Phenotypic characterization of two Ancylostoma caninum isolates with different susceptibilities to the anthelmintic pyrantel

Reflecting on the past and fast forwarding to present day anthelmintic resistant Ancylostoma caninum-A critical issue we neglected to forecast

Reports of anthelmintic resistance in Ancylostoma caninum are increasing in frequency in the United States of America (USA). In the last few years in vitro and in vivo studies characterized individual isolates, demonstrating multiple anthelmintic drug resistance (MADR). In 2021, the American Association of Veterinary Parasitologists initiated a hookworm task force to address this issue. The first report of drug resistant A. caninum occurred in 1987 in Australian racing Greyhounds. In the last five years multiple case reports and investigations show drug resistant A. caninum is becoming a much greater problem in the USA and now extends beyond racing Greyhounds into the general companion animal dog population. The literature, regarding drug resistance in livestock and equine nematodes, provides helpful guidance along with diagnostic methods to better understand the evolution and selection of canine MADR hookworms; however, there are limitations and caveats due to A. caninum's unique biology and zoonotic potential. Mass drug administration (MDA) of anthelminthic drugs to humans to reduce morbidity associated with human hookworms (Necator americanus) should consider the factors that contributed to the development of MADR A. caninum. Finally, as Greyhound racing undergoes termination in some regions and the retired dogs undergo subsequent rehoming, drug resistant parasites, if present, are carried with them. Drug resistant A. caninum requires greater recognition by the veterinary community, and small animal practitioners need to be aware of the spread into current pet dog populations. The current understanding of anthelmintic resistance, available treatments, and environmental mitigation for these drug resistant A. caninum isolates must be monitored for horizontal spread. A major goal in this emerging problem is to prevent continued dissemination.

Hymenolepis diminuta Reduce Lactic Acid Bacterial Load and Induce Dysbiosis in the Early Infection of the Probiotic Colonization of Swiss Albino Rat

Tapeworm infection continues to be an important cause of morbidity worldwide. Recent metagenomics studies have established a link between gut microbiota and parasite infection. The identification of gut probiotics is of foremost importance to explore its relationship and function with the parasite in the host. In this study, the gut content of hosts infected with tapeworm Hymenolepis diminuta and non-infected host gut were disected out to determine their Lactic acid bacterial (LAB) population in MRS agar and microbial community was analysed by metagenomics. The bacterial count was calculated on a bacterial counting chamber and their morphology was determined microscopically and biochemically. Further, to determine the safety profile antibiotic resistance test, antimicrobial, hemolytic activity, and adhesion capability were calculated. We found six dominant probiotic strains and a decrease in LAB load from 1.7-2.3 × 10⁷ CFU/mL in the uninfected group to a range of 8.4 × 10⁵ CFU/mL to 3.2 × 10⁵ CFU/mL in the infected groups with respect to an increase in the parasite number from 10-18. In addition, we found a depletion in the probiotic relative abundance of Lactobacillus and an enrichment in potentially pathogenic Proteobacteria, Fusobacteria, and Streptococcus. Phylogenetic analysis of the six probiotics revealed a close similarity with different strains of L. brevis, L. johnsonii, L. taiwansis, L. reuteri, L. plantarum, and L. pentosus. Thus, this study suggests that the parasite inhibits probiotic colonization in the gut during its early establishment of infection inside the host.

Gastrointestinal helminths in dogs: occurrence, risk factors, and multiple antiparasitic drug resistance

