Pathogens are microorganisms, such as bacteria, viruses, fungi, and parasites, that can cause disease in horses. These microorganisms interact with the equine immune system, often leading to a range of health issues that can affect individual horses or entire populations. Pathogens can be transmitted through various routes, including direct contact, vectors, or environmental exposure. Common equine pathogens include Streptococcus equi, Equine Herpesvirus, and Strongylus vulgaris. Understanding the interactions between equine hosts and pathogens is essential for disease prevention, management, and treatment. This page compiles peer-reviewed research studies and scholarly articles that explore the identification, transmission, and impact of pathogens on equine health.
Snyder SP, England JJ, McChesney AE.Five of six immunodeficient Arabian foals that died of adenoviral infection were found to be infected with an intestinal coccidian of the genus Cryptosporidium. Various developmental stages of the organism were found in the microvillous border of the intestinal mucosa. The foals had diarrhea but it was not possible to separate the effects of the cryptosporidial infection from those of the concomitant adenoviral enteritis.
Lewis J, Poland J.The ability of erythromycin in liquid medium to suppress the growth of eight species of acholeplasma and of 13 species of mycoplasma was tested. The Acholeplasma spp and two glycolytic Mycoplasma spp from horses--a slow glucose-metabolising (SGM) mycoplasma and a strain N3, related to M mycoides--were sensitive to erythromycin. Thus the growth of acholeplasmas can be suppressed when attempts are made to isolate pathogens from the porcine respiratory tract, but, in the case of horses, erythromycin would suppress not only Acholeplasma spp but also two Mycoplasma spp of unknown pathogenicity in t...
Dyson DA, Smith GR.When incorporated in solid medium at a concentration of 15 per cent, the defibrinated blood of certain horses strongly suppressed the growth of some, but not all, strains of Mycoplasma mycoides subsp mycoides so that many colonies failed to develop to a visible size. Blood from a single rabbit was tested and found to exert a similar effect. There was striking variation in the degree of inhibition produced by different samples of horse blood and, of five strains of the organism examined, the T1 vaccine strain was the most susceptible. The results suggested that the effect was not due to antibod...
Lee CG, Ross AD.Klossiella equi in the kidney of a horse is described. Gametocytic and sporogonic stages were observed in the epithelium of the collecting tubules in association with schizonts in the glomeruli and proximal convoluted tubules. The condition was asymptomatic and caused only minor renal damage and inflammation.
Dubey JP, Streitel RH, Stromberg PC, Toussant MJ.Hearts, diaphragms, esophagi, and spinal cords from 266 horses were obtained at slaughter in Creston, Ohio. Tissues were examined microscopically for Sarcocystis in sections, digested in trypsin to obtain bradyzoites, and fed to 10 dogs and 10 cats. Intramuscular cysts were found in selections of two hearts from 57 horses and four esophagi from 107 horses. The cysts were up to 900 micron long and up to 70 micron wide. The cyst wall was 1 to 2 micron thick and cross-striated. The enclosed bradyzoites were banana-shaped, 15 to 20 by 20 to 3 micron, and contained several PAS-positive granules. Br...
Magnarelli LA.Blood-engorged Coquillettidia perturbans, Psorophora ferox, Culex, Culiseta, and Aedes mosquitoes were collected principally by sweep net from salt marsh and woodland habitats in Connecticut. Of the 570 mosquitoes tested, precipitin tests identified the origins of 517 blood meals and revealed distinct host feeding patterns. Aedes mosquitoes fed chiefly on mammals; A. abserratus, A. cantator, and A. vexans showed selectivity for cattle and (or) horses. A. cantator also obtained blood from avian hosts and, in some instances, showed mixed passerine-mammal blood meals. These findings increase the ...
