Advances in diagnosis of gastrointestinal nematodes in livestock and companion animals

Diagnosis of gastrointestinal nematodes in livestock and companion animals has been neglected for years and there has been an historical underinvestment in the development and improvement of diagnostic tools, undermining the undoubted utility of surveillance and control programmes. However, a new impetus by the scientific community and the quickening pace of technological innovations, are promoting a renaissance of interest in developing diagnostic capacity for nematode infections in veterinary parasitology. A cross-cutting priority for diagnostic tools is the development of pen-side tests and associated decision support tools that rapidly inform on the levels of infection and morbidity. This includes development of scalable, parasite detection using artificial intelligence for automated counting of parasitic elements and research towards establishing biomarkers using innovative molecular and proteomic methods. The aim of this review is to assess the state-of-the-art in the diagnosis of helminth infections in livestock and companion animals and presents the current advances of diagnostic methods for intestinal parasites harnessing (i) automated methods for copromicroscopy based on artificial intelligence, (ii) immunodiagnosis, and (iii) molecular- and proteome-based approaches. Regardless of the method used, multiple factors need to be considered before diagnostics test results can be interpreted in terms of control decisions. Guidelines on how to apply diagnostics and how to interpret test results in different animal species are increasingly requested and some were recently made available in veterinary parasitology for the different domestic species.

Anthelmintic resistance in ruminants: challenges and solutions

Anthelmintic resistance (AR) is a growing concern for effective parasite control in farmed ruminants globally. Combatting AR will require intensified and integrated research efforts in the development of innovative diagnostic tests to detect helminth infections and AR, sustainable anthelmintic treatment strategies and the development of complementary control approaches such as vaccination and plant-based control. It will also require a better understanding of socio-economic drivers of anthelmintic treatment decisions, in order to support a behavioural shift and develop targeted communication strategies that promote the uptake of evidence-based sustainable solutions. Here, we review the state-of-the-art in these different fields of research activity related to AR in helminths of livestock ruminants in Europe and beyond. We conclude that in the advent of new challenges and solutions emerging from continuing spread of AR and intensified research efforts, respectively, there is a strong need for transnational multi-actor initiatives. These should involve all key stakeholders to develop indicators of infection and sustainable control, set targets and promote good practices to achieve them.

Initial assessment of the economic burden of major parasitic helminth infections to the ruminant livestock industry in Europe

We report a European wide assessment of the economic burden of gastrointestinal nematodes, Fasciola hepatica (common liver fluke) and Dictyocaulus viviparus (bovine lungworm) infections to the ruminant livestock industry. The economic impact of these parasitic helminth infections was estimated by a deterministic spreadsheet model as a function of the proportion of the ruminant population exposed to grazing, the infection frequency and intensity, the effect of the infection on animal productivity and mortality and anthelmintic treatment costs. In addition, we estimated the costs of anthelmintic resistant nematode infections and collected information on public research budgets addressing helminth infections in ruminant livestock. The epidemiologic and economic input data were collected from international databases and via expert opinion of the Working Group members of the European Co-operation in Science and Technology (COST) action COMbatting Anthelmintic Resistance in ruminants (COMBAR). In order to reflect the effects of uncertainty in the input data, low and high cost estimates were obtained by varying uncertain input data arbitrarily in both directions by 20 %. The combined annual cost [low estimate-high estimate] of the three helminth infections in 18 participating countries was estimated at € 1.8 billion [€ 1.0-2.7 billion]. Eighty-one percent of this cost was due to lost production and 19 % was attributed to treatment costs. The cost of gastrointestinal nematode infections with resistance against macrocyclic lactones was estimated to be € 38 million [€ 11-87 million] annually. The annual estimated costs of helminth infections per sector were € 941 million [€ 488 - 1442 million] in dairy cattle, € 423 million [€ 205-663 million] in beef cattle, € 151million [€ 90-213 million] in dairy sheep, € 206 million [€ 132-248 million] in meat sheep and € 86 million [€ 67-107 million] in dairy goats. Important data gaps were present in all phases of the calculations which lead to large uncertainties around the estimates. Accessibility of more granular animal population datasets at EU level, deeper knowledge of the effects of infection on production, levels of infection and livestock grazing exposure across Europe would make the largest contribution to improved burden assessments. The known current public investment in research on helminth control was 0.15 % of the estimated annual costs for the considered parasitic diseases. Our data suggest that the costs of enzootic helminth infections which usually occur at high prevalence annually in ruminants, are similar or higher than reported costs of epizootic diseases. Our data can support decision making in research and policy to mitigate the negative impacts of helminth infections and anthelmintic resistance in Europe, and provide a baseline against which to measure future changes.

Mind the gaps in research on the control of gastrointestinal nematodes of farmed ruminants and pigs

Gastrointestinal (GI) nematode control has an important role to play in increasing livestock production from a limited natural resource base and to improve animal health and welfare. In this synthetic review, we identify key research priorities for GI nematode control in farmed ruminants and pigs, to support the development of roadmaps and strategic research agendas by governments, industry and policymakers. These priorities were derived from the DISCONTOOLS gap analysis for nematodes and follow-up discussions within the recently formed Livestock Helminth Research Alliance (LiHRA). In the face of ongoing spread of anthelmintic resistance (AR), we are increasingly faced with a failure of existing control methods against GI nematodes. Effective vaccines against GI nematodes are generally not available, and anthelmintic treatment will therefore remain a cornerstone for their effective control. At the same time, consumers and producers are increasingly concerned with environmental issues associated with chemical parasite control. To address current challenges in GI nematode control, it is crucial to deepen our insights into diverse aspects of epidemiology, AR, host immune mechanisms and the socio-psychological aspects of nematode control. This will enhance the development, and subsequent uptake, of the new diagnostics, vaccines, pharma-/nutraceuticals, control methods and decision support tools required to respond to the spread of AR and the shifting epidemiology of GI nematodes in response to climatic, land-use and farm husbandry changes. More emphasis needs to be placed on the upfront evaluation of the economic value of these innovations as well as the socio-psychological aspects to prioritize research and facilitate uptake of innovations in practice. Finally, targeted regulatory guidance is needed to create an innovation-supportive environment for industries and to accelerate the access to market of new control tools.

