Nematode Parasites Of Ruminants Research Articles

Some larval morphological characteristics of Camelostrongylus mentulatus and Nematodirus spathiger

Monitoring of gastrointestinal nematode parasites in ruminants (domestic and wild) is often based on fecal examination techniques, looking for excreted eggs and larval forms using morphological keys. These, are more available in domestic ruminants, in which helminths are widely studied, than in wild ruminants. This study tried to provide certain morphological elements that will help to recognize the L3 larvae of Camelostrongylus mentulatus and Nematodirus spathiger that could parasite either domestic or wild ruminants. For that, we resorted first to the culture of L3 larvae from fecal samples taken from African antelopes, and second by the microscopic characterization of each isolated larval morphological pattern previously identified by sequencing of its internal transcribed spacer (ITS-2) regions of the ribosomal DNA. The results of different microscopic captured images showed that Camelostrongylus mentulatus larva is 16 intestinal cells that measuring approximately 820 µm length, ‎≈ 25 µm wide, and ‎≈ 47 µm for its sheath tail extension and by this be closer to Teladorsagia circumcincta characteristics. For Nematodirus spathiger, it possesses 8 gut cells and measuring about 1020 µm long, ‎≈ 25 µm wide, and‎ ≈ 143 µm for its sheath tail extension with specific tail appendages. Have done this, we were able to get some clarifications on the morphology of the studied larvae, and we believe thus that this study will contribute to the establishment of morphological identification keys especially for parasitic nematodes of wild ruminants.

Targeted flock/herd and individual ruminant treatment approaches

In Europe, most nematodoses are subclinical involving morbid rather than mortal effects and control is largely achieved using anthelmintics. In cattle, the genera most associated with sub-optimal performance are Ostertagia and Cooperia whereas in sheep and goats, subclinical losses are most often caused by Teladorsagia and Trichostrongylus. In some regions, at certain times, other species such as Nematodirus and Haemonchus also cause disease in sheep and goats. Unfortunately, anthelmintic resistance has now become an issue for European small ruminant producers. One of the key aims of the EU-funded PARASOL project was to identify low input and sustainable approaches to control nematode parasites in ruminants using refugia-based strategies. Two approaches to optimise anthelmintic treatments in sheep and cattle were studied; targeted treatments (TT) – whole-group treatments optimised on the basis of a marker of infection e.g. faecal egg count (FEC), and targeted selected treatment (TST) – treatments given to identified individuals to provide epidemiological and/or production benefits. A number of indicators for TT and TST were assessed to define parasitological and production-system specific indicators for treatment that best suited the regions where the PARASOL studies were conducted. These included liveweight gain, production efficiency, FEC, body condition score and diarrhoea score in small ruminants, and pepsinogen levels and Ostertagia bulk milk tank ELISA in cattle. The PARASOL studies confirmed the value of monitoring FEC as a means of targeting whole-flock treatments in small ruminants. In cattle, bulk milk tank ELISA and serum pepsinogen assays could be used retrospectively to determine the levels of exposure and hence, in the next season to optimise anthelmintic usage. TST approaches in sheep and goats examined production efficiency and liveweight gain as indicators for treatment and confirmed the value of this approach in maintaining performance and anthelmintic susceptibility in the predominant gastrointestinal nematodes. There is good evidence that the TST approach selected less heavily for the development of resistance in comparison to routine monthly treatments. Further research is required to optimise markers for TT and TST but it is also crucial to encourage producers/advisors to adapt these refugia-based strategies to maintain drug susceptible parasites in order to provide sustainable control.

Managing anthelmintic resistance: Is it feasible in New Zealand to delay the emergence of resistance to a new anthelmintic class?

