An attempt to implement the nematode-trapping fungus Duddingtonia flagrans in biological control of trichostrongyle infections of first year grazing calves

Safety and efficacy of BioWorma® (Duddingtonia flagrans NCIMB 30336) as a feed additive for all grazing animals

Following a request from the European Commission, the EFSA Panel on Additives and products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on the safety and efficacy of BioWorma® (Duddingtonia flagrans NCIMB 30336) when used as a zootechnical feed additive for all grazing animals. Duddingtonia flagrans belongs to a group of nematophagous fungi that physically entrap nematodes through an adhesive hyphal net. The additive contains the fungus in the form of chlamydospores and is intended to control pathogenic nematodes on pasture, with subsequent benefits for grazing animals. No conclusions could be drawn on the safety for the target species due to lack of data. ■■■■■ As it is not possible to exclude the presence of secondary metabolites (other than flagranones) produced during fermentation and their potential carry-over into animal products, safety for the consumer could not be established. The Panel concluded that the additive is not irritant to skin and eyes but is irritant to the respiratory tract and a respiratory sensitiser. No conclusion could be drawn on its skin sensitisation potential. Since D. flagrans is a naturally inhabiting soil organism of world-wide distribution, the Panel considered that use of an additive based on this organism does not pose a risk for the environment under the intended conditions of use. The strain under application reduced the number of parasitic nematodes on pasture to the benefit of grazing animals when used at the recommended application rate of 3 × 104 chlamydospores/kg bodyweight and day.

A review of the epidemiology and control of gastrointestinal nematode infections in cattle in Zimbabwe

In this review, the main gastrointestinal nematodes infecting cattle in Zimbabwe and the epidemiological factors influencing their occurrence are reviewed and discussed. Nineteen gastrointestinal nematode species that belong to seven families have been found to occur in cattle in Zimbabwe. The main genera reported to date are Cooperia, Haemonchus, Trichostrongylus and Oesophagostomum and the dominant species are Cooperia pectinata, Cooperia punctata, Haemonchus placei and Trichostrongylus axei. The mixed infection by several species from the genera is the cause of parasitic gastroenteritis in cattle in Zimbabwe. Production and husbandry practices, season, host age and environment are considered to be the main factors that influence gastrointestinal nematode infection in cattle. The geographical distribution of the gastrointestinal nematodes is also reviewed in relation to the climatic conditions of the country. Various control options are discussed and how they are applicable to the Zimbabwean situation. Based on reports and existing data on the epidemiological features of the gastrointestinal nematode infection in cattle, practical control measures are critically reviewed and recommendations are made for a national control programme.

Kinetics of capture and infection of infective larvae of trichostrongylides and free-living nematodes Panagrellus sp. by Duddingtonia flagrans

Duddingtonia flagrans, a nematode-trapping fungus, has been investigated as an agent for biological control against infective larvae of gastrointestinal nematode parasites of production animals. The initial process of nematode-trapping fungi infection is based on an interaction between the trap structure of the fungus and the surface of the nematode cuticle. This report investigates by light and scanning electron microscopy the kinetics of capture and infection during the interaction of D. flagrans with the infective larvae (L(3)) of trichostrongylides and the free-living nematode Panagrellus sp. D. flagrans was cultivated for 7 days in a Petri dish containing agar-water. L(3) and Panagrellus sp. were inoculated in the Petri dishes and the samples consisting of agar-L(3)-fungi and agar-Panagrellus sp.-fungi were collected after 10, 20, 30, 40, 50, 60, and 70 min and 3, 4, 5, 10, 15, 20, and 25 h of interaction. All samples were observed by light microscopy. The samples with 1, 5, 15, and 25 h of interaction were also analyzed by scanning electron microscopy. The interaction was monitored up to 25 h. An initial differentiation of predation structures was observed after 30 min of interaction. The presence of traps and of captured L(3) or Panagrellus sp. occurred after 70 min. The live captured nematodes were observed up to 3 h of interaction. However, after 4 h, all Panagrellus sp. were dead. It took 15 h of interaction for the fungus to invade the L(3), and the presence of hyphae inside the nematode near the region of penetration was evident. At this time, the hyphae had filled the whole body of Panagrellus sp. The complete occupation of the body of L(3) occurred at 20 h of interaction and with 25 h the nematode was completely damaged except for the cuticle. Although the double cuticle of L(3) slows the penetration of D. flagrans, it was possible to verify that the process of trap formation and capture occurs quickly when both nematodes were tested, suggesting that the organisms would eventually be killed once in contact with the fungi encouraging the use of the fungus as a biological control agent.

