D. Van Aken

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.

Comparative study of strongyle infections of cattle and buffaloes in Mindanao, the Philippines

Faecal samples were collected from 500 cattle and 385 buffaloes belonging to backyard farmers from 24 villages in the province of Bukidnon, Mindanao, the Philippines. Strongyle nematode infections were studied on these samples by faecal egg counts and infective larvae differentiation. The effects of animal species and age on the prevalence and intensity of infections were studied. The overall prevalence of strongyle infection was 53% for cattle and 28% for buffaloes. The prevalence decreased with increasing age in both animal species. Faecal egg counts were significantly lower in buffaloes than in cattle. Adult animals had lower egg counts than calves. This age effect was most pronounced in buffaloes. Six genera of strongyle nematodes were identified from the faecal cultures in both animal species, Mecistocirrus, Haemonchus, Trichostrongylus, Cooperia, Bunostomum and Oesophagostomum. The distribution of larvae did not vary much with age.

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.

PATHOPHYSIOLOGICAL ASPECTS OF MECISTOCIRRUS DIGITATUS (NEMATODA: TRICHOSTRONGYLIDAE) INFECTION IN CALVES

Three groups of four calves were experimentally infected with infectious larvae of Mecistocirrus digitatus. One group received a trickle infection of 5000 L3 per day for 8 days, the other two groups received a single infection of 5000 and 40,000 L3, respectively. All animals were necropsied 120 days after infection. Prepatent periods varied between 61 and 79 days, and maximal faecal egg output was reached between 80 and 100 days after infection. Repeated infections were not additive and worm counts at 120 days after infection varied between 100 and 440 in the first two groups and between 120 and 1700 in the last group. There was no significant difference in worm counts between the different infection regimes. However, there was a significant positive relationship between worm burden and faecal egg counts. In addition, there were significant negative relationships between worm burden and packed cell volume, and weight gain. The relative decreases in packed cell volume and weight gain emerged 70-80 days after infection. Serum pepsinogen levels were significantly elevated by the end of the trial, but the observed positive relationship between worm burden and pepsinogen was not significant. An enzyme immunoassay based on crude adult antigen was able to detect M. digitatus infection at 90 and 100 days after infection, but again there was no significant association between worm burden and antibody levels. Therefore, anaemia and a reduction in weight gain caused by the haematophagous activity of adult stages seem to be the most important pathogenic effects of M. digitatus infection in calves.

Epidemiology of Mecistocirrus digitatus and other gastrointestinal nematode infections in cattle in Mindanao, Philippines

Over a period of 14 months, faecal and serum samples were collected monthly from cattle of 1 to 30 months old on three ranches (20-25 animals ranch-1 sample-1) in Mindanao, Philippines. Individual faecal egg counts, serum pepsinogen levels and Mecistocirrus digitatus specific antibodies were determined, and infective larvae from pooled faecal samples were examined. Post mortem worm counts were carried out on tracer calves (n = 16) that had been kept for 30 days with the herds on two of the ranches. A number of gastrointestinal nematode species were present: M. digitatus, Haemonchus placei, H. similis, Trichostrongylus axei, Cooperia punctata, C. pectinata, Bunostomum phlebotomum and Oesophagostomum radiatum. Strongyle eggs first appeared in the faeces of calves of two months old, egg counts peaked when animals were 3-6 months old, after which they steadily and significantly declined. Faecal egg output of M. digitatus increased up to the age of 10 months, after which there was a steady but not significant decline until the age of 24 months. In faecal cultures the relative proportion of Cooperia larvae decreased from over 70% in 0-6 month old animals to 30% in 19-24 month old animals, and a corresponding 30% increase in the proportion of Mecistocirrus was observed. Both serum pepsinogen and M. digitatus specific antibodies levels increased during the first year of life, and then remained at the same level in older animals. Whereas the total faecal egg output did not significantly vary throughout the year, worm counts from tracer calves indicated a marked seasonality in transmission.

