Expression of cyclooxygenase-1 and -2 in naturally occurring squamous cell carcinomas in horses

OBJECTIVE: To assess expression of cyclooxygenase (COX)-1 and -2 in naturally occurring squamous cell carcinomas (SCCs) and the analogous normal tissues in horses. SAMPLE POPULATION: Tissue samples collected from 3 conjunctival, 2 vulvar, 4 preputial, and 5 penile SCCs during surgical excision in 14 horses and from corresponding body regions (conjunctiva [n = 5 horses], vulva [2], prepuce [3], and penis [3]) in 5 horses euthanized for reasons unrelated to neoplasia. PROCEDURES: Tissue samples were snap frozen in liquid nitrogen and stored at -80 degrees C until analysis. Protein was extracted from the frozen tissues, and western blot analyses were performed. Nonneoplastic and abnormal tissues from each body region were run on the same blot, and blots were run in triplicate. Molecular-weight markers and COX-1 and 2 ovine standards (positive control samples) were run concurrently on the gels; negative control samples were not used. RESULTS: All tissues, including the nonneoplastic and SCC tissues, expressed both COX-1 and -2 proteins. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that the expression of COX proteins in both nonneoplastic and SCC-affected tissues in horses is markedly different from that in other species. The reason for the potential benefit of COX-2 inhibitors in horses and other species is unknown. Further research needs to be performed to evaluate the efficacy of COX-2 inhibitors as cancer treatments in horses. Investigation of the mechanisms of tumor development in horses should be performed to increase understanding of this disease and ascertain how the mechanisms differ from those in other animals.     

Enzootiology of Trypanosoma evansi in Pantanal, Brazil

In order to better understand the enzootiology of trypanosomiasis caused by Trypanosoma evansi in the Brazilian Pantanal we examined domestic and wild mammals by microhematocrit centrifuge technique (MHCT), immunofluorescence antibody test (IFAT) and polymerase chain reaction (PCR). T. evansi infection was detected in all species sampled with exception of the sheep and the feral pig. High parasitemias were observed in capybaras (5/24), coatis (18/115), horses (31/321) and dogs (3/112). Among these species, only the capybaras did not develop anemia. Low parasitemias, only detected by PCR, were found in buffaloes (18/43), bovines (29/331), marsupials (1/4), small rodents (14/67), bats (7/18), and one armadillo (1/8). The highest prevalence of T. evansi infection was recorded in horses (73%), although no neurological signs in infected horses were observed. Diagnosis through standard parasitological tests and IFAT should be used with caution since they may overlook comprovedly infected horses. The relationship between ranch management and T. evansi infection in horse was investigated. The importance of other transmission mechanisms apart from the tabanids and reservoir hosts are discussed.     

Passive surveillance for ticks on horses in Saskatchewan

Passive surveillance of ticks on horses in Saskatchewan revealed that the horses were parasitized by 3 species, Dermacentor albipictus, D. andersoni, and D. variabilis. The nymphs and adults of D. albipictus occurred on horses earlier in the year than did adults of the 2 other species.     

Development of Immunologic Assays to Measure Response in Horses Vaccinated with Xenogeneic Plasmid DNA Encoding Human Tyrosinase

Xenogeneic plasmid DNA constructs have been developed and optimized for immunotherapies targeting cancer in both humans and dogs. Specifically, plasmid vectors containing the tumor antigen tyrosinase have demonstrated immunoreactivity and clinical benefit in the treatment of melanocytic tumors in these species. Overexpression of tyrosinase has also been noted in equine melanocytic tumors, supporting its role as a valid tumor antigen in the horse. Vaccination with plasmid constructs containing tyrosinase may thus have translational immunoreactivity in the treatment of equine melanomas. Here, we describe a methodology that is highly sensitive and specific for the detection of both humoral and cell-mediated immunoreactivity against tyrosinase in equine patients. These antigen-specific immunoassays are used to measure the humoral and cell-mediated responses in a cohort of horses vaccinated with xenogeneic plasmid DNA encoding human tyrosinase. Serum humoral responses were measured using standard enzyme-linked immunosorbent assay technique against the full-length recombinant human tyrosinase protein. Peripheral blood mononuclear cells were collected from vaccinated horses and stimulated with tyrosinase-specific peptides. Cell-mediated responses were then measured using a novel quantitative real-time-polymerase chain reaction technique to determine resultant interferon-γ expression. All horses developed significantly positive humoral and cell-mediated immune responses compared with their individual prevaccination values. No adverse reactions or signs of autoimmunity were detected. Vaccination with xenogeneic plasmid DNA expressing tyrosinase appears to elicit tumor antigen-specific reactivity and should be evaluated in a larger cohort of horses with melanocytic tumors.     