P-glycoproteins play a role in ivermectin resistance in cyathostomins

Anthelmintic resistance is a global problem that threatens sustainable control of the equine gastrointestinal cyathostomins (Phylum Nematoda; Superfamily Strongyloidea). Of the three novel anthelmintic classes that have reached the veterinary market in the last decade, none are currently licenced in horses, hence current control regimens focus on prolonging the useful lifespan of licenced anthelmintics. This approach would be facilitated by knowledge of the resistance mechanisms to the most widely used anthelmintics, the macrocyclic lactones (ML). There are no data regarding resistance mechanisms to MLs in cyathostomins, although in other parasitic nematodes, the ABC transporters, P-glycoproteins (P-gps), have been implicated in playing an important role. Here, we tested the hypothesis that P-gps are, at least in part, responsible for reduced sensitivity to the ML ivermectin (IVM) in cyathostomins; first, by measuring transcript levels of pgp-9 in IVM resistant versus IVM sensitive third stage larvae (L3) pre-and post-IVM exposure in vitro. We then tested the effect of a range of P-gp inhibitors on the effect of IVM against the same populations of L3 using the in vitro larval development test (LDT) and larval migration inhibition test (LMIT). We demonstrated that, not only was pgp-9 transcription significantly increased in IVM resistant compared to IVM sensitive L3 after anthelmintic exposure (p < 0.001), but inhibition of P-gp activity significantly increased sensitivity of the larvae to IVM in vitro, an effect only observed in the IVM resistant larvae in the LMIT. These data strongly implicate a role for P-gps in IVM resistance in cyathostomins. Importantly, this raises the possibility that P-gp inhibitor-IVM combination treatments might be used in vivo to increase the effectiveness of IVM against cyathostomins in Equidae.

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Pgp-9 transcript levels were higher in ivermectin resistant versus susceptible cyathostomin populations.

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P-gp inhibitors increased ivermectin effect against cyathostomins in vitro.

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P-gp activity may play a role in ivermectin resistance in cyathostomins.

The occurrence and genetic characterization of Cryptosporidium and Giardia species in foals in Belgium, The Netherlands, Germany and Greece

Faecal samples were collected from foals between the age of 1 week and 6 months in Belgium, The Netherlands, Germany and Greece. A quantitative direct immunofluorescence assay based on the commercial MERIFLUOR Cryptosporidium/Giardia kit was performed to evaluate the presence of (oo) cysts. Parasite positive samples were genotyped, based on the 18S ribosomal DNA gene and the heat shock protein (HSP70) gene for Cryptosporidium and on the β-giardin gene and the triose phosphate isomerase (TPI) gene for Giardia. In total, 134 foals from Belgium, 44 foals from The Netherlands, 30 foals from Germany and 190 foals from Greece were examined. No Cryptosporidium oocysts were identified in faecal samples from foals in Germany and The Netherlands. In Belgium and Greece, 4.5% and 1.1% of the foals examined were Cryptosporidium positive, respectively, all with a low oocyst excretion ranging from 100 to 2450 oocysts per gram of faeces. For Giardia, 14.2%, 11.4%, 10.0% and 11.6% of the foals in Belgium, The Netherlands, Germany and Greece, respectively, were found to excrete cysts, with a range of 50 up to 4,000,000 cysts per gram of faeces. Younger animals secreted significantly more Giardia cysts than older horses (p<0.05), but no significant correlation between Giardia infection and diarrhoea was observed. Most Giardia positive samples belonged to assemblage AI and/or BIV, but also assemblage E was detected in two samples. Together with the identification of Cryptosporidium horse genotype, this suggests only a low risk for zoonotic transmission.

Real-time PCR detection for quantification of infection levels with Ostertagia ostertagi and Cooperia oncophora in cattle faeces

A quantitative real-time polymerase chain reaction (qPCR) based on hydrolysis (TaqMan) probes is described for robust and sensitive detection of the infection levels with eggs and third stage larvae (L3) of Cooperia oncophora and Ostertagia ostertagi isolated from cattle faeces. The current microscopic method for identification of strongyle nematodes in cattle faeces is labour-intensive where reliable species determination also requires trained expertise, which is increasingly lacking. The goal of this study was to develop a sustainable non-labour intensive diagnostic qPCR assay to detect and determine the levels of infection with the two most common gastro-intestinal nematodes (GIN) in cattle faeces targeting the second internal transcribed spacer of nuclear ribosomal DNA (ITS2) region (rDNA). According to our results, this procedure allows to reliably detect the relative proportions of eggs and L3 for each of the two species. This assay produced consistent results when mixtures with known numbers of L3 of both species were tested, although it was also demonstrated that the calculated copy numbers of ITS2 between single L3 sometimes varied very much. In addition, a positive correlation (r(2)=0.23) between the proportion of eggs and L3 in different paired samples collect in the field was observed for both species. Thus, for the first time a qPCR assay is reported, which can discriminate between the two most important cattle nematode parasites in temperate regions. This is of major importance to the livestock sector as it can be used with great precision to demonstrate strategic treatment efficacy that is important for the detection of anthelmintic resistance (AR).

The role of culture media on embryonation and subsequent infectivity of Capillaria obsignata eggs

This study investigated whether infectivity of Capillaria obsignata eggs depends on media culture used for embryonation. Intact female worms were kept in one of following four media: 0.5 % formalin, 2 % formalin, 0.1 % potassium dichromate and 0.1 N sulfuric acid. Embryonation rates of the eggs were quantified either daily in intact females for 16 days, or weekly in disrupted females. Infectivity of the embryonated eggs was tested through an experimental infection of chickens with a single dose of 250 eggs/ bird. The vast majority of the eggs (>82 %) in the first two thirds of the uteri was able to complete embryonation, irrespective of the culture media used for incubation. However, only 32.6 % of total eggs could be harvested after disruption of the intact females. Embryonation rates of the eggs from disrupted worms were different among four culture media, with 0.1 N sulfuric acid resulting in the highest embryonation rate (44.2 %). All the experimentally infected birds harboured mature worms, with varying establishment rates depending on the culture media (P < 0.001). Incubation of the eggs in potassium dichromate 0.1 % resulted in a lower (P < 0.001) establishment rate (10.2 %) when compared with formalin (70.5 and 47.9 % for concentrations at 0.5 and 2 %, respectively) or with 0.1 N sulfuric acid (57.5 %). It can be concluded that most of the eggs in first two thirds of the uteri in the intact females have the potential to complete embryonation without being influenced by the culture media. However, disruption of the intact females results in lower number of harvestable embryonated eggs, with a considerable variation due to culture media used. With the exception of 0.1 % potassium dichromate, any of the three media, particularly 0.1 N sulfuric acid, can be suggested for embryonation of C. obsignata eggs.