Helminth infections are detrimental to the overall health of dogs; therefore, this study aimed to identify antiparasitic-resistant helminths and evaluate the infection rate and risk factors for parasitism in canines. For this purpose, a parasitological evaluation of 38 randomly selected animals was performed, followed by the evaluation of the anthelminthic efficacy of three drugs: pyrantel pamoate with praziquantel (Canex Composto®), fenbendazole (Fenzol Pet®), and milbemycin oxime with praziquantel (Milbemax C®). Among the evaluated animals, 22/38 (57.89%) tested negative and 16/38 (42.71%) tested positive for Ancylostoma caninum infection. Evaluation of the efficacy of antiparasitic drugs showed that 12/16 (75%) dogs were infected with helminths that were susceptible to pyrantel pamoate with praziquantel. Among those for which pyrantel pamoate with praziquantel was not effective, 3/4 (75%) were susceptible to fenbendazole, while the remaining case resistant to both pyrantel pamoate with praziquantel and fenbendazole was sensitive to milbemycin oxime with praziquantel (100%). The odds ratio of infection in dogs inhabiting environments containing soil or grass was 6.67 times higher than that in dogs inhabiting impermeable environments. Mixed-breed dogs (SRD) were 6.54 times more likely to be infected compared to purebred dogs. A. caninum resistant to pyrantel pamoate with praziquantel (4/16, 25%) and fenbendazole (1/4, 25%) were detected. The results of this study demonstrated the importance of coproparasitological monitoring by professionals before and after treatments to assess antiparasitic drug effectiveness, ensure animal health and welfare, and minimize animal exposure to risk factors.

Action of Carvacrol on Parascaris sp. and Antagonistic Effect on Nicotinic Acetylcholine Receptors

Parascaris sp. is the only ascarid parasitic nematode in equids and one of the most threatening infectious organisms in horses. Only a limited number of compounds are available for treatment of horse helminthiasis, and Parascaris sp. worms have developed resistance to the three major anthelmintic families. In order to overcome the appearance of resistance, there is an urgent need for new therapeutic strategies. The active ingredients of herbal essential oils are potentially effective antiparasitic drugs. Carvacrol is one of the principal chemicals of essential oil from Origanum, Thymus, Coridothymus, Thymbra, Satureja and Lippia herbs. However, the antiparasitic mode of action of carvacrol is poorly understood. Here, the objective of the work was to characterize the activity of carvacrol on Parascaris sp. nicotinic acetylcholine receptor (nAChR) function both in vivo with the use of worm neuromuscular flap preparations and in vitro with two-electrode voltage-clamp electrophysiology on nAChRs expressed in Xenopus oocytes. We developed a neuromuscular contraction assay for Parascaris body flaps and obtained acetylcholine concentration-dependent contraction responses. Strikingly, we observed that 300 µM carvacrol fully and irreversibly abolished Parascaris sp. muscle contractions elicited by acetylcholine. Similarly, carvacrol antagonized acetylcholine-induced currents from both the nicotine-sensitive AChR and the morantel-sensitive AChR subtypes. Thus, we show for the first time that body muscle flap preparation is a tractable approach to investigating the pharmacology of Parascaris sp. neuromuscular system. Our results suggest an intriguing mode of action for carvacrol, being a potent antagonist of muscle nAChRs of Parascaris sp. worms, which may account for its antiparasitic potency.

Efficacy evaluation of anthelmintic products against an infection with the canine hookworm (Ancylostoma caninum) isolate Worthy 4.1F3P in dogs

Ancylostoma caninum is the most prevalent intestinal nematode of dogs, and has a zoonotic potential. Multiple-drug resistance (MDR) has been confirmed in a number of A. caninum isolates, including isolate Worthy 4.1F3P, against all anthelmintic drug classes approved for hookworm treatment in dogs in the United States (US). The cyclooctadepsipeptide emodepside is not registered to use in dogs in the US, but in a number of other countries/regions. The objective of this study was to evaluate the efficacy of emodepside + praziquantel, as well as three commercial products that are commonly used in the US for treatment of hookworms, against a suspected (subsequently confirmed) MDR A. caninum isolate Worthy 4.1F3P. 40 dogs infected on study day (SD) 0 with 300 third-stage larvae, were randomly allocated to one of five treatment groups with eight dogs each: pyrantel pamoate (Nemex®-2), fenbendazole (Panacur® C), milbemycin oxime (Interceptor®), emodepside + praziquantel tablets and non-treated control. Fecal egg counts (FEC) were performed on SDs 19, 20, 22, 27, 31 and 34. All treatments were administered as per label requirements on SD 24 to dogs in Groups 1 through 4. Two additional treatments were administered on SDs 25 and 26 to dogs in Group 2 as per label requirements. Dogs were necropsied on SD 34 and the digestive tract was removed/processed for worm recovery and enumeration. The geometric mean (GM) worm counts for the control group was 97.4, and for the pyrantel pamoate, fenbendazole, milbemycin oxime, and emodepside + praziquantel groups were 74.8, 72.0, 88.9, and 0.4, respectively. These yielded efficacies of 23.2%, 26.1%, and 8.8%, and 99.6%, respectively. These data support previous findings of the MDR status of Worthy 4.1F3P as treatments with pyrantel pamoate, fenbendazole and milbemycin oxime lacked efficacy. In sharp contrast, Worthy 4.1F3P was highly susceptible to treatment with emodepside + praziquantel.

