Poor parasite management leads to drug resistance

The combination of good summer rainfall in most parts of the country and warm weather has resulted in favourable conditions for the hatching of internal parasites.

According to the latest report from the Ruminant Veterinary Association of South Africa (RuVASA), roundworm infestations, especially of wireworm, had been reported in all provinces, while incidents of resistance were reported in most. Coccidiosis infestations were reported in all provinces except Mpumalanga.

Dr Faffa Malan, managing director of RuVASA, said ignorance and the irresponsible use of antiparasitic products were the main causes of failures in anthelmintics (antiparasitic drugs).

“We have only 10 registered active dewormer groups in South Africa.

“Some farmers, unfortunately, only make use of dewormers for internal parasite management, and then when they run into resistance problems, they switch to another group.”

He said a faecal egg count reduction test (FECRT) needed to be carried out yearly to establish whether the dewormers used on the farm were still effective.

In the report, Malan, and other veterinary specialists Dr Gareth Bath and Dr Jan van Wyk, advised farmers to use a holistic management approach to combat antiparasitic resistance.

According to them, the old approach of ‘dosing clean’ needed to be abandoned, and a system of targeted selective treatment needed to be followed instead. Only animals that needed to be treated should thus be treated.

Instead of dosing an entire herd, animals needed to be separated into groups, according to their vulnerability. Lambs, weanlings, in-lamb and lactating ewes, for example, were more susceptible to internal parasites than other animals. The groups needed to be grazed, treated and managed as distinct entities.

New animals needed to be quarantined for at least four weeks in a wormunfriendly pen, such as bare earth or concrete, and treated intensively using the most suitable drugs and treatment schedule.

An FECRT could also be run to ensure minimum carry-over of drug-resistant parasites. Furthermore, low faecal egg counts and the FAMACHA chart could be used to select rams and ewes resistant to, or resilient against, wireworm.

Measures also needed to be taken to reduce the parasitic load in camps; this, in turn, would result in lower infection rates.

It could be done by resting camps for at least three months in subtropical and temperate climates, and at least one month in tropical climates.

In addition, farmers needed to establish which parasites were most prevalent in their areas, and consult their veterinarians about the best treatment.

Medicines needed to be given exactly according to instructions. – Glenneis Kriel