Adaptation and evaluation of three different in vitro tests for the detection of resistance to anthelmintics in gastro intestinal nematodes of cattle

Three different in vitro methods, the Larval Development Test (LDT), the Larval Migration Inhibition Test (LMIT) and the Micromotility Meter Test (MMT) have been adapted to detect anthelmintic resistance in cattle nematodes. Nematode eggs and third stage larvae of different Ostertagia ostertagi and Cooperia oncophora isolates were obtained from faecal cultures of experimentally infected calves. Additionally, adult C. oncophora were evaluated in the MMT for the detection of resistance to ivermectin (IVM). For all three in vitro tests standard operating procedures (SOPs) were established and successfully used for the detection of responses of non-parasitic and parasitic stages to different anthelmintic substances and the description of dose-response curves. In the LDT ivermectin (IVM) and thiabendazole (TBZ) were tested, in the LMIT IVM and levamisole (LEV) and in the MMT only IVM was evaluated. Susceptible isolates of C. oncophora and O. ostertagi, an IVM-resistant isolate of C. oncophora and a TBZ-selected isolate of O. ostertagi were used in all (C. oncophora) or only some of these tests (O. ostertagi). For all isolates sigmoidal dose-response curves and EC(50) values for the tested substances were obtained using a four-parameter logistic model. For the LDT, the previously reported problem in development of larvae was successfully overcome with mean development rates between 80% and 87% in negative controls. Following optimization of incubation times, temperatures, mesh sizes (LMIT only), nutritive medium (LDT only) and group size (MMT only) all three test systems reliably detected significant differences in the response to IVM between the susceptible and IVM-resistant isolate of C. oncophora (p<0.0001), resulting in an resistance ratio (RR) value of approximately 5 for IVM and 2.8 for LEV in C. oncophora. The LDT also detected differences in the response to TBZ between the susceptible and BZ-selected O. ostertagi isolates (p<0.001) with an RR of 2 for TBZ. With the standardization of the described tests we report reproducible and reliable in vitro methods for the detection of resistance to IVM (LDT, LMIT and MMT) and TBZ (LDT) for cattle parasitic nematodes.

The use of a simplified faecal egg count reduction test for assessing anthelmintic efficacy on Belgian and German cattle farms

Anthelmintic resistant cattle nematodes have been reported in different regions around the world. However, in Western Europe the assessment of the problem relies largely on case reports and no prevalence data based on wide-scale surveys are available. Therefore, we performed a survey to (1) screen for reduced anthelmintic efficacy in Belgian and German cattle farms; (2) evaluate the usefulness of a simplified faecal egg count reduction test (FECRT), where efficacies are based on the mean FECs of 10 at random collected faecal samples pre- and post-treatment per farm and (3) identify possible risk factors for reduced anthelmintic efficacy. Of 88 farms included in this study, 84 farms used macrocyclic lactones (MLs). A FECR <95% was observed on 39% of these 84 farms. However, using a Markov chain Monte Carlo simulation analysis, to correct for the used McMaster FEC technique with a detection limit of 50 epg, reduced efficacy could only be confirmed in 25% of the farms (21/84). Only Cooperia spp. were found in significant numbers in the coprocultures post-treatment. Reduced efficacy was significantly associated with farm type and with a lower efficacy in beef herds compared to dairy herds. Four farms were revisited and a standardized FECRT was performed to confirm anthelmintic resistance (AR). Surprisingly, macrocyclic lactone resistance against Cooperia oncophora was only confirmed in one of four farms. In conclusion, our results show that a reduced efficacy observed in a FECRT are not only caused by AR but that the detection limit of the FEC technique used and the (in)correct administration of the anthelmintic drugs are confounding factors of major importance.

Putative G protein-coupled receptors in parasitic nematodes--potential targets for the new anthelmintic class cyclooctadepsipeptides?

Parasitic nematodes cause major problems in livestock animals. Resistances to the most commonly used drugs are arising. The cyclooctadepsipeptide emodepside belongs to a new class of anthelmintics. A receptor for emodepside, Hc110-R, was previously identified in Haemonchus contortus. We have identified the complete coding sequences of putative orthologues in Cooperia oncophora and Ostertagia ostertagi, tri-chostrongyles in cattle. The putative receptors were named depsiphilins. The deduced amino acid sequence of C. oncophora depsiphilin has a similarity of 91% to the O. ostertagi sequence. The similarity of both the C. oncophora and O. ostertagi depsiphilin to Hc110-R is 89%, based on the amino acid sequence. The depsiphilins share 46% identity with the latrophilin-like protein 1 in Caenorhabditis elegans and 47% identity with a hypothetical protein in Caenorhabditis briggsae. Hc110-R and the latrophilin-like proteins of C. elegans were previously reported to be putative G protein-coupled receptors (GPCRs) and to be related to mammalian latrophilins. A seven transmembrane domain, a GPCR proteolytic site, and other conserved domains characteristic of receptors of the latrophilin group were identified within the depsiphilins. Therefore it seems reasonable to allocate the depsiphilins to the previously described latrophilins and latrophilin-like proteins.

Efficacy of toltrazuril as a metaphylactic and therapeutic treatment of coccidiosis in first-year grazing calves

A multicentric, placebo–controlled, randomised, blinded and blocked field study was conducted to evaluate the efficacy and safety of toltrazuril (Baycox^®, Bayer AG, Leverkusen, Germany) in the treatment of coccidiosis in first–year grazing calves naturally infected with Eimeria spp. Three–hundred and thirty–one calves were enrolled in the study and allocated to one of two treatments at a ratio of 1:1. One hundred and sixty–seven animals were treated once orally with 15 mg/kg toltrazuril, and 164 animals served as placebo–treated controls. Two treatment regimes were compared, a metaphylactic (treatment on the day, or 1 day after, turn out) and a therapeutic treatment (4 or 7 days after turn out). During an observation period of 14 days after treatment the animals were clinically examined for diarrhoea and faecal samples were regularly assessed for Eimeria oocysts. Other possible causes of diarrhoea were excluded on the basis of microbiological and virological examination. Animals were predominantly infected with Eimeria alabamensis. Number of days with diarrhoea in animals treated with toltrazuril was significantly lower compared to the placebo–treated group (therapeutic treatment: P=0.0024; metaphylactic treatment: P<0.0001). Furthermore, the number of animals with diarrhoea during the observation period for a minimum of at least 3 days, the number of animals positive for Eimeria oocysts, and the number of animals with both diarrhoea for a period of at least 3 days and positive for Eimeria oocysts, were signiflicantly lower (P<0.01), in the toltrazuril– compared to the placebo–treated animals. Body weight in the toltrazuril–treated animals significantly exceeded that of the placebo–treated animals at the end of the observation period. Mean difference in body weight was higher in the metaphylactic (+7.3 kg) compared to the therapeutic treatment group (+3.4 kg). No adverse reactions were observed. The results indicate that toltrazuril is highly efficacious and safe in the metaphylactic and therapeutic treatment of coccidiosis caused by E. alabamensis in first–year grazing calves.

