Abstract:
Parasitism is a wide-spread lifestyle adopted by more than 50 % of living organisms on Earth. Under natural conditions, almost every host species is simultaneously infected with multiple parasite species (viruses, bacteria, protozoan, fungi and helminths) over the course of their lifetime. However, our knowledge on interspecific interactions of all the different parasites species that live together have been poorly understood. This symbiotic associations can be either synergistically with mutualistic benefit from parasites and host or antagonistically with elimination of one parasite species or harm to the host.
In this thesis, I investigated factors that structure parasite communities with emphasis on symbiosis of parasites in a free ranging population of African indigenous cattle breeds (ca. 1300 animals). The Sudan Savannah and the Sahel habitats of Cameroon are endemic for trypanosomes, tick and tick-borne pathogens, gastro-intestinal helminths and filarial nematodes.
In order to get a better understanding of the whole parasite communities, blood, skin and faecal samples of Zebu and taurine cattle were examined using microscopy, PCR and Sanger sequencing. The cattle body condition, live-weight and the haematocrit was measured. As expected, almost all animals were infected with at least one parasite.
Using molecular tools, I found seven species of trypanosomes and fifteen tick-borne pathogens (TBD) were found in the blood, co-occurring with the microfilariae of Setaria labiatopapillosa. I found an antagonistic polarizing effect with view to the presence of either pathogenic or non-pathogenic trypanosomes, while mutualistic associations with TBPs lead to protection of cattle against pathogenic TBD and exotic breeds invasion.
Using microscopy, 15 genera/species of helminths and protozoa were identified in the gut and five species of Onchocerca filariae were found in the skin, respectively. There was mutualistic association between flukes, helminths, sporozoan, Eimeria spp. and Onchercerca filarial species. Antagonistic associations were found between different parasite communities. The facilitating factors were tropical climatic conditions, vectors abundance and host susceptibility. The newly introduced Zebu cattle were more susceptible to parasite-caused pathology than the indigenous taurine cattle. A subset of 700 cattle was genotyped for 53,714 single nucleotide polymorphisms (SNPs) and the whole-genome of 5 cattle was sequenced (WGS). Our search for the genomic regions under selection at the genome-wide level revealed novel genomic variants and pathways associated with tropical adaptation, diseases susceptibility and immunological regulation.
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