Inhomogeneity of the density of Parascaris spp. eggs in faeces of individual foals and the use of hypothesis testing for treatment decision making

The effect of anthelmintic treatment and efficacy on the faecal microbiota of healthy adult horses

Changes to the faecal microbiota of horses associated with administration of anthelmintic drugs is poorly defined. This study included horses with cyathostomin infection where susceptibility and resistance to oxfendazole and abamectin was known. This study assessed the changes to the faecal microbiota associated with administration of two different anthelmintics in this population. Twenty-four adult horses were included. Faecal egg counts were performed on all horses prior to random allocation into abamectin (n=8), oxfendazole (n=8) or Control groups (n=8) and at Day 14 post treatment. Faecal samples were collected for microbiota analysis prior to anthelmintic administration and on Day 3 and Day 14. From each faecal sample, DNA was extracted prior to PCR amplification, next generation sequencing and analysis using QIIME2. Anthelmintic treatment was associated with changes in alpha diversity (p <0.05), with increased evenness and diversity at Day 14 and increased richness at Day 3 within the abamectin group. Differences in relative abundance of bacteria at the phyla, family and genus taxonomic levels occurred after treatment; indicating that the microbiota was altered with anthelmintic administration. The results support that anthelmintic administration and removal of cyathostomins from the large intestine of horses is associated with changes in the faecal microbiota. The results suggest that removal of cyathostomins is associated with greater differences in microbiota, compared to anthelmintic drug administration that is ineffective in reducing cyathostomin infection. Cyathostomin removal was supported by adequate reduction of faecal egg counts, determined by faecal egg count reduction testing.

BEVA primary care clinical guidelines: Equine parasite control

BACKGROUND

There is a lack of consensus on how best to balance our need to minimise the risk of parasite-associated disease in the individual horse, with the need to limit the use of anthelmintics in the population to preserve their efficacy through delaying further development of resistance.

OBJECTIVES

To develop evidence-based guidelines utilising a modified GRADE framework.

METHODS

A panel of veterinary scientists with relevant expertise and experience was convened. Relevant research questions were identified and developed with associated search terms being defined. Evidence in the veterinary literature was evaluated using the GRADE evidence-to-decision framework. Literature searches were performed utilising CAB abstracts and PubMed. Where there was insufficient evidence to answer the research question the panel developed practical guidance based on their collective knowledge and experience.

RESULTS

Search results are presented, and recommendation or practical guidance were made in response to 37 clinically relevant questions relating to the use of anthelmintics in horses.

MAIN LIMITATIONS

There was insufficient evidence to answer many of the questions with any degree of certainty and practical guidance frequently had to be based upon extrapolation of relevant information and the panel members' collective experience and opinions.

CONCLUSIONS

Equine parasite control practices and current recommendations have a weak evidence base. These guidelines highlight changes in equine parasite control that should be considered to reduce the threat of parasite-associated disease and delay the development of further anthelmintic resistance.

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

Benzimidazoles resistance is widespread in strongyle parasitic nematodes and associated with polym orphisms in the codons 167, 198 and 200 of isotype 1 β-tubulin (tbb-1). In ascarids, benzimidazole (BZ) resistance has rarely been reported and in none of these cases were any of these polymorphisms detected. Here, available genome and transcriptome data from WormBase ParaSite were used to compare the complete β-tubulin reservoirs of Parascaris univalens, Ascaris suum and Ascaris lumbricoides. Adult Parascaris spp. specimens collected in Australia from horses after BZ treatment (susceptible, n = 13) or surviving BZ treatment and collected after ivermectin treatment (resistant, n = 10) were genotyped regarding codons 167, 198 and 200 using Sanger sequencing. Phylogenetic analyses clearly showed that there are no one-to-one ascarid orthologs of strongyle tbb-1 genes. In the reference genomes, as well as phenotypically susceptible and resistant Parascaris spp. from Australia, six out of seven β-tubulin genes showed a BZ-susceptible genotype (F167, E198, F200). The only exception were the testis-specific β-tubulin D genes from all three ascarid species that encode tyrosine at codon 200. This was observed independently of the BZ-susceptibility phenotype of Parascaris spp. These data suggest that different mechanisms lead to BZ resistance in ascarid and strongyle nematodes.

