Evaluation of a larval development assay (DrenchRite) for the detection of anthelmintic resistance in cyathostomin nematodes of horses

A larval development assay (LDA, DrenchRite) was evaluated to determine the effectiveness of this method in detecting anthelmintic resistance in cyathostomin nematodes of horses. A total of 15 horse farms from Georgia and South Carolina (USA) and Population S ponies from the University of Kentucky (USA) were included in this study. Nematode eggs were extracted from pooled fecal samples and placed into the wells of a DrenchRite plate for testing against thiabendazole (TBZ), levamisole (LEV) and 2 ivermectin (IVM) analogs (IVM-1, IVM-2). After a 7-day incubation larvae in each well were counted and data were analyzed by logistic regression. Resistance status of each farm for different drugs was determined in a separate study using a fecal egg count reduction test. LDA were performed on the 15 farms once, however, the Population S cyathostomins were assayed on 3 separate occasions to estimate the consistency of results between assays. Mean TBZ LC50 for oxibendazole resistant, suspected resistant and sensitive farms were 0.2015, 0.1625, and 0.1355 microM, respectively. For LEV, mean LC50 for PYR resistant, suspected resistant and sensitive farms were 1.590, 1.8018 and 1.4219 microM, respectively. All 15 farms had worms susceptible to IVM; mean LC50 for IVM-1 and for IVM-2 were 7.5727 and 87.9718 nM, respectively. A linear mixed model was fitted to the data to determine the relationship between LC50 and LC95 and resistance status for each farm. No meaningful relations were found. Consistency of assays varied between drugs, being best for TBZ and worst for LEV and IVM-1. All farms in this study had benzimidazole-resistant nematodes; therefore usefulness of DrenchRite for discriminating susceptibility versus resistance to this drug class could not be accurately assessed. Moreover, since all farms tested were sensitive to IVM and resistance to this drug class has not yet been reported in cyathostomins, it is not possible to assess accurately the usefulness of DrenchRite LDA for detecting IVM resistance at this time. Assay results for LEV suggest that LEV in a LDA does not yield data that is useful in estimating PYR efficacy in vivo. Based on results for PYR/LEV, the current high prevalence of benzimidazole resistance, no known cases of IVM resistance, and the sometimes extreme variation in results seen in many of the assays, DrenchRite LDA cannot be considered a useful tool for the diagnosis of resistance in cyathostomins of horses at present.     

Analysis of the strongylid nematodes (Nematoda: Strongylidae) community after deworming of brood horses in Ukraine

Communities of intestinal helminths in horses are commonly studied post mortem. The study objectives were here to examine the species composition of the strongylid community in brood horses in Ukraine after deworming with an aversectin drug Univerm. The site distribution of the strongylid species was analysed according to dynamics of their expulsion in faeces. Forty-four horses of different ages from Poltavska oblast (22 horses), Kyivska oblast (17 horses) and Sumska oblast (5 horses) of Ukraine were included in the study. Horses were treated with Univerm anthelmintic (0.2% aversectin) at a dose rate of 0.5mg aversectin preparation per kg body weight. Faecal sampling (200 g each) was performed at 24, 36, 48 and 60 h post treatment, and all nematodes expelled were collected and identified. The largest numbers of strongylids were expelled at 24--36 h after treatment. Twenty-five nematode species from the subfamilies Strongylinae and Cyathostominae were identified. The number of strongylid species found per horse ranged from 7 to 20, on an average 11+/-3.6 (S.D.). The number of cyathostomin species found per horse ranged from 7 to 16, on an average 10+/-2.3 (S.D.). Cylicocyclus nassatus and Cyathostomum catinatum were the most dominant species were found in 100% of horses, amounting to 36.3% and 17.6% of the total number of strongylids collected, respectively. C. longibursatus, C. ashworthi, Cylicostephanus calicatus, C. leptostomus and C. minutus were identified in more than 80% horses and represented 39.9% of the total number of strongylids collected. The dynamics of the different strongylid species expelled was irregular. Correlation between the time of cyathostomin species expulsion in faeces and their predicted localisation inside the horse intestine was found. Species mainly localised in the caecum were found in faeces later than those species localised in the dorsal and ventral colons. Larvae and adult Parascaris equorum, Oxyuris equi and botfly larvae from the genus Gasterophilus were also found in horse faeces. This investigation shows that is possible to study the horse strongylid community after deworming with aid of an aversectin drug. The results obtained here correspond to those recorded in previous autopsy surveys in other countries.     

