Indiscriminate Use of Anthelmintics and its Implications on Human Health
Dr. Monika, Dr. Gayatri Gujar
Department of Veterinary Parasitology
College of Veterinary and Animal Science, Bikaner
Rajasthan University of Veterinary and Animal Sciences,
Bikaner-334001, India
There is an array of veterinary drugs that is used to treat livestock disease, such as aminoglycosides, macrolides, tetracyclines, b-agonists, and anthelmintics. Among these, anthelmintics (also called parasiticides, endectocides, and nematocides), are usually used to treat parasitic worm infections, including flatworms (tapeworms and flukes) and roundworms (nematodes), which usually infect human, livestock, and crops, affecting food production. For instance, gastrointestinal nematodes are parasites that cause important economic losses to livestock worldwide due to reduced appetite, lower body weights, reduced egg production (poultry), and death.
To combat helminthiasis, several approaches have been proposed including regulation of parasitic vectors populations, zootechnical strategies, and breeding of resistant animals. However, treatment with anthelmintics is the option most widely used as vaccines have proven ineffective till date.
Worm control in most farms is exclusively based on anthelmintic treatments rather than on management practices that embraces integrated strategies.
The currently available anthelmintics belong to different drug classes, i.e.
- Macrocyclic lactones (MLs)
- Benzimidazoles (BZs)
- Tetrahydropyrimidines-imidazothiazoles
- Aminoacetonitrile derivatives (AADs)
- Spiroindoles
In general, broad-spectrum anthelmintics are effective, although most of them are usually used for specific infections. However, over the years there has been continuous and significant development of anthelmintic resistance by the parasitic worms infecting livestock. Anthelmintic resistance can be defined as the ability of parasites to survive doses of drugs that would normally kill parasites of the same species and stage. It is inherited and selected for because the survivors of treatments pass genes for resistance onto their offspring. These resistant genes are initially rare in the population or arise as rare mutations, but as selection continues, their proportion in the population increases as does the proportion of resistant parasites
New compounds have been developed to overcome drug resistance to conventional anthelmintics caused by direct exposure of helminths to the drug at therapeutic doses.
Moreover, the presence of anthelmintic residues in livestock may have serious consequences on consumers, and international organizations and governments have established maximum residue limits (MRLs) of these compounds in several matrices, in order to assure food safety. The unauthorized or incorrect use of anthelmintics can result in the introduction of harmful residues into the food chain.
Although anthelmintics are effective against worms, they may also affect the host itself based on the same biochemical mechanism that operates against the parasite or by specific mechanism to the host.
The widespread use of anthelmintics implies the possibility of the presence of residues in edible tissues, and toxic effects in humans could be associated with chronic exposure to these compounds, such as:
- Teratogenicity
- Congenital malformations
- Diarrhea
- Anemia
- Pulmonary edema
- Necrotic lymphadenopathy
Although anthelmintics are more toxic to parasites than mammals, food produced from treated animals should not contain residues of such drugs which would pose a food safety risk. Therefore, the need of the hour is to establish MRLs of these drugs in foodstuffs by national and international organizations.
Furthermore, the development of resistance to the currently used anthelmintics is an issue of increasing importance. In this sense, the development of new compounds, such as AAD, are needed in order to improve the characteristics of conventional classes of anthelmintics such as lower toxicity, favorable pharmacokinetic properties, and broad-spectrum capacities.
https://www.pashudhanpraharee.com/anthelminthic-resistance-an-overview/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC100151/
