W.K. Munyua

Effects of three nematode anthelmintic treatment regimes on flock performance of sheep and goats under extensive management in semi-arid Kenya

A study was undertaken in a semi-arid area of Kenya between August 1991 and June 1993 to evaluate the effects of anthelmintic treatment using ivermectin before or during the rains, on performance of mixed sheep and goat flocks, in comparison with an untreated flock. Performance parameters measured included age and weight of dams at first parturition, parturition intervals, body weights of dams and offspring, and birth weights, growth rates, and mortality rates of offspring. Among these parameters, birth weights and growth rates of offspring were found to be significantly improved by the treatment administered before the rains compared with the other two treatments. Mortality was lower in lambs and kids with high birth weights. Treatment, either before or during the rains, significantly reduced the faecal egg output and improved body weight, packed cell volume and flock fertility. Liveweight was confirmed to be a better measure of sexual maturity than age. It was further shown that lambs and kids, born of dams at their first lambing or kidding, experienced higher mortality rates than lambs and kids born of dams in their second and subsequent parturitions. Overall, treatment with ivermectin before the onset of rains was equal to or better, in terms of the performance parameters measured, than treatment during the rains, whilst treatment compared with no treatment increased performance in almost all of the parameters measured.

Comparison of antibody- and antigen-detection enzyme immunoassays for the diagnosis of Trypanosoma evansi infections in camels

A total of 183 camels from Kenya were examined for circulating trypanosomal antigens by four methods: (1) a monoclonal antigen-detection enzyme-linked immunosorbent assay (Ag-ELISA) and circulating anti-trypanosomal antibodies; (2) antibody-detection enzyme-linked immunosorbent assay (Ab-ELISA); (3) buffy-coat examination (BCE); (4) mouse subinoculation (MI). Thirty-seven camels (20%) were parasite-positive by BCE and 60 camels (33%) were parasite-positive by MI. Sixty-three camels (34%) tested positive on Ag-ELISA. Of the 24 camels which could not be detected by BCE, Ag-ELISA detected 18 (75%). Ab-ELISA detected 90 (49%) positive camels. Of all the parasite-positive camels (61), Ag-ELISA detected 93% and Ab-ELISA 95%. Based on the results of 55 camels, there was a significant statistical difference (P < 0.0001) in Ag-ELISA optical density (OD) values (of either serum or plasma antigen analysis) between parasite-positive and parasite-negative camels. No significant difference was observed in Ab-ELISA OD values between parasite-positive and parasite-negative camels. Diagnosis of T. evansi infection in camels by the use of Ag-ELISA alone or in combination with BCE could therefore be a more preferred approach in assessing patient infection than the use of Ab-ELISA.

Development, Survival and Availability of Gastrointestinal Nematodes of Sheep and Pastures in a Semi-arid Area of Kajiado District of Kenya

A study was carried out on a ranch in the semi-arid area of Kajiado District in Kenya during the period July 2000 to June 2001 to determine the seasonal patterns of development and survival of gastrointestinal nematodes of sheep on pastures. A series of plots were contaminated with sheep faeces every month and pasture samples were collected weekly for the recovery and identification of larvae. The availability of infective larvae on naturally contaminated pastures was also monitored on the paddocks grazed by sheep and around the night pen and the watering point every month from July 2000 to June 2001. The results from the examination of the pasture samples indicated that rainfall distribution was the major factor governing the development and survival of the pre-parasitic stages. No parasitic larvae were detected from the plots contaminated during the dry months from July to October 2000, but development and translocation of infective larvae on pastures occurred on plots contaminated during the rainy seasons and soon after when relatively high moisture was present in the herbage (November 2000 to June 2001). During this period, peak larval counts occurred between the first and the second week post contamination, then declined to undetectable levels between week 4 and 16 post contamination. The lack of development of infective larvae during the dry season and the relatively rapid decline of their population during the wet season presents an opportunity for the use of pasture spelling as a means of helminth control in the study area. The availability of infective larvae on naturally contaminated pastures, around the night pen and around the watering point also followed the rainfall distribution pattern. Infective larvae were consistently recovered around the watering point throughout the study period. This indicated that the point is an important source of infection for sheep, especially during the dry season when other pastures are non-infective.

