Epidemiology and control of bovine fasciolosis and schistosomosis in the Southern highlands of Tanzania
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Date
201
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Publisher
Sokoine University of Agriculture.
Abstract
The main purpose of this study was to determine if anthelmintic treatment of early
patent primary fasciolosis and schistosomosis would prevent development of acute
disease and would improve productivity of calves which continue grazing high
potential natural transmission areas, without causing unwanted side effects or
interfering with the development of immunity. Aspects of transmission biology and
host parasite relationship were also investigated. Field studies, including cattle and
snails, were performed at Lulanzi dairy farm where the trematode infections were
highly prevalent. In addition experimental Schistosoma bovis infections were carried
out in confined calves. The results from snail studies showed that Bulinus natalensis
was the most abundant freshwater snail, which was responsible for the transmission
of Schistosoma bovis mainly towards the end ofthe rainy season. Results ofthe field
study, where cattle were naturally exposed, showed that acquisition of trematode
infections was gradual. It took five months for the peak egg excretion to be reached,
followed by a gradual decline to a very low level. Both triclabendazole and
praziquantel drugs were highly efficacious and reduced Fasciola and Schistosoma
worms by 100% and 95.6% respectively; while for S. bovis faecal and tissue eggs the
reduction was 98.9% and 79-96%, respectively. Treatment kept the faecal egg
excretion of both parasites species at a very low level for more than seven months
and did not affect the development of immunity. Deterioration of the body weights
pathological lesions, mainly fibrosis of the liver, were observed in the treated
experimentally infected animals than in the untreated ones. However, no clinical
and haematological parameters were only seen during the dry season and it was more
severe in the untreated compared to the treated, challenged calves. More severe
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signs were associated with such changes and there was a gradual resolution of the
pathological lesions. In the experimental S. bovis infections it was shown that, along
the small intestine, eggs were mainly deposited in the anterior part at week seven, in
the central part at week 18 and evenly distributed at week 32 post infection. The key
findings from the present study are that B. natalensis for the first time was proved to
transmit S. bovis and that such an infection occurred in the snails that had an existing
amphistome infection. The animal studies have demonstrated that natural Fasciola
and Schistososma infections in cattle are mainly sub-clinical and their impact is seen
mainly during the dry season when feed supply is limited. Although treatment of
early infections transiently causes additional liver fibrosis, treatment prevents
development of acute disease and does not interfere with the development of
immunity. Furthermore, treatment prevents further deterioration of the health of the
cattle during the dry period. In addition, the observed reduction in faecal egg
excretion has an epidemiological impact of reducing the transmission of these
infections. In general, the present findings raise the possibility of strategic use of
anthelmintics for preventing the development of acute trematode disease in young
ruminants, improving their productivity and reducing the transmission intensity in
endemic areas
Description
PhD Thesis
Keywords
Epidemiology, bovine fasciolosis, schistosomosis