Parasite Control Programs Research Articles

An update on cyathostomins: Anthelmintic resistance and diagnostic tools

Cyathostomins represent a potential cause of equine morbidity and have become the main focus of endoparasite control in managed horses. All grazing horses are at risk of infection with cyathostomins; therefore, the application of appropriate management measures is essential. Anthelmintics currently comprise the main method of control for equine nematodes and the ready availability of these products in some countries has resulted in their use becoming dissociated from veterinary involvement. This is concerning given the levels of anthelmintic resistance that have been recorded in cyathostomin populations. It is important that veterinarians re-establish control over the implementation of parasite control programmes, a major objective of which should be the preservation of anthelmintic efficacy. This article details the principles of cyathostomin control in horses with particular reference to anthelmintic resistance, and the use and interpretation of diagnostic tests for detecting cyathostomins and identifying anthelmintic resistance.

Discovery and Development of Veterinary Antiparasitic Drugs: Past, Present and Future

Despite investment in programs to manage the development of resistance to existing agents, this continues to drive the need for discovery of novel antiparasitic agents for veterinary medicine. Historically, antiparasitic drug discovery was driven by empirical screening, but technological advances have lead to an increased focus on mechanism-based approaches to drug discovery and this is projected to increase as our capabilities advance to improve both the throughput of assays and the quality of data generated. Investment in the development of combination products with novel agents is increasing and, despite regulatory hurdles in some regions, efforts to globally harmonize regulations will aid in delivering safe, efficacious drugs to help in resistance management and integrated parasite control programs.

Ticks and tick-borne diseases of pets in the UK: risks to travellers

The ticks most commonly found on dogs and cats in the UK are Ixodes ricinus, Ixodes hexagonus and Ixodes canisuga with other Ixodes species rarely seen. Ixodes ricinus is known to transmit some diseases in the UK. Dermacentorreticulatus and Haemaphysalis punctata also are indigenous and found occasionally on pets in some areas. Rhipicephalus sanguineus has been identified after importation on pets from continental Europe and elsewhere, despite the requirements for treatment for ticks under the pet travel scheme. The increasing movement of pets between the UK and countries with a high incidence of tick-borne disease will require the use of strong parasite control programmes to prevent the spread and import of tick-borne disease. Tick-borne diseases of pets are briefly described.

Epidemiological Intelligence for Grazing Management in Strategic Control of Parasitic Gastroenteritis in Small Ruminants in India – A Review

Because of the environmental and consumer concerns arising out of exponential growth in human population the world over, a term Sustainable Development has become an integral international concept, which is defined as one which meets the needs of the present without compromising the ability of future generations to meet their own needs. Ruminant animals appear sustainable as they do not compete with man for food, play a crucial role in the conversion of low quality plant material and crop residues to high quality human food as well as return valuable plant nutrients to the soil. Parasite control in ruminant livestock is a first-order input in any sustainable animal production system. As sustainable development is a compromise between reducing environmental degradation and positive economic growth, sustainable parasite control should aim towards less intensive, lower input, lesser risk of parasite induced losses with greater opportunities for integration of all available control resources. The compound scenario of rising anthelmintic resistance, food and environmental security and apathy of the pharmaceutical industry to go for the invention of new anthelmintic compounds has triggered the need for optimising the use of available anthelmintics with integration of all other alternative means for sustainable worm control. The “Sustainable Control of Parasitic Gastroenteritis in Ruminants” is thus encompasses a multidisciplinary approach involving integration of chemotherapy, grazing management, biological control, worm vaccines, genetic resistance of hosts, mathematical model based decision support and other strategies, if any. There is no single requirement more crucial to the rational and sustainable control of helminth parasites in grazing animals than a comprehensive knowledge of the epidemiology of the parasite as it interacts with the host in a specific climatic, management and production environment. In its absence, anthelmintic treatment is either given suppressively which provokes resistance or therapeutically which risks clinical disease and production losses. Sustainable parasite-control programmes require knowledge of seasonal larval availability, origin of larvae contributing to any peaks and climatic requirements for worm egg hatching, larval development and survival. Control measures based on this knowledge include strategic anthelmintic treatments and various forms of grazing management. While these measures can reduce the frequency of anthelmintic treatment required, their effect on selection for drench resistance is more problematical, unless they can be combined with other forms of control to reduce our current dependence on anthelmintics. The present article deals with sustainable nematode parasite control in small ruminants in India through grazing management using epidemiological intelligence.

