Cold and Hungry: Heterothermy Is Associated with Low Leptin Levels in a Bulk Grazer during a Drought

AbstractReduced energy intake can compromise the ability of a mammal to maintain body temperature within a narrow 24-h range, leading to heterothermy. To investigate the main drivers of heterothermy in a bulk grazer, we compared abdominal temperature, body mass, body condition index, and serum leptin levels in 11 subadult Cape buffalo (Syncerus caffer caffer) during a drought year and a nondrought year. Low food availability during the drought year (as indexed by grass biomass, satellite imagery of vegetation greenness, and fecal chlorophyll) resulted in lower body condition index, lower body mass relative to that expected for an equivalent-aged buffalo, and lower leptin levels. The range of 24-h body temperature rhythm was 2°C during the nondrought year and more than double that during the drought year, and this was caused primarily by a lower minimum 24-h body temperature rhythm during the cool dry winter months. After rain fell and vegetation greenness increased, the minimum 24-h body temperature rhythm increased, and the range of 24-h body temperature rhythm was smaller than 2°C. In order of importance, poor body condition, low minimum 24-h air temperature, and low serum leptin levels were the best predictors of the increase in the range of 24-h body temperature rhythm. While the thermoregulatory role of leptin is not fully understood, the association between range of 24-h body temperature rhythm and serum leptin levels provides clues about the underlying mechanism behind the increased heterothermy in large mammals facing food restriction.

The heterogeneous herd: Drivers of close-contact variation in African buffalo and implications for pathogen invasion

Many infectious pathogens are shared through social interactions, and examining host connectivity has offered valuable insights for understanding patterns of pathogen transmission across wildlife species. African buffalo are social ungulates and important reservoirs of directly-transmitted pathogens that impact numerous wildlife and livestock species. Here, we analyzed African buffalo social networks to quantify variation in close contacts, examined drivers of contact heterogeneity, and investigated how the observed contact patterns affect pathogen invasion likelihoods for a wild social ungulate. We collected continuous association data using proximity collars and sampled host traits approximately every 2 months during a 15-month study period in Kruger National Park, South Africa. Although the observed herd was well connected, with most individuals contacting each other during each bimonthly interval, our analyses revealed striking heterogeneity in close-contact associations among herd members. Network analysis showed that individual connectivity was stable over time and that individual age, sex, reproductive status, and pairwise genetic relatedness were important predictors of buffalo connectivity. Calves were the most connected members of the herd, and adult males were the least connected. These findings highlight the role susceptible calves may play in the transmission of pathogens within the herd. We also demonstrate that, at time scales relevant to infectious pathogens found in nature, the observed level of connectivity affects pathogen invasion likelihoods for a wide range of infectious periods and transmissibilities. Ultimately, our study identifies key predictors of social connectivity in a social ungulate and illustrates how contact heterogeneity, even within a highly connected herd, can shape pathogen invasion likelihoods.

Variation in herbivore space use: comparing two savanna ecosystems with different anthrax outbreak patterns in southern Africa

BACKGROUND

The distribution of resources can affect animal range sizes, which in turn may alter infectious disease dynamics in heterogenous environments. The risk of pathogen exposure or the spatial extent of outbreaks may vary with host range size. This study examined the range sizes of herbivorous anthrax host species in two ecosystems and relationships between spatial movement behavior and patterns of disease outbreaks for a multi-host environmentally transmitted pathogen.

METHODS

We examined range sizes for seven host species and the spatial extent of anthrax outbreaks in Etosha National Park, Namibia and Kruger National Park, South Africa, where the main host species and outbreak sizes differ. We evaluated host range sizes using the local convex hull method at different temporal scales, within-individual temporal range overlap, and relationships between ranging behavior and species contributions to anthrax cases in each park. We estimated the spatial extent of annual anthrax mortalities and evaluated whether the extent was correlated with case numbers of a given host species.

RESULTS

Range size differences among species were not linearly related to anthrax case numbers. In Kruger the main host species had small range sizes and high range overlap, which may heighten exposure when outbreaks occur within their ranges. However, different patterns were observed in Etosha, where the main host species had large range sizes and relatively little overlap. The spatial extent of anthrax mortalities was similar between parks but less variable in Etosha than Kruger. In Kruger outbreaks varied from small local clusters to large areas and the spatial extent correlated with case numbers and species affected. Secondary host species contributed relatively few cases to outbreaks; however, for these species with large range sizes, case numbers positively correlated with outbreak extent.

