The prospects for biological control of the free-living stages of nematode parasites of livestock

Antagonistic effects of native strains of the soil fungus Paecilomyces against gastrointestinal nematode and protozoan parasites of pigs in Panama

A variety of gastrointestinal parasites naturally infect domestic pigs in Panama which may also occur as zoonotic infections in humans. Anthelmintic drug treatment, including mass drug administration, can lead to drug resistance, reflecting a need for alternatives. The objectives of this exploratory and observational study were: (1) to isolate and cultivate natives species of Paecilomyces from natural soils in Panama, and (2) to evaluate isolated strains for their capacity to parasitize endemic gastrointestinal nematode and protozoan parasites recovered from naturally infected domestic pigs by observing cultures for spore adhesion and hyphae penetration phases. Using microcultivation and inoculation techniques, four strains of Paecilomyces were isolated from three locations in Panama, out of which three successfully adhered to and penetrated free-living stages (eggs, cysts and oocysts) of Balantidium suis, coccidia, Trichuris suis and hookworm. To our knowledge, this is the first published report of a nematophagous fungus such as Paecilomyces successfully infecting this range of gastrointestinal parasites, particularly protozoan parasites.

Nematicide activity of microfungi (Orbiliales, Orbiliaceae) after transit through gastrointenstinal tract of “Gallus gallus domesticus”

SUMMARY Parasites are common in intensive or organics systems destined for chickens, which is more conducive to the emergence of gastrointestinal parasites, favored by direct contact with soil and other organisms. The growing demand for animal protein stimulates an expansion of production systems, increasing the stocking density. Outdoor poultry breeding systems (organic or not) that enable lower population density and higher animal welfare does not exclude these animals the presence of environmental pathogens. The control of gastrointestinal helminthosis in non-organic intensive and extensive systems is accomplished by administering anthelmintics with high cost and results unsatisfactory due to the misuse of drugs with consequent selection parasite strains resistant to chemical bases. This problem stimulate research into alternative control measures. Nematophagous fungi are used by its enzymatic action in controlled conditions and how environmental biocontrolers of larvae of gastrointestinal nematodes of livestock. This study evaluated the capacity of conidia/chlamydospores of nematophagous fungi as Duddingtonia flagrans (AC001 and CG722) and Monacrosporium thaumasium (NF34A) for cross the gastrointestinal tract of domestic chickens (Gallus gallus domesticus), and yours germination after traffic and predatory activity “in vitro” on larvae of Panagrellus spp. Fungi conidia/chlamydospores was identified in feces of chickens at times of 6, 12 and 24 hours after administration and spores viability was found after observing the germination, mycelial growth, followed by production of traps, capture and death of Panagrellus spp larvae in feces. Fungi Nematophagous are alternative control measures, efficient and innovative technology for the biological control of helminth parasites of chickens.

Integrated parasite management with special reference to gastro-intestinal nematodes

Domestic animals are susceptible to a large number of parasitic diseases, which lead to severe economic losses to livestock industry. So, it is necessary to control parasitic infections in these animals. Control of these helminths is undertaken mostly by anthelmintics, but because of their widespread use there is development of resistance across the globe. However, total dependence on a single method of control has proved to be non-sustainable and cost ineffective in the long term. A combination of treatment and management is necessary to control parasitism so that it will not cause further economic losses to producer as well as to livestock industry. To become practically and ecologically sustainable, parasitic control schemes need to be based on integrated parasite management.

Biological Control of the Nematode Infective larvae of Trichostrongylidae Family With Filamentous Fungi

Background:

Biological control of parasitic nematodes by microorganisms is a promising approach to control such parasites. Microorganisms such as fungi, viruses and bacteria are recognized as biocontrol agents of nematodes.

Objectives:

The current study mainly aimed to evaluate the in vitro Potential of various saprophyte soil-fungi in reducing the infective larvae stage of parasitic nematode Trichostrongylidae family.

