Diversity, prevalence, and intensity of gastrointestinal helminth infections in migratory, resident, and sedentary plains zebras (Equus quagga) in Masai Mara National Reserve and Lake Nakuru National Park, Kenya.

The diversity, prevalence and intensity of parasitic infections are influenced by factors such as movement patterns and land area available to the host. Zebras are known to harbour various genera of gastrointestinal helminths and facilitate parasite movement across large geographic areas through migration. Despite the harmful effects of helminths and their consequences on host population dynamics, little is known regarding helminth infection patterns in migratory, resident, and sedentary zebras. This study compared the diversity, prevalence, and intensity of helminth infections in zebras with different host movement patterns and space availability. Faecal samples were collected from migratory, resident, and sedentary groups of zebras between 2014 and 2015 and screened for helminth infection. They were infected by diverse groups of helminths including nematodes, trematodes and cestodes with the most prevalent being strongyle type nematodes. No significant difference in the diversity and prevalence was observed between the "three groups". Larvae were also recovered and identified species, cyathostomes, Strongylus edentatus, S.vulgaris, S. equinus, and Trichostronglus in order of abundance. The intensity of infection with the strongyle type nematodes, was highest in the migratory, then sedentary and lowest in resident zebras. It is plausible that the migratory zebras have higher energy demands and poor nutrition, resulting in reduced immune function hence high nematode burdens. Similarly, the sedentary population had high nematode burdens possibly due to high pasture contamination and depressed immunity due to the artificially restricted movement. The latter observation is particularly important in the design and size of sanctuaries in relation to parasitism.

Infectious pancreatic necrosis virus isolated from farmed rainbow trout and tilapia in Kenya is identical to European isolates.

Infectious pancreatic necrosis virus (IPNV) is an aquabirnavirus that causes serious diseases in a variety of fish species worldwide. It has been isolated from a large number of healthy fresh and marine water fish. Prior to this study, there was no record of the presence of IPNV infection in Kenya. Here, the presence of IPNV in farmed rainbow trout and tilapia was examined in Nyeri County of central Kenya. Head kidney samples taken from five rainbow trout and three tilapia farms and stored in RNALater® were processed by PCR followed by sequencing of a segment A fragment covering nucleotide positions 2,120-2,343 bp. IPNV was detected in all the farms sampled with infection ratios ranging from 0.3 to 0.78 although the infections were not associated with any specific clinical signs of disease. These findings were supported by immunohistochemistry staining of the virus in the kidney and exocrine pancreas of rainbow trout. Sequence alignment and phylogenetic analysis revealed that the Kenyan isolates were identical to European isolates, suggesting a common origin. These findings highlight the need for better biosecurity procedures with more stringent surveillance programmes and control for fish diseases, especially focusing on imported breeding materials to Kenya.

The influence of supplementation with urea-molasses blocks on weight gain and nematode parasitism of dairy calves in central Kenya.

The effect of feeding urea-molasses blocks (UMB) on the growth and gastrointestinal nematode parasitism of dairy weaner calves grazing on the same pasture was investigated on a farm in Thika District, central Kenya. Twenty-six female calves, with an average age of 9 months, were initially treated orally with albendazole (10 mg/kg body weight) and assigned into two groups: animals in group I were fed urea-molasses blocks (UMB) prepared using a cold process and those in group II were the controls. The UMB were given in the evening, when the animals returned from grazing, and were consumed during the night at a rate of 550 g/head per day. Supplementation was undertaken on three occasions for three consecutive months, between July and August 1999, and between January and March and July and September 2000. The body weights of the calves and the faecal egg counts were measured monthly and larval cultures were performed on positive faecal samples from each group. Significant differences (p < 0.05) were found in the cumulative weight gains of the two groups of calves from September onwards. The UMB group averaged (+/- SD) 311.2 +/- 14.9 g/day over the study period, while the control group averaged 235.7 +/- 23.5 g/day; the UMB group also reached breeding weight earlier (p < 0.05) than the control group. There was no significant difference (p > 0.05) in the faecal egg counts between the groups, the predominant genera of gastrointestinal nematodes in faecal cultures being Haemonchus spp. and Trichostrongylus spp. Other nematodes were Cooperia spp., Bunostomum spp. and Oesophagostomum spp.

Effect of urea-molasses block supplementation on grazing weaner goats naturally infected with gastrointestinal nematodes.