Cimprich RE, Rooney JR.Corynebacterium equi is a pathogen associated with respiratory disease in the foal. This paper discusses two cases of Corynebacterium equi infection, one acute and one chronic, in which the major damage was intestinal. Necrosis of Peyer's patches was the only lesion seen in the small intestine of both foals. The foal with acute disease had distinct green-tan focal necrosis and thickened mucosa of the large intestine. In the foal with chronic disease, the mucosa of the large intestine was thickened, rugose, and mottled red-tan. Histologically, the predominant lesions were villous atrophy, mucos...
Perryman LE, McGuire TC, Hilbert BJ.Selective immunoglobulin M deficiency was diagnosed in 5 foals, on the basis of reduced serum immunoglobulin M concentrations (more than 2 standard deviations below the normal mean). All 5 foals had clinical signs or lesions involving the respiratory tract. Lkebsiella sp was isolated from joint fluids, bronchial lymph nodes, or tracheal washings from the 3 foals in which such samples were available for microbiologic evaluation.
The Journal of hygieneDecember 1, 1976
Volume 77, Issue 3 401-408 doi: 10.1017/s0022172400055789
Platt H, Atherton JG, Orskov I.An account is given of K. pneumoniae capsule types occurring in horses, with particular reference to strains originating from the genital tract in the mare and the external genitalia of the stallion. A survey of the prevalence of K. pneumoniae and E. aerogenes strains in the preputial flora of healthy stallions is described. The majority of horses were found to be carriers of these organisms. The cultural characteristics of these preputial strains are described and compared with those of K. pneumoniae strains associated with epidemic metritis in mares. The epidemiological significance of certa...
Morales GA, Wells EA, Angel D.Discovery of two ill horses and three dogs naturally infected with Trypanosoma evansi near an experimental station in the Eastern Plains of Colombia led to a search for reservoir hosts of the parasite. Infection was detected in 8/33 healthy capybaras (Hydrochoerus hydrochaeris), none of the remaining 14 horses, and none of 32 Zebu cattle (Bos indicus), 18 paca (Cuniculus paca) and 20 spiny rats (Proechimys sp.). Contrary to common opinion, the results indicated a carrier state in the capybara. Diagnosis was based on morphology, behaviour in albino rats, and pathogenicity and host range in dome...
Pascoe RR.A survey of 568 horses in training and 2,535 horses on breeding farms has shown 32 percent of the horses in training to be clinically affected while only 1.1 percent of breeding horses were affected with pathogenic dermatophytes. The majority of lesions on racing horses were located on the girth areas. Trichophyton equinum var. autotrophicum, M. canis and M. equinum were found to be restricted to racing horses only. M. gypseum occurred in racing, riding and breeding horses.
Whitwell KE.A rodent pathogen, Bacillus piliformis, has been recognised as causing a rapidly fatal hepatitis in 4 foals in England. The disease in foals has been recognised in America since 1973. A clinico-pathological account of the 4 cases is given and the differential diagnosis discussed. The 4 foals' ages fell within a very narrow range (24-34 days). Some of the properties of this unusual intracellular pathogen are reviewed. For the first time in the equine the bacillus was seen in association with myocardial lesions. There are marked differences in the epidemiology of the disease in the mouse and in ...
Scherer WF, Anderson K, Pancake BA, Dickerman RW, Ordonez JV.Seventy-four strains of Venezuelan encephalitis (VE) virus recovered from sentinel hamsters or mosquitoes at enzootic habitats in Guatemala in the two years following the 1969 epidemic-equine epizootic were examined for ability to produce small plaques in Vero African green monkey kidney cell cultures, like isolates obtained during the epizootic. (a) One strain recovered from a sentinel hamster in late October 1969 at an enzootic habitat near the epicenter of the hemagglutination-inhibition (HI) and equine-virulence properties like epizootic virus; this strain retained its small plaque charact...
