Tyzzer's disease is a fatal disease in foals caused by Bacillus piliformis . Then, if the infected mosquito bites a horse, it deposits the virus. For the encephalitides, the horse is usually a dead-end host. This means that while the horse might develop the disease, it is unlikely to propagate the virus. Mosquitos can also vector VEE, EEE, and WEE from rodents, and the virus can live in mosquito populations until passed to a warm-blooded host.
Horses also can pick up diseases from birds that share their housing.
Cryptococcus neoformans is associated with wild birds, including pigeons, and with domestic chickens. Feces also figure in the transmission of histoplasmosis or salmonella from domestic birds, and Tyzzer's disease from rodent feces. Dogs and cats are low on the list of dangers to horses. Rabies is an example of a problem that could be spread from a dog or cat to a horse, but that would be very unusual, says Timoney. I suppose there is the potential for leptospirosis being transmitted from dogs, but it is unlikely.