CONCLUSIONS

Our results provide new information on the spatiotemporal structuring of ranging movements of anthrax host species in two ecosystems. The results linking anthrax dynamics to host space use are correlative, yet suggest that, though partial and proximate, host range size and overlap may be contributing factors in outbreak characteristics for environmentally transmitted pathogens.

High-Specificity Test Algorithm for Bovine Tuberculosis Diagnosis in African Buffalo (Syncerus caffer) Herds

Ante-mortem bovine tuberculosis (bTB) tests for buffaloes include the single comparative intradermal tuberculin test (SCITT), interferon-gamma (IFN-γ) release assay (IGRA) and IFN-γ-inducible protein 10 release assay (IPRA). Although parallel test interpretation increases the detection of Mycobacterium bovis (M. bovis)-infected buffaloes, these algorithms may not be suitable for screening buffaloes in historically bTB-free herds. In this study, the specificities of three assays were determined using M. bovis-unexposed herds, historically negative, and a high-specificity diagnostic algorithm was developed. Serial test interpretation (positive on both) using the IGRA and IPRA showed significantly greater specificity (98.3%) than individual (90.4% and 80.9%, respectively) tests or parallel testing (73%). When the SCITT was added, the algorithm had 100% specificity. Since the cytokine assays had imperfect specificity, potential cross-reactivity with nontuberculous mycobacteria (NTM) was investigated. No association was found between NTM presence (in oronasal swab cultures) and positive cytokine assay results. As a proof-of-principle, serial testing was applied to buffaloes (n = 153) in a historically bTB-free herd. Buffaloes positive on a single test (n = 28) were regarded as test-negative. Four buffaloes were positive on IGRA and IPRA, and M. bovis infection was confirmed by culture. These results demonstrate the value of using IGRA and IPRA in series to screen buffalo herds with no previous history of M. bovis infection.

Identification and Characterisation of Nontuberculous Mycobacteria in African Buffaloes (Syncerus caffer), South Africa

Diagnosis of bovine tuberculosis (bTB) may be confounded by immunological cross-reactivity to Mycobacterium bovis antigens when animals are sensitised by certain nontuberculous mycobacteria (NTMs). Therefore, this study aimed to investigate NTM species diversity in African buffalo (Syncerus caffer) respiratory secretions and tissue samples, using a combination of novel molecular tools. Oronasal swabs were collected opportunistically from 120 immobilised buffaloes in historically bTB-free herds. In addition, bronchoalveolar lavage fluid (BALF; n = 10) and tissue samples (n = 19) were obtained during post-mortem examination. Mycobacterial species were identified directly from oronasal swab samples using the Xpert MTB/RIF Ultra qPCR (14/120 positive) and GenoType CMdirect (104/120 positive). In addition, all samples underwent mycobacterial culture, and PCRs targeting hsp65 and rpoB were performed. Overall, 55 NTM species were identified in 36 mycobacterial culture-positive swab samples with presence of esat-6 or cfp-10 detected in 20 of 36 isolates. The predominant species were M. avium complex and M. komanii. Nontuberculous mycobacteria were also isolated from 6 of 10 culture-positive BALF and 4 of 19 culture-positive tissue samples. Our findings demonstrate that there is a high diversity of NTMs present in buffaloes, and further investigation should determine their role in confounding bTB diagnosis in this species.

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.

Co-infection best predicts respiratory viral infection in a wild host

The dynamics of directly transmitted pathogens in natural populations are likely to result from the combined effects of host traits, pathogen biology, and interactions among pathogens within a host. Discovering how these factors work in concert to shape variation in pathogen dynamics in natural host-multi-pathogen systems is fundamental to understanding population health. Here, we describe temporal variation in incidence and then elucidate the effect of hosts trait, season and pathogen co-occurrence on host infection risk using one of the most comprehensive studies of co-infection in a wild population: a suite of seven directly transmitted viral and bacterial respiratory infections from a 4-year study of 200 free-ranging African buffalo Syncerus caffer. Incidence of upper respiratory infections was common throughout the study-five out of the seven pathogens appeared to be consistently circulating throughout our study population. One pathogen exhibited clear outbreak dynamics in our final study year and another was rarely detected. Co-infection was also common in this system: The strongest indicator of pathogen occurrence for respiratory viruses was in fact the presence of other viral respiratory infections. Host traits had minimal effects on odds of pathogen occurrence but did modify pathogen-pathogen associations. In contrast, only season predicted bacterial pathogen occurrence. Though a combination of environmental, behavioural, and physiological factors work together to shape disease dynamics, we found pathogen associations best determined infection risk. Our study demonstrates that, in the absence of very fine-scale data, the intricate changes among these factors are best represented by co-infection.