Shortened strongyle-type egg reappearance periods in naturally infected horses treated with moxidectin and failure of a larvicidal dose of fenbendazole to reduce fecal egg counts

Deworming horses with anthelmintics that have activity against encysted small strongyle larvae (L 3 and L 4) is a common practice in parasite control programs. The two drugs currently available for this use are moxidectin (MOX) administered in a single dose of 0.4 mg/kg and fenbendazole (FBZ) given at the larvicidal dose (10 mg/kg for 5 days). Here, we report the efficacy of MOX and the larvicidal dose of FBZ for reducing counts of strongyle-type eggs per gram of feces in naturally infected horses. Fecal egg counts (FECs) of 15 yearlings were observed following deworming. On day 0, 6 of the 15 yearlings were administered a larvicidal dose of FBZ; 14 days later, all 15 yearlings received MOX at a single dose of 0.4 mg/kg. Feces were collected on day 0 for pre-treatment egg counts. Feces were collected at weekly intervals thereafter during FEC observation periods. FECs of FBZ-treated horses were compared at day 0 and 14 days post-treatment. The difference in means pre- and post-treatment with FBZ was not statistically significant ( p = 0.65). On days 0 and 42 of the MOX treatment observation period the mean FEC of the yearlings that had not received the FBZ treatment did not differ significantly from that of the FBZ-treated yearlings. MOX was effective in reducing fecal egg counts to 0 EPG for 21 days. At day 35 all but 2 of the yearlings had some eggs present (range = 4–361 EPG) and at day 42 all but 1 yearling had eggs present (range = 3–432 EPG). At day 42 the group mean FEC reduction had fallen from 100% to 67%. Results of this study do not support the use of the larvicidal dose of FBZ for small strongyle control. Larger field studies will be needed to investigate whether egg reappearance periods are shortening for MOX-treated horses.

Efficacy of anthelminthic control programs against naturalMuellerius capillarisinfection in sheep in the north-west of Spain. Effect on blood gases and pH in venous blood samples

The field efficacy of a single dose treatment against natural M. capillaris infection using different anthelmintic drugs, extensively employed in ovine parasite control programs in Galicia (N.W. Spain), and the effect of protostrongylid infection on ovine respiratory functions, were evaluated. Five groups (n = 5) of ewes were used in this study; animals were treated with injectable ivermectin 10.2 mg/kg), levamisole (7.5 mg/kg) and albendazole (5 mg/kg) and monitored at 0, 7, 21, 42 and 63 days posttreatment (d.p.t.) by enumeration of the lungworm larvae per gram of faeces (l.p.g.) and determination of gas tension and pH in venous blood using an i-Stat portable clinical analyzer. No statistical difference was found either in larval elimination between untreated and treated groups or in the reduction in larval counts in all of the treated groups. A significant increase in partial oxygen tension (pO2) and saturation (sO2) between day 0 and 7 p.t. was observed in all treated animals. These values decreased significantly at day 21 to previous levels. There were no statistical differences in blood gases between uninfected and treated groups. We can conclude that under Galician field conditions, parasitic control programs are not totally effective against M. capillaris infection.

Eradication of Taenia solium cysticercosis: A role for vaccination of pigs

Taenia solium is the causative agent of neurocysticercosis, a disease responsible for substantial human morbidity and mortality. It is a zoonotic parasite, involving pigs as intermediate hosts. The parasite’s full life cycle is restricted to poor people in developing countries. Attempts to date to control transmission of the parasite have been relatively poorly effective and not sustainable. Over the past decade research has been undertaken to develop practical vaccines for use in pigs to prevent transmission of T. solium. The most effective of these vaccines in controlled experimental trials has been the TSOL18 vaccine. More recently, TSOL18 has been proven to be highly effective against naturally acquired infection with T. solium in pigs. Application of TSOL18 together with a single treatment of pigs with oxfendazole achieved the complete elimination of transmission of the parasite by pigs involved in the field trial. This strategy may provide a relatively low cost and sustainable control tool which could assist towards the goal of achieving eradication of the parasite. An assessment is made of the potential value of various control measures that are available for T. solium, and two options are suggested as potential parasite control programs.

