Anthelmintic resistance of gastrointestinal parasites in small ruminants

First Report of Anthelmintic Resistance in Gastrointestinal Nematodes in Goats in Romania

Currently, there are three classes of anthelmintics most commonly used in small ruminants: the benzimidazoles (BZs), macrocyclic lactones (MLs) and cholinergic agonists (especially levamisole; LEV). The widespread use of those products has led to the emergence of drug-resistant parasite strains which represents a serious threat to the livestock industry. In the present study, we describe for the first time a case of resistance to anthelmintics in goats in Romania. The study was carried out in 2021 in a dairy goat herd from the Transylvania region. Two types of diagnostic methods were used to confirm anthelmintic resistance (AR). First, the faecal egg count reduction test (FECRT), an in vivo AR diagnostic method, was used to evaluate the efficacy of eprinomectin (EPM). The results of this test were analysed applying two different calculative methods that are used only in treated animals (without the control group). Furthermore, two in vitro methods were used: the egg hatch test (EHT) for the detection of resistance to BZs, and the larval development test (LDT) for detection of resistance to all three classes of anthelmintics. The results of FECRT indicate the resistance of gastrointestinal nematodes (GINs) to EPM in both calculative methods (FECR₁ = -88% and FECR₂ = -202%). In addition, the results obtained for ivermectin aglycone (IVM-AG) in LDT also indicate resistance to drugs from MLs group, especially avermectins. Similarly, the results of in vitro methods (EHT and LDT) indicate resistance to BZs in this herd. LEV was the only drug that stopped the development of L3 larvae 100% (LDT). H. contortus was the only nematode species found in coproculture after EPM treatment. Furthermore, H. contotus L3 larvae was the only species found in the wells with the highest concentrations of thiabendazole (TBZ) and IVM-AG in LDT. This suggests that resistance to both BZs and MLs was present for that species.

Presentation, Clinical Pathology Abnormalities, and Identification of Gastrointestinal Parasites in Camels (Camelus bactrianus and Camelus dromedarius) Presenting to Two North American Veterinary Teaching Hospitals. A Retrospective Study: 1980-2020

Old World Camelids (OWC) represent two species (Camelus bactrianus and Camelus dromedarius) with increasing numbers in North America. Gastrointestinal (GI) parasitism is a major cause of clinical disease in camelids and leads to significant economic impacts. Literature reporting on clinical parasitism of camels is localized to India, Africa, and the Middle East, with limited information available on OWCs in North America. Objectives of this study were to report on clinical presentation and diagnostic findings in Camelus bactrianus and Camelus dromedarius with GI parasitism and provide a comparative analysis between geographic regions. Medical records of OWCs presenting to two veterinary teaching hospitals (of the University of Tennessee and University of Wisconsin) were evaluated. Thirty-one camels including 11 Bactrians and six dromedaries (14 species not recorded) were included for the clinical component of this study, reporting on signalment, presenting complaint, and clinical pathology. Anorexia, weight loss, and diarrhea were the most common presenting complaint. Clinical pathology findings included eosinophilia, hypoproteinemia, and hyponatremia. For the second component of this study, a total of 77 fecal parasite examination results were evaluated for parasite identification and regional variation. Trichuris, Capillaria, Strongyloides, Nematodirus, Dictyocaulus, Moniezia, and protozoan parasites (Eimeria, Cryptosporidium, Giardia) were recorded. Strongyle-type eggs predominated, followed by Trichuris and Eimeria spp. There was a statistically significant variation in prevalence of coccidia between the two regions, with fecal examinations from Tennessee more likely to contain Eimeria (P = 0.0193). Clinicians treating camels in North America should recognize anorexia, weight loss, and diarrhea combined with clinical pathologic changes of hypoproteinemia, eosinophilia and hyponatremia as possible indications of GI parasitism. Clinicians should also consider the potential for regional variation to exist for GI parasites of camels in different areas of North America.

Anthelmintic resistance and prevalence of gastrointestinal nematodes infecting sheep in Limpopo Province, South Africa

Background and Aim:

Previous studies recorded the prevalence of gastrointestinal nematodes (GIN) in Limpopo Province. However, the studies did not address the seasonal patterns of infection and did not cover all districts of Limpopo Province, namely; Capricorn, Sekhukhune, Waterberg, Mopani, and Vhembe. It is, therefore, important to provide up to date information on the prevalence and seasonal occurrence data of GIN in all districts of Limpopo province. The present study was conducted to determine the occurrence of anthelmintic resistance (AR) and document the prevalence of GIN infecting sheep in five districts of Limpopo Province, South Africa.

