The pathology of naturally-occurring bovine schistosomiasis in the Sudan

A retrospective study on Schistosoma spindale infection in domestic ruminants, Andhra Pradesh, India

The present study was undertaken to determine the prevalence of Schistosoma spindale infection in domestic ruminants in Krishna district, Andhra Pradesh by coprological and necropsy examination. Examination of 177 buffaloes, 283 sheep and 166 goats faecal samples (n = 626) revealed 2.25, 2.82 and 1.80% of S. spindale infection, respectively. Necropsy examination of 21 buffaloes, 185 sheep and 217 goats revealed 14.2, 1.08 and 3.68% of S. spindale infection, respectively. Overall, microscopic examination of faecal smears revealed 2.39% (n = 15) prevalence of S. spindale infection in ruminants in the study area, while 3.07% (n = 13) of ruminants were found to be positive for S. spindale during postmortem examination. Adult worms collected from the mesenteric veins were processed and identified as S. spindale. Grossly, the infected livers were found with petechial haemorrhages, cirrhotic changes and pinpoint granulomas in parenchymatous tissue. Histological sections of livers revealed microgranulomas with infiltration of mononuclears, eosinophils and fibroblast cells surrounding the Schistosome ova. The intestinal mucosa was thickened, edematous and haemorrhagic with copious mucous exudates. Cut section of infected intestines revealed severe inflammatory reactions in the mucosa and sub mucosa and granulomatous changes surrounding the Schistosoma eggs.

Bovine schistosomiasis in some selected areas of South Wollo and Oromia Zones of Amhara Region, North-East Ethiopia

A cross-sectional coprological and pathological study was conducted in five districts of South Wollo and Oromia Administrative Zones, Amhara regional state, Ethiopia from November 2020 to June 2021 to determine the prevalence and associated risk factors of Bovine Schistosomiasis and to characterize pathological lesions induced by the adult worm of Schistosoma bovis. For coprological examination, a total of 768 fecal samples were collected both from the field (384) and the abattoirs (384). An abattoir survey was carried out on 384 cattle to evaluate the performance of the sedimentation method. The risk factors were identified using multivariable mixed-effect logistic regression analyses. The diagnostic efficacy of the sedimentation technique was determined by calculating sensitivity and specificity considering postmortem examination as a reference test. The overall prevalence of bovine shistosomiasis using coprological examination was found to be 16.7% (95% CI = 14.10–19.49). The prevalence of shistosomiasis based on post-mortem examination was found to be 17.19% (95% CI = 13.55–21.34). Local cattle breed (OR = 2.44, 95%CI = 1.34–4.43), poor body condition (OR = 4.09, 95% CI = 2.45–6.83) and adult (OR = 1.78, 95% CI = 1.21–3.28) cattle are more likely to acquire shistosomiasis than crossbreed, good body condition, and young cattle. The sensitivity and specificity of sedimentation techniques, keeping postmortem examination as a reference test were 74.24% (95%CI = 61.99–84.22) and 98.11% (95%CI = 95.94–99.30), respectively. The major gross lesions were observed in the liver and intestinal tracts. In conclusion, adult local cattle with medium and poor body conditions should be prioritized for deworming and future surveillance.

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.

Serum enzyme changes in calves experimentally infected with Schistosoma bovis

The activities of the enzymes SD, GD, AAT, 5'NT, GGT, LDH and CPK were determined weekly in sera of two calves each infected with 10,000 S. bovis cercariae and in two controls. In infected animals, LDH activity increased from the first week of exposure and remained high throughout the experiment (22 weeks). GGT activity increased nine weeks after exposure and remained high. CPK activity was elevated during weeks 8-15 of infection. No change was detected in the activity of the other enzymes, nor in any enzymes of the controls.

Immunization of sheep against Schistosoma bovis using an irradiated schistosomular vaccine

S. bovis is an economically important parasite of cattle and possibly of sheep and other domestic stock in many African and Mediterranean countries. Control of this infection by chemotherapy and mollusciciding is impractical and this has stimulated interest in vaccination. Previous work in sheep with the Central and South African species S. mattheei has led to the development of an effective vaccine which incorporates irradiated schistosomula produced by artificial transformation of cercariae. In the present experiments a similar S. bovis vaccine has been used in sheep. Fifteen 5 month old Border Leicester × Suffolk crossbred wethers were divided into three groups, two were vaccinated with either 10000 or 20000 6 krad irradiated S. bovis schistosomula, and the third kept as unvaccinated controls. All sheep were challenged with 6700 normal S. bovis cercariae.

Worm recoveries and tissue egg counts at necropsy showed that vaccination with 10000 irradiated schistosomula produced a reduction of 71% in the mean worm burden resulting from challenge of the controls and the mean densities of eggs in the tissues were reduced by 75–82%. Immunization with 20000 irradiated schistosomula was not more effective. Histopathological observations showed that both groups of vaccinated sheep had much milder lesions in the intestines than the non-vaccinated controls. There was also a clear reduction in the severity of liver lesions in 4 of the 5 sheep given the lower dose of irradiated schistosomula but the livers of sheep vaccinated with 20000 irradiated schistosomula had severe and widespread lesions due mainly to a massive accumulation of eosinophils and other inflammatory cells around the vessels.

Immunization of calves against Schistosoma bovis using irradiated cercariae of schistosomula of S. bovis

Fourteen 9-month-old zebu calves were immunized with 10000 irradiatedSchistosoma bovisschistosomula given in 1–3 intramuscular or subcutaneous doses, and 4 more calves were immunized with 10000 irradiated cercariae administered percutaneously in a single dose. Eight weeks after the beginning of the experiment these calves, together with four non-immunized controls were challenged percutaneously with 10000 normalS. boviscercariae/calf. Comparative clinical, parasitological, pathological and pathophysiological observations subsequently revealed significant differences between the vaccinated and non-vaccinated calves. The vaccinated calves showed significantly higher growth rates, and a superior body composition as indicated by their lower total body water content. The beneficial effects of vaccination were also shown by significantly lower faecal egg outputs in the vaccinated calves and by their lower tissue egg and adult worm counts. The reduced tissue egg counts were also reflected in the milder histopathological changes seen in the vaccinated calves. The vaccinated calves had significantly higher packed cell and circulating red blood cell volumes than the challenged controls, longer red blood cell half lives, and somewhat lower blood volumes and rates of red blood cell synthesis. No untoward clinical effects that could be attributed to vaccination were recorded. These results indicate that zebu cattle can be effectively protected againstS. bovisby vaccination with irradiated organisms. We are now evaluating this type of vaccine in a field trial in an enzootic area in the Sudan.

The pathology of experimental Schistosoma bovis infection in sheep

Five desert sheep were exposed to 5000 or 10000 Schistosoma bovis cercariae each, and the parasitological clinical and pathological parameters were recorded. The pre-patent period was approximately 7 weeks and from that time onwards, the animals became progressively ill and emaciated. Following necropsy at the 12th week, a percentage schistosome recovery ranging from 36%--63.6% was found, and there were high egg densities in the intestinal tract and the liver. These organs revealed severe pathological lesions which were described in detail along with the changes occurring in other tissues.