J. De Bont

The epidemiology of Schistosoma spindale Montgomery, 1906 in cattle in Sri Lanka

During 1988 and 1989, the mesenteric veins of 901 cattle were examined for the presence of schistosomes at the Kandy slaughterhouse (Sri Lanka). The overall prevalence of infection was 31.2%. Animals younger than 2 years were less infected (21.3%) than those older than 5 years (47.9%). Based on the number of paired worms counted, three intensities of infection were recognized: low (1-20 pairs), moderate (21-100 pairs) and heavy (greater than 100 pairs). Intensities increased with the age of the animals but remained low (average 10 worm pairs). The worm burden increased by approximately 20% for each step in age group. The number of miracidia/100 g faeces was measured in 85 animals of all age groups and intensities of infection; 77% of the samples contained less than 100 miracidia. Miracidia counts decreased with age; moderately and heavily infected animals in each age group had the highest and the lowest counts, respectively. This may be due to a host immune response. The results raise questions on the sensitivity of faecal egg counts as a diagnostic method for visceral schistosomiasis in cattle.

Failure of a recombinant Schistosoma bovis-derived glutathione S-transferase to protect cattle against experimental Fasciola hepatica infection.

The potential of a recombinant Schistosoma bovis 28-kDa glutathione S-transferase (rSb28GST) to protect cattle against Fasciola hepatica was tested in a vaccination trial. Thirty two calves were randomly divided into four groups of eight animals. Calves of the three vaccine groups received two intramuscular injections at 3 weeks interval, of 0.250mg rSb28GST in either aluminium hydroxide (Al(OH)(3)), Quil A, or PBS emulsified in an equal volume of Freunds complete adjuvant (FCA).Animals of the control group received injections of Al(OH)(3)/PBS only. All animals were challenged orally with a total of 360 metacercariae of F. hepatica, spread over 6 weeks. All groups of vaccinated animals produced measurable IgG antibody titers to rSb28GST after vaccination. Animals immunised with FCA adjuvanted vaccine had the highest and more durable antibody titers and only sera from this group recognised an approximately 24kDa protein band from F. hepatica, that is thought to be a F. hepatica GST. Despite a good antibody response differences in cumulative faecal egg output between the groups were not statistically significant. In addition, no significant difference was found between groups in terms of total worm numbers or percentage of immature flukes recovered at necropsy. In conclusion, the recombinant S. bovis 28kDa GST was not found to adequately protect cattle against experimental F. hepatica challenge, using either aluminium hydroxide, Quil A or FCA as adjuvant.

Potential of a recombinant Schistosoma bovis-derived glutathione S-transferase to protect cattle against experimental and natural S. mattheei infection

The potential of a recombinant Schistosoma bovis-derived glutathione S-transferase (rSb28GST) to protect cattle against S. mattheei infection was tested in Zambia. All animals were challenged 2 weeks after the second inoculation with either 0.250 mg rSb28GST in adjuvants (vaccinated calves, n = 14) or adjuvants alone (controls, n = 14). In a first experiment, 7 vaccinated and 7 control animals were exposed to 10000 S. mattheei cercariae percutaneously. All animals developed clinical schistosomiasis 7-8 weeks after challenge. At perfusion, 12 weeks after challenge, vaccinated and control groups had averages of 887 and 541 eggs per gramme (epg) faeces, 6515 and 5990 worms, and 4.2 and 3.4 million tissue eggs, respectively. These results indicate that the immunization protocol used did not protect these calves against the massive single experimental challenge. In a second experiment, another 2 groups (n = 7) of vaccinated and control animals were challenged naturally over a period of 9 months on a farm known to be endemic for S. mattheei. The natural infections were much lighter in intensity, as indicated by the mean faecal egg count (13 epg), worm count (139) and tissue egg count (294000) in non-vaccinated controls. In vaccinated calves, significant reductions in female worm burdens (50%), faecal egg count (89%) and miracidial counts (93%) were recorded. Total tissue egg counts were also reduced by 42% in vaccinated animals. It therefore appears that the rSb28GST can provide significant protection in cattle against S. mattheei under conditions of low to moderate natural infection.