Enzootic viral abortion on a stud farm in east Switzerland

An outbreak of abortion due to the equine herpesvirus-1 (EHV-1) in the eastern part of Switzerland is reviewed. Seven of eleven pregnant mares aborted within twenty-three days in January 1989. Four weeks later another foal died a few minutes after parturition. Three mares delivered live foals in February, March and April without any complications. The examination of the eight dead foals revealed an EHV-1 Infection. The clinical signs and the pathology are discussed. Severe complications during the early post-parturient time are in contrast to the uncomplicated outcome mentioned by other authors. Procedures for prevention and control are listed.     

Jejunoileal anastomosis following small intestinal resection in horses: seven cases (1999-2001)

OBJECTIVE: To report the postoperative outcome in horses undergoing jejunoileal anastomosis performed with a 2-layer simple continuous technique. DESIGN: Retrospective study. ANIMALS: 7 horses. PROCEDURE: Information regarding signalment, clinical signs, findings at surgery, and postoperative complications was obtained from medical records of horses that underwent exploratory ventral midline celiotomy, small intestinal resection, and jejunoileal anastomosis to correct various small intestinal strangulating lesions. Follow-up information was obtained via telephone conversations with owners or trainers. RESULTS: Six males and 1 female of various breeds aged 10 months to 27 years and weighing 312 to 785 kg (686.4 to 1,727 lb) were included. The most common complications were mild to moderate tachycardia and mild to moderate signs of abdominal pain. Two horses developed incisional infections and soft, fluctuant swelling at the incision site following resolution of the infection. Follow-up time ranged from 7 to 17 months after surgery. Owners reported no further colic episodes and no diet change necessary following surgery. All horses had returned to their intended level of use. CONCLUSIONS AND CLINICAL RELEVANCE: Advantages to the jejunoileal technique include maintaining the normal ileocecal valve and a postoperative recovery period similar to that described following other small intestinal anastomoses. Jejunoileal anastomosis is a viable alternative to ileal bypass. This technique appears to result in a postoperative complication rate similar to that reported following jejunojejunostomy procedures.     

Allergic dermatitis (sweet itch) of Icelandic horses in Sweden: an epidemiological study

A survey of allergic dermatitis (sweet itch) in Sweden contained information on 441 Icelandic horses. Results of a questionnaire indicated that approximately 15 per cent of the country's Icelandic horses suffered from the disease. The prevalence of allergic dermatitis was significantly higher among horses imported from Iceland (26.2 per cent) compared to that of Swedish-born animals (6.7 per cent). In addition, horses born in Iceland were significantly more severely affected than horses born in Sweden. The risk of allergic dermatitis in Sweden appeared to be more than six times higher for horses exported from Iceland to Sweden relative to that of horses originally born in Sweden. The prevalence of disease for horses of seven years or older was 30 per cent for Icelandic-born individuals as compared to 7.3 per cent for horses born in Sweden. Similarly, the risk of allergic dermatitis in Sweden for horses of seven years or older appeared to be nearly 10 times higher for horses imported from Iceland relative to that of horses born in Sweden. Allergic dermatitis usually appeared during the third grazing season for imported horses and during the fourth season for horses born in Sweden. Furthermore, the course of the disease tended to become worse with time. Analysis of the prevalence of allergic dermatitis relative to gender revealed no significant differences. Certain geographical variations in the prevalence of the disease was also found.     

Effect of repeated oxfendazole treatments on small strongyle infections in Shetland ponies

Overwintering of horse cyathostomes as inhibited third stage larvae (L3) and the effect of repeated oxfendazole (OFZ) treatment on strongyle infections were studied in an experiment with two groups of three Shetland ponies. Both groups were grazed together from May 28 to November 11, 1986 and subsequently housed. Treatments with 10 mg OFZ kg-1 were given on May 26, July 1 and July 28 and again one week before each group was necropsied in December and April, respectively. Worm populations of both groups were dominated by inhibited early L3. The proportion of fourth stage larvae (L4) was significantly higher in April than in December. The faecal egg counts showed that the OFZ treatment in May was more effective than those in July. This resulted in high pasture larval counts from the end of August onwards. The final treatments revealed a low efficacy against L3 and L4 but not against adult worms.     

Prevalence of some internal parasites found (1971–1989) in horses born on a farm in central kentucky

