Benzimidazole resistance of equine stronygles--critical tests of six compounds against population B

Critical tests were conducted on eight horses naturally infected with several species of large and small strongyles from population B. Tested were six benzimidazoles, including thiabendazole (2 lots) (44 mg/kg of body weight); mebendazole (8.8 mg/kg); cambendazole (two formulations) (20 mg/kg); fenbendazole (10 mg/kg); oxibendazole (10 mg/kg); and oxfendazole (10 mg/kg). All compounds were administered by stomach tube except one of the two cambendazole formulations which was an intraoral paste. Removal of large strongyles (when present), Strongylus vulgaris and Strongylus edentatus, was 100% by each drug. In general, five species of small strongyles (Cyathostomum catinatum, Cyathostomum coronatum, Cylicocyclus nassatus, Cylicostephanus goldi, and Cylicostephanus longibursatus) exhibited varying degrees of resistance (% removal) to all of the drugs except oxibendazole. A total of 19 other species of small strongyles from seven genera, including the three described earlier were about 100% removed by the six benzimidazoles. Poor removal of immature (fourth-stage larvae) forms was also characteristic of the six drugs.     

Resistance of population-B equine strongyles to thiabendazole, oxfendazole, and phenothiazine (1981 to 1987)

Critical tests were completed on foals (n = 15) naturally infected with benzimidazole (BZ)-resistant population-B strongyles during the period between 1981 and 1987. Thiabendazole at a dosage of 44 mg/kg was tested in 8 foals, oxfendazole at 10 mg/kg was tested in 4 foals, and phenothiazine at 55 mg/kg, cambendazole at 20 mg/kg, and fenbendazole at 5 mg/kg were tested in 1 foal each. Efficacies of thiabendazole, cambendazole, and fenbendazole against the 5 species of BZ-resistant small strongyles (Cyathostomum catinatum, Cyathostomum coronatum, Cylicocylus nassatus, Cylicostephanus goldi, and Cylicostephanus longibursatus) were partial. Removals in the aggregate averaged 48%, 52%, and 68%, respectively, indicating continued resistance of the 5 species of small strongyles to thiabendazole, cambendazole, and fenbendazole. In contrast, oxfendazole was efficacious, removing an aggregate average of 95% of the 5 BZ-resistant species of small strongyles in the 4 foals. This apparent reversion to susceptibility to oxfendazole may be attributable to paucity of reference data (1 test foal) done in 1976. All 5 species of the BZ-resistant small strongyles had cross resistance to phenothiazine (38% aggregate removal), whereas 9 of the BZ-susceptible species were effectively (99%) removed. This suggests a similar mode of action between phenothiaznie and the BZ compounds.     

Possible resistance of small strongyles from female ponies in The Netherlands against albendazole

To determine resistance of small strongyles to albendazole, 3 female ponies (group 1) were grazed on a pasture from May to November 1985 and were treated with 7.5 mg of albendazole/kg of body weight, PO, 2 days before turnout in May and again in June and in July. Three other female ponies (group 2) grazed on a similar pasture from May to July, were treated with 7.5 mg of albendazole/kg, and were removed to another pasture until November. In December, ponies from both groups were treated with 7.5 mg of albendazole/kg, and 8 days later, they were euthanatized and necropsied for a critical test. Worm egg counts in the ponies' feces revealed that the May treatment of group 1 and the July treatment of group 2 were more effective than were later treatments. Numbers of small strongyles were higher in group 1 than in group 2. Efficacy of treatment against all developmental stages of small strongyles was higher in group 2 than in group 1. Efficacy was low in both groups against parasitic 3rd- and 4th-stage larvae. Fifteen species of small strongyles were identified at necropsy. Efficacy was limited against adult Cyathostomum coronatum, Cya labratum, Cylicostephanus calicatus, and Cyl poculatus in both groups; Cylicocyclus nassatus, Cyl minutus, and Cyl longibursatus in group 1; and Cya labiatum in group 2. Efficacy was 100% against Cya catinatum, Cyl goldi, and 5 other species that were found in low numbers.     