Interspecific competition between the nematode-trapping fungus,Duddingtonia flagrans, and selected microorganisms and the effect of spore concentration on the efficacy of nematode trapping

The fungus,Duddingtonia flagrans, is able to trap and kill free-living nematode larvae of the cattle parasiteCooperia oncophorawhen chlamydospores are mixed in cattle faeces. Isolates ofBacillus subtilis(two isolates),Pseudomonasspp. (three isolates) and single isolates of the fungal generaAlternaria,Cladosporium,Fusarium,TrichodermaandVerticilliumwere isolated from cattle faeces and shown to reduceD. flagransgrowth on agar plates. When these isolates were added to cattle faeces containingD. flagransand nematode larvae ofC. oncophora, developing from eggs, none of the isolates reduced nematode mortality attributed toD. flagrans. Similarly, the coprophilic fungusPilobolus kleinii, which cannot be cultivated on agar, also failed to suppress the ability ofD. flagransto trap and kill developing larvae ofC. oncophora. Increasing chlamydospore doses ofD. flagransin faecal cultures resulted in higher nematode mortality. Thus, no evidence of interspecific or intraspecific competition was observed. The consequences of these findings are discussed.

Biotic and abiotic factors influencing growth rate and production of traps by the nematode-trapping fungus Duddingtonia flagrans when induced by Cooperia oncophora larvae

A series of experiments on corn meal agar was carried out to evaluate the efficacy of the nematode-trapping fungus Duddingtonia flagrans in different abiotic and biotic conditions which occur in cow pats. Above a concentration of 50 parasitic larvae (L3) cm–2 the fungus produced a maximum of between 500 and 600 nets cm–2 at 20°C in 2 days on the surface of corn meal agar. There were no differences in the trap-producing capacity of three strains of D. flagrans (CIII4, CI3 and Trol A). On agar at 30° and 20°C, the fungus responded to Cooperia oncophora L3 very quickly producing a maximum of trapping nets 1 day after induction. At 10°C, traps were produced slowly starting on day 4 after induction and continued over the following week. Duddingtonia flagrans (CI3) grew at a normal rate at least down to an oxygen concentration of 6 vol.% O2, but it did not grow anaerobically. On agar, D. flagrans (CI3) did not produce trapping nets in an anaerobic atmosphere. Moreover, C. oncophora L3 stopped migration under anaerobic conditions. When the fungal cultures were transferred to a normal aerobic atmosphere, after 1 and 2 weeks under anaerobic conditions, the C. oncophora L3 resumed migrating on the agar and, in response, D. flagrans produced traps in the same amount as when it had not been under anaerobic stress. Under microaerophilic conditions (6 vol.% O2) D. flagrans was able to grow, but the C. oncophora L3 were not able to induce trapping nets in D. flagrans (Trol A) because of larval immobility. But, as under anaerobic conditions, the fungus could return to a nematode-trapping state when transferred to a normal aerobic atmosphere within 1 or 2 weeks if migrating nematodes were present. Under natural conditions in the cow pat it is expected that the fungus will be ready to attack parasitic larvae, when the oxygen tension increases as a result of, for example the activity of the coprophilic fauna. Artificial light giving 3000–3400 Lux on the surface of the agar significantly depressed the growth rate and the production of trapping nets in D. flagrans (CI3). On agar, D. flagrans (CI3) could grow and produce trapping nets at pH levels of 6.3 to 9.3. Net-production has its optimum between pH 7 and 8. On dry faeces mycelial growth was 7–10 mm during a 15 day period while on moist faeces the fungus expanded 15–20 mm during the same period. Based on the parameters investigated, D. flagrans is expected to be especially active in the well aerated surface layer of a cow pat, an area which normally contains a high concentration of infective nematode parasite larvae, but also an area where the temperature can be high and the water content low.

The ability of the nematode-trapping fungus Duddingtonia flagrans to reduce the transmission of

The ability of two isolates of the nematode-trapping fungus Duddingtonia flagrans to reduce the numbers of gastrointestinal nematode larvae on herbage was tested in three plot studies. Artificially prepared cow pats containing Ostertagia ostertagi eggs, with and without fungal spores, were deposited on pasture plots two or three times during the grazing season in 1995, 1996 and 1997. The herbage around each pat was sampled fortnightly over a period of 2 months and the number of infective larvae was recorded. At the end of the sampling period, the remainder of the faecal pats was collected to determine the wet weight, dry weight, and content of organic matter. The infective larvae remaining in the pats were extracted. Faecal cultures showed that both fungal isolates significantly reduced the number of infective larvae. Significantly fewer larvae were recovered from herbage surrounding fungus-treated pats compared with control pats in all three experiments, reflecting the ability of the fungus to destroy free-living larval stages in the faecal pat environment. After 8 weeks on pasture there were no differences between control and fungus-treated pats with respect to wet weight, dry weight, and organic matter content. This indicates that the degradation of faeces was not negatively affected by the presence of the fungus.

