The disease is spread from an infected hare to a susceptible hare by means of ticks. Ticks are only present on hares from May through September. The disease essentially disappears from October through April. The second cycle occurs in water. Beaver and muskrats are the primary hosts.
Infected animals die in a slough, pond or lake.
As the carcass decomposes, large numbers of bacteria are released into the water. Susceptible animals are exposed when they drink or swim in the water. In Alaska, this disease is most common in the Interior. In the latter stages of disease, hares become very slow. Sometimes, white spots may also be seen on these organs.