Materials and Methods:

Sheep feces were employed to provide the required third stage larvae source for the experiments. The nematode infective larvae of Trichostrongylidae family including three species of Ostertagia circumcincta, Marshalgia marshali and Heamonchos contortus were collected by Berman apparatus. Fifteen isolates of filamentous fungi were tested in the current study. One milliliter suspension containing 200 third stage larvae of Trichostrongylidae family was separately added to the fungal cultures in 2% water-agar medium Petri-dishes. Every day the live larvae were counted with light microscope (10X) and the number of captured larvae was recorded on different days.

Results:

Significant differences were observed in the results of co-culture of nematodes larva and fungi after seven days. The most effective fungi against the nematodes larvae were Cladosporium sp., Trichoderma sp., Fusarium equisetti, after seven days of incubation.

Conclusions:

The studies on fungi could be applied as suitable tools in biocontrol of nematode infections. However, additional surveys are required to select efficient with the ability to reduce the nematode larvae in the environment.

Efficacy and toxicity of thirteen plant leaf acetone extracts used in ethnoveterinary medicine in South Africa on egg hatching and larval development of Haemonchus contortus

Background

Helminthiasis is a major limitation to the livestock industry in Africa. Haemonchus contortus is the singular most important helminth responsible for major economic losses in small ruminants. The high cost of anthelmintics to small farmers, resistance to available anthelmintics and residue problems in meat and milk consumed by humans further complicates matters. The use of plants and plant extracts as a possible source of new anthelmintics has received more interest in the last decade. Our aim was not to confirm the traditional use, but rather to determine activity of extracts.

Based on our past experience acetone was used as extractant. Because it is cheaper and more reproducible to evaluate the activity of plant extracts, than doing animal studies, the activity of acetone leaf extracts of thirteen plant species used traditionally in ethnoveterinary medicine in South Africa were determined using the egg hatch assay and the larval development test. Cytotoxicity of these extracts was also evaluated using the MTT cellular assay.

Results

Extracts of three plant species i.e. Heteromorpha trifoliata, Maesa lanceolata and Leucosidea sericea had EC₅₀ values of 0.62 mg/ml, 0.72 mg/ml and 1.08 mg/ml respectively for the egg hatch assay. Clausena anisata; (1.08 mg/ml) and Clerodendrum glabrum; (1.48 mg/ml) extracts were also active. In the larval development assay the H. trifoliata extract was the most effective with an EC₅₀ of 0.64 mg/ml followed by L. sericea (1.27 mg/ml). The activities in the larval development test were generally lower in most plant species than the egg hatch assay. Based on the cytotoxicity results C. anisata was the least toxic with an LC₅₀ of 0.17 mg/ml, while Cyathea dregei was the most toxic plant with an LC₅₀ of 0.003 mg/ml. The C. anisata extract had the best selectivity index with a value of 0.10 and 0.08 for the two assays, followed by H. trifoliata and L. sericea with values of 0.07, 0.07 and 0.05, 0.04. The C. dregei extract had the worst selectivity index with a value of 0.00019 for both assays.

Conclusion

The result of this study indicates which species should be further investigated in depth for isolation of compounds.

Isolation and characterization of the nematophagous fungus Arthrobotrys conoides

The spread of organic farming and the development of resistance to anthelmintics by parasites, especially in small ruminants, have necessitated the search for alternative methods of nematode control. Biological control using nematophagous fungi is one option; however, few studies have been conducted with native strains. The present study was divided into two phases. In the first phase, we aimed to isolate, identify, and assess the in vitro predatory activity of nematophagous fungi that had been isolated on Trichostrongylidae third-instar larvae. In the second phase, the isolate with superior predatory activity in vitro was molecularly characterized, and its morphological plasticity was observed using scanning electron microscopy (SEM) on Haemonchus third-instar larvae. Of the 56 soil samples from different regions of Paraná State, Brazil, 57 fungal strains were recovered, of which four exhibited predatory activity. Two pure isolates were obtained: the CED and LIN strains. After demonstrating 96.35 % predatory activity for the CED strain, this strain was selected and characterized using molecular criteria by sequencing the rDNA internal transcribed spacer and was identified as Arthrobotrys conoides (GenBank ID: JN191309). Morphological patterns in this strain during the interaction between the fungus and the nematode were revealed by SEM, in which two extensions of the infection bulb that was used to pierce the nematode's cuticle were clearly visible.

