Advances in developing molecular-diagnostic tools for strongyloid nematodes of equids: fundamental and applied implications

Comparative phylogenetic and sequence identity analysis of internal transcribed spacer 2 and cytochrome c oxidase subunit I as DNA barcode markers for the most common equine Strongylidae species

Morphologically, 64 strongylid species have been described in equines. Co-infections are common, with up to 29 species reported in a single horse. Morphological identification of these species is time consuming and requires expert knowledge due to their similar appearance. Therefore, non-invasive identification methods are needed. DNA barcoding offers a rapid and reliable tool for species identification and the discovery of cryptic species for these most common parasitic nematodes of equines. In total, 269 cytochrome c oxidase subunit I (COI) gene and 312 internal transcribed spacer 2 (ITS-2) sequences from 27 equine Strongylidae species, including sequences from two uncharacterised species, Coronocyclus sagittatus and Triodontophorus tenuicollis, were generated and combined with COI and ITS-2 sequences data from six Cyathostominae species from previous studies. This study represents a comprehensive DNA barcoding analysis of 22 Cyathostominae and six Strongylinae species using mitochondrial COI gene and ITS-2 sequences. Maximum likelihood phylogenetic trees were constructed and the intra- and interspecific genetic distances for both markers were compared. Analysis revealed complex phylogenetic relationships. Para- and polyphyletic relationships were observed among most genera within Strongylinae and Cyathostominae. This challenges current morphological classifications. Although both markers showed overlapping pairwise identities in intra- and inter-species comparisons, COI had higher discriminatory power than ITS-2. Expanding the COI and ITS-2 reference database, including the first sequences for Coronocyclus sagittatus and Triodontophorus tenuicollis, improve a reliable species identification and advanced studies on Strongylinae and Cyathostominae diversity using barcoding and metabarcoding.

Molecular diagnostics for gastrointestinal helminths in equids: Past, present and future

This review is aimed to (i) appraise the literature on the use of molecular techniques for the detection, quantification and differentiation of gastrointestinal helminths (GIH) of equids, (ii) identify the knowledge gaps and, (iii) discuss diagnostic prospects in equine parasitology. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for systematic reviews, we retrieved 54 studies (horses: 50/54; donkeys and zebras: 4/54) from four databases. Polymerase chain reaction (PCR) was employed in all of the studies whereas PCR amplicons were sequenced in only 18 of them. Other techniques used (including modifications of PCR) were reverse line blot, quantitative (q)PCR, restriction fragment length polymorphism, nested-PCR, PCR-directed next-generation sequencing, Southern blotting, single strand conformation polymorphism, PCR-enzyme linked immunosorbent assay, matrix-assisted laser desorption/ionisation-time of flight and random amplification of polymorphic DNA. Most of the studies (53/54) used nuclear ribosomal RNA (including the internal transcribed spacers, intergenic spacer, 5.8 S, 18 S, 28 S and 12 S) as target loci while cytochrome c oxidase subunit 1 and random genomic regions were targeted in only three and one studies, respectively. Overall, to date, the majority of molecular studies have focused on the diagnosis and identification of GIHs of equids (i.e. species of Anoplocephala, Craterostomum, cyathostomins, Oesophagodontus, Parascaris, Strongylus, Strongyloides and Triodontophorus), with a recent shift towards investigations on anthelmintic resistance and the use of high-throughput nemabiome metabarcoding. With the increasing reports of anthelmintic resistance in equid GIHs, it is crucial to develop and apply techniques such as advanced metabarcoding for surveillance of parasite populations in order to gain detailed insights into their diversity and sustainable control. To the best of our knowledge, this is the first systematic review that evaluates molecular investigations published on the diagnosis and quantification of equid GIHs and provides useful insights into important knowledge gaps and future research directions in equid molecular parasitology.