Effect of nematophagous fungusDuddingtonia flagransand energy supplementation on the epidemiology of naturally infected kids

Gastrointestinal (GI) nematode infection is a major constraint for grazing livestock production. The increasing prevalence and severity of anthelmintic-resistant nematodes in many parts of the world has led to a search for non-chemical control options. Under experimental conditions, the nematophagous fungus Duddingtonia flagrans is emerging as an alternative to chemotherapy for the control of GI nematode infection in biological production systems. Also, recent information points to the role of energy nutrition to increase the immune response against GI nematode infection. In this study the effect of D. flagrans and energy supplementation on the epidemiology of GI nematode infections is explored on grazing kids. Four groups of 10, 4-month old goats were turned out on infected pasture in the early spring and allocated to four separate paddocks where they were rotationally grazed for 16 weeks. One of these groups (F) received 0.5 x 10(6) D. flagrans spores/kg BW/d. Another group (S) was supplemented with 100 g barley grain per day. A third group (F+S) received both nematophagous fungi and barley supplement treatments simultaneously while the fourth group (C) was used as a non-treated control. Both nematophagous fungi and barley supplement had a significant effect (P<0.01) on reducing pasture infectivity, faecal egg excretion and worm burdens at slaughter that was particularly evident for Trichostrongylus colubriformis. The combination of both treatments showed a synergistic effect on the control of gastrointestinal nematode infections. At slaughter, the average total post-mortem worm count of the F+S group was reduced by 65% compared with the non-treated control. The results herein show that D. flagrans can act as an efficient biological control agent against kid GI nematode infections on pasture, which could further improve carcass characteristics. While small amounts of energy supplement can also reduce kid infection, the effect of D. flagrans as a biological control agent appeared clearly enhanced both in magnitude and duration by energy supplementation. This has clear implications for grazing animals and provides an efficient method for the practical control of parasitic nematodes in biological production systems.

Control of gastrointestinal nematodes in goats on pastures in South Africa using nematophagous fungi Duddingtonia flagrans and selective anthelmintic treatments

The effectiveness of selective anthelmintic treatments and use of nematophagous fungi Duddingtonia flagrans in reducing levels of gastrointestinal nematodes in goats was investigated at Onderstepoort, South Africa. Nineteen (19) naturally infected indigenous male goats, aged 10 months, were separated into four groups and grazed in separate previously ungrazed paddocks for two worm seasons (February 2002-March 2003). Two groups of goats were fed D. flagrans chlamydospores daily and two groups did not receive fungi. The FAMACHA system was used to determine which goats required anthelmintic treatments. Twice as many goats in the no-fungi fed group required treatments as compared with the fungi fed group. Mean FAMACHA scores in the no-fungi fed group were higher during most of the sampling occasions compared to the group fed fungi, but the difference was not significant. The group-mean faecal egg counts and PCV% were comparable between the two treatment groups throughout the study. Haemonchus was the predominant parasite genus in composite group faecal cultures. Group-mean body weights and body condition scores were higher for the no-fungi fed group from May 2002 up to the end of the study, though statistical differences were not significant. Mean worm burdens indicated that the most abundant species infecting animals were Haemonchus contortus and Trichostrongylus spp. and were higher in the fungi fed group. More animals required individual anthelmintic treatments in the no-fungi fed group. The requirement for extra treatments in the no-fungi fed group must, however, be considered against the financial cost of the fungi, the requirement of daily feeding of the fungi, the lower performance and higher worm burdens in the fungi fed group.

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.

Evaluation of gastro-intestinal nematode parasite control strategies for first-season grazing cattle in Sweden

