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Topic:Disease Etiology
Disease etiology in horses refers to the study of the causes and development of diseases within equine populations. It encompasses various factors, including genetic predisposition, environmental influences, infectious agents, and nutritional imbalances, that contribute to the onset and progression of diseases in horses. Understanding disease etiology is essential for identifying risk factors and implementing preventative measures in equine health management. This topic includes research on pathogen-host interactions, the impact of management practices on disease incidence, and the role of genetic and environmental factors in disease susceptibility. This page compiles peer-reviewed research studies and scholarly articles that explore the mechanisms, contributing factors, and implications of disease etiology in horses.
Fatal equine gas gangrene associated with Clostridium septicum in the Brazilian Amazon: clinicopathological and molecular characterization of a 20-case series. Clostridial gas gangrene is an acute necrotizing infection of skeletal muscle characterized by rapid tissue destruction and severe systemic toxemia in horses; however, systematically documented case series from tropical settings remain scarce. Here, we describe a clinicopathological and molecularly confirmed series of 20 fatal equine gas gangrene cases diagnosed in the eastern Brazilian Amazon (Pará State) between 2018 and 2026. Horses presented with abrupt onset of severe lameness, rapidly progressive swelling of a limb or muscle group, and palpable subcutaneous crepitus, frequently followin...
Identification and phylogenetic analysis of Mannheimia haemolytica isolated from nasal samples of horses. The Mannheimia genus, which is part of the upper respiratory tract microbiota, harbours species that have the potential to cause progressive infections, such as haemorrhagic septicaemia and enzootic pneumonia, when the host immune system is suppressed. Among these species, Mannheimia haemolytica is considered the most pathogenic, and horses can be a host for this agent. This study aimed to investigate the occurrence of Mannheimia haemolytica in horses with and without respiratory clinical signs and to assess the potential pathogenic significance of isolates recovered from animals through serot...
Isolation of Moraxella spp. strains in horses. Two species of Moraxella were isolated from swabs obtained from two symptomatic horses suffering from conjunctivitis and rhinitis. The isolates were identified via MALDI-TOF as Moraxella osloensis and Moraxella equi respectively, with a good genus identification and a probable species identification score. The first one was also confirmed by BLAST sequence analysis with a high homology (99%). Antimicrobial susceptibility testing obtained by minimum inhibitory concentration method showed that the two isolates were sensitive to all the tested molecules. The therapeutic protocols applied had an e...
Equine Sarcoid: From BPV-Driven Oncogenesis to Host-Sustained Tumor Persistence. Equine sarcoid is the most common cutaneous neoplasm of equids and represents a distinctive model of virus-associated tumor persistence. Although bovine papillomaviruses, particularly BPV-1 and BPV-2, are recognized as the main etiological agents, viral infection alone does not fully explain the clinical heterogeneity, frequent recurrence, and limited spontaneous regression of these lesions. This review summarizes current evidence on the molecular and cellular mechanisms underlying equine sarcoid pathogenesis, with emphasis on the interaction between BPV infection, host signaling pathways, tum...
Risk Factors for Disease in Military Working Equines. Diseases can impact Military Working Equids (MWEs) readiness and limit days in service. The objectives of this study are to categorize diseases in MWEs and evaluate potential risk factors for disease. Methods: Pathology reports from MWEs from 2005 to 2025 were retrieved from the Joint Pathology Center archives. Disease processes with ≥5 cases were evaluated for potential risk factors, including MWE breed, sex, neuter status, geographic location, and age at sampling. Results: Diagnoses included inflammation (n = 30), neoplasia/proliferation (n = 24), within normal limits (n = 12),...
Rethinking Equine Cystitis: Evidence from Four Atypical Clinical Presentations. In this case series, four equines were diagnosed with cystitis, resulting in divergent clinical outcomes. Three animals achieved complete clinical resolution without recurrence, whereas one required euthanasia due to progressive clinical deterioration. All diagnoses were established through a dual-modality investigative protocol comprising cystoscopic evaluation and histopathological examination of bladder mucosal biopsies. The cohort exhibited considerable etiological heterogeneity. One case was classified as chronic idiopathic cystitis, while another was attributed to an opportunistic bacter...
Oxidative Stress and Immunomarkers in Equine Dermal Melanomatosis: Single-Case Comparison with Healthy Individual. Dermal melanomatosis is a common tumor in grey horses, characterized by cutaneous/subcutaneous lesions with metastatic potential. While clinically well-described, oxidative stress involvement remains poorly understood. This case report compared oxidative stress markers and antioxidant enzymes' activities in total protein extracts from melanomatosis lesions (grey horse) versus healthy control skin (black horse), alongside histopathology and immunohistochemistry, to correlate oxidative imbalance and tumor behavior. Melanomatosis tissue exhibited decreased antioxidant defenses confirmed by catala...