Moisture requirements for the free-living development of Haemonchus contortus: quantitative and temporal effects under conditions of low evaporation

The key influence of moisture availability on development of the free-living stages of Haemonchus contortus is well-documented, although quantitative relationships between moisture variables and development are poorly defined. A factorial experiment (3x2x2) was conducted in programmable incubators to determine the effects of amount and distribution of simulated rainfall on H. contortus development at low evaporation rates (approximately 2 mm/day) under temperatures typical of summers on the Northern Tablelands of NSW, Australia. Sheep faeces containing H. contortus eggs were placed in experimental units containing sterile soil and had one of the three amounts (12, 24 and 32 mm) of simulated rainfall applied, in either a single event on the day after deposition (d 1) or three split events over 6 days (d 1, 3 and 6). Treatments were applied either in week 1 only, or in weeks 1 and 2. Recovery of infective larvae (L3) at 4, 7 and 14 days post-contamination increased with each incremental amount of simulated rainfall over the range of 12-32 mm and was significantly higher under the single "rain" event (2.8%), compared with the three smaller, split events (1.9%). The second application of simulated rainfall in week 2 had only a very small influence on L3 recovery, suggesting that the majority of development to L3 occurred in response to simulated rainfall events in the first 7 days. Both faecal moisture content and the cumulative ratio of precipitation and evaporation (P/E) were strongly and positively correlated with recovery of L3. Recovery of L3 from treatments, which received simulated rainfall in week 1 only was best described by P/E at d 5. Whether the relationships observed in this study hold under field conditions, where macroclimatic conditions such as evaporation rate are substantially more limiting to free-living development, is yet to be determined.

The requirement for early exposure of Haemonchus contortus larvae to Bacillus thuringiensis for effective inhibition of larval development

The potential for a nematocidal Bacillus thuringiensis (Bt) to target the free-living larval stages of Haemonchus contortus was examined using in vitro larval development and migration assays. Bt toxicity in larval development assays decreased as the time period between egg hatch and initial exposure to the Bt was increased; a time lag of 48 h resulted in a 350-fold increase in the IC(50) (from 2.6 ng/ml to 910 ng/ml). The effects on larval migration largely paralleled the effects on larval development, indicating that the larvae which reached the infective stage after exposure to Bt were generally as 'fit' as control worms in terms of migration ability. However, a comparison of the two assays also showed the presence of a level of Bt exposure which showed significantly more toxicity in migration assays than development assays, indicating that, in some cases, fully developed Bt-exposed larvae were less able to migrate than controls, and hence may be compromised in their ability to infect sheep. The rapid decrease in toxicity when exposure to the Bt is delayed highlights a significant issue concerning the use of Bt for control of the free-living larval stages of animal-parasitic nematodes. Targeting the larvae by delivering bacterial spores to the faeces through the host animal's digestive tract would require the spores to germinate upon defecation, grow through a vegetative phase, to then produce crystal toxin protein upon subsequent sporulation. This period of bacterial development will introduce a time lag between worm egg hatching and initial exposure of the larvae to the Bt, which, as demonstrated in the present study, may allow the worm larvae to develop to late larval stages which are relatively insensitive to the toxin.