Prevalence of intestinal parasitic infections and genetic differentiation of Strongyloides stercoralis among migrant workers from Myanmar, Lao PDR and Cambodia in northeastern Thailand

Intestinal parasitic infections (IPIs) remain a public-health problem worldwide, including in countries of the Lower Mekong subregion. Increases in human migration from neighboring countries might cause reemerging parasitic infections, leading to spread of parasites in the landscape. Here, we conducted a cross-sectional study to identify the prevalence of IPIs in migrant workers from Myanmar, Lao PDR, and Cambodia who were dwelling in Nakhon Ratchasima Province, northeastern Thailand. The identification of Strongyloides species and genetic differentiation of worms from migrant workers with different countries of origin was also assessed. Fresh stool samples were collected from 338 migrant workers and examined for evidence of IPIs using agar plate culture (APC) and the formalin-ethyl acetate concentration technique (FECT). Among those nine samples positive for nematodes by APC, the Strongyloides or hookworm species present was confirmed using the polymerase chain reaction (PCR) followed by DNA sequencing. This revealed eight cases of Strongyloides stercoralis infection and one of Necator americanus. Fifty-one out of 338 individuals (15.09%) were positive for IPIs using FECT and APC. Eggs of Opisthorchis-like flukes were the most common parasite (11.83% of samples), followed by S. stercoralis (2.37%), Entamoeba coli (1.50%), hookworm (0.89%), Taenia sp. (0.60%) and Hymenolepis nana (0.30%). The genetic differentiation of S. stercoralis recovered from migrant workers with different countries of origin was analyzed. Specimens of S. stercoralis isolated from workers from Lao PDR, Cambodia and Myanmar were genetically similar to those sequenced from Thailand. However, there were population-genetic differences between S. stercoralis from these Southeast Asian countries and other regions of the world. This study demonstrated that IPIs were prevalent in migrant workers in the northeastern region of Thailand. Our findings provided molecular confirmation of the presence of S. stercoralis and explored the genetic differentiation of S. stercoralis from those infected migrant workers. An effective anti-parasitic drug should be provided for migrant workers and its administration enforced.

Morphomolecular characterization of Strongylus vulgaris isolated from donkeys with special references to histopathological study on the affected organs

Equine gastrointestinal tract is infected with Strongylus vulgaris (S. vulgaris) which is highly pathogenic parasite for its harmful effect on cranial mesenteric artery during its migration. So, this study was applied for identification of S. vulgaris in donkeys ultramorphologically and molecularly. In addition to, detection of the pathological effect of larval stage of S. vulgaris on the mesenteric arterial system using histopathology and immunohistochemistry. During the period from September to December; 2019, 60 male and 20 female donkeys at the Giza Zoo was postmortem examined. S. vulgaris adults and larvae were collected from the large intestine and cranial mesenteric arteries (CMAs), respectively. Ultramorphological examination of the collected adults was done using scanning electron microscope (SEM). DNA was extracted from 5 larvae and 6 adults for further conventional PCR studies and sequencing of the internal transcriped spacer 2 (ITS2) gene. The ITS2 gene were amplified and showed bands at 148 base pair (bp). The ITS2 gene nucleotide sequences of all isolates were aligned using Basic Local Alignment Search Tool (BLAST). Histological sections of S. vulgaris affected mesenteric arteries exhibited the presence of the parasite larvae either in the lumen with thrombus formation or attached to the intima. Most of the detected inflammatory cell populations were CD68-positive cells. From these results, it can be concluded that the ribosomal spacers genes could be used as markers for Strongylus species identification in eggs collected from equine feces as a beneficial method of diagnosis. Also, it could be important in disease surveillance, improving preventive measures and developing an effective control strategy.