Fecal egg counts after anthelmintic administration to aged horses and horses with pituitary pars intermedia dysfunction

To determine effects of pituitary pars intermedia dysfunction (Cushing's disease) and age on fecal egg count and time to egg reappearance after anthelmintic treatment in horses residing in similar environments. Cross-sectional study. 29 healthy horses (4 to 35 years old) and 13 horses with PPID (13 to 33 years old). Fecal egg counts were performed by use of a modified Wisconsin flotation method at 2-week intervals before and after ivermectin treatment. Horses with PPID had higher fecal egg counts before and 8, 10, and 12 weeks after ivermectin treatment, compared with counts for site-matched healthy horses. There was no difference in the period for < 90% reduction in fecal egg counts between the 2 groups. Age did not affect fecal egg counts at any time point. For similar environmental conditions, horses with PPID were more likely to have higher fecal egg counts than were healthy horses. Therefore, horses with PPID may need to have a more aggressive parasite prevention program than do healthy horses. Age did not affect fecal egg counts or time to egg reappearance after anthelmintic treatment, which suggested age alone does not likely require special consideration when designing a parasite control program for adult horses.

Sustainable use of anthelmintics in an Integrated Parasite Management Program for sheep nematodes

Anthelmintic resistance is a major problem affecting sheep nematode control; however, chemical treatments will always be a likely routine part of any parasite control program. The present paper, with the aim of minimising the selection pressure for worsening anthelmintic resistance, outlines important practical and strategic aspects of planning the anthelmintic component of an integrated approach to sheep worm management.

Endoparasite control management on horse farms – lessons from worm prevalence and questionnaire data

Increasing prevalence of anthelmintic resistance in equine nematodes calls for a reexamination of current parasite control programmes to identify factors influencing control efficacy and development of resistance. To investigate if associations occur between prevalence of parasitic nematodes and management practices. German horse farms (n = 76) were investigated in 2003 and 2004. Information on farm and pasture management with respect to endoparasite control measures obtained using a questionnaire survey. Faecal examinations were performed in parallel. Horses (n = 2000) were examined by faecal nematode egg counts, grouped into foals, yearlings and mature individuals for statistical analyses. Farms were categorised into 3 types, riding, stud farms and small holdings. Count regression models were used to analyse strongyle faecal egg count data. Following dichotomisation of faecal egg count (FEC) data, prevalence of strongyle and Parascaris equorum infections were assessed by logistic regression models as a function from various management factors. Yearlings on stud farms showed a 2-fold higher risk of being positive for strongyle FEC, higher (i.e. > or =3 per year) anthelmintic drug treatment frequencies were associated with reduced strongyle infection rates only in mature individuals but not in foals or yearlings, foals on farms fertilising pastures with horse manure had a significantly higher risk of being P. equorum FEC positive and yearlings on stud farms were more often showing incomplete FECR following anthelmintic treatment compared to yearlings on other farm types. The mean yearly treatment frequencies per age group were: foals 4.52, yearlings 3.26 and mature horses 2.72 times, respectively. To delay the development of anthelmintic, resistance management should include additional nonchemotherapeutic parasite control strategies, FEC-monitoring, controlled quarantine treatment of new arrivals and control of efficacy by the faecal egg count reduction test on a regular basis.