Piperazine resistance in population-B equine strongyles: a study of selection in Thoroughbreds in Kentucky from 1966 through 1983

Observations were completed over an 18-year period (1966 through 1983) in Thoroughbred mares (15/year) and yearlings (11 to 24/year) on a farm where benzimidazole-resistant small strongyles had emerged previously (1962 to 1965). This farm was operated as a closed, nonboarding type, which included a racing stable for its home-bred foals. At 2-week intervals, counts of worm eggs per gram of feces (EPG) and larvae per gram of feces were done to monitor strongyle infections and efficacies of bimonthly (every 8 weeks) antiparasitic treatments that were administered by stomach tube or were fed (dichlorvos pellets) to 1 group of yearlings during a 7-year period (1970 through 1976). The study included several drugs or mixtures, including thiabendazole (TBZ), phenothiazine (PTZ) + piperazine (PPZ)-carbon disulfide (CS2) complex, PTZ + PPZ + trichlorfon (TCF), dichlorvos, and pyrantel pamoate. These were used selectively in treated subgroups (usually 3/year) of mares and yearlings. The horses in drug treatment subgroups grazed together on common pastures; thus, efficacy comparisons between drugs were limited or nullified. However, annual mean EPG and larvae per gram of feces counts of mares and yearlings tended to increase over time, and for the yearlings treated with TBZ + PPZ and PTZ + PPZ-CS2, the buildup of these mean counts was statistically significant (P less than 0.05 for regression coefficients).(ABSTRACT TRUNCATED AT 250 WORDS)     

Climatic influences on development and survival of free-living stages of equine strongyles: implications for worm control strategies and managing anthelmintic resistance

Development of resistance to anthelmintic drugs by horse strongyles constitutes a growing threat to equine health because it is unknown when new drug classes can be expected on the market. Consequently, parasite control strategies should attempt to maintain drug efficacy for as long as possible. The proportion of a parasite population that is not exposed to anthelmintic treatment is described as being "in refugia" and although many factors affect the rate at which resistance develops, levels of refugia are considered the most important as these parasites are not selected by treatment and so provide a pool of sensitive genes in the population. Accordingly, treatment should be avoided when pasture refugia are small because such treatments will place significant selection pressure for resistance on worm populations. Given this new paradigm for parasite control, it has become important to identify seasons and circumstances wherein refugia are diminished. Free-living stages of equine strongyles are highly dependent on climatic influences, and this review summarises studies of strongyle development and survival under laboratory and field conditions in Northern (cool) temperate, Southern (warm) temperate and subtropical/tropical climates. In Northern temperate climates, refugia are smallest during the winter. In contrast, refugia are lowest during the summer in warm temperate and subtropical/tropical climates. Although adverse seasonal changes clearly have significant effects on the ability of free living stages of strongyle nematode parasites to survive and develop, available data suggest that climatic influences cannot effectively "clean" pastures from one grazing season to the next.     

Fenbendazole in equids: further controlled tests with emphasis on activity of multiple doses against naturally occurring infections of migratory large strongyles

Two controlled tests (experiments D and E) were done to evaluate a fenbendazole (FBZ) paste dosage regimen (10 mg/kg once a day for 5 days) for activity against naturally occurring infections of migrating Strongylus vulgaris and S edentatus in the mesenteric arteries and ventral abdominal wall, respectively. Data were also obtained on other internal parasites of the gastrointestinal tract and eyes in experiment E. Eight pony yearlings were used in experiment D (4 treated and 4 nontreated) and 6 horse weanlings were used in experiment E (3 treated and 3 nontreated). Intervals, expressed as days between treatment and necropsy of animals, were 42 (n = 1) or 52 (n = 7) for experiment D and 52 or 53 for experiment E. Animals were on pasture during all or a portion of post-treatment intervals of both experiments. Efficacious killing of retroperitoneal forms of S edentatus in the ventral abdominal wall was observed in both experiments. The average numbers of live 4th-stage forms in equids were 0.0 (treated) and 2.25 (nontreated) for experiment D and 2.0 (treated) and 1.7 (nontreated) for experiment E. The average numbers of 5th-stage S edentatus were 0.5 (treated) and 4.0 (nontreated) for experiment D and 1.3 (treated) and 23.3 (nontreated) for experiment E. Fragments of dead specimens of S edentatus were also found in nodules in treated animals in both experiments, but not in nontreated animals. Consistency of the retroperitoneal lesions provided additional evidence of the killing action of the FBZ treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

