Rangelia spp are phylogenetically related to Babesia spp, and this parasite is highly prevalent in young hunting dogs in south and southeast regions of Brazil, thought to be transmitted by Rhipicephalus sanguineus and Amblyomma aureolatum.
Following transmission of the parasite by ticks, a circulating parasitemia is observed in dogs which peaks between 9 - 11 days, with the parasite infecting not only erythrocytes, but also leucocytes and endothelial cells. Subsequently, the parasitemia becomes reduced due to inflammatory cytokine release and the protozoan can be observed in circulating leukocytes 17 - 21 days post-infection.
Affected dogs primarily present with lethargy, fever and anorexia, but other symptoms such as dyspnea, petechiae, hematemesis, bloody diarrhea, splenomegaly, hepatomegaly, lymphadenopathy. icterus and bilirubinuria may also exist. A characteristic feature of this disease is hemorrhage in the gastrointestinal tract, and persistent bleeding from the nose, oral cavity and tips, margins and outer surface of the pinnae.
The disease usually progresses with the presence of intracytoplasmic parasitophorous vacuoles in the endothelial cells of capillaries of various organs and tissues and inflammatory infiltrate in organs such as the kidneys, heart and liver.
Blood tests usually reveal leukopenia due to neutropenia and eosinopenia, along with lymphocytosis, monocytosis and a regenerative immune-mediated hemolytic anemia and thrombocytopenia, although hypoalbuminemia, hyperglobulinemia and elevated levels of ALT, AST and creatine kinase are commonly observed.
Diagnosis is based on microscopic visualization of piroplasms obtained from bone marrow samples (parasite not usually visible in peripheral blood).
A definitive diagnosis requires PCR exclusion of other blood parasites such as Babesia spp.
Many urban dogs, which are the majority exposed to this parasite, may succumb to infection without veterinary intervention.
Supportive therapy such as intravenous fluids and blood transfusions should be employed when necessary.
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