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.

Immunological Evidence of Variation in Exposure and Immune Response to Bacillus anthracis in Herbivores of Kruger and Etosha National Parks

Exposure and immunity to generalist pathogens differ among host species and vary across spatial scales. Anthrax, caused by a multi-host bacterial pathogen, Bacillus anthracis, is enzootic in Kruger National Park (KNP), South Africa and Etosha National Park (ENP), Namibia. These parks share many of the same potential host species, yet the main anthrax host in one (greater kudu (Tragelaphus strepsiceros) in KNP and plains zebra (Equus quagga) in ENP) is only a minor host in the other. We investigated species and spatial patterns in anthrax mortalities, B. anthracis exposure, and the ability to neutralize the anthrax lethal toxin to determine if observed host mortality differences between locations could be attributed to population-level variation in pathogen exposure and/or immune response. Using serum collected from zebra and kudu in high and low incidence areas of each park (18- 20 samples/species/area), we estimated pathogen exposure from anti-protective antigen (PA) antibody response using enzyme-linked immunosorbent assay (ELISA) and lethal toxin neutralization with a toxin neutralization assay (TNA). Serological evidence of pathogen exposure followed mortality patterns within each system (kudus: 95% positive in KNP versus 40% in ENP; zebras: 83% positive in ENP versus 63% in KNP). Animals in the high-incidence area of KNP had higher anti-PA responses than those in the low-incidence area, but there were no significant differences in exposure by area within ENP. Toxin neutralizing ability was higher for host populations with lower exposure prevalence, i.e., higher in ENP kudus and KNP zebras than their conspecifics in the other park. These results indicate that host species differ in their exposure to and adaptive immunity against B. anthracis in the two parks. These patterns may be due to environmental differences such as vegetation, rainfall patterns, landscape or forage availability between these systems and their interplay with host behavior (foraging or other risky behaviors), resulting in differences in exposure frequency and dose, and hence immune response.

Mammal road-type associations in Kruger National Park, South Africa: Common mammals do not avoid tar roads more than dirt roads

The majority of Africa's parks and conservation areas have a vast road network, facilitating motorized vehicle game viewing. These roads have an influence that is both road type- and species-specific, on the surrounding ecosystem. Due to their higher traffic volumes, we hypothesized that tar roads and their immediate surrounds within the Kruger National Park, South Africa, are avoided to a greater extent by medium-to-large mammals than comparable dirt roads in the park. We systematically recorded the presence of medium-to-large mammal species from our vehicle, recording data at 401 tar and 369 dirt road stops in the Kruger National Park. In addition to species presence, we also estimated the proximity of animals to the road, as well as herd sizes. Our results indicate an equal likelihood of viewing the commonly recorded medium-to-large mammal species from both road types. The likelihood of observing larger herd sizes was also similar between tar and dirt roads for the three most commonly observed species, African elephant (Loxodonta africana), impala (Aepyceros melampus), and plains zebra (Equus quagga), and the likelihood of viewing impala and zebra close to the road also did not differ between tar and dirt roads. However, elephant was observed more often close to tar roads, compared to dirt roads. We interpreted this as the result of potentially increased woody cover associated with more water runoff in close proximity to tar roads compared with dirt roads. Our results not only have ecological significance, supporting the notion that many of the park's species are habituated to human infrastructure, but also management implications, informing park officials about the influence of road traffic and road type on wildlife distributions.

Intestinal ciliates (Ciliophora) from the wild plains zebra (Equus quagga) in South Africa, with notes on the microtubule cytoskeleton organisation

Investigation of the ciliate communities from the digestive tract of different wild vertebrates is important in context of host-specificity of different ciliate species and the detection of any cases of non-specific infection. Here we present a description and analysis of the fauna of ciliates (Litostomatea, Trichostomatia) inhabiting the intestine of the wild plains zebra (Equus quagga Boddaert, 1785) in South Africa. Nineteen species belonging to 12 genera of five families were found. Five species were specific to Equus quagga; one was also found in Equus zebra; 29 are common to different equids; and one had been previously described from rhinoceros. For the first time, we used immunofluorescent staining to investigate microtubule cytoskeletons in trichostomatids. We found that this staining method is useful for the identification of trichostomatids.

Population structure, inbreeding and stripe pattern abnormalities in plains zebras

One of the most iconic wild equids, the plains zebra occupies a broad region of sub-Saharan Africa and exhibits a wide range of phenotypic diversity in stripe patterns that have been used to classify multiple subspecies. After decades of relative stability, albeit with a loss of at least one recognized subspecies, the total population of plains zebras has undergone an approximate 25% decline since 2002. Individuals with abnormal stripe patterns have been recognized in recent years but the extent to which their appearance is related to demography and/or genetics is unclear. Investigating population genetic health and genetic structure are essential for developing effective strategies for plains zebra conservation. We collected DNA from 140 plains zebra, including seven with abnormal stripe patterns, from nine locations across the range of plains zebra, and analyzed data from restriction site-associated and whole genome sequencing (RAD-seq, WGS) libraries to better understand the relationships between population structure, genetic diversity, inbreeding, and abnormal phenotypes. We found that genetic structure did not coincide with described subspecific variation, but did distinguish geographic regions in which anthropogenic habitat fragmentation is associated with reduced gene flow and increased evidence of inbreeding, especially in certain parts of East Africa. Further, zebras with abnormal striping exhibited increased levels of inbreeding relative to normally striped individuals from the same populations. Our results point to a genetic cause of stripe pattern abnormalities, and dramatic evidence of the consequences of habitat fragmentation.