Very low intraspecific sequence variation in selected nuclear and mitochondrial Parascaris univalens genes

Equines were over decades considered to be infected by two morphologically virtually indistinguishable ascarid species, Parascaris univalens and Parascaris equorum. Reliable species discrimination is only possible using enzyme isoelectric focussing and karyotyping with P. univalens having one and P. equorum two chromosome pairs. However, presumably the complexity of both methods prevented their routine use in nearly all previous studies about prevalence and drug resistance of Parascaris spp. These have barely been performed on the species level although most studies stated presence of one or the other species. Recently, only P. univalens has been identified by karyotyping and the last published study identifying P. equorum dates back to 1989. In order to improve species-specific detection, molecular markers are required. Here, partial 12S rRNA, cytochrome oxidase I (COI) and complete internal transcribed spacer (ITS)-1 and - 2 sequences were obtained from 24 karyotyped Parascaris specimens from Poland and 6 German specimens (not karyotyped) and used in phylogenetic analyses with orthologous sequences from GenBank. All karyotyped specimens were identified as P. univalens. In the phylogenetic analysis, they formed very homogenous clusters for all target genes and in a multi-locus analysis. Within this cluster, almost all sequences from GenBank were also included, no matter if they had been assigned to P. univalens or P. equorum. However, a small number of P. univalens ITS and COI sequences originating from donkeys from a single farm in China formed a highly supported sister cluster suggesting that they might represent another Parascaris genotype or species. Our data also strongly suggest that nearly all ITS and COI sequences previously deposited in GenBank and assigned to P. equorum actually represent P. univalens. The fact that significantly different sequences can be found in Parascaris spp. suggests that PCR-based species diagnosis will be possible once molecular markers have been identified for P. equorum from karyotyped specimens.

The application of faecal egg count results and statistical inference for clinical decision making in foals

This study investigated the impact of variability in Parascaris spp. and strongyle faecal egg counts (FEC) from foals on treatment decision-making and detection of a patent infection. A single faecal sample was collected once daily for three days from 53 foals and a FEC was performed on three separate portions of each sample (total of nine egg counts per foal). Differences in the decision to administer an anthelmintic using the results of a single count (C₁), the mean of three (X¯_1-3) or nine counts (X¯_1-9) and the upper 5% confidence limit of the gamma confidence interval (CI) of the estimate of the distribution mean (μ) from three (UCL_1-3) and nine counts (UCL_1-9) were determined for a range of egg count thresholds. The UCL_1-9 was used as the best estimate of μ, hypothesis testing for treatment and the comparison of treatment decision-making using C₁, X¯_1-3, X¯_1-9 and UCL_1-3. The results of this study demonstrated that a point estimate (C₁ or X¯_1-3) was of limited value for estimating the distribution mean of egg counts in faeces and there was overall poor agreement in treatment decision-making for individual foals using C₁ compared with UCL_1-9. Of the foals with C₁ of zero eggs per gram, 54% and 47% had Parascaris and strongyle eggs in subsequent counts, respectively. The egg density in faeces is inhomogeneous, resulting in considerable variability in egg count results for an individual foal: between faecal piles, different portions of a faecal pile and days. The use of the negative binomial distribution CI for μ takes this variability into account and is recommended for use when interpreting FEC data from horses.

Systematic review of gastrointestinal nematodes of horses from Australia

Background

Equine gastrointestinal nematodes (GINs) have been the subject of intermittent studies in Australia over the past few decades. However, comprehensive information on the epidemiology of equine GINs, the efficacy of available anthelmintic drugs and the prevalence of anthelmintic resistance (AR) in Australasia is lacking. Herein, we have systematically reviewed existing knowledge on the horse GINs recorded in Australia, and main aspects of their pathogeneses, epidemiology, diagnoses, treatment and control.

Methods

Six electronic databases were searched for publications on GINs of Australian horses that met our inclusion criteria for the systematic review. Subsets of publications were subjected to review epidemiology, diagnoses, pathogeneses, treatment and control of GINs of horses from Australia.

Results

A total of 51 articles published between 1950 to 2018 were included. The main GINs reported in Australian horses were cyathostomins (at least 28 species), Draschia megastoma, Habronema muscae, H. majus, Oxyuris equi, Parascaris equorum, Strongyloides westeri and Trichostrongylus axei across different climatic regions of Queensland, New South Wales, Victoria, and Western Australia. Nematodes are diagnosed based on the traditional McMaster egg counting technique, though molecular markers to characterise common GINs of equines were characterised in 1990s. The use of anthelmintic drugs remains the most widely-used strategy for controlling equine GIN parasites in Australia; however, the threshold of faecal egg count that should trigger treatment in horses, remains controversial. Furthermore, anthelmintic resistance within GIN population of horses is becoming a common problem in Australia.

Conclusions

Although GINs infecting Australian horses have been the subject of occasional studies over the past few decades, the effective control of GIN infections is hampered by a generalised lack of knowledge in various disciplines of equine parasitology. Therefore, coordinated and focused research is required to fill our knowledge gaps in these areas to maximise equine health and minimise economic losses associated with the parasitic infections in Australia.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3445-4) contains supplementary material, which is available to authorized users.