Multiple drug resistance in the canine hookworm Ancylostoma caninum: an emerging threat?

Background

The canine hookworm, Ancylostoma caninum is the most prevalent and important intestinal nematode parasite of dogs in the USA. Hookworms are typically well controlled by treatment with all commonly used anthelmintics that are approved for this use in dogs. However, in the past few years, cases of recurrent/persistent canine hookworm infections appear to have dramatically increased, suggesting that anthelmintic resistance (AR) may have evolved in this parasite. These cases are highly overrepresented by greyhounds, but multiple other breeds are also represented. The aim of this study was to characterize several of these suspected resistant isolates using in vitro, genetic and clinical testing to determine if these cases represent true anthelmintic resistance in A. caninum.

Methods

Fecal samples containing hookworm eggs from three cases of persistent hookworm infections; one from a greyhound, one from a miniature schnauzer and one from a hound-mix, were received by our laboratory. These were then used to establish infections in laboratory dogs and to perform egg hatch assays (EHA) and larval development assays (LDA) for detecting resistance to benzimidazoles and macrocyclic lactones, respectively. Additional EHA and LDA were performed on eggs recovered from the laboratory-induced infections. Fecal egg count reduction tests were performed to detect resistance to pyrantel. Deep amplicon sequencing assays were developed to measure the frequency of non-synonymous single nucleotide polymorphisms (SNP) at codons 167, 198 and 200 of the A. caninum isotype-1 β-tubulin gene.

Results

Resistance ratios for the three A. caninum isolates tested ranged from 6.0 to > 100 and 5.5 to 69.8 for the EHA and LDA, respectively. Following treatment with pyrantel, reduction in faecal egg counts was negative or 0%. Deep amplicon sequencing of the isotype-1 β-tubulin gene identified a high frequency of resistance-associated SNPs at codon 167 in all three resistant isolates and in two additional clinical cases.

Conclusions

These data conclusively demonstrate multiple anthelmintic resistance in multiple independent isolates of A. caninum, strongly suggesting that this is an emerging problem in the USA. Furthermore, evidence suggest that these resistant hookworms originate from racing greyhound farms and kennels, though additional research is needed to confirm this.

Probiotic therapy: a promising strategy for the control of canine hookworm

Canis familiaris is a domestic animal which plays an important role as a pet; however, it is very likely to develop diseases characterized by high morbidity and mortality. In this sense, there are some Ancylostomatidae species that can lead to anemia, weight loss, and abdominal pain. Therefore, the treatment with allopathic drugs is essential for eliminating the parasitism. However, the increasing occurrence of resistance to allopathic treatments stimulates the search for new therapeutic inputs, among which the probiotics stand out and are able to positively alter the intestinal microbiota and exert immunomodulatory effect. Therefore, the present study aimed to evaluate the applicability of using species of Lactobacillus (L. acidophilus ATCC 4536, L. plantarum ATCC 8014, and L. delbrueckii UFV H2B20) to control canine ancylostomiasis. A probiotic preparation containing 1 × 10⁶ CFU of each strain was administered to 10 naturally infected animals, on alternate days for 28 days. It was observed that the treatment with the probiotic preparation led to a significant reduction in EPG of feces (88.83%/ P < 0.05), as well as an increase in leukocyte and lymphocyte counts, highlighting the potential use of Lactobacillus species in the control of canine ancylostomiasis.