The Incidence of Aeromonas Species in the Feces of Nondiarrheic Horses

Aeromonas species have been isolated from the feces of diarrheic adult horses and foals. However, Aeromonas species have also been isolated from the feces of approximately 5% of clinically normal adult horses outside the United States. The objectives of this study were to determine whether Aeromonas species can be shed in the feces of nondiarrheic adult horses and identify any effects of season of year, transportation, and hospitalization on possible fecal shedding of Aeromonas species. Feces were cultured for Aeromonas and Salmonella species from 138 nondiarrheic adult horses examined in the hospital and by field services for complaints other than gastrointestinal disease. Fecal Aeromonas and Salmonella species were isolated from 6.5% and 2.2% of nondiarrheic horses, respectively. All Aeromonas isolates were identified as A caviae. There were no apparent effects on time of year, hospitalization, or transport on isolation of Aeromonas species from feces. Isolation of Aeromonas species from diarrheic horses in the absence of other possible enteric pathogens indicates intestinal disease as a result of Aeromonas infection, but Aeromonas species can also occur as copathogens with Salmonella infections.     

Antimicrobial resistance in bacteria from horses: Epidemiology of antimicrobial resistance

Antimicrobial resistance poses a significant threat to the continued successful use of antimicrobial agents for the treatment of bacterial infections. While the epidemiology of antimicrobial resistance in bacteria from man has been studied extensively, less work has been undertaken in companion animals, particularly horses. Methicillin‐resistant Staphylococcus aureus has been identified as a cause of infections, with a low prevalence of nasal carriage by horses in the community but higher for hospitalised horses. Molecular characterisation has shown methicillin‐resistant Staphylococcus aureus strains either to be predominantly of types associated with horses or of sequence type ST398. Antimicrobial‐resistant Escherichia coli (including multidrug‐resistant and extended spectrum β‐lactamase‐producing isolates) have caused infections and been documented in faecal carriage by horses, with many significant resistance mechanisms identified. More sporadic reports and molecular characterisation exist for resistance in other bacteria such as enterococci, Salmonella, Acinetobacter and Pseudomonas species. Limited work has been undertaken evaluating risk factors and much of the epidemiology of antimicrobial resistance in bacteria from horses remains to be determined.     

Plasma and liver copper values in horses with equine degenerative myeloencephalopathy.

Equine degenerative myeloencephalopathy (EDM) is a common spinal cord disease in the horse. The etiology of EDM currently is unknown. In other species, there are similarities in the clinical signs and neuropathological changes observed in EDM and in copper deficiency. The objective of this study was to determine if horses affected with EDM had low levels of plasma or liver copper. Plasma copper values were determined in 25 EDM affected horses and 35 normal horses. Liver copper levels were determined on 13 EDM affected horses and 22 normal horses. Plasma and liver copper values were not significantly lower in EDM affected horses than in control horses.     

Expulsion of small strongyle nematodes (cyathostomin spp) following deworming of horses on a stud farm in Sweden

This study was conducted on a stud farm in Sweden to investigate the species composition of cyathostomins expelled in the faeces of horses after deworming using three different anthelmintic preparations. Twenty-seven horses excreting > or = 200 strongyle eggs per gram faeces (EPG) were divided into three comparable groups and dewormed on day 0 with either of following compounds: 0.2 mg ivermectin per kg body weight (bw), 19 mg pyrantel pamoate per kg bw or 7.5 mg fenbendazole per kg bw. For each of the 3 days following anthelmintic treatment faeces was collected from individual horses and subsamples were fixed in formalin. Four days after the anthelmintic treatment all horses were re-treated with ivermectin and faeces was collected on day 5. Individual subsamples from each of the four sampling occasions were examined for cyathostomin nematodes. Sixty-three to 270 worms per horse were identified to the species level. The majority of the worms recovered were expelled during the first day from horses treated with ivermectin or pyrantel pamoate, and during the second day from horses treated with fenbendazole. Fifteen cyathostomin species were identified and the six most prevalent were Cylicocyclus nassatus, Cyathostomum catinatum, Cylicostephanus longibursatus, Cylicocyclus leptostomus, Cylicostephanus minutus and Cylicostephanus calicatus. These species composed 91% of the total burden of cyathostomins. The number of species found per horse ranged from 6 to 13, with an average of 9. No significant differences in species composition or distribution were found between the treatment groups. On day 5, i.e. 1 day after the last ivermectin treatment, 93% of the adult worms were recovered from horses in the fenbendazole group.This study showed that it was possible to identify cyathostomins expelled in faeces of dewormed horses, and that the most prevalent species corresponded to those found in autopsy surveys performed in other countries.     

