Distribution of boophilus microplus and boophilus decoloratus and associated occurrence of babesia species in cattle in the Soutpansberg region, Northern Province, South Africa

Abstract

Bovine babesiosis occurs worldwide and is one of the most costly tick-borne cattle diseases in the tropics. The Soutpansberg region of the Northern Province in South Africa is endemic for Babesia bigemina, but Babesia bovis was only reported from this area in the 1980s when some farmers experienced heavy losses due to Asiatic redwater. The main objectives of the study were to confirm the presence of the tick vector Boophilus microplus in the Soutpansberg region where it had not been reported previously, and to determine the seroprevalence of Babesia bovis and Babesia bigemina in cattle in these areas. Other objectives were to assess the relative numbers of Boophilus microplus in relation to Boophilus decoloratus and to determine a possible displacement of Boophilus decoloratus by Boophilus microplus. It was also the intention to map the potential distribution of the Boophilus ticks in the area and to more accurately predict the further spread of Boophilus microplus. Tick collections and serological surveys were carried out during 1999 and 2000 on cattle at 30 communal dip tanks and on 5 commercial farms in the Soutpansberg, Dzanani, Mutale, Thohoyandou and Vuwani Districts. Of the 25,042 Boophilus ticks collected, 93.9 % were Boophilus microplus and 6.1 % were Boophilus decoloratus. At 8 of the dip tanks/farms both Boophilusspecies were found, and the displacement of Boophilus decoloratus by Boophilus microplus was monitored at 4 of these sites. There was a distinct displacement of Boophilus decoloratus at those dip tanks/farms where repeated tick collection was possible. Cattle at the communal dip tanks carried larger Boophilustick numbers than cattle on the commercial farms. Boophilus microplus was the most common Boophilustick collected at the dip tanks, and during the survey it also became the Boophilustick most commonly found on the commercial farms. CLIMEX was used to map the potential distribution of Boophilus microplus and Boophilus decoloratus in the survey area during years with average as well as double average rainfall. Ecoclimatic Indices were computed for each sampling location, using 30 years of climatic information. The displacement patterns of Boophilus species were also discussed. Blood samples (n = 2201) were collected for Indirect Fluorescent Antibody (IFA) testing. Serological evidence of Babesia bovis was detected in 97 % of the communal dip tank herds and in 100 % of the commercial farm herds. The overall seroprevalence of Babesia bovis in the dip tank herds during 1999 and 2000 was 63 %. The seroprevalence of Babesia bovis in the commercial herds increased significantly from 19 % in 1999 to 57.5 % in 2000. There was a slight increase in endemic stability in comparable herds from 1999 to 2000. The increase in seroprevalence and endemic stability probably came as a result of the influx of Boophilus microplus into the survey area. There was a significant correlation between the presence of Boophilus microplus in the survey area and the increasing seroprevalence of Babesia bovis, which confirms that Boophilus microplus is the main and probably the only vector of Babesia bovis in South Africa. Serological evidence of Babesia bigemina was detected in 100 % of communal dip tank and commercial farm herds. The overall seroprevalence of Babesia bigemina in the dip tank herds decreased significantly from 56.1 % in 1999 to 49.3 % in 2000. There was a marked decrease in endemic stability for Babesia bigemina in comparable dip tank herds from 1999 to 2000. The decrease in seroprevalence and endemic stability to Babesia bigemina in these herds was probably due to the substantial increase of Boophilus microplus in the survey area. This may indicate that Babesia bigeminaa was transmitted less effectively by Boophilus microplus than by Boophilus decoloratus. The seroprevalence of Babesia bovis was significantly higher than that of Babesia bigemina at those dip tanks/farms where only Boophilus microplus was present during 1999 and 2000. This may be explained by the possibility that Boophilus microplus transmits Babesia bigemina less effectively than it transmits Babesia bovis. This survey raises several questions on the ability of the African strain of Boophilus microplus to transmit African Babesiastrains. There are indications that the African Boophilus microplus is different to the Australian Boophilus microplus. More research needs to be done to investigate how the Babesia species are transmitted in Africa.