Influence of host nutrition on the development and consequences of nematode parasitism in ruminants.

Control of gastrointestinal nematodes of ruminants is based largely on use of anthelmintics combined, where practical, with pasture management. The increasing prevalence of resistance to anthelmintics has led to the search for alternative sustainable control strategies. Here, we consider how nutrition, as a short-term alternative, can influence the host--parasite relationship in ruminants, using gastrointestinal nematode infections of sheep as the model system. Nutrition can affect the ability of the host to cope with the consequences of parasitism and to contain and eventually to overcome parasitism. It can also affect the parasite population through the intake of antiparasitic compounds.     

Anthelmintic resistance in nematode parasites of cattle: a global issue?

Acceptable performance of grazing cattle frequently depends on the availability of effective broad-spectrum anthelmintics to remove, or prevent infection with, gastrointestinal nematodes. This control is increasingly threatened by populations of nematodes resistant to the most commonly used anthelmintics. Although this appears to have developed more slowly than in nematodes infecting small ruminants, the number of reports in the literature over the past five years suggests a rapidly escalating problem. This review discusses this literature, several issues unique to cattle parasitism and anthelmintics, and how previous research in small ruminants can improve the management of anthelmintic resistance in cattle.     

Pro and cons of targeted selective treatment against digestive-tract strongyles of ruminants

The increasing prevalence of resistance to anthelmintics among gastrointestinal nematodes and the desire for lower input agriculture have promoted the idea that targeted selective treatment (treating the animals in need of such a treatment and only them) could be a sustainable solution for controlling internal parasites of ruminants. The pros are the slowing of resistance prevalence, lower residues of anthelmintics in meat and milk, and lower cost; the cons are the difficulty and time spent on selecting animals in need of treatment and the possibility of lower production. Using actual experiments and modelling we show that targeted selective treatment can be used to sustainably control gastrointestinal nematode infections in flock.     

Control of gastrointestinal strongyles in goats

Gastrointestinal (GI) parasitism are the most serious problem affecting sheep and goats worldwide. Economic losses caused by GI strongyles are related to decreased production, costs for treatment and prophylaxis and animal death. Effective control of internal parasites in small ruminants is one of the most difficult challenges encountered by veterinary in practice. For control of helminth parasites in grazing animals it is important knowledge of epidemiology of the parasite as it interacts with the host in a specific climatic, management and production environment. Sheep and goats are infected by many of the same GI nematodes, but feeding and management practices alter levels of parasitism between the two ruminants. The most commonly anthelmintics used for helminth control in small ruminants include three chemical groups: Imidazothiazoles/Pyrimidines (Im/Pm), Benzimidazoles/Probenzimidazoles (Bz/Pbz) and Macrocyclic Lactones (ML). The control of gastrointestinal strongyles infections in goats shows specific patterns. The use of anthelmintics in goats is based upon anthelmintics goats-suited dose rates taking into account the specific pharmacokinetics features of some anthelmintics in this species. Several types of control strategies: deworming programs, grazing management, biological control, supplementary feeding and breeding approaches are discussed.     

Advances in the diagnosis of key gastrointestinal nematode infections of livestock,with an emphasis on small ruminants

Parasitic nematodes (roundworms) of livestock have major economic impact globally. In spite of the diseases caused by these nematodes and some advances in the design of new therapeutic agents (anthelmintics) and attempts to develop vaccines against some of them, there has been limited progress in the establishment of practical diagnostic techniques. The specific and sensitive diagnosis of gastrointestinal nematode infections of livestock underpins effective disease control, which is highly relevant now that anthelmintic resistance (AR) is a major problem. Traditional diagnostic techniques have major constraints, in terms of sensitivity and specificity. The purpose of this article is to provide a brief background on gastrointestinal nematodes (Strongylida) of livestock and their control; to summarize conventional methods used for the diagnosis and discuss their constraints; to review key molecular-diagnostic methods and recent progress in the development of advanced amplification-based and sequencing technologies, and their implications for epidemiological investigations and the control of parasitic diseases.     

