Duration of circulating antibody and immunity following infection with equine influenza virus.

This study explores the duration and effectiveness of immunity to influenza A/equine/Newmarket/79 (H3N8) in ponies following exposure to the virus. The research observes complete clinical protection persisting for at least 32 weeks, partial clinical protection for a year, and evaluates the production of virus-specific antibodies during primary and secondary infections.

Duration of Clinical Protection

• The study assessed the lasting immunity of ponies to equine influenza virus by subjecting them to repeated exposure of the virus via aerosol infection.
• Complete clinical protection, characterized by an absence of febrile responses and coughing, was observed in ponies 16 and 32 weeks after initial infection.
• Partial clinical protection extended beyond a year, as indicated by the absence of coughing and a decrease in febrile responses in ponies that were infected 62 weeks after the initial infection.
• This contrasted significantly with ponies that had not previously been exposed to the virus, which exhibited symptoms like fever, difficulty breathing, nasal discharge and coughing.

Antibody Production and Measurement

• The research also investigated the kinetics of virus-specific antibody production in primary and secondary influenza infections by using the single radial haemolysis test and a radioisotopic antiglobulin binding assay. These tests measured virus-specific immunoglobulin (IgGab) antibody isotype and antibody for the haemagglutinin.
• It was found that antibody for the haemagglutinin declined rapidly after the primary infection, while IgGab responses to the whole virus antigen persisted longer.
• The single radial haemolysis test was particularly useful in detecting antibody responses in multiple infections or exposures to influenza antigens, while the radioisotopic antiglobulin binding assay was more sensitive in identifying infections that had occurred over six months prior.
• This was determined by anamnestic (memory-based) IgGab responses in ponies with low levels of antibody before the rechallenge.

Implications of the Study

• This research is significant in understanding the duration and effectiveness of immunity following infection from the equine influenza virus. It also validates the use of particular tests in identifying and measuring virus-specific antibodies and their duration in the body.
• The understanding of these immune responses and their duration could aid in the development of more effective treatments and preventive strategies against equine influenza.