Parasite control in the age of drug resistance and changing agricultural practices

The benefits of using antiparasitic drugs in farm animals are unquestionable. However, despite anthelmintic use as the predominant control strategy, extreme parasite infection cases are appearing in sheep and goat production; these impact productivity and have show mortality rates reaching pre-drug use levels. This was a predictable situation resulting from the loss of efficacy by all available products, particularly when some products were used as the sole intervention. The concepts of agroecology and holistic agriculture, which advocate the use of integrated management strategies, such as target selected treatment, herbal medicine, and the application of other parasite control alternatives, are not completely new, but are undergoing a resurgence because of their more sustainable appeal. The objective of this review article is to examine the problem of parasite control in the face of parasite drug resistance and to outline some strategies that may be used in parasite control programmes. Before they are accepted and recommended by the WAAVP, agroecological methods such as those listed above and described in detail herein should be validated based on scientific evidence of their efficacy for parasite control and should be tested for both host and environmental safety.

Frequency of treatment and production performance using the FAMACHA method compared with preventive control in ewes

The rapid escalation of anthelmintic resistance in parasites suggests the adoption of different strategies for parasite control in small ruminants instead of relying only on the use of chemicals. The integrated system of parasite control (SICOPA) program uses the FAMACHA method, which is used to separately identify sheep that are resistant/resilient or susceptible to Haemonchus contortus, or together with other management practices, such as pasture rotation or the monitoring of drug efficacy. The objective of this work was to compare two methods of parasite control in ewes. A flock of ewes (n=90) of Ile de France and Texel breeds was monitored from August 2001 to July 2003 under suppressive treatment (45-day treatment interval) and from August 2003 to July 2006 under the partial selective regimen based on FAMACHA evaluations. Fecal samples were collected for fecal egg counts (EPG) and larval identification to monitor infection during the 5-year period. After the partial selective evaluations, an average of 19% of the animals was treated each year between 2003 and 2006. The reproductive indexes of parturition (89%), birth rate (119%), lamb weight (4.1kg) and lamb mortality (5.2%) were similar under the partial selective regimen and the previous suppressive treatment period. H. contortus was the most prevalent species, and EPG values were not statistically different across periods or among treatment regimes. The results demonstrate that the FAMACHA method allowed a large number of naturally infected ewes to be raised with reduced anthelmintic treatment without a negative impact on their reproductive indexes. It is indicated, though, that this method be applied together with other available strategies. Culling was based on clinical signs and ranged from 5.5 to 20% per year. The results suggest that an important host-specific effect may have regulated the rate of infection, expressing the resistant/resilient characteristic within the flock with an important economical benefit.

Pneumonia from Angiostrongylus Vasorum Infection in a Red Panda (Ailurus Fulgens Fulgens)

A 9-year-old, male, captive red panda (Ailurus fulgens fulgens) in an urban zoo in the United Kingdom presented with respiratory distress and weight loss. The animal was euthanatized, and a postmortem examination was performed. The lungs were diffusely consolidated with extensive mineralization. Microscopically, there was extensive obliteration of normal pulmonary architecture by sheets and coalescing nodules of partially mineralized fibrous tissue and granulomatous inflammation centered on large numbers of nematode larvae and eggs. First stage nematode larvae were isolated from lung tissue and were characterized as Angiostrongylus vasorum on the basis of their morphology and sequencing of the 18S ribosomal RNA gene and the entire second internal transcribed spacer. Although A. vasorum has previously been reported in red pandas in a zoological collection in Denmark, this study is the first reported case in the United Kingdom and occurs against a background of geographical spread and increased incidence of disease in domestic and wild canids. Angiostrongylus vasorum should be considered a differential diagnosis for respiratory disease in the red panda and taken into account when planning parasite and pest control programs for zoological collections.

Genetic analysis of a relationship between macrocyclic lactone and benzimidazole anthelmintic selection on Haemonchus contortus

