A two-year epidemiology study of helminths of small ruminants involved the collection of
viscera from 655 sheep and 632 goats from 4 abattoirs in eastern Ethiopia. A further more
detailed epidemiology study of gastro-intestinal nematode infections used the Haramaya
University (HU) flock of 60 Black Head Ogaden sheep. The parasitological data included
numbers of nematode eggs per gram of faeces (EPG), faecal culture L3 larvae, packed red
cell volume (PCV), adult worm and early L4 counts, and FAMACHA eye-colour score
estimates, along with animal performance (body weight change).
There were 13 species of nematodes and 4 species of flukes present in the sheep and
goats, with Haemonchus contortus being the most prevalent (65–80%), followed by
Trichostrongylus spp. The nematode infection levels of both sheep and goats followed the
bi-modal annual rainfall pattern, with the highest worm burdens occurring during the two
rain seasons (peaks in May and September). There were significant differences in worm
burdens between the 4 geographic locations for both sheep and goats. Similar seasonal but
not geographical variations occurred in the prevalence of flukes. There were significant
correlations between EPG and PCV, EPG and FAMACHA scores, and PCV and
FAMACHA scores. Moreover, H. contortus showed an increased propensity for arrested
development during the dry seasons.
Faecal egg count reduction tests (FECRT) conducted on the HU flocks, and flocks in
surrounding small-holder communities, evaluated the efficacy of commonly used
anthelmintics, including albendazole (ABZ), tetramisole (TET), a combination (ABZ +
TET) and ivermectin (IVM). Initially, high levels of resistance to all of the anthelmintics
were found in the HU goat flock but not in the sheep. In an attempt to restore the
anthelmintic efficacy a new management system was applied to the HU goat flock,
including: eliminating the existing parasite infections in the goats, exclusion from the
traditional goat pastures, and initiation of communal grazing of the goats with the HU sheep
and animals of the local small-holder farmers. Subsequent FECRTs revealed high levels of
efficacy of all three drugs in the goat and sheep flocks, demonstrating that anthelmintic
efficacy can be restored by exploiting refugia.
Individual FECRTs were also conducted on 8 sheep and goat flocks owned by
neighbouring small-holder farmers, who received breeding stock from the HU. In each
FECRT, 50 local breed sheep and goats, 6–9 months old, were divided into 5 treatment
groups: ABZ, TET, ABZ + TET, IVM and untreated control. There was no evidence of
anthelmintic resistance in the nematodes, indicating that dilution of resistant parasites,
which are likely to be imported with introduced breeding goats, and the low selection
pressure imposed by the small-holder farmers, had prevented anthelmintic resistance from
emerging.