Failure of Duddingtonia flagrans to reduce gastrointestinal nematode infections in dairy ewes

A field study was conducted on three Swiss farms to investigate the efficacy of Duddingtonia flagrans against naturally acquired infections of gastrointestinal nematodes in adult dairy sheep. On each farm the ewes were divided into two equal groups. One group received Duddingtonia during a period of 4 months at a daily dose rate of 10(6) chlamydospores per kilogram body weight, the second group acted as controls. At an overall moderate infection level in all farms D. flagrans did not have a significant effect on the observed parasitological parameters with the exception of a significantly reduced herbage infectivity in one farm. In contrast, the results from faecal cultures indicated a mean suppression of larval development during the fungus-feeding period between 82, 89 and 93% on the three farms, respectively. The discrepancy observed between the fungus efficacy in coprocultures and on pasture, which was also observed in several other studies deserves further research.

The ecology of nematode-trapping hyphomycetes in cattle dung from three plateau pastures

This paper investigated the influence of season and altitude on the occurrence of nematode-trapping fungi in cattle faeces. Six hundred and sixty samples of cattle faeces deposited on three plateau pastures with different altitudes in the west of Yunnan Province, China, were examined in 2004. A total of 17 species of nematode-trapping hyphomycetes were isolated from these samples. The predominant species from all three plateau pastures were Arthrobotrys oligospora, A. musiformis, Monacrosporium ellipsosporum, and M. thaumasium. Species with adhesive networks were the most frequently isolated. Overall, species diversity index was negatively correlated with altitude and was different among seasons within the same site. Levels of diversity were highest in the summer, followed by autumn, spring, and winter. The conidia of the hyphomycetes isolated here germinated normally on medium containing cattle faeces, with species developing adhesive networks having the highest rate of germination. However, the rate of conidial trap (CT) formation was lower in species with adhesive networks than those in other species.

Prolonged persistence of fecally excreted ivermectin from reindeer in a sub-arctic environment

In December 2001 and 2002, feces from reindeer calves treated with ivermectin were distributed on plots established on two types of forested reindeer pasture in northern Finland. The ungrazed plots were on an enclosure that had been fenced to prevent reindeer access for the last 6 years. The grazed plots were on an area that had been heavily stocked by reindeer during the last 5 years. After enclosures had been established, reindeer and large wildlife were prevented from entering by a fence. Topsoil samples (feces, vegetation, and soil) were collected monthly during the summers of the following 2 years, over a period of from 25 to 95 weeks after deposition. The samples were analyzed for ivermectin using HPLC. Although ivermectin degradation rapidly took place during the first spring, considerable residual ivermectin could be measured throughout the sampling time, showing that ivermectin in feces on pasture may not be photodegraded as rapidly as previously believed. The results support the need for further environmental evaluation studies on the use of ivermectin to control reindeer parasites.

A Sampling of Factors Relative to the Epidemiology of Gastrointestinal Nematode Parasites of Cattle in the United States

Gastrointestinal nematodosis of cattle is a parasitic condition resulting from an immense and seemingly forever-expanding array of factors. Countless determinants influence the incidence and severity of the species-specific infections that occur in cattle, determinants that affect the free-living or environmental stages of the parasites and the parasitic stages. The vast majority of animals have a subclinical or economic level of parasitism undetectable to the eye but quantified more accurately by treatment-induced improved performance (e.g., feed efficiency, nitrogen balance, weight gain, milk production). Unfortunately, the results of treatment (effectiveness and improved animal performance) sometimes can be as varied as the parasitisms that are being treated.

Alternatives to anthelmintics for the control of nematodes in livestock

Efficient and welfare-friendly livestock production demands the control of nematode infection. Current control measures rely upon anthelmintic treatment but are threatened by the widespread evolution of drug-resistance in parasite populations. Several methods have been advocated to control nematodes without relying on effective anthelmintics. These include grazing management, biological control, nutritional supplementation, vaccination, and genetic approaches. Each method has its advantages and disadvantages. There are several grazing management schemes that can reduce the severity of infection but they are insufficient on their own to control infection. Biological control includes the use of predatory fungi to control nematode populations and the use of pasture species that can reduce the intensity of infection. Fungi can control nematodes but the current requirement for daily feeding means that this approach will be most useful for animals that are handled daily. Feeding supplementary protein can control nematode infection. The method is simple but can be expensive and may not be cost-effective for some marginal enterprises. Genetic approaches include the use of resistant breeds and selective breeding. Some breeds will thrive in conditions that kill animals from other breeds but substitution of resistant breeds is not always feasible. Selective breeding is effective and inexpensive but requires a high level of expertise. The most appropriate method or set of methods to minimize the adverse consequences of nematode infection may vary among farms.