The influence of feeding urea-molasses blocks (UMB) on growth and gastrointestinal (GI) nematode parasitism of weaner goats grazing the same pasture was investigated on a farm in Nyandarua District, Kenya. Thirty female Small East African goat kids at an average age of 5 months were initially treated with albendazole orally (5 mg kg(-1) body mass) and randomly assigned into one of two groups: group I were fed UMB prepared using a cold process and group II kids (controls) received no block supplementation (NBS). The UMB were given in the evening when the animals returned from grazing and were consumed during the night at a rate of 95.0 g head(-1) day(-1). Supplementation was undertaken for 3 consecutive months from July to September 2001 and January to March 2002. Body mass of the kids and faecal egg counts were measured monthly and larval cultures were performed on positive faecal samples of kids of each group. Five goats from each group were randomly selected for slaughter and total counts and identification of worms at the end of June 2002. Significant differences (P < 0.05) were found in cumulative mass gains of kids in group I from September compared with those in group II. On termination of the study kids in group I had gained an average of (+/- SD) 20.4 +/- 1.4 kg while those in group II had gained 11.8 +/- 1.1 kg. From January 2002, faecal egg counts of the kids in the UMB group differed significantly (P < 0.05) from those of the NBS group and at slaughter, the mean (+/- SD) worm counts for the UMB group was 482 +/- 299 while that of the NBS group was 1 302 +/- 410. In all the goats, Haemonchus contortus was the predominant nematode recovered. These results indicate that UMB had significant effects in the control of GI nematode parasitism and enhanced growth of the young goats.

Effect of feeding urea-molasses blocks with incorporated fenbendazole on grazing dairy heifers naturally infected with gastrointestinal nematodes.

Between June 1999 and August 2000, the effects of feeding medicated urea-molasses supplement blocks on the growth of dairy heifers in a marginal area of central Kenya were assessed by comparing the live-weight gain of supplemented and unsupplemented heifers grazing the same pasture. Thirty-nine heifers with an average age of 9.6 months were initially treated orally with albendazole (10 mg/kg body weight) and assigned to 3 groups: group I was fed urea-molasses blocks with incorporated fenbendazole (MUMB), group II was fed urea-molasses blocks (UMB) and group III heifers (control) received no block supplementation (NBS). Body weights of the heifers and faecal egg counts (FECs) were measured monthly and larval cultures were made of positive faecal samples of each group. The mean cumulative live-weight responses of the MUMB and UMB groups were significantly greater than the NBS group (P < 0.05). However, at the end of the experimental period, the mean weight gain of the MUMB group did not differ from that of the UMB group (P > 0.05). The FECs were moderate to low in all groups and decreased progressively with increasing age of the animals; FECs for the urea-molasses-supplemented groups remained significantly lower than those of the NBS group throughout the experimental period (P < 0.05). Haemonchus and Trichostrongylus were the predominant nematode genera found in the heifers, but Cooperia, Bunostomum and Oesophagostomum were also present. These results indicate that feeding of urea-molasses blocks substantially reduced production losses attributable to nematode infection of young grazing cattle, and confirms previous observations that well-fed animals are better able to overcome the effects of helminth infections.

Seasonal availability of gastrointestinal nematode larvae to cattle on pasture in the central highlands of Kenya.

The type and level of infective strongylid nematode larvae on pasture were monitored fortnightly from July 1995 to June 1996 in the central highlands of Kenya. The number of larvae on pasture was moderate, reaching > 1,200 kg(-1) dry matter of grass during the period of, and soon after, the rains, and remained low in the dry seasons. The number of larvae on pasture was directly related to the rain-fall pattern which was found to be the most important factor for the development of eggs and free-living stages. Haemonchus was the predominant genus, followed in decreasing order by Trichostrongylus, Cooperia, Oesophagostomum and Bunostomum. The mean total adult worm burdens of tracer calves released at monthly intervals were related to the levels of herbage larvae and there was a positive correlation between faecal worm egg counts and worm burdens (r = 0.58) during the study period. These results indicate that a reduction in the contamination of pasture with nematode eggs before the rains could result in pastures carrying fewer larvae and thus form the basis of effective worm control programmes for cattle.

The epidemiology of gastrointestinal nematodes of dairy cattle in central Kenya.