Interactions of anthelmintic drugs in Caenorhabditis elegans neuro-muscular ion channel mutants

Due to the increasing development of anthelmintic resistance in nematodes worldwide, it is important to search for anthelmintic compounds with new modes of action and also to investigate the possibility to combine compounds with possible synergistic effects. There might also be the chance to take advantage of the fact that nematode populations which have developed resistance against one anthelmintic class might respond hypersusceptibly to another drug class. The aim of this study was to investigate responses of Caenorhabditis elegans populations with mutations in neuro-muscular ion channels to different anthelmintic classes. Furthermore, potential synergistic effects between two anthelmintic compounds from different classes, i.e. emodepside and tribendimidine, were studied. Although there was neither a synergistic nor an antagonistic effect between emodepside and tribendimidine, other types of interactions could be identified. The C. elegans GABAA-receptor (GABAA-R) unc-49 mutants, showing decreased emodepside susceptibility, were more susceptible to tribendimidine than wild-type C. elegans. In contrast, the reverse phenomenon - hypersusceptibility to emodepside in tribendimidine resistant acetylcholine-receptor (AChR) loss of function mutants - was not observed. Moreover, the slo-1 mutant strain (completely emodepside resistant) also showed hypersusceptibility to piperazine. Interestingly, neither the GABAA-R unc-49 mutants nor the AChR mutants showed decreased susceptibility against piperazine, although there were some studies that indicated an involvement of GABAA-R or AChR in the piperazine mode of action. In conclusion, the present study provides evidence suggesting that interactions between commercially available anthelmintic drugs with different modes of action might be a relatively common phenomenon but this has to be carefully worked out for each anthelmintic and each anthelmintic drug combination. Moreover, results obtained in C. elegans will have to be confirmed using parasitic nematodes in the future.

Selective effect of the anthelmintic bephenium on Haemonchus contortus levamisole-sensitive acetylcholine receptors

Acetylcholine receptors (AChRs) are pentameric ligand-gated ion channels involved in the neurotransmission of both vertebrates and invertebrates. A number of anthelmintic compounds like levamisole and pyrantel target the AChRs of nematodes producing spastic paralysis of the worms. The muscle AChRs of nematode parasites fall into three pharmacological classes that are preferentially activated by the cholinergic agonists levamisole (L-type), nicotine (N-type) and bephenium (B-type), respectively. Despite a number of studies of the B-type AChR in parasitic species, this receptor remains to be characterized at the molecular level. Recently, we have reconstituted and functionally characterized two distinct L-AChR subtypes of the gastro-intestinal parasitic nematode Haemonchus contortus in the Xenopus laevis oocyte expression system by providing the cRNAs encoding the receptor subunits and three ancillary proteins (Boulin et al. in Br J Pharmacol 164(5):1421-1432, 2011). In the present study, the effect of the bephenium drug on Hco-L-AChR1 and Hco-L-AChR2 subtypes was examined using the two-microelectrode voltage-clamp technique. We demonstrate that bephenium selectively activates the Hco-L-AChR1 subtype made of Hco-UNC-29.1, Hco-UNC-38, Hco-UNC-63, Hco-ACR-8 subunits that is more sensitive to levamisole than acetylcholine. Removing the Hco-ACR-8 subunit produced the Hco-L-AChR2 subtype that is more sensitive to pyrantel than acetylcholine and partially activated by levamisole, but which was bephenium-insensitive indicating that the bephenium-binding site involves Hco-ACR-8. Attempts were made to modify the subunit stoichiometry of the Hco-L-AChR1 subtype by injecting five fold more cRNA of individual subunits. Increased Hco-unc-29.1 cRNA produced no functional receptor. Increasing Hco-unc-63, Hco-unc-38 or Hco-acr-8 cRNAs did not affect the pharmacological characteristics of Hco-L-AChR1 but reduced the currents elicited by acetylcholine and the other agonists. Here, we provide the first description of the molecular composition and functional characteristics of any invertebrate bephenium-sensitive receptor.

