Reliability and reproducibility of the larval paralysis test as an in vitro method for the detection of anthelmintic resistance of nematodes against levamisole and morantel tartrate.
In order to study the reliability of the larval paralysis test as an in vitro assay for the detection of resistance of nematodes to levamisole and morantel tartrate, the influence of different parameters was evaluated using resistant and susceptible Ostertagia ostertagi strains. The operator, the sample (10% of the larvae present in the suspension), the incubation time (24, 48 or 72 h), the incubation temperature (20 or 25 degrees C) and the observation period of the larvae (5 or 15 s) had no statistically significant influence on the test results. Statistical differences were obtained only when L3 larvae of different ages (1 or 2 months) were used. Reversibility of the paralysis did not occur when concentrations of levamisole of less than or equal to 200 micrograms ml-1 or morantel tartrate of less than 2000 micrograms ml-1 were used. The reproducibility of the test was fairly good, with a mean standard deviation of 21.3% for the LC50 values. Morantel resistance in a strain of O. ostertagi was not confirmed as such by the larval paralysis test. The resistance factor was less than or equal to 1, in spite of an efficacy of morantel of 77.4% as shown in vivo.
Geerts
S
S
Institute of Tropical Medicine, Antwerp, Belgium.
Brandt
J
J
Borgsteede
F H
FH
Van Loon
H
H
D000818:Animals; D004351:Drug Resistance; D007814:Larva / Q000187:drug effects; D007978:Levamisole / Q000494:pharmacology*; D009015:Morantel / Q000494:pharmacology*; D010028:Ostertagia / Q000187:drug effects*; D011743:Pyrimidines / Q000494:pharmacology*; D013048:Specimen Handling; D013696:Temperature; D013997:Time Factors
D011743:Pyrimidines; D007978:Levamisole; D009015:Morantel