Several blood parasites, such as Babesia spp., infect erythrocytes in dogs and may lead to hemolytic anemia. Babesiosis in domestic dogs and wild canids is caused by several vector-borne, geographically widespread hemoprotozoan parasites belonging to the Babesia and Theileria genera, and the most commonly reported species in Europe include B. canis, B. gibsoni, B. vogeli and T. annae[1, 2]. T. annae is also called Babesia microti-like or Spanish isolate/agent because it is endemic in Galicia, Northwestern Spain. T. annae has also been identified in Portugal, Croatia and in one dog in North America[2–7]. Ixodes hexagonus is the likely vector of T. annae in Northwest Spain, but other ticks such as Rhipicephalus sanguineus, Ixodes ricinus and Dermacentor spp. have also been proposed as possible transmitters[2, 8, 9]. A vertical (transplacental) transmission of T. annae is also likely as it has been detected in a German shepherd bitch and her 2-month old pup[7]. T. annae has also been detected in a dog confiscated from dogfighting operations in North America suggesting that T. annae may be transmitted by dog bites as occurs with B. gibsoni[6].

T. annae causes severe illness, and dogs may present with weakness, fever, lethargy, hemoglobinuria, tachycardia and tachypnea[2]. Laboratory findings in dogs from Northwest Spain include moderate to severe regenerative anemia (hematocrit below 31%), with marked reticulocytosis. Moderate to severe thrombocytopenia is a common finding, with 50% of the dogs having platelet counts below 23 × 109/L. Leukocytosis and evidence of hepatic disease are uncommon. Azotemia has been recorded in 10–36% of dogs infected with T. annae at the time of diagnosis, which is a poor prognostic marker, with a 22% fatality rate within a week post diagnosis[5, 10, 11].

T. annae appears as a small (less than 2 μm), single, ring-shaped intraerythrocytic piroplasm in blood smears from infected canids. Mostly, the parasitemia is of low level[5, 12]. Specific diagnosis of the parasite is confirmed by polymerase chain reaction (PCR) analysis of blood samples. 18S RNA gene has been used for conventional and nested PCR[5, 6, 11, 12]. A reverse line blot (RBL) assay has recently been developed that simultaneously detects and separates the major vector-borne dog pathogens, including T. annae, in Southern Europe and the Middle East[4].

T. annae appears to be resistant and poorly responds to imidocarb dipropionate (Imizol, at 5–6.6 mg/kg)[2, 11]. Therefore, other drugs, such as Epoximicin and Artesunate, are being investigated as potential therapeutics[13, 14]. T. annae infection in dogs has been hypothesized to be lifelong[1]. Unless I. ricinus could serve as a vector, T. annae is not likely to become endemic in Sweden because of an absence of a suitable vector. However, global warming and increased dog traveling and importation may potentially change the distribution patterns of European tick populations, potentially leading to spread of infectious agents, such as T. annae, to Scandinavia.

The purpose of this first report of T. annae infection in a dog in Scandinavia is to alert Scandinavian veterinarians of the presence of this infection. It should be a differential diagnosis in dogs with regenerative, hemolytic anemia. This first case report of T. annae infection was a 12-week old Swedish, part pit bull puppy with severe regenerative anemia. It was unexpected to find this hemoprotozoan in such a young, Swedish dog and the parasite species had not been diagnosed in Scandinavia previously.