Bacillus anthracis in South Africa, 1975-2013: are some lineages vanishing?

The anthrax-causing bacterium Bacillus anthracis comprises the genetic clades A, B, and C. In the northernmost part (Pafuri) of Kruger National Park (KNP), South Africa, both the common A and rare B strains clades occur. The B clade strains were reported to be dominant in Pafuri before 1991, while A clade strains occurred towards the central parts of KNP. The prevalence of B clade strains is currently much lower as only A clade strains have been isolated from 1992 onwards in KNP. In this study 319 B. anthracis strains were characterized with 31-loci multiple-locus variable-number tandem repeat analysis (MLVA-31). B clade strains from soil (n = 9) and a Tragelaphus strepsiceros carcass (n = 1) were further characterised by whole genome sequencing and compared to publicly available genomes. The KNP strains clustered in the B clade before 1991 into two dominant genotypes. South African strains cluster into a dominant genotype A.Br.005/006 consisting of KNP as well as the other anthrax endemic region, Northern Cape Province (NCP), South Africa. A few A.Br.001/002 strains from both endemic areas were also identified. Subclade A.Br.101 belonging to the A.Br.Aust94 lineage was reported in the NCP. The B-clade strains seems to be vanishing, while outbreaks in South Africa are caused mainly by the A.Br.005/006 genotypes as well as a few minor clades such as A.Br.001/002 and A.Br.101 present in NCP. This work confirmed the existence of the rare and vanishing B-clade strains that group in B.Br.001 branch with KrugerB and A0991 KNP strains.

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.

A retrospective study of anthrax on the Ghaap Plateau, Northern Cape province of South Africa, with special reference to the 2007-2008 outbreaks.

Anthrax is a zoonotic disease caused by the gram-positive, endospore-forming and soil-borne bacterium Bacillus anthracis. When in spore form, the organism can survive in dormancy in the environment for decades. It is a controlled disease of livestock and wild ungulates in South Africa. In South Africa, the two enzootic regions are the Kruger National Park and the Ghaap Plateau in the Northern Cape province. Farms on the Plateau span thousands of hectares comprising of wildlife - livestock mixed use farming. In 2007-2008, anthrax outbreaks in the province led to government officials intervening to aid farmers with control measures aimed at preventing further losses. Because of the ability of the organism to persist in the environment for prolonged periods, an environmental risk or isolation survey was carried out in 2012 to determine the efficacy of control measures employed during the 2007-2008, anthrax outbreaks. No B. anthracis could be isolated from the old carcass sites, even when bone fragments from the carcasses were still clearly evident. This is an indication that the control measures and protocols were apparently successful in stemming the continuity of spore deposits at previously positive carcass sites.