The distribution of Babesia bigemina and Babesia bovis transmitted by Rhipicephalus spp. on a farm in the Eastern Cape
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Date
2020-01
Authors
Marais, Abre
Journal Title
Journal ISSN
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Publisher
University of the Free State
Abstract
Rhipicephalus (Boophilus) microplus, the Asiatic blue tick, was introduced from Madagascar to South Africa during 1896, after a rinderpest epidemic. Displacement of Rhipicephalus (Boophilus) decoloratus, the African blue tick, by R. (B.) microplus has been reported in the Eastern Cape and Limpopo provinces. These two tick species are known vectors for protozoan bovine blood parasites. With the introduction of R. (B.) microplus, Babesia bovis, one of these parasites, was also introduced into South Africa. Babesia bovis is more virulent than B. bigemina, the native species. Control of the disease, babesiosis, caused by these blood parasites, is mainly accomplished by control of the tick vector with chemicals. This however is becoming less effective due to emerging resistance of both tick species to these chemicals. Methods for detecting B. bigemina and B. bovis are therefore becoming all the more important to be able to detect outbreaks early, as well to determine new areas where both the vectors and blood parasites are present. The aim of this study was to confirm the presence of both vector species, R. (B.) decoloratus and R. (B.) microplus, on an Eastern Cape farm after reports of possible B. bovis infections. Larvae, collected by field drags, and adult ticks, collected from cattle, were identified morphologically by using a dissection microscopes. The presence of the protozoan parasites B. bigemina and B. bovis in the blood of cattle hosts was further investigated through Giemsa-stained blood smears from blood samples, collected from 10% of the cattle on the farm. DNA extractions and PCR were performed on the progeny of adult ticks and blood collected from cattle hosts, to scan for Babesia infections. Morphological identification of larval and adult ticks indicated that both R. (B.) decoloratus and R. (B.) microplus were present on the test farm. Over the study period, R. (B.) microplus was found in all camps investigated but R. (B.) decoloratus was present in significantly higher numbers than R. (B.) microplus with 97% (P = 0.0000402) of the larvae and 98% (P = 0.000041) of the adults collected, identified as R. (B.) decoloratus. Displacement of R. (B.) decoloratus by R. (B.) microplus thus did not take place since the first discovery of R. (B.) microplus on the farm during 2014. By means of Polymerase chain reactions the presence of B. bigemina was found in two adult ticks and B. bovis in one. The blood smears yielded one positive B. bovis identification in the blood of one host animal that was confirmed with PCR. DNA extracted and PCR performed on a second blood sample showed one animal host with a double infection of both B. bigemina and B. bovis. The presence of both parasite species, although at a low frequency of 1.85% for B. bovis and 1.08% for B. bigemina, was also confirmed for this farm. It was however only identified from three camps of the 11 camps tested. This study confirmed the prevalence of both of the tick vector species well as the pathogens they transmit on this commercial farm. The presence of R. (B.) microplus and B. bovis, currently still present in low numbers, should be monitored for potential further distribution of this parasite to prevent unexpected outbreaks of babesiosis and the financial implication it can cause.
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Keywords
Dissertation (M.Sc. (Zoology and Entomology))--University of the Free State, 2020, Polymerase chain reaction (PCR), Blue ticks, Cattle, Blood smears, Babesia, Babesiosis, Larvae, Lifecycle, DNA, Babesia bovis