A survey of drug resistance in salmonellae isolated from animals in England and Wales from 1979 to 1981

Resistance to eight antibacterial drugs was tested in 12 903 Salmonella strains isolated from animals and their environment (6046 isolates from cattle, 3892 from poultry and other birds, 601 from pigs, 302 from sheep and 2062 from other species of animal and the environment) during the three-year period 1979 to 1981. Two thousand eight hundred and thirty-four (21 · 9%) strains were found to be sensitive to all eight drugs.Fifty-nine, 56 and 54 resistance patterns were recorded in strains isolated during 1979, 1980 and 1981 respectively; a higher number of such patterns was noted among Salmonella typhimurium strains (50, 47 and 43 respectively) than S. dublin (10, 10 and seven respectively) or other serotypes (32, 27 and 32 respectively). The 12 most common resistance patterns encountered are discussed with special reference to four chloramphenicol-multiresistant patterns CSSuT, ACNSSuT, CSSuTTm and ACNSSuTTm noted among strains of S. typhimurium particularly those isolated from cattle.The percentage of isolates (all serotypes) resistant to the individual drugs—compound sulphonamides 50 μg (Su), streptomycin 10 μg (S), chlortetracycline 10 μg (T), chloramphenicol 10, μg (C), neomycin 10 μg (N), ampicillin 10 μg (A), trimethoprim/sulphamethoxazole 25 μg (Tm) and furazolidone 15 μg (FR) for each of the three years is reported. The results pertaining to the resistance of S. typhimurium (5204 isolates), S. dublin (1729) and to isolates belonging to 121 other serotypes (5970 strains) are given separately.The findings of the present survey are discussed in relation to previous surveys carried out during the period 1971 to 1978.     

Managing anthelmintic resistance: Modelling strategic use of a new anthelmintic class to slow the development of resistance to existing classes

AIM: To test the hypothesis that a single strategic treatment with a new class of anthelmintic could slow the development of resistance to existing classes of anthelmintic.

METHODS: An existing model was used to simulate nematode parasite dynamics and the development of anthelmintic resistance. Variations on a five-drench preventive programme of treatments for lambs, in which either zero, the first, third or fifth treatment was substituted with a different class of drug, were compared for the time to reach treatment failure (defined as efficacy <95%). The sensitivity to variations in the death rate of adult worms, that varied from 1 to 5%, and the dominance of resistance genes were also assessed.

RESULTS: Replacing one of the five treatments with a different class of anthelmintic almost always slowed the development of resistance, and was never worse than using the same drug for all treatments. Further, there were large differences in the relative time to treatment failure depending on which treatment was substituted. Changing the first treatment always had the least benefit, whereas changing the fifth treatment always had the greatest. This pattern was independent of the daily death rate of adult worms, and was not influenced by the dominance of resistance under treatment.

CONCLUSIONS: The results indicated that strategic substitution of a single treatment with a new class of anthelmintic, at the end of a series of preventive treatments to lambs using an existing class, could slow the further development of resistance to the latter. This strategic use of a new anthelmintic class has the potential to greatly extend the life of existing anthelmintics if these are still effective.     

The causative organism of contagious equine metritis 1977: proposal for a new species to be known as Haemophilus equigenitalis.

The aetiological agent of contagious equine metritis (CEM) has been investigated bacteriologically in a wide range of cultural and conventional biochemical tests, in the eletron microscope, for DNA base composition (36.1 per cent GC), for susceptibility to various antimicrobial agents and antigenically by means of tube and slide agglutination tests. The organism is a fastidious, Gramnegative, non acid-fast coccobacillus which in biochemical tests is very unreactive. In conventional tests, only the oxidase, catalase and phosphatase tests were positive. Dependance on neither X nor V factors could be demonstrated, but some stimulation of growth by X factor was observed. The organism could not be identified with any known species and even allocation to an appropriate characters, we propose the organism as a new species of the genus Haemophilus: H. equigenitalis, type strain NCTC 11184 (61717/77).     

