A collaberative effort between six veterinary schools and human medical research centers tackled the question of why some horses get severe neurological disease with West Nile Virus infection, while others don’t.
Only one in 10 horses infected with the WNV develop neurological signs. The dose of virus received and immune-system impairment from diet or age are among the factors that influence how severe the infection will be, but when horses are side-by-side with no glaring differences, more may be going on.
The immune system’s response to a virus comes in two phases — a nonspecific reaction that kicks in early and a more sophisticated response with antibodies that takes about two weeks to develop if the horse was never exposed before.
The researchers found that the risk of infection was closely linked to variations in a gene complex called OAS1. They found this cluster of genes is similar to a human’s, and both are different from species that are more resistant to WNV, like dogs or cattle.
Interferon is a protein/cytokine released by the innate immune system when an invading virus is detected. Interferon then interacts with the OAS1 gene to trigger the release of a protein that blocks the DNA from the virus from being reproduced. This helps to keep the number of viruses under control until more sophisticated immune responses can be mounted.
The researchers believe that weak response to interferon from this gene leading to failure to strongly control the virus from multiplying is what gives the virus a better chance of reaching the immune system. Although this doesn’t give us a treatment, it does give researchers a focus for future work.