The predatory capability of Arthrobotrys cladodes var. macroides in the control of Haemonchus contortus infective larvae

One hundred compost samples were examined for the presence of nematophagous fungi on the sheep farms of Mazanderan, province, Iran. Arthrobotrys cladodes var. macroides (IRAN 677C=CBS 143565) was isolated from 3% of the samples examined. Nematophagous activity of this fungus which was shown for the first time in this study, revealed the addition of 1000, 8000, 20000 and 100000 conidia per gram of feces of sheep reduced significantly (P<0.001) the number of Haemonchus contortus infective larvae in the feces by 41.71%, 63, 27%, 73.49% and 94.96%, respectively. These results show that A. cladodes var. macroides is a promising candidate for biological control of H. contortus.

Efficiency of feeding Duddingtonia flagrans chlamydospores to grazing ewes on reducing availability of parasitic nematode larvae on pasture

Gastrointestinal nematodes are of concern in sheep production because of production and economic losses. Control of these nematodes is primarily based on the use of anthelmintic treatment and pasture management. The almost exclusive use of anthelmintic treatment has resulted in development of anthelmintic resistance which has led to the need for other parasite control options to be explored. The blood sucking abomasal parasitic nematode Haemonchus contortus causes severe losses in small ruminant production in the warm, humid sub-tropic and tropics. This study evaluated the effectiveness of a nematode trapping fungus, Duddingtonia flagrans, in reducing availability of parasitic nematode larvae, specifically H. contortus, on pasture. Chlamydospores of D. flagrans were mixed with a supplement feed which was fed daily to a group of crossbred ewes for the duration of the summer grazing season. A control group was fed the same supplement feed without chlamydospores. A reduction in infective larval numbers was observed in fecal cultures of the fungus-fed group. Herbage samples from the pasture grazed by the fungus-fed group also showed a reduction in infective larvae. There were no significant (P > 0.05) differences in overall fecal egg count, packed cell volume or animal weight between fungus-fed and control groups. Tracer animals were placed on the study pastures at the end of the study to assess pasture infectivity. Although tracer animals were only two per group, those that grazed with the fungus-fed group had substantially reduced (96.8%) nematode burdens as compared to those from the control group pasture. Results demonstrated that the fungus did have activity against nematode larvae in the feces which reduced pasture infectivity and subsequently nematode burdens in tracer animals. This study showed that D. flagrans, fed daily to grazing ewes, was an effective biological control agent in reducing a predominantly H. contortus larval population on pasture.

Controle biológico de helmintos parasitos de animais: estágio atual e perspectivas futuras

O controle biológico é um método desenvolvido para diminuir uma população de parasitas pela utilização de antagonista natural. A administração de fungos nematófagos aos animais domésticos é considerada uma promissora alternativa na profilaxia das helmintíases gastrintestinais parasitárias. Os fungos nematófagos desenvolvem estruturas em forma de armadilhas, responsáveis pela captura e destruição dos estágios infectantes dos nematóides. Os fungos dos gêneros Arthrobotrys, Duddingtonia e Monacrosporium têm demonstrado eficácia em experimentos laboratoriais e no campo no controle de parasitos de bovinos, eqüinos, ovinos e suínos. Diversas formulações fúngicas têm sido avaliadas, no entanto, ainda não há nenhum produto comercial disponível. A associação dos grupos de pesquisa e o envolvimento das indústrias poderão colaborar para o sucesso na implementação desta forma de controle.