Inability of kaolin treatment to remove nonspecific inhibitors from equine serum for the hemagglutination inhibition test against equine H7N7 influenza virus.

The hemagglutination inhibition test is used by many diagnostic and surveillance laboratories for detection of antibodies to influenza viruses. It is well known that the hemagglutination inhibition test is affected by nonspecific inhibitors present in equine serum. Several serum treatments are in use to remove these inhibitors, including treatment with kaolin. Discrepant results were observed in the authors' laboratories when using kaolin treatment before testing equine sera for antibodies against equine influenza virus (EIV) subtype-1 (H7N7). It is demonstrated here that kaolin treatment leads to false positive results when testing for antibodies against EIV subtype-1, as compared to other standard serum treatments (trypsin-periodate, receptor-destroying enzyme). Against EIV subtype-2 (H3N8), however, false positive results were not evident. Trypsinperiodate and receptor-destroying enzyme (RDE) treatments appear to be superior to kaolin for removal of nonspecific inhibitors from equine serum and should be used for serological diagnosis and surveillance of equine influenza virus.     

Activity of ivermectin against natural infections by abomasal nematodes in lambs in controlled tests: evaluation of equine and bovine injectable formulations administered intraorally

The efficacy of 2 injectable formulations of ivermectin, administered intraorally at the dosage of 200 micrograms/kg of body weight, was evaluated against naturally occurring infections by abomasal nematodes in lambs in 2 controlled tests. One test (A) included 17 lambs treated with the equine formulation and 16 nontreated lambs. For the other test (B), 14 lambs were treated with the bovine formulation, and 12 were nontreated. In controlled test A, only mature nematodes were recovered, and removals were 98% to 100% for Haemonchus contortus, Ostertagia circumcincta male, O trifurcata male, Ostertagia spp female, and Trichostrongylus axei. For controlled test B, removals were 99% to 100% for Haemonchus spp (immature), H contortus (mature), Ostertagia spp (immature), O circumcincta male (mature), O trifurcata male (mature), Ostertagia spp female (mature), Trichostrongylus spp (immature), and T axei (mature). Toxicosis was not evident in treated lambs.     

Evaluation of the opsonic capacity of core lipopolysaccharide antiserum of equine origin against smooth Escherichia coli 0111:B4, using macrophage chemiluminescence

A study was performed to determine whether equine antiserum to core lipopolysaccharide (LPS) would enhance phagocytosis of smooth gram-negative (GN) organisms by equine macrophages. Five healthy adult horses (group A) were immunized with a bacterin prepared from the J-5 mutant of Escherichia coli 0111:B4 and Salmonella minnesota R595 to produce antibodies to core LPS. Five horses (group B) served as nonimmunized controls and were given physiologic saline solution instead of the rough mutant bacterin. Serum antibody titers to core LPS and to smooth E coli 0111:B4 were determined by indirect ELISA. Four serum pools were prepared: pool 1 = sera from horses in group B prior to immunization; pool 2 = sera from horses in group A prior to immunization (preimmune serum); pool 3 = sera from horses in group B, 7 days after the last saline injection; pool 4 = sera from horses in group A, 7 days after the last immunization (core LPS antiserum). The serum pools, either unheated or heated 30 minutes at 56 C, in 3 dilutions (1/50, 1/100, 1/500) were used to opsonize smooth E coli 0111:B4 in an assay of equine peritoneal macrophage chemiluminescence (CL). Peritoneal fluid was collected from clinically normal horses and the macrophages were purified by adherence to borosilicate glass scintillation vials. Each serum type and dilution was added to triplicate vials containing 10(7) colony-forming units of E coli 0111:B4. Luminol-dependent CL was measured with a liquid scintillation counter in the out-of-coincidence mode. Each serum dilution was tested in duplicate vials without bacteria to asses serum-induced nonspecific CL.(ABSTRACT TRUNCATED AT 250 WORDS)     

