Babesia rossi, an intraerythrocytic protozoan, causes a severe, often life-threatening disease of domestic dogs.
Dogs treated early for B. rossi infection usually recover from the disease, but dogs left untreated or treated at
a later stage of infection seldom survive. Dogs infected with B. rossi have varied clinical manifestations that can
be categorized as uncomplicated (with a good prognosis) or complicated (with a poor prognosis). One hundred
twenty-one blood samples were collected from dogs presented to the Onderstepoort Veterinary Academic
Hospital and diagnosed with babesiosis by the use of a thin blood smear. An additional 20 samples were
obtained from Babesia-infected dogs from private clinics around the Onderstepoort, Johannesburg, Durban,
White River, and Cape Town areas. The samples were screened by PCR targeting the Babesia rossi erythrocyte
membrane antigen gene (BrEMA1) and by sequencing of the polymorphic region (i.e., region with a variable
number of hexapeptide repeats). Analysis of PCR products revealed 11 different gene profiles, visualized by gel
electrophoresis. Twelve distinct BrEMA1 genotypes were identified by sequencing, but the numbers of hexapeptide
repeats varied from 6 to 31 (classified as genotype6 to genotype31). The genotypes were retrospectively
compared to the clinical case data. The most frequently encountered B. rossi parasites were those attributed to
genotype19 (36.2%), genotype28 and genotype29 (20.6% each), and genotype11 (12.7%). These genotypes were
also the ones associated with the poorest prognosis. This preliminary finding suggests clinically important
differences between the various B. rossi genotypes identified.