Prevalence of several species of naturally acquired internal parasites are reported from a total of 97 horses (mostly mixed lighthorse type) from a farm in central Kentucky. The horses were born and raised in 2 adjacent fields (No. 4 - n=44 and No. 10 − n=53) over a 19-year-period (1971–1989). They were 100 to 537 days old (av. 281) when examined; an exception was a 819-day-old not calculated in the average age. Some of the horses were not examined for all of the parasites. These horses (never previously treated) were all used in critical or controlled tests for evaluation of antiparasitic activity of drugs. Dams and other horses in the fields rarely were given an antiparasitic compound.Prevalence and aggregate mean numbers of parasites in infected animals (in parentheses) for the 97 horses are: bots — Gasterophilus intestinalis 2nd instar, 65%(45), 3rd instar, 96%(210), Gasterophilus nasalis 2nd instar, 18%(10), 3rd instar, 63%(10); stomach worms — Habronema muscae, 73%(78), Draschia megastoma, 42%(53); ascarids — Parascaris equorum mature, 75%(45), immature 36%(29), tapeworms — Anoplocephala perfoliata, 33%(7); large strongyles — Strongylus vulgaris, 95%(80) (data on horses ≥180 days old), Strongylus edentatus, 94%(34) (data on horses ≥330 days old); pinworms — Oxyuris equi, 43%(87); eyeworms — Thelazia lacrymalis, 61%(6); S. vulgaris in cranial mesenteric artery, 92%(53); and S. edentatus in ventral abdominal wall, 98% (56). Differentiation was made for the data by season and by age of the horses when they were examined. Information from this research reflects the transmission patterns and prevalence of these parasites under natural conditions.     

End-to-end jejuno-ileal anastomosis following resection of strangulated small intestine in horses: a comparative study

REASONS FOR PERFORMING STUDY: Small intestinal resection and anastomosis is a relatively common procedure in equine surgical practice. This study was designed to test objectively the subjective opinions of surgeons at the Liphook Equine Hospital that an end-to-end jejuno-ileal anastomosis (JIA) is an effective and clinically justifiable procedure, contrary to conventional recommendations. HYPOTHESIS: An end-to-end JIA carries no greater risk of morbidity and mortality than an end-to-end jejunojejunal anastomosis (JJA). METHODS: A retrospective observational study was performed on a population of 100 horses that had undergone small intestinal resection and end-to-end anastomosis. Two groups were identified; Group 1 (n = 30) had undergone an end-to- end JIA and Group 2 (n = 70) an end-to-end JJA. The 2 populations were tested for pre- and intraoperative comparability and for their equivalence of outcomes. RESULTS: The 2 populations were comparable in terms of their distributions of preoperative parameters and type of lesion present. The observations used as outcome parameters (incidence risk of post operative colic, incidence risk of post operative ileus, duration of post operative ileus, rates of functioning original anastomoses at the time of discharge and at 12 months, survival rates at 6 months and 12 months) were equivalent between the 2 groups. CONCLUSION: End-to-end JIA carries no greater risk of morbidity and mortality than an end-to-end JJA. POTENTIAL RELEVANCE: Surgeons faced with strangulating obstructions involving the jejuno-ileal junction in which there remains an accessible length of viable terminal ileum may reasonably perform an end-to-end JIA. This has the potentially significant advantage over a jejunocaecal anastomosis of preserving more anatomical and physiological normality to the intestinal tract. The study was, however, relatively small for an equivalence study and greater confidence would be gained with higher numbers.     

Characterization of trypanosome isolates from naturally infected horses on a farm in Kenya

Following an outbreak of trypanosomosis in horses on a farm in Kenya, 18 trypanosome isolates were collected from the infected animals over a period of one and a half years and cryopreserved for characterization. The characterization was done on the basis of morphology using Giemsa-stained blood and buffy coat smears, infectivity to mice, recombinant DNA hybridization, and chromosome separation by orthogonal field alternation gel electrophoresis (OFAGE). Morphologically, all the trypanosome isolates were identified as belonging to the subgenus Nannomonas, and a total of 16 out of the 18 isolates grew in mice. Using the recombinant DNA hybridization technique, the isolates were further classified as the 'savannah' type of Trypanosoma congolense. Furthermore, chromosome separation by OFAGE, carried out on six clones derived from different isolates, exhibited a profile characteristic of T. congolense, 'savannah' type. However, there were differences in the number and positions of the medium-sized and minichromosomes indicating a diversity of serodemes within the isolates. Hence the infecting trypanosomes in this disease outbreak were T. congolense, 'savannah' type, and comprised several serodemes or strains.     

The identification of Anaplasma spp. isolated from fallow deer (Dama dama) on a free-range farm in eastern Poland

The aim of the present study was to investigate the occurrence of Anaplasma spp. in group of 50 fallow deer (Dama dama) from free-range farm in eastern Poland and determine what species of Anaplasma could infect these animals based on PCR gene sequencing. The PCR technique revealed the presence of 16S RNA Anaplasma spp. genetic material in the blood of 7 out of 50 examined animals. The sequences of the PCR products obtained showed a 100% homology with each other and 100% homology with GU 183908 sequence of A. phagocytophilum, isolated in our earlier study from a horse with clinical form of anaplasmosis. Here, we report the first molecular evidence of Anaplasma spp. among naturally infected fallow deer in eastern Poland.     

