Susceptibility of Indigenous Cattle Breeds to Co-Infection with Multiple Tick-Borne Pathogens

Abstract

The control of tick-borne diseases in an endemic region is very challenging and costly due to the presence of multiple pathogens from the seven globally-important livestock intracellular pathogens. This problem is exacerbated by the availability of competent vector ticks for each pathogen strain, thus resulting in enhanced transmission efficiency and higher infection prevalence of disease among cattle from the tropical region than the temperate region. Unfortunately, these diseases are poorly controlled in sub-Saharan Africa largely due to lack of understanding of the infection biology of the pathogen species. Understanding the species composition of pathogens of infected cattle in Ghana will allow for the formulation of cost effective interventions that will enable the development of applicable control strategies and improve the adaptive capacity of tick-borne diseases. In this thesis, Anaplasma marginale, Babesia bigemina and Theileria species were used as model bacterial and protozoan blood-feeding pathogens to examine whether genetic diversity in cattle correlates with quantitative differences in co-infection prevalence among indigenous breeds of cattle from different Agro-ecological zones in Ghana. A low-cost molecular approach (multiplex PCR) was developed to assess the multi- pathogen complex situation in the indigenous cattle of four distinct breeds (Sanga, Gudali, West African Shorthorn (WASH) and White Fulani). The overall pathogen co-infection prevalence in indigenous cattle breeds examined was 26.4% (105/397). Out of this total, only six cattle, representing 1.5% (6/397) of the population were co-infected with all three different tick-borne pathogens - Theileria species, Anaplasma marginale, and Babesia bigemina. 95 cattle 23.9% (95/397) were co- infected with Anaplasma marginale and Theileria species, whereas four cattle 1.0% (4/397) were co-infected with Anaplasma marginale and Babesia bigemina. Surprisingly, no individual cattle were found to be co-infected with Babesia bigemina and Theileria species. The overall infection prevalence of cattle was 62.9% (250/397). Significant (p=0.00) variation was observed in co-infection prevalence between breeds of indigenous cattle examined. Comparisons of quantitative differences in the number of different strains among cattle from diverse agro-ecological zones strongly support the significant (p=0.01) effect of the type of ecological zone on the number of tick-borne pathogens that circulate in cattle. The data also demonstrated that 145 cattle 36.5% (145/397), harboured single pathogen species. Out of the total number of single infected cattle, Anaplasma marginale alone constituted 36.3% (144/397). Only one cattle 0.3% (1/397) was infected with Theileria species alone. Notably no cattle were infected with Babesia bigemina pathogen alone at the time of the study. Importantly high progression of the number of multiple-pathogen infected cattle, over the duration of infection, at both the level of the individual host and the population was found, suggesting the lack of immunity against co- infection of cattle in the endemic region.