The gastrointestinal nematodes of plains and Grevy's zebras: Phylogenetic relationships and host specificity

Equids are chronically infected with parasitic strongyle nematodes. There is a rich literature on horse strongyles, but they are difficult to identify morphologically and genetic studies on strongyles infecting other equid species are few, hampering studies of host specificity. We sequenced expelled worms from two sympatric zebra species in central Kenya to expand the strongyle phylogeny and used DNA metabarcoding on faecal samples to genetically characterize zebra nemabiomes for the first time. We generated sequences for several species new to public genetic reference databases, all of which are typical strongyles in wild zebras (i.e., the three species of Cylindropharynx and Cyathostomum montgomeryi), and identified their closest relatives. We also discovered an apparent fungus infecting a quarter of the expelled Crossocephalus viviparus worms, a hyperabundant nematode species in the family Atractidae, hinting at the possibility that zebra host-parasite dynamics may involve a zebra-fungus mutualism. The two zebra species had similar nemabiomes; we found a complete overlap in the list of nematode species they carry and very similar prevalence (i.e., proportion of hosts infected) for the different nematode species. Our study suggests limited host-specificity in zebra strongyles and high potential for transmission between the plains zebra and the endangered Grevy's zebra.

Genetic variability, cryptic species and phylogenetic relationship of six cyathostomin species based on mitochondrial and nuclear sequences

Cyathostomins are important intestinal nematode parasites of equines and include 50 accepted species. Their taxonomy has been frequently revised and the presence of cryptic species suggested. Furthermore, usually molecular- and morphology-based phylogenetic analyses give divergent results. In this study, the nucleotide sequences of the nuclear second internal transcribed spacer (ITS-2) and the mitochondrial partial cytochrome c oxidase subunit I (COI) were determined for adults of six cyathostomin species (Coronocyclus coronatus, Coronocyclus labiatus, Cylicocyclus nassatus, Cylicostephanus calicatus, Cylicostephanus longibursatus, Cylicostephanus minutus) collected from different equine species within two geographic regions. Maximum likelihood trees were calculated for ITS-2, COI, and concatenated data. No obvious differentiation was observed between geographic regions or equine host species. As previously reported, Coronocyclus coronatus and Cylicostephanus calicatus revealed a close relationship. Cryptic species were detected in Cylicostephanus minutus and Cylicostephanus calicatus. Cylicocyclus nassatus and Coronocyclus labiatus showed diverse mitochondrial and nuclear haplotypes occurring in different combinations, while Cylicostephanus longibursatus was comparatively homogenous. In conclusion, a combined analysis of nuclear and mitochondrial haplotypes improved resolution of the phylogeny and should be applied to the remaining cyathostomin species and across additional equine host species and geographic regions.

Oxidative stress in Strongylus spp. infected donkeys treated with piperazine citrate versus doramectin

BACKGROUND

Parasitic infection is one of the main problems in equidae, particularly donkeys.

AIM

This study evaluated the oxidative stress in donkeys infected with Strongylus spp by determining the correlation between antioxidants levels; malondialdehyde (MDA), total antioxidant capacity (TAC), and the severity of parasitic infection. It also compared the therapeutic efficacy of piperazine citrate as an oral anthelmintic drug and Doramectin as an injectable one.

METHODS

The study was conducted on 40 donkeys naturally infected with Strongylus spp. These donkeys were divided into two groups (20 donkeys each) according to treatment; One group was treated with piperazine citrate (PipTG) and the other with doramectin (DoraTG). Thorough clinical examination, hematological, biochemical, and parasitological assays were performed before (Day 0) and after treatment (Days 7, 14, 21, and 28). All data were statistically analyzed by independent-sample t-test or paired t-test.

RESULTS

In both groups, mean values of MDA were significantly reduced, while those of TAC were significantly elevated after treatment on days 7, 14, 21, and 28. These significant changes were reported after treatment between PipTG and DoraTG in favor of DoraTG. Serum concentrations of MDA were significantly reduced, while those of TAC were significantly elevated for DoraTG treatment group when their values were compared with those of PipTG either on days 7, 14, 21, or 28. Significant correlations were reported in PipTG and DoraTG. Negative significant correlations were reported between fecal egg count (FEC) and each of whole blood picture indices (RBCS, Hb, and PCV), serum TAC and faecal egg count reduction percentage FECR%. A positive correlation was seen between FEC and MDA. MDA exhibited a negative correlation with both blood picture and TAC; hence, TAC was positively correlated with these blood picture indices in both PipTG and DoraTG. In PipTG, anthelmintic resistance (R) was present on days 7 and 14, while it was suspected (S) at day 21 then it was absent (N) at day 28. In DoraTG, anthelmintic resistance was suspected (S) on day 7, then it became absent (N) on days 14, 21, and 28 post therapy.