Influence of nematophagous fungi, earthworms and dung burial on development of the free-living stages of Ostertagia (Teladorsagia) circumcincta in New Zealand

Biological options for nematode parasite control are being sought, as the long-term efficacy of conventional anthelmintics comes increasingly under threat from drug-resistant parasites. Three biological methods with the potential to reduce pasture contamination by parasitic nematode larvae were examined: (a) killing of larvae developing in dung by nematophagous fungi; (b) removal of dung through earthworm ingestion; (c) burial of dung in soil as might occur through the action of dung beetles. Field trials with the test bio-control agents were carried out in autumn and spring by adding dung from sheep infected with Ostertagia (Teladorsagia) circumcincta to pots of ryegrass/white clover. The factorial treatment structure included five fungal treatments (individual applications of Duddingtonia flagrans, Monacrosporium gephyropagum and Harposporium helicoides, a combination of all the three fungi together and an untreated control), two dung burial treatments (dung buried or deposited on the soil surface) and two earthworm treatments (earthworms present or absent). D. flagrans and H. helicoides, individually or in combination, reduced recovery of infective stage larvae in experiment 1, while only H. helicoides reduced recovery in experiment 2. In both the experiments, dung burial increased the total number of larvae recovered, while the number of infective larvae were reduced by the action of earthworms. Increased recovery following burial, along with the fact that larvae moved rapidly from soil onto herbage, suggests that soil may provide a protective reservoir for infective larvae infesting herbage.

The potential of nematophagous fungi to control the free-living stages of nematode parasites of sheep: feeding and block studies with Duddingtonia flagrans

A series of feeding trials was conducted with penned sheep harboring Trichostrongylus colubriformis infections. They were offered barley grains supporting the growth of the nematophagous fungus Duddingtonia flagrans. It was shown that as little as 5g of grain/sheep per day was sufficient to virtually eliminate larval numbers from faecal culture. This effect persisted for the time that the fungal grains were fed, and for up to 2 days following cessation of feeding this material. Macerated fungal grains were also incorporated into a range of feed block formulations. In all these, D. flagrans was found to survive the manufacturing process and resulted in significant reductions in larval numbers in faecal cultures set up during the feeding period to sheep. This was observed even for sheep that showed only modest and irregular block consumption. These studies demonstrate that supplementary feeding or block administration offer potential deployment options for D. flagrans as a means of biological control of nematode parasites of livestock.

Screening for Indian isolates of predacious fungi for use in biological control against nematode parasites of ruminants

Four isolates of predacious fungi, two each of Arthrobotrys oligospora isolated from a sheep and a male crossbred calf and of Duddingtonia flagrans isolated from a sheep and a female buffalo in western India, were studied for their suitability as biocontrol agents against parasitic nematodes of ruminants, using growth assay, predatory activity, germination potential and ability to survive passing through the ruminants gut as criteria. The study showed that isolates of D. flagrans grew well in artificial media, had encouraging predatory activity, produced profuse chlamydospores that germinated easily at 25 degrees C and could survive passage through the ruminant gut. The ovine isolate of D. flagrans was superior in all respects to the isolate from buffalo and was the most promising candidate for biological control of nematode parasites of ruminants.

Historical perspective of cyathostomes: prevalence, treatment and control programs

Small strongyles are highly prevalent in horses and can be found worldwide. Even though over 50 species of these parasites have been described, about 10 species comprise the bulk of the total number present in horses. Efforts to control small strongyles and other equine internal parasites have been undertaken for many years. Some of the early medications and control measures provided questionable activity against endoparasites; whether effective or not, they could be detrimental to the horse. Beginning in the early 1900s, scientific effort was used to evaluate activity of antiparasitic compounds. Only a relatively low number of classes of compounds has been used for parasite control. Progressively, in time, newer drugs have become broad-spectrum, safer, and available in lower dose rates than previously. With extensive use of parasiticides, small strongyles have been found to be resistant to all commercially-available classes of compounds except the macrocyclic lactones. Innovative parasite-control programs, relying less on drugs, need to be developed.