Stage-dependent transcriptional changes and characterization of paramyosin of the bovine lungworm Dictyocaulus viviparus

The bovine lungworm Dictyocaulus viviparus is of major economic importance in cattle farming in the temperate zones. The invertebrate protein paramyosin is one of the main components of muscle thick filaments but can also exhibit immunomodulatory functions. It represents a promising vaccine candidate in parasitic helminths. In this study, D. viviparus paramyosin (DvPmy) was characterized on the transcriptional as well as genomic level. The identified genomic sequence comprises 19 introns compared to only 10 introns in the Caenorhabditis elegans orthologue. Quantitative real time PCR transcriptional analysis revealed paramyosin transcription throughout the whole parasite's life cycle with the highest transcription rate in the agile moving first-stage larvae and the lowest in motionless hypobiosis induced third stage larvae. Recombinantly expressed DvPmy was found to bind collagen and IgG. Thereby the present study is the first showing that nematode paramyosin has the capability for immunomodulation and thus may be involved in host immune defence.

Foreword: Towards markers for anthelmintic resistance in helminths of importance in animal and human health

Anthelmintic resistance is a serious problem in veterinary medicine and appears to be developing in some helminths of importance to human health. Anthelmintic drugs remain the principal means of control of helminth infections in animals and humans and the continued dependence on these pharmaceuticals will continue to impose selection pressure for resistance development. Our ability to detect anthelmintic resistance before control breaks down and to monitor the spread of anthelmintic resistance is quite limited. We are currently dependent on biological methods which are not sufficiently sensitive to detect low levels of drug resistance and are particularly difficult to perform on helminth parasites of humans. There is a serious need for new molecular markers for detecting and monitoring for anthelmintic resistance. The problem of anthelmintic resistance is already very serious in nematode parasites of livestock. In addition, there should be great concern about possible anthelmintic resistance development and the lack of tools and efforts for monitoring it as part of the major worldwide programmes to control helminth parasites in people. An international Consortium has been formed to develop Anthelmintic Resistance Single nucleotide polymorphism markers (CARS). Discussions within the Consortium have addressed the need for such markers, the current state of knowledge about them, possible mechanisms of anthelmintic resistance and approaches and constraints to the development of markers. Summaries of the state of the art in these areas are presented in a series of papers in this Special Issue of Parasitology.

Cases of reduced cyathostomin egg-reappearance period and failure of Parascaris equorum egg count reduction following ivermectin treatment as well as survey on pyrantel efficacy on German horse farms

In 2003 and 2004, on a total of 63 different German horse farms, a survey using the faecal egg count reduction (FECR) test was performed to investigate the efficacy of ivermectin (IVM, Ivomec) and pyrantel (PYR, Banminth) treatment against gastro-intestinal nematodes in a total of 767 horses. IVM treatment resulted in 100% reduction of the cyathostomin egg production 14 and 21 days post-treatment (d.p.t.) on 37 farms. On the remaining five farms, the mean faecal egg count reduction ranged between 97.7 and 99.9%. The mean cyathostomin FECR following PYR treatment ranged between 92.2 and 100% on the 25 farms tested. Therefore, based on the 90% FECR threshold suggested for detection of anthelmintic resistance in horses, neither IVM nor PYR anthelmintic resistance was detected. However, if the thresholds recommended for the detection of resistance in small ruminants were applied, on one and four farms signs of reduced IVM and PYR efficacy, respectively, were observed. In 2005, to further investigate these findings, the cyathostomin egg-reappearance period (ERP) following IVM treatment was examined on six selected farms, two of which were found to show less than 99.8% FECR in the previous survey. On these two latter farms, the ERP was less than 5 weeks, while on the other four it was at least 8 weeks. Earlier investigations described IVM cyathostomin ERP of at least 9 weeks. The efficacy of IVM to reduce Parascaris equorum egg excretion was also studied. On one farm in 2 consecutive years, IVM treatment did not lead to a significant reduction in P. equorum faecal egg counts in one and five young horses, respectively.

Blastocystis: subtyping isolates using pyrosequencing technology

Blastocystis is a prevalent single-celled enteric parasite of unresolved clinical significance. Efforts based on molecular methodologies to establish whether pathogenicity is linked to specific isolates of the genetically diverse genus of Blastocystis have been scarce and so far yielded ambiguous results which can be difficult to interpret. To alleviate some of the problems related to unravelling the molecular epidemiology of Blastocystis infections we developed and evaluated a simple and high-throughput sequence analysis (SQA) pyrosequencing technique based on the detection of genotype-specific nucleotide polymorphisms in the 18S small subunit rRNA gene for a rapid and cost-effective post-PCR screening of Blastocystis genotypes. The method was effectively capable of genotyping 48/48 isolates positive by nested PCR in approximately one hour, and in 94% of the cases the isolate detected by PCR and pyrosequencing was also detected by one of two different PCR assays with subsequent dideoxy sequencing.

The detection of anthelmintic resistance in nematodes of veterinary importance

Before revised World Association for the Advancement of Veterinary Parasitology (WAAVP) guidelines on the detection of anthelmintic resistance can be produced, validation of modified and new methods is required in laboratories in different parts of the world. There is a great need for improved methods of detection of anthelmintic resistance particularly for the detection of macrocyclic lactone resistance and for the detection of resistant nematodes in cattle. Therefore, revised and new methods are provided here for the detection of anthelmintic resistance in nematodes of ruminants, horses and pigs as a basis for discussion and with the purpose that they are evaluated internationally to establish whether they could in the future be recommended by the WAAVP. The interpretation of the faecal egg count reduction test has been modified and suggestions given on its use with persistent anthelmintics and continuous release devices. An egg hatch test for benzimidazole (BZ) resistance is described. A microagar larval development test for the detection of benzimidazole and levamisole resistance provides third stage larvae for the identification of resistant worms. The sensitivity of these two tests can be increased by using discriminating doses rather than LD(50) values. Details are given of a PCR based test for the analysis of benzimidazole resistance in strongyles of sheep and goats, horses and cattle. Although promising for ruminant trichostrongyles, quantitative determination of gene frequency using real time PCR requires further development before PCR tests will be used in the field. Apart from faecal egg count reduction tests there are currently no satisfactory tests for macrocylic lactone resistance despite the great importance of this subject. Except for treatment and slaughter trials there are no validated tests for fasciolicide resistance or for the detection of resistance in cestodes.