CONCLUSION

The immunological status of the infected donkeys had greatly improved after treatment. The therapeutic efficacy of injectable doramectin was more efficient than that of oral piperazine citrate in Strongylus spp. infected donkeys.

Faecal bacterial composition in horses with and without free faecal liquid: a case control study

Free faecal liquid (FFL) is a condition in horses which manifests as differential defecation of solid and liquid phases of faeces. The etiology of FFL is currently unknown, but deviances in the hindgut microbiota has been suggested to be of importance. The present study aimed to compare the faecal bacterial composition of farm-matched horses with (case, n = 50) and without (control, n = 50) FFL. Samples were collected at three different occasions. The V3 and V4 regions of the 16S rRNA gene were amplified and sequenced using Illumina sequencing. Also, samples were cultivated for detection of Clostridioides difficile and Clostridium perfringens. Analysis revealed similar faecal bacterial composition between case and control horses, but an effect of sampling period (p = 0.0001). Within sampling periods, 14 genera were present in higher or lower proportions in case compared to control horses in at least one sampling period. Compared to controls, case horses had higher relative abundance of Alloprevotella (adjusted p < 0.04) and lower relative abundance of Bacillus spp. (adjusted p < 0.03) in at least two sampling periods. All horses tested negative for C. difficile and C. perfringens by culture of faeces. Further studies are required to establish the clinical relevance of specific bacterial taxa in FFL.

Meta-analysis of cyathostomin species-specific prevalence and relative abundance in domestic horses from 1975-2020: emphasis on geographical region and specimen collection method

Background

Cyathostomins infect virtually all horses, and concomitant infections with 10 or more species per horse is standard. Species-specific knowledge is limited, despite potential species bias in development of disease and anthelmintic resistance. This is the first meta-analysis to examine effects of geographical region and cyathostomin collection method on reported composition of cyathostomin communities.

Methods

Thirty-seven articles published in English in 1975 or later, in which adults of individual species were systematically enumerated, were included. Seven regions; North America, South America, eastern Europe, western Europe, northern Europe, southern Africa, and Oceania, and three cyathostomin collection methods; (i) standard necropsy recovery from the large intestine, (ii) critical test collection from post-treatment feces and necropsy, and (iii) diagnostic deworming recovery solely from post-treatment feces, were considered. Generalized mixed linear models analyzed the effects of region and collection method on species-specific prevalence and relative abundance. Species richness was analyzed by mixed linear models.

Results

Definitively, the most prevalent and relatively abundant species were Cylicocyclus nassatus (prevalence = 93%, relative abundance = 20%), Cylicostephanus (Cys.) longibursatus (93%, 20%), and Cyathostomum catinatum (90%, 16%). A bias toward horses with high infection intensities and cyathostomin collection from feces resulted in North American critical tests and eastern European diagnostic deworming overestimating the species-specific prevalence and underestimating the relative abundance of rare/uncommon species compared to respective intra-regional standard necropsies. North American critical tests underestimated species richness due partially to identification key errors. Inter-regional standard necropsy comparisons yielded some species-specific regional differences, including a significantly higher Cys. longibursatus prevalence and relative abundance in North America (92%, 33%) than in eastern Europe (51%, 7%) (P > 0.0001). Localization of critical tests to North America and diagnostic deworming to Eastern Europe precluded expansive ‘region by collection method’ interaction analyses.

Conclusion

We provide substantial data to inform study design, e.g. effect and study size, for cyathostomin research and highlight necessity for method standardization and raw data accessibility for optimal post-factum comparisons.