Comparative pharmacokinetics of meloxicam in clinically normal horses and donkeys

OBJECTIVE: To determine the disposition of a bolus of meloxicam (administered IV) in horses and donkeys (Equus asinus) and compare the relative pharmacokinetic variables between the species. ANIMALS: 5 clinically normal horses and 5 clinically normal donkeys. PROCEDURES: Blood samples were collected before and after IV administration of a bolus of meloxicam (0.6 mg/kg). Serum meloxicam concentrations were determined in triplicate via high-performance liquid chromatography. The serum concentration-time curve for each horse and donkey was analyzed separately to estimate standard noncompartmental pharmacokinetic variables. RESULTS: In horses and donkeys, mean +/- SD area under the curve was 18.8 +/- 7.31 microg/mL/h and 4.6 +/- 2.55 microg/mL/h, respectively; mean residence time (MRT) was 9.6 +/- 9.24 hours and 0.6 +/- 0.36 hours, respectively. Total body clearance (CL(T)) was 34.7 +/- 9.21 mL/kg/h in horses and 187.9 +/- 147.26 mL/kg/h in donkeys. Volume of distribution at steady state (VD(SS)) was 270 +/- 160.5 mL/kg in horses and 93.2 +/- 33.74 mL/kg in donkeys. All values, except VD(SS), were significantly different between donkeys and horses. CONCLUSIONS AND CLINICAL RELEVANCE: The small VD(SS) of meloxicam in horses and donkeys (attributed to high protein binding) was similar to values determined for other nonsteroidal anti-inflammatory drugs. Compared with other species, horses had a much shorter MRT and greater CL(T) for meloxicam, indicating a rapid elimination of the drug from plasma; the even shorter MRT and greater CL(T) of meloxicam in donkeys, compared with horses, may make the use of the drug in this species impractical.     

Pancytopenia in two horses following administration of potentiated sulfonamide antimicrobials

Adverse drug reactions to potentiated sulfonamide antimicrobial drug combinations have been reported in many species, including horses. This report describes the occurrence of pancytopenia in 2 horses, one subsequent to an immune mediated reaction and the other bone marrow aplasia following the administration of trimethoprim and sulfadimidine. These cases highlight the importance of judicious use of antimicrobial agents and describe adverse drug reactions in horses receiving potentiated sulfonamide antimicrobials.     

Rickettsial infection in domestic mammals and their ectoparasites in El Valle de Antón, Coclé, Panamá

The present research evaluated the presence of Rickettsia spp. on ectoparasites of horses and dogs (using PCR techniques), and their sera (using immunofluorescence assay) in El Valle de Antón town in Panama. A total of 20 horses and 20 dogs were sampled, finding four species of ectoparasites on dogs (the ticks Rhipicephalus sanguineus, Amblyomma ovale, Amblyomma oblongoguttatum, and the flea Ctenocephalides felis), and two tick species on horses (Amblyomma cajennense and Dermacentor nitens). DNA of Rickettsia amblyommii was found in pools of A. cajennense, D. nitens, and R. sanguineus, while Rickettsia felis was detected in C. felis pools. Overall, 70% (14/20) and 65% (13/20) of the horses and dogs, respectively, were seroreactive (titer ≥ 64) to spotted fever group rickettsiae. Sera from six dogs and five horses reacted to R. amblyommii antigens with titers at least four-fold higher than those for the other antigens tested (Rickettsia bellii, Rickettsia parkeri, Rickettsia rhipicephali, R. felis, and R. rickettsii). These serological results, coupled with our molecular findings, suggest that these dogs and horses were infected by Rickettsia amblyommii. More studies need to be realized afford to identify the Rickettsia species responsible for other serological and molecular positive results, and their ecological importance.     

EFFECT OF STRESS ON STEROID HORMONE LEVELS IN RACEHORSES

SUMMARY Cortisol and testosterone were measured by radioimmunoassay in plasma samples from race horses. None of 6 stressed male horses had Iow cortisol levels but testosterone levels (0.81 ± 0.15 nmol/l) were significantly lower than in healthy horses (1.86 ± 0.31 nmol/l). The conclusion was made that adrenocortical insufficiency is not a common association of stress in race horses. The reduction in testosterone levels is probably a nonspecific response similar to that seen in other species.     