The sensory amphidial structures of Caenorhabditis elegans are involved in macrocyclic lactone uptake and anthelmintic resistance

Parasitic nematodes represent formidable pathogens of humans, livestock and crop plants. Control of these parasites is almost exclusively dependent on a small group of anthelmintic drugs, the most important of which belong to the macrocyclic lactone class. The extensive use of these drugs to control the ubiquitous trichostrongylid parasites of grazing livestock has resulted in the emergence of both single and multi-drug resistance. The expectation is that this resistance will eventually occur in the human parasites such as the common and debilitating soil transmitted nematodes and vector-borne filarial nematodes. While the modes of action of anthelmintics such as ivermectin, have been elucidated, notably in the model nematode Caenorhabditis elegans, the molecular nature of this resistance remains to be fully determined. Here we show that the anterior amphids play a key role in ivermectin uptake and mutations in these sensory structures result in ivermectin resistance in C. elegans. Random genetic mutant screens, detailed analysis of existing amphid mutants and lipophilic dye uptake indicate that the non-motile ciliated amphid neurons are a major route of ivermectin ingress; the majority of the mutants characterised in this study are predicted to be involved in intraflagellar transport. In addition to a role in ivermectin resistance, a subset of the amphid mutants are resistant to the non-related benzimidazole class of anthelmintics, raising the potential link to a multi-drug resistance mechanism. The amphid structures are present in all nematodes and are clearly defined in a drug-sensitive strain of Haemonchus contortus. It is predicted that amphidial drug uptake and intraflagellar transport may prove to be significant in the development of single and multi-drug resistance in the nematode pathogens of veterinary and human importance.     

In vitro anthelmintic effect of Melia azedarach L. and Trichilia claussenii C. against sheep gastrointestinal nematodes

The control of parasitic diseases in small ruminants is mainly done with the use of synthetic anthelmintics. However, incorrect and indiscriminate use of these products has caused the emergence of parasite resistance. Plants with anthelmintic activity are used in folk veterinary medicine, but it is necessary to investigate and scientifically validate low-cost phytotherapeutic alternatives for future use to control gastrointestinal nematodes in small ruminants by family farmers. Thus, the aim of this study was to evaluate the in vitro anthelmintic effect of plant extracts from Melia azedarach and Trichilia claussenii by the egg hatch test (EHT) and larval development test (LDT) against sheep gastrointestinal nematodes. The hexane extract of M. azedarach fruits was extracted through cold percolation and the methanol extract of T. claussenii leaves was obtained by extraction at room temperature in solvents in order of increasing polarity. The efficacy results were analyzed using the Probit program of SAS. The M. azedarach extract showed a LC(50) of 572.2 μg/mL and LC(99) of 1137.8 μg/mL in the EHT, and LC(50) of 0.7 μg/mL and LC(99) of 60.8 μg/mL in the LDT. In turn, the T. claussenii extract presented a LC(50) of 263.8 μg/mL and LC(99) of 522.5 μg/mL in the EHT and LC(50) of 1.1 μg/mL and LC(99) of 26.4 μg/mL in the LDT. Comparing the extracts of the species from the Meliaceae family, T. claussenii showed greater anti-parasite potential in vitro than M. azedarach. However, studies on the isolated compounds, toxicity and administration forms to animals are also needed to validate low-cost alternative herbal remedies for use to control gastrointestinal nematodes by family farmers.     

Evaluation of broad-spectrum anthelmintic activity in a novel assay against Haemonchus contortus, Trichostrongylus colubriformis and T. sigmodontis in the gerbil Meriones unguiculatus

The gerbil Meriones unguiculatus, infected with three species of nematodes, each located in a separate part of the gastrointestinal tract, provided a reliable laboratory assay for the evaluation of broad-spectrum anthelmintic activity. Gerbils harbouring 6-day-old infections of Haemonchus contortus, Trichostrongylus colubriformis and T. sigmodontis were given selected broad-spectrum anthelmintics by gavage. Three benzimidazoles, thiabendazole, oxfendazole and albendazole, a tetrahydropyrimidine, morantel, an imidazothiazole, levamisole hydrochloride, a macrocyclic lactone, ivermectin and an experimental natural product, paraherquamide, were active against all three nematodes at various dosages. Trichostrongylus colubriformis was most sensitive to levamisole hydrochloride, morantel, thiabendazole and paraherquamide whereas ivermectin, oxfendazole and albendazole were more effective against H. contortus. All compounds were active against the caecal nematode T. sigmodontis although it was less sensitive than T. colubriformis. Haemonchus contortus was more sensitive than T. sigmodontis to all anthelmintics tested except thiabendazole.     

