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Investigation of intestinal nematode responses to naphthalophos and pyrantel using a larval development assay
A C Kotze1, P A Stein, R J Dobson
1CSIRO Animal Production, McMaster Laboratory, Blacktown, NSW, Australia. a.kotze@amprodcsiro.au
Abstract:
Responses of several nematode species to naphthalophos and pyrantel/levamisole were examined using a larval development assay in order to determine the potential of this assay for detection of resistance. Haemonchus contortus and Ostertagia circumcincta showed concentration-dependent responses to naphthalophos, however, the assay was unsuitable for Trichostrongylus colubriformis due to the low toxicity of the drug to the larval stages of this nematode. Measurement of concentration-dependent response to pyrantel in susceptible T. colubriformis was limited by a reduced toxicity against larvae at high drug concentrations, resulting in a parabolic response with a development-inhibition maxima of less than 100%. This limits the usefulness of the assay to detect pyrantel resistance in this species as the presence of a small resistant fraction in a field isolate may be indistinguishable from the parabolic susceptible response. On the other hand, responses of susceptible T. colubriformis to levamisole, and susceptible H. contortus to pyrantel and levamisole showed 100% development inhibition over a range of drug concentrations, indicating that the appearance of a resistant fraction in a field population would be readily discernible from the susceptible response, allowing resistance detection for these drug/parasite combinations. This study has highlighted the varied suitability of the larval development assay technique for resistance detection with different combinations of drugs and parasite species.
Insights
The larval development assay shows promise for detecting nematode resistance to certain drugs like levamisole and pyrantel in Haemonchus contortus. However, its effectiveness varies across different parasite species and drug combinations.
Area of Science:
- Veterinary Parasitology
- Drug Resistance Studies
- Nematology
Background:
- Anthelmintic resistance in nematodes poses a significant threat to livestock health and productivity.
- Accurate detection of resistance is crucial for effective parasite control strategies.
- The larval development assay is a potential tool for assessing drug resistance in nematodes.
Purpose of the Study:
- To evaluate the suitability of the larval development assay for detecting resistance in various nematode species.
- To assess the efficacy of naphthalophos, pyrantel, and levamisole against different nematode larval stages.
- To determine the reliability of the assay for specific drug-parasite combinations.
Main Methods:
- Larval development assay was used to test nematode responses to different drug concentrations.
- Concentration-dependent responses were measured for Haemonchus contortus, Ostertagia circumcincta, and Trichostrongylus colubriformis.
- The assay's ability to distinguish susceptible from resistant parasite populations was analyzed.
Main Results:
- Haemonchus contortus and Ostertagia circumcincta showed concentration-dependent responses to naphthalophos.
- The assay was unsuitable for Trichostrongylus colubriformis with naphthalophos due to low toxicity.
- A parabolic response limited pyrantel resistance detection in T. colubriformis, unlike levamisole.
- Susceptible T. colubriformis and H. contortus showed 100% development inhibition with levamisole and pyrantel, indicating assay suitability.
Conclusions:
- The larval development assay's utility for detecting nematode resistance varies significantly depending on the drug and parasite species.
- The assay is effective for detecting levamisole resistance in T. colubriformis and pyrantel/levamisole resistance in H. contortus.
- Further validation is needed for other drug-parasite combinations to ensure reliable resistance detection.