Clinical and epidemiological characteristics of Eimeria infections in first-year grazing cattle

Infections with Eimeria parasites can lead to severe diarrhoea with considerable clinical and economic consequences in first-year grazing stock. To identify and characterise the cause of diarrhoea observed during previous years, 164 animals on 14 dairy farms in northwestern Germany were included in this study. The calves were physically and parasitologically examined prior to turnout and until 21 days post turnout (d.p.t.). Mean animal weights decreased from 194.9 kg at the start to 189.3 kg bodyweight at the end of the study. In all herds, oocyst counts were very low prior to turnout and increased after the calves had been kept on pasture for at least 7 days. On Day 9 post turnout, 90% and at the end of the study (21 d.p.t.) 70% of all animals showed Eimeria-positive faecal samples. During the course of the study, 79 (48.2%) animals passed faecal samples with more than 100,000 oocysts per gram. The predominant species identified was Eimeria alabamensis, which accounted for more than 83% of the oocysts counted. These parasitological findings matched the clinical observations. Diarrhoea was found in 130 (79.3%) of the study animals. At 5 d.p.t. and thus prior to the rise of faecal oocyst counts, a significant increase in diarrhoea was recorded. Calves showing diarrhoea excreted statistically significantly more often over 100,000 E. alabamensis oocysts per gram faeces (0.28; p = 0.0002) than calves without diarrhoea. Diarrhoea was also found during significantly more study days in animals with high oocyst counts (0.39; p = 0.0001). These data indicate that in endemic areas first-year grazing calves must be considered at risk to develop clinical coccidiosis due to E. alabamensis infection during the first 2–3 weeks post turnout.

Efficacy of two cyclooctadepsipeptides, PF1022A and emodepside, against anthelmintic-resistant nematodes in sheep and cattle

Resistance against the major currently available anthelmintics has reached a critical level in many small ruminant herds world-wide, and is increasingly becoming a problem in horses and cattle. Therefore, new products with different modes of action are urgently needed. Recently, such a new class of compounds, the anthelmintically active cyclooctadepsipeptides, was described. Here, the effects of cyclooctadepsipeptides on benzimidazole-, levamisole- and ivermectin-resistant populations of Haemonchus contortus in sheep as well as an ivermectin-resistant Cooperia oncophora population in cattle were studied. Experimentally infected sheep and cattle were used. Animals were treated orally, subcutaneously, or intravenously with cyclooctadepsipeptides. The anthelmintic effects were assessed by means of fecal egg count reductions and/or worm count reductions. Both, PF1022A and emodepside were found to be fully effective against these parasite populations. These findings confirm that this new class of compounds acts by a different mode of action compared to the above-mentioned anthelmintics.

Compensated overexpression of procollagens alpha 1(I) and alpha 1(III) following perilla mint ketone-induced acute pulmonary damage in horses

Interstitial lung disease with chronic fibrosis is a frequent cause of reduced performance in horses. The aim of this study was to establish a model of acute alveolar damage and interstitial lung disease in horses that could be used to monitor the histopathological lesions and changes in expression levels of genes relevant to pulmonary fibrosis. Six adult horses were given a single intravenous injection (6 mg per kg body weight) of perilla mint ketone (PMK). Transthoracic lung biopsy samples (1 x 0.2 x 0.2 cm) were collected before and after (days 1, 4, 8, 11, 15, 18, 22, 25 and 29) the administration of PMK. Light and electron microscopy revealed severe acute alveolar damage (days 1 to 4), proliferation of type II pneumocytes (days 4 to 11) and finally complete healing at about day 18. However, unexpectedly severe clinical signs necessitated euthanasia in two horses on days 9 and 11. The expression levels of the collagen genes COL1AI and COL3AI as well as transforming growth factor (TGF)-beta were examined in the biopsy samples by reverse transcription-real time quantitative polymerase chain reaction. COL1AI and COL3AI gene expressions were upregulated (3- and 17-fold, respectively) between days 1 and 29 in all six horses, whereas TGF-beta was upregulated in two horses (2- and 4-fold, respectively), between days 4 and 18. Although the gene expression analyses indicated a strong activation of the pro-fibrotic pathway, no interstitial fibrosis was seen in any horse. A complete necropsy performed on day 60 revealed complete recovery of the lungs of the four surviving horses, with no evidence of fibrosis. Unidentified compensatory mechanisms may have prevented pulmonary fibrosis, despite strong upregulation of pro-fibrotic genes.

Quantification of MDR-1 gene expression in canine tissues by real-time reverse transcription quantitative polymerase chain reaction

MDR-1 gene product mediated multidrug resistance is thought to play a major role in the outcome of chemotherapy in some canine tumors, especially malignant lymphoma. In the present study, MDR-1 RNA expression in normal lymph node and liver tissue as well as in tumor biopsies from 23 dogs with lymphomas and two dogs with liver tumors was measured by real-time RT-quantitative PCR. MDR-1 gene expression was detected in all samples analyzed. Comparably high MDR-1 RNA levels were measured in all normal liver tissues, one of the lymphomas and a cholangiocarcinoma. MDR-1 expression levels in canine lymphomas were found to vary over a wide range with most tumors expressing relative low levels. Interestingly, gastrointestinal lymphomas expressed higher MDR-1 RNA levels than multicentric lymphomas (p = 0.03). In conclusion, real-time RT-quantitative PCR appears to be a suitable method for sensitive and quantitative determination of MDR-1 gene expression in canine normal and neoplastic tissues.

EVIDENCE OF P-GLYCOPROTEIN SEQUENCE DIVERSITY IN CYATHOSTOMINS

P-glycoproteins (Pgps) are adenosine triphosphate-binding transporter proteins thought to be associated with multi-drug resistance in mammals and protozoans and have been suggested to be involved in the mechanism of ivermectin (IVM) resistance in Haemonchus contortus. Until now, resistance to IVM has not been reported in cyathostomins in horses in spite of its widespread and frequent use. Reasons for this might be differences in the molecular mechanism of the development of resistance. Based on this hypothesis, the present study was carried out to find homologues of Pgp in cyathostomins. A 416-bp polymerase chain reaction (PCR) product was generated using complementary DNA (cDNA) of Cylicocyclus elongatus and Cylicocyclus insigne and degenerate primers, located in the conserved Pgp nucleotide-binding domains. Resulting PCR products showed interspecific nucleotide and amino acid sequence identities of 73.3 and 76.8%, respectively. Specific primers were designed based on the Cc. elongatus sequence, and a PCR product of 268-bp was amplified from cDNA of single adults of Cylicocyclus radiatus, Cc. insigne, Cylicocyclus nassatus, Cc. elongatus, Cylicostephanus hybridus (2 individuals), Cylicostephanus goldi, Cyathostomum pateratum, Cyathostomum coronatum, and Cyathostomum catinatum. Two clusters of sequences were found representing 2 different internucleotide-binding domains (IBDs). A further distinct IBD is represented by the 416-bp PCR product of Cc. insigne. Therefore, a total of 3 clearly different sequences of the IBD were cloned and sequenced, suggesting that at least 2 Pgp genes exist in cyathostomins.

