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What are Anthelmintics?

Anthelmintics are a type of medicine that kills helminths. Helminths are worm-like parasites such as flukes, roundworms, and tapeworms.

It is important that anthelmintics are selectively toxic to the parasite and not the host. Some work by inhibiting metabolic processes that are vital to the parasite but absent or not vital in the host.

Other anthelmintics are poorly absorbe through the gut, which means the parasite is expose to much higher concentrations of the anthelmintic than the host. Starvation or paralysis or the parasite result, follow by subsequent expulsion or digestion.

Anthelmintic resistance

Anthelmintic resistance in parasites is now widespread. It is a major threat to the sustainability of modern ruminant livestock production, resulting in reduce productivity, compromise animal health and welfare, and increased greenhouse gas emissions through increase parasitism and farm inputs.

A database of publish and unpublish European AR research on gastrointestinal nematodes was collate in 2020.

The ability of parasites to survive treatments that are generally effective at the recommend doses is a major threat to the future control of worm parasites in small ruminants and horses.

This is especially true of nematodes, and has help spur development of aminoacetonitrile derivatives for treatment against drug-resistant nematodes, as well as exploration of doxycycline to kill their endosymbiotic Wolbachia bacteria.

The resistance is measure by the “fecal egg count reduction” value which varies for different types of helminths.

Treatment with an antihelminthic drug kills worms whose phenotype renders them susceptible to the drug, but resistant parasites survive and pass on their “resistance” genes. Resistant varieties accumulate, and treatment failure finally occurs.

Cestode anthelmintics

Tapeworms attach to the intestinal tract by a sucker or a sucking groove on the head (scolex). Unlike the nematodes and trematodes, tapeworms do not enter the host tissues. As a result, tapeworm infections in general are more easily treat than infections cause by worms that penetrate host tissues.

Nematode anthelmintics

Treatment of roundworms is complicate by the fact that some live in blood, lymphatics, and other tissues (filarial worms) and thus require use of drugs that are absorbed from the intestinal tract and penetrate into tissues. Others are found primarily or solely in the intestinal tract (intestinal nematodes).

Trematode anthelmintics

Praziquantel is the most effective drug in treating infections cause by intestinal, liver, and lung flukes and is the drug of choice in the treatment of schistosomiasis (infections of blood flukes).