A continent-wide high genetic load in African buffalo revealed by clines in the frequency of deleterious alleles, genetic hitchhiking and linkage disequilibrium

A high genetic load can negatively affect population viability and increase susceptibility to diseases and other environmental stressors. Prior microsatellite studies of two African buffalo (Syncerus caffer) populations in South Africa indicated substantial genome-wide genetic load due to high-frequency occurrence of deleterious alleles. The occurrence of these alleles, which negatively affect male body condition and bovine tuberculosis resistance, throughout most of the buffalo’s range were evaluated in this study. Using available microsatellite data (2–17 microsatellite loci) for 1676 animals from 34 localities (from 25°S to 5°N), we uncovered continent-wide frequency clines of microsatellite alleles associated with the aforementioned male traits. Frequencies decreased over a south-to-north latitude range (average per-locus Pearson r = -0.22). The frequency clines coincided with a multilocus-heterozygosity cline (adjusted R2 = 0.84), showing up to a 16% decrease in southern Africa compared to East Africa. Furthermore, continent-wide linkage disequilibrium (LD) at five linked locus pairs was detected, characterized by a high fraction of positive interlocus associations (0.66, 95% CI: 0.53, 0.77) between male-deleterious-trait-associated alleles. Our findings suggest continent-wide and genome-wide selection of male-deleterious alleles driven by an earlier observed sex-chromosomal meiotic drive system, resulting in frequency clines, reduced heterozygosity due to hitchhiking effects and extensive LD due to male-deleterious alleles co-occurring in haplotypes. The selection pressures involved must be high to prevent destruction of allele-frequency clines and haplotypes by LD decay. Since most buffalo populations are stable, these results indicate that natural mammal populations, depending on their genetic background, can withstand a high genetic load.

Assessment of Vegetation Structure of the African Buffalo (Syncerus caffer) Habitat in Kainji Lake National Park, Nigeria

The study assessed the relative abundance and vegetation structure of African buffalo (Syncerus caffer) including plant parameters: frequency, diameter at breast height (dbh), tree height, diversity, evenness, richness, Margalef, dominance in Kainji Lake National Park. Point – Centered Quarter method was used for woody species enumeration. A total of twenty-eight (28) randomly sampled plots of 150m by 100m given 112 points per plot were established in the study area. The abundance and distribution, tree frequencies, heights, dbh and plant biodiversity indices were calculated using the Paleontological Statistics Software (PAST) for scientific data analysis. The results revealed that relative abundance of African buffalo in both morning and evening of dry and wet seasons in various habitats of the Park were 13.33 ± 4.41 and 11.33 ± 4.40 respectively. The study showed the highest mean value of 21.75 ± 6.94 representing 87 individuals in dry season compared to wet season with mean value of 15.25 ± 5.11 representing 61 individuals. A total of 91 woody plant species and 29 tree families were recorded in African buffalo habitats representing 80, 77, 68 and 59 tree species respectively. The highest average girth size of tree species was class between >10cm -50cm with 59.14 ± 4.06 and the highest mean tree height was height class of >3 - 10m with 91.43 ± 5.44. There were significant differences at (p<0.05) between the values of dbh, tree height, diversity, richness and evenness of plant species recorded in different habitats studied in the Park.

Viral dynamics and immune responses to foot-and-mouth disease virus in African buffalo (Syncerus caffer).

Foot-and-mouth disease (FMD) is one of the most important livestock diseases restricting international trade. While it is clear that African buffalo (Syncerus caffer) act as the main wildlife reservoir, viral and immune response dynamics during FMD virus acute infection have not been described before in this species. We used experimental needle inoculation and contact infections with three Southern African Territories serotypes to assess clinical, virological and immunological dynamics for thirty days post infection. Clinical FMD in the needle inoculated buffaloes was mild and characterised by pyrexia. Despite the absence of generalised vesicles, all contact animals were readily infected with their respective serotypes within the first 2-9 days after being mixed with needle challenged buffaloes. Irrespective of the route of infection or serotype there were positive associations between the viral loads in blood and the induction of host innate pro-inflammatory cytokines and acute phase proteins. Viral loads in blood and tonsils were tightly correlated during the acute phase of the infection, however, viraemia significantly declined after a peak at 4 days post infection (dpi), which correlated with the presence of detectable neutralising antibodies. In contrast, infectious virus was isolated in the tonsils until the last sampling point (30 dpi) in most animals. The pattern of virus detection in serum and tonsil swabs was similar for all three serotypes in the direct challenged and contact challenged animals. We have demonstrated for the first time, that African buffalo are indeed systemically affected by FMD virus and clinical FMD in buffalo is characterized by a transient pyrexia. Despite the lack of FMD lesions, infection of African buffalo was characterised by high viral loads in blood and oropharynx, rapid and strong host innate and adaptive immune responses and high transmissibility.

