Anthelmintic and acaricide resistance in small ruminants of North West Province, South Africa

Abstract

In South Africa, anthelmintic and acaricidal resistance is a growing problem and poses a real economic threat to communal livestock raised by rural communities. The development of new anthelmintic and acaricidal drug products is exceptionally costly, so it is important to trace errors that can be reversed to maximize production in rural smallscale farming. This study aimed to assess the level of anthelmintic and acaricide resistance in small stock in the North West province of South Africa. A questionnaire survey was conducted to assess treatment strategy and farm management practices to 86 small- scale farmers in North West province. Results indicated that small-scale farmers (89%) relied solely on the use of anthelmintics, while 11% did not practice any form of worm control practice. Worm infection was ranked the second most important constraint of productivity in livestock as compared to ticks. Most farms that used anthelmintics preferred Benzimidazoles (BZD) (89%), Oxytetracycline (OXY) (78.14%), Levamisole (LEV) (18%) and Macrocyclic lactones (ML) (3.44%). Generally, 58.97% of farmers treated 2 times a year. Treatments in most farms depended on visible clinical signs not the epidemiology of parasites. The most common risk factor associated with the occurrence of resistance in both districts was the use of anthelmintics without weighing the animals to determine the correct dosage. Limited farming experience was also shown as one of the risks based on the questionnaire results. The faecal egg count reduction test (FECRT%) was used to assess the development of anthelmintic resistance (AR) of BZD, LEV, and ML in sheep and goats of small holder farmers. Anthelmintic efficacy of 50% was considered as the threshold for development of AR. No significant difference was shown in nematode egg count after 14 days (p=0.380). High levels of AR development, particularly against BZD was detected. Unprecedented levels of AR appear to be enabled by under/overdosing and lack of drug rotation.

Egg hatch assay (EHA) and larval mortality assay (LMA) was used to determine AR at a discriminating dose (DD) of 0.1 μg/ml TBZ. The EHA and LMA results showed development of AR against TBZ in all districts. A strong correlation existed between FECRT, EHA, and LMA as tests confirmed the occurrence of AR in all the districts identified. Resistant nematodes after treatment were confirmed using polymerase chain reaction (PCR) targeting the Internal transcribed spacer 2 (ITS2) gene using genus specific primer pairs. PCR detected the presence of Haemonchus spp. and Oesophagostomum spp post AR tests. Haemonchus spp. was identified by coproculture, and PCR tests as the most dominant resistant nematode genera. Acaricidal resistance (ACR) against fluazuron 2.5% and flumethrin 1% (Drastic Deadline extreme®) (DDE) pour on was assessed using adult immersion test (AIT) on Rhipicephalus evertsi evertsi. Results obtained on trial showed high efficacy (>99%) against the ticks. Oviposition was inhibited, indicating ability of fluazuron 2.5% and flumethrin 1% to inhibit tick oviposition reproductive parameters of ticks. In both districts, this study reported the presence of ACR to GIN infections on sheep and goat farms, but no ACR was detected against the currently used acaricide.