Occurrence of tick-borne haemoparasites in cattle in the Mungwi district, Northern Province, Zambia

Abstract

The most important tick-borne diseases (TBDs) occurring in Zambia that affect domestic animals, particularly cattle and small ruminants, are theileriosis (East Coast fever and Corridor disease), anaplasmosis (gall sickness), babesiosis (red water), and heartwater (cowdriosis). Of these, theileriosis is the most important, causing significantly more deaths than the other tick-borne diseases combined. Despite their importance, little is known about the occurrence and prevalence of haemoparasites in cattle in the communal areas of Zambia. Clinical signs and post mortem lesions are pathognomonic of mixed tick-borne infections especially babesiosis, anaplasmosis and East Coast fever (ECF). The main objective of this study was, therefore, to screen selected communal herds of cattle for tick-borne haemoparasites and identify the tick vectors associated with the high cattle mortalities due to suspected TBDs in the local breeds of cattle grazing along the banks of the Chambeshi River in Mungwi, Zambia. East Coast fever is endemic to the district of Mungwi, Northern Province, Zambia and vector control using acaricides has proved to be very costly for the small scale farmers. Also, Mungwi experiences increased cattle mortalities between December to March and May to July. All age groups of cattle are affected. A total of 299 cattle blood samples were collected from July to September 2010 from Kapamba (n=50), Chifulo (n=102), Chisanga (n=38), Kowa (n=95) and Mungwi central (n=14) in the Mungwi District, Northern Province, Zambia. Ticks were also collected from the sampled cattle from April to July 2011. DNA was extracted and the parasite hypervariable region of the small subunit rRNA gene was amplified and subjected to the reverse line blot (RLB) hybridization assay. The results of the RLB assay revealed the presence of tick-borne haemoparasites in 259 samples occurring either as single or mixed infections. The most prevalent species present were the benign Theileria mutans (54.5%) and T. velifera (51.5%). Anaplasma marginale (25.7%), Babesia bovis (7.7%) and B. bigemina (3.3%) were also detected in the samples. Nine percent of the samples tested negative for the presence of haemoparasites. In a number of samples (4%) the PCR products failed to hybridize with any species-specific probes but hybridized only with the genus-specific probes which could suggest the presence of a novel species or variant of a species. Of the four Theileria species known to occur in Zambia (T. parva, T. mutans, T. velifera and T. taurotragi), T. parva is the most economically important, causing Corridor disease in the Southern, Central, Lusaka and the Copper-belt provinces, while causing ECF in the Northern and Eastern provinces of Zambia. In our study, only one sample (from Kapamba) tested positive for the presence of T. parva. This was an unexpected finding; also because the tick vector, Rhipicephalus appendiculatus, was identified on animals from Kowa (14%), Chisanga (8.5%), Chifulo (6%) and Kapamba (1.4%). We can only speculate that the RLB hybridization assay may not have been able to detect the parasite in the animals sampled due to a too low parasitaemia. The samples should also be subjected to the T. parva specific real-time PCR assay to determine a more accurate T. parva prevalence in cattle in the Mungwi district, Northern Province. In Zambia, Babesia bovis and B. bigemina are recognized as being of economic importance in cattle. In our study, B. bovis was present in 7.7% of the sampled animals and B. bigemina in 3.3% of the animals. We detected B. bovis in all of the five sampled areas with the highest detection in Mungwi central (14.3%) and Kowa (10.5%). As expected, the tick vector Rhipicephalus (Boophilus) microplus was identified from animals from all of these areas. Babesia bigemina was only reported from Kowa (10.5%). The most abundant ticks identified from the sampled animals from Kowa were Rhipicephalus (Boophilus) decoloratus (36.3%) and Rhipicephalus (Boophilus) microplus (8.8%). These tick vectors have been implicated in the transmission of B. bigemina. Our findings are in concordance with results obtained by other authors who have speculated that an increase in the detection of B. bovis may indicate that B. bovis is becoming endemic in this part of the country. This could be due to uncontrolled movement of cattle that frequently occurs within Zambia. Heartwater (cowdriosis) is caused by Ehrlichia ruminantium, a rickettsial disease that affects domestic and wild ruminants. In Zambia, heartwater is mainly a disease of cattle, although outbreaks in sheep and goats have been reported and recorded. In our study, only one sample (from Kapamba) tested positive for the presence of E. ruminantium even though Amblyomma variegatum ticks were identified from 52.9% of the sampled animals from all study areas. The cattle sampled in our study are not regularly dipped and no game has been spotted in cattle grazing areas. It is possible that these cattle may have attained a state of endemic stability to heartwater. It is also possible that the RLB hybridization assay may not have been sensitive enough to detect E. ruminantium infections if the parasitaemia was very low. Samples should also be subjected to the E. ruminantium-specific pCS20 real-time PCR assay to determine more accurately the E. ruminantium prevalence in cattle in the Mungwi district, Northern Province. Anaplasma marginale (the causative agent of bovine anaplasmosis) has previously been shown to be present in all the provinces of Zambia and is the only Anaplasma species of importance to cattle in Zambia. In our study, 25.7% of the sampled cattle tested positive for A. marginale; it was detected in all areas except Chisanga. Amblyomma variegatum was identified from 52.9% of the sampled cattle, and Rhipicephalus (Boophilus) microplus from 12.1% of the cattle. Rhipicephalus (Boophilus) microplus has been incriminated as being a vector of A. marginale. Furthermore, three samples (from Kowa) tested positive for the presence of Anaplasma centrale. To our knowledge, no vaccination regime using A. centrale is being conducted in the Mungwi district of Zambia. The presence of A. centrale is, therefore, an interesting finding. The results of our study suggest that the cause of cattle mortalities in Mungwi during the winter outbreaks is mainly due to A. marginale, B. bovis and B. bigemina infections. This was confirmed by the results of the RLB hybridization assay, clinical manifestation of the disease in the affected cattle (own observation) and the tick species identified on the animals. It appears that in Mungwi, babesiosis due to B. bovis mostly infects cattle above one year of age. Calves appear to be less affected by B. bovis infection. There is need for further epidemiological surveys in Mungwi district, Northern Province, Zambia to get a better understanding of the epidemiology of these tick-borne haemoparasites affecting cattle. We conclude that integrated control policies should be developed to take account of multi-species pathogen communities that are commonly associated with clinical and sub-clinical TBD infections in Zambia.