Biological control of nematode parasites of livestock in Fiji: screening of fresh dung of small ruminants for the presence of nematophagous fungi

Approximately 2500 faecal samples were collected per rectum from sheep and goats from 26 farms located on four of the Fijian islands where most of the small ruminants in this country are raised. The purpose was to screen these samples to isolate nematode-trapping fungi that had been acquired by these animals during the course of their feeding and which had remained viable following passage through their gastrointestinal tract. From these samples, 23 examples of nematophagous fungi were noted in the initial appraisal, from which 12 pure isolates (all of the genus Arthrobotrys) were made. A number factors emerged from this work which may have restricted the opportunities in which nematophagous fungi were detected, or isolated.

International approaches to the concept of integrated control of nematode parasites of livestock

Livestock production systems throughout the world are under severe and sustained pressures. These are diverse and multi-factorial, ranging from the need to redress the oversupply of livestock commodities from the protected industries of the industrialised world, meeting animal welfare expectations, attempts to ease animal-induced land degradation and pollution, and competition with alternative products. As a consequence, funding for research to the ruminant livestock industries has been contracting universally. This applies particularly to research on those diseases of grazing livestock that are not zoonotic, threats to trade, or major "killer" diseases. Gastrointestinal helminths fall outside these priorities. The last decade has witnessed a major contraction throughout the world in the number of research centres and staff involved in applied veterinary parasitology research. This coincides with a time when these livestock industries need the most help. Resistance to anthelmintic drugs amongst the major nematode parasites of sheep and goats has now reached alarming proportions throughout the world and threatens the future viability of continued small ruminant production in many countries. Anthelmintic resistance is also increasing in the important nematode parasites of cattle. Also, this time coincides with the apparent reduction in the discovery and development of entirely new anthelmintic products by the pharmaceutical industry. As a consequence, those remaining researchers and extension personnel who have the responsibility of providing support to the ruminant livestock industry, are showing innovation and lateral thinking in ways to combat the perennial problem of internal parasites in grazing livestock. There are a number of excellent examples of parasite-control schemes, which do not rely entirely on anthelmintic treatment. These are now being supplemented with some exciting novel approaches to dealing with particularly pressing parasite problems. Also there is a move towards the development of true integrated approaches in the control of nematode parasites of livestock, which employ several of these methods when appropriate. This proves that as far as worm control in livestock is concerned, the old adage "necessity is the mother of invention", holds true.

Integrated control of nematode infections in cattle: a reality? A need? A future?

Helminth infections are a major cause of production loss in cattle. Great progress has been achieved in the design of control strategies for these infections. Control is based mainly on the use of anthelmintics, and these have become more potent and easier to administer. However, the most effective control is possible only through the integration of different approaches. Moreover, an increasing number of disadvantages of chemotherapy/prophylaxis--biological, economical and environmental--have been suggested. In sheep, the high incidence of anthelmintic resistance has simply forced veterinarians/producers to adopt alternative control strategies; in cattle, no real need for deviation from the actual control programmes seems to exist. Therefore, the following questions are discussed: (1) Based on the distribution of cattle worldwide, what are the target parasites? (2) Can we continue to rely on control based mainly on the use of (highly effective) anthelmintics? (3) What are the prospects for non-chemical control? (4) Who will develop and implement integrated control systems? (5) In the case of parasite control in Western Europe, has it been efficient and can/need it be changed? (6) How can we integrate helminth control in the general design of herd disease control?

