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PubMed1990

Overberg Research Projects. VII. Anthelmintic sales in the Swellendam area of the southern Cape.

In the Swellendam area, benzimidazoles held 34.5% of the market for sheep and goat nematocides in 1988, ivermectin 30.1%, levamisole 13.7%, combination products 13.5%, salicylanilides 6.8% and morantel 1.4%, while products containing benzimidazole accounted for 48.1% of sheep and goat nematocide sales. The sheep and goat nematocide and cestocide markets in the Swellendam area totalled 1,386,280 and 94,080 therapeutic doses respectively, costing R448 887,10 and R79 242,02, while the cattle anthelmintic market totalled 12,209 therapeutic doses, costing R30 520,22. A mean of 3.45 therapeutic doses of nematocide were purchased for sheep and goats during 1988 at a per capita cost of R1.12 at December 1988 prices. Furthermore, the mean per capita expenditure on anthelmintics against both the nematodes and cestodes of these animals, amounted to R1.31. Nematocides used for sheep and goats in this market segment, cost 36 cents per dose. The mean escalation of anthelmintic prices between January and December 1988 was 10%, ranging from -6 to 30%.

Animals↗
PubMed1997

[Endoparasitic fauna and incidence of species in yearling and adult horses in Upper Bavarian breeding farms with regular anthelmintic prophylaxis lasting for many years].

In this epidemiological study 127 horses from five breeding farms in Upper Bavaria were included. The horses were coproscopically examined in intervals of four weeks over a 16-month period. Since 1992 in all farms regular prophylactic treatments with anthelmintics have been carried out. In 127 horses at least five species were established, such as Parascaris equorum, Anoplocephala perfoliata, Gasterophilus intestinalis and small strongyles, whose third stage larvae were characterized by eight or twelve intestinal cells. Infections with small strongyles occurred most frequently, followed by G. intestinalis, A. perfoliata and P. equorum. Seven horses excreted eggs of P. equorum, three yearlings, and a two, four, five and seven year old animal, each. 113 of the 127 examined horses showed infections with strongyles, hence, almost all animals of the farms I-V. The evaluation of horses with strongyle infections as regards to the frequency of the coproscopically established eggs revealed a high incidence independent of age. The maximal epg-values showed no obvious age-dependent differences varying between < or = 67 and 3733. The horses excreted strongyle eggs with epg-values of > or = 333 predominantly during the summer. With an epg-value of > or = 333, independently of age the 23 horses treated with Ivomec-P as well as 20 of the 24 horses given Banminth remained coproscopically negative three to four weeks after treatment. The animals treated with Rintal or Panacur continued to excrete strongyle eggs three to four weeks following the anthelmintic application. The use of anthelmintics in horses with epg-values < 333 revealed analogous results. Infections with A. perfoliata were established in all farms, altogether in 32 horses independently of the age of the animals. Eggs of G. intestinalis have been observed only in two farms, but almost in all horses there.

Age Factors↗
PubMed2006

A dual anthelmintic treatment strategic scheme for the control of fasciolosis in dairy sheep farms.

A clinical longitudinal field trial was conducted on a dairy sheep farm in southern Italy to assess the effectiveness of a novel anthelmintic treatment strategic scheme against Fasciola hepatica. The scheme utilizes a dual anthelmintic treatment (DAT), i.e., the use of either one of two different anthelmintics on the flock, albendazole sulphoxide (SO) at 1-month intervals and rafoxanide at 2-month intervals, administered to the lactating and non-lactating animals, respectively. The DAT strategic scheme lasted 3 years. In Year 1 and Year 2, shotgun monthly DATs for 5 consecutive months (July, August, September, October, and November) were performed on the flock. In Year 3 there was only one monthly DAT, in July. Overall, the DAT scheme reduced the prevalence of F. hepatica infection by 94.4% (from an average prevalence of 71.1% during the pre-DAT period to an average prevalence of 4.0% during Year 3), and the eggs/gram of faeces (EPG) from 29.3 to 1.3. In conclusion, the DAT strategic scheme reported in the present study successfully reduced both the prevalence and EPGs of F. hepatica to a level at which there were no longer any clinical symptoms of the disease. This scheme did not influence the albendazole SO efficacy against GI nematodes and might be used for the treatment of fasciolosis in dairy sheep farms.