A three-year grazing experiment (1998-2000) was conducted with first-season grazing cattle (FSGC) on improved pastures in central-eastern Sweden. Comparison was made between five groups with 10 calves in each group where four of these were set stocked and either (1) untreated, (2) ivermectin bolus treated, (3) subjected to biological control with the nematophagous fungus Duddingtonia flagrans, or (4) treated with a copper wire particle bolus. The fifth treatment was an evasive grazing strategy, whereby untreated calves were turned out onto pasture used by older cattle the previous year and then these calves were moved to silage aftermath in mid-July. To introduce low-levels of parasite infection to the experiment, each animal received a 'priming dose' of approximately 5,000 Ostertagia ostertagi and 5,000 Cooperia oncophora infective third stage larvae immediately prior to the start of the first grazing year of the trial. Results showed that efficient and sustainable parasite control of FSGC was possible to achieve without the use of anthelmintics by using turnout pastures that the previous year had been grazed by older cattle, in combination with a mid-July move to aftermath leys. Biological control also proved beneficial but the efficacy was impaired if high faecal egg counts coincided with rapid dung pat degradation due to heavy rainfall. No indication of parasite control was observed with the copper wire particle bolus. It was also demonstrated that the impact of gastrointestinal (GI) parasitism varied between years and that the level of overwintering contamination is important but likewise, is unpredictable. Although faecal egg counts in 1999 were low, due both to a delayed turnout and drought for the major part of the grazing season, deposited eggs successfully developed to infective larvae and overwintered in large numbers. The population of overwintered infective larvae at the time of turnout in early May played an important role in the course of infection in 2000 and resulted in an average 65 kg advantage of the ivermectin treated calves compared with the untreated calves.Thus, this three-year grazing experiment has emphasised the importance of subclinical gastrointestinal nematode infections in FSGC in Sweden. In addition, the study has shown that adequate parasite control may be achievable without the use of anthelmintics.

Predacious activity of Duddingtonia flagrans within the cattle faecal pat

Two studies were conducted to investigate the growth and activity of the fungus, Duddingtonia flagrans, within cattle faecal pats. Artificial faecal pats were constructed with the centre separated from the outer layer by a nylon mesh. Eight treatments were tested, by varying the presence/absence of Cooperia oncophora eggs and fungal spores within each layer. With parasite eggs in the centre layer, a statistically lower recovery of larvae was observed compared to both pats with parasite eggs in the periphery and pats with parasite eggs throughout both layers. Regardless of location within the pat, if co-located with the parasite egg, D. flagrans was found to be effective in trapping developing larvae. The reduction in recovery of larvae from pats with parasite eggs and fungal spores in the centre was found to be significantly higher than when parasite eggs were in the centre and fungal spores in the periphery. In the second study, pats were made up in two treatments: pats containing fungal spores and C. oncophora eggs (fungus) and pats containing C. oncophora eggs (control). The pats were incubated at low or high humidity. Ten pats were used in a cross over where five pats incubated at low humidity for 7 weeks were removed, water added and then incubated at a high humidity for 1 week. Another five pats were incubated at a high humidity for 7 weeks, aerated and incubated at a low humidity for 1 week. There was no apparent growth of fungus in faecal pats incubated at a high humidity and less than 20% of larvae were recovered. The growth of D. flagrans was observed in faecal pats incubated at a low humidity, but a corresponding reduction in the percentage recovery of larvae did not occur, except in week 4. No statistical difference between fungal and control pats was seen in the change over pats. Nematophagous activity was assessed throughout the study and observed in the first 4 weeks within the pats containing fungus.

Biological control of trichostrongylid infections in calves on pasture in Lithuania using Duddingtonia flagrans, a nematode-trapping fungus

The effect on the pasture contamination level with infective trichostrongylid larvae by feeding the nematode-trapping fungus, Duddingtonia flagrans at two dose levels to first time grazing calves was examined in Lithuania. Thirty heifer-calves, aged 3-6 months, were divided into three comparable groups, A, B and C. Each group was turned out on a 1.07 ha paddock (a, b and c). The paddocks were naturally contaminated with infective trichostrongylid larvae from infected cattle grazing the previous year. Fungal material was fed to the animals daily during a two month period starting 3 weeks after turnout. Groups A and B were given 10(6) and 2.5x10(5) chlamydospores per kg of live weight per day, respectively, while group C served as a non-dosed control group. Every two weeks the heifers were weighed and clinically inspected. On the same dates, faeces, blood and grass samples were collected. From mid-July onwards, the number of infective larvae in grass samples increased markedly (P<0.05)on paddock c, whereas low numbers of infective larvae were observed on paddocks a and b grazed by the fungus treated groups. However, the results indicate that administering fungal spores at a dose of 2.5x10(6)chlamydospores per kg live weight per day did not significantly prevent parasitism in calves, presumably due to insufficient suppression of developing infective larvae in the faeces. In contrast, a dose of 10(6) chlamydospores per kg lowered the parasite larval population on the pasture, reduced pepsinogen levels (P<0.05), and prevented calves from developing parasitosis.

