Animal health officials are reporting an outbreak of potentially deadly Venezuelan equine encephalitis in Bagaces and Liberia.
The disease can infect humans, too, and is carried by mosquitoes.
The animal health agency, the Servicio Nacional de Salud Animal, said it was taking steps to import vaccine. So far there are only two cases reported.
The virus disease attacks the nervous system of both horse and humans. Online sources say that healthy humans may experience flu-like symptoms, Those with low immune systems are in more danger.
Horses suffer fever and depression and may experience motor difficulties, said the animal health agency.
The agency said that humans should take steps to eliminate places where mosquitoes reproduce, wear clothes that cover their body and be more alert at times when mosquitoes feed, which is dawn and dusk.