Materials and Methods:

Forty animals in each district were used for fecal egg count reduction test (FECRT) to determine AR against ivermectin (0.2 mg/kg), levamisole (LEV) (5 mg/kg), and albendazole (7.5 mg/kg). Egg hatch test (EHT) was used to determine AR against thiabendazole (TBZ) and micro-agar larval development test (MALDT) was used for both TBZ and LEV. Naturally, infected sheep (n=780) were sampled for prevalence across five districts of Limpopo. FAMACHA^© eye-color score estimations were also performed for each study animal.

Results:

FECRT showed occurrence of AR in most of the districts and a few with suspected resistance. EHT results showed AR development against TBZ for all districts, while the MALDT showed no AR against LEV in all districts, but detected AR against TBZ in Sekhukhune, Capricorn, and Waterberg. Haemonchus contortus was the most resistant species. A high nematode prevalence (88-100%) and 1210-1861 eggs per gram (EPG) was observed in all districts during the hot wet season, decreasing to 75-80% (453-1202 EPG) during the cold dry season. The sheep revealed a FAMACHA^© mean score of 3, indicating mild anemia during the hot wet season except for Vhembe district that revealed a FAMACHA^© mean score of 4 during the hot wet season, indicating anemia.

Conclusion:

AR recorded in Limpopo Province may be due to under-dosing caused by lack of weighing equipment and high treatment frequencies due to lack of proper training on anthelmintic use. The detection of AR in Limpopo is an important finding because it will help in outlining effective management systems against GIN.

Genome-wide association study to identify genetic loci associated with gastrointestinal nematode resistance in Katahdin sheep

Resistance to gastrointestinal nematodes has previously been shown to be a moderately heritable trait in some breeds of sheep, but the mechanisms of resistance are not well understood. Selection for resistance currently relies upon faecal egg counts (FEC), blood packed cell volumes and FAMACHA visual indicator scores of anaemia. Identifying genomic markers associated with disease resistance would potentially improve the selection process and provide a more reliable means of classifying and understanding the biology behind resistant and susceptible sheep. A GWAS was conducted to identify possible genetic loci associated with resistance to Haemonchus contortus in Katahdin sheep. Forty animals were selected from the top and bottom 10% of estimated breeding values for FEC from a total pool of 641 sires and ram lambs. Samples were genotyped using Applied Biosystems™ Axiom™ Ovine Genotyping Array (50K) consisting of 51 572 SNPs. Following quality control, 46 268 SNPs were included in subsequent analyses. Analyses were conducted using a linear regression model in plink v1.90 and a single‐locus mixed model in snp and variation suite. Genome‐wide significance was determined by a Bonferroni correction for multiple testing. Using linear regression, loci on chromosomes 2, 3, 16, 23 and 24 were significantly associated at the genome level with FEC estimated breeding values, and we identified a region on chromosome 2 that was significant using both statistical analyses. We suggest a potential role for the gene DIS3L2 for gastrointestinal nematode resistance in Katahdin sheep, although further research is needed to validate these findings.

Development of amplicon sequencing for the analysis of benzimidazole resistance allele frequencies in field populations of gastrointestinal nematodes

Anthelmintic resistant gastrointestinal helminths have become a major cause of poor health in sheep and goats. Sensitive and specific molecular markers are needed to monitor the genotypic frequency of resistance in field parasite populations. Gastrointestinal nematode resistance to benzimidazole is caused by a mutation in one of three positions within the isotype 1 β-tubulin gene. In the absence of markers for resistance to the other broad spectrum anthelmintic classes, these provide a relevant study example. Determination of the prevalence of these single nucleotide polymorphisms in field nematode populations can be impractical using conventional molecular methods to examine individual parasites; which can be laborious and lack sensitivity in determining low levels of resistance in parasite populations. Here, we report the development of a novel method based on an Illumina MiSeq deep amplicon sequencing platform to sequence the isotype 1 β-tubulin locus of the small ruminant gastrointestinal nematode, Teladorsagia circumcincta, and determine the frequency of the benzimidazole resistance mutations. We validated the method by assessing sequence representation bias, comparing the results of Illumina MiSeq and pyrosequencing, and applying the method to populations containing known proportions of resistant and susceptible larvae. We applied the method to field samples collected from ewes and lambs on over a period of one year on three farms, each highlighting different aspects of sheep management and approaches to parasite control. The results show opportunities to build hypotheses with reference to selection pressures leading to differences in resistance allele frequencies between sampling dates, farms and ewes or lambs, and to consider the impact of their genetic fixation or otherwise. This study provides proof of concept of a practical, accurate, sensitive and scalable method to determine frequency of anthelmintic resistance mutations in gastrointestinal nematodes in field studies and as a management tool for livestock farmers.