Nuclear and mitochondrial marker sequences reveal close relationship between Coronocyclus coronatus and a potential Cylicostephanus calicatus cryptic species complex

The Cyathostominae (Nematoda, Strongyloidea) parasitising equines represent a diverse group currently including 50 species. However, their taxonomy has been repeatedly revised and occasionally the presence of cryptic genospecies was suggested. Moreover, molecular- and morphology-based phylogenetic analyses give divergent results. For instance, molecular data have suggested close relationship between Coronocyclus coronatus and Cylicostephanus calicatus, although morphology-based taxonomy places them in different genera. Here, nuclear (internal transcribed spacer 2, ITS-2) and mitochondrial (cytochrome oxidase I, COI) sequences were obtained from the same individual, morphologically identified worms. In both morphospecies, two ITS-2 sequences types were observed: In Cor. coronatus, a small PCR product of 278 bp (nuclear haplotype group nHGBco) was always present but often in combination with a larger 369-370 bp fragment (nHGAco). In Cys. calicatus, either a large 370 bp product (nHGAca) or a short 281 bp amplicon (nHGBca) were found, but never both. Sequence identity between morphospecies was up to 100%. The smaller differed from the larger fragments by deletion of the region 110-198 in Cor. coronatus and 112-203 in Cys. calicatus. In COI, three and five mitochondrial haplotype groups (HGs), mtHG1co-mtHG3co and mtHG1ca-mtHG5ca were identified for Cor. coronatus and Cys. calicatus, respectively. In Cor. coronatus, there was no particular association of mtHG with nuclear genotypes (only nHGBco vs. both nHGBco plus nHGAco). In Cys. calicatus the nHGAca was always associated with the mtHG1ca, mtHG2ca or mtHG5ca whereas nHGBca was exclusively associated with mtHG3ca or mtHG4ca. Despite up to 100% identity in the nHGs, no mixing of mtHGs was observed between both species. Clear separation of certain nHGs with particular mtHGs in Cys. calicatus, despite the fact that the same host individuals were infected with both groups simultaneously, suggests presence of two non-interbreeding genospecies within Cys. calicatus, which needs further confirmation using additional samples from diverse geographical origins.

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.

Simultaneous detection of the feline lungworms Troglostrongylus brevior and Aelurostrongylus abstrusus by a newly developed duplex-PCR

In addition to Aelurostrongylus abstrusus (Strongylida: Angiostrongylidae), referred to as the feline lungworm, Troglostrongylus brevior (Strongylida: Crenosomatidae) has recently been identified as an agent of bronco-pulmonary infestations in cats. These two parasites have a similar biology, share ecological niches, potentially co-infesting cats, but are difficult to be differentiated due to the morphological similarities of their first-stage larvae (L1). This paper describes a molecular tool, based on single-step duplex polymerase chain reaction (duplex-PCR) on the ribosomal internal transcribed spacer 2 region (ITS-2) for the simultaneous detection and differentiation of T. brevior and A. abstrusus. L1 of both species were collected from faecal samples, morphologically identified, and single larval specimens isolated. An aliquot of faeces was used as a test sample for a case of mixed natural infestation. The duplex-PCR was performed using species-specific forward primer sets for the ITS-2 region (i.e., A. abstrusus: 220bp; T. brevior: 370bp). The detection limit of the molecular assay was also assessed by serial dilutions of DNA from single larvae of both species (from ≈ 4.0 to 4.0 × 10(-5) μg/μl). The duplex-PCR carried out on individual DNA samples was able to detect as low as 5.2 × 10(-3) μg/μl of DNA for A. abstrusus, 4.9 × 10(-3)μg/μl for T. brevior, and as low as 4.0 × 10(-3) μg/μl for samples containing both species. Species-specific bands of the expected sizes and two bands were simultaneously amplified from the faecal sample containing both species. The phylogenetic analyses of the ITS-2 sequences here examined and those available for other metastrongyloids were concordant in clustering them with those of other Troglostrongylus brevior and A. abstrusus sequences available in GenBank database. This molecular approach proved to be effective and highly sensitive for the simultaneous detection of the two lungworms species and it might be used for molecular epidemiological studies and for monitoring therapeutic protocols.

