Equine influenza in the Netherlands during the winter of 1978-1979; antigenic drift of the A-equi 2 virus.

The study reports on an outbreak of equine influenza in the Netherlands during the winter of 1978-1979. Despite being vaccinated, horses were infected and exhibited clinical symptoms. This was attributed to a significant antigenic drift in the influenza virus.

Background and Objectives

The research investigated an outbreak of equine influenza, caused by the A-equi 2 (Heq2Neq2) virus, in the Netherlands in the winter of 1978-1979. The main aim of the study was to identify the virus strain responsible for the outbreak and its antigenic properties.

Methods

• The research was initiated in response to an epizootic, or disease outbreak, among horses in the Netherlands.
• The horses involved had been vaccinated with specific antiviral strains, A/Equi/Praha/56 (HEq1Neq1) and A/Equi/Miami/63 (Heq2Neq2).
• The properties of the virus causing the outbreak were examined closely because the vaccinated horses still experienced infection and showed clinical signs.
• The researchers used a technique called hemagglutination-inhibition assay to measure the levels of antibodies that could neutralize the influenza virus in infected ferrets.

Results

• The investigation revealed that the virus responsible for the outbreak had a marked antigenic drift (an evolutionary mechanism in which mutations accumulate in the antigenic sites of viruses) from the prototype and vaccine strain A/Equi/Miami/63 (Heq2Neq2).
• The Dutch/79 isolates, when used to infect ferrets, led to high levels of antibodies that neutralized a number of A-Equi 2-1963, 1968, and 1979 viruses.

Conclusions and Implications

• The research concluded that the strain of the virus implicated in the outbreak had significantly evolved, leading to the failure of the vaccines to provide protection to the horses.
• Based on these findings, the researchers recommended that this new strain of the virus should be considered for inclusion in future influenza vaccines to provide immunity against the evolved virus.