Pathogenesis in horses refers to the biological mechanisms that lead to the development and progression of diseases within equine species. This process involves a complex interaction between the horse's immune system, genetic predispositions, environmental factors, and infectious agents such as bacteria, viruses, or parasites. Understanding pathogenesis is essential for identifying how diseases manifest and progress in horses, which can inform diagnostic and therapeutic strategies. Research in this area often focuses on specific diseases, examining factors such as pathogen entry, immune response, tissue damage, and recovery processes. This page compiles peer-reviewed research studies and scholarly articles that explore the mechanisms, contributing factors, and implications of pathogenesis in equine health.
Swerczek TW.Four experiments were performed to elucidate the pathogenesis of toxicoinfectious botulism in horses and foals. Groups of horses and foals were inoculated with one of the following: (1) crude toxin of Clostridium botulinum, type B, given IV, (2) C botulinum spores, given IM, (3) C botulinum spores, given IM, in necrotic lesions, and (4) C botulinum spores, given orally with and without dexamethasone. Toxin of C botulinum in minute amounts is toxic to horses. Clostridium botulinum spores produced toxicosis only when necrotic lesions were present. When C botulinum spores were given orally, they ...
Barclay WP, White KK, Williams A.Nineteen cases of villonodular synovitis as identified in 14 horses are presented. Physical and radiographic findings are discussed and the surgical correction described. Case histories indicate that surgical extirpation of the lesion is corrective and that rest without surgical intervention is ineffective. Radiation therapy following surgery does not appear to be necessary.
Keeler RF, Balls LD, Shupe JL, Crowe MW.Cows, ewes, and mares varied considerably in susceptibility to toxicoses from the oral administration of the piperidine alkaloid, coniine. Cows were most susceptible and ewes least. Only calves had teratogenic effects from maternal administration of coniine during gestation; lambs and foals were apparently resistant. Results suggest that the marked differences between cattle and sheep are probably not due to variation in gut absorption or rumen metabolism.
van Nie CJ, van der Kamp JS.A case of tricuspid atresia in a premature foal associated with large atrial septal and ventricular septal defects is reported. This anomaly is compared with other cases in horses as reported in the literature. As tricuspid atresia in horses is usually not diagnosed so that relatively few cases have been reported, a classification similar to that of human anomalies is not possible. It is suggested that the present malformation is due to abnormal development of the atrioventricular canal. The factors involved in the pathogenesis of this abnormal development are obscure.
Roumillat LF, Feorino PM, Lukert PD.Infection of a human lymphoblastoid cell line (Jijoye line derived from a Burkitt lymphoma which contains Epstein-Barr virus) with equine herpesvirus 1, maintained and observed for 53 days, was characterized by the continuous production of infectious extracellular and intracellular virus. Maximum virus production correlated with active cell multiplication. Less than 15% of the cells possessed viral capsid antigen at any one time. Five percent of the cells in the Jijoye line possess Epstein-Barr viral capsid antigen; 80% of the Epstein-Barr viral caspid-containing cells also contained equine he...
Clayton HM, Duncan JL.Following infection with 8000 Parascaris equorum eggs in two- to four-week-old foals reared under worm-free conditions a high percentage of the infective dose completed its tissue migration and returned to the small intestine. Patent infections were establisehd between 81 and 104 days after infection and high faecal egg counts were recorded. A group of six- to 12-month-old foals, which had been either reared under worm-free conditions or exposed to natural ascarid and strongyle infections on pasture, received a similar infection of 8000 P equorum eggs. Compared with the younger foals there was...
Jackson DS.This paper reviews some of the biochemical modifications involved in fibrous tissue formation and discusses possible ways of controlling fibrosis in clinical conditions. The lathyritic agents, beta-aminoproprionitrile (BAPN) and penicillamine, appear in certain situations to be able to control fibrosis by blocking the biosynthesis of collagen. There are no compounds that are yet known which are capable of reversing pre-existing fibrosis and future research may perhaps be more profitably directed towards the stimulation of collagen catabolism rather than the inhibition of its synthesis.