Schistosoma mattheei infections in cattle: changes associated with season and age

The Schistosoma mattheei egg output was monitored in 31 cattle over a 18-month period on a dairy farm near Lusaka (Zambia). The animals were kept on pasture with free access to two streams which were suitable for the intermediate host, Bulinus globosus. Individual faecal egg excretion reached an average peak of 130 eggs per gram, around 9 months after birth and decreased markedly before the age of 18 months. Average counts declined significantly with age, down to less than five eggs per gram in adult cows. A seasonal increase in B. globosus snails and S. mattheei transmission during the rainy season had no effect on the egg output of animals older than 18 months. Two calves and two adult cows were necropsied to compare fluke and tissue egg counts in young and old infections. There was a marked decline in tissue egg accumulation in older cows, in spite of an increase in the numbers of adult female flukes, as compared with young animals. A shift of egg accumulation from the large intestine towards the liver was also observed as infection progressed. It is concluded from the results of faecal egg counts that cattle reared under conditions of continuous challenge develop acquired resistance to S. mattheei infection within the first year following primary infection. Comparison of fluke and tissue egg counts in farm animals of different ages suggests the acquisition of an anti-fecundity effect as infection progresses.

Cattle schistosomiasis in Zambia

A total of 358 cattle was examined for schistosome infection in Zambian slaughterhouses. A total of 542 worms collected from 104 infected individuals was examined for glucose-6-phosphate dehydrogenase and phosphoglucomutase using isoelectric focusing. The overall prevalence of infection was 51%. Ninety three percent of the infected animals had less than 100 worm pairs in the mesenteric veins. Schistosoma mattheei was the predominant species (75%); S. leiperi (12%) and S. margrebowiei (2%) were also identified. The remaining 11% of the worms showed one of two distinct heterozygote patterns. Pattern A is identical to that of a laboratory-produced F1 S. mattheei x S. haematobium hybrid, but could also represent a S. mattheei x S. leiperi hybrid. Further studies are required to elucidate the origins of pattern B.

The prevalence and pathology of Schistosoma nasale Rao, 1933 in cattle in Sri Lanka

During 1987 a total of 1393 cattle was examined for Schistosoma nasale infection at the Kandy slaughterhouse, Sri Lanka. The overall prevalence was 12.6% (monthly range 3-17%). Based on the appearance of macroscopic lesions, 6 types (0-5) were recognized; type 5 being the most severe, with cauliflower-like growths obstructing the nasal cavity. Older bovines with 8 permanent incisors were more heavily infected (29.1%) than younger ones with no permanent incisors (6.0%). The severity of the lesions increased also with the age of the animals. Observations on the localization of the lesions showed that the first sessile nodular areas appear on the medial septum, on the dorsal edge of the ventral nasal concha and on the lateral wall of the middle meatus of the nasal cavity. Later, they gradually spread over the whole mucosal surface of the anterior part of the cavity but were rarely found further than 10 cm posterior to the nasal opening. The histopathology showed that granuloma formation due to the presence of eggs was the most common feature of the respiratory mucosa.

Transplacental transfer of schistosomal circulating anodic antigens in cows

The present work investigated the transplacental passage of circulating anodic schistosome antigens (CAA) and the production of foetal antibodies in response to antigenic stimulation in Schistosoma mattheei infected cows. Three groups were available: six calves born to non‐infected cows received colostrum from a pool from non‐infected cows (group 1), six calves born to non‐infected cows (group 2) and six calves born to infected cows (group 3) received colostrum from a pool from infected cows. Schistosoma‐specific IgG1antibody and CAA levels were measured in the colostrum pools, the sera collected from the cows, and the sera collected from the calves at birth, after intake of colostrum and at day 30. The specific IgG1antibody levels were significantly higher in the sera from cows of group 3. In four cows of group 3 high CAA levels were detected. The specific IgG1antibody levels were 0.646 and 0.176 OD for the infected and non‐infected colostrum pool, respectively, and the CAA levels were 5667 and 2557 pg CAA/mL, respectively. At birth high levels of specific IgG1antibody and CAA were detected in 4 calves of group 3; levels in the other two calves were negligible. After intake of colostrum, specific IgG1antibody levels of group 1 increased slightly at day 1 to become again insignificant at day 30. In group 2 specific IgG1antibody levels increased significantly between days 0 and 1, to decrease, although not significantly, at day 30. Finally, in group 3 the delta OD values increased at day 1 and remained high until day 30. After intake of colostrum the CAA level increased very slightly for groups 1 and 2 to become again undetectable at day 30. In group 3 a nonsignificant decrease in CAA levels was observed at day 1 followed by a further significant decrease to reach low levels at day 30. The suggested intrauterine antigenic stimulation may be important not only for generating immune responses to natural early infections, but also for enhancing the immunogenicity and efficacy of vaccines administered to newborns.