The effects of experimental Trypanosoma (Trypanozoon) (brucei) evansi infection on the fertility of male goats.

The effects on the fertility of small East African male goats of intravenous infection with Trypanosoma (t) (b) evansi were studied. Six infected bucks developed erratic, low but persistent parasitaemia, the packed cell volume dropped gradually but significantly (p<0.001) and they became emanciated. Half of these bucks developed clinical orchitis. Two bucks died of the disease during the experiment.Semen from all the infected bucks deteriorated in quality and quantity and those with clinical orchitis became totally aspermic. Spermatozoal abnormalities and the number of dead spermatozoa rose significantly. Later in the disease, the testicles of the infected bucks atrophied. Histologically, the testicles from the infected animals became devoid of spermatozoa, the testicular blood vessels contained microthrombi and there was infiltration of inflammatory cells. Subsequently, diffuse calcification set in, with calcium deposits obliterating most of the seminiferous vesicles and ducts and also the epididymal ducts.

Prevalence of Eimeria species in cattle in Kenya

A total of 620 bovine faecal samples collected from unselected animals brought for post-mortem to the Department of Veterinary Pathology and Microbiology or from animals in the Kabete (Kenya) practice area of the Faculty of Veterinary Medicine were examined to determine the types and prevalence of Eimeria spp. present. Coccidian oocytes were detected in 67.4% of the samples and eight different species of Eimeria were recognized. The species detected (and their prevalence) were E. bovis (79.0%), E. zuernii (60.2%), E. ellipsoidalis (26.1), E. cylindrica (13.4%), E. auburnensis (28.4%), E. alabamensis (10.3%), E. subspherica (5.0%) and E. wyomingensis (6.1%). E. bovis and E. zuernii led to few cases of clinical coccidiosis and the greatest number of E. bovis in one of the samples from the clinical cases was 30,600 oocysts per gram of faeces (OPG). Age and seasonal variation appeared to have an influence on the intensity of infection.

Isolation of Besnoitia wallacei in Kenya.

The development of Besnoitia wallacei was studied in 13 cats fed on tissues of mice and rats previously infected with B. wallacei. The cats were serially killed between Day 1 and Day 16 of infection, and histological sections from the liver and intestines were examined. Asexual stages were seen in both the small intestines and the liver between Day 6 and Day 16 post-infection. Mature microschizonts in intestinal epithelial cells measured 22.6 microns x 14.7 microns (n = 15). Macroschizonts in intestinal lamina propria measured 66.6 microns x 50.3 microns (n = 25). Those in the liver measured 70.9 microns x 55.0 microns (n = 5). Sexual stages were seen in epithelial cells of the small intestines only.

Relapses in dogs experimentally infected with Trypanosoma brucei and treated with diminazene aceturate or isometamidium chloride.

Twenty dogs of mixed local East African breeds were used. Five of the dogs were uninfected controls and 15 were infected with T. brucei (ILRAD 273). Five of the infected dogs were untreated controls, five were treated with a high curative dose of diminazene aceturate, (7 mg kg-1 body weight (wt.), and five were given a subcurative dose of isometamidium chloride (1 mg kg-1 body wt.). The drugs, given at 8 days post infection (d.p.i..), led to apparent recovery. The antibody titres, however, remained high in both groups and at 42-49 d.p.i. there was at least one relapse in each treatment group. Parasite populations from relapsed animals were more resistant to the drugs than the original infecting populations. The implications of these findings are discussed.

The effect of weather on the occurrence and magnitude of periparturient rise in trichostronglyid nematode egg output in Dorper ewes in a semi-arid area of Kajiado District of Kenya.

