Single Anthelmintic Treatment Research Articles

The effect of climate, season, and treatment intensity on anthelmintic resistance in cyathostomins: A modelling exercise

Anthelmintic resistance is widespread in equine cyathostomin populations across the world, and with no new anthelmintic drug classes in the pharmaceutical pipeline, the equine industry is forced to abandon traditional parasite control regimens. Current recommendations aim at reducing treatment intensity and identifying high strongylid egg shedders in a targeted treatment approach. But, virtually nothing is known about the effectiveness of these recommendations, nor their applicability to different climatic regions, making it challenging to tailor sustainable recommendations for equine parasite control. This study made use of a computer model of the entire cyathostomin life-cycle to evaluate the influence of climate and seasonality on the development of anthelmintic resistance in cyathostomin parasites. Furthermore, the study evaluated the impact of recommended programs involving selective anthelmintic therapy on delaying anthelmintic resistance development. All simulations evaluated the use of a single anthelmintic (i.e., ivermectin) over the course of 40 model years. The study made use of weather station data representing four different climatic zones: a cold humid continental climate, a temperate oceanic climate, a cold semi-arid climate, and a humid subtropical climate. Initially, the impact of time of the year was evaluated when a single anthelmintic treatment was administered once a year in any of the twelve months. The next simulations evaluated the impact of treatment intensities varying between 2 and 6 treatments per year. And finally, we evaluated treatment schedules consisting of a combination of strategic treatments administered to all horses and additional treatments administered to horses exceeding a predetermined fecal egg count threshold. Month of treatment had a large effect on resistance development in colder climates, but little or no impact in subtropical and tropical climates. Resistance development was affected by treatment intensity, but was also strongly affected by climate. Selective therapy delayed resistance development in all modelled scenarios, but, again, this effect was climate dependent with the largest delays observed in the colder climates. This study is the first to demonstrate the value of cyathostomin parasite refugia in managing anthelmintic resistance, and also that climate and seasonality are important. This modelling exercise has allowed an illustration of concepts believed to play important roles in anthelmintic resistance in equine cyathostomins, but has also identified knowledge gaps and new questions to address in future studies.

A model for the development and growth of the parasitic stages of Parascaris spp. in the horse

Literature documenting the growth and development of Parascaris spp. infections was used to develop a model describing worm dynamics in the young horse. The model incorporates four main variables; the rate at which larvae migrate through host tissues to return to the small intestine, the proportion of migrating larvae which succeed in returning to the small intestine, the rate of growth in size of maturing and adult worms and the survival rate of maturing and adult worms. In addition, the number of eggs laid each day by adult female worms is calculated as a function of worm size (length) and is used to calculate faecal egg output of the foal. Published data describing the rate of migration through host tissues, and the growth of worms following their return to the small intestine, was used to derive relationships describing these processes. However, only limited data exists relating the survival of migrating larvae and mature worms in the intestine to host age and experience of infection. Therefore, relationships and coefficients describing these variables were modified so that output aligned with published experimental results. As a consequence, the model has not yet been evaluated against an independent data set, and so remains as the best ‘current hypothesis’ for the dynamics of this parasite. Hopefully, future experiments designed to test specific assumptions and outputs of the model will lead to a better understanding of the biology of this important parasite. For example, the most influential variable in determining model output is the survival rate of worms in the small intestine. In the model, worm survival declines in response to both the increasing age of the horse and the increasing cumulative length of worms in the intestine (used as a proxy for crowding). Given the importance of this variable to model behaviour and the paucity of experimental data on this topic this would seem a priority for future study. Initial experiments using the model suggest that a single anthelmintic treatment, administered soon after patency of initial infection, may effectively control environmental contamination with Parascaris spp. eggs while allowing a small ‘refugia’ of susceptibility to delay the emergence of anthelmintic resistance. Further evaluations of the practicality of this approach may be worthwhile.