Albendazole↗
PubMed2001

Are Teladorsagia circumcincta (Nematoda) morphs equally able to survive under anthelmintic treatment in sheep on pastures?

The nematode Teladorsagia circumcincta is a polymorphic species, morphs T. c. trifurcata and T. c. circumcincta being the most frequent. Among other traits, T. c. trifurcata has lower infectivity than T. c. circumcincta. Anthelmintic treatments that regularly remove populations should favour the more infective T. c. circumcincta. The present investigation was intended to test the respective capabilities of the two morphs to withstand anthelmintic pressure. The nematode strain was susceptible to imidazothiazole and partly resistant to benzimidazole at the onset of experiment. A 2-year grazing season study was undertaken under four levels of anthelmintic pressure [from untreated controls to frequently treated with a poorly efficient benzimidazole (fenbendazole) or an efficient imidazothiazole (levamisole)]. The strain previously maintained in laboratory conditions regained its natural, original proportion of T. c. trifurcata during the first grazing season. The two morphs were equally resistant to fenbendazole; and the proportion of resistant nematodes did not vary between the two morphs. During the second grazing season, the treatments indirectly depleted the proportions of T. c. trifurcata, probably due to the poor infectivity of this morph.

Animals↗
PubMed1989

Selection for thiabendazole resistance in Ostertagia spp. by low efficiency anthelmintic treatment.

Thiabendazole (TBZ) treatment of grazing weaners infected with a predominantly susceptible strain of Ostertagia reduced worm burdens by 90%. The surviving sub population had a level of resistance four times greater than the original population when compared to similarly infected, but untreated, weaners. TBZ treated and control weaners were relocated to worm-free pasture so that the contamination on the plots grazed by TBZ treated weaners was from the survivors of the drench. The anthelmintic treated groups were subsequently managed under a two summer drench programme while control groups remained so throughout the experiment. Monitoring both parasite population size and the degree of resistance over the following 2 years indicated that after three anthelmintic treatments, resistance developed to a level where TBZ was ineffective. When compared to control groups, a mean reduction in population size of around 80% was maintained in the TBZ treated groups for 1 year. This difference, however, disappeared by the second year. A similar study over 1 year with a moderately TBZ resistant strain of Ostertagia indicated that TBZ treatment produced no significant reduction in population size but more than doubled the level of resistance. The study indicated the critical need for highly efficient anthelmintic treatment, particularly in situations where, through ecology or management, post treatment contamination is likely to contribute substantially to future generations of worms.

Animals↗
PubMed1988

Controlled release devices for the delivery of anthelmintics in cattle.

Control of cattle helminths is not so much a problem of drug choice, but of drug delivery and livestock management. Several effective anthelmintics are available for domestic livestock, but their efficiency in limiting infection and disease attributed to important parasites such as Ostertagia and Haemonchus has been mainly due to good management practice and strategically timed treatment based on detailed epizootiological studies of parasite transmission. In most situations, treated animals remain fully susceptible to reinfection if continually grazed on contaminated pastures, and this is the rationale behind techniques for continuous or multiple treatment with anthelmintics. In response to these treatment requirements, the animal health industry has developed controlled release devices, or boluses, that can be implanted orally into the rumen (Fig. 1) to release anthelmintics over an extended period - either in a delayed or pulsed fashion. In this article, Gary Zimmerman and Eric Hoberg discuss same of the most promising of such devices.

Journal Article↗
PubMed1995

A comparison of early and mid grazing season suppressive anthelmintic treatments for first year grazing calves and their effects on natural and experimental infection during the second year.

A comparison was made of the efficacy and parasitological sequelae over 2 years, of continuous and intermittent periods of anthelmintic suppression applied both early and in the middle of the first grazing season of calves. Five groups of 15 calves grazing separate paddocks within the same field were allotted to one of the following treatment regimes during their first year at grass: Group 1, untreated controls; Group 2, treated with ivermectin injections at 3, 8 and 13 weeks after turnout; Group 3, treated with ivermectin injections at 10, 15 and 20 weeks after turnout; Group 4, treated with a morantel slow release intraruminal bolus at turnout; Group 5, treated with a morantel slow release bolus at 10 weeks after turnout. Five animals from each group were slaughtered at the end of both grazing seasons. Two months after the end of the second season the remaining five calves were challenged with an experimental infection of 250,000 third-stage larvae (L3) of both Ostertagia ostertagi and Cooperia oncophora. All treatment regimes protected the respective calves from parasitic gastroenteritis. Over the 2 year observation period Groups 2 and 4 showed significantly better weight gain than other groups, and at the end of the first season, they were found to harbour significantly fewer O. ostertagi in the early fourth stage of development. During Year 1, Groups 2 and 3 excreted much lower percentages of Ostertagia spp. eggs than other groups. In Year 2, Group 2 excreted a higher percentage of Ostertagia spp. eggs although the total egg output was approximately half that of Group 1 during the same period. The results showed that the effects of anthelmintic suppression on egg output of different nematode species was affected by the activity of the anthelmintic used.