Myers DM.Three pathogenic leptosipras and 12 saprophytic Leptospira biflexa strains were isolated from 72 apparently normal horse kidneys collected at an abattoir in Argentina. Cross-agglutination reaction patterns of the pathogens showed that they were antigenically homologous with members of the Hebdomadis group. When one of the strains was compared to Hebdomadis serotypes in reciprocal agglutination-absorption tests, it was found to be serologically homologous to serotype hardjo. This is the first known report of an isolation of this serotype from horses. Serological tests were also carried out on r...
Moorthy AR, Spradbrow PB.Mycoplasmas were isolated from two of 43 nasal swabs taken from live horses, and from one of 28 tracheal swabs taken from slaughtered horses. The slaughtered horse that yielded mycoplasmas had no gross pathological changes in the respiratory tract, but the nasal isolations were made from horses with rhinitis. The three mycoplasmas could be distinguished by cultural characteristics, and probably they represent three different species.
Gürler AT, Bölükbaş CS, Açici M, Umur S.Helminths of equines are one of the most important agents of parasitic diseases. Therefore, many studies have been conducted on helminths of equines in Turkey. In this article, a check list and prevalence rates of helminths of equines in Turkey have been given.
Azzie MA.Contrary to common belief, Gastrodiscus aegyptiacus can be pathogenic to horses. History of cases of a particular stud, necropsy findings, diagnosis, and successful treatment with hexachlorophene and with dichlorvos are recorded. The presence of eggs can be established by a special flotation technique.
Sugita S, Oki H, Hasegawa T, Ishida N.Estimation formulas for the morbidity of horses infected with equine influenza virus by linear regression, logistic regression and probit transformation were developed, using data from the outbreak at the Sha Tin Racing Track in Hong Kong in 1992. Using these formulas, we estimated the equine influenza virus morbidity rates at training centers belonging to the Japan Racing Association (JRA) in October 1997 and in October 1998. In 1998 JRA started a new vaccination program, and every horse must now be vaccinated twice per year. At that time, the vaccine included two US lineage virus strains, th...
Erzinclioglu YZ.The unusual structure of the mouth hooks of the third instar larvae of the species of Gasterophilus and Gyrostigma, parasites of the alimentary canal of Equideae and Rhinocerotidae respectively, is described.
Giguère S, Prescott JF.The remarkable ability of the horse and other animals to prevent infection by most bacterial pathogens encountered is the result of a complex set of distinct but overlapping defense mechanisms. This article summarizes the current state of knowledge on innate and adaptive immunity to bacterial pathogens and reviews various ways in which some bacteria have evolved in order to evade components of the host response.
Moorthy AR, Spradbrow PB.Mycoplasmas were isolated from two of 43 nasal swabs taken from live horses, and from one of 28 tracheal swabs taken from slaughtered horses. The slaughtered horse that yielded mycoplasmas had no gross pathological changes in the respiratory tract, but the nasal isolations were made from horses with rhinitis. The three mycoplasmas could be distinguished by cultural characteristics, and probably they represent three different species.
Divers TJ, Mongodin EF, Miller CB, Belgrave RL, Gardner RB, Fraser CM, Schutzer SE.Antemortem diagnosis of neuroborreliosis in horses has been hindered by both the low sensitivity of PCR testing for in CSF and the low specificity of serum:CSF ELISA ratios used to determine intrathecal antibody production against the bacterium. PCR testing of the CSF of an adult horse with acute neurologic disease for the flagellin gene was negative. However, we enriched DNA through nucleic acid hybrid capture, followed by next-generation sequencing, and identified in the CSF of the horse, confirming a diagnosis of neuroborreliosis.
Gautsch S, Beckmann G, Amtsberg G, Dieckmann M, Deegen E.100 faecal samples from clinically healthy horses of different age groups and feeding habits, 50 samples of faeces from horses suffering from enteropathy accompanied by diarrhoea and small and/or large intestine from 25 horses that had died after an intestinal disease were examined for the presence of Clostridium (Cl.) perfringens. The frequency with which Cl. perfringens was detected was 22% in clinically healthy horses, 32% in horses with diarrhoea and 52% in the dead horses. In two faecal samples from the horses with diarrhoea the microbial count of Cl. perfringens was ca. 10(6) cfu/g faece...
