An 8-week-old puppy in Van Buren County, Michigan has died from infection by a virus that normally infects horses. This is a rather rare occurrence of a nonetheless devastating infection. The puppy was euthanized after developing seizures and other neurological abnormalities, and Eastern equine encephalitis (EEE) virus infection was ultimately diagnosed. Testing for this and other viruses was probably undertaken because of concerns about rabies.
EEE virus is a mosquito-borne virus that circulates in the bird population and is spread by mosquitoes. Horses are the main victims of infection but disease can occur in various other mammals, including people and dogs.
Canine infections are very rare and this can be considered an "oddball" infection. There’s no evidence that dogs are at any elevated degree of risk compared to previous years, but it is a reminder that while infections are rare, dogs can be susceptible to EEE. The puppy’s young age probably played a role and certain groups (e.g. puppies, elderly dogs, dogs with compromised immune systems) are presumably at greater risk of illness than the normal dog population. The other obvious implication of this report is that it is clear that EEE is circulating in mosquitoes in the area. That means other susceptible species, namely horses and people, are also at risk of exposure.
EEE in people is pretty high on the badness scale. It’s fortunately rare but when it strikes, it’s usually fatal. The same is true for horses. There is a vaccine for horses but not for people, so the main protective mechanism for people is mosquito avoidance.
As with EEE in horses, infected dogs pose no real risk to humans. The virus is not spread by regular contact and dogs don’t develop high enough viral levels in their blood to be able to infect more mosquitoes (who could then infect people). There’s a potential risk of transmission through contact with infected tissues during post mortem examination (necropsies) but standard practices used to prevent transmission of other diseases (e.g. rabies) should be effective for EEE as well.