Animal Feed↗
PubMed2005

The larval feeding inhibition assay for the diagnosis of nematode anthelmintic resistance.

A larval feeding assay for detection of nematode anthelmintic resistance to macrocyclic lactones and imidazothiazoles is described. The estimated concentration of anthelmintic required to inhibit larval feeding in 50% of L1's (IC50) that were resistant to either macrocyclic lactones or imidazothiazoles were significantly higher (P < or = 0.05) than those of susceptible isolates. Some variations in IC50 values were observed during the patent period of infection in all strains, although the pattern of the IC50 followed the same course. IC50 values varied in larvae developing from eggs shed throughout the patent period, with low values in the earliest larvae followed by higher values as the infection progressed, before decreasing at 70-90 days post-infection, although the low values of the first part of the patent period were not reached. However, the IC50 differences between all resistant and susceptible strains were significant throughout the whole patent period for ivermectin and levamisole. These results suggest that this technique may provide an alternative in vitro to detect anthelmintic resistance.

Animals↗
PubMedDate not supplied

Controlling internal parasites in grazing ruminants without recourse to anthelmintics: approaches, experiences and prospects.

Interest in ways of raising stock without using anthelmintics has been stimulated by the desire for intensive grazing systems to adopt more sustainable methods of internal parasite control and by potential premiums for "organic" produce. This requires grazing management systems which are practicable and achieve levels of parasite control sufficient to meet realistic production objectives. This paper will summarise 3 years experience of lamb and cattle production without a recourse to anthelmintics on 2 production systems: a mixed cropping, lamb finishing, and cattle rearing unit and an all grass, mixed-stock, hill country unit in which all non-replacement lambs are sold at weaning. On both units parasite control was almost entirely dependent on integrated grazing management of sheep and cattle and strict systems of grazing management had to be rigidly applied. Acceptable productivity could be more readily achieved in sheep than cattle. Rams selected for resistance to nematodes were also used in both sheep flocks. Their influence on lamb production was equivocal. There is a need for more information on factors influencing parasite epidemiology and for consideration of strategies other than alternate grazing. The impact of pasture species on parasite epidemiology needs to be clarified. Current research indicates substantial differences between grasses in terms of parasite burdens acquired and production losses suffered by lambs grazing them. Grazing management may need to vary with pasture species. Also, specialty forage crops, particularly those containing condensed tannins (i.e. Hedysarum coronarium, Lotus pedunculatus and Lotus corniculatus) hold special promise as a means of countering parasite-induced production losses and dagginess. Using biological control of free-living larval stages and vaccination, may in the long term, also prove useful. Developing effective and acceptable systems for raising stock without using anthelmintics presents a considerable challenge, to parasitologists, as well as to plant breeders, agronomists, and farming systems researchers.

Animal Husbandry↗
PubMed1995

Trichostrongylus colubriformis infection in rabbits: persistence of the distal adaptive response to parasitism after anthelmintic treatment.

Mucosal changes associated with anthelmintic treatment in Trichostrongylus colubriformis-infected rabbits were assessed along the entire length of the small intestine. The following groups, each of five rabbits, were compared: infected (group I); infected and treated on day 21 with fenbendazole (group IT); uninfected but given fenbendazole on day 21 (group C, controls). All animals were killed on day 28. In the proximal part of the small intestine of group I rabbits, the worms were associated with shortening of the villi and a significant depletion in alkaline phosphatase activity, which differed significantly from the findings in groups C and IT. In the same region, no difference was found between groups C and IT. In the distal small intestine, hypertrophy of villi and crypts (an adaptive response to the infection), coupled with an increase in enzymic activity, were present in both groups I and IT, in contrast to group C. These results suggest that a complete mucosal restoration occurred within 7 days of anthelmintic treatment in the parasitized part of the intestine. In contrast, the adaptive response observed beyond the main site of parasitism was not abolished by treatment. The functional significance of these findings is discussed in relation to the compensatory growth commonly observed after anthelmintic treatment in ruminants.