Gastrointestinal nematodes and dietary fibre: Two factors to consider when using FN for wildlife nutrition monitoring

Faecal nitrogen (FN) – the combination of metabolic nitrogen and residual food nitrogen – has been used as a proxy for diet quality in wild and domestic ruminants for over half a century. However, a common misconception in some of these studies is that FN is a direct proxy for dietary N, in spite of experimental evidence that links FN to general diet digestibility. Additionally, gastrointestinal nematodes (GIN) can alter N metabolism and increase FN by various mechanisms. To clarify the role of dietary N, fibre and GIN as a factor in FN excretion, 10 naturally parasitised sheep were fed two different isocaloric diets (LPF: low-protein, low-fibre; HPF: high-protein, high-fibre). One month after these diets began, a single anthelmintic treatment was applied to remove GIN, after which the sheep were kept on the same diet for an additional 2 weeks. Throughout the experiment, individual faecal samples were obtained to estimate both FN and GIN intensity (using faecal egg counts, FEC). In addition, two blood samples were taken before and after deworming to measure serum total protein concentrations (TP) as a proxy for protein absorption. In spite of the difference in dietary protein, FN was higher on an LPF diet, supporting the overall digestibility concept. The influence of GIN on FN was later revealed by the anthelmintic treatment, which led to a decrease of FEC and FN in both dietary groups. Serum total protein showed a slight but non-significant increase in both groups after the anthelmintic treatment. Our study supports not only the concept that FN is a proxy for diet digestibility, and not directly for dietary N, but also that gastrointestinal nematodes limit its use as a proxy for diet quality in ruminants, especially under high parasite loads (e.g., 1000 faecal eggs per gram of faeces). Such limitations should be considered before using FN for wildlife nutrition monitoring. Some recommendations are given to avoid misinterpretations.

Effects of anthelmintic treatment on milk production in Sarda dairy ewes naturally infected by gastrointestinal nematodes

The objective of this work was to investigate the effects of a single anthelmintic treatment on milk production. In 2008, in a flock of Sarda ewes naturally infected by gastrointestinal nematodes, 162 adult and 72 primiparous ewes were allocated into four groups. For each age class, one group was drenched with albendazole after lamb weaning whilst the other was left untreated as control. The efficacy of single anthelmintic treatment at the beginning of lactation was obtained by a faecal egg count reduction test. The effect of drenching on milk yield and components was studied both using single test date and lactation records. After 1 month geometric mean of eggs per gram of treated ewes decreased up to 1% of the initial value (3.40 eggs/g versus 322.63 eggs/g in primiparous and 2.14 eggs/g versus 312.70 eggs/g in adult ewes). The anthelmintic treatment showed a significant effect only on lactation milk yield of treated adult ewes that produced 19.2 L/year more than control ewes. Production level was investigated as a criterion to apply targeted selective treatment. High producer multiparous ewes produced 32.7 L/year more than control ones. Overall results confirm a beneficial effect of anthelmintic treatment on milk production without any detrimental effect on milk composition only on adult ewes markedly if high producers. Thus, depending on milk price and the required length of the period of discarded milk, the increased milk yield can counterbalance treatment's costs.

ANTIHELMINTIC TREATMENT OF GOATS ON AN ARID RANGE AND ITS EFFECT ON MILK PRODUCTION EARLY IN LACTATION

The effect of a single anthelmintic treatment at thebeginning of lactation on milk production and composition, live weight change and blood chemistry in mix-breeds goats was studied in an arid zone of northern Mexico. Ten adult goats were treated with Closantel ® subcutaneously at 8.0mg kg-1 BW. Eleven adult goats were used as untreated controls. The overall total trial reduction in fecal egg counts due to anthelmintic treatment was 96%, but this fecal egg counts reduction did not affect live weight change (-13 ±0.5 and -15 ± 0.3 g d-1 for treated and control does), milk yield(30.7 ± 0.4 and 33.6 ± 0.8 L in 73 days of lactation for treated and control does). No significant differences were seen in milk composition and blood profiles between treated and untreated goats. It was concluded that, in the present context of goat exploitation under traditional extensive village system in an arid environment, parasite burdens at the beginning of lactation were not sufficiently severe to affect milk production and weight change of goats. KEY WORDS: Anthelmintic treatment, blood chemistry, body weight, goats, milk production, gastrointestinal nematodes.