Slauson DO, Lewis RM.Glomerulonephritis constitutes an important category of renal diseases in animals and has been recognized with increasing frequency in the last decade. We report here the comparative morphologic aspects of glomerulonephritis as a naturally occurring disease of animals. We briefly review the immunopathogenesis of glomerulonephritis. The morphology of renal lesions occurring in glomerulonephritis in dogs, cats, cattle, sheep, horses and swine has been reviewed with emphasis on the range and specificity of various glomerular lesions and on the comparison of lesions between various species. A dist...
Klevjer-Anderson P, Cheevers WP, Crawford TB.Equine dermal fibroblasts persistently infected with equine infectious anemia virus (EIAV) show no alterations in cell morphology or growth kinetics when compared to uninfected cells. The percentage of cells immunofluorescent positive for viral proteins fluctuated, depending upon the stage of the cell cycle, while production of extracellular virus was uniform throughout the cell cycle, increasing only as the cell number increased. This was shown in log versus stationary phase cultures as well as in cultures synchronized by sterum starvation. The establishment of productive infection did not re...
Lancaster WD, Theilen GH, Olson C.DNAs from bovine papilloma virus(BPV)-induced hamster tumors and from equine connective tissue tumors of unknown etiology were examined for BPV DNA sequences by molecular hybridization. DNA from two distinct classes of BPV (type 1 and type 2) was labeled in vitro and used as probes. Analysis of DNA-DNA reassociation kinetics indicated that both virus types were capable of tumor induction in the hamster. DNA isolated from 6 of 7 equine tumors accelerated the reassociation of the BPV DNA probes. BPV type 1 or type 2 DNA hybridized extensively to DNA from 3 tumors, while 3 other tumors contained ...
Bennett D.The gross and histological features of multiple bone infection in two foals are described. In both cases the lesions were confined to the region of the growth plate. Bone and, in some cases, growth plate cartilage destruction has occurred associated with an extensive inflammatory cell infiltration. The significance of the pathological observation is discussed in relation to the pathogenesis of bone infection in the foal.
Srihakim S, Swerczek TW.Parasite-free pony foals (n = 10) were infected orally with 1000,000 Parascaris equorum embryonated eggs. One pony foal each was euthanatized on days 1, 3, 5, 7, 11, 16, 23, 27, 42, or 80 after infection. Foals infected for more than 7 days showed signs of coughing, anorexia, rough coat, and weight loss. Cellular changes in the blood were mild anemia, marked eosinophilia, and leukopenia. Gross postmortem lesions included hemorrhage, edema, and white-to-yellow necrotic foci (0.5 to 1.00 mm) in lungs, liver, and bronchial and hepatic lymph nodes. Microscopically, the liver was hemorrhagic and ha...
Kiryu K, Kaneko M, Satoh H.Histopathololgical observations were performed on the heart and cardiac nervous system of 5 horses affected with wandering pacemaker. The histopathological lesions common to all the animals were as follows: (1) Focal fibrosis in the atrial myocardium just beneath the subendocardium and/or in the endo- and subendocardium, and existence of atrial Purkinje-like fibers within the fibrotic lesions, (2) Microvascular altetation, characterized by edematous-loosening and/or fibrous swelling of the walls of the small and minute arteries, in both the atria, (3) Edema in the intracadiac nerves of both th...
Davies ME.A detailed study was made of 194 equine strains of E. coli, involving biochemical and serological characters. In these, the equine strains closely resembled E. coli from other sources, and shared antigenic characters with strains isolated from different animal species.
Morris CM, Field HJ.Tissue specimens obtained from equine herpesvirus-1 (EHV-1), subtype 1-infected aborted foetuses were analysed for the presence of virus DNA by means of Southern blot and dot blot hybridisations. The specificity of the methods was confirmed although the sensitivity was inferior to classical techniques such as virus isolation. However, the possibility of detecting the state of the virus DNA and the ability to distinguish between subtypes were important features, and the dot blot method was shown to have potential for a rapid diagnostic test. This report demonstrates some potential practical app...