An assessment of genetic variability in the mitochondrial cytochrome c oxidase subunit 1 gene of Cercopithifilaria sp. (Spirurida, Onchocercidae) from dog and Rhipicephalus sanguineus populations

This study investigates sequence variation in mitochondrial cytochrome c oxidase subunit 1 gene within Cercopithifilaria sp. recorded recently in Italy. Fourteen sequence types (haplotypes) were characterized for 163 (7.7%) amplicons from 2111 Genomic DNA samples prepared from skin samples from dogs and from Rhipicephalus sanguineus (ticks) from different geographical areas of the Mediterranean basin (i.e., Italy, Spain and Greece). The most prevalent sequence types represented haplotypes I (70.5%) and X (16.0%), followed by haplotype VIII (4.9%) and other 11 haplotypes (8.6%). Three haplotypes (II, V and VI) were found exclusively in ticks. The overall intraspecific nucleotide variation among pcox1 haplotypes ranged from 0.4 to 3.5% (mean = 1.6%), whereas a mean interspecific difference of 9.5% was detected as compared with other onchocercids. Phylogenetic analysis of the nucleotide sequence data showed a clustering of Cercopithifilaria sp. with the other Cercopithifilaria species (with strong statistical support) to the exclusion of other onchocercids. The number of haplotypes identified here might be explained by complex ecology and transmission patterns as well as the high mutation rate of mitochondrial DNA and/or inbreeding associated with hosts and their vectors.

Molecular differentiation of nocturnally periodic and diurnally sub-periodic Wuchereria bancrofti by Randomly Amplified Polymorphic DNA (RAPD)

Wuchereria bancrofti, a nematode parasite, is responsible for causing 90% of lymphatic filariasis infection in the world. In India, W. bancrofti exists in two physiological forms, nocturnally periodic in the main land and diurnally sub-periodic in Car Nicobar group of islands. Differentiation of these two parasitic forms by conventional microscopic methods difficult requiring good skill and hence tedious. Therefore, we developed a simple and rapid Random Amplified Polymorphic DNA (RAPD) assay to differentiate these parasitic forms. Also, the phylogenetic relationship between periodic and sub-periodic W. bancrofti and also Brugia malayi populations was analyzed using RAPD profile generated. Distinct RAPD profiles were observed among the three parasites with the formation of three distinct clusters in the phylogenetic tree. Substantial genetic diversity (Nei's genetic diversity H) was observed among periodic (H = 0.0577) and sub-periodic (H = 0.1415) W. bancrofti populations.

In vitro development of cyathostomin larvae from the third stage larvae to the fourth stage: morphologic characterization, effects of refrigeration, and species-specific patterns

A mixed population of equine cyathostomin (Nematoda, Strongyloidea) infective third stage larvae (L3) was cultured in vitro using a cell-free medium. Some L3 were cultured immediately after Baermann collection from fecal cultures, while others were kept in water at 4 degrees C for 7 days before initiating the in vitro cultures. Cultures were examined daily for viability. At days 2, 7, 14 and 21 larvae were collected for identification of developmental stage and morphological changes, using both light and scanning electron microscopy. Larvae were classified as early L3 (EL3), developing L3 (DL3), late L3 (LL3) and fourth stage larvae (L4) on the basis of morphological features. Viability remained high throughout the entire study period in cultures of both non-refrigerated (84.7%) and refrigerated (77.4%) larvae. However, viability of the non-refrigerated was significantly greater from 7 through 21 days of culture. Significant differences were also observed in the percentage of DL3 between the non-refrigerated and refrigerated larval cultures by day 7. The highest percentage of DL3 larvae (22.5%) was reached at the end of study in those larvae that were not previously refrigerated. The data suggests that prior refrigeration decreases viability and slows L3 development. At day 21 LL3 larvae were only a small percentage of the DL3: 6.9 and 5% in non-refrigerated and refrigerated cultures, respectively. Few of these larvae freed themselves from the L3 cuticle and moulted to L4 stage. Characteristics of individual species in vitro developmental patterns were determined by the molecular identification of individual larvae in pools of larvae randomly collected at days 0 and 21. Seven species (Coronocyclus coronatus, Cylicostephanus goldi, Cylicostephanus longibursatus, Cyathostomum catinatum, Cylicocyclus nassatus, Cylicocyclus ashworthi, Petrovinema poculatum) were identified in the day 0 pool. The greatest tendency to develop in vitro was shown by the genus Cylicostephanus with the species C. goldi and C. longibursatus that developed to the LL3-L4 stages. C. nassatus, C. ashworthi and C. coronatus did not progress in their development beyond the EL3 stage, while no apparent signs of development were registered for C. catinatum.