The recent registration in New Zealand of the first new class of broad-spectrum anthelmintic, for use against nematode parasites of ruminants, in nearly three decades has raised the possibility that parasite management practices could be improved to minimise the emergence of resistance to the new drug. A review of knowledge pertaining to the selection of anthelmintic resistance in nematode parasites of sheep highlights a number of management practices which could be altered to achieve this. A number of previously common practices such as whole-flock treatment of adult ewes around lambing, and treatment of lambs as they are moved onto pastures with low parasite contamination have been clearly identified as high risk for selecting resistant parasites. Once high-risk practices have been identified steps can be taken to either eliminate their use or mitigate the associated risk. Much of the focus on the management of resistance around the world is on the retention of susceptible genotypes in refugia. While approaches to retaining unselected parasites are likely to vary around the world, empirical studies indicate that the practice is likely to be effective at slowing the development of resistance. The challenge for farmers and advisors will be to strike a balance between retaining sufficient susceptible para-sites to usefully delay the development of resistance while not unduly compromising animal performance and farm profitability. The merits of combining different classes of anthelmintic in order to slow the development of resistance remains somewhat contentious in some countries. However, the attributes of oral anthelmintics are such that they seem likely to meet most, if not all, of the criteria for combinations to be highly effective at slowing the build-up of resistance in nematode parasites. It is evident that considerable progress has been made in understanding the factors involved in selecting anthelmintic-resistant nematodes since the last broad-spectrum anthelmintic class was released in the early 1980s. Therefore, it should be possible to manage a new class of anthelmintic in such a way as to significantly extend its effective life. The challenge is likely to be in convincing farmers of the merits of adopting such pro-active strategies.

Hatching behaviour of Nematodirus filicollis in a flock co-infected with Nematodirus battus

The development and survival of larvae of Nematodirus filicollis, an important nematode parasite of ruminants, were extensively investigated in the laboratory for the first time, using eggs harvested from sheep grazing in the UK in winter. Third-stage larvae (L3s) developed within the eggs between 12 and 25 degrees C, with the proportion of eggs developing successfully being highest at the upper end of this range. Eggs required chilling below 10 degrees C before being able to hatch at all, and maximum hatch was observed only following chilling to 4 degrees C. Hatching occurred above 6 degrees C, and peaked at 13 degrees C, with the proportion of eggs hatching decreasing to 17-20 degrees C, which appears to form an upper threshold temperature for hatching. When fully developed eggs were placed at 11-13 degrees C, L3 emerged very rapidly with hatching being completed within 6 days. Mortality of emerged L3s increased with temperature, particularly above 20 degrees C. For this parasite, given the low minimum hatching thresholds and the rapid emergence of L3, the existence of an upper hatching threshold is likely to have limited impact on patterns of larval availability on pasture. The strict requirement for chilling is surprising, being at odds with both previous observations and the wide geographical distribution of this species. It is possible that the proportion of eggs requiring chilling is an adaptable trait, enabling early infection of naïve hosts in the face of competition from N. battus, yet also persistence in regions that do not provide good conditions for the chilling of eggs. Further study of selectable variation in this trait could help us to understand the contrasting geographical ranges and disease patterns within the genus, and how different species might respond to climate change.

Development and application of a PCR diagnostic assay for the accurate and rapid identification of the nematophagous fungus Duddingtonia flagrans

The nematophagous fungus, Duddingtonia flagrans is a potential biocontrol agent against nematode parasites of ruminants. Improved methods for the rapid and accurate detection of D. flagrans would aid the evaluation of this fungus as a biocontrol agent and its suitability for environmental release. To date, detection and identification of D. flagrans is reliant on morphological methods, which can be laborious, time-consuming, and error prone. In this study, a PCR assay using species-specific primers located in the ITS regions was developed for the rapid and accurate identification of D. flagrans. The PCR assay was specific to five different isolates of D. flagrans and was capable of detecting a minimum concentration of 100 chlamydospores per gram of soil. In contrast to cultured-based detection and identification methods, this assay is amenable to high throughput screening of environmental samples. The assay detected D. flagrans in faecal, leaf litter, and soil samples collected from 80 % of the Irish farms tested indicating that the fungus is abundant in Ireland.

