Ticks are commonly found on dogs during the acute stage. The clinical signs in the this phase may be mild and nonspecific, however some cases may present as severe and life threatening. The incubation period is 8-20 days.

The acute phase of the disease may last from 1-2 weeks. Signs may include depression, lethargy, anorexia, pyrexia, lymphadenomegaly, splenomegaly and mild weight loss. Dogs may present with bleeding tendencies, mainly petechias and ecchymoses of the skin, mucous membranes and occasional epistaxis.