A Minnesota woman has died of Powassan virus encephalitis, a very rare neurological disease transmitted by ticks. Powassan virus is most often found in parts of Ontario, Quebec and New Brunswick, but there is evidence of it in many other parts of North America as well, and as far away as Russia. Human infections are very rare, but when they occur neurological disease is severe, mortality rates are high, and survivors often have residual neurological problems.

Powassan virus is a flavivirus, related to St. Louis encephalitis virus and West Nile virus, but unlike these, the reservoir of Powassan virus seems to be wild small mammals, with transmission via ticks (as opposed to a bird reservoir and transmission via mosquitoes for the others). The virus has been detected in mosquitoes but it’s not known whether they can transmit the virus.  Ticks are considered the major (and possibly only) route of infection.

The risk to animals in areas where Powassan virus can be found is very limited. Natural infections of dogs, cats or horses have not been reported, as far as I know.  However, that doesn’t 100% rule out the possibility of disease, since you have to look in order to find, and specific investigation of Powassan virus transmission is uncommon. Neurological disease has been reproduced experimentally in horses, but not dogs and cats.

Overall, the risk to pet owners and pets posed by Powassan virus is very low. Taking measures to avoid ticks is the key, and such precautions should be taken for many reasons beyond Powassan virus exposure.