Global Epidemiology, Ecology and Control of Soil-Transmitted Helminth Infections

Soil-transmitted helminth (STH) infections are among the most prevalent of chronic human infections worldwide. Based on the demonstrable impact on child development, there is a global commitment to finance and implement control strategies with a focus on school-based chemotherapy programmes. The major obstacle to the implementation of cost-effective control is the lack of accurate descriptions of the geographical distribution of infection. In recent years, considerable progress has been made in the use of geographical information systems (GIS) and remote sensing (RS) to better understand helminth ecology and epidemiology, and to develop low-cost ways to identify target populations for treatment. This review explores how this information has been used practically to guide large-scale control programmes. The use of satellite-derived environmental data has yielded new insights into the ecology of infection at a geographical scale that has proven impossible to address using more traditional approaches, and has in turn allowed spatial distributions of infection prevalence to be predicted robustly by statistical approaches. GIS/RS have increasingly been used in the context of large-scale helminth control programmes, including not only STH infections but also those focusing on schistosomiasis, filariasis and onchocerciasis. The experience indicates that GIS/RS provides a cost-effective approach to designing and monitoring programmes at realistic scales. Importantly, the use of this approach has begun to transition from being a specialist approach of international vertical programmes to becoming a routine tool in developing public sector control programmes. GIS/RS is used here to describe the global distribution of STH infections and to estimate the number of infections in school-age children in sub-Saharan Africa (89.9 million) and the annual cost of providing a single anthelmintic treatment using a school-based approach (US$5.0-7.6 million). These are the first estimates at a continental scale to explicitly include the fine spatial distribution of infection prevalence and population, and suggest that traditional methods have overestimated the situation. The results suggest that continent-wide control of parasites is, from a financial perspective, an attainable goal.

Anthelmintic Treatment of Goats on an Arid Range and its Effect on Milk Production in Late Lactation

Mellado, M., González, H., García, J.E. and García, R. 2004. Anthelmintic treatment of goats on an arid range and its effect on milk production in late lactation. J. Appl. Anim. Res., 25: 91–95. The effect of a single anthelmintic treatment (ClosantelR; subcutaneously at 8.0 mg kg1 BW) on milk production and its composition, live weight change and blood chemistry in mix-bred goats was studied in an arid zone of northern Mexico. Twelve adult goats towards the end of lactation (120 d; end of the rainy season) were treated, whereas ten adult goats were used as untreated controls. Fecal egg count (FEC) in the treated group dropped 93% (P<0.01) 21 days after treatment, but this FEC reduction did not affect liveweight change, milk yield and milk composition. These data suggest a high resilience of the host against the sub-clinical nematode infection, therefore, in this area goat milk producers are likely not to be benefited economically by using anthelmintics.

Risk Factors for High Endoparasitic Burden and the Efficiency of a Single Anthelmintic Treatment of Danish Horses

A questionnaire survey regarding endoparasite control practices in Danish horse herds was carried out in 1995. The participating veterinarians and herd owners were sampled using convenience and purposive sampling. In the analysis of risk factors for development of a high endoparasitic burden (>200 eggs per gram faeces) 903 horses were sampled and the analysis of the efficiency of a single anthelmintic treatment was based on 605 horses. The following factors had a significant effect on the endoparasitic burden: herd type, age of the horses, use of pasture rotation, anthelmintic treatment of horses visiting the herd, use of an adviser in the planning of endoparasite control and advice regarding pasture rotation. An interaction between pasture rotation and advice regarding pasture rotation was found, but due to high collinearity this was not reported. The factors influencing significantly on the reduction of the faecal egg count after a single anthelmintic treatment were the type of herd, the age of the horse, the drug used, and the anthelmintic-resistance-status of the herd. A negative effect of permanent pastures was observed. If pasture hygiene was performed on the advice of the veterinarian, the effect of a single anthelmintic treatment was less compared to a single anthelmintic treatment without any advice. An interaction between the treatment group and the resistance-status of the herd was found. Additional factors, normally accounted for, when endoparasites and anthelmintic resistance is discussed, were investigated, but not found significant in this study.

