Recent microsatellite studies of two African buffalo (Syncerus caffer) populations in South Africa indicated a high genetic load due to genome-wide high-frequency occurrence of deleterious alleles. These alleles have a negative effect on two male traits: body condition and bovine tuberculosis resistance. Here, we study the occurrence of these male-deleterious alleles throughout most of the buffalo’s range using previously published microsatellite data (2-17 microsatellite loci genotyped on 1676 animals from 34 localities). We uncovered a continent-wide frequency cline of microsatellite alleles associated with male-deleterious traits, with frequencies decreasing from 25 °S to 5 °N (adjusted R2 = 0.87). Further, there was a continent-wide presence of linkage disequilibrium (LD) between male-deleterious-trait-associated alleles at five linked locus pairs (interlocus distance: 0.5-28 Megabase). The fraction of positive interlocus associations among these locus pairs was 0.65 (95% CI: 0.52-0.77; expected fraction with free recombination: 0.5), indicating that many male-deleterious alleles co-occur in haplotypes. We argue that the allele-frequency cline and LD likely result from genome-wide balancing selection of male-deleterious alleles with equilibrium allele and haplotype frequencies determined by the activity of a sex-chromosomal gene-drive system, the latter which was indicated in earlier studies and seemingly originated in southern Africa. The selection pressures involved must be high to prevent destruction of the allele-frequency cline and haplotypes by LD decay. Since most buffalo populations are stable, our results indicate that natural mammal populations can withstand a high genetic load. Nevertheless, we expect that a high genetic load makes many buffalo populations relatively sensitive to environmental stresses.
Vectors of emerging infectious diseases have expanded their distributional ranges in recent decades due to increased global travel, trade connectivity, and climate change. Transboundary range shifts, arising from the continuous movement of humans and livestock across borders, are of particular disease control concern. Several tick-borne diseases are known to circulate between eastern Uganda and the western counties of Kenya, with one fatal case of Crimean-Congo haemorrhagic fever (CCHF) reported in 2000 in Western Kenya. Recent reports of CCHF in Uganda have highlighted the risk of cross-border disease translocation and the importance of establishing inter-epidemic, early warning systems to detect possible outbreaks. We therefore carried out surveillance of tick-borne zoonotic pathogens at livestock markets and slaughterhouses in three counties of western Kenya that neighbour Uganda. Ticks and other ectoparasites were collected from livestock and identified using morphological keys. The two most frequently sampled tick species were Rhipicephalus decoloratus (35%) and Amblyomma variegatum (30%), and Ctenocephalides felis fleas and Haematopinus suis lice were also present. In total 486 ticks, lice, and fleas were screened for pathogen presence using established molecular workflows incorporating high-resolution melting analysis and identified through PCR-sequencing of PCR products. We detected CCHF virus in Rh. decoloratus and Rhipicephalus sp. cattle ticks and 82 of 96 pools of Am. variegatum were positive for Rickettsia africae. Apicomplexan protozoa and bcteria of veterinary importance, such as Theileria parva, Babesia bigemina, and Anaplasma marginale, were primarily detected in rhipicephaline ticks. Our findings show the presence of several pathogens of public health and veterinary importance in ticks from livestock at livestock markets and slaughterhouses in western Kenya. Confirmation of CCHF virus, a Nairovirus that causes haemorrhagic fever with a high case fatality rate in humans, highlights the risk of under-diagnosed zoonotic diseases and calls for continuous surveillance and the development of preventative measures.