Morphology and diagnosis of some fourth-stage larvae of cyathostomines (Nematoda: Strongyloidea) in donkeys Equus asinus L. from Ethiopia

Fourth-stage larvae of four species of the Cyathostominae Nicoll, 1927 parasitic in donkeys Equus asinus L. from Ethiopia were identified mainly using moulting specimens. They are Cylicocyclus asini Matthee, Krecek & Gibbons, 2001, C. auriculatus (Looss, 1900) Chaves, 1930, Cyathostomum tetracanthum (Mehlis, 1831) Molin, 1861 (sensu Looss, 1900) and Cylindropharynx brevicauda Leiper, 1911. The larva of Cylicocyclus asini is similar to those of C. nassatus (Looss, 1900) Chaves, 1930 and C. leptostomum Kotlán, 1920, but differs from the former by the shape of the dorsal tooth in the oesophageal funnel, which is notably smaller than in C. asini but similar to that of C. leptostomum. However, the larva of C. asini differs from that of C. leptostomum in the size of the buccal capsule, which is notably larger than in C. leptostomum but similar to that of C. nassatus. The larva of C. auriculatus is very similar to that of C. insigne (Boulenger, 1917) Chaves, 1930. The larva of Cyathostomum tetracanthum is similar to those of Cylicostephanus bidentatus (Ihle, 1925) Lichtenfels, 1975, C. goldi (Boulenger, 1917) Lichtenfels, 1975 and Cyathostomum catinatum Looss, 1900. The larva of Cylindropharynx brevicauda is similar to that of Petrovinema skrjabini (Ershov, 1930) Ershov, 1943 but smaller in size. Including the four cyathostomine species identified in the present study, 36 species belonging to 13 genera have so far been described and identified of a total of 64 recognised and confirmed species of equine strongyles.

Detection and semi-quantification of Strongylus vulgaris DNA in equine faeces by real-time quantitative PCR

Strongylus vulgaris is an important strongyle nematode with high pathogenic potential infecting horses world-wide. Several decades of intensive anthelmintic use has virtually eliminated clinical disease caused by S. vulgaris, but has also caused high levels of anthelmintic resistance in equine small strongyle (cyathostomin) nematodes. Recommendations aimed at limiting the development of anthelmintic resistance by reducing treatment intensity raises a simultaneous demand for reliable and accurate diagnostic tools for detecting important parasitic pathogens. Presently, the only means available to differentiate among strongyle species in a faecal sample is by identifying individual L3 larvae following a two week coproculture procedure. The aim of the present study is to overcome this diagnostic obstacle by developing a fluorescence-based quantitative PCR assay capable of identifying S. vulgaris eggs in faecal samples from horses. Species-specific primers and a TaqMan probe were designed by alignment of published ribosomal DNA sequences of the second internal transcribed spacer of cyathostomin and Strongylus spp. nematodes. The assay was tested for specificity and optimized using genomic DNA extracted from identified male worms of Strongylus and cyathostomin species. In addition, eggs were collected from adult female worms and used to evaluate the quantitative potential of the assay. Statistically significant linear relationships were found between egg numbers and cycle of threshold (Ct) values. PCR results were unaffected by the presence of cyathostomin DNA in the sample and there was no indication of PCR inhibition by faecal sources. A field evaluation on faecal samples obtained from four Danish horse farms revealed a good agreement with the traditional larval culture (kappa-value=0.78), but with a significantly higher performance of the PCR assay. An association between Ct values and S. vulgaris larval counts was statistically significant. The present assay can reliably and semi-quantitatively detect minute quantities of S. vulgaris eggs in faecal samples.