The epidemiology of H. placei and of other gastrointestinal nematodes in yearling dairy cattle was examined on two farms in Kiambu District, central Kenya during each of 13 one-month periods from April 1993 to April 1994. On each farm, 32 newly weaned dairy calves were given a single dose of albendazole and then placed on experimental pastures. Twelve of the animals were designated for bimonthly slaughter (n = 2) and analysis of worm population characteristics and 20 were designated for blood and faecal collection and for weighing. Two parasite-free tracer calves were grazed alongside the weaner calves each month throughout the study period and were also slaughtered for analysis of worm populations. Faecal egg counts, haematological and serum pepsinogen determinations, herbage larval counts, and animal live weight changes were recorded monthly. The study revealed that Haemonchus placei, Trichostrongylus axei, Cooperia spp. and Oesophagostomum radiatum were responsible for parasitic gastroenteritis and that H. placei was the predominant nematode present in the young cattle on both farms. Faecal egg counts from resident cattle and necropsy worm counts revealed that pasture larval levels were directly related to the amount of rainfall. The total worm burdens in the animals were highest during the rainy season (March-June and October-December) and lowest during the dry seasons (July-September and January-February). The very low recovery of immature larvae of H. placei from the tracer calves indicated that arrested development is not a feature of the life cycle of this parasite in central Kenya. The maintenance of the parasite population depended on continuous cycling of infection between the host and the pasture. The agroclimatic conditions of the study area were such that, in general, favourable weather conditions for the development and survival of the free-living stages of gastrointestinal nematodes existed all year round.

The prevalence and intensity of helminth and coccidial infections in dairy cattle in central Kenya.

A survey of gastrointestinal parasite infections of young (< 6 months old), immature (6-12 months old) and adult (> 12 months old) dairy cattle on 16 farms in Kiambu District, Kenya was conducted during a dry season (September 1991 to January 1992) and during a wet season (March to July 1992). The survey was based on monthly coproparasitological examination of cohorts and worm counts in tracer calves. The effects of age, sex, farm and season on the prevalence and intensity of helminth and coccidial infections were determined. Faecal egg and oocyst counts revealed that the overall prevalences were: strongyles (including trichostrongyles) (85.5%), liver flukes (Fasciola gigantica) (34.0%), coccidia (30.9%) and tapeworms (9.6%). Eight species of the protozoan Eimeria were identified, the most prevalent species being E. bovis and E. zuernii. The most prevalent nematode genera were Haemonchus, Cooperia, Oesophagostomum and Trichostrongylus. Season, farm and age of the animals had a significant (p<0.05) influence on the intensity of infection with strongyles, liver flukes and coccidia, whereas the sex of the animals had no significant (p>0.05) effect on the prevalence or intensity of infections. A higher intensity of infection with strongyles and coccidia was found in the wet season than in the dry season (p<0.05). The age-specific intensity was in the following order: for strongyles, immature animals of 6-12 months of age had the highest egg counts, followed by young calves and adults. Calves had significantly (p<0.05) higher oocyst counts than immatures or adults. Liver fluke egg counts did not differ significant (p>0.05) between immatures and adult cattle.

An abattoir survey of gastrointestinal nematode infections in cattle in the central highlands of Kenya.

The gastrointestinal tracts of 672 crossbred cattle were obtained from various abattoirs in Kiambu District, Kenya from August 1992 to July 1993, and examined for the presence of gastrointestinal nematodes. Eight nematode species were found in 583 (86.8%) of the animals. The nematodes were, in order of prevalence: Haemonchus placei (67.0%), Cooperia pectinata (53.0%), Cooperia punctata (41.7%), Oesophagostomum radiatum (38.4%), Trichostronglyus axei (24.3%), Nematodirus helvetianus (19.6%), Trichuris globulosa (9.7%) and Strongyloides papillosus (3.6%). The intensity of the nematode infection was moderate; the mean burden being less than 7000 worms. H. placei accounted, on average, for 52.3% of the total burden. The total burden was least during the dry seasons and increased gradually during the rainy seasons. Adult H. placei persisted in the host throughout the year and there was no indication of hypobiosis. The heaviest gastrointestinal worm burdens were detected in 1.5- to 3-year-old animals. These findings are discussed with regard to their relevance for strategic control of gastrointestinal nematodes in cattle.

