Multiple anthelmintic drug resistance in hookworms (Ancylostoma caninum) in a Labrador breeding and training kennel in Georgia, USA

Anthelmintic Resistance in Ancylostoma caninum: A Comprehensive Review

Ancylostoma caninum, a zoonotic hookworm species, significantly affects the global health of companion animals, humans and wildlife populations. This parasitic infection is prevalent in various environments, particularly in regions with warm climates, and affects a wide range of canids, including dogs, where it is most commonly found. A. caninum is a major concern not only due to its zoonotic potential but also because of its growing resistance to anthelmintic treatments. The development of resistance in parasitic species is primarily driven by genetic mutations that allow the parasite to survive treatment with commonly used drugs and presents a serious challenge to parasite control efforts. This review explores the biology and epidemiology of A. caninum, focusing on the mechanisms and prevalence of anthelmintic resistance. By reviewing worldwide studies, this paper highlights the prevalence of resistance across different anthelmintic classes and its implications for veterinary and public health. The findings emphasize the need for better management strategies and innovative solutions to address this growing problem.

Investigation of risk factors associated with Ancylostoma spp. infection and the benzimidazole F167Y resistance marker polymorphism in dogs from the United States

Ancylostoma caninum is the most significant intestinal nematode parasite of dogs. We acquired fecal surveillance data from a large population of dogs in the United States (US). A diagnostic test using real-time PCR (qPCR) for Ancylostoma spp. and allele-specific qPCR detecting the SNP F167Y in the isotype 1 of the Beta-tubulin gene, was used in 885,424 randomized canine fecal samples collected between March 2022 and December 2023. Overall, Ancylostoma spp. had a prevalence of 1.76% (15,537/885,424), with the highest in the South 3.73% (10,747/287,576), and the lowest in the West 0.45% (632/140,282). Within the subset of Ancylostoma spp.-detected dogs used for further analysis, the F167Y SNP had an overall prevalence of 14.44% with the highest in the West and the lowest in the Midwest (10.76%). The greyhound exhibited a higher prevalence of Ancylostoma spp. infections (17.03%) and a higher prevalence of the F167Y polymorphism (33.6%) compared to non-greyhounds (13.7% and 2.08%), respectively, but were not associated with the highest risk for the F167Y polymorphism. Sex did not influence hookworm infection nor F167Y polymorphism prevalence. Intact dogs had a prevalence of hookworm infection and F167Y polymorphism of 3.88% and 15.66%, respectively. Puppies showed increased prevalence of hookworms (3.70%) and the F167Y SNP (17.1%). Greyhounds, bluetick coonhounds, and boerboels had the highest relative risks for hookworm infection, while Cavalier King Charles spaniels, Havanese, and shiba inus had the lowest. The top and bottom three with the highest and lowest RR for the F167Y SNP were the old English sheepdog, American foxhound, and toy poodle Toy, and shih tzu, Maltese, and Australian cattle dogs, respectively. This study highlights the value of an accessible diagnostic qPCR test with fast turnaround in unraveling the molecular epidemiology of hookworms and benzimidazole resistance, as well as explore potentially important risk factorsin dogs with routine veterinary care.

Unraveling the mechanisms of benzimidazole resistance in hookworms: A molecular docking and dynamics study

BACKGROUND

Benzimidazole resistance is an emerging challenge among parasitic helminths. It is caused by single nucleotide polymorphisms (SNPs) in specific loci in helminths' β-tubulin genes. Field studies and laboratory investigations reported resistance-associated SNPs in 4 codon locations with 7 allelic variations among hookworms. This study aimed to determine the effects of these mutations on the binding efficiency and behavior of the β-tubulin protein in four hookworm species against four benzimidazole drugs.

METHODS

β-tubulin gene coding sequences of Ancylostoma caninum, A. duodenale, A. ceylanicum, and Necator americanus were retrieved, assessed phylogenetically, and used to construct the 3D structure models of the proteins. The modeled protein structures were verified and edited to contain the reported SNPs: Q134H, F167Y, E198A, E198K, E198V, F200L, and F200Y. Benzimidazole drugs such as albendazole (ABZ), fenbendazole (FBZ), mebendazole (MBZ) and oxfendazole (OBZ) were used as ligands. Molecular docking experiments were performed with the wild-type and mutated proteins. Molecular dynamics simulation assessed the dynamic behavior of the β-tubulin-benzimidazole complex.

RESULTS

In silico docking assessments showed that various amino acid substitutions due to resistance-associated SNPs cause alterations in binding affinities and positions. E198K and Q134H in hookworm β-tubulins substantially weakened the binding affinities and altered the binding positions of benzimidazole drugs. Molecular dynamics analysis revealed that these mutations also caused marked reductions in the binding free energies owing to diminished hydrogen bond contacts with the benzimidazole ligands.

CONCLUSION

The evidence shown herein indicates that mutations at positions 198 and 134 are detrimental to conferring benzimidazole resistance among hookworms. The presence of these mutations may alter the efficacy of pharmacological interventions. Hence, further studies should be conducted to assess their emergence among hookworms in endemic areas with histories of chemotherapy.

