Disease of the upper respiratory tract in horses following the human influenza epidemic of 1957.

The research examines an incident of upper respiratory tract disease in horses, marked by severe symptoms, which followed a human influenza epidemic in Kharkov in 1957, challenging previous notions that horses were not susceptible to the influenza virus.

Background

• In October 1957, Kharkov experienced a high infection rate due to the Asian influenza, with a morbidity rate of up to 30% in some human population groups.
• Contemporaneous to this human influenza epidemic, an outbreak of upper respiratory tract disease was recorded in horses at Kharkov race-course, specifically following the epidemic among the race-course staff.

Findings and Observations

• The disease among the horses presented its symptoms differently from known forms of equine influenza. The symptoms were more similar to a disease described in Czechoslovakia caused by A-equi/Praha/56.
• The primary symptom observed was an infectious catarrh, an inflammation of the mucous membrane in the upper respiratory tract.
• The disease had an unusually severe course in some cases, marked by loss of appetite, general debility, and an increase in temperature up to 40.50C. The elevated temperature persisted for three to five days, but in some cases, it lasted up to fifteen days.
• Of the fifteen horses monitored, four experienced a secondary phase of fever.

Disease Timeline and Spread

• The most severe form of the disease started on 1 November and lasted until 5 November. However, some symptoms, including bronchitis and tracheitis, were observed as early as 20 October, yet at this point, the horses maintained normal temperature.
• The period of illness among the racecourse staff started on 15 October 1957, and ended on 1 November, indicating that the severe disease symptoms in the horses began shortly after the human influenza epidemic had ended.
• While infections among horses were noted across all departments, severe cases were concentrated in Department II, with 18 out of the 25 horses affected. Other departments saw one to three cases.
• The investigators did not identify any specific cause for this clustering of severe cases in Department II.