Susceptible trichostrongyloid species mask presence of benzimidazole-resistant Haemonchus contortus in cattle

Abstract

Background Benzimidazole (BZ) anthelmintics are widely used to control infections with parasitic nematodes, but BZ resistance is an emerging threat among several nematode species infecting humans and animals. In Sudan, BZ-resistant Haemonchus contortus populations were recently reported in goats in South Darfur State. The objective of this study was to collect data regarding the situation of BZ resistance in cattle parasitic nematodes in South Darfur using phenotypic and molecular approaches, besides providing some epidemiological data on nematodes in cattle. Methods The faecal egg count reduction test and the egg hatch test (EHT) were used to evaluate benzimidazole efficacy in cattle nematodes in five South Darfur study areas: Beleil, Kass, Nyala, Rehed Al-Birdi and Tulus. Genomic DNA was extracted from pools of third-stage larvae (L3) (n = 40) during trials, before and after treatment, and pools of adult male Haemonchus spp. (n = 18) from abattoirs. The polymorphisms F167Y, E198A and F200Y in isotype 1 β-tubulin genes of H. contortus and H. placei were analysed using Sanger and pyrosequencing. Results Prevalence of gastro-intestinal helminths in cattle was 71% (313/443). Reduced albendazole faecal egg count reduction efficacy was detected in three study areas: Nyala (93.7%), Rehed Al-Birdi (89.7%) and Tulus (88.2%). In the EHT, EC50 values of these study areas ranged between 0.032 and 0.037 µg/ml thiabendazole. Genus-specific PCRs detected the genera Haemonchus, Trichostrongylus and Cooperia in L3 samples collected after albendazole treatment. Sanger sequencing followed by pyrosequencing assays did not detect elevated frequencies of known BZ resistance-associated alleles in codon F167Y, E198A and F200Y in isotype 1 β-tubulin gene of H. placei (≤ 11.38%). However, polymorphisms were detected in H. contortus and in samples with mixed infections with H. contortus and H. placei at codon 198, including E198L (16/58), E198V (2/58) and potentially E198Stop (1/58). All pooled L3 samples post-albendazole treatment (n = 13) were identified as H. contortus with an E198L substitution at codon 198. Conclusions To the knowledge of the authors, this is the first report of reduced albendazole efficacy in cattle in Sudan and is the first study describing an E198L substitution in phenotypically BZ-resistant nematodes collected from cattle.

Absence of Polymorphisms in Codons 167, 198 and 200 of All Seven β-Tubulin Isotypes of Benzimidazole Susceptible and Resistant Parascaris spp. Specimens from Australia

“…Initially, the amino acid exchanges F200Y [ 21 , 22 ], F167Y [ 23 , 24 ] and sometimes E198A [ 25 ] were predominantly reported in many resistant parasite populations. Recently, additional exchanges in codons 198, in particular E198L and E198V in resistant strongyle nematodes, have raised attention at least in some geographical regions [ 26 , 27 , 28 , 29 , 30 , 31 ]. Based on the knowledge that these mutations can confer resistance to BZs, epidemiological surveys have been established to rapidly identify BZ-resistant parasite populations, using methods such as pyrosequencing [ 26 , 27 , 28 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ], droplet digital PCR [ 31 , 40 ] or deep amplicon sequencing [ 29 , 41 ].…”

Confounding factors affecting faecal egg count reduction as a measure of anthelmintic efficacy

“…In mixed-species GIN infections in sheep in Scotland, FECR indicated AE of 65–77%, but Teladorsagia circumcincta dominated post-treatment FEC and was more highly resistant to both BZD and ML than undifferentiated FECR would suggest [ 59 ]. In cattle in Sudan, resistant Haemonchus contortus was found in cattle despite FECR exceeding 95% because of their low abundance relative to other species such as H. placei [ 68 ]. High levels of AR in minority species can therefore be missed by FECRT unless specific identification is included.…”

Resistance of bovine gastrointestinal nematodes to four classes of anthelmintics in the semiarid region of Paraíba state, Brazil

“…On the other hand, Soutello et al (2007) detected anthelmintic resistance on only 20% (5/25) of the farms examined, with an average FECR of 75.9%. In Sudan, Mohammedsalih et al (2021) reported that a reduction (< 90%) in the effectiveness of albendazole on bovine gastrointestinal nematodes had occurred.…”

“…The resistance of bovine gastrointestinal nematodes to most drugs available on the market has become an emerging problem worldwide (O'Shaughnessy et al, 2014;Rose et al, 2015;Berk et al, 2016;Lobayan et al, 2017;Baiak et al, 2019). In several countries, there are high rates of resistance, such as in New Zealand (Leathwick & Luo, 2017), Australia (Bullen et al, 2016), Germany, Belgium and Sweden (Demeler et al, 2009), Sudan (Mohammedsalih et al, 2021), United States (Gasbarre, 2014) and Argentina (Cristel et al, 2017). In Brazil, there have been reports of resistance to benzimidazoles (Ramos et al, 2020;Fávero et al, 2020), macrocyclic lactones (Neves et al, 2014;Borges et al, 2015;Ramos et al, 2020), imidazothiazoles (Neves et al, 2014;Ramos et al, 2020) and salicylanilides (Silva et al, 2017;Ramos et al, 2020).…”