Postoperative infection with Actinobacillus spp in horses: 10 cases (1995-2000)

OBJECTIVE: To determine features of postoperative wound infection caused by Actinobacillus spp in horses undergoing clean, elective surgery and to evaluate bacterial susceptibility profiles of bacteria isolated. DESIGN: Retrospective study. ANIMALS: 10 horses. PROCEDURE: Data were retrieved from medical records and the microbiology laboratory database. RESULTS: 1,604 horses underwent clean, elective surgical procedures during the study period. Of these, 23 (1.43%) had postoperative wound infections, and Actinobacillus spp was isolated from 10 of these 23 (43%). Surgical procedures in these 10 horses included laryngoplasty with ventriculocordectomy (n = 3), arthroscopy (3), desmotomy of the accessory ligament of the superficial digital flexor tendon (2), removal of laryngoplasty prostheses (1), and hygroma resection (1). Seven horses survived, and 3 were euthanatized. All 10 Actinobacillus isolates were resistant to penicillin, and 6 were resistant to trimethoprim-sulfamethoxazole. All isolates were susceptible to ceftiofur and gentamicin. During the 5-year period of the study, Actinobacillus organisms were isolated from 35 of 513 (6.8%) samples from the general hospital population submitted for bacterial culture and antimicrobial susceptibility testing. CONCLUSIONS AND CLINICAL RELEVANCE: During the study period, Actinobacillus spp was isolated from a higher than expected percentage of horses that developed postoperative wound infections after clean, elective surgery. Susceptibility profiles for these isolates were different from typical susceptibility profiles for Actinobacillus isolates, suggesting that a pattern of resistance may be emerging.     

Efficacy of metoclopramide for treatment of ileus in horses following small intestinal surgery: 70 cases (1989–1992)

Summary: In this retrospective study, postoperative ileus was studied in horses having resection of the small intestine followed by a jejunojejunal (n=35) or a jejunocaecal (n=35) anastomosis. Twenty-six horses received no metoclopramide, 27 received metoclopramide as an intermittent intravenous infusion and 17 horses received metoclopramide as a continuous intravenous infusion (0.04 mg/kg/hour). Horses receiving a continuous infusion of metoclopramide had a reduced total volume (P< 0.001), shorter duration (P< 0.001), and a slower rate (P< 0.001) of postoperative gastric reflux, and a shorter postoperative hospital stay (P< 0.01) when compared to horses receiving no metoclopramide and horses receiving metoclopramide as an intermittent infusion. Horses having jejunocaecostomy performed had a larger volume (P< 0.05), longer duration (P< 0.05), and a greater rate (P< 0.05) of postoperative gastric reflux, and a longer postoperative hospital stay (P< 0.001) than horses undergoing jejunojejunostomy. Horses that had an abdominal drain placed during surgery had a longer length of intestine resected (P< 0.05) and a longer postoperative hospital stay (P< 0.05) than horses without an abdominal drain. Horses that died or were euthanased during the postoperative period had a greater total volume (P< 0.05), longer duration (P< 0.05), and greater rate of postoperative gastric reflux (P< 0.01), a longer length of small intestine resected (P< 0.01), and a shorter postoperative hospital stay (P< 0.05) than horses that survived until discharge from the hospital. In a multivariate regression analysis the continuous infusion of metoclopramide was the only variable that contributed significantly to predicting the total volume (P< 0.001; r²= 0.24), duration (P< 0.001; r²= 0.24) and rate (P< 0.001; r²= 0.25) of postoperative gastric reflux. We concluded that metoclopramide given as a continuous intravenous infusion decreased the incidence and severity of ileus following small intestinal resection and anastomosis in horses.     

Parascaris equorum in foals and in their environment on a Swedish stud farm, with notes on treatment failure of ivermectin

Environmental contamination and the egg excretion pattern of the ascarid Parascaris equorum (Nematoda) was investigated in relation to anthelmintic treatment on a Swedish stud farm. Faecal samples from 15 foals, dewormed every 8th-week with a paste formulation of ivermectin at the standard dose rate of 0.2 mg/kg bodyweight, were collected at five sampling occasions between August and November 2006. In addition, soil samples were obtained from four paddocks used by these foals in November 2006. The number of eggs per gram (epg) was counted in both faeces and soil. Egg excretion started when the foals were 3-4 months, and reached the highest levels when they were approximately 5-month-old, and was then followed by a decline. Egg excretion seemed to be unaffected by ivermectin despite these foals were dewormed at regular intervals. In four out of five foals examined 10 days after treatment, epg actually increased. In contrast, when either fenbendazol or pyrantel embonate were used instead of ivermectin, treatments were effective. The number of eggs in soil was significantly higher in the permanent paddock compared to in the temporarily used soil paddock and in the summer paddocks.