Occurrence of helminths in pig fattening units with different management systems in Northern Germany

The helminth infections on 13 pig fattening farms with different management systems (complete or partial all-in-all-out system or continuous fattening) in North-Western Germany were investigated over at least three fattening periods. Pooled faecal samples were taken from pens once before and three times after anthelmintic treatment. At the beginning of fattening 34.9% of the samples contained helminth eggs, mainly from Oesophagostomum spp. (27.5%). Ascaris suum eggs were found in 10.5% of the samples, while other parasites were only rarely found. The number of pig-supplying farms was positively correlated with the helminth infection prevalence. Immediately after deworming, all pen samples were free of helminth eggs. However, the prevalences increased again, and by the end of fattening A. suum was found in 33.0% and strongylids in 6.0% of the samples. Pens harbouring A. suum-excreting pigs at the beginning of fattening had higher infection levels at the end, and this was also the case for nodular worms. The final prevalence of Ascaris was higher in partial exchange systems than in complete all-in-all-out systems and in old pig houses compared to new ones. Transmission of both Ascaris and Oesophagostomum was highest in autumn and winter. Thus, a single anthelmintic treatment at the beginning of fattening could not prevent infection during fattening, and the state of infection at the beginning was associated with the helminth burden at slaughter. Therefore, the purchase of parasite-free pigs in combination with appropriate hygiene management may minimise the initial infection pressure and keep subsequent infection of the herd at a minimum.

Effect of strategic gastrointestinal nematode control on faecal egg count in traditional West African cattle.

This paper reports on the effect of strategic anthelmintic treatments and other determinants on faecal egg counts (FEC) of Trichostrongyles in N'Dama cattle of a west African village. Initially, 527 animals from 13 private N'Dama cattle herds were monitored in a longitudinal study from October 1989 to December 1994. Each herd was stratified by age and animals were sequentially allocated to two groups with similar age distributions. One group received a single anthelmintic treatment of fenbendazole (7.5 mg/kg BW), in October 1989 (n = 250), whereas the other group remained untreated (n = 277) throughout the study. In the next rainy season (June to October), the treated animals were treated twice (in July and September). The same treatment schedule was used in the subsequent rainy seasons until December 1994. Biannual anthelmintic treatments decreased the level of FEC between 31% (late dry season) and 57% (rainy season), when compared to untreated controls. The highest levels of FEC were found during the rainy season from June to October. FEC levels decreased until 4 years of age, after which they remained on a constant low level. The variability of returns to anthelmintic treatments between herds did not seem to be influenced by FEC at the herd level. The financial evaluation of anthelmintic interventions cannot be predicted from FEC and must necessarily rely on the direct monitoring of livestock productivity parameters.

Effect of strategic gastrointestinal nematode control on fertility and mortality of N'Dama cattle in The Gambia