We have found that in a laboratory strain of the nematode parasite of ruminants, Haemonchus contortus, repeated ivermectin treatment, in vivo in sheep, selected against TTC, coding for Phe, and for TAC, coding for Tyr, at codon 200 in beta-tubulin isotype 1. This 200Tyr single nucleotide polymorphism (SNP) has been associated with benzimidazole anthelmintic resistance. In this study, we investigated the alpha-tubulin and beta-tubulin sequences of 17 different field and laboratory strains/isolates of H. contortus with known treatment history and status for susceptibility or resistance to macrocyclic lactone (ML) or benzimidazole anthelmintics. DNA (genomic or cDNA) from 10 to 32 male parasites was sequenced for alpha-tubulin or beta-tubulin for each strain/isolate and the frequency of coding SNPs was compared between the different strains/isolates with known treatment history and drug resistance status. We have analyzed alpha-tubulin and beta-tubulin isotypes 1 and 2 genes from the different H. contortus strains/isolates and found that repeated ivermectin or moxidectin (both ML anthelmintics) use changes the frequency of beta-tubulin isotype 1 alleles and selects for the following SNPs: either from TTC (Phe) to TAC (Tyr) at codon 200 or codon 167, or from GCA (Ala) to GAA (Glu) at codon 198. 200Tyr and 167Tyr were associated with GTT (Val) or CTC/CTT (Leu) at codon 368, whereas 200Phe or 167Phe were associated with either ATT (Ile) or GTT (Val) at codon 368 in beta-tubulin isotype 1. The SNPs 200Tyr, 167Tyr in beta-tubulin isotype 1 have been described to confer benzimidazole resistance in nematodes and recently 198Ala has also been associated with benzimidazole resistance. Although MLs exert their antiparasitic effect through binding to ligand-gated chloride channels, benzimidazoles interact with beta-tubulin. These genetic analyses indicate that there is a correlation between exposure and/or resistance to MLs and an increase in the frequency of the beta-tubulin alleles containing codons, which are determinant for benzimidazole resistance. ML use may predispose parasitic nematodes to benzimidazole resistance. This has major implications for parasite control programs dependent on MLs/benzimidazole rotations and on the use of ML/benzimidazole combination therapy, such as for human lymphatic filariasis and nematode control in ruminant livestock.

The ecology of horse cyathostomin infective larvae (Nematoda-Cyathostominae) in tropical southeast Brazil

Experimental studies about the recovery, survival and migration to pasture of cyathostomin infective larvae (L 3) from fresh feces depositions were conducted from February 2005 to March 2007 in a tropical region of southeast Brazil. Grass and feces were collected weekly at 8 a.m., 1 and 5 p.m. and processed by the Baermann technique. Multivariate analysis (principal components method) showed the influence of time and environmental variables on the number of infective larvae recovered from the feces and pasture. In the rainy period (October–March), more infective larvae were recovered on the feces and grass apex. In contrast, in the dry period (April–September), the recovery was higher only on the grass base, as well as the L 3 survival on feces and grass. More larvae were recovered at 8 a.m., except from the grass apex, where the highest recovery was at 1 p.m. Few studies investigating the seasonal transmission of equine cyathostomin have been conducted in South American tropical climates. These results demonstrate that in tropical conditions L 3 are available on feces and pasture throughout the year. Knowledge of climatic influences on the development and survival of L 3 is crucial to designing integrated parasite control programs that provide effective protection while slowing the development of anthelmintic resistance.

Fatal gastrointestinal parasitism in goats: 31 cases (2001–2006)

To evaluate signalment, history, clinical and pathologic findings, and seasonal weather patterns in association with fatal gastrointestinal parasitism in goats. Retrospective case series. 152 goats that were > 1 day of age. Characteristics including age and counts of coccidia oocysts and trichostrongyle ova (eggs) per gram of feces (EPG) in goats that died because of gastrointestinal parasitism and goats that died because of other causes were compared. Weather data and annual incidence of caprine fatal gastrointestinal parasitism were investigated. Death was attributed to gastrointestinal parasitism in 31 of 152 (20%) goats (median age, 5 months; range, 1 month to 7 years); deaths were attributed to coccidiosis (n = 7 goats; median age, 4 months; median EPG, 2,225), trichostrongylosis (6 goats; median age, 1.25 years; median EPG, 3,700), or dual infection (18 goats; median age, 6.7 months; median EPG, 8,088 coccidia and 5,475 trichostrongyles). Sudden onset of weakness or death was a common historical finding; diarrhea was evident in 15 goats. Common postmortem findings in these goats included cachexia, tissue pallor, poorly formed feces, and mesenteric lymphadenomegaly. Wet weather in spring and summer was associated with increased annual incidence of fatal gastrointestinal parasitism in goats. Gastrointestinal parasitism is an important cause of death in goats. Clinical signs may not develop until just prior to death, and diagnosis is achieved via parasitologic evaluation of feces and necropsy. Seasonal weather patterns should be considered on an annual basis when designing parasite control programs for goats.