Prevalence of Haemonchus contortus Infections in Sheep and Goats in Nyagatare District, Rwanda

This study investigated the overall prevalence of Haemonchus contortus infection in sheep and goats from five purposively selected subdivisions (sectors) of Nyagatare district from January to December 2014, after a high prevalence of gastrointestinal parasites and generalized poor productivity was reported in small ruminants in some districts of Rwanda. Faecal egg counts (FEC) were performed using the Modified Wisconsin Sugar Floatation method and the Fluorescent-labeled peanut-lectin agglutination test while enumerations, as log (FEC), were done using the modified McMaster method. The overall prevalence of H. contortus infection in sheep and goats was 75.7% (n=949). The overall prevalence of H. contortus infection in sheep (83.4%, n=314) was higher than in goats (71.8%, n=635) (Odds Ratio [OR] 1.98, 95% Confidence Interval [CI]: 1.40-2.79, and p≤0.001). The prevalence of H. contortus infection in female goats (74.2%) was higher than in male goats (64.3%) (OR 1.60, 95% CI: 1.09-2.36, and p=0.01). The prevalence of H. contortus infection in goats from Nyagatare was higher than in goats from Matimba (OR 3.25, 95% CI: 1.76-5.99, and p≤0.001) and from Katabagemu (OR 3.67, 95% CI: 2.04-6.59, and p≤0.001). The prevalence of H. contortus infection in goats from Karangazi was higher than in goats from Matimba (OR 4.72, 95% CI: 2.40-9.28, and p≤0.001). The overall mean monthly log (FEC) for H. contortus in sheep and goats were highest in April (18.9±0.2 and 14.05±0.1, respectively) and October (19.25± 0.2 and 13.75±0.1, respectively). Though, overall, sheep in Nyagatare district were at greater risk of H. contortus infection and goats from Nyagatare and Karangazi sectors were paradoxically at greater risk of H. contortus infection. It was also apparent that young female goats were at greater risk of H. contortus infection than young male goats. H. contortus infection is endemic in small ruminants in Nyagatare district and possibly other districts in Rwanda. Targeted selective treatment (TST) using FAMACHA with emphasis on low-lying swampy pastures and appropriate anthelmintic drugs may be the most economically viable solution in the short term. In the long term breeding of H. contortus resistant small ruminants and strategic grazing using the concept of refugia may bring about considerable relief from H. contortus infection in Nyagatare district, in particular, and Rwanda at large.

Genotypic and phenotypic evaluation for benzimidazole resistance or susceptibility in Haemonchus contortus isolates

Haemonchus contortus isolates were evaluated for benzimidazole (BZ) resistance or susceptibility by allele-specific PCR based on β-tubulin isotype 1 gene polymorphisms at the F167Y, E198A, and F200Y sites. Two isolates, one presumed susceptible from wild pronghorn antelope (PH) and one known to be resistant from goats (VM), were also assayed phenotypically for BZ resistance or susceptibility in the larval development assay (Drenchrite®). The BZ EC50 was 0.198 μM (intermediate between susceptible and weak resistant) for PH with critical well 5 (intermediate between susceptible and weak resistant) and 1.456 μM (intermediate weak resistant and resistant) for VM with critical well 8.5 (resistant). Genotypically, DNA extracted from pooled VM L3 larvae in the Drenchrite® wells with the highest BZ concentration was homozygous susceptible (SS) at the F167Y and E198A sites and homozygous resistant (RR) at the F200Y site by PCR, and sequence analysis bore this out. PH L3 larvae DNA from a control well (no BZ) was SS at all three sites by PCR, confirmed by sequence analysis. All single adult worm samples (N = 21) from PH, VM, Egypt goat (EG), and a Texas llama were SS at F167Y and E198A by PCR; however, only 3 PH worms and 1 EG worm were SS at F200Y. Three additional PH worms were RS and upon cloning two clones were identified as resistant by sequencing and two as susceptible. Clones from single adult worms VM, llama, and EG samples that were RR by PCR at F200Y were sequence verified as resistant. In this study, F200Y was the most frequently found genotypic marker for BZ resistance or susceptibility in the different Haemonchus isolates.