An investigation was carried out to assess the effects of weather on the occurrence and magnitude of the periparturient rise (PPR) in trichostrongylid nematode egg output in breeding Dorper ewes. The study was conducted over three breeding seasons on a ranch in the semi-arid area of Kajiado District in Kenya between June 1999 and December 2001. During each breeding season 20 ewes randomly selected from the breeding stock and 20 others selected from the unmated yearlings were monitored for faecal strongyle egg counts every 3 weeks. The lambing seasons were timed to coincide with the onset of the short rains (October–November 1999), the mid-short rains (November–December 2000) and the end of the dry season (September–October 2001). In each season higher egg outputs were recorded in the peri-parturient ewes compared to the unmated yearlings. The highest PPR occurred in September 2001, when lambing coincided with the end of the dry season, possibly as a result of maturation of hypobiotic larvae. The lowest PPR occurred in November 2000 when the onset of lambing coincided with the mid-short rains, possibly owing to low pasture infectivity associated with a long dry spell between January and October of the same year. The results of this study indicate that PPR occurred when lambing coincided with both the wet and the dry seasons. However, the magnitude was greatly influenced by the season when lambing occurred. It was also influenced by resumption of development of hypobiotic larvae and the nutritional status of the ewes. Not only should control of gastrointestinal nematode parasites in this area aim at preventing the occurrence of PPR by treating ewes 2–3 weeks before they are to lamb and during lactation, but the anthelmintic used must also eliminate hypobiotic larvae. In addition, the animals must be given supplementary feeding during this period.

The Effects of a Controlled-Release Albendazole Capsule (Proftril-Captec) on Parasitism in Grazing Corriedale Ewes in the Nyandarua District of Kenya

Munyua, W.K., Githigia, S.M., Mwangi, D.M., Kimoro, C.O. and Ayuya, J.M., 1997. The effects of a controlled-release albendazole capsule (Profitril-Captec) on parasitism in grazing Corriedale ewes in the Nyandarua district of Kenya. Veterinary Research Communications, 21 (2), 85-99The effects of intraruminal sustained-release capsules (IRSRCs) on parasitism in grazing Corriedale ewes were investigated over a period of 119 days (4 June-30 September 1993) using 40 ewes aged approximately 2 years and randomly divided into two groups of 20 ewes each. Each of the ewes in the treatment group received an IRSRC while the controls were left untreated. The groups were placed on adjacent 2.5-acre paddocks obtained by subdividing a 5.0-acre permanent pasture which had previously been grazed by young untreated sheep, so exposing both groups of ewes to a similar challenge from a contaminated paddock. The faecal egg counts, herbage larval counts and worm burdens of the major gastrointestinal parasites of sheep were significantly reduced by the use of the IRSRC. These parasitological effects were reflected in the increased live weight gains and heavier fleeces of the IRSRC-treated ewes. The control ewes required occasional salvage treatments during the trial period and the herbage on their paddock was heavily contaminated with infected larvae, reflected in the high worm burdens in the control ewes necropsied at the end of the trial and in tracer sheep introduced into the paddocks during the initial (day 30), interim (day 58) and final (day 89) stages of the experiment. Most capsules were exhausted within 95 days of administration, leading to a rise in the count of eggs per gram in the faeces in the treated group towards the end of the study.

Haemolytic complement and class-specific antibody levels in goats during infection with Trypanosoma evansi and after treatment with diminazene aceturate

Following infection with Trypanosoma evansi, goats mounted a strong class-specific antibody response, characterized by elevation of IgM and IgG antibody levels. Concomitant with the rising antibody levels and parasitaemia, was a drop (P 39 °C), slight dyspnoea, and fall in haematocrit levels (P < 0.01). Clinical examination revealed evidence of muscle wasting, lethargy and paleness of mucous membranes. Post-mortem examination carried out on one goat showed enlargement of lymph nodes, spleen and liver and oedema of the lungs and kidneys and a flabby heart. There was accumulation of sero-sanguineous fluid in the peritoneal, thoracic and pleural cavities and petechial haemorrhages on the serosa, pleura and intestinal mucosae. The brain was oedematous and showed evidence of congestion and meningeal petechiation. Cerebrospinal fluid (CSF) taken from infected goats did not show changes suggestive of any central nervous system (CNS) invasion by the parasites. Following treatment with diminazene aceturate, and the disappearance of parasites from the blood, the haematocrit status and haemolytic complement levels recovered by the 4th week. There was a rapid fall in the IgM-specific antibodies to near pre-infection levels. However, IgG-specific antibody levels were still elevated by the end of the study. The study shows that infection with this parasite may significantly affect goat production, because it causes changes which may lead to immunosuppression and organ failure. With the exception of IgG class-specific antibodies, these changes are quickly reversed by chemotherapeutic intervention. Levels of IgM and IgG class-specific antibodies may be a suitable indicator of the exposure status of goats to this parasite because the former fall rapidly after treatment or cure, while the latter may persist for long periods.