Parasitic infestation and nutritional status among schoolchildren in Vientiane, Lao PDR

To investigate the prevalence of intestinal parasitic infestation among school-aged children residing in Vientiane capital city; and to assess the impact of its infestation on nutrition status of those children. The school-based cross-sectional study was conducted from December 2005 to February 2006. The systemic random samplings were employed to select schools and schoolchildren. Five hundred and thirty-six schoolchildren (350 high-school children and 186 parents of elementary-school children) were completely interviewed by semistructured questionnaire and performed anthropometric measurement. The direct faecal smear was employed to analyse 299 (55.8%) stool samples. The SPSS version 12.01 and Epi Info version 6.0 were used for data analysis. The overall prevalence of parasitic infestation was 38.1%, with 18.1% of Opisthorchis viverrini and 14.7% of Ascaris lumbricoides. The prevalences of stunting and underweight were 20.2% and 20.0%, respectively. The prevalences of stunting (OR = 3.28; P < 0.01) and underweight (OR = 2.69; P < 0.05) were higher among high-school children who were infested by intestinal parasites. Approximately one-third of schoolchildren in Vientiane capital city were infested by intestinal parasites. The persistent parasitic infestation seemed to be associated with growth rate pattern among those children. School-based parasite control programme and health promotion are needed to eliminate this major public health problem in Lao People Democratic Republic.

Epidemiological Study of Non‐systemic Parasitism in Dogs in Southeast Mediterranean Spain Assessed by Coprological and Post‐mortem Examination

The prevalence and risk factors of non-systemic canine ecto- and endoparasitism and anthelminthic use in Murcia located at the centre of the Spanish Mediterranean coastal arch, was investigated by coprology and necropsy in up to 275 pet, city shelter and stray dogs in 2001-2004. Faecal parasite stages were detected in 25% of dogs. Species frequency was 6-10% for Toxocara canis, Ancylostomatidae spp., Toxascaris leonina and Isospora canis, and 0.4-1% for Trichuris vulpis, Giardia lamblia, and Dipylidium caninum. Logistic regression indicated that the risk of intestinal parasitism was highest for dogs <or=1 year old, in the middle to low weight range and kept at the city shelter. Although risk factors varied according to the species, T. canis was most common in <1 year old and Ancylostomatidae spp. was more prevalent in older dogs. This suggests that the dominant species was Uncinaria spp. and not the more zoonotically important Ancylostoma spp. This was further supported by necropsy findings; however, the degree of agreement between post-mortem and coprological examination for intestinal parasites was generally poor. Necropsy revealed 10%G. lamblia, 12%Taenia spp. 38%D. caninum infections. Fleas, ticks and lice were also found in 38%, 6% and 2% of necropsied stray dogs. These results demonstrate the need for an urgent parasite control programme at the city dog shelter and the need to improve the owner's education on zoonotic risks, the proper use of anthelminthics, and other parasite control practices.

A survey of anthelmintic use and internal parasite control in farmed deer in New Zealand

