While surveys in Southern Africa indicate anthelmintic resistance of
gastrointestinal nematodes to be common in small ruminants in South
Africa, Kenya and Zimbabwe, there have been no reports of resistance in
Zambia. The objective of this study was to determine whether
anthelmintic resistance occurs in Zambia, and to obtain information on
nematode control practices in the country. During the rainy season
six commercial sheep farms were
selected in and around Lusaka and Chisamba. Worm control practices were
gauged by means of a questionnaire, and the Faecal Egg Count Reduction
Test was performed for assessing anthelmintic efficacy of albendazole,
levamisole and ivermectin. On all farms, anthelmintic treatment was the
only approach used to control nematode infections. Frequency of
treatment varied from twice a year to every 6 weeks and drugs of different
anthelmintic groups were alternated within the same year. There was a
wide range in faecal egg counts of individual sheep before treatment,
with some individual counts of up to 87 000. Larval identification
showed that Haemonchus was almost the only genus recovered from the
faecal cultures before and after treatment. Albendazole resistance was
found on five of the six farms. On each of the four farms where ivermectin gave
less than 95% reduction in egg counts, there was resistance to
albendazole as well. Levamisole showed an efficacy of 95% or higher on
all six farms.
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