Encephalitis caused by louping ill virus in a group of horses in Ireland.

The study details an outbreak of Louping ill (LI) virus infection in a group of free-range horses, resulting in neurological disturbance and death in some cases. The virus was isolated from affected animals and analysed.

About Louping ill Virus

• Louping ill (LI) is a viral infection affecting sheep, cattle, and in rare cases, horses. It’s primarily transmitted by infected ticks.
• The infection affects the nervous system of the animals, causing inflammation of the brain and spinal cord (encephalomyelitis). This can result in neurological signs such as difficulty walking, seizures, and in severe cases, death.

Details of the Outbreak

• Three out of four free-range horses showed signs of central nervous system (CNS) disturbance, indicating neurological damage. Two of these horses died after illnesses lasting 2-12 days.
• A mare’s brain and cervical cord were sampled, yielding a virus antigenically indistinguishable from a reference strain of LI virus. This confirms that the horses were indeed suffering from LI infection.

Investigating the Immune Response

• Serum samples, or blood samples without clotting factors, were also taken from three of the horses to measure their immune response. Researchers found hemagglutination inhibition (HI), complement fixation (CF), precipitating, and neutralising antibodies to the LI virus. These are all different types of immune responses that can be triggered by viral infection.
• In two of these horses, a rise in antibody titre (quantity) was observed, indicating an active attempt by the horses’ immune systems to fight off the virus.

Conclusions

• This study documents a rare outbreak of LI infection in horses, adds to understanding about the virus, and potentially offers insights about how to prevent and treat future cases.
• It further emphasizes the importance of surveillance and control measures for ticks in grazing areas to prevent outbreaks of infections such as LI.