A large-scale longitudinal study was undertaken to investigate the effects of a strategic treatment of gastrointestinal nematodes on the mortality and fertility of N'Dama cattle under village conditions. Initially, 1046 animals from 26 private N'Dama cattle herds, were monitored from October 1989 to December 1994. Each herd was stratified by age and the animals were randomly allocated to two groups with a similar average age. One group received a single anthelmintic treatment of fenbendazole (Panacur TM, 7.5 mg/kg BW, Hoechst Veterinä AG) in October 1989, whereas the other group remained untreated. In July 1990, the herds were subdivided into two different treatment schemes. In the herds of scheme 1, the treated animals (Treatment group I) were treated once (in August), whereas in the herds of scheme 2, the treated animals (Treatment group II) were treated twice (in July and September). The same treatment schedule was used in the subsequent rainy seasons until December 1994. One group in every herd of both schemes served as control (Treatment group 0) and received no anthelmintic treatment throughout the study. The average and annual cumulative incidence mortality between 0–1 year was more than two times higher in treated animals compared to their controls (21% against 7.5%). No differences were found in older age categories. Survival analysis confirmed differences in mortality from 0–1 year, but were not significant in proportional hazard models. The 25% quantities of age at first calving was used to quantify differences between twice treated animals (50.2 months) and its controls (58.3 months) which represents a decrease of 8 months in twice treated animals. Annual calving rates of twice treated animals were 52.2% compared to 43.6% in the control group ( P<0.001), which is an increase of 8.6% to the control rate. Possible causes of increased mortality in 0–1 year old treated calves are discussed. We can conclude that in the present epidemiological situation and the given parasite spectrum, gastro-intestinal nematodes mainly affect host fertility. Strategic control of gastro-intestinal nematodes is thus recommended for young heifers up to their age of first calving provided the overall financial analysis of the intervention is beneficial.

Effect of strategic gastrointestinal nematode control on growth of N'Dama cattle in Gambia

From October 1989 to December 1994, a longitudinal study on the control of gastrointestinal nematodes was done on 1000 N'Dama cattle in 20 private herds in Gambia. Each herd was divided into two groups with an even distribution of age and sex. One group received a single anthelmintic treatment of Fenbendazole, Panacur Hoechst Veterinär GmbH, 7.5 mg kg −1 BW in October 1989, whereas the other group served as an untreated control. In July 1990, the herds were subdivided into two different treatment schemes. In the herds of the first scheme the treated animals (Treatment group I) were treated once (in August), whereas in the herds of the second scheme the treated animals (Treatment group II) were treated twice (in July and September). The same treatment schedule was used in the subsequent rainy sensons until December 1994. One group in every herd served as control (Treatment group 0) and received no anthelmintic treatment throughout the study. One annual fenbendazole treatment had no significant effect on liveweights, whereas two annual treatments significantly increased liveweights of the age group 12–24 and 24–36 months by 9.4%, and 17.5%, respectively. Animals less than 12 months old had 6.3% higher liveweights after two treatments, the difference was statistically not significant ( P < 0.06). Average weights of 3- and 4-year-old, twice-treated animals were 13.1% and 8.2%, respectively, higher compared with their controls. No effect of anthelminthic treatment on liveweights was found in 5-year-old and older animals. Herd structure analysis demonstrated that overall male offtake rates ranged from 12 to 28% in the 3-, 4- and 5-year-old age categories. The age categories within which deworming improves liveweights thus coincides with the age at which males are mainly sold. These results suggest that biannual metaphylactic treatments (end of July and beginning of September) of all animals from birth to an age of 4 years should be recommended, provided that the financial analysis demonstrates the profitability of this intervention.

Effect of a single dry season anthelmintic treatment of N'Dama cattle on communal pastures in The Gambia.

The effect of a single anthelmintic treatment of cattle during the early dry season was studied. One hundred and sixty-six N'Dama cattle, 1-3 years old, were selected from five herds. There were 65 males and 101 females divided into two groups of 83 animals each. One group was treated with fenbendazole at 7.5 mg/kg body weight by mouth in November 1992; the other group remained as the untreated control. At monthly intervals from November 1992 to April 1993, each animal was weighed and the number of eggs/g of faeces (epg) was determined. The infective larvae (L3) were examined following culture of pooled samples from each group of animals. In April 1993, 6 animals (3 treated and 3 controls) from the herds under study were necropsied. The difference in the weight gains (4.6 kg) of the two groups was highly significant (p < 0.0001). The difference in the weight gains and the epg between the treated and control groups was influenced by the age of the animals. Of the treated animals, one contained no nematodes, one contained only 25 Oesophagostomum radiatum, and the third contained 25 Cooperia L4. The three untreated animals were all infected. It was concluded that the treatment in early dry season, with an anthelmintic effective against both adults and larvae, led to a significant reduction in egg counts, to elimination of adults and hypobiotic larvae and, consequently, to an increase in the body weight gain by the treated animals.