Biological control of helminths

As a potential component in future integrated parasite-control strategies, biological control by means of predacious fungi seems to be moving from a promising possibility toward becoming a reality, and the netforming nematode-destroying fungus Duddingtonia flagrans appears to be the candidate of choice. Not only has this fungus been found in, and isolated from, fresh sheep, cattle and horse faeces, but it also appears to be the only fungus that is able to consistently and significantly reduce the number of infective trichostrongyle larvae in faeces from animals fed fungal spores. Results from the last few years have shown that D. flagrans is able to trap and destroy free-living stages of the most important and common trichostrongylid larvae with very similar external life-cycles, as well as larvae of parasites with a slightly different transmission biology (Nematodirus spp., Dictyocaulus viviparus). The introduction of microfungi for biological control could be as part of a feed supplement or incorporated in feed-blocks presented to animals which are raised under relatively intensive conditions and constant surveillance. Apart from the special niche for organic farmers, such a product would be suited for horses, small ruminants (as either milking herds or housed daily for other reasons), cattle in special situations and free-roaming pigs. The most important constraint, still, for a major breakthrough in biological control in the latter is the lack of good antagonists against the long-lived and rather resistant infective stages of parasites, being transmitted as larvae inside the egg. Since the first Conference on Novel Approaches to the Control of Helminth Parasites of Livestock in Armidale, Australia, 1995, there has been a steady evolution within the area of biological control of parasitic nematodes. Today this principle is being exploited and tested out in almost all parts of the world, under various climatic conditions and production systems. Where, in the past, a large part of the work focused on cattle and to a lesser degree horse and sheep parasites, the focus of the research in many of the newly involved countries is on small ruminants, because of their importance to primarily small-scale farmers in local communities. Today research and trials are either on-going or being planned in many developing countries, as well as in countries in transition. The involvement of multinational agencies in addition to national and industrial interests is very welcome and should increase the chances and keep up the momentum for development and implementation of biological control in future animal production around the world.

Nematode parasite control of livestock in the tropics/subtropics: the need for novel approaches

Because parasites are more abundant, small ruminants in the tropical/subtropical regions of the world experience much greater ravages from internal parasitic disease than those in the temperate regions. In the tropics/subtropics, the limiting ecological factor influencing the severity of parasitism is rainfall, as temperatures almost always favour hatching and development of the free-living stages. Attempts to expand sheep and goat production by replacing traditional village production systems, which rarely involve anthelmintic treatment, with large-scale intensive commercial enterprises invariably induce complete reliance on anthelmintics to control nematode parasites. This has led to the widespread development of high level, multiple anthelmintic resistance throughout the tropics/subtropics, and in certain regions this has reached the ultimate disastrous scenario of total chemotherapeutic failure. Immediate concerted efforts are needed to resolve this crisis. Significant benefits are likely to emerge from research into non-chemotherapeutic approaches to nematode parasite control, such as grazing management, worm vaccines, breed selection and biological control. However, it is likely that none, in isolation or collectively, will completely replace the need for effective anthelmintics. What is needed is the integration of all methods of parasite control as they come to hand, with the underlying aim of reducing the use and thus preserving the effectiveness of anthelmintics. Although cheap and simple procedures, based on sound epidemiological principles, can achieve dramatic benefits in worm control, they have been poorly adopted by livestock owners. Clearly then, the greatest need is for technology transfer and education programmes, but these activities are generally found to be chronically under-resourced.

Sustainable helminth control of ruminants in developing countries

Widespread anthelmintic resistance, at least amongst the important nematode parasites of small ruminants, threatens the sustainability of these livestock industries throughout both the developed and developing world. The exacerbation of this problem over the last decade or so, has provided the impetus for research into non-chemotherapeutic parasite control alternatives, such as host genetic resistance, grazing management, worm vaccines and biological control. Although some of these options provide practical benefits if currently adopted, or exciting prospects for the future, collectively they are unlikely to dispense with the need for the timely intervention of effective anthelmintic treatment. The issue of sustainability of helminth control practices therefore rests with the preservation of anthelmintic effectiveness through the implementation of principles of integrated pest management. Herein lies the difficulty-putting the principles into practice. Much of the research into sustainable nematode parasite control of ruminants has been done in the developed rather than the developing world, and the efforts to transfer this information to livestock owners has also been commensurately greater in the former. However the need for research and technology transfer is much more urgent in the developing world because of the lack of scientific and financial resources, the greater dependence on livestock industries and the much greater severity of the problem of anthelmintic resistance. This will require a major philosophical change in the affluent western world to the funding of national and international aid organisations who are largely responsible for these activities.