The distribution of Fasciola hepatica and Fasciola gigantica within southern Tanzania--constraints associated with the intermediate host.

In East Africa, Fasciola gigantica is generally the causative agent of fasciolosis but there have been reports of F. hepatica in cattle from highland regions of Kenya, Ethiopia, Uganda and Zaire. The topography of the Southern Highlands of Tanzania provides an environment where the climatic conditions exist for the sustenance of lymnaeid species capable of supporting both Fasciola hepatica and F. gigantica. Theoretically this would allow interaction between fasciolid species and the possible creation of hybrids. In this report we present molecular data confirming the existence of the snail, Lymnaea truncatula, at high altitude on the Kitulo Plateau of the Southern Highlands, Tanzania, along with morphometric and molecular data confirming the presence of F. hepatica in the corresponding area. At lower altitudes, where climatic conditions were unfavourable for the existence of L. truncatula, the presence of its sister species L. natalensis was confirmed by molecular data along with its preferred fasciolid parasite, F. gigantica. Analysis based on a 618 bp sequence of the 28S rRNA gene did not reveal the presence of hybrid fasciolids in our fluke samples.

Distribution, prevalence and intensity of Schistosoma bovis infection in cattle in Iringa district, Tanzania.

Monthly abattoir, farms and village surveys were carried out to determine the distribution, prevalence and intensity of Schistosoma bovis infection in cattle in Iringa district in the southern highlands of Tanzania between August 1991 to August 1992. Abattoir surveys were conducted at the Iringa regional abattoir and age, sex, live animal grade and livestock market of origin of each of 342 animals examined were recorded. Five grams of the central part of the jejunum were collected from each animal and schistosome egg counting was carried out after tissue digestion. Nine farms and six villages were randomly selected and age, sex and origin of 501 cattle was recorded. Faecal samples were collected from each animal and quantification of schistosome eggs was carried out by means of the Modified Bell filtration technique. Abattoir surveys revealed S. bovis to be present in 116 out of 342 cattle examined in 10 out of the 12 livestock markets surveyed giving a point prevalence of 34%. A high frequency (70.1%) of low tissue egg counts (< 200 eggs per gram) was observed among the infected animals. The prevalence and intensities of infection observed in the slaughtered cattle were not related to the age-group, sex and grade of the animals. Results from faecal egg counts in nine farms and six villages disclosed that the infection was predominant in four farms (Lulanzi, Igumbiro, Ruaha and Mlolo) and three villages (Itunundu, Ibumu and Lulanzi). Egg counts per gram of faeces (EPGF) at Lulanzi dairy farm revealed a peak egg excretion in 1-3 yr old animals which was followed by a decline in the number of EPGF within the age group of 3- to 9-yr old animals. However, the faecal egg excretion tended to rise again in animals over 9 years old. Deaths of four animals which were preceded by signs of intermittent diarrhea, loss of condition, anaemia and high faecal egg counts was observed at Lulanzi farm. Postmortem examination of the dead animals revealed that they had severe schistosomal lesions and higher tissue egg counts than the slaughtered cattle. It was concluded from the present study that S. bovis infection in cattle is very common in foci in Iringa district and possibly the whole of the southern highlands of Tanzania and in some enzootic farms it could be among the major causes of ill-health and lowered productivity.

Lesions of the enteric nervous system and the possible role of mast cells in the pathogenic mechanisms of migration of schistosome eggs in the small intestine of cattle during Schistosoma bovis infection.

The enteric nervous system in the small intestine of cattle during Schistosoma bovis infection was studied by histological stains and immunohistochemical methods. Lesions due to migration of schistosoma eggs were located mainly in the mucous and the submucous layer overlaying the submucous vascular arcades. Granulomas destroyed ganglia, neurons, nerves fibre strands and nerve fibres. Ganglia situated within or near granulomas were infiltrated by mast cells, eosinophils, lymphocytes, globule leukocytes, neutrophils and macrophages. Mast cells were in close contact with degenerating neuronal perikarya. Whereas vasoactive intestinal peptide-like immunoreactivity in the nerves and neurons in the ganglia within and around granulomas was increased, the neurofilament-like immunoreactivity was reduced. Compared to the myenteric and external submucous plexuses, the internal submucous and mucous plexuses were the most damaged. These changes imply reduced functional capacity in the nervous tissue which might cause reduced motility, malabsorption and partly account for the loss of body weight and condition and failure to thrive which occur in schistosomosis. Biotinylated affinity purified swine anti-rabbit and mouse anti-rabbit immunoglobulins reacted nonspecifically with a subset of mast cells. The reaction revealed many mast cells in early forming granulomas and around schistosome egg tracts and infiltration of mast cells into the ganglia of intestinal nerve plexuses. The observation shows a localized, Type I hypersensitivity reaction suggesting for the release of mast cell-derived chemical mediators in the intestinal reaction to trap or evict S. bovis eggs and to cause diarrhoea.