Absence of obvious short-term impact of the nematode-trapping fungus Duddingtonia flagrans on survival and growth of the earthworm Aporrectodea longa

The nematode-trapping fungus Duddingtonia flagrans may be used in biological control of parasitic nematode larvae in faeces of domestic host animals after feeding the hosts with fungal chlamydospores. In this experiment a possible undesirable fungal impact on earthworms, of the species Aporrectodea longa, was investigated. As earthworms eat animal faeces, D. flagrans may come into contact with earthworms both in their alimentary tract and on their body surface. However during the experimental period of 20 days, when earthworms were living in soil and eating cattle faeces that were heavily infested with viable chlamydospores of D. flagrans there were no indications of internal or external mycosis among the earthworms.

Efficacy of the nematophagous fungus Duddingtonia flagrans in reducing equine cyathostome larvae on pasture in south Louisiana

The effectiveness of Duddingtonia flagrans in reducing the free living third stage larvae (L(3)) of equine cyathostomes on pasture when fed to horses has been demonstrated in cold temperate climates. The objective of this experiment was to assess the efficacy of D. flagrans against equine cyathostomes in the subtropical environment of southern Louisiana. Fecal pats were prepared by mixing feces obtained from a parasite-free horse fed D. flagrans at a dose of approximately 2 x 10(6) spores kg(-1), with feces containing cyathostome eggs from a parasitized horse. Control pats contained feces from a parasite-free horse mixed with feces containing cyathostome eggs. The fecal pats were placed on pasture in six replicates at 4-week intervals from March 1997 until January 1998. Comparison of recoveries of L(3) from non-treated control pats in the field with non-treated coprocultures maintained in the laboratory indicated that L(3) survival on pasture was reduced during the months of May, June, July, August and September. The efficacy of the fungus was determined by L(3) recovery from grass surrounding the fecal pats of treated and control groups. D. flagrans significantly reduced L(3) during the months of April, May, and October 1997 to January 1998 (range 66-99% reduction, p=0.0001), and for the year as a whole (p=0.0001).

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.

A new isolate of the nematophagous fungus Duddingtonia flagrans a biological control agent against free-living larvae of horse strongyles

An experiment was carried out in 1997 to test the efficacy of an isolate of the microfungus Duddingtonia flagrans against free-living stages of horse strongyles under conditions in the field and to assess the eventual effect of the fungus on the normal degradation of faeces. Faecal pats were made from faeces of a naturally strongyle infected horse, which had been fed fungal material at a dose level of 106 fungal unit/kg bwt. Control pats without fungi were made from faeces collected from the same animal just before being fed fungi. Faecal cultures set up for both groups of faeces to monitor the activity of the fungus under laboratory conditions showed that the fungus significantly reduced the number of infective third-stage larvae (L3) by an average of 98.4%. Five faecal pats from each batch of faeces were deposited on pasture plots at 3 times during spring-summer. The herbage around each pat was sampled fortnightly to recover L3 transmitted from faeces. The results showed that the herbage infectivity around fungus-treated pats was reduced by 85.8-99.4%. The remaining faecal material at the end of each sampling period was collected, and the surviving L3 were extracted. Significantly fewer larvae were recovered from the fungus-treated pats. Analysis of wet and dry weight of the collected pats, as well as their organic matter content, were performed to compare the degradation of faeces of both groups. The results indicated that the presence of the fungus did not alter the degradation of the faeces.

The efficacy of two isolates of the nematode-trapping fungus Duddingtonia flagrans against Dictyocaulus viviparus larvae in faeces

A series of experiments was carried out to examine the effects of two different isolates of the nematode-trapping fungus Duddingtonia flagrans to reduce the number of free-living larvae of the bovine lungworm, Dictyocaulus viviparus. A laboratory dose-titration assay showed that isolates CI3 and Troll A of D. flagrans significantly reduced (P < 0.05 to P < 0.001) the number of infective D. viviparus larvae in cultures at dose-levels of 6250 and 12,500 chlamydospores/g of faeces. The larval reduction capacity was significantly higher for Troll A compared to CI3 when lungworm larvae were mixed in faecal cultures with eggs of Cooperia oncophora or Ostertagia ostertagi and treated with 6250 chlamydospores/g of faeces. Both fungal isolates showed a stronger effect on gastrointestinal larvae than on lungworm larvae. Two plot trials conducted in 1996 and 1997 involved deposition of artificial faecal pats containing free-living stages of D. viviparus and C. oncophora on grass plots. Herbage around the pats was collected at regular intervals and infective larvae recovered, counted and identified. These experiments showed that both D. flagrans isolates reduced the number of gastrointestinal as well as lungworm larvae in faecal pats. During both plot trials, the transmission of C. oncophora larvae, but not D. viviparus, from faecal pats to the surrounding herbage was clearly affected by climatic conditions. After collection of faecal pats from the grass plots one month after deposition, the wet and dry weight of pats as well as organic matter content were determined. No differences were found between the fungus-treated and non-treated control pats. This indicated that the rate of degradation of faeces was not affected by the addition of the fungus.