Breeding sheep in New Zealand that are less reliant on anthelmintics to maintain health and productivity

Breeding sheep that are less reliant on the use of anthelmintics to maintain acceptable health and productivity is one of several options that may assist farmers to manage the growing anthelmintic-resistance problem in New Zealand and meet consumer demands to minimise drug usage in livestock. Although it has been known for many years that genetic factors contribute to the ability of sheep to cope with roundworm challenge, attempts to selectively breed for such factors have occurred only recently. Two host traits, ‘resistance’ and ‘resilience’, are thought to be involved in limiting the deleterious effects of roundworms on the health and productivity of sheep, and the associated need for treatment with anthelmintics. Over the last decade, considerable advances have been made in our understanding of the feasibility and implications of breeding for these traits under practical conditions. The experimental breeding lines developed as part of this research are now proving to be a valuable resource for further work directed at identifying genes and/or genetic markers associated with host resistance and understanding the mechanisms of host immunity to nematode parasites in ruminants. This review provides an up-to-date summary of the results of research in this field, with particular reference to dual-purpose sheep in New Zealand, and describes how this information is being applied in practical breeding programmes.

Drug-resistant parasites and aggregated infection--early-season dynamics.

We investigate the effect of spatial aggregation in the infection dynamics of nematode parasites in ruminants. We show that a high degree of spatial aggregation is likely to lead to a dramatically enhanced rate of invasion by drug-resistant strains.

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.

Ingestion of host immunoglobulin by three non-blood-feeding nematode parasites of ruminants

Host immunoglobulin was detected in homogenates of adult worms or fourth stage larvae of Haemonchus contortus, Ostertagia ostertagi, O circumcincta and Dictyocaulus viviparus, but not in preparasitic third stage larvae of H contortus. All the worms had been washed in detergent before being homogenised to remove any immunoglobulin adhering to the cuticle. This procedure, the concentrations of immunoglobulin detected and observations on sections of the worms stained with fluorescent antisheep immunoglobulin, all suggested that the immunoglobulin had been ingested, even by the non-blood-feeding species. This finding suggests that the Ostertagia species and D viviparus may be susceptible to vaccination by the gut antigen approach, a method with considerable promise for blood-feeding parasites like H contortus and Boophilus microplus.

Prospects for biological control of nematode parasites of ruminants

Control of nematode parasites in ruminants is directed almost exclusively at the parasitic stage in the host using conventional anthelmintic therapy. However, to complete their life cycle, parasites have to develop through a series of free-living stages on pasture. It is within this environment that there is a vast range of cohabiting micro-organisms, some of which are known to infect or prey on nematodes. These include bacteria, protozoa, viruses and fungi. To date, most interest has been focused on those organisms producing chemical toxins which have been developed as anthelmintics, e.g. Streptomyces/avermectins. Yet the potential of predacious and nematoxic fungi and bacteria for the biological control of nematode parasites of livestock remains largely untapped. These organisms may well offer a cheaper and more sustainable approach to reducing the impact of parasitism in livestock.

Derivatives of epinephrine, norepinephrine, octopamine and histamine formed by homogenates of Trichostrongylus colubriformis, a nematode parasite of ruminants

1. 1. Radiolabeled epinephrine, norepinephrine, octopamine and histamine were introduced into homogenates of mixed sexes of the nematode Trichostrongylus colubriformis and the labeled derivatives formed during incubation were identified by HPLC. Vanillylmandelic acid (VMA), 4-hydroxy-3-methoxyphenyl glycol (HMPG) and metanephrine were formed from epinephrine. 2. 2. VMA, HMPG and normetanephrine were produced from norepinephrine. 3. 3. Octopamine was converted into norepinephrine, synephrine and epinephrine. 4. 4. Imidazole-4-acetic acid, 1,4-methylimidazole acetic acid and acetylhistamine were formed from histamine. 5. 5. Inhibitors of monoamine oxidase, catechol- O-methyltransferase and phenylethanolamine- N-methyltransferase were tested for their e ffects on the formation of certain of these derivatives, and the results suggested that these enzymes were active in the homogenate.