Current concepts of hyperlipaemia in horses and ponies

Hyperlipaemia is an important condition in ponies, not just because of the seriousness of the clinical signs and biochemical changes involved, but because of the distress it causes owners and breeders that have had animals suffer from it. Hyperlipaemia occurs most commonly in fat ponies in late pregnancy and is rarely seen in larger horses. The syndrome has similarities with conditions in other species but the definitive aetiologies are not yet known. The condition in ponies is undoubtedly related to stress. The biochemical mechanisms involved in equine hyperlipaemia are considered and an hypothesis of possible pathogenesis is put forward. This hypothesis is tested by presenting the results of a preliminary study to evaluate glucose and lipid metabolism in horses and ponies. It appears that the pony is markedly insensitive to insulin compared to larger horses which means that triglycerides are more readily mobilised and the animal is therefore susceptible to hyperlipaemia in a situation of negative energy balance. The effect of stress is to increase cortisol levels which only exacerbates the insulin insensitivity and so creates a vicious circle. The importance of an innate insulin insensitivity may also be important in the pathogenesis of such conditions as laminitis.     

Organic matter and macromineral digestibility in domestic rabbits (Oryctolagus cuniculus) as compared to other hindgut fermenters

It is generally assumed that animal species differ in physiological characteristics of their digestive tract. Because investigating digestive processes is often labour‐intensive, requiring lengthy adaptation and collection periods, comparisons are often made on the basis of data collated from different studies. We added a new data set on dietary crude fibre (CF) and macromineral (Na, K, Ca, P, Mg) composition and apparent digestibility (aD) of organic matter (OM) and macrominerals in rabbits (Oryctolagus cuniculus; a total of 180 measurements with 12 individuals and 10 different diets) to a literature data collection for rodents and domestic horses (Equus caballus). Significant negative relationships between dietary CF and aD OM were obtained, but the significant difference in digestive efficiency between rabbits and guinea pigs (Cavia porcellus) reported from studies where both species had been investigated under identical conditions were not detectable in the larger data collection. However, the 95% confidence interval of the negative slope of the CF–aD OM relationship did not overlap between domestic horses on the one hand, and rabbits and guinea pigs on the other hand, indicating a less depressing effect of CF in horses. Akaike's information criterion indicated that aD of a macromineral did not only depend on its concentration in the diet, but also on the individual and various other diet characteristics and the presence of other macrominerals, indicating complex interactions. The data indicate similar mechanisms in the absorption of macrominerals amongst rabbits, rodents and horses, with the exception of Na and K in guinea pigs and Ca in chinchillas (Chinchilla laniger) that should be further corroborated. In particular, the occurrence of high aD Ca in hindgut fermenters, regardless of whether they employ a digestive strategy of coprophagy or whether they have fossorial habits, suggests that this peculiarity might represent an adaptation to hindgut fermentation in general.     

Hendra (equine morbillivirus)

Hendra has been recognized in Australia as a new zoonotic disease of horses since 1994/5 and subsequent work has shown that the viral agent is endemic in certain species of fruit bat. The Hendra virus is the type species of a new genus within the sub-family Paramyxovirinae, which also contains another newly identified zoonotic bat virus, namely Nipah. It is assumed that contact with bats has led to the Hendra virus being transferred to horses on each of the three separate incidents that have been reported in the last five years. No evidence has been found for widespread subclinical infection of horses.Infected horses can develop a severe and often fatal respiratory disease characterized by dyspnoea, vascular endothelial damage and pulmonary oedema. Nervous signs may also occur. Fatal respiratory disease has been seen in cats and guinea pigs following experimentally induced infections. Transmission of the virus from horses to other horses or man seems to have taken place, but very close contact was required. Three human cases have been recognized, all in association with equine cases. There have been two human fatalities, one due to respiratory failure and the other from a delayed-onset encephalitis. A number of diagnostic methods have been developed, but great care must be taken in obtaining samples from suspected cases.     

Comparison of Hydrolytic and Conjugative Biotransformation Pathways in Horse, Cattle, Pig, Broiler Chick, Rabbit and Rat Liver Subcellullar Fractions

To complete a studyaimed at investigating the pattern of the basal activities of liver xenobioticmetabolizing enzymes in major and minor species intended for meat production, microsomal carboxylesterases and some conjugating enzyme activities were determined and compared in liver preparations from horses, cattle, pigs, rabbits and broiler chicks, using the rat as a reference species. Horses and broiler chicks exhibited a lower microsomal carboxylesterase activity towards indophenyl or p-nitrophenyl acetate than that measured in cattle or pig subfractions. Among food-producing species, the rate of glucuronidation of either 1-naphthol or p-nitrophenol was in the order pigs ∼rabbits > horses >> cattle > broiler chicks. The widest variations were observed in the acetylation capacity towards p-aminobenzoic acid or isoniazid, which in rabbits was 3-fold to 11-fold greater than that displayed by any other examined species; low but measurable activities were found in equine and bovine cytosols. The activity of cytosolic glutathione S-transferase (GST) accepting the general substrate 1-chloro-2,4-dinitrobenzene was significantly higher in rabbits, horses and pigs than in rat, broiler chicks and cattle. Finally, an uneven pattern of activity towards the other tested GST substrates – 3,4-dichloronitrobenzene, ethacrinic acid or 1,2-epoxybutane – was observed, possibly reflecting the species-related expression of different GST classes; in this respect, the conjugative capacity displayed by horses was higher than or comparable to that found in the other food-producing species.     