Risk alleles for tuberculosis infection associate with reduced immune reactivity in a wild mammalian host

Integrating biological processes across scales remains a central challenge in disease ecology. Genetic variation drives differences in host immune responses, which, along with environmental factors, generates temporal and spatial infection patterns in natural populations that epidemiologists seek to predict and control. However, genetics and immunology are typically studied in model systems, whereas population-level patterns of infection status and susceptibility are uniquely observable in nature. Despite obvious causal connections, organizational scales from genes to host outcomes to population patterns are rarely linked explicitly. Here we identify two loci near genes involved in macrophage (phagocyte) activation and pathogen degradation that additively increase risk of bovine tuberculosis infection by up to ninefold in wild African buffalo. Furthermore, we observe genotype-specific variation in IL-12 production indicative of variation in macrophage activation. Here, we provide measurable differences in infection resistance at multiple scales by characterizing the genetic and inflammatory variation driving patterns of infection in a wild mammal.

The complete genome sequence of the African buffalo (Syncerus caffer)

BACKGROUND

The African buffalo (Syncerus caffer) is an important role player in the savannah ecosystem. It has become a species of relevance because of its role as a wildlife maintenance host for an array of infectious and zoonotic diseases some of which include corridor disease, foot-and-mouth disease and bovine tuberculosis. To date, no complete genome sequence for S. caffer had been available for study and the genomes of other species such as the domestic cow (Bos taurus) had been used as a proxy for any genetics analysis conducted on this species. Here, the high coverage genome sequence of the African buffalo (S. caffer) is presented.

RESULTS

A total of 19,765 genes were predicted and 19,296 genes could be successfully annotated to S. caffer while 469 genes remained unannotated. Moreover, in order to extend a detailed annotation of S. caffer, gene clusters were constructed using twelve additional mammalian genomes. The S. caffer genome contains 10,988 gene clusters, of which 62 are shared exclusively between B. taurus and S. caffer.

CONCLUSIONS

This study provides a unique genomic perspective for the S. caffer, allowing for the identification of novel variants that may play a role in the natural history and physiological adaptations.

Serological Evidence of Rift Valley Fever Virus Circulation in Domestic Cattle and African Buffalo in Northern Botswana (2010-2011)

Rift Valley fever (RVF) is endemic in many countries in Sub-Saharan Africa and is responsible for severe outbreaks in livestock characterized by a sudden onset of abortions and high neonatal mortality. During the last decade, several outbreaks have occurred in Southern Africa, with a very limited number of cases reported in Botswana. To date, published information on the occurrence of RVF in wild and domestic animals from Botswana is very scarce and outdated, despite being critical to national and regional disease control. To address this gap, 863 cattle and 150 buffalo sampled at the interface between livestock areas and the Chobe National Park (CNP) and the Okavango Delta (OD) were screened for the presence of RVF virus (RVFV) neutralizing antibodies. Antibodies were detected in 5.7% (n = 863), 95% confidence intervals (CI) (4.3–7.5%) of cattle and 12.7% (n = 150), 95% CI (7.8–19.5%) of buffalo samples. The overall prevalence was significantly higher (p = 0.0016) for buffalo [12.7%] than for cattle [5.7%]. Equally, when comparing RVF seroprevalence in both wildlife areas for all pooled bovid species, it was significantly higher in CNP than in OD (9.5 vs. 4%, respectively; p = 0.0004). Our data provide the first evidence of wide circulation of RVFV in both buffalo and cattle populations in Northern Botswana and highlight the need for further epidemiological and ecological investigations on RVF at the wildlife–livestock–human interface in this region.

Description of Events Where African Buffaloes (Syncerus caffer) Strayed from the Endemic Foot-and-Mouth Disease Zone in South Africa, 1998-2008