New method for simultaneous species-specific identification of equine strongyles (nematoda, strongylida) by reverse line blot hybridization

The ability of a reverse line blot (RLB) assay to identify 13 common species of equine small strongyles (cyathostomins) and to discriminate them from three Strongylus spp. (large strongyles) was demonstrated. The assay relied on the specific hybridization of PCR-amplified intergenic spacer DNA fragments of the nuclear ribosomal DNA to membrane-bound species-specific probes. All cyathostomins examined were unequivocally identified and simultaneously discriminated from each other and from three large strongyles (Strongylus edentatus, Strongylus equinus, and Strongylus vulgaris). This assay will enable the accurate and rapid identification of equine cyathostomins irrespective of their life cycle stage, opening important avenues for a better understanding of their biology and epidemiology and of the pathogenesis of cyathostomin-associated disease. In particular, this RLB method promises to be a powerful diagnostic tool to determine the roles of individual species in the pathogenesis of mixed infections and to elucidate some aspects of cyathostominosis. Also, it could represent a basic step toward the development of a rapid and simple molecular test for the early detection of drug-resistant genotypes of horse strongyle species.

Molecular tools--advances, opportunities and prospects

Modern molecular technologies are having a substantial impact in many fundamental and applied areas of parasitology. In particular, polymerase chain reaction (PCR)-coupled approaches have found broad applicability because their sensitivity permits the enzymatic amplification of gene fragments from minute quantities of nucleic acids from tiny amounts of parasite material. Also, high-resolution electrophoretic and genomic methods are finding increased utility. This paper briefly discusses some developments and applications of DNA methods to parasites and highlights their usefulness or potential for those of veterinary importance. Selected examples of applications with implications in fundamental (systematics, population genetics, epidemiology and ecology) and applied (diagnosis, prevention and control) areas are presented. The focus is mainly on tools for the accurate identification of parasitic nematodes and protozoa of socio-economic importance, the diagnosis of infections and the detection of genetic variability using PCR-coupled mutation scanning technology.

Definition of genetic markers in nuclear ribosomal DNA for a neglected parasite of primates, Ternidens deminutus (Nematoda: Strongylida) – diagnostic and epidemiological implications

Ternidens deminutus (Strongylida) is a parasitic nematode infecting non-human and human primates in parts of Africa, Asia and the Pacific islands. The present study genetically characterized T. deminutus and defined genetic markers in nuclear ribosomal DNA (rDNA) as a basis for developing molecular-diagnostic tools. The sequences of the second internal transcribed spacer (ITS-2) of rDNA were determined for adult specimens of T. deminutus (Nematoda: Strongylida: Oesophagostominae) from the Olive baboon and the Mona monkey. The length and G+C content of the ITS-2 sequences was 216 bp and approximately 43%, respectively. While there was no sequence variation among individual T. deminutus specimens from the baboon, 6 (2.8%) nucleotide differences were detected in the ITS-2 between the parasite from baboon and that of the Mona monkey, which is similar to the difference (3.2%) between 2 other species of Oesophagostominae (Oesophagostomum bifurcum and O. stephanostomum) from non-human primates, suggesting significant population variation or the existence of cryptic (i.e. hidden) species within T. deminutus . Pairwise comparisons of the ITS-2 sequences of the 2 operational taxonomic units of T. deminutus with previously published ITS-2 sequences for selected members of the subfamilies Oesophagostominae and Chabertiinae indicated that species from primates (including those representing the subgenera Conoweberia and Ihleia) are closely related, in accordance with previous morphological studies. The sequence differences (27-48.3%) in the ITS-2 between the 2 taxonomic units of T. deminutus and hookworms (superfamily Ancylostomatoidea) enabled their identification and delineation by polymerase chain reaction (PCR)-based mutation scanning. The genetic markers in the ITS-2 provide a foundation for improved, PCR-based diagnosis of T. deminutus infections and for investigating the life-cycle, transmission patterns and ecology of this parasite.