Foot-and-mouth disease virus localisation on follicular dendritic cells and sustained induction of neutralising antibodies is dependent on binding to complement receptors (CR2/CR1)

Previous studies have shown after the resolution of acute infection and viraemia, foot- and-mouth disease virus (FMDV) capsid proteins and/or genome are localised in the light zone of germinal centres of lymphoid tissue in cattle and African buffalo. The pattern of staining for FMDV proteins was consistent with the virus binding to follicular dendritic cells (FDCs). We have now demonstrated a similar pattern of FMDV protein staining in mouse spleens after acute infection and showed FMDV proteins are colocalised with FDCs. Blocking antigen binding to complement receptor type 2 and 1 (CR2/CR1) prior to infection with FMDV significantly reduced the detection of viral proteins on FDCs and FMDV genomic RNA in spleen samples. Blocking the receptors prior to infection also significantly reduced neutralising antibody titres. Therefore, the binding of FMDV to FDCs and sustained induction of neutralising antibody responses are dependent on FMDV binding to CR2/CR1 in mice.Author SummaryFoot and mouth disease virus causes a highly contagious acute vesicular disease, resulting in more than 50% of cattle, regardless of vaccination status, and almost 100% of African buffalo becoming persistently infected for long periods (months) of time. Yet, the mechanisms associated with establishment of persistent infections are still poorly understood. Infected animals are characterised by the presence of long-lived neutralising antibody titres, which contrast with the short-lived response induced by vaccination. We have used a mouse model to understand how foot and mouth disease virus is trapped and retained in the spleen for up to 28 days post infection and how the absence of antigen in the germinal centre prevents a sustainable neutralising antibody response, in the mouse. Our results highlight the importance of targeting antigen to FDCs to stimulate potent neutralising antibody responses after vaccination.

Pathological findings in African buffaloes (Syncerus caffer) in South Africa

The African buffalo (Syncerus caffer) is an iconic species of South African megafauna. As the farmed buffalo population expands, the potential impacts on population health and disease transmission warrant investigation. A retrospective study of skin biopsy and necropsy samples from 429 animals was performed to assess the spectrum of conditions seen in buffaloes in South Africa. Determination of the cause of death (or euthanasia) could not be made in 33.1% (136/411) of the necropsy cases submitted due to autolysis or the absence of significant lesions in the samples submitted. Infectious and parasitic diseases accounted for 53.5% (147/275) of adult fatal cases and non-infectious conditions accounted for 34.9% (96/275). Abortions and neonatal deaths made up 11.6% (32/275) of necropsy cases. Rift Valley fever, bovine viral diarrhoea, malignant catarrhal fever, tuberculosis, bacterial pneumonia, anaesthetic deaths, cachexia and hepatotoxic lesions were the most common causes of death. The range of infectious, parasitic and non-infectious diseases to which African buffaloes were susceptible was largely similar to diseases in domestic cattle which supports concerns regarding disease transmission between the two species. The similarity between diseases experienced in both species will assist wildlife veterinarians in the diagnosis and treatment of diseases in captive African buffaloes. The present study likely does not represent accurate disease prevalence data within the source population of buffaloes, and diseases such as anthrax, brucellosis and foot and mouth disease are under-represented in this study. Hepatic ductal plate abnormalities and haemorrhagic septicaemia have not, to our knowledge, been previously reported in African buffaloes.