Beta-Tubulin Complementary DNA Sequence Variations Observed Between Cyathostomins From Benzimidazole-Susceptible and -Resistant Populations

The molecular mechanism of benzimidazole (BZ) resistance in cyathostomins of horses is still unclear. Previous studies revealed that the TTC or TAC polymorphism in codon 200 of the beta-tubulin isotype 1 gene is not as strictly correlated with BZ resistance as in trichostrongyles in sheep. To identify further sites of polymorphism within the beta-tubulin gene related to BZ resistance, complete complementary DNAs (cDNAs) encoding beta-tubulin of adult worms of Cylicocyclus nassatus, Cyathostomum pateratum, Cyathostomum coronatum, Cyathostomum catinatum, Cylicostephanus longibursatus, and Cylicostephanus goldi of a BZ-resistant cyathostomin population were characterized using specific primers. The cDNA sequence of each species spans 1,429 bp, encoding a protein of 448 amino acids. The interspecific identities are 95.2-99.6% at the nucleotide and 98.7-100.0% at the peptide level. The comparison of the amino acid sequences of individuals isolated from the BZ-resistant cyathostomin population with those from individuals of Cc. nassatus, Cy. coronatum, Cy. pateratum, and Cy. catinatum of a BZ-susceptible one showed differing amino acids in 11 positions. The commonness of a phenylalanine to tyrosine mutation at position 167 in all the 6 cyathostomin species isolated from a BZ-resistant population suggests its involvement in the molecular mechanism in BZ resistance.

Prevalence of benzimidazole resistance on horse farms in Germany

Faecal egg counts (FECs) were made on samples from 1383 horses on 64 farms in northern Germany between August 2000 and November 2001. There were significant differences between the mean FECs in the two years; in 2000, 59.6 per cent of 369 samples were positive and in 2001, 32.6 per cent of 1014 samples were positive for strongyle eggs. The results of a FEC reduction test indicated that resistance to fenbendazole was present on all 10 farms where it had been used, including in 33 of 60 horses tested. In contrast, treatment with ivermectin resulted in the complete elimination of nematode eggs in all the 77 horses tested. The mean LD50 values of the egg hatch test for thiabendazole indicated resistance on all 20 farms investigated and in 94 of 134 samples (70 per cent).

Anthelminthika-Resistenzen bei Pferde- und Wiederkäuerhelminthen: neueste Forschungsergebnisse aus molekularbiologischer Sicht

Gegenwärtig sind Anthelminthika-Resistenzen bei Pferdeund Wiederkäuerhelminthen bereits weit verbreitet. Es handelt sich dabei in erster Linie um Resistenzen gegen Wirkstoffe aus den Gruppen der Benzimidazole (BZ) und bei kleinen Wiederkäuern auch der makrozyklischen Laktone (ML). Das Angriffsziel der BZ ist das Beta-Tubulin. Gemeinsam mit dem Alpha-Tubulin bildet dieses Protein die röhrenartigen Mikrotubulin-Strukturen in den Zellen der Parasiten und Wirte. Die BZ binden an das Beta-Tubulin und blockieren dadurch den Aufbau von Mikrotubuli. Ohne Mikrotubuli können wichtige Zellstoffwechselvorgänge, wie z. B. der intrazelluläre Transport von Stoffen oder die Zellteilung, nicht mehr stattfinden, sodass der betroffene Organismus abstirbt. Durch molekularbiologische Untersuchungen konnte nachgewiesen werden, dass bei BZ-resistenten Trichostrongyliden des Schafes im Vergleich zu BZ-empfindlichen Würmern Unterschiede in der Gensequenz des Beta-Tubulins auftreten. Dabei wird durch die Expression von Tyrosin anstelle von Phenylalanin, vor allem an der Position 200 des Proteins, die Bindungsintensität zwischen BZ und dem Zielprotein erheblich reduziert. Beim Pferd sind in erster Linie Populationen der auch als Palisadenwürmer bezeichneten kleinen Strongyliden (Cyathostominae) von BZ-Resistenz betroffen. Ähnlich wie bei den Trichostrongyliden wurden auch hier Veränderungen der Beta-Tubulin- Gensequenz im Zusammenhang mit der Resistenz beobachtet. Allerdings scheint hier die Veränderung in der Position 200 nur eine untergeordnete Bedeutung zu haben. Die molekularen Zusammenhänge der Resistenz gegen ML sind bisher nur vergleichsweise wenig untersucht. Neueste Daten zum Resistenzmechanismus bei Cooperia oncophora des Rindes weisen auf Veränderungen im glutamatgesteuerten Chloridionenkanal, dem Zielprotein dieser Wirkstoffklasse, hin.

Analysis of the beta-tubulin codon 200 genotype distribution in a benzimidazole-susceptible and -resistant cyathostome population

To study the prevalence of the polymorphism in position 200 of the beta-tubulin gene in the mechanism of benzimidazole (BZ) resistance in cyathostomes of horses, an allele-specific PCR was used to detect the genotype of individuals of BZ-susceptible and BZ-resistant populations. The molecular analysis of 100 adults recovered from an anthelmintic-naïve horse revealed 80% homozygous TTC/TTC individuals, 17% heterozygous TTC/TAC and 3% homozygous TAC/TAC. A naturally infected horse was treated with increasing fenbendazole (FBZ) dosages to select a BZ-resistant population of cyathostomes. The PCR based analysis of 3rd-stage larvae (L3) during the experiment revealed a decrease of the homozygous TTC/TTC genotype and an increase in heterozygous TTC/TAC and homozygous TAC/TAC individuals. After treatment 42.3% of the adults (n=104) were homozygous TTC/TTC, 55.8% were heterozygous TTC/TAC and only 1.9% showed the homozygous genotype TAC/TAC. The results of the molecular analysis lead to the proposal that polymorphism within codon 200 is not the only reason for the development of BZ resistance in small strongyles.