Guida N, Mesplet M, Di Gennaro E, Digilio P, Moras EV.Aspergillus fumigatus is a cosmopolitan opportunistic fungal associated to rhinopharyngitis, sinusitis and guttural pouches infection with nasal discharges. All them are similar with Strangle's sign, the infectious disease produced by Streptococcus equi spp. The aim of this work was to detect A. fumigatus in healthy horses living in boxes and field. 226 nasopharyngeal swabbing samples were obtained by mycological routine. A. fumigatus was isolated in 26 (11.5%) horses.
Lewis J, Poland J.The ability of erythromycin in liquid medium to suppress the growth of eight species of acholeplasma and of 13 species of mycoplasma was tested. The Acholeplasma spp and two glycolytic Mycoplasma spp from horses--a slow glucose-metabolising (SGM) mycoplasma and a strain N3, related to M mycoides--were sensitive to erythromycin. Thus the growth of acholeplasmas can be suppressed when attempts are made to isolate pathogens from the porcine respiratory tract, but, in the case of horses, erythromycin would suppress not only Acholeplasma spp but also two Mycoplasma spp of unknown pathogenicity in t...
Hunyadi L, Papich MG, Pusterla N.The purpose of this study was to determine if a low dose of diclazuril (0.5mg/kg of 1.56% diclazuril pellets) given to six healthy adult horses every 3-4 days for a total of five administrations would achieve steady-state plasma concentrations known to be inhibitory to Sarcocystis neurona and Neospora caninum. Blood was collected via venipuncture immediately before (trough concentrations) and 10h after (peak concentrations) each diclazuril administration and analysed by high-pressure liquid chromatography. The mean population-derived peak concentration was 0.284μg/mL and the mean terminal hal...
Russo AM, Ebermayer SE, Mancebo OA, Monzón CM.The fungus Curvularia verruculosa, which produces eumycotic mycetomas, was isolated from skin of horses with granulomatous lesions on the legs. The isolation was made in Sabouraud dextrose agar medium. The horses came from Comandante Fontana suburb, Formosa-Argentina. This finding would be the first report of Curvularia in horses in Argentina.
Moorthy AR, Spradbrow PB.Mycoplasmas were isolated from two of 43 nasal swabs taken from live horses, and from one of 28 tracheal swabs taken from slaughtered horses. The slaughtered horse that yielded mycoplasmas had no gross pathological changes in the respiratory tract, but the nasal isolations were made from horses with rhinitis. The three mycoplasmas could be distinguished by cultural characteristics, and probably they represent three different species.
Sutcliffe IC, Trigg J, Harrington D.Using preparative electrophoresis, a low molecular weight protein has been partially purified from a cell extract of the equine pathogen Streptococcus equi susp. equi. N-terminal sequence analysis and Western blotting revealed the protein to be HPr, a central component of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). Interestingly, the only form of the HPr protein detected in S. equi was one with the amino-terminal methionine removed, a modification that has previously been associated with surface localization of streptococcal HPr proteins.
Gallen F, Kernaonet E, Foulet A, Goldstein A, Lebon P, Babinet F.Rhodococcus Equi, a strictly aerobic Gram positive coco-bacillus, is a pathogen for horses and foals. It may induce opportunistic infections and is described in AIDS infected patients. We report the case of a 47-year old man, breeder of horses, with kidney transplant who has presented, 8 years after his graft, an impairment of health, a fever and evidence of pulmonary disease. The pulmonary biopsy under scanner guidance and microbiology study, has displayed the diagnosis of Rhodococcus equi infection. The evolution has been favorable with double antibiotherapy (follow-up 27 months). Ten compar...
