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Epidemiological studies on bovine fasciolosis in Botswana

Mochankana, Molefe Ernest (2014) Epidemiological studies on bovine fasciolosis in Botswana. PhD thesis, Murdoch University.

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Fasciolosis, commonly known as liver fluke disease, is a disease of the liver of domestic livestock, principally ruminants, caused by pathogenic trematodes of the genus Fasciola, which comprises two species, F. hepatica and F. gigantica. Fasciola hepatica is the more common and important of the two, with a worldwide distribution, whereas F. gigantica is more restricted, found primarily in warmer parts of the world where it causes tropical fasciolosis in cattle, sheep and goats.

Fasciola gigantica infection in cattle is potentially one of the most important parasitoses affecting the productivity of herds in many developing countries by being an impediment to reproduction and growth, causing damage to livers, which can occasionally become inedible for humans and, in some cases, can result in the death of affected animals. The economic importance of fasciolosis is mainly due to direct losses from condemnation of infected livers during meat inspection at abattoirs. The disease is also a zoonosis, however, it is rarely diagnosed in humans. Prior to the study reported in this thesis, little was known on the epidemiology of this parasitic disease in Botswana. Therefore, the main aim for undertaking this study was to determine the prevalence and estimate the economic significance of fasciolosis in cattle, as well as to determine the geographical distribution of the intermediate host snail, Lymnaea natalensis.

Lymnaea natalensis is an aquatic snail that has generally been accepted as the intermediate host that plays an essential role in the epidemiology of F. gigantica infection in Africa, even though a miscellany of other Lymnaeid snails can be involved in the transmission of the fluke.

The present study determined the prevalence and assessed the economic importance of F. gigantica infections in cattle through retrospective and prospective studies, by acquisition of data from meat inspection records and regular visitation to inspect livers of slaughtered cattle at selected abattoirs, respectively. In addition, a cross-sectional survey of fasciolosis was carried out through a coprological examination of live animals to determine the prevalence in live cattle from six districts in Botswana. This information will be used as the basis for future epidemiological surveillance of this important parasitic disease of ruminants in Botswana. An understanding of the epidemiology of fasciolosis and distribution of the intermediate host would assist in the design of appropriate control programmes in Botswana.

The results from the present study have indicated that F. gigantica infection is present in cattle in Botswana, but the prevalence is very low (0.74%; 95% CI: 0.57, 0.94%) and not widespread as previously anticipated. The disease was present in only one (Central) of the six districts covered by this study, and was localized within the Tuli Block area, in Machaneng village, at the eastern margin of the country. Although the exact geographical origins of some of the fasciolosis-positive cattle was occasionally difficult to ascertain in abattoirs in the south of the country, it was highly likely that they originated from the northern part of the country and were already infected before being moved to the south, where they were eventually sent to the abattoirs.

The prevalence reported in this study rank among the lowest, not just in Africa, but the world as a whole, in terms of prevalence, infection intensity and economic impact in cattle. The study also revealed that the only species of liver fluke found in Botswana is F. gigantica. The results of the financial losses demonstrated a low financial burden as a consequence of condemnation of Fasciola-infected livers during the twelve-year period under consideration. These findings suggest that bovine fasciolosis is neither a major cause of liver condemnations at abattoirs nor a significant cause of reduced productivity in cattle in Botswana.

In spite of the low prevalence of F. gigantica infections in cattle, the disease showed a significantly higher prevalence in adult animals than weaners and calves. Gender differences in susceptibility were observed, with females demonstrating a significantly higher infection than males. Also of note was an indication of breed differences in susceptibility to infection. The Brahman and Brahman crosses exhibited a higher prevalence whereas the Nguni cattle showed no infection at all. These findings imply varying levels of immunity in these breeds, with a higher resilience and resistance shown by the Nguni native breed.

The population dynamics of the intermediate host snail, L. natalensis, was not determined since no snails were detected from the potential habitats investigated. The failure to detect snails was most likely linked to the drought that prevailed in Botswana during the two years this research was carried out.

The present study was able to reveal the existence of concurrent natural infection of cattle with liver fluke, F. gigantica, and the stomach fluke, amphistome, in Botswana. There was a significant positive association between the two trematode infections, as has also been reported in other parts of Africa. However, the prevalence of co-infection was low (0.16%; 95% CI: 0.09, 0.27%) and this could be attributable to the absence of F. gigantica infection in the other five districts of study.

It is concluded that infection of cattle from Botswana, with F. gigantica, is low and the distribution of the fluke is linked to suitable environmental and climatic conditions for the intermediate host.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Supervisor(s): Robertson, Ian
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