Babesia leo n. sp. from lions in the Kruger National Park, South Africa, and its relation to other small piroplasms.

Babesia leo, a small piroplasm isolated from lions in South Africa is described as a distinct species based on a phylogenetic analysis of the 18S rRNA gene. Intraerythrocytic trophozoite and merozoite stages of B. leo are morphologically indistinguishable from other small piroplasms of felids. Previous studies showed that B. leo was biologically and antigenically distinct from B. felis, which is known to infect wild and domestic felids in South Africa. Molecular characterization showed strong support for the phylogenetic seperation of B. leo as a distinct species from B. felis and other felid piroplasms. Phylogenetic analysis also showed that Babesia microti and all of the felid piroplasms from Africa with known 18S rRNA gene sequences available, including B. leo, formed a single, separate clade, sister to the other babesial and theilerial piroplasm parasites.

Continuous in vitro cultivation of Babesia gibsoni.

Two stocks of the protozoan parasite Babesia gibsoni, one of the causative agents of canine piroplasmosis, were propagated continuously in dog erythrocytes in microaerophilous stationary-phase culture. Cultures of both stocks were initiated in a humidified 5% CO2, 2% O2, 93% N2 atmosphere at 37 degrees C at a time when very few parasites (<0.01%) were detected in a thin blood smear. Cultures of one stock were also initiated in a humidified atmosphere of 5% CO2 in air at 37 degrees C during a patent parasitaemia (2.6%) in the donor animal. The culture medium was a modified HL-1 medium supplemented with dog serum, L-glutamine and antibiotics. Culture-derived parasites were cryopreserved and resuscitated. Cultures of each stock were propagated for 102 days and 51 days, respectively, before they were terminated.

Screening of five drugs for efficacy against Babesia felis in experimentally infected cats.

The efficacy of 5 drugs was tested against experimental Babesia felis infection in domestic cats. Two of the drugs, rifampicin and a sulphadiazine-trimethoprim combination, appeared to have an anti-parasitic effect, but were inferior to primaquine. The other 3 drugs, buparvaquone, enrofloxacin and danofloxacin, had no significant anti-babesial effect.

A possible new piroplasm in lions from the Republic of South Africa.

A small piroplasm was detected in blood smears from lions (Panthera leo) in the Kruger National Park (KNP; Republic of South Africa) during 1991/1992. The parasite was identified provisionally as Babesia felis, but sera from these lions tested negative to B. felis antigen in the indirect immunofluorescent antibody test (IFAT). Blood from an infected lion was subsequently subinoculated into a domestic cat and two leopards in an attempt to identify the parasite. A lion also was infected with B. felis (from a cat). Serum samples collected from these animals were tested against B. felis, the KNP small piroplasm, and Cytauxzoon felis antigen in the IFAT. The serological results indicate that the KNP small piroplasm isolated from the lion is probably a distinct species from B. felis and C. felis.

Isolation of a South African vector-specific strain of Babesia canis.

A South African strain of Babesia canis parasites was isolated and shown to be vector-specific to only one of the two vectors in the region, Haemaphysalis leachi. This tick was found to transmit the parasite in its adult instar. When infected as larvae, the ticks would not transmit in the proceeding nymphal instar. The vector-specific strain was named the 'Thomas strain' after one of the dogs involved in isolating it. A survey revealed a prevalence of > 50% of this strain in four widely separated areas of the country. Rhipicephalus sanguineus, which transmits B. canis vogeli elsewhere, has not been shown to be a vector of the South African strain of B. canis.

Sterilisation of Babesia canis infections by imidocarb alone or in combination with diminazene.

Babesia canis infections were apparently sterilised by a single dose of imidocarb at 7.5 mg kg-1, as well as by a single dose of diminazene at 3.5 mg kg-1, followed by a single dose of imidocarb at 6 mg kg-1 the following day. This was confirmed by subinoculation of blood from these dogs to splenectomised recipients. Sterilisation of the infection is not recommended in endemic areas; a more rational approach would be to allow a state of premunity to develop in dogs at risk to repeated infections.

Immune responses to South African Babesia canis and the development of a preliminary vaccine.

The immune responses of 2 Beagles to live parasites of an isolated B. canis strain were tested. The dogs were infected with live parasites and were carefully treated to allow the parasites to remain in the dogs' bodies for long enough to evoke an immune response. Once recovered from the initial infections, both dogs received 2 separate homologous challenges with live parasites. During the second challenge, neither dog showed clinical signs of disease. An experimental vaccine was developed against the isolated B. canis strain by growing parasites in a micro-aerophilous stationary phase cell culture system to provide (a) antigen-containing supernatant material and (b) pellet material containing dead parasites. Two dogs each were inoculated with the different formulations of the vaccine on 2 separate occasions. Three weeks after the second inoculation, all 4 dogs were challenged with live parasites. Three of the 4 dogs recovered from the challenge without any anti-babesial treatment.

The transovarial transmission of Babesia trautmanni by Rhipicephalus simus to domestic pigs.

Rhipicephalus simus was, for the first time, experimentally proven to be a transovarial vector of Babesia trautmanni of domestic pigs. The nymphal and adult progeny of experimentally infected female ticks transmitted the infection to 2 susceptible splenectomized pigs. Features of the infection included a prepatent period of 6-8 days post-tick infestation, a febrile reaction for 3 days and a maximum parasitaemia score of 15 (more than 6 parasites per 300 red blood cells). Other clinical signs in both pigs were mild inappetence and listlessness. Both pigs recovered without any antibabesial therapy.