In vitro and in vivo efficacy of tribendimidine and its metabolites alone and in combination against the hookworms Heligmosomoides bakeri and Ancylostoma ceylanicum

Worldwide, 3 billion people are at risk of hookworm infection, particularly in resource-poor countries. While control of soil-transmitted helminthiases relies mostly on chemotherapy, only few drugs are available and concern about potential emergence of drug resistance is rising. In the present study, tribendimidine, a derivative of amidantel, and its metabolites deacylated amidantel (dADT) and acetylated deacylated amidantel (AdADT) were tested in vitro and in vivo against Heligmosomoides bakeri and Ancylostoma ceylanicum, two hookworm rodent models, alone or in combination with standard drugs. Tribendimidine achieved IC(50)s ≤ 5 μg/ml against both H. bakeri third-stage larvae and adults in vitro and a single 2 mg/kg oral dose resulted in complete worm elimination in vivo. Comparable results were obtained with dADT, whereas AdADT displayed no effect in vitro and gave a moderate worm burden reduction of 42.9% in H. bakeri-infected mice. Tribendimidine combined with albendazole, levamisole or ivermectin revealed antagonistic interactions against H. bakeri in vitro and no significant killing effect in vivo. Tribendimidine and dADT exerted high efficacies against A. ceylanicum third-stage larvae (IC(50)s < 0.5 μg/ml) whereas adults were moderately affected in vitro (IC(50)s > 88 μg/ml). In vivo at single oral doses of 10 mg/kg, dADT showed a slightly higher efficacy than tribendimidine, achieving worm burden reductions of 87.4% and 74.8%, respectively. At the same dose, AdADT reduced the worm burden by 57.9%. Synergistic interactions were observed with tribendimidine-levamisole combinations against A. ceylanicum in vitro (combination index at IC(50)=0.5), and in vivo (combination index at ED(90)=0.19). In conclusion, tribendimidine and dADT show potent anti-hookworm properties. The potential of the promising tribendimidine-levamisole combination should be investigated in greater detail.

Nitazoxanide: In vitro and in vivo drug effects against Trichuris muris and Ancylostoma ceylanicum, alone or in combination

Soil-transmitted helminths cause more than 1 billion human infections globally, mostly in the poorest regions of the world. Control relies essentially on a limited panel of four drugs, and drug resistance might be inescapable. Nitazoxanide, an anti-infective drug, has been shown to exert anthelmintic activity in human clinical trials. In the present work, nitazoxanide was tested alone or combined with commercialized anthelmintics on Trichuris muris, a whipworm mouse model, and Ancylostoma ceylanicum, a hookworm hamster model, in vitro and in vivo. IC50s of ⩽1 and 12.87 μg/ml were achieved with nitazoxanide on T. muris third-stage larvae (L3) and adult worms in vitro, respectively. An IC50 of ⩽1 μg/ml was obtained exposing A. ceylanicum adults worms to nitazoxanide, whereas A. ceylanicum L3 were not affected. Using scanning electron microscopy, the tegument of adult T. muris appeared unchanged following nitazoxanide treatment, whereas swellings were seen on the tegument of the anterior region of half of the A. ceylanicum specimen analyzed. Synergism was observed in vitro when nitazoxanide was combined with levamisole or ivermectin on T. muris adult worms, and when combined with levamisole, pyrantel pamoate, or ivermectin on A. ceylanicum adult worms. In T. muris-infected mice, oral nitazoxanide achieved worm burden reductions of 56.09% and 17.37% following a single dose of 100 mg/kg and three doses of 50 mg/kg, respectively. None of the tested drug combinations displayed activity on T. muris in vivo. In A. ceylanicum-infected hamsters, no effect was observed for oral nitazoxanide alone, and none of the tested combinations reached the threshold for additive effect. In conclusion, nitazoxanide failed to demonstrate promising activity against T. muris and A. ceylanicum in vivo, regardless whether tested as monotherapy or combined with standard drugs. Reasons for the discrepancy of these findings compared to results obtained in clinical trials remain to be elucidated.