Efficacy of Commercial Bovine Serum as a Component of Media Used to Grow Cooperia punctata In vitro

Several commercial serums-agamma calf, bovine, fetal bovine, from calves 10 days to 6 months old, and from calves younger than 10 days-were incorporated into Ae medium (Leland, 1963, 1965). Each serum's efficacy in promoting in vitro growth and development of Cooperia punctata, a nematode parasite of ruminants, was compared with medium Ae containing from a donor calf. Culture tubes inoculated with exsheathed, 3rd-stage C. punctata larvae were maintained in a roller drum at 38.5 C for 35 or 56 days; some cultures were transferred weekly into new media and some were not. At termination, worms were preserved, measured, and counted, and data for each medium were compared and evaluated. All serums tested, when used as a component of Ae, promoted growth and development of C. punctata to the adult stage. Bovine was least effective as a substitute for obtained from a donor calf. Although medium containing fetal bovine was unsatisfactory because it tended to precipitate after thawing, it resulted in good growth and development during the first 3 weeks of culture. A minus gamma globulin (agamma serum) is our choice as a substitute for serum; this resulted in a clear medium and L, from eggs laid in vitro were observed after 28 days. Living worms were observed in all media in which worms were grown for 56 days without transfer, but weekly transfers into new media produced better cultures in tubes maintained that long. After 35 days in culture, a negative correlation between size of inoculum and percentage of worms reaching the adult stage was noted, although no correlation was observed between size of inoculum and size of adults. Largest adults were produced in cultures maintained for 56 days but transferred weekly into new media. Largest females were produced in media containing either from a donor calf (Ae) or commercial fetal (AeF); largest males were produced in AeF. The parasitic stages of Cooperia punctata grow well in medium Ae which normally contains from calves; omitting the results in fewer and smaller adult worms, and females so grown produce no eggs (Leland, 1963). In contrast, nonparasitic stages of C. punctata (L1 and L2) do not develop in medium containing (Leland, 1967b). If a readily available commercial could be substituted for helminth-free serum it would facilitate experimentation using the in vitro culture system, and also might simplify comparisons of studies from different laboratories. Thus we tested the efficacy of Ae medium in which various commercially available bovine serums were substituted for obtained from

Development and Survival on Pasture of Gastrointestinal Nematode Parasites of Cattle

Development and survival of the larvae of gastrointestinal nematode parasites of cattle under nearly natural conditions were studied in 14 trials during 1960-64 at the Agricultural Research Center, Beltsville, Maryland. Fecal pats containing nematode eggs were deposited on pasture; at subsequent intervals, the pats and surrounding herbage were examined for larvae. Trials with Ostertagia ostertagi, Cooperia oncophora, and C. punctata were begun in spring, autumn, and winter, with Oesophagostomum radiatum in spring and winter, with Haemonchus contortus sensu lato in summer, and with Nematodirus helvetianus in spring. The average monthly temperatures for good development of Ostertagia larvae were 55 to 70.3 F, and for Cooperia and Oesophagostomum, 60.3 to 70.3 F. The monthly precipitations for good development of all three genera were 1.04 to 3.75 inches. The average monthly temperatures for good recovery of Ostertagia larvae from the herbage were 44 to 70.3 F, for Cooperia, 50.9 to 75.6 F, for Oesophagostomum, 69.8 F, and recovery of all three genera was maximal at 69.8 F. The monthly precipitations for good recovery of larvae from the herbage were 1.77-5.42 inches. Initial, peak, and final recoveries of infective larvae from the feces occurred 1.5 to 9 (avg 4), 1.5 to 23 (avg 6), and 1.5 to 26.5 (avg 14) weeks after deposition of the pats, respectively. Initial, peak, and final recoveries of infective larvae from the herbage occurred 1 to 11 (avg 5), 1.5 to 23 (avg 11), and 5 to 35 (avg 16) weeks after deposition of the pats, respectively. The ranges in periods of recovery were attributed primarily to differences between seasons. Summaries of some of our knowledge of factors affecting the development and survival of the free-living stages of gastrointestinal nematode parasites of ruminants on pasture are given by Lucker (1941), Kates (1950), Gordon (1957), Crofton (1963), and Levine (1963). In six trials at the Agricultural Research Center, Beltsville, Maryland (Goldberg and Rubin, 1956; Goldberg and Lucker, 1959, 1963), infectiousness of different pasture plots was determined in four to six tests per trial by grazing helminth-free calves on the plots at various intervals after contaminating them with feces containing worm eggs. The trials were begun in spring, summer, and autumn. The study of development and survival of larvae within feces, under natural conditions, has been very limited. Information on development and survival of larvae within the feces, as well as infectiousness of the herbage, was obtained in the autumn trials (Goldberg and Lucker, 1963) by examination of the feces and herbage for infective larvae at intervals after deposition of the feces. In the present study, development and survival of larvae in feces and infectiousness of herbage were studied by direct examination. The trials were Received for publication 31 May 1968. begun under a wider range of weather conditions than in the previous trials, and tests per trial were more numerous. MATERIALS AND METHODS Fourteen trials were conducted during 1960-64. Development and survival of Ostertagia ostertagi and Cooperia (C. oncophora and C. punctata) larvae were studied in 11 and nine of them, respectively, begun in spring, autumn, and winter. Oesophagostomum radiatum was studied in seven of them begun in spring and winter, Haemonchus contortus sensu lato in the three begun in July, and Nematodirus helvetianus in the one begun in May. A few Trichuris eggs were present in some trials. In 11 of the trials, the feces containing nematode eggs were obtained from naturally infected cattle; in three, feces were obtained from experimentally inoculated calves. Batches of feces were thoroughly mixed in an electric mixer and from 7 to 18 (avg 9) pats per batch were prepared. The pats were nearly hemispherical, approximately 11 cm in diameter and 5 cm high, and had the consistency of normal cattle feces. They weighed 300 g in 10 trials, 200 g in two, and 150 and 50 g in one each. In each trial, two pats were mixed with amounts of charcoal and water considered close to optimum for larval development and were cultured in the laboratory under approximately optimal ambient temperatures, except in summer when the ambient temperature was usually above optimum. The numbers of larvae recovered from these cultures provided an index of the potential for production of infective larvae by the eggs in the pats. These cultures are referred to hereinafter

