C.J. Ng'ang'a

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.

Caprine besnoitisis: studies on the experimental intermediate hosts and the role of the domestic cat in transmission

A study was conducted to test the infectivity of bradyzoites of a Besnoitia species infecting goats in Kenya to rats, mice, rabbits, sheep and goats. Only goats developed infection resulting in tissue cyst formation. Eighteen cats were tested for their role in transmission of this Besnoitia species. Ten of the cats were fed on goat tissues with numerous Besnoitia cysts; four cats were orally inoculated with bradyzoites and four others fed on mice and rat carcasses previously inoculated with bradyzoites. None of these cats produced Besnoitia oocysts in their faeces for 30 days.

The prevalence of gastrointestinal helminth infections in pigs in Kenya

The prevalence of helminth infection, species spectrum and worm burdens in Kenyan pigs was examined. A total of 115 gastrointestinal tracts (GIT) from 61 growers and 54 adult pigs were examined between February 2005 and January 2006. Seventy eight (67.8%) had one or more helminth parasites, of which thirty six (31.3%) were mixed infection. Ten types of helminth parasites encountered in descending order of prevalence were, Oesophagostomum dentatum (39.1%), Trichuris suis (32.2%), Ascaris suum (28.7%), Oesophagostomum quadrispinulatum (14.8%), Trichostrongylus colubriformis (10.4%), Trichostrongylus axei (4.3%), Strongyloides ransomi (4.3%), Hyostrongylus rubidus (1.7%), Ascarops strongylina (1.7%) and Physocephalus sexalutus (0.9%). Oesophagostomum dentatum was the most prevalent species (51.9%) in the adult pigs, while Trichuris suis was the most prevalent species (44.3%) in growers. The highest worm counts were recorded in the out door production system. Oesophagostomum quadrispinulatum, Trichostrongylus colubriformis, Trichostrongylus axei, Hyostrongylus rubidus, Ascarops strongylina and Physocephalus sexalutus were recorded in Kenya for the first time. The high prevalence and wide spectrum observed in the present study suggests that helminth infection may be a constraint to economic pig production in the country and there is need to institute control measures.

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.

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.

Efficacy of ivermectin delivered from a sustained-release bolus against gastrointestinal nematodes in field grazing calves in Nyandarua district of Kenya

The effect of ivermectin delivered by an orally administered prototype sustained-release (IVM SR) bolus was evaluated over a period of 140 days using 12 steers aged approximately 8-10 months and ranging in weight from 150 to 175 kg. They were allocated to two groups of 6 steers each by restricted randomization based on their liveweight. Each of the treatment group received an IVM SR bolus designed to deliver 12 mg of the ivermectin/day for 135 days. The other group was designated as non-medicated controls. The groups were placed on adjacent 3 acre paddocks obtained by sub-dividing of 6.0 acre permanent pasture which had previously been grazed by young untreated cattle so exposing experimental steers to a similar challenge of a contaminated paddock. The faecal egg counts, herbage larval counts and worm burdens of the major gastro-intestinal nematodes of cattle were significantly reduced by the use of the IVM SR boluses. These parasitological effects were reflected in the increased liveweight gains in the IVM SR bolus-treated steers. The control steers required occasional salvage treatments over the trial period and the herbage on their paddock was heavily contaminated with infective larvae as reflected in the high worm burden in the control steers necropsied at trial termination and in tracer calves introduced into the paddocks during the initial (Day 31), interim (Day 69) and final (Day 100) stages of the experiment.

Relationship between the Prevalence of Ectoparasites and Associated Risk Factors in Free-Range Pigs in Kenya

A cross-sectional study was undertaken to determine the prevalence of ectoparasites and possible risk factors in free-range pigs from 135 farms of Busia District, Kenya. Three hundred and six pigs were examined for presence of external parasites using standard parasitological methods. Data on management practices including housing and history of acaricide spraying were also collected. The ectoparasites found in the pigs were Haematopinus suis (96.1%), Sarcoptes scabiei (63.7%), and ticks (29.7%). The tick species included Rhipicephalus appendiculatus (70%), Boophilus decoloratus (31%), and Amblyomma variegatum (12%). The occurrence of the infestations was associated with age, being highest in sows (S. scabiei) and finishers (ticks and H. suis). Male pigs had highest prevalences of H. suis and ticks, while female pigs had highest prevalence of S. scabiei. The prevalence of the parasitic infestations was significantly (P < 0.05) associated with their origin being either lower (H. suis and S. scabiei) or higher (ticks) in pigs originating from divisions with high rainfall. Housed pigs had significantly (P < 0.05) lower prevalence of H. suis and ticks than those from households without pig housing. It is concluded that the free-range pigs have high prevalence of ectoparasites, and effective control strategies focussing on improved animal husbandry and acaricide use should be implemented.