Ramzan PH, Palmer L, Barquero N, Newton JR.There are few published data to support the ages of emergence of permanent dentition widely reported in horses. Objective: To clarify the chronology and sequence of permanent premolar (PM) tooth emergence in Thoroughbred racehorses. Methods: A prospective study was undertaken in which records were kept of deciduous PM 'cap' extractions performed during routine dental examinations in Thoroughbred racehorses. Mixed effects multiple regression analysis was used to relate the observed ages, measured in days, for PM 'cap' extractions simultaneously with different predictive variables. Care was take...
Bennett D.The gross and histological features of multiple bone infection in two foals are described. In both cases the lesions were confined to the region of the growth plate. Bone and, in some cases, growth plate cartilage destruction has occurred associated with an extensive inflammatory cell infiltration. The significance of the pathological observation is discussed in relation to the pathogenesis of bone infection in the foal.
The importance of the horse industry to the economy of the United States and the impact of parasitic infections on the industry are well documented. However, contemporary research activity on internal parasites of horses has not kept pace with growth of the horse population. Parasitic infections are a major facet of enteritis and colic in horses. Parasites are also associated with poor growth and development, respiratory tract disease, dermatitis, and CNS lesions. Babesia infections remain a threat to horses imported from some regions of the world. Most research activity has dealt with the dev...
Ambrose NC, Mijinyawa MS, Hermoso de Mendoza J.Dermatophilus congolensis is a filamentous branching actinomycete that causes dermatophilosis, an exudative dermatitis in ruminants. The pathogenesis of this disease is poorly understood and virulence factors of D. congolensis have not been characterised. Culture filtrate (CF) of 14 D. congolensis isolates from cattle, 15 from sheep and four from horses were examined for proteolytic activity using azocasein as a non-specific substrate. The isolates were from a variety of geographical locations. All the isolates examined produced extracellular proteolytic activity. CF from 24 and 48 h cultures ...
de Laat MA, Spence RJ, Sillence MN, Pollitt CC.Equine laminitis is a disease of the digital epidermal lamellae typified by epidermal cell proliferation and structural collapse. Most commonly the disease is caused by hyperinsulinemia, although the pathogenesis is incompletely understood. Insulin can activate the epidermal growth factor (EGF) system in other species and the present study tested the hypothesis that upregulation of EGF receptor (EGFR) signalling is a key factor in laminitis pathophysiology. First, we examined lamellar tissue from healthy Standardbred horses and those with induced hyperinsulinemia and laminitis for EGFR distrib...
Cook CP, Scott DW, Erb HN, Miller WH.A retrospective study using light microscopy was performed to assess the prevalence of surface and follicular bacteria and fungi in skin biopsy specimens from 247 horses with inflammatory dermatoses and from 27 horses with healthy skin. Cocci were found on the surface of specimens from 23% (95% confidence interval 18%, 29%) and 7% (95% confidence interval, 0%, 19%), respectively, of horses with skin disease and horses with healthy skin. Of the nine dermatoses with at least 10 cases in our series of horses, bacterial folliculitis had a higher prevalence of surface bacteria (57%; 95% confidence ...
Lopes MA, Salter CE, Vandenplas ML, Berghaus R, Hurley DJ, Moore JN.To investigate the effect of ex vivo exposure to lipopolysaccharide (LPS) on the expression of inflammatory genes in leukocytes from horses with gastrointestinal (Gl) disease and determine whether the pattern or magnitude of the response to LPS correlated with the type of disease and outcome. Methods: 49 horses with Gl disease and 10 healthy horses Methods: Leukocytes were isolated from blood samples and submitted to 3 protocols: immediate freezing, freezing after 4-hour incubation in medium, and freezing after 4-hour incubation in medium containing LPS. Expression of 14 genes associated with ...
Janicke H, Taylor PM, Bryant CE.Equine endotoxaemia is an important cause of morbidity and mortality in horses caused by the interaction of bacterial lipopolysaccharide (LPS) with cells such as macrophages and vascular smooth muscle. In this study we isolated equine vascular smooth muscle from a variety of vessels and stimulated it with LPS and human interferon (hIFN)-gamma. Using reverse transcriptase polymerase chain reaction (rt-PCR) and Western blot analysis we show that cyclooxygenase-2 (COX-2) is readily expressed in equine vascular smooth muscle. Vascular smooth muscle cells produced prostaglandin E2 in response to LP...