Adaptation, Physiological↗
PubMed1997

How long before resistance makes it impossible to control some field strains of Haemonchus contortus in South Africa with any of the modern anthelmintics?

This paper describes an exceptional spectrum of multiple anthelmintic resistance in two strains of Haemonchus contortus in South Africa, one from Howick in KwaZulu-Natal, and the other from Badplaas, in Mpumalanga. Apparently for the first time, a helminth strain is described with resistance to compounds from all five of the modern anthelmintic groups used for nematode control in sheep; also, two strains of H. contortus show resistance to the two substituted phenols, dinitrophenol and nitroxynil. Only closantel at 5 mg kg-1 of nine compounds tested appears to have undiminished efficacy against the Howick strain, but even in the case of closantel, the residual activity and minimal effective level need to be tested before it can be concluded that its efficiency is unaffected. The exceptional resistance of the Howick strain is demonstrated by the fact that sequential daily drenching of sheep infected with the strain, with levamisole at 18 mg kg-1, oxfendazole at 20 mg kg-1, levamisole at 20 mg kg-1 and a mixture of fenbendazole at 10 mg kg-1 plus trichlorfon at 132 mg kg-1 on the fourth day, failed to clear sheep of the infection. There are strong indications that side-resistance occurs between dinitrophenol and nitroxynil, on the one hand, and the salicylanilides, on the other, and it is suggested that, before long, strains of H. contortus will be found with high levels of resistance to all the currently available anthelmintics.

Animals↗
PubMed1983

A survey of anthelmintic usage for sheep: a time for change.

A sample survey of anthelmintic usage and farmers; drenching policies was conducted on 614 sheep farms, in the North and South Islands, selected from among those carrying 1500 or more breeding ewes. The survey was based on information for the 1978179 and 1979/80 farming years recorded on questionnaires completed during personal interviews between Livestock Officers and the farmers concerned. Results show that there were no significant between-Island differences in mean drenching frequencies for any age class of sheep. In 1979/80, the overall New Zealand drenching frequencies were 6.3 for lambs, 1.8 for 1-2-year-olds and 1.2 for sheep older than 2 years. Of the farmers surveyed, 20% did not drench 1-2-year-old sheep and 29% did not drench sheep older than 2 years. There were also no between-Island differences in timing of drenches and alternation of drench brands. Sixty-nine per cent of the farmers followed a pre-determined drenching programme whereas 27% stated that they drenched if and when necessary. For lambs, some drenching was carried out in all months of the year hut fewer farmers drenched during the mid-winter to mid-spring period (July-October). Older stock were drenched in all months also but there was a general acceptance by farmers of the practices of pre-tupping and pre or post-lambing drenching. At the time of the survey, 48% of the farmers were using three or more brands of drench with a maximum of nine. Analysis of data relating to brands of drench used shows that whereas 39% of the farmers w,ere alternating drench families [i.e. benzimidazoles (BZ) c.f. non-benzimidazoles (NBZ)] within a single farming year, only 3% were practising a strict alternation of drench families between years. General comments by the farmers surveyed indicate a disturbing degree of misunderstanding and misconception regarding the properties and limitations of current anthelmintics. The survey also revealed a lack of appreciation of the rationale of prophylactic (;preventive;) parasite control. These aspects are discussed in relation to currently recommended control strategies and the problem of anthelmintic resistance.

Journal Article↗
PubMed1983

A survey of nematode control measures used by milking goat farmers and of anthelmintic resistance on their farms.