鸡舍环境耐药细菌气溶胶及其向环境传播的研究

通过对舍内粪便、空气和舍外环境(10、50、100m)中的空气分离到的细菌鉴定，包括细菌DNA分子生物学检测及药物敏感实验以及细菌含量统计学分析，证明三者之间存在着内在联系；舍内环境微生物气溶胶包括耐药细菌通过舍内外气体交换排往鸡舍周围环境，舍周边环境在一定范围内受到生物污染。研究显示，在粪便、舍内空气、舍外环境10、50、100m空气中分离的金黄色葡萄球菌和链球菌80％以上对氯霉素(CMP)和对苯唑青霉素(OXA)耐药；粪便和舍内外环境空气中的80％以上的大肠杆菌和沙门氏菌对氨苄青霉素(AMP）、氯霉素(CMP)、头孢唑啉(CFZ)均为抑制。证明该鸡舍曾经使用过这些药物治疗或作为添加剂在饲料中添加，鸡群产生了耐药细菌菌株，并向环境传播。测量数据统计结果指出，十里河鸡场鸡舍内环境空气中的大肠杆菌、沙门氏菌、金黄色葡萄球菌和链球菌与舍外环境中相应菌群含量比较差异显著或极显著(P＜0．05或P＜0．01)，但舍外10、50、100m之间的相应菌群比较差异不显著(P＞0．05)，这说明鸡舍内环境细菌气溶胶含量产生多，含量高，菌源强度大；另一方面，反应了鸡舍内环境微生物气溶胶包括耐药细菌能向舍外环境扩散，位舍外环境在一定的范围内受到动物源性生物污染，影响范围大于100m。通过对鸡舍环境微生物气溶胶来源的探讨发现，粪便中的大肠杆菌、沙门氏菌、金黄色葡萄球菌和链球菌与舍内空气相应菌群数量关系比较，呈现正相关(r=0.99)。这从一个侧面揭示了粪便可能是微生物气溶胶的主要来源。     

Use of the forced oscillating airflow technique to measure the resistance of the equine upper airway: effects of laryngoventriculectomy and laryngoplasty

Investigations were carried out to determine whether measurements of total respiratory resistance (TRR) made in resting animals could detect changes due to laryngeal hemiplegia. Control values of TRR were obtained in eight ponies and in six of these the measurements were repeated after division of the left recurrent laryngeal nerve in the mid-cervical region; two were retained as controls. A further set of measurements were made before two of the operated animals were subjected to left laryngoventriculectomy (Hobday operation). A laryngoplasty ('tie-back' operation) was performed on another two animals. Measurements of TRR were made at three-monthly intervals on all eight ponies for the next two years. Endoscopic examination of the larynx was carried out at the time of the measurements. All ponies showed a marked, but regular, variation in TRR over the two-year observation period. Nerve section was shown to be associated with an increase in TRR in five ponies. The Hobday operation decreased TRR in one animal and had no marked effect in the second. The tie-back operation was associated with a decreased TRR in one pony and an increase in the second. Autopsies were carried out on all six operated ponies and measurements of TRR and lower respiratory resistance (LRR) were made immediately before the animals were killed. Evidence of regeneration of the recurrent laryngeal nerve was seen in one of the ponies which underwent the Hobday operation. Histological evidence of regeneration was found in another pony.(ABSTRACT TRUNCATED AT 250 WORDS)     

Demonstration of continuously seropositive population against Borna disease virus in Misaki feral horses,a Japanese strain: a four-year follow-up study from 1998 to 2001

Borna disease virus (BDV)-specific antibodies were monitored in Misaki feral horses annually for 4 years using an electrochemiluminescence immunoassay (ECLIA). Among 130 horses examined, 35 (26.9%) with an ECLIA count above 1000 once or more were judged as BDV seropositive. Throughout the study period, p24 antibodies were more frequent than p40 antibodies in almost all positive animals. Among the 35 seropositive horses, the ECLIA count was consistently high in 12 cases. Eleven horses seroconverted from negative to positive and 7 underwent reversal. The count in the remaining 95 horses (73.1%) remained low for 4 years and these animals were judged as seronegative.