Rickards KJ, Page CP, Hamblin AS, Goode NT, Cunningham FM.Lymphocytes play an important role in allergic inflammation and have been implicated in the pathogenesis of equine allergic skin and respiratory disease. Targeting intracellular signalling pathways in human lymphocytes has demonstrated a role for both phosphodiesterase and protein kinase C in cell activation. The aim of this study was to measure total cyclic nucleotide hydrolysing phosphodiesterase activity and to identify the phosphodiesterase and protein kinase C isoenzymes present in equine lymphocytes. The functional significance of these isoenzymes was then investigated by examining their...
Sellon DC, Russell KE, Monroe VL, Walker KM.Seven ponies were infected with the virulent wild-type Wyoming strain of equine infectious anaemia virus (EIAV). Infection status was monitored by serum reverse transcriptase activity, rectal temperature, and complete blood count. Preinfection serum and serum obtained during the initial febrile episode following infection were assayed for interleukin 6 (IL-6) activity. Postinfection IL-6 activity was significantly increased as compared to preinfection values. The magnitude of increase in IL-6 was positively correlated with reverse transcriptase activity (an indirect measure of viraemia) but wa...
Wong SS, Ngan AH, Riggs CM, Teng JL, Choi GK, Poon RW, Hui JJ, Low FJ, Luk A, Yuen KY.The newly described brittle tail syndrome causes weakening and breakage of the tail hair of horses. Extensive mycological and molecular studies showed that a novel fungus Equicapillimyces hongkongensis gen. nov., sp. nov. is the most likely cause of this syndrome. It is a septate branching hyaline mould which grows optimally at 30°C, requires nicotinic acid but is inhibited by cycloheximide, and specifically infects horse hair. Hyphae fill the core of infected hair shafts with short-necked structures resembling ascomata containing banana-shaped septate ascospore-like structures perforating th...
Anthauer K, Mülling C, Budras KD.This study aimed to carry out a comprehensive morphological examination of the structure and ultrastructure of the membrane-coating granules (MCG) and membrane-coating material (MCM) common to all hoof segments as well as segment-specific features in the MCG and MCM regarding their synthesis, structure and biochemical composition. Tissue samples from the hooves of the left front and right hind limb of 20 adult riding horses were used. Samples were preserved and embedded for histological routine methods as well as for histochemical techniques and tracer techniques for light and electron microsc...
Liu Q, Yu YY, Wang HY.Increasing evidence suggests that DNA methylation has key roles in the replication of retroviruses, including lentiviruses, and pathogenesis of diseases. However, the precise characteristics of CpG islands are not known for many retroviruses. In this study, we compared the distribution of CpG islands among strains of equine infectious anemia virus (EIAV), a lentivirus in the family Retroviridae and a model for HIV research. We identified CpG islands in 32 full-length EIAV genomic sequences obtained from the GenBank database using MethPrimer. Only one CpG island, from 100 to 120 bp, was identi...
Costa LR, Santos IK, Issel CJ, Montelaro RC.Cardinal features of equine infectious anemia (EIA) include fever, hemolytic anemia and thrombocytopenia during the acute phase of the disease, and cachexia and anemia seen during the chronic phase. These signs are thought to result from the release of inflammatory cytokines such as TNF-alpha. In order to determine if TNF-alpha has a role in the pathogenesis of acute EIA and vaccine-induced disease enhancement, we measured plasma concentrations of TNF-alpha in ponies immunized with virus enriched major core protein-p26 and/or experimentally infected with EIAV. Naturally infected inapparent EIA...
Clyne MJ.Proteoglycan degradation is central to the development of degenerative joint disease. Proteoglycans may be degraded by lysosomal enzymes from chondrocytes, synoviocytes or leucocytes. Collagen and matrix degradation occurs either by direct damage or due to degrading enzymes released into synovial fluid. Once the pathological sequence has begun it continues in a cyclic manner unless arrested by the ability of chondrocytes to synthesise sufficient matrix components. Treatment should ideally be directed to this end.
