Nationwide USA re-analysis of amplicon metabarcoding targeting β-tubulin isoform-1 reveals absence of benzimidazole resistant SNPs in Ancylostoma braziliense, Ancylostoma tubaeforme and Uncinaria stenocephala

Nationwide sampling by Venkatesan and colleagues (2023) described the resistance status of the canine hookworm, Ancylostoma caninum, to benzimidazoles across the USA via β-tubulin isotype-1 amplicon metabarcoding. In this study, we aimed to use the existing public amplicon metabarcoding data and mine it for the presence of β-tubulin isotype-1 sequences that belong to hookworm species other than A. caninum. Through bioinformatics analysis we assigned species to A. caninum, Ancylostoma braziliense, Ancylostoma tubaeforme and Uncinaria stenocephala. All non-A. caninum sequences contained only the benzimidazole susceptible residues of β-tubulin isotype-1. Using two β-tubulin isotype-1 metabarcoding sequence data (assay targeting 134 and 167 codons, and assay targeting 198 and 200 codons), 2.0% (6/307) and 2.9% (9/310) individual samples had hookworms other than A. caninum (A. braziliense n = 5, A. tubaeforme n = 4 and U. stenocephala n = 2), respectively. We identified one sample containing A. braziliense in each of the Northeastern region and Midwestern region, and in three samples from the Southern region. Presence of A. tubaeforme in dog faeces is considered as pseudoparasitism. There were no statistically significant regional differences for the distribution of each species, for either of the two assays independently or combined (χ2 tests, P > 0.05). Our work demonstrates the utility of the amplicon metabarcoding for the identification of species through antemortem assays, thus resolving the dilemma of assigning hookworm species based on either post-mortem or egg sizes for the identification of hookworms.

Ancylostoma in dogs in the Caribbean: a review and study from St. Kitts, West Indies

Background

Little is known about the prevalence of Ancylostoma in dogs in the Caribbean. In view of the number of owned free-roaming and feral dogs within the islands and the ideal subtropical climate for parasite development and environmental survival, Ancylostoma could pose a threat to the health of the dogs as well as a zoonotic risk to people.

Methods

To determine whether generalities about Ancylostoma in dogs in the Caribbean could be made and to obtain a better understanding of the prevalence, published (Scielo, Scopus, and PubMed databases) and gray (e.g., student theses, conference presentations) literature was reviewed. Retrieved manuscripts were screened, and relevant data (year, location, dog population, method of diagnosis, positivity rate) were extracted. Data from two dog populations on St. Kitts also were included: a 2014 field study involving dogs with limited veterinary care and data from the Ross University School of Veterinary Medicine’s Veterinary Clinic records for 2018–2019.

Results

Fourteen manuscripts from the 1950s to 2019, representing ten of the Caribbean islands/countries and the Bahamas, were identified. Methods of diagnosing infection status ranged from simple qualitative or quantitative flotation methods to centrifugation with Sheather’s sugar flotation solution or necropsy. Dog populations sampled included stray, owned free-roaming, and owned confined. Reported rates of Ancylostoma infection ranged from 10 to 91%. Studies from the last 10 years indicate positivity rates of 21 to 73%. Ancylostoma positivity rates in the St. Kitts’ populations were 61% and 10% for the 2014 and 2018–2019 populations, respectively.

Conclusions

There was no indication that hookworm prevalence has changed over time in the Caribbean, and there were no obvious differences between owned and unowned dogs or free-roaming and confined dogs. The data from St. Kitts were on par with positivity rates from the other islands within the last 10 years and reflective of the impact that veterinary care, including anthelmintic treatment, is expected to have on parasites in pets. There is a clear need to expand the available data for the region and improve control programs for Ancylostoma infections to protect both canine and human health.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05254-2.

Field application of a novel multiplex qPCR assay reveals the occurrence of the zoonotic hookworm Ancylostoma braziliense in Nigerian dogs

A number of gastrointestinal parasites have been reported to infect dogs in Nigeria, some of which have zoonotic potential. Of these, hookworms are the most prevalent, with both Ancylostoma caninum and Uncinaria stenocephala reported in the country. In this study, we subjected 203 hookworm microscopy-positive samples of the 885 individual faecal samples collected from dogs in Nigeria to a recently developed multiplex qPCR for the detection and characterisation of canine hookworm species. The qPCR demonstrated a diagnostic sensitivity of 98% (95% CI 95-99.4) allowing the detection of A. caninum and A. braziliense in 81.3% (165/203, 95% CI 75.3-86.1) and 51.2% (104/203, 95% CI 44.4-58) of the microscopy-positive faecal samples of dogs from Nigeria, respectively and 34.5% (70/203, 95% CI 28.3-41.3) of mixed infections with both hookworm species. The finding of A. braziliense is particularly worrisome given this is a well-known agent of persistent cutaneous larva migrans, commonly referred to as "creeping eruptions" in humans. Although this parasite has been diagnosed in locals and in people travelling in Nigeria suffering from dermatological illnesses, this represents the first molecular identification of A. braziliense in its canine reservoir in the country. These results update the occurrence and distribution of hookworm species affecting dogs in Nigeria highlighting the suitability of the newly developed multiplex qPCR assay as a high-throughput tool for the surveillance of zoonotic hookworms, globally.