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.     

The effect of a topical insecticide containing permethrin on the number of Culicoides midges caught near horses with and without insect bite hypersensitivity in the Netherlands

Insect bite hypersensitivity (IBH) in horses is most likely caused by Culicoides species, although other insects may also play a role. Until now no effective cure has been found for this condition, although numerous therapeutic and preventive measures have been used to control insect hypersensitivity. One such method is to apply a topical insecticide to horses. In this study, the effect of a topical insecticide containing permethrin (3.6%) was examined in seven pairs of horses. The horses were placed inside a tent trap to collect Culicoides spp. and other insects attracted to the horses on two subsequent evenings. On the first evening, both horses were untreated. After the end of this session, one horse of each pair was treated with the pour-on insecticide; treated horses were kept separate from untreated horses. The next evening the pairs of horses were again placed inside the tent trap and insects were collected. Similar percentages of Culicoides were trapped as in earlier studies (C. obsoletus 95.34% and C. pulicaris 4.54%), with healthy horses attracting more Culicoides than horses affected by IBH. The number of Culicoides, the percentage of blood-fed Culicoides obsoletus, and the total number of insects attracted to horses 24 hours after treatment with permethrin were reduced but the reduction was not statistically significant. No negative side effects of permethrin administration were observed.     

Salinomycin poisoning in horses

Six cases of accidental salinomycin poisoning in horses are described. The horses were fed a contaminated ration and presented clinical signs which were extremely varied in nature and severity. However, the range of signs, including anorexia, colic, weakness and ataxia bore similarities to those described in horses poisoned with the related ionophore monensin. Other similarities became apparent in serum biochemical profiles of the clinical cases. Although ionophore toxicity is rarely reported in horses they appear to be particularly susceptible, and it should therefore be considered as a differential diagnosis of digestive upsets or locomotory disorders at establishments where ionophore-treated feeds are used therapeutically in other species.     

Bacterial infection of the lower respiratory tract in 34 horses

OBJECTIVE: To investigate associations between the bacteriology and aspects of history, clinical presentation, outcome and pathology of lower respiratory tract disease of 34 horses. PROCEDURE: Detailed aerobic and anaerobic bacteriological investigations were performed on clinical specimens from horses with pneumonia, lung abscessation and necrotic pneumonia with or without pleurisy in an attempt to identify those bacteria that might contribute to the initiation and progression of infection. RESULTS: Bacteria were cultured from 33 of the 34 horses. In ten cases, only aerobic/facultatively anaerobic isolates were cultured while aerobic/facultatively anaerobic bacteria and obligately anaerobic bacteria were isolated in the other 23 cases. Moderate to large numbers of anaerobic bacteria were isolated only when the estimated duration of illness was at least five days. Bacteria were not cultured from 12 of the pleural fluid samples but were always cultured from pulmonary samples (either transtracheal aspirates from live horses or pulmonary lesions at necropsy). Streptococcus equi subsp zooepidemicus was isolated in the three cases where only one bacterial species was cultured. In the other 30 cases, multiple species were isolated. These included most often and in greatest numbers, Streptococcus equi subsp zooepidemicus, Pasteurellaceae, Escherichia coli, anaerobic cocci, Eubacterium fossor, Bacteroides tectum, Prevotella heparinolytica, Fusobacterium spp, and pigmented members of the genera Prevotella and Porphyromonas. Aerobic/facultatively anaerobic organisms were isolated from 97% of horses, while obligately anaerobic organisms were cultured from 68% of horses. CONCLUSION: There was no association between the isolation of any specific bacterium and the outcome of disease. However, obligately anaerobic bacteria (such as anaerobic cocci, Bacteroides tectum, P heparinolytica and Fusobacterium spp) and the facultatively anaerobic species Escherichia coli, were recovered more commonly from horses that died or were euthanased than from those that survived. There was an association between failure of horses to recover from pleuropneumonia and delay in diagnosis and initiation of treatment.