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.

Biological control of Haemonchus contortus infective larvae in ovine faeces by administering an oral suspension of Duddingtonia flagrans chlamydospores to sheep

A single oral dose of an aqueous suspension containing 11,350,000 chlamydospores of a Mexican isolate of Duddingtonia flagrans (FTHO-8) given to sheep, resulted in a maximum reduction of 88% (range 86.7-90.4%) of the population of Haemonchus contortus infective larvae in the faeces. The effect of this treatment continued for 4-5 days after administration of the suspension. The possible use of this treatment as a method of control of ovine haemonchosis is discussed.

Comparison of the trapping ability of Arthrobotrys robusta and Monacrosporium gephyropagum on infective larvae of Strongyloides papillosus

In an in vitro trial, the trapping ability of Arthrobotrys robusta and Monacrosporium gephyropagum against Strongyloides papillosus infective larvae on corn meal agar plates, was evaluated after seven days of interaction at 25 degrees C. Monacrosporium gephyropagum trapped 93.1% of the larvae whereas A. robusta trapped only 32.3%. Variability in the capture of S. papillosus infective larvae by both trapping fungi is discussed.

Dung-derived biological agents associated with reduced numbers of infective larvae of equine strongyles in faecal cultures

Two sets of dung-derived organisms from soil routinely fertilized with manure (MA) and soil chemically fertilized (CH) were cultured separately in the laboratory. Baermannized organisms from these cultures were added to 20 g of faeces from strongyle-infected horses to form three treatment groups: (i) no soil organisms; (ii) low inoculum of soil organisms containing all organisms present in a suspension of approximately 100 adult female free-living nematodes; and (iii) high inoculum containing those soil organisms present with approximately 1000 adult female free-living nematodes. Three studies were conducted using MA cultures and faeces containing 50 stronglye epg, CH cultures and faeces containing 1500 strongyle epg, and a mixture of soil organisms from the two cultures (MC) and faeces containing 600 strongyle epg. Within each study, five control cultures and 15 each of low and high inoculum cultures were prepared and incubated at 24 degrees C and 95% humidity in a climate chamber for 15 days. Parasitic and free-living nematodes were then recovered by the Baermann technique and counted. The numbers of third stage larvae were significantly lower in the high inoculum group compared to controls. The percent reductions in the number of third stage larvae for the low and high inoculum groups were 63.6% and 90.9%, 85.1% and 97.1%, 84.5% and 98.4% for MA, CH, and MC studies, respectively, indicating that mortality increased with the number of soil organisms added to cultures. Examination of the source cultures detected the presence of two species of nematophagous fungi and three genera of free-living nematodes reported to be predacious.

Effect of the nematode-trapping fungus Duddingtonia flagrans on the free-living stages of horse parasitic nematodes: a pilot study

A plot experiment was conducted to investigate the ability of the nematode-trapping fungus Duddingtonia flagrans to reduce the transmission of infective horse strongyle larvae from deposited dung onto surrounding herbage. At three different times during the summer 1995, three groups of horses, naturally infected with large and small strongyles, were fed different doses of D. flagrans spores, while a fourth group of animals served as non-fungal controls. Faeces from all four groups of horses were deposited as artificial dung pats on a parasite-free pasture. Every second week for 8 weeks after dung deposition, a subsample of the herbage surrounding each dung pat was collected and the number of larvae on the grass determined. Also, the larval reduction capacity of the fungus was evaluated by faecal cultures set up from all groups of horses. The faecal cultures showed that a sufficient number of spores of D. flagrans survived passage through the horses alimentary tract to significantly reduce the number of developing larvae. A lower reduction of larval numbers was observed when a different batch of fungal material was used at the beginning of the season. Dry climatic conditions affected the transmission of infective larvae in all groups, resulting in low numbers of larvae on the herbage. During the rainy periods a significant reduction in the number of larvae recovered was observed around all fungal containing pats. There were no significant differences between the number of fungal spores and the level of reduction caused by the fungus.

Biological control of gastro-intestinal nematodes--facts, future, or fiction?

The potential of using fungi to prevent nematodosis caused by parasites with free-living larval stages is well documented today. In this respect Duddingtonia flagrans, a net-trapping, nematode-destroying fungus, appears to be the most promising candidate. Laboratory experiments and in-vivo studies, where fungal spores have survived passage through the gastro-intestinal tract of cattle and horses, plus field studies with cattle, horses and pigs, demonstrate significant reduction in the number of infective larvae that develop in the faecal environment. In field trials this reduction subsequently leads to reduced infectivity of herbage and also reduced worm burdens in grazing animals. A status of the present situation, primarily based upon work performed in Denmark within the last 6-8 years, plus an outlook for practical implementation of an integrated control strategy including the use of nematode-destroying fungi in the future is discussed.