African buffaloes (Syncerus caffer) are reservoir hosts of Southern African Territories (SAT) foot-and-mouth disease (FMD) virus strains. In South Africa, infected buffaloes are found in the FMD-infected zone comprising the Kruger National Park (KNP) and its adjoining reserves. When these buffaloes stray into livestock areas, they pose a risk of FMD transmission to livestock. We assessed 645 records of stray buffalo events (3124 animals) from the FMD infected zone during 1998-2008 for (i) their temporal distribution, (ii) group size, (iii) age and gender composition, (iv) distance from the infected zone fence and (v) outcome reported for each event. A maximum entropy model was developed to evaluate spatial predictors of stray buffalo events and assess current disease control zones. Out of all buffaloes recorded straying, 38.5% escaped from the FMD infected zone during 2000/2001, following floods that caused extensive damage to wildlife fences. Escape patterns were not apparently influenced by season. The median size of stray groups was a single animal (IQR [1-2]). Adult animals predominated, comprising 90.4% (620/686) of the animals for which age was recorded. Of the 315 events with accurate spatial information, 204 (64.8%) were recorded within 1 km from the FMD infected zone. During late winter/spring (June-October), stray buffaloes were found significantly closer to the FMD infected zone (median = 0.3 km, IQR [0.1-0.6]). Less than 13% (40/315) of stray groups reached the FMD protection zone without vaccination, posing a higher risk of spreading FMD to these more susceptible livestock. Model outputs suggest that distance from the FMD infected zone, urban areas and permanent water sources contributed almost 85% to the spatial probability of stray buffalo events. Areas with a high probability for stray buffalo events were well covered by current disease control zones, although FMD risk mitigation could be improved by expanding the vaccination zone in certain areas.

Preliminary assessment of bovine tuberculosis at the livestock/wildlife interface in two protected areas of northern Botswana

Protected areas of northern Botswana such as the Okavango Delta (OD) or Chobe National Park (CNP) are well-known hot spots for the conservation of African wildlife. However, their infection status regarding bovine tuberculosis (BTB) at the domestic/wildlife interface has never been investigated. To provide preliminary baseline data on the circulation of Mycobacterium bovis in those sites, we performed a cross-sectional survey on 130 buffalo in both protected areas (60 individuals from CNP and 70 from OD) and 818 cattle in their surrounding communal lands (369 in CNP and 449 in the OD). Whole-blood samples were tested using a commercial interferon-gamma assay (IFN-γ) with modifications. The apparent BTB prevalence in buffalo was nil in CNP and 0.7% 95% CI [0.2-1.9] in the OD, while the apparent BTB prevalence in cattle was 0.7% 95% CI [0.2-2.1] in the OD and 2.4% 95% CI [1.2-4.7] in CNP. True prevalence values calculated on the basis of the locally applicable IFN-γ test performance suggested that BTB prevalence was nil in both buffalo populations and in cattle from the OD interface, but reached 2.3% 95% CI [0.2-4.5] in cattle populations around CNP. The results of a questionnaire survey conducted among a sample of farmers living in the communities adjacent to each conservation area (97 and 38 persons in the OD and CNP, respectively) suggested a higher risk of the circulation of M. bovis at the wildlife/livestock interface of the CNP than at that of the OD. However, further comprehensive studies are needed to confirm the circulation of M. bovis and to monitor the inter-species and transboundary transmission of BTB in northern Botswana.

Rift valley Fever in Kruger national park: do buffalo play a role in the inter-epidemic circulation of virus?

Rift Valley fever (RVF) is a zoonotic mosquito-borne virus disease of livestock and wild ruminants that has been identified as a risk for international spread. Typically, the disease occurs in geographically limited outbreaks associated with high rainfall events and can cause massive losses of livestock. It is unclear how RVF virus persists during inter-epidemic periods but cryptic cycling of the virus in wildlife populations may play a role. We investigated the role that free-living African buffalo (Syncerus caffer caffer) might play in inter-epidemic circulation of the virus and looked for geographic, age and sex patterns of Rift Valley fever virus (RVFV) infection in African buffalo. Buffalo serum samples were collected (n = 1615) in Kruger National Park (KNP), South Africa, during a period of 1996-2007 and tested for antibodies to RVF. We found that older animals were more likely to be seropositive for anti-RVFV antibody than younger animals, but sex was not correlated with the likelihood of being anti-RVFV antibody positive. We also found geographic variation within KNP; herds in the south were more likely to have acquired anti-RVFV antibody than herds farther north - which could be driven by host or vector ecology. In all years of the study between 1996 and 2007, we found young buffalo (under 2 years of age) that were seropositive for anti-RVFV antibody, with prevalence ranging between 0 and 27% each year, indicating probable circulation. In addition, we also conducted a 4-year longitudinal study on 227 initially RVFV seronegative buffalo to look for evidence of seroconversion outside known RVF outbreaks within our study period (2008-2012). In the longitudinal study, we found five individuals that seroconverted from anti-RVFV antibody negative to anti-RVFV antibody positive, outside of any detected outbreak. Overall, our results provide evidence of long-term undetected circulation of RVFV in the buffalo population.