Bienzle D.This article describes the indications for sampling of bone marrow, the technical aspects of obtaining marrow core biopsies and aspirates, and the preparation of marrow smears. All aspects are illustrated with clinical cases. The information that can be expected from the pathologist's report of marrow samples is outlined, and the clinical features and prognosis of different types of leukemia are detailed.
Causey RC, Paccamonti DL, Todd WJ.A total of 22 clinical streptococcal isolates, predominantly Streptococcus zooepidemicus, associated with endometritis in horses were tested for their ability to withstand the natural bactericidal properties of freshly obtained blood. During a 3-hour incubation in blood from a single horse, 8 of these isolates survived and grew, the remainder were killed. To determine whether this ability to grow extended to blood of other horses, 5 of these growing isolates were tested for their ability to grow in the blood of 5 additional horses. The same 5 horses were used for each isolate. The isolates gre...
Pechacek D, Hwangbo M, Moreland R, Liu M, Ramsey J. 4s is a Gram-negative bacterium found in the equine intestinal ecosystem alongside diverse other coliform bacteria and bacteriophages. This announcement describes the complete genome of the T7-like 4s podophage Penshu1. From its 39,263-bp genome, 54 protein-encoding genes and a 179-bp terminal repeat were predicted.
Pusterla N, Vaala W, Bain FT, Chappell DE, Craig B, Schneider C, Barnett DC, Gaughan E, Papich MG.Equine protozoal myeloencephalitis (EPM) has remained a devastating neurological disease of the Americas, especially in young performance horses. Prophylactic treatment strategies with diclazuril have shown to reduce seroprevalence and titer levels to Sarcocystis neurona in healthy horses continuously exposed to the apicomplexan parasite. The goal of this study was to determine if the FDA-labeled dose of 1 mg/kg of 1.56% diclazuril (Protazil) given once weekly to healthy adult horses would achieve steady-state concentrations in plasma known to be inhibitory to S. neurona in cell culture. Five ...
Hoffman AM, Viel L, Prescott JF.Despite the high incidence of distal respiratory tract infection of undetermined cause on farms, to our knowledge, the microbiologic effects of conventional antimicrobial treatment for this condition have not been studied. We evaluated the possible pathogenic role of bacterial isolates from the distal airways of foals with clinical respiratory tract disease, by correlating changes in their numbers (increase or decrease) with clinical, endoscopic, and pulmonary cytologic signs of disease resolution during treatment with antimicrobial drugs. We also determined qualitative changes in in vitro ant...
Woolcock JB.An atypical variety of Streptococcus equi is described. It was shown to be deficient in capsular material, to be very virulent for mice and to possess a cell-wall protein similar to the M-like protein of classical Str equi. Antiserum prepared against classical Str equi effectively opsonised the atypical strains, and induced the formation of long chains by these atypical strains. It is possible that this variant of Str equi can be used to overcome many of the current problems associated with the manufacture and use of strangles vaccines.
Hain-Saunders N, Knight DR, Bruce M, Riley TV.Recent increases in community-associated Clostridioides difficile infections have highlighted the importance of monitoring toxigenic C. difficile from animal and environmental sources. We provide the complete circularized genomes of two toxigenic C. difficile strains isolated from feral horse faeces. Genome N64 (sequence type 964) consists of a single chromosome of 4,078,791 bp, while genome H251 (sequence type 963) comprises one chromosome (4,304,722 bp) and three plasmids (150,942 bp, 11,534 bp, and 9,074 bp).
Rakaki ME, van der Walt M, Williams J, Venter M.We detected Shuni virus in horses and ovine fetuses and Shamonda virus in a caprine fetus in South Africa. We identified a Shuni/Shamonda virus reassortant in a horse and Shuni/Caimito, Shamonda/Caimito, and Shamonda/Sango virus reassortants in Culicoides midges. Continued genomic surveillance will be needed to detect orthobunyavirus infections in Africa.