Genetic resistance to haemonchosis in sheep

Parasitic nematodes cause huge economic losses to the domestic livestock industry. Control requires skilled farm management and heavy use of anthelmintics, but breeding for resistant animals has long been held a possibility. For about 20 years after World War ll, the genetics of association between sheep breeds and Haemonchus contortus - the main parasite of importance in sheep - was studied in the USA and Europe. Since the early 1970s, however, such studies have received greater emphasis in Australia, where anthelmintic resistance has become widespread. In this article, Douglas Gray discusses the background to breeding programmes for resistance to hoemonchosis - paying homage to the 'Golden Ram', a Merino believed to have carried a single major gene for immunological resistance to Haemonchus and Trichostrongylus.     

Nicotinic acetylcholine receptors: A comparison of the nAChRs of Caenorhabditis elegans and parasitic nematodes

Nicotinic acetylcholine receptors (nAChRs) play a key role in the normal physiology of nematodes and provide an established target site for anthelmintics. The free-living nematode, Caenorhabditis elegans, has a large number of nAChR subunit genes in its genome and so provides an experimental model for testing novel anthelmintics which act at these sites. However, many parasitic nematodes lack specific genes present in C. elegans, and so care is required in extrapolating from studies using C. elegans to the situation in other nematodes. In this review the properties of C. elegans nAChRs are reviewed and compared to those of parasitic nematodes. This forms the basis for a discussion of the possible subunit composition of nAChRs from different species of parasitic nematodes. Currently our knowledge on this is largely based on studies using heterologous expression and pharmacological analysis of receptor subunits in Xenopus laevis oocytes. It is concluded that more information is required regarding the subunit composition and pharmacology of endogenous nAChRs in parasitic nematodes.     

The diversity of ABC transporter genes across the Phylum Nematoda

It is estimated that one billion people globally are infected by parasitic nematodes, with children, pregnant women, and the elderly particularly susceptible to morbidity from infection. Control methods are limited to de-worming, which is hampered by rapid re-infection and the inevitable development of anthelmintic resistance. One family of proteins that has been implicated in nematode anthelmintic resistance are the ATP binding cassette (ABC) transporters. ABC transporters are characterized by a highly conserved ATP-binding domain and variable transmembrane regions. A growing number of studies have associated ABC transporters in anthelmintic resistance through a protective mechanism of drug efflux. Genetic deletion of P glycoprotein type ABC transporters in Caenorhabditis elegans demonstrated increased sensitivity to anthelmintics, while in the livestock parasite, Haemonchus contortus, anthelmintic use has been shown to increase the expression of ATP transporter genes. These studies as well as others, provide evidence for a potential role of ABC transporters in drug resistance in nematodes. In order to understand more about the family of ABC transporters, we used hidden Markov models to predict ABC transporter proteins from 108 species across the phylum Nematoda and use these data to analyze patterns of diversification and loss in diverse nematode species. We also examined temporal patterns of expression for the ABC transporter family within the filarial nematode Brugia malayi and identify cases of differential expression across diverse life-cycle stages. Taken together, our data provide a comprehensive overview of ABC transporters in diverse nematode species and identify examples of gene loss and diversification in nematodes based on lifestyle and taxonomy.     

Genomics of reproduction in nematodes: prospects for parasite intervention?

Understanding reproductive processes in parasitic nematodes has the potential to lead to the informed design of new anthelmintics and control strategies. Little is known, however, about the molecular mechanisms underlying sex determination, gametogenesis and reproductive physiology for most parasitic nematodes. Together with comparative analyses of data for the free-living nematode Caenorhabditis elegans, molecular investigations are beginning to provide insights into the processes involved in reproduction and development in parasitic nematodes. Here, we review recent developments, focusing on technological aspects and on molecules associated with sex-specific differences in adult nematodes.     