Age Resistance of Cattle to Nematodes of the Gastrointestinal Tract

The literature is replete with references to a greater resistance in older animals than in younger ones against the establishment of nematode parasites. Experimental data confirming the existence of resistance have been presented for a variety of nematode host systems: viz, Ancylostoma braziliense in cats and dogs (Sarles, 1929) ; Nippostrongylus muris in rats (Graham, 1932 and Chandler, 1932); Strongyloides ratti in rats (Sheldon, 1937); Trichinella spiralis in rats (Nolf and Zaiman, 1941); and Ascaridia galli in chickens (Ackert, Porter and Beach, 1935). On the other hand, there was no evidence of resistance to Trichostrongylus calcaratus in rabbits (Sarles, 1932) or to T. colubriformis in guinea pigs (Herlich, 1958). Although there has been considerable reference to resistance against nematode parasites in ruminants, evidence of this phenomenon is largely empirical being based primarily on field observations of naturally infected cattle. Under these circumstances, varying degrees of acquired immunity cannot be ruled out as a factor in the causation of the observed facts. Experimental data have been presented by Lucker (1952) and Goldberg (1952) suggesting that older sheep are somewhat more resistant than younger ones to infection with Haemonchus contortus and Oesophagostomum venulosum. However, Gordon (1950) stated that age resistance appears to be practically absent as far as haemonchosis is concerned in sheep Furthermore, Stewart and Gordon (1953) reported that 7 of 10 threeto four-yearold sheep raised worm-free died from experimental exposure to T. colubriformis. Host appeared to have no influence on susceptibility to infection with 0. radiatum and Bunostomum phlebotomum in calves ranging from 0.5 to 1.25 years old (Mayhew, 1940) or to Cooperia punctata in cattle up to 1 year old (Bailey, 1949). On the other hand, the course of infections of calves with Strongyloides papillosus was affected by of the host (Vegors, 1954). In rather striking contrast, however, various investigators (Bailey and Herlich, 1953; Andrews et al, 1953; and Bailey and Thorson, 1954) have incriminated gastrointestinal nematodes as the cause of severe clinical parasitism and deaths in adult cattle. As there is a paucity of unequivocal experimental evidence of resistance to nematode parasites in cattle, some experiments were conducted in an attempt to clarify the status of this phenomenon; the results are herein reported. Some of the data from one of the experiments have been previously published in abstract form (Herlich, 1956b).