can exhibit a range of skeletal and neurological abnormalities.
The most common clinical signs in deformed calves are arthrogryposis, vertebral malformations, brachygnathia inferior, and malformations of the central nervous system, including hydranencephaly, porencephaly, hydrocephalus, cerebellar hypoplasia, and micromyelia.
Histologic lesions observed include lymphohistiocytic meningoencephalomyelitis and necrosis in the brain stem of calves. Micromyelia was characterized by a loss of gray and white matter, with few neurons remaining in the ventral horn in calves. The skeletal muscles often have myofibrillar hypoplasia.
Presumptive diagnosis can be made on clinical signs an supportive evidence found during postmortem of dead cattle.
Definitive diagnosis of Chuzan 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 and PCR tests are highly sensitive and specific prognosticators of infection.
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 Schmallenberg virus.
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.
- Lim SI et al (2007) Sero-survey on Aino, Akabane, Chuzan, bovine ephemeral fever and Japanese encephalitis virus of cattle and swine in Korea. J Vet Sci 8(1):45-49