Analysis of codon usage in beta-tubulin sequences of helminths

Codon usage bias has been shown to be correlated with gene expression levels in many organisms, including the nematode Caenorhabditis elegans. Here, the codon usage (cu) characteristics for a set of currently available beta-tubulin coding sequences of helminths were assessed by calculating several indices, including the effective codon number (Nc), the intrinsic codon deviation index (ICDI), the P2 value and the mutational response index (MRI). The P2 value gives a measure of translational pressure, which has been shown to be correlated to high gene expression levels in some organisms, but it has not yet been analysed in that respect in helminths. For all but two of the C. elegans beta-tubulin coding sequences investigated, the P2 value was the only index that indicated the presence of codon usage bias. Therefore, we propose that in general the helminth beta-tubulin sequences investigated here are not expressed at high levels. Furthermore, we calculated the correlation coefficients for the cu patterns of the helminth beta-tubulin sequences compared with those of highly expressed genes in organisms such as Escherichia coli and C. elegans. It was found that beta-tubulin cu patterns for all sequences of members of the Strongylida were significantly correlated to those for highly expressed C. elegans genes. This approach provides a new measure for comparing the adaptation of cu of a particular coding sequence with that of highly expressed genes in possible expression systems.Finally, using the cu patterns of the sequences studied, a phylogenetic tree was constructed. The topology of this tree was very much in concordance with that of a phylogeny based on small subunit ribosomal DNA sequence alignments.

Quantitative analysis of ITS2 sequences in trichostrongyle parasites

Real-time PCR assays were developed to identify and quantify common gastrointestinal nematodes of ruminants. The assays were based on genus-specific primer and probe combinations derived from the second internal transcribed spacer (ITS2) ribosomal DNA transcription unit of Haemonchus contortus, Ostertagia leptospicularis, Trichostrongylus colubriformis and Cooperia curticei. The TaqMan probes for the first two species were labelled with 6-carboxyfluorescein and those for the latter two with VIC and all were synthesised as dihydrocyclopyrroloindole minor groove binder conjugates. Cloned ITS2 DNA or genomic DNA isolated from first stage larvae, derived from overnight cultures, were used as template. The real-time PCRs reproducibly allowed the identification of at least 100 copies of cloned ITS2 DNA or one hundredth part of a single larval genomic DNA equivalent. The assays proved to be genus-specific since the addition of DNA from heterologous trichostrongyle genera did not change the cycle threshold values obtained with only homologous DNA. Furthermore, the use of genomic DNA of several other ruminant nematode parasite genera gave negative results. In duplex experiments, 6-carboxyfluorescein-labelled H. contortus or O. leptospicularis probes were used together with the VIC-labelled T. colubriformis and C. curticei probes, respectively, confirming the specificity and sensitivity of the probes found in the simplex experiments. The primer and probe combinations gave comparable results when applied with core reagents from different suppliers and with both the M x 4000 and the ABI 7700 instruments. This technique provides means for a rapid, reliable and quantitative detection and differentiation of the most important parasitic nematodes of sheep and cattle.

Allele-specific PCR for the beta-tubulin codon 200 TTC/TAC polymorphism using single adult and larval small strongyle (Cyathostominae) stages

It has been shown that benzimidazole (BZ) resistance in sheep gastrointestinal nematodes is linked with an increase in beta-tubulin codon 200 tyrosine-expressing alleles in the resistant parasite populations. Here, an allele-specific PCR has been developed for the discrimination of the TAC/TTC polymorphism in the beta-tubulin 200 codon of small strongyles. One reverse primer was used in 2 separate amplifications with 1 of 2 forward primers that differed only in their final 3' nucleotide. The primers flank a facultative intron/exon. Therefore, the amplified fragments are either 251 or 308 bp in size, depending on the presence or absence of the intron in individual worms. Amplification of genomic DNA isolated from single adult small strongyles from a set of 7 species consistently generated allele-specific products. Three worms each of the following species were used: Cylicocyclus nassatus, Cylicocyclus insigne, Cylicocyclus elongatus, Cylicocyclus radiatus, Cyathostomum pateratum, Cyathostomum catinatum, and Cyathostomum coronatum. PCR with DNA isolated from single larvae also reproducibly generated specific fragments. This method might be applied for the future assessment of allele frequencies in susceptible and resistant populations to further investigate the mechanism of BZ-resistance in small strongyles.

Filaricidal efficacy of anthelmintically active cyclodepsipeptides

PF 1022A, a novel anthelmintically active cyclodepsipeptide, and Bay 44-4400, a semisynthetic derivative of PF 1022A were tested for filaricidal efficacy in Mastomys coucha infected with Litomosoides sigmodontis, Acanthocheilonema viteae and Brugia malayi. The parent compound PF 1022A showed limited anti-filarial efficacy in L. sigmodontis and B. malayi infected animals. Oral doses of 5 x 100 mg/kg on consecutive days caused only a temporary decrease of microfilariaemia levels. By contrast, Bay 44-4400 was highly effective against microfilariae of all three species in single oral, subcutaneous and cutaneously applied (spot on) doses. Minimum effective doses (MED, reducing parasitaemia density by > or =95%) determined 3 and 7 days after treatment were 3.125-6.25 and 6.25-12.5mg/kg, respectively. Using the spot on formulation, doses of 6.25mg/kg (L. sigmodontis), 12.5mg/kg (A. viteae) and 25mg/kg (B. malayi) were required to cause reductions of microfilaraemia levels by > or =95% until day 56. Adulticidal effects, determined as minimum curative doses (MCD, eliminating adult parasites within 56 days by >95%) after single dose treatment were limited to A. viteae (MCD, 100mg/kg independent of the route of administration). Repeated oral treatment (100mg/kg on 5 consecutive days) killed all adult L. sigmodontis but did not affect B. malayi. However, single doses of 6.25 and 25mg/kg resulted in severe pathological alterations of intrauterine stages of L. sigmodontis and B. malayi, respectively. These alterations may be responsible for long-lasting reductions of microfilaraemia even when curative effects could not be achieved.

Activity of the cyclic depsipeptide emodepside (BAY 44-4400) against larval and adult stages of nematodes in rodents and the influence on worm survival

The present investigations deal with the activity of the cyclic depsipeptide emodepside (BAY 44-4400) against larval and adult stages of three rodent nematodes. While emodepside acts strongly against the adult stages of the rat nematodes Nippostrongylus brasiliensis and Strongyloides ratti, as well as against the mouse nematode Heligmosomoides polygyrus, its actions against the larval stages of these nematodes vary according to the species. Thus, emodepside is highly effective against the lung and intestine larval stages of N. brasiliensis and S. ratti. By contrast. the larval stages of H. polygyrus in the intestine are only partly affected by higher emodepside dosages.