Long-term parasitological consequences and production responses in ewes and lambs after a single post-parturient anthelmintic treatment of ewes

Abstract A study was made of the long-term parasitological and production consequences of a post-parturient (docking) anthelmintic treatment for spring-lambing ewes given about 3 weeks after the mean lambing date. During summer, treated and untreated ewes continued to graze their respective pastures which were subsequently grazed by lambs during the autumn and winter. Faecal egg counts of the treated ewes were significantly lower than those of untreated controls throughout spring and summer. In the lambs, there was no significant difference in the mean egg counts at weaning. On all sampling occasions in autumn and winter, mean faecal egg counts of lambs on pasture previously grazed by treated ewes in summer were lower than those of lambs on pasture grazed by untreated ewes. The difference was significant on 50% of the sampling dates. Maximum larval availability on pasture grazed by the treated ewes was respectively 78, 58, and 35% lower in summer, autumn, and winter than on pasture grazed by the untreated...

Plasma pepsinogen levels in some experimental infections of Ostertagia ostertagi in cattle.

Two groups of calves were infected with larvae of Ostertagia ostertagi to establish large numbers of adults and arrested larvae. In one group symptoms of ostertagiasis were seen and there was a loss of three months growth; in the other, in which adult worms were removed by a single anthelmintic treatment, there was only a transient reduction in live-weight gain. Plasma pepsinogen levels were however the same in the two groups and followed the same course. Even after 25 weeks, when calves had been growing normally for up to three months, plasma pepsinogen values were still around 5 iu per litre, well above the level generally regarded as diagnostic of ostertagiasis. The relevance of these findings to the use of the test in the diagnosis of ostertagiasis is discussed. The literature is reviewed.

AN ECONOMIC ANALYSIS OF TWO SCHEMES FOR THE ANTHELMINTIC CONTROL OF HELMINTHIASIS IN WEANED LAMBS

The economic benefit obtained from 2 schemes for the strategic control of helminthiasis in weaned lambs has been assessed in the Western District of Victoria. The results were compared with those from sheep in control groups which were given a single anthelmintic treatment during an outbreak of helminthosis. Mortality in sheep receiving the critical treatment scheme of 2 appropriately timed anthelmintic treatments was 12%, compared with 22% in the group receiving the traditional series of summer and autumn treatments, and 26% in the control group. As a result of this difference in mortality rate, the critical treatment scheme was the most profitable control strategy at 1970-71 prices, yielding a net benefit of $70 per 100 sheep in comparison with the control group which received no strategic treatment. This is 538% return on funds invested in anthelmintic treatment. The benefit from this scheme was not unduly affected by variation in wool or sheep prices, nor to possible differences in mortality rate within the expected range. The traditional treatment scheme also yielded positive net returns, but the results were adversely affected by a small change in mortality rate and therefore could not be recommended for routine use on commerical farms.

An evaluation of the parasitological and production responses to a single pre-lambing anthelmintic treatment of ewes

Abstract Three trials were conducted in successive years to evaluate the parasitological and productivity responses, in both ewes and lambs. to a single pre-lambing treatment of ewes with thiabendazole. The treatment did not significantly increase the live-weight gain of lambs from birth to weaning, or significantly reduce the faecal egg count of lambs up to weaning. In one trial there was a significant increase in the greasy fleece weight of treated ewes, and in two trials there was a significant improvement in wool growth. In one trial there was a reduction in cotting and tenderness of wools from treated ewes. Treatment did not affect style grading of fleeces in any of the three trials. The results suggest that pre-lambing anthelmintic treatment of ewes is of doubtful economic value as a routine control procedure.

The effect of a single anthelmintic treatment at varying intervals before lambing on the peri-parturient rise of faecal nematode egg counts in ewes.

The effect of a single anthelmintic treatment at varying intervals before lambing on the peri-parturient rise of faecal nematode egg counts in ewes.

The post-parturient rise in the faecal nematode egg count of ewes: some host-parasite relationships.

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