Nematode-trapping fungi in biological control of Dictyocaulus viviparus

Larvae of the cattle lungworm Dictyocaulus viviparus were cultured in experimental units of 200 g cattle faeces placed in semi-transparent trays in the laboratory. In each of 4 experimental series using this experimental unit, chlamydospores (chl) of the nematode-trapping fungus Duddingtonia flagrans were admixed to half of the faecal cultures in a concentration of 50.000 chl/g. In all 4 series there was a significant reduction in the development and subsequent release of infective lungworm larvae from faecal cultures containing chlamydospores. The average reduction in larval release, caused by fungal spores, was 86%.

Induction of traps by Ostertagia ostertagi larvae, chlamydospore production and growth rate in the nematode-trapping fungus Duddingtonia flagrans

Biological control of parasitic nematodes of domestic animals can be achieved by feeding host animals chlamydospores of the nematode-trapping fungus Duddingtonia flagrans. In the host faeces, D. flagrans develop traps that may catch nematode larvae. In experiments on agar, D. flagrans had a growth rate between 15 and 60 mm/week at temperatures between 20 and 30 degrees C. The presence of nematodes induces the fungus to produce traps. The rate of trap formation in D. flagrans has an optimum at 30 degrees C, producing 700-800 traps/cm2/2 days, when induced by 20 nematodes/cm2 on agar. Approaching 10 and 35 degrees C the ability to produce traps is gradually reduced. The response of chlamydospore production on agar to changes in temperature is the same as that for trap formation. On agar, at 10, 20 and 30 degrees C D. flagrans loses its trap inducibility after 2-3 weeks. During the ageing process, increasing numbers of chlamydospores are produced up to a certain limit. The time for reaching maximum chlamydospore concentration coincided with the time for loss of induction potential. The implications of these results in relation to biological control in faeces are discussed.

Prospects for integration of novel parasite control options into grazing systems

Novel parasite control methods are considered under criteria of efficacy, cost, ease of implementation and sustainability, together with a subjective assessment of when they are likely to become available commercially. It is concluded that vaccines, genetically resistant hosts, biological control, anthelmintics directed against free-living stages, and grazing management will probably satisfy all of these criteria, but that most of these methods are at least 5-10 years away from commercial exploitation. The exception is grazing management, which can be used immediately and at low cost, to minimise current use of anthelmintics. Research is required to assess the possibility of control programs based on grazing management that avoid anthelmintic treatment altogether. Extension of such control programs, in a context of declining government enthusiasm for provision of agricultural extension services, may be their greatest barrier to widespread adoption.

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

Control of nematode parasites of livestock is focused almost entirely on the parasitic stages within the host. Current methods rely on anthelmintic drugs, but these are under increasing threat with the development of resistance covering the whole spectrum of anthelmintics amongst the important nematode species of a range of livestock. However, invariably the greatest proportion of the parasite biomass resides not within the animal hosts, but in the external environment-commonly on pasture. It is in this environment that the free-living stages are vulnerable to a range of abiotic factors (extremes in temperature and desiccation) and biotic factors (macro- and micro-organisms) that may decimate their numbers. Of the latter, there are organisms, which exert their effects either indirectly by rendering faecal deposits inimical for the development of nematode eggs through to infective larvae, or directly by acting as pathogens or by exploiting the free-living stages as a food source. Within this vast assemblage of organisms, which include microarthropods, protozoa, viruses, bacteria and fungi, could well emerge a variety of biological control agents of nematode parasites. At present, greatest interest lies with the nematode-destroying fungi. Work has progressed from Petri dishes, to plots, to paddocks with several species of the genus Arthrobotrys and Duddingtonia flagrans. These studies indicate that the voracious nematophagous capabilities of these fungi, clearly demonstrated in vitro, translate to reductions in the number of infective larvae on pasture and indicate that levels of control, comparable to conventional schemes using anthelmintics, can be achieved. The challenge now lies in developing methods of administration of fungi to animals which can be applied under practical farm conditions. However, the pursuit of candidates for biological control of nematode parasites of livestock should not involve just a few species of nematophagous fungi. More than 100 species of fungi have been identified as possessing nematode destroying capabilities. These need to be more specifically investigated for their effects on free-living stages of nematode parasites of livestock, together with other classes of organisms, particularly bacteria, which have proved successful as biological control agents of arthropods.