Apprich V, Spergser J, Rosengarten R, Stanek C.The effects of two dermatophytes (Microsporum gypseum and Trichophyton mentagrophytes) and four moulds (Scopulariopsis brevicaulis, Alternaria alternata, Geotrichum candidum and Penicillium spp.) on living keratinocyte cultures were examined in vitro using primary human keratinocytes. Rates of apoptosis of infected cells were determined using a colorimetric TUNEL system which detects the characteristic nuclear DNA fragmentation of apoptotic cells. The cytotoxicity of the individual fungi was tested by quantitatively measuring cytosolic enzyme lactate dehydrogenase, released upon cell lysis, in...
Timoney JF.An R antigen of the group C streptococcus S. equi that cross reacts with a similar antigen of S. zooepidemicus has been identified and characterized. It is acid, heat and trypsin resistant, but pepsin sensitive and has an isoelectric point of 4.8. The amino acids in highest concentration are glutamic, aspartic, alanine, leucine, and valine. Bacterial components released in a French Press contain large amounts of R antigen, which is present also in culture supernatants and acid extracts. It has a molecular weight of about 82,000. Trypsin extraction of cells yields molecules of predominantly 56,...
Sanclemente JL, Rivera-Velez SM, Horohov DW, Dasgupta N, Sanz MG.Foals that develop pulmonary ultrasonographic lesions on Rhodococcus equi (R. equi) endemic farms are treated with antibiotics because those at risk of developing clinical pneumonia (~20%) cannot be recognised early. Candidate biomarkers identified using metabolomics may aid targeted treatment strategies against R. equi. Objective: (1) To describe how foal ageing affects their plasma metabolome (birth to 8 weeks) and (2) to establish the effects that experimental infection with Rhodococcus equi (R. equi) has on foal metabolome. Methods: Experimental study. Methods: Nine healthy newborn foals...
Popović N, Djuricić B, Valcić M.A study of literature concerning Lyme borreliosis related to animals was done. In the research work the epidemiology, pathogenesis, diagnosis and treatment of horses, cattle and dogs affected with Lyme borreliosis have been discussed. The clinical signs of Lyme borreliosis in horses are: chronic weight loss, sporadic lameness, laminitis, low grade fever, swollen joints, muscle tenderness and anterior uvetitis. In addition to these clinical sings, neurological sings such as depression, behavioral changes, dysphagia and encephalitis can be seen in chronic cases. Cattle affected with acute Lyme b...
Grünig G, Von Fellenberg R, Maier R, Corboz L.Seventeen out of 21 horses had pulmonary microbial organisms which reached considerable numbers in seven cases. Elastase-producing microorganisms from the environment (Streptomyces species and to a lesser extent Bacillus species) constituted 22 per cent to 99 per cent (mean 79 per cent) of the total growth. There was a considerable number of microorganisms with in vitro-produced elastases which were not or only slightly affected by horse serum. There was no correlation between numbers of organisms and pulmonary histopathological findings thus the significance of these microorganisms in the pat...
Newton-Clarke MJ, Divers TJ, Valentine BA.A study was conducted over a 12 month period to assess the accuracy of the 'slap test' in the diagnosis of laryngeal adductor myopathy. The thoraco-laryngeal reflexes of 15 horses with no clinical signs of idiopathic laryngeal hemiplegia (ILH) were recorded using a video-endoscope. These 'slap test' responses were examined independently by 3 assessors. The horses were subsequently subjected to euthanasia and samples taken from the cricoarytenoideus lateralis (CAL) muscles for histopathological examination and assessment of denervation atrophy. Despite normal adductory responses, moderate to se...
Steward KF, Harrison T, Robinson C, Slater J, Maskell DJ, Harris SR, Holden MTG, Waller AS.Opportunistic pathogens must adapt to and survive in a wide range of complex ecosystems. Streptococcus zooepidemicus is an opportunistic pathogen of horses and many other animals, including humans. The assembly of different surface architecture phenotypes from one genotype is likely to be crucial to the successful exploitation of such an opportunistic lifestyle. Construction of a series of mutants revealed that a serine recombinase, PinR, inverts 114 bp of the promoter of SZO_08560, which is bordered by GTAGACTTTA and TAAAGTCTAC inverted repeats. Inversion acts as a switch, controlling the tra...
