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Investigation on the role of flies and free-living amoebae as potential vectors of bacillus anthracis in the Kruger national park
Dissertation (MSc (Veterinary Sciences))--University of Pretoria, 2016.
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2026
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| access_status_str | Open Access |
| author2 | van Heerden, H. |
| author_browse | van Heerden, H. |
| author_facet | van Heerden, H. |
| collection | Thesis |
| description | Dissertation (MSc (Veterinary Sciences))--University of Pretoria, 2016. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/110124 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:36:55.109Z |
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| publishDate | 2026 |
| publishDateRange | 2026 |
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| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/110124 Investigation on the role of flies and free-living amoebae as potential vectors of bacillus anthracis in the Kruger national park van Heerden, H. lizanne7basson@gmail.com Rossouw, J. Beyer, W. Gilbert, AE. Basson, Lizánne Bacillus anthracis Free living amoebae Kruger National Park Anthrax Blowflies Dissertation (MSc (Veterinary Sciences))--University of Pretoria, 2016. Bacillus anthracis is a soil-borne pathogen and the causal agent of anthrax. Despite the long history of anthrax, the ecology and aspects of the B. anthracis life cycle are still poorly understood. Various vectors like insects (blowflies Chrysomya marginalis and Ch. albiceps and biting flies), scavengers and water have been incriminated in the dissemination of anthrax in Kruger National Park (KNP) in South Africa. More recently an alternative hypothesis has been introduced where amoeba, common in moist soils and pools of standing water, was suggested to serve as amplifiers of B. anthracis spores by enabling germination and intracellular multiplication. The aim of this project was to assess the potential of blowflies and free-living amoebae as biological or mechanical vectors of B. anthracis in the KNP, South Africa. To achieve this aim, the following approaches were adopted (i) to investigate the presence of B. anthracis on the external and internal body surfaces of flies after feeding on an anthrax-contaminated Page | xx carcass; (ii) to determine the role of flies in disseminating B. anthracis onto the surrounding vegetation; (iii) to determine the fate of B. anthracis in the alimentary canal of Chrysomya albiceps and Ch. marginalis; (iv) to determine transovarial transmission of B. anthracis in a controlled laboratory experiment and (v) to determine the fate of B. anthracis spores and vegetative cells in free living amoeba species. To examine blowflies for the presence of B. anthracis on their external body surface and in their alimentary canal after feeding on an anthrax-contaminated carcass, blowflies (57 in total) were collected from two confirmed 2 – 3 day old anthrax-positive carcasses found in the northern regions of the KNP. The blowflies were identified to species level, followed by the isolation and quantification of possible B. anthracis spores and vegetative cells from the exterior and interior body surfaces of all the collected blowflies. A total of 26 blowflies (46%) were positive for the presence of B. anthracis on either the external or the internal body surfaces. An average of 50 colony forming units per fly (CFU/fly) was isolated from the exterior surfaces of the blowflies and an average of 37 CFU/fly was isolated from the interior surfaces of the blowflies. The results show that blowflies do carry anthrax in and on their bodies and therefore have the potential to be carriers of anthrax to infect food and other substrates away from the source of infection. To determine the role of flies in disseminating B. anthracis onto the surrounding vegetation, vegetation with blowfly discard/faecal droplets surrounding the two confirmed anthraxpositive carcasses found in the northern regions of the KNP was collected and analysed for the presence of B. anthracis. No B. anthracis was isolated from leaves (collected from one of the anthrax-positive carcasses) identified as Abutilon angulatum which exhibited antimicrobial activity against, amongst others, B. anthracis Sterne strain. From twigs (collected from the second anthrax-positive carcass) with blowfly droplets about 500 B. anthracis spores were isolated. These results indicate that blowflies excrete droplets in the vicinity of anthrax-infected carcasses that are potentially infective. The infectivity of the droplets is dependent on the antimicrobial activity of the leaves on which the droplets are excreted. Therefore, if the leaves have no antimicrobial activity against B. anthracis a Page | xxi significant proportion of infective discard/faecal droplets are present and available for ingestion by herbivores. To determine the fate of B. anthracis in the alimentary canal of Chrysomya albiceps and Ch. marginalis, females and males of both species were bred in a controlled environment in the laboratory. Female blowflies were allowed to feed on three, avirulent, green fluorescent protein (gfp)-labelled B. anthracis strains in either spore or vegetative cell form. All the blowflies were investigated for the presence of B. anthracis in their alimentary canals. Quantifications were also done to