Thelazia rhodesii (Desmarest, 1828) infections in cattle in Mindanao, Philippines

Thelazia rhodesii was found in the eyes of 149 of 643 bovine heads (23%) that were examined at the abattoir of Cagayan de Oro City, Philippines, during the period February 1994 to February 1995. In nearly half of the animals both eyes were infected and an average of 4.1 worms per infected animal was recovered. Of the 1286 eyes examined, 17% were infected; worm burdens ranged from one to 36 (average 2.9) worms per infected eye. Monthly prevalence of infection ranged from 13% to 36%. T. rhodesii infection was significantly more common in cattle of more than 3 years of age (25%) than in younger animals (15%). Ocular lesions were observed in 73 (11%) cattle; 22% of these were infected with T. rhodesii. There was no relationship between presence of T. rhodesii and ocular lesions.

Mammomonogamus laryngeus (Railliet, 1899) infections in cattle in Mindanao, Philippines

During one year, 597 cattle were examined for Mammomonogamus laryngeus infections in the abattoir of Cagayan de Oro, Philippines. The overall prevalence was 23% with no obvious seasonal variations. The infection rate was 19% in animals up to 4 years old and 24% in animals 4-12 years old. In infected animals up to 8 years old an average of eight parasite pairs was found; infected animals of 8-12 years old had 5.2 parasite pairs on average. All worms were located on the posterior side of the epiglottis. Field observations on cattle in Mindanao revealed that adult M. laryngeus had developed on the epiglottis of a tracer calf that had been on pasture for 30 days and then kept away from possible nematode infection for 28 days.

Studies of the relationships between Schistosoma nasale and S. spindale and their snail host Indoplanorbis exustus

Infectivity and cercarial production of Indoplanorbis exustus related to variation of miracidial dose (1, 4, 10 or 20) with Schistosoma nasale and S. spindale from Sri Lanka were studied. The intermediate host-parasite relationships of the two schistosome species showed marked differences under the conditions of observation recorded in this study. Prepatent death rates (PDR) were on average higher for S. spindale (30%) than for S. nasale (10%). The size of the miracidial dose to which snails had been exposed had no effect on PDR. The infection rates (IR) were on average higher for S. nasale (41%) compared with S. spindale (27%). Highest IR occurred after exposure to 4 miracidia in S. nasale infections (79%) and after exposure to 10 miracidia in S. spindale infections (60%). The highest daily average cercarial production per snail was recorded for S. nasale at a level of 4 miracidia (1311), and for S. spindale at a level of 10 miracidia (1615). At low level (1 or 4 miracidia) of exposure, I. exustus showed a better compatibility with S. nasale than with S. spindale. An opposite tendency was observed at higher levels (10 or 20 miracidia) of exposure. Unsuccessful infections of Lymnaea luteola with either S. nasale or S. spindale indicate that this species is not involved in transmission.

Use of enzyme electrophoresis for differentiating Schistosoma nasale and S. spindale infections of Indoplanorbis exustus in Sri Lanka

Indoplanorbis exustus is the intermediate snail host of both Schistosoma nasale and S. spindale in Sri Lanka. Due to the similar morphology of the cercariae difficulties exist in identifying the species of schistosome infecting snails at transmission sites. Isoelectric focusing in polyacrylamide gels of malate dehydrogenase, glucose phosphate isomerase, phosphoglucomutase and acid phosphatase has been carried out on extracts of cercariae and potentially useful diagnostic markers have been identified. Cellulose acetate membrane electrophoresis has been used to separate two glucose phosphate isomerase phenotypes each of which appears to be diagnostic for one of the species. This simple electrophoretic technique has been used to identify schistosome infections in Indoplanorbis exustus collected at two transmission sites in Sri Lanka. Out of a total of 1,240 snails collected, 13 snails were shown to be infected with S. nasale, 19 with S. spindale and two snails were found to have mixed infections.