Investigation of equine influenza cases exhibiting neurological disease: coincidence or association?

This research investigated cases of equine influenza in horses that showed signs of neurological disease during a 2003 outbreak in the UK, finding potential evidence that the influenza virus could result in encephalitis, possibly due to a flawed immune response.

Background

• Equine influenza is usually a disease that is brief and self-limiting. However, in a 2003 UK outbreak, more severe symptoms were noticed, particularly in unvaccinated animals.
• Notably, two horses that were infected with the influenza showed neurological signs. Ultimately, one of these horses was euthanized.

Methodology

• Post-mortem examination of the euthanized horse’s brain revealed indications of viral-type non-suppurative encephalitis, a type of brain inflammation.
• Immunolabelling of sections of the nasal mucosa was used to demonstrate the presence of the influenza virus antigen.

Findings

• The study found a condition known as influenza-associated encephalopathy, which has been previously described in humans, could potentially be present in horses as well.
• This phenomena was not definitively proven, but the data from the study suggests that similar disease mechanisms could be at play in both species.
• It was proposed that the presence of encephalitis in these horses could be the result of an aberrant immune response to the equine influenza virus infection.

Implications

• The findings suggest that equine influenza virus can potentially cause encephalitis in horses, its natural host, possibly due to an aberrant immune response, thus exhibiting more severe clinical signs.
• This opens up further questions about the types of neurological impacts that can occur from viral infections and underscores the importance of vaccination.