The Transcriptomic and Proteomic Molecular Signatures of Equine Multiple-System Neuropathy (Grass Sickness). Equine grass sickness (EGS or equine dysautonomia) is a predominantly fatal multi-system neuropathy affecting grazing horses, likely caused by a neurotoxic phospholipase A2 (nPLA2) derived from a plant or microorganism. We studied neuronal tissue gene and protein expression patterns in EGS to elucidate the possible mechanisms of neurotoxicity and neurodegeneration. Tissue from the cranial cervical ganglion of eight EGS horses and six controls was examined histologically and used for transcriptomic analysis. These transcriptomic data were compared with previously published EGS-related proteomic...
Morphological investigation of myocardial sleeves with potential relevance to atrial fibrillation in Norwegian-Swedish Coldblooded Trotters. Myocardial sleeves (MSs) are thin layers of cardiac muscle that extend from the atria into the caval and pulmonary veins. They are recognised as important structures in both initiating and maintaining atrial tachycardia, and especially atrial fibrillation (AF), which is the most clinically important cardiac arrhythmia in horses with a reported prevalence of 1.3-2% in Standardbred racehorses. In contrast, the Norwegian-Swedish Coldblooded Trotter (NSCT) has a much lower prevalence of AF despite experiencing similar physical demands. The purpose of this study was to describe the macro-, and micr...
Altered gene expression in the liver and small intestine of horses with equine neuroaxonal dystrophy. Equine neuroaxonal dystrophy/degenerative myeloencephalopathy (eNAD/EDM) is the second most common diagnosis of spinal ataxia in horses in the United States. The disease develops due to a combination of vitamin E deficiency and an unknown genetic risk factor(s), and there currently is no effective treatment. Objective: We performed transcriptomic profiling of the liver and small intestine of horses with and without eNAD/EDM, as both tissues are the main locations for absorption, metabolism, and delivery of vitamin E to the nervous system. Methods: Case-control exploratory study. Methods: Post...
Preliminary Assessment on Pathogenicity of an African Horse Sickness Virus Serotype 1 Strain in Guinea Pigs and Horses. African horse sickness (AHS), a noncontagious insect-borne disease affecting equids, is caused by the African horse sickness virus (AHSV) and is associated with extremely high morbidity and mortality. AHSV has nine distinct serotypes (AHSV-1 to AHSV-9). In a previous study, we characterized the genome and in vitro growth properties of AHSV/C, a cell-adapted derivative of an AHSV-1 strain imported into China 60 years ago, and verified its safety in mice. This study preliminarily explored the pathogenicity of AHSV/C in guinea pigs and horses (its natural host). Six groups of guinea pigs were ino...
MUSCULAR SARCOCYSTIS INFECTIONS IN HORSES IN NORTH AMERICA: ETIOLOGY, CLINICAL DISEASE, PERSONAL PERCEPTION, AND DEPOSITION OF SPECIMENS IN THE SMITHSONIAN MUSEUM. Uncertainty shrouds the number and identity of the species of Sarcocystis infecting horses in the United States. Horses are intermediate hosts for Sarcocystis fayeri, for which the domestic dog is the definitive host. Clinical signs and lesions associated with S. fayeri are not defined. Granulomatous myositis, especially involving the chest and dysphagia, is one of the clinical presentations associated with S. fayeri infections. Whether S. fayeri is the sole species that forms sarcocysts in equine muscles in the United States is not clear. Little is known of the molecular diagnosis of Sarcocys...
Complete genome of Bacillus anthracis strain ter21 from an infected zoo pony in Ternopil, Ukraine, 2021. Using rapid nanopore whole-genome sequencing, we assembled the genome of strain ter21 (5,229,480 bp), a Tsiankovskii-I group isolate cultured from a fatal case in 2021 of a pony from a zoo in Ternopil, Ukraine, identifying virulence plasmid pXO1 that encodes anthrax toxin, and pXO2.
Ulcerative dermatitis, tendinitis, tenosynovitis, and desmitis caused by chronic infection with Serratia odorifera in a racehorse. We investigated a case of severe infection in a racehorse. The horse had developed progressive lameness associated with swelling of the left tarsal region, which progressed to ulcerative dermatitis, tendinitis, tenosynovitis, and desmitis. The plantar side of the superficial digital flexor (SDF) tendon was visible through the skin ulcer, and coalescing nodules were present in the dermis. The horse was euthanized and an autopsy was performed. Grossly, in addition to the changes described above, severe edema of the soft tissues was associated with the ulcer. Microscopically, necrotizing and ulc...
