The prevalence of gastrointestinal parasitism, control practices and occurence of anthelmintic resistance in commercial pig farms in Thika district, Kenya
Abstract
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.
Citation
Masters Degree in Veterinary ParasitologyPublisher
University of Nairobi Department of Veterinary Pathology, Mtcrobiology and Parasitology