Effects of Bay 44-4400, a new cyclodepsipeptide, on developing stages of filariae (Acanthocheilonema viteae, Brugia malayi, Litomosoides sigmodontis) in the rodent Mastomys coucha

Bay 44-4400 was used as a spot on formulation and administered in single doses of 25 and 100 mg/kg to Acanthocheilonema viteae, Brugia malayi, and Litomosoides sigmodontis infected Mastomys coucha on various dates during prepatency, aiming to affect third stage larvae, fourth stage larvae or preadult worms. Microfilaraemia levels were controlled in comparison to untreated controls until necropsies were performed 100 days p.i. (A. viteae, L. sigmodontis) and 150 days p.i. (B. malayi) to determine the numbers of surviving worms and the condition of intrauterine developing stages. A significant proportion (86-100%) of larval and preadult stages of A. viteae were killed by Bay 44-4400 at a dose of 100 mg/kg. A dose of 25 mg/kg had only insignificant effects on the developing parasites, however, it strongly reduced microfilaraemia levels caused by surviving worms in the early phase of patency. Larval and preadult B. malayi and L. sigmodontis were not killed by Bay 44-4400 to a significant degree. Microfilaraemia developing by surviving parasites was generally and significantly reduced throughout the observation period when treatment was performed to affect the preadult parasites. In the other cases variable results were obtained. Intrauterine early embryonic stages were found to be pathologically altered in worms which had been treated at a preadult stage.

Sequence variations in the introns of the triosephosphate isomerase genes of Oesophagostomum dentatum and O. quadrispinulatum

Degenerated primers were used to amplify DNA fragments of the triosephosphate isomerase (TPI) gene from complementary DNA (cDNA) and from genomic DNA of two species of porcine gastrointestinal nematodes, Oesophagostomum dentatum and O.quadrispinulatum. Polymerase chain reaction (PCR) fragments amplified from cDNA were 520 bp in size for both species, while genomic fragments were 1,035 bp for O. dentatum (GC-content: 45%) and 1,331 bp for O. quadrispinulatum (44%). Sequence analyses revealed blocks of high homology in the exons interrupted by more variable parts in the intron regions. Five exons were predicted from the genomic sequences in the conserved regions which corresponded to the respective cDNA sequences with 6% interspecific differences. The predicted protein sequences (161 amino acids) were 98% similar between the species and showed 71% similarity to the putative protein of Caenorhabditis elegans. As a housekeeping gene, TPI could be amplified from cDNA of both infectious third-stage larvae and adults. Interspecific variations in the non-coding regions allow the PCR-based differentiation of the two Oesophagostomum spp.

Novel small strongyle (Cyathostominae) beta-tubulin sequences

Several coding sequences of the benzimidazole (BZ) target beta-tubulin have been described for different parasitic nematodes. However, until recently no tubulin sequences from Cyathostome species were available, despite the importance of BZ resistance in horses in the field. Here, we describe several full-length beta-tubulin coding sequences of two major small strongyle species, namely Cylicocyclus nassatus and Cyathostomum coronatum. In the latter sequence, the putative BZ resistant mutation in codon 200 leading to a Phe to Tyr exchange is present. High nucleotide sequence similarities (>95%) were found among the tubulin sequences of the two different genera. This will be of advantage for the development of an allele-specific BZ resistance polymerase chain reaction (PCR) for multiple small strongyle species.

Synergistic action of a cyclic depsipeptide and piperazine on nematodes

The present study describes the synergistic effects of the cyclic depsipeptide BAY 44-4400 and piperazine in the treatment against the nematodes Trichinella spiralis, Heligmosomoides polygyrus, and Heterakis spumosa. The in vitro anthelmintic activity of a combination of the two compounds (1.7 motility units) against T. spiralis larvae was significantly higher than the sum of the individual drug effects (1.3 motility units). With regard to the rate of expulsion of H. polygyrus worms from the intestine of infected mice, an additive effect was observed; piperazine alone exerted an efficacy of 54.4% and BAY 44-4400 alone, one of 44.4%, whereas the combination of these compounds had an efficacy of 97.5%. With regard to the expulsion of H. spumosa worms, the effect of the combination was more than 5 orders of magnitude greater than the sum of the effects of the single compounds, i.e., there was a considerable potentiation of the actions of BAY 44-4400 and piperazine. Moreover, the combination exerted a significantly higher degree of degenerative effects on the intestine and on the nerve chords of H. spumosa as compared with the single compounds.

In vivo activities of the new anthelmintic depsipeptide PF 1022A

PF 1022A is a member of a new class of cyclic depsipeptides with antiparasitic activity. Following in vitro and laboratory animal studies it was tested for its anthelmintic efficacy in companion and livestock animals against a wide spectrum of intestinal nematodes and lungworms. Studies were carried out in rats, dogs, horses, sheep, and cattle. Animals were either naturally or experimentally infested. The efficacy of PF 1022A was investigated against the following parasite species: Strongyloides ratti and Nippostrongylus brasiliensis in rats, Ancylostoma caninum in dogs, small strongyles (cyathostomes) in horses, Trichostrongylus colubriformis and Haemonchus contortus in sheep, and Dictyocaulus viviparus in cattle. Doses varied from 1 to 10 mg/kg body weight for oral, subcutaneous or intravenous application in companion and livestock animals. High degrees of efficacy were found in all the above-cited examinations, and no clinical signs of intolerability were observed.

Characterisation of the beta-tubulin gene of Cylicocyclus nassatus?

mRNA and genomic DNA were isolated from adult Cylicocyclus nassatus, and the mRNA was reverse transcribed. The cDNA was PCR amplified using degenerate primers designed according to the alignment of the beta-tubulin amino acid sequences of other species. To complete the coding sequence, the 3' end was amplified with the 3' RACE, and for amplification of the 5' end the SL1-primer was used. The cDNA of the beta-tubulin gene of C. nassatus spans 1429 bp and encodes a protein of 448 amino acids. Specific primers were developed from the cDNA sequence to amplify the genomic DNA sequence and to analyse the genomic organisation of the beta-tubulin gene. The complete sequence of the genomic DNA of the beta-tubulin gene of C. nassatus has a size of 2652 bp and is organised into nine exons and eight introns. The identities with the exons of the gru-1 beta-tubulin gene of Haemonchus contortus range between 79% and 97%.