Integrated transcriptomic profiling reveals oncogenic pathways and chimeric transcripts in equine sarcoid lesions with predominant BPV1 detection. Sarcoids are the most common cutaneous tumors in horses, representing up to 90% (35%-90%) of skin neoplasms. Mostly caused by Bovine Papillomavirus (BPVs) infections, sarcoids are highly resistant to therapy and prone to recurring, posing a significant threat to equine health. The aim of this study is to explore molecular pathogenetic mechanisms underlying the development of equine sarcoids, by applying transcriptomic approach. After testing samples for viral DNA, both mRNA and small RNA expression was analyzed via high-throughput Illumina sequencing comparing 12 sarcoids and 12 healthy skin s...
Bacteroides fragilis – an overlooked cause of abortion in the mare? A near late-term pregnant mare developed purulent vaginal discharge, fever and peripheral edema. Preterm foaling was medically induced, and the mare delivered a weak foal that was subsequently euthanized. Necropsy revealed an extensive, severe allantochoroiditis affecting the entire corpus segment. Necrosuppurative choroiditis with multiple colonies of gram-negative bacilli and suppurative bronchioalveolitis was found at histology. Anaerobic culture of the chorion revealed a mixed culture clearly dominated by Bacteroides fragilis. B. fragilis has not previously been associated with abortion in...
A retrospective study of morbidity and mortality in captive Przewalski’s horses (Equus przewalskii) between 1973 and 2021. Przewalski's horses (Equus przewalskii) were declared extinct in the wild in 1996, but reintroduction programmes initiated in 1997 have enabled the re-establishment of free-ranging populations. The maintenance of healthy captive populations remains essential to support these conservation efforts, yet systematic pathological investigations in captive Przewalski's horses are lacking. This study provides the first necropsy-based overview of morbidity and mortality in a captive European population. Pathology reports from 64 horses examined between 1973 and 2021 were reviewed retrospectively. Acros...
Molecular detection of Toxoplasma gondii in an aborted equine fetus and serological evidence of infection in mares enrolled in embryo transfer programs in Brazil. Toxoplasma gondii infection is widely recognized as an important cause of reproductive losses in goats and sheep. However, the impact of this parasitic infection in mares remains poorly investigated, reflecting the neglect of this pathogen in equine production. The present study aimed to conduct a serological survey in 100 mares from farms enrolled in embryo transfer (ET) programs in Northeastern Brazil, report the first molecular detection of T. gondii in the placenta and aborted fetus of a mare in the country, and evaluate potential risk factors associated with infection. Anti-T. gondii IgG ...
Syndrome of High Gamma-Glutamyl Transferase in Racehorses. Horses in racing and race training can develop high gamma-glutamyl transferase (GGT) syndrome (HGS), or increased GGT without overt evidence of primary liver disease. Current evidence points toward overtraining and a response to oxidative stress, but the etiology is incompletely understood. Evidence for an association of HGS with poor performance is mixed. Without a clear understanding of the etiology, the only evidence-based treatment option is rest or reduced training intensity. More research is needed to determine whether HGS is a physiologic adaptation, perhaps indicative of overtraining b...
Molecular and parasitological evidence of Leishmania (Mundinia) martiniquensis infection in a horse from Brazil. Leishmania (Mundinia) martiniquensis is an emerging human pathogen with increasing reports of infection in domestic animals. This study describes a naturally infected mare from Brazil with no history of international travel, presenting with persistent nodular cutaneous lesions and cervical lymph node enlargement, without evidence of systemic involvement. Considering the endemicity of cutaneous and visceral leishmaniasis in the study area, as well as previous reports of equine leishmaniasis, infection by Leishmania (Leishmania) infantum was initially suspected. Anti-L. (L.) infantum antibodies ...
Viral Hepatitis. Since 2012, 2 viral causes of hepatitis have been identified in horses. Much remains to be discovered about their transmission, risk factors for clinical disease, diagnosis, and treatment approaches. Equine parvovirus-hepatitis has been identified as the cause of acute hepatic necrosis, previously known as Theiler's disease. Equine hepacivirus is recognized as a cause of chronic fibrosing hepatitis. Diagnosis relies on ruling out other causes of hepatitis and documenting infection by serum or liver polymerase chain reaction. There is no direct antiviral for either condition and treatments are ...
Pathology of sudden death in racehorses: a review. Sudden death (SD) is the second most important syndrome associated with death in racehorses. The cause of SD in a large number of horses remains undetermined, and, in many of these cases, causes are not found by gross or microscopic postmortem examinations. Among the known causes of SD are traumatic injuries, including fractures of skull, neck, and pelvis; intoxications (e.g., anticoagulant rodenticides); and others. For many cases of SD in which no significant lesions are found, heart failure, probably associated with arrhythmias, is suspected. Precise phenotypic characterization of SD in hor...