Breeding cattle and sheep for resistance to gastrointestinal nematodes

Gastrointestinal nematodes are an important cause of reduced production of meat, milk and wool in domestic livestock. It is generally believed that problems caused by these parasites have increased owing to the intensification of animal husbandry(1-3) of resistance to anthelmintics, current research is focussed on alternative control strategies that do not rely on anthelmintics. Here, Bram Kloosterman, Henk Parmentier and Harm Ploeger review work on the genetic resistance of domestic ruminants to these nematodes and discuss the practicality of breeding programmes.     

To treat or not to treat: diagnostic thresholds in subclinical helminth infections of cattle

Helminth infections of cattle place significant burdens on livestock production and farm economic efficiency. Heavy infections are relatively easy to detect and treat with anthelmintics. However, subclinical infections have major but often hidden impacts on animals, necessitating more refined diagnostics to detect them and ideally inform farmers about the likely impact of anthelmintic treatment on animal and herd performance. Here, we review recent advances in diagnosing three major cattle helminth infections – gastrointestinal nematodes (GINs), liver flukes, and lungworms – and the search for subclinical infection thresholds to guide treatment decisions. Combining refined diagnostic thresholds with farm-specific information on grazing systems and animal history enables farmers to tailor helminth treatments to specific epidemiological circumstances, thereby limiting anthelmintic resistance (AR) and boosting agricultural efficiency and food security.     

The cys-loop ligand-gated ion channel gene family of Brugia malayi and Trichinella spiralis: a comparison with Caenorhabditis elegans

Nematode cys-loop ligand gated ion channels (CLGIC) mediate neurotransmission and are important targets for anthelmintics in parasitic nematodes. The CLGIC superfamily in nematodes includes ion channels gated by acetylcholine, γ-amino butyric acid (GABA), glutamate, glycine and 5-HT. The macrocyclic lactones and the nicotinic agonists are important groups of anthelmintics that target the glutamate gated chloride channels and the nicotinic acetylcholine receptors, respectively. The model organism Caenorhabditis elegans has the most diverse families of cys-loop LGIC known in any organism. Many parasitic nematodes have homologues of C. elegans receptors but to date no genome wide investigations have been done. The genome sequencing projects of Brugia malayi (clade III) and Trichinella spiralis (clade I) have allowed us to characterise the CLGIC families in these species. Although the main groups of CLGICs targeted by anthelmintics are represented in both the nematode genomes investigated here, the CLGIC family is much smaller in B. malayi and T. spiralis, suggesting that care must be taken when using C. elegans as a model organism for distantly related nematodes.     

Emodepside and SL0-1 potassium channels: a review

Nematode parasites infect humans and domestic animals; treatment and prophylaxis require anthelmintic drugs because vaccination and sanitation is limited. Emodepside is a more recently introduced cyclooctadepsipeptide drug that has actions against GI nematodes, lungworm, and microfilaria. It has a novel mode of action which breaks resistance to the classical anthelmintics (benzimidazoles, macrocyclic lactones and cholinergic agonists). Here we review studies on its mode of action which suggest that it acts to inhibit neuronal and muscle activity of nematodes by increasing the opening of calcium-activated potassium (SLO-1) channels.     

Succinate dehydrogenase and fumarate reductase activity in Aspiculuris tetraptera and Ascaris suum and the effect of the anthelmintics cambendazole,thiabendazole, and levamisole

Comley John C. W. and Wright Spdenis J. 1981. Succinate dehydrogenase and fumarate reductase activity in Aspiculuris tetraptera and Ascaris suum and the effect of the anthelmintics cambendazole, thiabendazole, and levamisole. International Journal for Parasitology11: 79–84. Succinate dehydrogenase and fumarate reductase activities from a particulate fraction of A. tetraptera and a soluble extract of A. suum have been determined using spectrophotometric methods. Fumarate reductase activity in A. suum could only be detected anaerobically. Succinate dehydrogenase activity from A. suum was partially characterized and shown to exist in several multimolecular forms (isoenzymes). The in vitro effect of the anthelmintics cambendazole, thiabendazole and levamisole on succinate dehydrogenase and fumarate reductase activity from the above nematodes are described. Significant inhibition of fumarate reductase activity of both nematodes was only achieved using 5 mM levamisole and 1 mM thiabendazole. After in vivo anthelmintic treatment of A. tetraptera only thiabendazole significantly inhibited fumarate reductase. It is suggested that the succinate dehydro-ogenase-fumarate reductase complex in these nematodes is unlikely to be the primary site chemotherapeutic attack for any of the anthelmintics tested.     

