The prevalence of gastrointestinal parasitism, control practices and occurence of anthelmintic resistance in commercial pig farms in Thika district, Kenya
Kagira, John Maina
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One of the objectives of the present study was to establish the prevalence and intensity of gastrointestinal (GI) parasites in 35 commercial pig farms in Thika District. Central Kenya. Faecal samples were collected from 830 pigs of all age groups and examined for eggs per gram (EPG) of faeces. using a modified McMaster technique with a level detection of 100 EPG. The study herds consisted of 31 to 6000 pigs of all ages. Oesophagostomum spp .. Ascaris suum. Trichuris suis and Strongyloides ransomi were the only nematodes detected with prevalences of27.6% (of the animals sampled). 8.3%. 6.8% and 2.3% respectively. In total. 99.4% of the farms were affected by at least one nematode genus. Oesophagostomum spp. was the most prevalent among the herds (88.6% of the herds). Age related prevalence of infection was observed with Oesophagostomum spp. affecting mostly the adults (44.2%): A. suum and T suis affected mostly the weaners (14.3% and 16%. respectively): and S. ransomi affected mostly the piglets (10%). The porkers. baconers and adults were not affected by S. ransomi. The distribution of all the parasites was overdispersed i.e.. majority of the parasites were parasitising few hosts. The EPG levels of different nematodes were also related to age of pigs. with the highest mean EPG levels of Oesophagostomum spp. (218). A. suum (215). T suis ( 127) and S. ransomi (24) recorded amongst the adults. weaners. porkers and piglets. respectively. The biggest range of EPG values were that of T suis. followed by A. suum. Oesophagostomum spp. and S. ransomi. (b) Control methods The second objective of this study was to investigate the use of anthelmintics and other management practises used in the control of nematode parasites. The presence of potential risk factors for the development of anthelmintic resistance was also studied using a questionnaire. was administered in personal interviews during the visits to the farms. In the study population. 97.1 % of the farms had a history of treating the animals with anthelmintics. The farm which was not using anthelmintics had been using Pyrethrum mark ~(0.08% wlw Pyrethrins-Pyrethrurn Board of Kenya) a pyrethroid product. Piperazine (mostly Ascarex ~ "Cosmos Ltd. Kenya). was used by most of the farmers (68.6%, 71.4%. and 71.4% between 1997 and 1999). The proportion of the farmers that used Wormicid\ (Cosmos Ltd. Kenya). Panacur" (Hoechst. Germany) or Pigworma" I Unizani (Bis Laboratories. Kenya) were 22%.9.5%. and 4.8%. respectively. Only 10.6% of the farmers used the avermectins (Noramectin !. Norbrook Laboratories. UK.). Some (50%) of the farmers treated their animals after every three months. Of the 34 fanners who were using anthelmintics. 70.2% had not changed the drug they had been using since 1997. Most (94.3%) of the farmers did not weigh the animals. but used visual perception of body weight to calculate anthelmintic dosage. The ease of administration and price greatly influenced the type of anthelmintic chosen. Only relatively few farmers treated their animals before they were introduced into the farm. Majority (60%) of the farmers had very little knowledge on effects of helminths on pig production. To determine the level of infection of the helminths in the farms. most (71.8%) farmers looked out for clinical signs such as unthriftness. and decreased growth rate. Expert veterinary advice was not readily available hence the farmers relied mostly on drugs salesmen for advice on the anthelmintic usage. Thus. quite a number of risk factors in favour of anthelmintic resistance development were encountered. Association on the occurrence of nematode species and herd management factors was examined using the chi-square analysis. Prevalence of the helminths was higher in farms where: irregular worm control program was used (67%). dung removal and washing of the floors was done irregularly (60.8%) and 61.2%. respectively). floor was not concrete (47.7%). bedding was not provided (51.2%). weaning age of animals was above 2 months (50.4%). herd sizes were small (43.1%) and animals were given non-commercial feeds (41.6%). These associations were most significant (p<0.05) for the Oesophagostomum spp. infections. Prevalence of infections with Oesophagostomum spp. (38.7%). A. suum (11.7%), T sui (8.4%) and S. ransomi (6%) was highest in the farms using Ascarex" (Cosmos Ltd. Kenya). Wonnicid~. (Cosmos Ltd. Kenya). Ascarex! - (Cosmos Ltd. Kenya) and Panacur~ (Hoechst. Germany), respectively. The prevalence of infections with Oesophagostomum spp. / Aisuum (0%). T suis (4%) and S. ransomi (0%) was lowest in the farms using Noramectini. (Norbrook Laboratories. UK) (0%). Panacuri (Hoechst. Germany) and Wormicidi. (Cosmos Ltd. Kenya). respectively. (c) Anthelmintic resistance The final objective of the study was to examine the prevalence of anthelmintic resistance (AR) in the study area. This was done by means of faecal egg count reduction test (FECRT) and larval development assay (LOA) test. Three different anthelmintic preparations were tested in 4 herds. Piperazine (Piperazine citrate~ -Kela Pharmaceuticals. Belgium) and levarnisole (Wormicid" - Cosmos Ltd. Kenya) were less than 95% effective (one farm each) against Oesophagostomum spp .. when the results were analyzed based on recommendations by World Association for Advancement of Veterinary Parasitology. Based on the same method of calculation. a resistant isolate of Tsuis against levarnisole (Wormicid" - Cosmos Ltd. Kenya) was also detected in one farm. When the results were subjected to a different method using the arithmetic mean and pretreatment EPG. the two methods only agreed in declaring resistance of Oesophagostomum spp. to levarnisole in the aforementioned farm. The resistance of Oesophagostomum spp. isolate against levarnisole (Wormicid" - Cosmos Ltd. Kenya) was confirmed using the LOA test. Although Ascarex! (piperazine-Cosmos Ltd Kenya) was the commonly used drug by the farmers. samples of this drug tested using the FECRT method showed that it was less effective than Piperazine citrate'" (100% piperazine citrate-Kela Laboratoria, O.V.. Belgium) in all the farms studied. All the Asuum isolates were susceptible to the drugs tested. Risk factors for development of AR such as continuous use of anthelmintic for a prolonged period of time. and possibility of underdosing due to the use of visual appraisal in estimation of body weight were found to be present in the farms studied and as such could have contributed to the occurrence of AR. In conclusion. the results of this study demonstrate that despite the extensive use of anthelrnintics. the GI nematode infections were prevalent in the area of study. To increase productivity of pigs in the study area it is suggested that control of GI nematodes be based on proper management practises such as appropriate strategic anthelmintic treatments. regular removal of dung and cleaning of floors. This study demonstrated the occurrence of AR. as well as factors that can be associated with its occurrence. This calls for concerted efforts between researchers. pharmaceutical companies and veterinarians to make the farmers aware of the problem and consequences of AR. Measures should be taken to control the development of AR and its spread such as annual rotation of drugs of different classes. proper weighing of animals before dosing with drugs and popuIarisation of anthelmintic alternative control programmes.