Forty-seven milking goat herds, located throughout New Zealand, were surveyed for anthelmintic usage and for gastrointestinal nematodes resistant to anthelmintics. Most farmers (62%) followed a predetermined drenching programme and usually (68%) had a policy of alternating between drench families. Alternation was generally within the farming year. Kids were on average being drenched 12.5 times during their first year (range 2-34). Does aged greater than one year were all being drenched at the same frequency (average 13.4, range 2-34) irrespective of age. On each of the 47 farms, a group of goats was treated with a benzimidazole (BZ) drench (oxfendazole, OFZ, at 4.5 mg/kg on 36 farms and thiabendazole, TBZ at 66 mg/kg on 11 farms); a second group was treated with a "cell membrane depolarizing" (CMD) drench (levamisole, LEV, at 8 mg/kg on 35 farms and morantel citrate, MOR, at 10 mg/kg on 12 farms); a third group remained untreated as controls. Faecal egg counts and larval cultures were done before dosing and one week later. Faecal egg count depressions of <80% were taken as being suggestive of anthelmintic resistance. On this basis resistance was found on 79% of farms surveyed. Resistance to BZs alone occurred on 36% of farms, resistance to CMDs alone on 4% and resistance to both on 38% of farms. On 23% of farms one or other of the drenches was without any apparent effect and on one farm both of the drenches tested failed to reduce the egg counts. Post-drenching larval cultures showed Trichostrongylus, Haemonchus and Ostertagia to be the most prevalent genera remaining after drenching with BZ on 14,11, and 8 farms, respectively. After drenching with LEV Ostertagia was the dominant species on 10 farms, Trichostrongylus on 2 and on one farm the two genera were equally common. Following treatment with MOR Trichostrongylus was the dominant species on 3 farms, Haemonchus on 2 and on one farm Trichostrongylus and Ostertagia were equally common. There was a positive association between drenching frequency and the presence of resistance on farms. Possible interpretations of this association are discussed.

Journal Article↗
PubMed1990

Evidence for multiple anthelmintic resistance in two nematode parasite genera on a Saanen goat dairy.

Multiple resistance was demonstrated within the experimental milking goat herd at the Ruakura Agricultural Centre. The development of this resistance was probably exacerbated by the atypical animal management and parasite control programmes under which the dairy was managed. Resistance by Teladorsagia (Ostertagia) spp. to members of the three broad-spectrum families of anthelmintic is reported for the first time. Worm counts in a controlled slaughter trial demonstrated multiple anthelmintic resistance in a mixed population of Teladorsagia (T. circumcincta and T. trifurcata) and Trichostrongylus spp. The efficacies of oxfendazole, morantel citrate and ivermectin in reducing the Teladorsagia population were 43.8%, 75.6% and 93.1%, respectively. Ivermectin removed more than 99% of the small intestinal Trichostrongylus spp. but oxfendazole and morantel were less effective, removing 37.9% and 87.7%, respectively. Only treatment with ivermectin totally eliminated faecal nematode egg counts 8 days after treatment. The lack of agreement between faecal nematode egg depressions and worm counts in lambs given ivermectin suggests that the drug may have affected the fecundity of the surviving nematode population or the assay lacked the sensitivity required. These data suggest that the sole use of faecal egg depression would be inappropriate for accurate assessment of anthelmintic effectiveness.

Journal Article↗
PubMed1994

The occurrence of anthelmintic-resistant sheep nematodes in the southern North Island of New Zealand.

An analysis of veterinary diagnostic cases submitted to the Batchelar Animal Health Laboratory for faecal egg count reduction testing in sheep between 1986 and 1992 showed that 63% of them originated from properties carrying anthelmintic-resistant worms. Most of these cases involved resistance to a single drench type only, with the benzimidazoles being implicated most frequently. Overall, the figures suggested a frequency of occurrence of resistance to benzimidazole anthelmintics of 74%, to levamisole-type anthelmintics of 23% and to benzimidazo-lelevamisole combinations of 30%. No cases of resistance to milbemycin/avermectin-type drenches were recorded.

Journal Article↗
PubMed1995

The identity of nematode genera involved in cases of ovine anthelmintic resistance in the southern North Island of New Zealand.

Larval cultures and faecal egg count reductions were used to determine the identities and frequencies of occurrence of nematode genera involved in cases of ovine anthelmintic resistance submitted to the Batchelar Animal Health Laboratory between 1992 and 1994. Based on an examination of 102 cases, it was found that, while there were some differences relating to the method of assessment, the genera most frequently involved were Trichostrongylus, Ostertagia and Nematodirus. Also implicated, although less commonly, were infections of Oesophagostomum/Chabertia, Haemonchus and Cooperia. The majority of cases involved resistance in two or more genera, with resistance in a single nematode genus occurring in 45% of cases. Most such monogeneric resistances comprised infections of Trichostrongylus (52%), Ostertagia (17%) or Nematodirus (11%). Anthelmintic resistance involving Haemonchus alone was found in only three cases. These results suggest that the potential role of narrow-spectrum drenches in the management and control of anthelmintic-resistant worms in New Zealand sheep is likely to be strictly limited.