Biological control. Aspects of biological control--with special reference to arthropods, protozoans and helminths of domesticated animals

Biological control describes situations in which a living antagonist (a predator, parasite, parasitoid or a pathogen) is distributed by man to lower pest (parasite) populations to acceptable sub-clinical densities or to keep the population at a non-harmful level. Ideally, biological control has no negative effects on the environment, whereas chemical control is not always so harmless. Laboratory and field observations have revealed many organisms, such as viruses, bacteria, fungi, protozoans, turbellarians, nematodes, earthworms, tardigrades, insects, copepods and mites as antagonists to parasitic arthropods, protozoans and helminths of domesticated animals. However, only very few of these antagonists have shown promising qualities as biological control agents within veterinary science. The lack of success should be linked to the lack of knowledge about complex natural biological systems and the antagonists that may be found there. This situation has restricted the interest of industry in developing biological products. In the future, however, industry may become more interested in biological control considering the increasing problems with parasite resistance to drugs in combination with the increasing cost of developing new chemical products, and because of increasing public concern about chemical residues in animal products and in the environment.

The capacity of the fungus Duddingtonia flagrans to prevent strongyle infections in foals on pasture

A field trial was conducted to evaluate the potential of the nematode-destroying fungus Duddingtonia flagrans to control free-living stages of horse strongyles. In late Spring 2 groups of horses (yearlings) with mixed infections of strongyles were allowed to contaminate 2 equal-sized pastures. One of the groups (F) received a daily dose of D. flagrans mixed in a feed supplement, while the other (C) received a similar amount of supplement without fungus. During a 3-month contamination period strongyle egg counts in faeces and number of infective strongyle larvae harvested from faecal cultures were determined. Grass samples were collected fortnightly. After the contamination period the yearlings were removed and 2 groups of young tracer foals (TF and TC) grazed the fungus and control pastures respectively for 4 weeks, housed for another 15 weeks and then killed to determine their worm burdens. The number of larvae in cultures from group TF was significantly lower than that in TC and herbage infectivity was reduced to a very low level on the pasture grazed by horses fed fungi. The number of Strongylus vulgaris and Strongylus edentatus larvae was also significantly lowered in group TF. Cyathostome larvae recovered from the mucosa of the ventral and dorsal colon and from the caecum were significantly lowered in group TF foals. Also, the number of strongyles found in the gut contents of group TF foals were significantly reduced in the dorsal colon, but numbers of worms in the ventral colon and in the caecum were similar to those of the controls.

Biological control of trichostrongyles in calves by the fungus Duddingtonia flagrans fed to animals under natural grazing conditions

The present study was conducted in the 1993 grazing season with yearling calves exposed to a pasture with a natural mixed trichostrongyle larval infection. It was shown that daily feeding with the microfungus Duddingtonia flagrans during the first 2 months of the season led to a lowered herbage infectivity and a reduced acquisition of Ostertagia sp. and Cooperia sp. later in the season. In addition, the procedure delayed the onset of clinical disease. This was due to the nematode-destroying effects of the fungi in the dung excreted by the fungus-treated calves, as evidenced by results from a parallel in vitro assay on faecal larval cultures. The paper discusses future research needs before practical biological control can be implemented.

Predacious activity of the nematode-trapping fungus Duddingtonia flagrans against cyathostome larvae in faeces after passage through the gastrointestinal tract of horses

This study was undertaken to examine the potential of the nematode-trapping microfungus Duddingtonia flagrans to survive passage through the gastrointestinal tract of horses and subsequently to destroy free-living stages of cyathostomes in faecal cultures. Three different oral dose levels were tested, two horses being used for each level. Faeces were collected twice daily and the numbers of parasite eggs per gram of faeces were determined. The numbers of infective third stage larvae which developed in faecal cultures were determined after the cultures had been incubated for 2 weeks at 24 degrees C. Results showed a positive relationship between dose level and reduction in the number of infective larvae. Fungi were recovered in faeces at times which corresponded to high larval reduction.

Prevention of clinical trichostrongylidosis in calves by strategic feeding with the predacious fungus Duddingtonia flagrans

The present investigation showed that strategic feeding of first-season calves with the microfungus Duddingtonia flagrans through the initial 3 months of the grazing season could prevent severe clinical trichostrongylidosis in the late summer. The successful prevention of disease was particularly noteworthy in view of the high stocking rate practiced on this permanent pasture, which was widely contaminated with a range of gastrointestinal nematodes. The results showed that larval populations of Ostertagia and Cooperia were significantly reduced on the pasture grazed by the fungus-treated calves. Numbers of Nematodirus seemed less affected. The present paper discusses the complexity of fungus-nematode interactions in dung pats under natural conditions.