In-vitro predatory activity of nematophagous fungi from Costa Rica with potential use for controlling sheep and goat parasitic nematodes

In tropical and subtropical regions of the world, parasitic diseases are a main cause of losses in livestock productivity. The increased acquired resistence to anthelmintics by gastrointestinal nematodes, requires biological control be considered as a potential feasible and effective alternative. The most effective natural soil enemies of nematodes are nematophagous fungi. In order to collect and identify predator nematophagous fungi (PNF), samples were obtained from 51 farms distributed throughout the seven provinces of Costa Rica. The origin samples included: soil from different crops (potatoes, tomatoes, bananas, ornamental plants, squash and coffee); animal feces (cattle, sheep, goat and horse); soil and fallen leaves from forest; and plants with signs of nematode infection. Each sample was processed using three techniques for the extraction of fungi from soil: sprinkling technique, soil dilution and humidity chamber. Twenty four strains of nematophagous fungi were found in 19 farms; 83.3% of the fungi were isolated by sprinkling technique. The following fungi were identified: Arthrobotrys oligospora (n = 13); Candelabrella musiformis (n = 9); and for the first time there was isolation of A. conoides (n = 1) and A. dactyloides (n = 1) in the country. Moreover, 16 strains from Trichoderma (n=13), Beauveria (n = 1), Clonostachys (n = 1) and Lecanicillium (n = 1) were obtained. In addition, pH of each possible fungal isolation source was measured, and it varied from 5.2 to 9.9, however PNF isolates fell within the range of 5.6 to 7.5. The PNF strains were cultivated in four different media for the production of chhlamydospores: potato dextrose agar (PDA); corn meal agar (CMA); malt extract agar (MEA) and potato carrot agar (PCA). Out of these cultures, 95.8% of the strains formed chlamydospores primarily in the PCA. Of these strains, the profilic spore producers were subjected to ruminant artificial gastrointestinal conditions. A total of 14 fungi were tested, out of which 42.9% survived the digestive analysis. Neither A. conoides nor A. dactyloides were viable following the in vitro gastrointestinal test. The PNF isolated in this study demonstrated an action against ovine and caprine gastrointestinal nematodes and are candidates for use in biological control of these organisms. Among these microorganisms, Candelabrella musiformis appears to be the most promising fungi for use as a biological control agent in Costa Rica.     

Tannins in tropical tree fodders fed to small ruminants: A friendly foe?

Livestock production systems worldwide rely largely on conventional feedstuffs. The current world food crisis highlights the need to improve the use of local resources for animal nutrition, such as fodder trees and shrubs. The detrimental effects of tropical tannin-rich plants (TRP) on animal production have been frequently described. In contrast, their potential benefits have long been neglected. This paper presents the potential positive effects of tropical TRP on small ruminants either as source of feed or as nutraceuticals with anthelmintic (AH) properties. It also analyses the host behavioral and physiological adaptations associated with exploitation of those tannin-rich resources. Both sheep and goats preferred a mixture of plants even when tannin-free forage was available. Moreover, the preference for TRP by goats and hair sheep were mainly associated with the digestible fraction of fiber and to a less extent with tannin content, which implies that they do not necessarily select against TRP. The addition of polyethylene glycol did not modify the preference or intake of TRP by goats and sheep. Evidence of physiological adaptation to TRP is presented and discussed. Both, experienced hair sheep and goats had saliva with tannin binding capacity, enabling both species to eat higher quantities of TRP which could lead to a higher availability of tannins in the gastrointestinal tract. Tannins in the gastrointestinal tract could be an AH against gastrointestinal nematodes (GIN). Indeed, in vitro and in vivo studies have shown AH effects of tannins from TRP, suggesting their possible use as natural anthelmintics against GIN. This paper supports the change in the current view of tannins in TRP as anti-nutritional compounds. If adequately managed, TRP can be a valuable component of sustainable small ruminant production systems.