Journal Article↗
PubMed1998

The effects of age, weaning, drench volume and yarding on ruminoreticulum bypass in sheep, with reference to the anthelmintic efficacy of benzimidazole drenches.

AIMS: To determine the incidence of ruminoreticulum bypass in lambs before and after weaning, following drenching with anthelmintic-equivalent volumes of fluid; to investigate the influence of withholding feed for 24 hours before drenching on the incidence of ruminoreticulum bypass; and to investigate the hypothesis that ruminoreticulum bypass occurs more frequently following drenching with large than with low volumes. The relationship between these factors and the efficacy of benzimidazole anthelmintic drenches has been widely promoted in New Zealand and Australia. METHODS: Video-taped fluoroscopy, using barium sulphate suspension with a specific gravity of 1.38 as a contrast medium, was used to study closure of the reticular groove and ruminoreticulum bypass in sheep. RESULTS: When lambs were drenched with 3 ml of barium sulphate suspension/10 kg liveweight soon after removal from pasture, ruminoreticulum bypass only occurred before weaning and during the first 8 weeks after weaning. However, when a low volume drench (1 ml/10 kg) was used in lambs soon after removal from pasture during the same period, ruminoreticulum bypass was not observed. When recently weaned lambs were yarded for 24 hours before drenching with barium sulphate suspension, substantial (> or = 20%) ruminoreticulum bypass occurred in 25-58% of the animals. When 8-9 month-old hoggets were yarded for 24 hours before drenching, substantial ruminoreticulum bypass occurred in 35% of the animals. Ruminoreticulum bypass was not observed in the same group of hoggets when drenched soon after removal from pasture, in a reversed crossover experiment. This effect of withholding feed for 24 hours on ruminoreticulum bypass was significant (p < 0.0001). In hoggets which had been yarded for 24 hours before drenching with barium sulphate suspension, the incidence of ruminoreticulum bypass was significantly lower (p = 0.0026) following the use of a low volume (1 ml/10 kg) when compared to high volume (3 ml/ 10 kg) of drench. Thus, the effect of withholding feed for 24 hours on ruminoreticulum bypass was largely overcome when the low volume drench was used. CONCLUSIONS: These results support the use of low volume formulations of benzimidazole drenches for New Zealand pasture-fed lambs less than 6 months old. The results indicate that, in order to obtain the optimum efficacy of benzimidazole anthelmintics in New Zealand pasture-fed sheep, which have been yarded for 24 hours, low volume drench formulations should be used.

Journal Article↗
PubMed2000

Ivermectin-resistant Ostertagia circumcincta from sheep in the lower North Island and their susceptibility to other macrocyclic lactone anthelmintics.

AIM: To confirm the ivermectin resistance status of a strain of Ostertagia circumcincta which was isolated from a sheep farm in the lower North Island of New Zealand and to assess the susceptibility of this strain to other macrocycliclactone anthelmintics. METHODS: Twenty-five lambs housed indoors were each infected with 12,000 L3 larvae of the above parasite strain. Approximately 3 weeks after infection the lambs were allocated to 1 of 4 treatment groups (3 groups of 6, and 1 group of 7 lambs), one of which remained untreated while the others were drenched orally with ivermectin, moxidectin or abamectin at 0.2 mg/kg liveweight. Faecal egg counts (FECs) before and after treatment, and post-mortem worm burdens 10 days after treatment were examined to assess efficacies of each anthelmintic. RESULTS: Treatment with ivermectin reduced the mean FEC by only 18% and the mean worm burden by only 42%, whereas moxidectin and abamectin reduced FECs by 92% and worm burdens by 95%. CONCLUSION: These results, together with a similar case described recently from the South Island , confirm the emergence of ivermectin resistance in nematode parasites of sheep in New Zealand. The superior efficacy of moxidectin and abamectin in this case indicates that, following the emergence of resistance to ivermectin, some short-term practical use may still be made of these other anthelmintics. However, their continued use will undoubtedly result in increased levels of resistance and eventual therapeutic failure of these products also.

Journal Article↗