Resistance of animal helminths to anthelmintics.

The research discusses the growing immunity of animal helminths, a type of worm parasite, to anthelmintics, the drugs used in their treatment. This resistance has caused numerous challenges for those treating worm infections in animals.

Understanding Anthelmintic Resistance

• The researchers define resistance as a significant increase in the ability of individuals within a strain to withstand doses of a compound, such as anthelmintics. These doses would typically be lethal to the majority of individuals in a normal population of the same species.
• Despite the introduction of broad-spectrum anthelmintics like phenothiazine and benzimidazole, resistant strains of parasitic helminths continue to develop.

The Impact of Anthelmintic Use

• An increase in the number of resistant helminths is associated with the widespread and often inappropriate use of anthelmintics. This growing immunity presents substantial challenges for chemotherapists working to treat helminth infections.
• Several species of ovine nematodes, or roundworms, have become resistant to anthelmintics following repeated exposures.

Documenting the Development of Resistance

• The first instances of Haemonchus contortus, a type of roundworm, showing resistance to phenothiazine were reported in the United States.
• Benzimidazole-resistant strains of these same roundworms have since been reported in the United States, as well as in Chile, Australia, South Africa, and West Malaysia.
• Two other helminth species, Trichostrongylus colubriformis and Ostertagia circumcincta, have also been found to develop resistance to these drugs.