Tennent-Brown BS, Morrice AV, Reed S.Neonatal encephalopathy is the most common neurologic condition affecting newborn foals and shares similarities with perinatal asphyxia syndrome of human infants. In many cases of neonatal encephalopathy there is no obvious episode of acute or chronic hypoxia and other mechanisms likely play a role in the pathogenesis. Increased concentrations of neuroactive progestagens are found in affected foals; whether these molecules are protective, as has been suggested, or play a role in the pathogenesis is unknown. Neurologic diseases other than neonatal encephalopathy affect foals occasionally and sh...
Winder NC, von Fellenberg R.Pulmonary parenchymal tissues from 6 healthy horses and from 9 horses with chronic bronchiolitis were evaluated by use of an indirect immunofluorescent technique. In horses of both groups, the diffuse interstitial immunofluorescence was most intense for immunoglobulin (Ig)G, moderate for IgA, and minimal for IgM. Intensity of fluorescence was increased markedly in diseased lungs exposed to anti-IgA and anti-IgG. Around small bronchi and large bronchioles of healthy horses, IgA-containing cells generally were more numerous than were IgG-Fc fragment (Fc)-containing cells; in small bronchioles, h...
Miszczak F, Pronost S, Vabret A.Equine arteritis virus (EAV) is the causative agent of equine viral arteritis, a disease observed only in equids. EAV is the prototype of the family Arteriviridæ within the order Nidovirales. EAV is an enveloped, positive-sense, single-stranded RNA virus with a considerable variation in the genome as observed in other RNA viruses. During natural infections, EAV may cause abortion and persistent subclinical infections in stallions which can shed the virus in the semen for years, or even lifetime. Chronically infected stallions represent the natural reservoir of the virus. They ensure the persi...
Geburek F, Deegen E, Hewicker-Trautwein M, Ohnesorge B.Verrucous pastern dermatitis is a chronic hyperplastic dermatopathy of the feet of horses which is characterized by a greasy, odorous coating of the skin and, in advanced stages, by clearly demarcated calluses and wart-like proliferations. The disease occurs almost exclusively in cold-blooded and other heavy horses, with certain breeds affected most frequently. It is considered a distinct disease entity within the framework of pastern dermatitis syndrome. There is no consensus in the literature about relationship of the disease to the sex and age of the horse. Horses with a high cannon circumf...
Leathwick DM, Sauermann CW, Donecker JM, Nielsen MK.Literature documenting the growth and development of Parascaris spp. infections was used to develop a model describing worm dynamics in the young horse. The model incorporates four main variables; the rate at which larvae migrate through host tissues to return to the small intestine, the proportion of migrating larvae which succeed in returning to the small intestine, the rate of growth in size of maturing and adult worms and the survival rate of maturing and adult worms. In addition, the number of eggs laid each day by adult female worms is calculated as a function of worm size (length) and i...
Oikawa M, Masawa N, Yoshikawa H.To test the hypothesis that mesenteric arterionecrosis (MA) occurs in horses with naturally occurring endotoxaemia (ET) and in those with experimentally induced ET, the mesentery and gastrointestinal tract of 21 Thoroughbred racehorses (15 with spontaneous colic suspected to be due to ET, and six with experimentally induced ET) were examined. MA, which occurred in 13 of the 15 horses with spontaneous colic and in all six of the cases of experimental ET, was morphologically similar in the two groups of animals. This suggested that the pathogenesis of the MA was fundamentally similar in the two ...
Clarke LL, Garner HE, Hatfield D.Acute laminitis-hypertension was produced by carbohydrate overloading of the gastrointestinal tract in 12 adult horses. Obel grade 3 (OG3) lameness developed 40 hours (+/- 3.5, SEM) after overfeeding. At OG3 lameness, mean plasma volume was significantly decreased (P less than 0.005) when compared with base-line values. Before OG3 lameness, transient decreases in serum phosphorus and calcium were recorded. Mild hyponatremia also developed before OG3 lameness and persisted. After establishment of OG3 lameness, persistent hypokalemia and increased plasma aldosterone concentration occurred coinci...