Survey on canine hookworms: Knowledge, perceptions and practices among U.S. veterinarians

Canine hookworms (Ancylostoma caninum) are highly prevalent in pet dogs in the United States of America (U.S.). They pose a significant health risk to infected dogs and are also a potential risk to humans as zoonotic agents. Veterinarians play a crucial role in managing this threat through the diagnosis and treatment of infections in pet dogs. However, the rising incidence of anthelmintic resistance in U.S. hookworm populations necessitates increased awareness among veterinarians. To determine U.S. veterinarian's knowledge, perceptions and practices about canine hookworms, a cross-sectional online survey was administered between February and December 2022. 208 veterinarians from 43 states participated in the study. Only 65 % of veterinarians reported awareness of hookworm prevalence. Hookworm infected dogs were encountered more frequently in the South than in Western states. Veterinarians perceived that hookworms were present in all breeds without breed predilection followed by mixed breeds, pit bulls and hound breeds. Most respondents reported that infections were rarely symptomatic, highlighting the importance of diagnostic testing. In-clinic diagnostic modalities were most preferred. Fenbendazole and pyrantel pamoate were the most commonly used anthelmintics. Most veterinarians followed up on infected dogs but retesting time after treatment varied. Awareness of multi-drug resistant hookworms was high but encountering persistent hookworm cases was lower. Veterinarians frequently educated clients about hookworms and prevention, but less about the zoonotic potential. This study provides insights for improving awareness, diagnostics, treatment protocols, and client education regarding canine hookworms in the U.S.. Overall, veterinarians play an active role in hookworm prevention and control.

Benzimidazole resistance-associated mutations improve the in silico dimerization of hookworm tubulin: An additional resistance mechanism

Background and Aim

Mutations in the β-tubulin genes of helminths confer benzimidazole (BZ) resistance by reducing the drug's binding efficiency to the expressed protein. However, the effects of these resistance-associated mutations on tubulin dimer formation in soil-transmitted helminths remain unknown. Therefore, this study aimed to investigate the impact of these mutations on the in silico dimerization of hookworm α- and β-tubulins using open-source bioinformatics tools.

Materials and Methods

Using AlphaFold 3, the α- and β-tubulin amino acid sequences of Ancylostoma ceylanicum were used to predict the structural fold of the hookworm tubulin heterodimer. The modeled complexes were subjected to several protein structure quality assurance checks. The binding free energies, overall binding affinity, dissociation constant, and interacting amino acids of the complex were determined. The dimer's structural flexibility and motion were simulated through molecular dynamics.

Results

BZ resistance-associated amino acid substitutions in the β-tubulin isotype 1 protein of hookworms altered tubulin dimerization. The E198K, E198V, and F200Y mutations conferred the strongest and most stable binding between the α and β subunits, surpassing that of the wild-type. In contrast, complexes with the Q134H and F200L mutations exhibited the opposite effect. Molecular dynamics simulations showed that wild-type and mutant tubulin dimers exhibited similar dynamic behavior, with slight deviations in those carrying the F200L and E198K mutations.

Conclusion

Resistance-associated mutations in hookworms impair BZ binding to β-tubulin and enhance tubulin dimer interactions, thereby increasing the parasite's ability to withstand treatment. Conversely, other mutations weaken these interactions, potentially compromising hookworm viability. These findings offer novel insights into helminth tubulin dimerization and provide a valuable foundation for developing anthelmintics targeting this crucial biological process.

Hookworm Anthelmintic Resistance: Novel Fecal Polymerase Chain Reaction Ancylostoma caninum Benzimidazole Resistance Marker Detection in a Dog

A 4 yr old castrated male greyhound presented with a history of chronic (>3 wk) intermittent diarrhea. Initial fecal analysis identified infection with Ancylostoma caninum. Despite treatment with routine anthelmintics, the dog remained persistently A caninum positive for several months. A novel fecal gastrointestinal real-time polymerase chain reaction (qPCR) parasite panel detected A caninum and the genetic benzimidazole (BZ) F167Y resistance marker in multiple samplings over 48 hr. This finding, together with the dog's clinical signs (diarrhea) and lack of response to routine anthelmintics, prompted treatment with cyclooctadepsipeptide emodepside, a drug currently not registered for dogs in the United States. The dog's clinical signs resolved and post-treatment fecal qPCR testing was negative. However, 5 mo later, retesting with fecal qPCR detected A caninum and concurrent BZ resistance marker, as well as Giardia. A presumptive diagnosis of re-infection was made and the emodepside treatment was continued. The dog again reverted to undetected (A caninum and the 167 resistance marker) on reassessment fecal qPCR. This case report describes the use of a novel fecal qPCR panel for gastrointestinal parasites, persistent hookworm and BZ F167Y resistance marker detection in a dog, and highlights the importance of a stepwise approach to clinical management, treatment, and retesting.

Altered larval activation response associated with multidrug resistance in the canine hookworm Ancylostoma caninum

Parasitic gastrointestinal nematodes pose significant health risks to humans, livestock, and companion animals, and their control relies heavily on the use of anthelmintic drugs. Overuse of these drugs has led to the emergence of resistant nematode populations. Herein, a naturally occurring isolate (referred to as BCR) of the dog hookworm, Ancylostoma caninum, that is resistant to 3 major classes of anthelmintics is characterized. Various drug assays were used to determine the resistance of BCR to thiabendazole, ivermectin, moxidectin and pyrantel pamoate. When compared to a drug-susceptible isolate of A. caninum, BCR was shown to be significantly resistant to all 4 of the drugs tested. Multiple single nucleotide polymorphisms have been shown to impart benzimidazole resistance, including the F167Y mutation in the β-tubulin isotype 1 gene, which was confirmed to be present in BCR through molecular analysis. The frequency of the resistant allele in BCR was 76.3% following its first passage in the lab, which represented an increase from approximately 50% in the founding hookworm population. A second, recently described mutation in codon 134 (Q134H) was also detected at lower frequency in the BCR population. Additionally, BCR exhibits an altered larval activation phenotype compared to the susceptible isolate, suggesting differences in the signalling pathways involved in the activation process which may be associated with resistance. Further characterization of this isolate will provide insights into the mechanisms of resistance to macrocyclic lactones and tetrahydropyrimidine anthelmintics.