Genomics in Equine MEED: Whole-Genome Sequencing and Target Mutation Identification. Multisystemic eosinophilic epitheliotropic disease (MEED) is a rare and severe equine disorder characterized by chronic eosinophilic inflammation, epithelial disruption, and multi-organ involvement, with an undefined genetic basis. We performed the high-depth (~40×) whole-genome sequencing of an affected horse and compared it to 40 control genomes. Over 6.3 million variants were identified, with moderate- and high-impact variants enriched in low-frequency categories, including rare and private variants absent from the controls. The affected horse was dominated by missense mutations, with rela...
An intronic variant in Ferredoxin Reductase (FDXR) creates a cryptic exon in Quarter Horses with Equine Juvenile Spinocerebellar Ataxia. Equine Juvenile Spinocerebellar Ataxia (EJSCA) is a novel autosomal recessive neurologic disease in Quarter Horses. Affected foals display a progressive proprioceptive ataxia by 1-5 weeks of age, leading to recumbency and necessitating euthanasia. Whole genome sequencing was performed on 7 EJSCA cases and unaffected horses that included 4 obligate carriers, 4 unaffected half or full-siblings, and 28 unrelated, unaffected control Quarter Horses. An 82 kb region of association was identified (EquCab3.0, chr11: 6963986-7045999), containing 9 candidate SNPs across four genes (FADS6, FDXR, GRIN2C a...
Heavy metals in horses: A review of the toxicity, clinical consequences and expected safe tissue concentrations. Trace elements arsenic, cadmium, lead, chromium, mercury, nickel, and zinc are high-density, naturally occurring metals notable for their toxicity and environmental persistence. Cadmium and mercury are particularly concerning due to their capacity for bioaccumulation and biomagnification within the food chain. Dispersed through both anthropogenic and natural sources, these elements pose significant threats to ecosystems and animal health. In equines, they induce oxidative stress by disrupting mitochondrial function, generating reactive oxygen species, and inhibiting antioxidant enzymes, leadin...
Additional Evidence Fails to Associate Variation in KCNE4 With Equine Anhidrosis. A prior genome-wide association (GWA; N = 200) including Thoroughbreds and stock horses implicated chromosome 6 (NC_009149.3) in owner-reported equine anhidrosis. A missense variant in KCNE4 (NC_009149.3:g.11813731A>G) was proposed as a risk allele, although its association with anhidrosis was not reported. Variant annotation and protein modelling in the original study suggested the G allele conferred risk. We reported no association of the G allele with anhidrosis in 50 horses phenotyped by an intradermal terbutaline sweat test (ITST); all horses produced sweat regardless of genotype. ...
Nucleolar proteins nucleolin and nucleophosmin 1 differentially relocalize during equid alphaherpesvirus 1 (EHV1) infection. We investigated equine nucleolar proteins nucleophosmin 1 (NPM1) and nucleolin (NCL) during EHV1 infection to develop understanding of EHV1-nucleolar interactions. Equine NPM1 primarily localized throughout nucleoli whereas NCL accumulated in a peri-nucleolar ring and localized throughout the nucleoplasm. EHV1 did not notably affect NPM1 or NCL protein levels but did alter their subnuclear localization. NPM1 accumulated in EHV1 replication compartments and remained nucleolus-associated until very late infection stages, characterized by a kidney bean-shaped nucleus and round cell morphology. NC...
Septic Endophthalmitis Following Suprachoroidal Cyclosporine Implant Placement in Two Horses With Equine Recurrent Uveitis. This article presents the clinical and histopathological findings from two horses that developed severe postoperative complications following suprachoroidal procedures routinely employed in the management of equine recurrent uveitis (ERU). Case 1 was a 5-year-old warmblood stallion that initially received a unilateral suprachoroidal triamcinolone injection, followed later by bilateral suprachoroidal cyclosporine implant (CSI) placement. At 9 weeks postoperatively, the right eye (which had undergone both procedures) developed secondary glaucoma necessitating enucleation. Case 2 was a 14-year-ol...
Small Genome-wide association study of insect bite hypersensitivity in Hucul horses. Insect bite hypersensitivity (IBH) is a prevalent allergic skin disease in horses that significantly affects animal welfare and shows evidence of genetic predisposition. Objective: Understanding the genetic basis of IBH can improve management and breeding strategies. The Equine80K BeadChip microarray was used to identify genomic regions associated with the occurrence of IBH in Hucul horses. Methods: Hair samples were collected from 127 Hucul horses, including both affected individuals and controls. DNA was extracted and genotyped. A genome-wide association study (GWAS) was performed to identif...