Standardization and application of a modified RFLP-PCR methodology for analysis of polymorphisms linked to treatment resistance in Ancylostoma braziliense

BACKGROUND

Single nucleotide polymorphisms (SNPs) in codons 167, 198 and 200 of the beta-tubulin isotype 1 gene are associated with benzimidazoles resistance in many helminths. Codon 167 mutation has never been described in hookworms; however, polymorphisms in codons 198 and 200 have been described for Ancylostoma caninum and Necator americanus. These mutations have never been investigated in Ancylostoma braziliense; therefore, it is not known if they are present in this species and whether they are correlated with treatment resistance. The RFLP-PCR technique has been used to analyze these polymorphisms in some nematodes, but depending on the species, these alterations do not create or eliminate any restriction enzyme cleavage site, making it impossible to use this technique. Here, we describe the standardization and application of a modified RFLP-PCR technique for detecting polymorphisms in individual A. braziliense worms recovered from naturally infected dogs in two Brazilian states.

RESULTS

The molecular techniques used were sensitive, specific, and easy to apply. To our knowledge, we report for the first time the presence of a polymorphism at codon 198 of the beta-tubulin gene of A. braziliense (1/81; 95% CI: 0-3.69%).

CONCLUSIONS

It is not known whether the presence of the mutation in codon 198 of the beta-tubulin gene of A. braziliense has importance for this parasite. However, based on studies of other helminths, it is possible that this polymorphism is directly related to the resistance to benzimidazoles. This may be a major concern, since this nematode has considerable relevance as a parasite of canids and felids and as one of the agents of cutaneous larva migrans in humans. Standardized methodologies will be useful for screening for polymorphisms in the beta-tubulin gene of canine hookworms in a broader population. The method could also be adapted for the analysis of other SNPs in other nematode species.

Cutaneous Larva Migrans

BACKGROUND

Cutaneous larva migrans is one of the most common skin diseases reported in travelers returning from tropical regions. Western physicians, however, are often not familiar of this condition.

OBJECTIVE

To review in depth the epidemiology, pathophysiology, clinical manifestations, complications, and treatment of cutaneous larva migrans.

METHODS

A PubMed search was completed in Clinical Queries using the key term "cutaneous larva migrans". The search included meta-analyses, randomized controlled trials, clinical trials, and reviews. Patents were searched using the key term "cutaneous larva migrans" from www.google.com/patents, www.uspto.gov, and www.freepatentsonline.com.

RESULTS

Cutaneous larva migrans is a zoonotic infestation caused by penetration and migration in the epidermis of filariform larva of different kinds of animal hookworms through contact with feces of infected animals. Cutaneous larva migrans is endemic in tropical and subtropical regions. Clinically, cutaneous larva migrans is characterized by an intensely pruritic erythematous migrating tortuous or serpiginous, slightly raised track. The diagnosis is mainly clinical, based on the history of travel to an endemic area and exposure to contaminated soil/sand and the characteristic serpiginous track. Treatment options as well as recent patents related to the management of cutaneous larva migrans are also discussed. Compared with oral antihelminthics, topical treatment over the affected area is less effective. Oral ivermectin is the treatment of choice.

CONCLUSION

The pruritic serpiginous track is pathognomonic. Oral ivermectin is the treatment of choice.

Efficacy of oral afoxolaner plus milbemycin oxime chewables against induced gastrointestinal nematode infections in dogs

The efficacy of oral afoxolaner plus milbemycin oxime combination chewables against induced gastrointestinal nematode infections in dogs was evaluated in six separate studies. Two studies were performed to evaluate the efficacy of the product against Toxocara canis, two studies evaluated the efficacy against Toxascaris leonina, one study evaluated the efficacy against Ancylostoma braziliense, and one study evaluated the efficacy against Ancylostoma caninum. In the A. caninum study, the efficacy of milbemycin oxime alone and afoxolaner alone was also evaluated. Dogs in all studies were inoculated with infective eggs or larvae and confirmed to have patent infections based on a fecal examination prior to allocation to study group and treatment. Each study utilized a randomized block design with blocks based on pre-treatment body weight. All dogs were assigned to blocks based on body weight, and then each dog within a block was randomly assigned to treatment group. There were two groups of 10 dogs each in the T. canis, T. leonina, and A. braziliense studies: 1) an untreated (control) group and 2) a group treated with afoxolaner plus milbemycin oxime chewables (NexGard Spectra(®), Merial). This group was treated at a dose as close as possible to the minimum effective dose of afoxolaner and milbemycin oxime (2.5mg+0.5mg per kg body weight, respectively) once on Day 0 using whole chews. There were four groups of 10 dogs each in the A. caninum study: 1) untreated (control), 2) NexGard Spectra(®) as described above, 3) milbemycin oxime alone (dose of at least 0.5mg per kg of body weight) and 4) afoxalaner alone (dose of at least 2.5mg per kg body weight). For parasite recovery and counts, dogs were euthanized humanely and necropsied seven days after treatment. The efficacy of the afoxolaner plus milbemycin oxime combination was ≥98% against T. canis, ≥95.8% against T. leonina, and 90.2% against A. braziliense. Efficacy of the combination against A. caninum was 99.7%, while the efficacy of milbemycin oxime alone was 99.6% and the efficacy of afoxolaner alone was 2.1%. Dogs treated with afoxolaner plus milbemycin oxime chewables had significantly (p≤0.0002) fewer nematodes than the untreated controls in all studies. There were no adverse events or other health problems that were related to treatment with Nexgard Spectra(®) in these studies. The results of these controlled studies demonstrate the high efficacy of the afoxolaner plus milbemycin oxime chewables against a broad range of canine intestinal nematode infections.