EVALUATION OF THE QUALITY OF IMMOBILIZATION AND CARDIORESPIRATORY EFFECTS OF ETORPHINE-MEDETOMIDINE-AZAPERONE COMBINATION IN PLAINS ZEBRAS (EQUUS QUAGGA): A PILOT STUDY

Five free-ranging male (subadults, n = 3; adults, n = 2) plains zebras (Equus quagga) were immobilized using a combination of etorphine (0.017 mg/kg), medetomidine (0.017 mg/kg), and azaperone (0.24 mg/kg) by means of a blank cartridge-fired projector. Time to recumbency was recorded and a descriptive score used to assess the quality of immobilization, manipulation, maintenance, and recovery. Physiological parameters were recorded at 5-min intervals for 20 min. At the end of the procedure, naltrexone (0.23 mg/kg) was administered intramuscularly and time to standing documented. The combination evaluated in this study allowed for successful immobilization and safe recovery of all animals, including during the subsequent 15 days. Despite the good outcome in this pilot study, as a result of the periodic apneic events and hypercapnia documented in the zebras, the authors suggest that physiological parameters be thoroughly monitored when using this protocol. Further studies are needed to improve upon chemical immobilization protocols in free-ranging plains zebras.

Noninvasive Detection of Equid Herpesviruses in Fecal Samples

Equid herpesviruses (EHVs) are pathogens of equid and nonequid hosts that can cause disease and fatalities in captivity and in the wild. EHVs establish latent infections but can reactivate, and most EHVs are shed via the nasal passage. Therefore, nasal swabs are generally used for EHV monitoring. However, invasive sampling of wild equids is difficult. While feces is a commonly used substrate for detecting other pathogens, to our knowledge, EHVs have never been detected in feces of naturally infected equids. We systematically tested zebra feces for EHV presence by (i) establishing nested PCR conditions for fecal DNA extracts, (ii) controlling for environmental EHV contamination, and (iii) large-scale testing on a free-ranging zebra population. A dilution minimizing inhibition while maximizing viral DNA concentrations was determined in captive Grévy's zebra (Equus grevyi) fecal samples from individuals shedding EHV nasally. Sixteen of 42 fecal samples (38%) were EHV positive. To demonstrate that the EHV positivity was not a result of environmental contamination, rectal swabs of wild zebras were screened (n = 18 [Equus quagga and E. zebra]), and 50% were EHV positive, indicating that the source of EHV in feces is likely the intestinal mucosa and not postdefecation contamination. Out of 270 fecal samples of wild zebras, 26% were EHV positive. Quantitative PCRs showed that the amount of virus DNA in feces was not significantly smaller than that in other samples. In summary, fecal sampling facilitates large-scale screening and may be useful to noninvasively investigate phylogenetic EHV diversity in wild and domestic equids.IMPORTANCE Equid herpesviruses (EHVs) establish latent infections, and many EHVs are shed and transmitted via nasal discharge primarily through droplet and aerosol infection. Obtaining nasal swabs and other invasive samples from wildlife is often not possible without capture and physical restraint of individuals, which are resource intensive and a health risk for the captured animals. Fecal EHV shedding has never been demonstrated for naturally infected equids. We established the conditions for fecal EHV screening, and our results suggest that testing fecal samples is an effective noninvasive approach for monitoring acute EHV shedding in equids.

DUST-BATHING BEHAVIORS OF AFRICAN HERBIVORES AND THE POTENTIAL RISK OF INHALATIONAL ANTHRAX

:  Anthrax in herbivorous wildlife and livestock is generally assumed to be transmitted via ingestion or inhalation of Bacillus anthracis spores. Although recent studies have highlighted the importance of the ingestion route for anthrax transmission, little is known about the inhalational route in natural systems. Dust bathing could aerosolize soilborne pathogens such as B. anthracis, exposing dust-bathing individuals to inhalational infections. We investigated the potential role of dust bathing in the transmission of inhalational anthrax to herbivorous wildlife in Etosha National Park, Namibia, an area with endemic seasonal anthrax outbreaks. We 1) cultured soils from dust-bathing sites for the presence and concentration of B. anthracis spores, 2) monitored anthrax carcass sites, the locations with the highest B. anthracis concentrations, for evidence of dust bathing, including a site where a zebra died of anthrax on a large dust bath, and 3) characterized the ecology and seasonality of dust bathing in plains zebra ( Equus quagga), blue wildebeest ( Connochaetes taurinus), and African savanna elephant ( Loxodonta africana) using a combination of motion-sensing camera traps and direct observations. Only two out of 83 dust-bath soils were positive for B. anthracis, both with low spore concentrations (≤20 colony-forming units per gram). We also detected no evidence of dust baths occurring at anthrax carcass sites, perhaps due to carcass-induced changes in soil composition that may deter dust bathing. Finally, despite observing some seasonal variation in dust bathing, preliminary evidence suggests that the seasonality of dust bathing and anthrax mortalities are not correlated. Thus, although dust bathing creates a dramatic cloud of aerosolized soil around an individual, our microbiologic, ecologic, and behavioral results in concert demonstrate that dust bathing is highly unlikely to transmit inhalational anthrax infections.