Confirmation of occurrence of Babesia vogeli in a dog in Windhoek, central Namibia

Although there is evidence of high seroprevalence of antibodies to Babesia spp. in dogs in central Namibia, clinical babesiosis is rarely diagnosed. Rhipicephalus sanguineus sensu lato, the vector of Babesia vogeli, is common in Namibia while Haemaphysalis elliptica, the vector of the highly virulent but morphologically indistinguishable Babesia rossi, has rarely been recorded, mainly in northern Namibia. On the basis of vector occurrence, clinical cases of canine babesiosis in Windhoek, central Namibia, have been ascribed to B. vogeli. DNA extracted from a blood smear made from a sick dog was subjected to the reverse line blot hybridisation assay. The polymerase chain reaction amplicons hybridised with the B. vogeli–specific probe, but not with the Babesia canis– and B. rossi–specific probes. Although attempts at cloning and sequencing of the full-length 18S rRNA gene were unsuccessful, we can confirm that B. vogeli occurs in central Namibia.


Introduction
Canine babesiosis is caused by either 'large' or 'small' piroplasms. The latter, primarily Babesia gibsoni, are not of major concern in southern Africa and are not further considered here (Matjila et al. 2007). Differences in clinical manifestation, immunology and vector specificity of isolates of 'large' babesias from various geographic regions were reported at an early stage (e.g . Brumpt 1919;Christophers 1907;Laveran & Nattan-Larrier 1913;Robertson 1901), but were mostly overlooked, and the organism was generally referred to as Babesia canis sensu lato. The situation changed when three groups of B. canis s. l. were distinguished and a new nomenclature was proposed (Uilenberg et al. 1989). The 'large' piroplasms are a complex of at least three morphologically similar but genetically distinct vector-specific species: B. canis, Babesia rossi and Babesia vogeli (Zahler et al. 1998). The pre-1989 literature on canine babesiosis should therefore be critically evaluated to determine which specific taxon is involved.
Babesia rossi, transmitted by Haemaphysalis elliptica and presumably also by Haemaphysalis leachi (Apanaskevich, Horak & Camicas 2007), is restricted to sub-Saharan Africa and causes the most virulent manifestation of canine babesiosis. The less virulent B. canis sensu stricto, transmitted by Dermacentor reticulatus, is restricted to Europe (Brumpt 1919). The least virulent species, B. vogeli, is transmitted by Rhipicephalus sanguineus sensu lato, which has a global distribution, but is most prevalent in tropical and subtropical regions (Gray et al. 2013).
Canine babesiosis is regarded as a major problem in South Africa, where it has been well studied (Jacobson 2006;Schoeman 2009). The vast majority of cases are caused by B. rossi: at the Onderstepoort Veterinary Academic Hospital (OVAH), only 5 of 350 cases (1.4%) were attributed to B. vogeli, the remaining 98.6% of the patients being positive for B. rossi (Matjila et al. 2008). At the OVAH, H. elliptica (reported as H. leachi) was collected from 304 of 395 dogs (77.0%) diagnosed with canine babesiosis, while R. sanguineus was collected from 146 (37%) of these dogs (Horak 1995).
Initial reports indicated that canine babesiosis is not common in Namibia (Schneider 1994). In a more recent study, Stübe (2004) identified Babesia piroplasms in 27 of 600 blood smears (4.5%) made from dogs in the Okahandja District of central Namibia. Using an enzyme-linked immunosorbent assay (ELISA) with B. canis antigen, 69% of the 600 dogs were found to be seropositive (Stübe 2004). This test is known to cross-react with antibodies to B. vogeli, while the IFA test using this antigen cross-reacts with both B. rossi and B. vogeli (Dyachenko et al. 2012;Jongejan et al. 2011;Pantchev et al. 2015). This would suggest either (1) an endemically stable situation, such as typically occurring with bovine babesiosis, or (2) the presence of a parasite of relatively low virulence.
Although there is evidence of high seroprevalence of antibodies to Babesia spp. in dogs in central Namibia, clinical babesiosis is rarely diagnosed. Rhipicephalus sanguineus sensu lato, the vector of Babesia vogeli, is common in Namibia while Haemaphysalis elliptica, the vector of the highly virulent but morphologically indistinguishable Babesia rossi, has rarely been recorded, mainly in northern Namibia. On the basis of vector occurrence, clinical cases of canine babesiosis in Windhoek, central Namibia, have been ascribed to B. vogeli. DNA extracted from a blood smear made from a sick dog was subjected to the reverse line blot hybridisation assay. The polymerase chain reaction amplicons hybridised with the B. vogeli-specific probe, but not with the Babesia canis-and B. rossi-specific probes. Although attempts at cloning and sequencing of the full-length 18S rRNA gene were unsuccessful, we can confirm that B. vogeli occurs in central Namibia. On the basis of the abundance of R. sanguineus s. l., Noden and Soni (2015) ascribed clinical canine babesiosis cases in Namibia to B. vogeli. We can confirm that B. vogeli occurs in Namibia.

Confirmation of occurrence of
In February 2015, a dog presented at Windhoek Animal Hospital showed typical clinical signs of babesiosis. A blood smear was made, and large babesias were seen (Figure 1). The dog received the usual treatment and made an uneventful recovery. A stained blood smear was sent to the Department of Veterinary Tropical Diseases (DVTD) for confirmation of the diagnosis.
On RLB, the PCR amplicons hybridised only with the B. vogeli-specific probe. Although attempts at cloning and sequencing of the full-length 18S rRNA gene were unsuccessful, we can confirm that B. vogeli occurs in central Namibia. This does not rule out possible occurrence of B. rossi, especially in the more mesic north-eastern parts of Namibia, including the Zambezi (previously Caprivi) region, where H. elliptica could occur since it is found in the adjoining Okavango region of Botswana (Walker 1991).
In sub-Saharan Africa, B. vogeli was first reported from clinically normal dogs in South Africa (Matjila et al. 2004). Its presence had probably been overlooked because of the preponderance of infections of the highly virulent B. rossi (Matjila et al. 2008). Babesia vogeli has also been reported from Sudan (Oyamada et al. 2005), Nigeria (Adamu et al. 2014;Kamani et al. 2013;Sasaki et al. 2007) and Cape Verde (Götsch et al. 2009). In Zimbabwe, B. vogeli has been reported from captive lions (Panthera leo), wild cats (Felis lybica) and servals (Leptailurus serval) and could presumably also occur in dogs (Kelly et al. 2014).
Rhipicephalus sanguineus s. l., the only known vector of B. vogeli, is now thought to be a species-complex comprising at least 17 sibling species, which may differ in vector capacity Dantas-Torres & Otranto 2015). Domestication of the dog benefitted this tick, which probably evolved as a parasite of burrowing carnivores in warm climates (Gray et al. 2013). Because of the worldwide spread of humans and dogs, this tick now has a global distribution. Rhipicephalus sanguineus s. l. is incriminated as vector of Hepatozoon canis and Ehrlichia canis in addition to B. vogeli. These pathogens could therefore be expected to occur throughout the geographic distribution of the vector (Gray et al. 2013). Indeed, 53.8% of 106 dogs from Windhoek, Namibia, were seropositive on a solid-phase dot ELISA based on a crude antigen of E. canis (Israeli strain) (Manyarara et al. 2015).
The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this article.