Tick-borne diseases in dogs: ehrlichiosis and babesiosis in clinical practice

Few conditions show up as often in canine practice as the so-called tick fever complex. Transmitted mainly by the brown dog tick (Rhipicephalus sanguineus), ehrlichiosis (Ehrlichia canis) and babesiosis (Babesia spp.) share a vector, overlapping clinical pictures and, frequently, occur as co-infection. For the small-animal clinician, mastering their phases, the diagnostic reasoning and the therapeutic options is an essential part of the routine.

Two agents, one vector

Canine monocytic ehrlichiosis is caused by the intracellular bacterium Ehrlichia canis, which infects mainly monocytes. Babesiosis is caused by protozoa of the genus Babesia, which parasitize red blood cells and lead to their destruction. Because both agents circulate in the same tick, co-infection is common — a situation that tends to make the picture more severe and the diagnosis less obvious.

The phases of ehrlichiosis

Ehrlichiosis is usually described in three phases, and recognizing them guides both the investigation and the prognosis.

• Acute phase: appears weeks after infection. Apathy, fever, anorexia, lymphadenomegaly and splenomegaly predominate. Thrombocytopenia is a striking laboratory finding already at this stage.
• Subclinical phase: the animal may appear recovered, with no evident clinical signs, while the agent persists in the body. Many dogs remain like this for long periods.
• Chronic phase: the most feared. It may present with pancytopenia, bone marrow hypoplasia, significant anemia, bleeding (epistaxis, petechiae) and multisystemic conditions that are difficult to manage.

Babesiosis, in turn, tends to present more acutely, with hemolytic anemia, pale or icteric mucous membranes, fever, weakness and, in severe cases, hemoglobinuria.

Clinical signs that should raise a flag

In the history and physical examination, some findings increase suspicion: a history of tick infestation, apathy, fever, weight loss, pale mucous membranes, enlarged lymph nodes and any sign of bleeding. In the laboratory, thrombocytopenia and anemia are pillars of suspicion for the complex. It is worth remembering that the absence of ticks at the time of the consultation does not rule out the diagnosis — the infection may have occurred weeks earlier.

Diagnostic reasoning

Diagnosis combines clinical signs, laboratory work and specific methods:

• Blood smear: may reveal Ehrlichia morulae inside monocytes or Babesia forms within red blood cells. It is cheap and fast, but has limited sensitivity — a negative smear does not rule out the disease.
• Serology: detects antibodies and helps with confirmation, especially in ehrlichiosis; it should be interpreted considering the phase of the disease and the possibility of prior exposure.
• PCR: identifies the agent's genetic material, with good sensitivity and specificity, being useful to confirm and differentiate species.

A complete blood count is indispensable and often the first to suggest the complex, by revealing thrombocytopenia, anemia or pancytopenia.

Treatment

For ehrlichiosis, doxycycline remains the antimicrobial of choice, administered over a prolonged period according to clinical assessment. In babesiosis, specific antiparasitic agents against the protozoan are used. In both, supportive care is decisive: hydration, management of anemia and, in selected cases of severe anemia, considering a blood transfusion. Serial laboratory follow-up — especially recovery of the platelet count and the hematocrit — is what confirms the therapeutic response.

Prevention: the vector is the target

Since everything starts with the tick, vector control is the most effective measure. Guiding the owner on the regular use of acaricidal antiparasitic products, environmental management and frequent inspection of the animal dramatically reduces the risk. Early removal of the tick also lowers the chance of transmission. Here, prevention is literally worth more than treatment.

Conclusion

Ehrlichiosis and babesiosis remain protagonists in canine practice in Brazil. Success depends on recognizing clinical signs early, correctly interpreting the blood count and specific tests, instituting the appropriate treatment and — above all — keeping the patient's progress in sight over the weeks. It is precisely in this follow-up, with an organized and accessible clinical record, that a favorable outcome is built.