Discriminatory dose of nitroxynil and albendazole sulfoxide using a modified egg hatch test of Fasciola hepatica

Fasciolosis is a food-borne anthropozoonotic disease caused by Fasciola spp. that affects multiple hosts, including ruminants and humans. In vitro testing of anthelmintics is of interest to establish the drug's activity without the need for time-consuming and expensive in vivo assays. This study was set to establish a discriminatory dose (DD) by running a dose-titration in vitro experiment (egg hatch test, EHT) of albendazole sulfoxide (ABZ.SO) and nitroxynil (NTX) on eggs of a field strain of Fasciola hepatica. Eggs were recovered from adult parasites isolated from intact bovine livers obtained from a single farm in Paraná, Brazil (FhPar2022 strain) with no ABZ or NTX treatment history. Two hundred eggs were exposed to 18 and 14 concentrations of ABZ.SO and NTX, respectively, for 12h and incubated for 16 days. Egg development and integrity were determined every other day, establishing an index of morphological modification of the different phases. A concentration-dependent effect was observed for egg development in both compounds. ABZ.SO solutions prevent egg hatch, except for the two lowest concentrations. We observed no egg hatch at 6.250-100.0 μmol L^-1 for NTX. NTX had an inhibition concentration of 50% (IC₅₀) of 0.043 μmol L^-1 with a correlation coefficient of (R²) 0.961. ABZ.SO had an IC₅₀ of 0.00099 μmol L^-1 with a low R² of 0.417. Morphological damage was also associated with the increasing concentration of both drugs. Moreover, it was noted that most eggs that reached the eye spot type could hatch, except at 0.39 and 3.12 μmol L^-1 of NTX. In ABZ.SO, hatching occurred only at 0.00038, 0.0007, and 0.0015 μmol L-1 concentrations. The obtained DDs of 0.043 μmol L^-1 for NTX and 0.00099 μmol L^-1 for ABZ.SO can be used to monitor efficacy in field isolates.