Efficacy of afoxolaner plus milbemycin oxime chewable tablets against naturally acquired intestinal nematodes in dogs

The efficacy of oral afoxolaner plus milbemycin oxime combination chewable tablets (NexGard Spectra, Merial) against naturally acquired intestinal nematode infections in dogs was evaluated in six negative control, blinded studies including a total of 114 dogs. Dogs were selected based on a pre-treatment fecal examination indicating patent infections with hookworms (two studies), Toxocara or Toxascaris ascarids (one study each) or Trichuris whipworms (two studies). In each study, dogs were assigned to blocks of two animals each, based on decreasing pre-treatment body weight and were randomly allocated to one of two groups consisting of eight, nine or 10 dogs: untreated (control) or treated with the combination chewable tablet formulation. Chewable tablets were combined to provide doses of actives as close as possible to the minimum effective dose of afoxolaner and milbemycin oxime, i.e., 2.5 mg/kg body weight and 0.5 mg/kg body weight, respectively, once on Day 0. For parasite recovery and count, dogs were euthanized humanely and necropsied seven or eight days after treatment. A single treatment with afoxolaner plus milbemycin oxime chewable tablets provided 94.8% and 90.9% efficacy against adult Ancylostoma braziliense and A. caninum, respectively, 97.8% and 99.4% efficacy against adult Toxocara canis and Toxascaris leonina, respectively, and ≥98.3% efficacy against adult Trichuris vulpis. Compared to untreated controls, nematode counts of the treated dogs were significantly reduced (F-test; p<0.002). In addition, analysis of the pooled data across studies revealed that treatment with afoxolaner plus milbemycin oxime chewable tablets reduced adult Uncinaria stenocephala burdens by 74.9% (p=0.002). All dogs tolerated the treatment well based on clinical observations post-treatment and daily clinical observations. No adverse experiences or other clinical problems related to the treatment were observed throughout the studies. The results of this series of controlled studies demonstrated high efficacy and excellent acceptability and safety of the afoxolaner plus milbemycin oxime chewable tablets when administered for treatment of a broad range of canine intestinal nematode infections.

Efficacy of a novel topical fipronil, (S)-methoprene, eprinomectin and praziquantel combination against naturally acquired intestinal nematode and cestode infections in cats

The efficacy of a novel topical combination formulation of fipronil, (S)-methoprene, eprinomectin and praziquantel against naturally acquired intestinal nematode and cestode infections in cats was evaluated in seven negative control, blinded studies. Cats were selected based on a pre-treatment faecal examination indicating a patent infection with at least hookworms (two studies), Toxocara ascarids (one study), taeniid cestodes (two studies) or Dipylidium cestodes (two studies). In each study, cats were assigned randomly to blocks of two animals each, based on decreasing pre-treatment body weight and were randomly allocated to one of two groups of six to 12 cats: untreated (control) or treated with topical fipronil (8.3%, w/v), (S)-methoprene (10%, w/v), eprinomectin (0.4%, w/v) and praziquantel (8.3%, w/v) (BROADLINE(®), Merial) at 0.12 mL/kg body weight (providing a minimum of 10mg fipronil+12 mg S-methoprene+0.5mg eprinomectin+10mg praziquantel per kg body weight). The topical treatment was administered directly on the skin in the midline of the neck in a single spot once on Day 0. For parasite recovery and count, cats were euthanized humanely and necropsied seven or ten days after treatment. A single treatment with the novel topical combination product provided 91% efficacy against Ancylostoma braziliense, ≥ 99% efficacy against Ancylostoma tubaeforme, and >97% efficacy against Toxocara cati. Similarly, excellent efficacy was established against Taenia taeniaeformis, Dipylidium caninum and Diplopylidium spp. as demonstrated by >97% and up to 100% reductions of cestode counts in the treated cats when compared to the untreated controls (P<0.01). All cats accepted the treatment well based on health observations post-treatment and daily health observations. No adverse experiences or other health problems were observed throughout the studies. The results of this series of controlled studies demonstrated high efficacy and excellent acceptability of the novel topical combination formulation of fipronil, (S)-methoprene, eprinomectin and praziquantel against a broad range of feline intestinal nematode and cestode infections.