Genotypic profile of benzimidazole resistance associated with SNP F167Y in the beta-tubulin gene of Necator americanus helminths obtained from Brazilian populations.

Necator americanus is a worm that parasites the small intestine of humans and is highly prevalent in regions with poor sanitary conditions. The main strategy to control this helminth is by mass benzimidazole administration, however, periodic use of these drugs can select strains of parasites resistant to treatment. Single nucleotide polymorphisms (SNPs) in the beta-tubulin isotype 1 gene located at codons 167, 198 and 200 have been associated with benzimidazole resistance in some nematodes. Previously, our group detected the presence of some of these SNPs in populations of soil-transmitted helminths collected in different locations in Brazil. Here, we evaluated the SNP at codon 167, which has recently been shown to be associated with failure of benzimidazoles to treat N. americanus. Our ARMS-PCR analyses were performed using 524 single N. americanus eggs from 48 patients' feces collected in six Brazilian states; however, we did not detect any mutated samples at codon 167. This study builds on previous work, helping us monitor the presence of resistance-related genotypes in Brazilian helminth populations. The data presented here can assist in the implementation of future control strategies.

The effect of tribendimidine and its metabolites against Necator americanus in golden hamsters and Nippostrongylus braziliensis in rats.

The antinematode effect of tribendimidine (TBD) and its metabolites has been studied. A total of 107 hamsters were each infected with 250 Necator americanus third stage infective larvae (NaL3) for 25 days. In the first test, 75 hamsters were divided equally into 15 groups for determination of ED(50) and ED(90.) Among them, five groups were treated orally with TBD or its metabolite, p-(1-dimethylamino ethylimino)aniline (aminoamidine, deacylated amidantel, BAY d 9216, dADT), at single doses of 1, 2, 4, 8, and 16 mg/kg. The remaining five groups were administered with acetylated dADT (AdADT) at single oral doses of 8, 12, 18, 24, and 30 mg/kg. In the second test, 20 hamsters were equally divided into four groups. Two groups were treated intramuscularly with TBD and dADT at a single dose of 16 mg/kg, while in the remaining two groups, single intramuscular dose of AdADT 15 or 30 mg/kg was administered. In the third test, two groups of six hamsters were treated orally with terephthalaldehyde (TPAL) and terephthalic acid (TPAC) at a single dose of 1,000 mg/kg. Other 85 rats, each infected with 300 Nippostrongylus braziliensis third stage infective larvae (NbL3), were used in three tests. For determination of ED(50) and ED(90) in the first test, five groups of five rats were treated orally with TBD or dADT at single doses of 3.0, 4.2, 5.9, 8.2, and 11.5 mg/kg or 2.0, 2.9, 4.2, 6.1, and 8.8 mg/kg, respectively. In the second test, three groups of eight to nine rats were treated orally with TBD at a single 8.4-mg/kg dose (ED(90)) and AdADT 100 or 200 mg/kg, respectively. In the third test, two groups of four rats were treated orally with TPAL and TPAC at a single dose of 1,000 mg/kg. Twenty-four to 48 h post-treatment, all the feces of each hamster and rat were collected for recovery of worms expelled from the feces. Following this period, all of the animals were sacrificed, and the adult hookworm or N. braziliensis from small intestine and large intestine were recovered and counted for calculation of worm burden reduction. The results showed that the ED(50) and ED(90) for TBD, dADT, and AdADT determined in treatment of N. americanus-infected hamsters were 1.849 and 13.598, 3.922 and 54.354, as well as 20.966 and 51.633 mg/kg, respectively. In intramuscular administration of TBD and dADT at single dose of 16 mg/kg or AdADT 30 mg/kg, similar worm burden reductions of 71.4-76.3% were observed. Two other metabolites, i.e., TPAL and TPAC, exhibited no effect against N. americanus. The ED(50) and ED(90) for TBD and dADT determined in treatment of rats infected with N. braziliensis were 3.234 and 8.435, as well as 2.345 and 5.104 mg/kg. Oral administration of AdADT at a higher single dose of 100 or 200 mg/kg resulted in worm burden reductions of 11.9-46.3%, which was significantly lower than 84.5% of worm burden reduction obtained from rats treated with TBD 8.4 mg/kg. The results indicate that in oral administration, TBD exhibits slightly better effect against N. americanus in hamsters than dADT, but AdADT possesses less effect; TBD, dADT, and AdADT show promising effect in intramuscular treatment of N. americanus-infected hamsters; the effect of oral dADT against N. braziliensis in rats is somewhat better than TBD, while AdADT endorses poor effect; and TPAL and TPAC are ineffective metabolites of TBD against both species of nematodes.