AIM: To survey parasite control programmes and anthelmintic usage over a 12-month period on deer farms in New Zealand. METHODS: A questionnaire of general farm data, policy and procedures for anthelmintic use, anthelmintic programmes for weaner and older deer, general information and understanding of parasite management practices was posted to 500 deer farmers in November 2004. RESULTS: Two hundred and twenty-seven (45.4%) replies were received, and 198 (39.6%) were suitable for analysis. Ninety-four percent of respondents used anthelmintics at least once in the 12-month period; 53% treated all classes of deer and 22% treated only weaners. Seventy-four percent based anthelmintic dose on weight of the heaviest animal, and 36% used a weigh scale. Weaner deer (n=175 farms) were treated 1–13 (mean 3.2) times in their first 12 months, at the earliest commencing in January and at the latest in November. The mean interval between treatments ranged from 41 to 46 days. Yearling and adult hinds and stags were treated at least once (range 1–7 times) on 55–64% of farms, depending on class of animal. Moxidectin was the anthelmintic most commonly used (46–58%, depending on class of animal), followed by abamectin, eprinomectin, oxfendazole, ivermectin, albendazole, levamisole and doramectin. Perceived efficacy was the most common reason for choosing a type of anthelmintic. Weight gain and body condition were the most common measures used for monitoring parasitism in weaners and older deer, respectively, and few respondents used faecal egg and/or larval counts. Coughing and/or scouring were associated with parasitism in weaners on 13–14% of farms, and deaths associated with lungworm and gastrointestinal parasites were recorded on 5% and 3% of farms, respectively. Veterinary input to diagnosis was involved in 23% of events. Production losses and/or death of yearling and/or adult deer due to parasitism were reported by 27% of respondents. When planning anthelmintic treatment programmes, 63% of respondents followed advice from veterinarians. Thirty-four percent always placed deer on clean or spelled pastures after treatment, while 32% did that often. Fifteen percent had incorporated forages and/or herbs with assumed anthelmintic properties into their parasite control programme. Forty-four percent were very confident of a return on investment when using anthelmintics for their deer. Respondents stated that their knowledge of the life cycle of the major parasites of deer was very good (8%), reasonably good (61%), poor (28%), or nil (3%). CONCLUSION: Anthelmintics are used on almost all deer farms, and practices and programmes vary considerably. Opportunities exist for veterinarians to assist deer farmer clients to improve their parasite control programmes.

Anthelmintic resistance and management of nematode parasites on beef cattle-rearing farms in the North Island of New Zealand

AIM: To provide information on current farmers’ opinions and farming practices thought to be related to anthelmintic resistance, and to test for associations between the presence of anthelmintic resistance and management practices on beef cattle- rearing farms in the North Island of New Zealand. METHODS: A study using an interview-based questionnaire about management of internal parasites was conducted on 62 beef cattle-rearing farms in the North Island of New Zealand, using case-control analyses to test for associations between management practices and the presence or absence of resistance to ivermectin or albendazole. Resistance was inferred from faecal nematode egg count (FEC) reduction (FECR) tests (FECRTs) when there was <90% reduction in FEC 7-10 days after treatment of calves <12 months of age. RESULTS: Of the 59 farmers who completed the questionnaire, most (n=40) ranked parasites highly, and at about the same level as quality and quantity of feed, as important production-limiting factors for their enterprises. In contrast, anthelmintic resistance was not perceived to be a problem on 13 farms, and its importance was rated low on 24, moderate on 15, and high on only six farms. Despite all farms having planned parasite control programmes, there was heavy reliance on clinical signs of parasitism to determine frequency of treatments. About one in three farmers with beef breeder cows routinely treated their calves at marking, one in five treated mixed-age cows, and almost half treated rising 2-year-old cows before calving. One in four farmers used anthelmintics on calves on 8–12 occasions in their first year of life. Co-grazing with other species was rare, but follow-on grazing within 3 months after older cattle or sheep was common. On most farms, grazing cattle was restricted to part of the farm, a finding with implications for parasite control and persistence of larvae in refugia. Macrocyclic lactone (ML) anthelmintics or their combinations with other action families were currently, and for the past 5 years, used more frequently than benzimidazoles and levamisole, and benzimidazole-levami- sole combinations. The prevalence of resistance to ivermectin was high (82%) and no plausible model of associations could be constructed from the data. The prevalence of resistance to albendazole was 60%, and the risk of resistance increased as the number of rising 1-year-old cattle present mid-winter increased, and decreased as the number of breeding cows >2 years old present mid-winter increased. CONCLUSION: It is clear that in practice anthelmintic resistance is a secondary consideration to obtaining productivity advantages from the use of anthelmintics in beef cattle. Farmers’ opinions were divided on many issues and the overall impres- sion was of confused and diverse thinking regarding the principles of the use of anthelmintics. The overall outlook regarding anthelmintic resistance in cattle is bleak unless the need for integrated and long-term research activities is acted upon soon.