Development and survival of infective larvae of gastrointestinal nematodes of cattle on pasture in central Kenya.

On a series of pasture plots, 2 kg pats of bovine faeces containing known numbers of strongylid (Haemonchus, Cooperia, Oesophagostomum and Trichostrongylus) eggs were deposited at intervals of 4 weeks from July 1995 to June 1996. The plots were sampled every 2 weeks after contamination and infective larvae were identified and counted. Larvae of all the genera developed throughout the year, but the pats exposed during the rainy season yielded more abundant larvae on the herbage. Irrespective of the season of deposition of the pats, larvae were found in larger numbers from 2 to 6 weeks after deposition and generally declined to below detectable levels within 12 to 16 weeks of contamination. The comparatively short survival times noted in this experiment may present opportunities for manipulation of the population dynamics of the gastrointestinal nematodes in the tropical environment of Kenya.

Multiple and multigeneric anthelmintic resistance on a sheep farm in Kenya.

The anthelmintic efficacy of benzimidazoles (albendazole, fenbendazole and oxfendazole), levamisole, oral ivermectin and closantel was evaluated on a farm in Kenya using faecal egg count reduction test, larval cultures and a controlled slaughter trial. The results of this study indicated simultaneous resistance of Haemonchus contortus against benzimidazoles, levamisole and ivermectin, and of Trichostrongylus colubriformis and Oesophagostomum spp. against levamisole on the same farm. Ivermectin resistance developed to 47% within 15 months of first use. Closantel was effective against the benzimidazoles, levamisole and ivermectin resistant H. contortus.

Multiple anthelmintic resistance on a goat farm in Kenya.

The anthelmintic efficacy of benzimidazoles, levamisole, rafoxanide and ivermectin was evaluated on an institutional farm in Kenya using faecal egg count reduction test, larval cultures and a controlled slaughter trial. The results of this study indicated simultaneous resistance of Haemonchus contortus against benzimidazoles, levamisole and rafoxanide and Trichostrongylus columbriformis and Oesophagostomum sp. against levamisole on the same farm. Injectable and orally administered ivermectin was effective against the benzimidazole and levamisole resistant H. contortus.

Multiple anthelmintic resistance in Haemonchus contortus on a sheep farm in Kenya.

Multiple resistance to albendazole, thiophanate, levamisole and orally administered invermectin was detected in an isolate of Haemonchus contortus in sheep on a farm where benzimidazole resistance had already been identified. Following a faecal egg count reduction test, this was confirmed by both critical and controlled anthelmintic tests. Different groups of sheep infected naturally or given an experimental infection with the benzimidazole-resistant isolate were treated with the recommended doses of various anthelmintics. Compared to the control group, the percentage reductions in the faecal egg counts of sheep treated with albendazole, thiophanate, levamisole and ivermectin varied between 38.2% and 79.1% and the residual worm counts between 27.3% and 57.5%. The results indicate the presence of multiple anthelmintic resistance in this isolate of H. contortus. Sheep treated with closantel showed 100% reductions in faecal egg and worm counts, indicating that this drug was very effective against the population of H. contortus on the farm.

Efficacy of morantel sustained release trilaminate bolus against gastrointestinal nematodes in grazing dairy calves in Kenya.

The efficacy of morantel sustained release trilaminate (MSRT) bolus against gastrointestinal nematodes was evaluated under field conditions over a 10-month period. Twenty weaner calves were randomly divided into 2 groups of 10 calves each and grazed from March to December on adjacent, similarly contaminated paddocks. Group 1 calves (T-1) served as untreated controls while group 2 calves (T-2) were dosed at turnout with MSRT bolus designed to release morantel tartrate continuously for 90 days. The efficacy of MSRT was assessed by comparison of parasitological data (faecal worm egg counts, herbage larval counts, worm counts from tracer calves and set-stocked trial calves, determination of haematological parameters and pepsinogen levels), weight gains and clinical status of the animals. Faecal egg counts from the treated group (T-2) were reduced by 100% (P < 0.001) following treatment and remained significantly (P < 0.05) lower than counts from T-1 calves up to trial termination. The use of MSRT bolus resulted in a reduction of 92% (P < 0.001) in the number of gastrointestinal nematodes in set-stocked calves at the end of the study and a 55 to 85.7% reduction in herbage larval infectivity as reflected in lowered parasite burdens in tracer calves. At the trial termination, the control calves had gained on average (+/- s.d.) 59.4 +/- 4.8 kg (200.0 +/- 7.4 g day-1) and the treated ones on an average 128.6 +/- 10.5 kg (530.0 +/- 13.1 g day-1).