Metabolic profiling and in vitro assessment of anthelmintic fractions of Picria fel-terrae Lour

Anthelmintic resistance is widespread in gastrointestinal nematode populations, such that there is a consistent need to search for new anthelmintics. However, the cost of screening for new compounds is high and has a very low success rate. Using the knowledge of traditional healers from Borneo Rainforests (Sarawak, Malaysia), we have previously shown that some traditional medicinal plants are a rich source of potential new anthelmintic drug candidates. In this study, Picria fel-terrae Lour. plant extract, which has previously shown promising anthelmintic activities, was fractionated via the use of a solid phase extraction cartridge and each isolated fraction was then tested on free-living nematode Caenorhabditis elegans and the parasitic nematode Haemonchus contortus. We found that a single fraction was enriched for nematocidal activity, killing ≥90% of C. elegans adults and inhibiting the motility of exsheathed L3 of H. contortus, while having minimal cytotoxic activity in mammalian cell culture. Metabolic profiling and chemometric analysis of the effective fraction indicated medium chained fatty acids and phenolic acids were highly represented.

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Chemical fractionation of Picria fel-terrae Lour. plant extract.

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Anthelmintic activity against Caenorhabditis elegans and Haemonchus contortus.

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Metabolic profiling and chemometric analysis of active fraction.

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Active fraction has minimal mammalian cytotoxicity.

Utilization of computer processed high definition video imaging for measuring motility of microscopic nematode stages on a quantitative scale: "The Worminator"

A major hindrance to evaluating nematode populations for anthelmintic resistance, as well as for screening existing drugs, new compounds, or bioactive plant extracts for anthelmintic properties, is the lack of an efficient, objective, and reproducible in vitro assay that is adaptable to multiple life stages and parasite genera. To address this need we have developed the "Worminator" system, which objectively and quantitatively measures the motility of microscopic stages of parasitic nematodes. The system is built around the computer application "WormAssay", developed at the Center for Discovery and Innovation in Parasitic Diseases at the University of California, San Francisco. WormAssay was designed to assess motility of macroscopic parasites for the purpose of high throughput screening of potential anthelmintic compounds, utilizing high definition video as an input to assess motion of adult stage (macroscopic) parasites (e.g. Brugia malayi). We adapted this assay for use with microscopic parasites by modifying the software to support a full frame analysis mode that applies the motion algorithm to the entire video frame. Thus, the motility of all parasites in a given well are recorded and measured simultaneously. Assays performed on third-stage larvae (L3) of the bovine intestinal nematode Cooperia spp., as well as microfilariae (mf) of the filarioid nematodes B. malayi and Dirofilaria immitis, yielded reproducible dose responses using the macrocyclic lactones ivermectin, doramectin, and moxidectin, as well as the nicotinic agonists, pyrantel, oxantel, morantel, and tribendimidine. This new computer based-assay is simple to use, requires minimal new investment in equipment, is robust across nematode genera and developmental stage, and does not require subjective scoring of motility by an observer. Thus, the "Worminator" provides a relatively low-cost platform for developing genera- and stage-specific assays with high efficiency and reproducibility, low labor input, and yields objective motility data that is not subject to scorer bias.

Gastrointestinal nematode infections in German sheep

The objective of the present study was to determine the prevalence and variation of natural gastrointestinal nematode (GIN) infections in lambs according to birth type, gender and breed based on individual faecal egg counts (FEC) from various regions in Germany. A total of 3,924 lambs (3 to 15 months old) with different genetic backgrounds (Merinoland, German Blackhead Mutton, Rhoen, Texel and Merino long-wool) were individually sampled during the grazing period between 2006 and 2008. Furthermore, pooled faecal samples from each of the farms were cultured in order to differentiate the third-stage larvae of the nematode spp. Sixty-three percent of the lambs were infected with GIN. The infections were mostly low to moderate and involved several nematode species. The Trichostrongylus spp. was the predominant species based on the percentage of larvae in faecal cultures. Only 11.4% of the lambs were free of Eimeria oocysts. Tapeworm eggs were encountered in 13.2% of all samples. The prevalence of GIN infections varied significantly (P < 0.001) among farms. A significantly higher FEC (P < 0.05) was observed in multiple-born lambs when compared with singletons. Moreover, male lambs were more susceptible to infection than females (P < 0.001). No significant differences (P > 0.05) were observed between breeds regarding FEC. Inter-individual variations were higher than inter-breed differences, which may indicate the possibility of selection within these breeds for parasites resistance as described in earlier studies.