Dersch K, Kreuder A, Wang C, Troy J.Surgical site infections (SSI) are a common postoperative complication of equine orthopedic surgery and often increase morbidity and mortality. Objective: This study aimed to determine if covering surgical instruments during surgery decreased bacterial environmental air contamination during early opening of surgical packs (EOSP). The authors hypothesized that covering instruments with sterile surgical towels would reduce the total number of bacterial colonies to which the instruments were exposed. Methods: Blood agar plates (BAP) were allocated into two groups (non-covered vs. covered with a s...
Onishi JC, Park JW, Prado J, Eades SC, Mirza MH, Fugaro MN, Häggblom MM, Reinemeyer CR.Carbohydrate overload models of equine acute laminitis are used to study the development of lameness. It is hypothesized that a diet-induced shift in cecal bacterial communities contributes to the development of the pro-inflammatory state that progresses to laminar failure. It is proposed that vasoactive amines, protease activators and endotoxin, all bacterial derived bioactive metabolites, play a role in disease development. Questions regarding the oral bioavailability of many of the bacterial derived bioactive metabolites remain. This study evaluates the possibility that a carbohydrate-induc...
Hoffman AM, Viel L, Staempfli HR, Muckle CA, Yager JA.One indication for referral of horses to veterinary hospitals is for diagnosis of the microbiologic cause of pneumonia, particularly when the initial treatment fails. Although endoscopic methods have long been available for microbiologic sample collection, accuracy of these methods under these conditions have not been studied in detail. We compared the bacteria isolated from samples obtained by bronchoalveolar lavage (BAL) with those obtained by protected catheter brush (PCB) from foals with unilateral pneumonia induced by inoculation with Klebsiella pneumoniae. As part of previously described...
Scherbarth R, Pózvári M, Heilkenbrinker T, Mumme J.From 1972 to 1991, presecretion on an average of 183 stallions per year had been examined. Facultatively pathogenic germs were ascertained in 13.5% of the samples. However, the portion showed considerable annual fluctuation, as did the percentage of the different kinds of germs. In most of the cases, only minimal growth had been observed in culture. Except for the total percentage, these results are contradictory to those we found during the examination of cervical swabs of mares. In order to ascertain the importance of the respective results and to render possible a correct interpretation, th...
Macpherson ML, Giguère S, Pozor MA, Runcan E, Vickroy TW, Benson SA, Troedsson MHT, Hatzel JN, Larson J, Vanden Berg E, Kelleman AA, Sanchez LC....Eleven pregnant pony mares (D270-326) were administered ceftiofur sodium intramuscularly at 2.2 mg/kg (n = 6) or 4.4 mg/kg (n = 5), once daily. Plasma was obtained prior to ceftiofur administration and at 0.5, 1, 2, 4, 8, 12, and 24 hr after administration. Eight pony mares were re-enrolled in the study at least 3 days from expected foaling to ensure steady-state concentrations of drug at the time of foaling. Mares were administered ceftiofur sodium (4.4 mg/kg, IM) daily until foaling. Parturition was induced using oxytocin 1 hr after ceftiofur sodium administration. Allantoic and am...
González F, Rodríguez C, De Lucas JJ, Waxman S, San Andrés MD, Serres C, Nieto J, San Andrés MI.Six donkeys each received 2 mg/kg marbofloxacin as a 10 per cent aqueous solution administered intravenously. Principal pharmacokinetic parameters were determined and two efficacy indices were computed by using pharmacokinetic parameters and selected mic90 values of marbofloxacin against pathogenic equine strains to predict the efficacy of the drug at this dose. The pharmacokinetics of marbofloxacin in donkeys was characterised by a large mean volume of distribution at a steady state (1.15 [0.09] l/kg) and a long mean (sd) elimination half-life of 9.24 (1.96) hours. It was also characterised b...