determine multiplication (replication), germination and sporulation in the alimentary canals of Ch. albiceps and Ch. marginalis depending on the strain fed to the blowflies as well as whether the feed was presented in spore or in vegetative cell form. Multiplication of B. anthracis occurred for 72 hrs in Ch. albiceps and to a lesser extent in Ch. marginalis when given vegetative cells. The observations in this study are preliminary, due to the limited number of blowflies (n = 3) examined at each time point. Spores germinate and remain in the alimentary canal of Ch. albiceps for up to 72 hrs, whereas the spores in Ch. marginalis do not germinate when feeding on B. anthracis spores. Results indicate that both Ch. albiceps and Ch. marginalis are potential mechanical vectors of B. anthracis (even though it is only for a very short time) depending on whether the infective feed was vegetative cells or spores. To determine transovarial transmission of B. anthracis in a controlled laboratory experiment Ch. albiceps and Ch. marginalis females were allowed to feed on three, avirulent, gfplabelled B. anthracis strains, followed by mating with uninfected male blowflies. The eggs, larvae, pupae and newly-emerged blowflies were screened for the presence of B. anthracis. Bacillus anthracis was detected in the eggs, second and third instar larvae and the pupae depending on which avirulent strain was investigated, but no B. anthracis was detected in any of the newly-emerged adult blowflies. Therefore, transovarial transmission of B. anthracis was observed. These results indicate that blowfly eggs/second instar larvae/third instar larvae/pupae are likely to play a role in anthrax transmission beyond the immediate generation (i.e. adult blowflies) feeding on infective material. Page | xxii To determine the fate of B. anthracis spores and vegetative cells in free-living amoeba species, a total of 48 free-living amoebae (FLA) were isolated from water and soil samples collected in the endemic anthrax area in the KNP. A multi-drug resistant bacterium Stenotrophomona maltophilia was repeatedly co-isolated with the FLA and continually outcompeted the FLA. Therefore, no co-culturing experiments with B. anthracis could be performed to determine the fate of the B. anthracis bacteria in the FLA. However, FLA of the Acanthamoeba and the Vahlkampfia genera were isolated from the water and soil collected in the northern regions of the KNP, indicating that the Acanthamoeba and Vahlkampfia genera are more abundant in soil and water in the northern regions of the KNP. In this study we observed that B. anthracis spores are found externally and internally on Ch. albiceps and Ch. marginalis as well as in discard/faecal droplets on vegetation surrounding infected anthrax carcasses. In the laboratory experiment where Ch. albiceps and Ch. marginalis were fed avirulent, gfp-labelled B. anthracis vegetative cells or spores, it was confirmed that blowflies are potential mechanical vectors of B. anthracis and not biological vectors. The hypothesis that free-living amoebae common in moist soils and pools of standing water serve as amplifiers of B. anthracis spores by enabling germination and intracellular multiplication could not be investigated. This study confirmed that Acanthamoeba and the Vahlkampfia species are the dominant FLA isolated from the water and soil in the northern regions of the KNP. The overall conclusion drawn from this study is that blowflies do have the potential to be major infectious agents of anthrax by way of depositing infective material on leaves (in the form of discard and/or faecal droplets) and carrying the bacteria for 2 - 3 days on or in their bodies (as a possible mechanical vector). Therefore, blowflies are playing an important role in the epidemiology of anthrax as well as the continuing of the B. anthracis life cycle in the environment. This supports views previously proposed in the literature that blowflies are a significant factor in maintaining anthrax epidemics. Veterinary Tropical Diseases MSc (Veterinary Sciences) 2026-05-15T17:26:22Z 2026-05-15T17:26:22Z 16/02/08 2016 Dissertation http://hdl.handle.net/2263/110124 en application/pdf |
| spellingShingle | Bacillus anthracis Free living amoebae Kruger National Park Anthrax Blowflies Investigation on the role of flies and free-living amoebae as potential vectors of bacillus anthracis in the Kruger national park |
| title | Investigation on the role of flies and free-living amoebae as potential vectors of bacillus anthracis in the Kruger national park |
| title_full | Investigation on the role of flies and free-living amoebae as potential vectors of bacillus anthracis in the Kruger national park |
| title_fullStr | Investigation on the role of flies and free-living amoebae as potential vectors of bacillus anthracis in the Kruger national park |
| title_full_unstemmed | Investigation on the role of flies and free-living amoebae as potential vectors of bacillus anthracis in the Kruger national park |
| title_short | Investigation on the role of flies and free-living amoebae as potential vectors of bacillus anthracis in the Kruger national park |
| title_sort | investigation on the role of flies and free living amoebae as potential vectors of bacillus anthracis in the kruger national park |
| topic | Bacillus anthracis Free living amoebae Kruger National Park Anthrax Blowflies |
| url | http://hdl.handle.net/2263/110124 |