Efficacy of closantel, albendazole and levamisole on an ivermectin resistant strain of Haemonchus contortus in sheep.

Following evidence of reduced efficacy of oral ivermectin in a field population of Haemonchus contortus on a sheep farm in Kenya, this strain of the parasite was submitted to a controlled anthelmintic test. One hundred and twenty worm-free lambs were randomly split into two groups of 60. Each lamb in the first group was infected with 5000 third stage larvae (L3) of the suspected resistant strain the remaining 60 lambs were each infected with 5000 (L3) of a H. contortus strain of known susceptibility to the major groups of anthelmintic compounds used in sheep. On day 28 post-infection, each group was subdivided according to egg counts and at random into six sub-groups of ten lambs, each of which was treated with closantel at 5.0 mg kg-1, albendazole at 5.0 mg kg-1, levamisole at 7.5 mg kg-1, oral ivermectin at 0.2 mg kg-1 or injectable (Inj.) ivermectin at 0.2 mg kg-1, or was left as an untreated control. At slaughter, 10 days later, all the anthelmintics had resulted in reduced worm burdens in animals infected with the susceptible strain (albendazole 99.0%, levamisole 99.5%, closantel, Inj. and oral ivermectin 100%). By contrast, in the lambs infected with the suspected resistant strain, closantel was 100% effective, but inj. ivermectin, oral ivermectin, albendazole and levamisole reduced worm counts by 47.6%, 24.2%, 38.5% and 41.4%, respectively. Anthelmintic resistance to the other chemical groups had been confirmed previously on this farm and although benzimidazoles and levamisole had not been used for the last 4 years, this strain was still highly resistant to albendazole and levamisole; closantel remained as the only drug evaluated which was still effective against this population of H. contortus.

Comparative efficacies of closantel, ivermectin, oxfendazole, thiophanate and levamisole against thiabendazole resistant Haemonchus contortus in sheep.

Forty-nine sheep artificially exposed to a thiabendazole (TBZ) resistant isolate of Haemonchus contortus were assigned to 7 groups of 7 animals each and used to conduct a controlled anthelmintic trial. One group of sheep served as untreated infected controls and 6 groups were treated as follows: closantel, 5.0 mg kg-1; ivermectin, 0.2 mg kg-1; oxfendazole, 5.0 mg kg-1; thiophanate, 50 mg kg-1, levamisole, 7.5 mgkg-1 and thiabendazole, 66 mg kg-1. Eggs per gram of faeces were determined on days 21, 24 and day 34 (10 days post-treatment) after infection and all animals were necropsied for residual worm counts. The calculated efficacies of the treatments against H. contortus as indicated by worm reduction were closantel (100%), ivermectin (99.3%), oxfendazole (35.2%), thiophanate (56.7%), levamisole (98.6%) and thiabendazole (24.3%). The data therefore indicate that the TBZ-resistant isolate of H. contortus used was highly resistant to the 2 benzimidazole (BZ) anthelmintics, oxfendazole and thiophanate. This is the first report in Kenya of a field strain of H. contortus resistant to thiophanate.

Autoradiographic quantification of the efficacy of niridazole in mice infected with 75Se-labelled cercariae of Schistosoma mansoni.

The effects of the anti-schistosomal drug, niridazole, on the migration of Schistosoma mansoni larvae, biosynthetically radioisotope-labelled with 75[Se]-selenomethionine, was evaluated by autoradiography of compressed tissues of mice treated daily from Days 6 to 10 post-infection with 200 mg kg-1 niridazole. The results were compared with the migration of schistosomula in untreated controls. The distribution of schistosomula was altered in niridazole-treated mice, where there was a delayed migration from the lungs relative to the controls and significantly fewer schistosomula in total appeared to reach the liver. The total percentage of schistosomula detected as autoradiographic foci was significantly lower in treated mice than in the untreated controls. Niridazole-treated mice were free of any foci 10 days after the last treatment and no adult worms were recovered on perfusion of the hepatic portal system relative to control mice from which 5.8% of the infective cercariae were recovered as adult worms at Day 42 post-infection.