An epidemic of Getah virus infection among racehorses: isolation of the virus.

In 1978, a disease outbreak observed in a Japanese horse training stable was linked to the Getah virus, a type of alphavirus, affecting approximately 13% of horses on the property. By collecting and analyzing samples from infected horses, scientists were able to isolate and identify the virus, while also determining that a significant proportion of the horse population had developed antibodies to the virus, suggesting prior infection.

Isolation and Identification of the Virus

• The disease that swept through the stable in the Kanto district of Japan in 1978 presented symptoms including fever and occasionally exanthema and oedema of the limbs in approximately 13% of the horse population.
• Researchers managed to isolate the virus causing this disease using one-day-old mice inoculated with samples from blood and nasal swabs taken from both naturally and experimentally infected horses.
• After obtaining the isolated virus, researchers used two monkey kidney cell lines to cultivate it, studying the complete cytopathic changes it produced in the host cells.
• After examination and analysis, the isolated virus was identified as the Getah virus, which is a member of the alphavirus subgroup of the Togaviridae family.

Serological Investigations

• On examination of the infected horses, it was noted that they developed neutralising, complement fixing, and haemagglutinin inhibiting antibodies against the Getah virus, indicating their immune system’s response to the viral infection.
• Serological investigations were conducted to measure the prevalence of these specific antibodies in the horse population of the training centre, which could suggest prior infection even in asymptomatic horses.
• The results indicated that around 56% of the horses in the training center had these antibodies, suggesting they had been infected with the Getah virus at some point.

Implications

• This research established the Getah virus as a cause of illness in the horse population in the Kanto district, identifying a specific fever-causing disease associated with this virus.
• By isolating and identifying the Getah virus from infected horses and conducting serological investigations, researchers were able to better understand the epidemiology of this disease in the horse population, evidence that can be used for management strategies to control further spread of the disease.