Abstract Borreliosis is a bacterial zoonosis transmitted by arthropods. The infection is more common in dogs than other domestic animals. A one-month-old puppy with fever, jaundice and digestion disorder was referred to Small Animal Hospital, University of Tehran. Laboratory findings included severely regenerative anemia, neutrophilia, thrombocytopenia, strong spirochetemia and significant changes in serum proteins. The attempt to isolate the bacteria in laboratory animals was unsuccessful. The infection was cured using antibiotic and the animal completely recovered.

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