Pathology of natural infections of Schistosoma spindale Montgomery, 1906, in cattle.

The pathology of natural Schistosoma spindale infections in cattle in Sri Lanka was studied. Hepatic lesions were moderate with periportal cell infiltration and periportal epithelioid cell granulomas within perilobular zones. Submucosal and mucosal granulomas accompanied by cellular changes were present in the small and large intestine. Two unusual observations included the migration of an adult worm from the mesenteric veins to the mucosa of the small intestine in one bull and the presence of epithelioid cell granulomas containing slender living eggs in the urinary bladder of one animal. Intensities of infections, histopathological changes and immunological responses are discussed and comparison is made with other schistosome species.

Circulating antigen levels in serum of cattle naturally infected with Schistosoma mattheei.

Levels of 2 Schistosoma circulating antigens, the circulating anodic antigen (CAA) and the circulating cathodic antigen (CCA), were determined in serum samples collected, on a monthly basis over a period of 1.5 years, from 32 farm animals of different ages and from 12 tracer calves exposed to Schistosoma mattheei infection on a Zambian farm. Faecal egg counts were monitored in all animals and worm burdens in tracers determined after perfusion. Antigen determination tests in serum, with sensitivities between 95 and 100% in heifers and adult cows, proved to be excellent tools for the diagnosis of cattle schistosomiasis. Also in young calves, some infections could be demonstrated earlier by CCA determination than by faecal egg examination. A poor correlation was seen between the data for faecal egg counts and for CAA and CCA levels. It therefore appears that circulating antigen measurements in serum are of limited value as indicators of the pathogenesis of infection in cattle. Although all tracer calves were found infected at perfusion, large variations were recorded in antigen levels. An unexpected finding was the observation in farm animals of a clear seasonal pattern in CAA levels, with significant increase between August and October during the second half of the dry season, when animals are subjected to heavy physical and nutritional stress. It therefore appears that, although circulating antigen determination may provide an indication of the worm burden in ageing infections, possible variations of antigen clearance rate with the physiological condition of the host may complicate the interpretation of the results.

Observations on worm population dynamics in calves naturally infected with Schistosoma mattheei.

The evolution of faecal egg output, worm burdens and tissue egg counts in young calves was monitored during the first year of natural exposure to Schistosoma mattheei infection on a Zambian farm. According to the duration of their stay on the farm, these calves were classified into 2 groups of 14 temporary tracers (TT calves) which were introduced on a 2-monthly basis for residential periods of 2 months, and 12 permanent tracers (PT calves) introduced either at the beginning of the experiment (Group A) or 2 months later (Group B) and gradually removed after residential periods of 2, 4, 6, 8, 10 and 12 months on the farm. Worm counts in the TT calves showed that infection occurred throughout the year on the farm and that levels of infection acquired during each period of 8 weeks correlated well with the respective infected snail densities observed at the main transmission site. Marked differences in worm population dynamics were recorded between the 2 groups of PT calves. In Group B animals which apparently were initially exposed to heavy transmission, according to the results from TT calves, much higher worm counts and greater susceptibility to reinfection were observed than in Group A animals initially exposed to lighter exposure. These results suggest that the development of resistance to natural infection with S. mattheei may depend on the initial exposure to the parasite. Low initial exposures may lead to resistance whereas high initial exposures may result in decreased immune responses resulting in susceptibility to infection.