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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.
Structural variation of the distal condyles of the third metacarpal and third metatarsal bones in the horse. This study examined 3-dimensional (3D) distribution of sectors with contrasting density in the equine third metacarpal (McIII) and third metatarsal (MtIII) bones with a view to explaining the aetiology of distal condylar fractures. Macroradiography and computed tomographic (CT) imaging were used in the nondestructive study of bones obtained from horses, most of which were Thoroughbreds in race training. Distal condylar regions of McIII and MtIII were also studied in microradiographs of 100 microm thick mediolateral sections cut perpendicular to the dorsal and palmar/plantar articular surfaces....
Pathology of the distal condyles of the third metacarpal and third metatarsal bones of the horse. This study examined material from Thoroughbred horses, the majority of which had been in race training, for evidence of pathology in the third metacarpal (McIII) and third metatarsal (MtIII) bones which might be related to the occurrence of distal condylar fractures. Whole bone samples were studied and documented by macrophotography prior to macroradiography and computed tomographic (CT) imaging. Microradiographs were made from 100 microm thick mediolateral sections cut perpendicular to the dorsal and palmar/plantar articular surfaces of distal condylar regions of McIII and MtIII. Blocks were ...
Aetiopathogenesis of parasagittal fractures of the distal condyles of the third metacarpal and third metatarsal bones–review of the literature. Fractures are the cause of considerable morbidity and mortality among Thoroughbred racehorses. A significant proportion of these injuries occur in the absence of any particular traumatic incident. Evidence of prefracture pathology interpreted as fatigue damage has been identified in some such cases, but the aetiology of many of these so-called 'spontaneous' fractures remains obscure. Parasagittal fractures of the third metacarpal (McIII) and third metatarsal (MtIII) bones are one of the more common fractures to affect Thoroughbred racehorses. The configuration of each of these fracture types i...
Hyperkalaemic periodic paralysis in homozygous and heterozygous horses: a co-dominant genetic condition. Historical, clinical and experimental data were collected from 9 horses homozygous for HYPP (H/H). All showed episodes of respiratory stertor, described as a rattling or honking sound, usually within the first week post partum. Five horses had one or more episodes of dysphagia, in 3 horses this was accompanied by drooling and in 3 by weight loss. In comparison, only one of 35 contemporaneous half siblings (of which approximately half would be expected to be of the H/N genotype and half N/N) was observed to have respiratory stertor prior to weaning and none had problems with dysphagia. One matu...
[Examination of systemic tumor necrosis factor activity under physiologic and pathophysiologic conditions]. Tumor necrosis factor (TNF) activity in the circulation of several animal species was determined by a bioassay, using the murine cell line L929. In healthy adult cattle, horses, pigs and dogs, species specific differences of systemic TNF activity were visible. In cattle, TNF activity in the circulation increased during growing up from calf to adult animal. In cattle suffering from various diseases, unchanged, elevated, but also reduced systemic TNF activity have proved to possess clinical relevance. Low systemic TNF activity frequently occurs during lethal inflammatory diseases and may be an i...
Fumonsin B1, B2, and B3 content of commercial unprocessed maize imported into South Africa from Argentina and the USA during 1992. The widespread occurrence of F. moniliforme and the toxic effects of its secondary metabolites, the fumonisins B1(FB1), B2(FB2) and B3(FB3), make it imperative that fumonisin contamination of maize, a major constituent of animal feed as well as the staple diet of many populations, be closely monitored to reduce the risk of fumonisin exposure. Equine leukoencephalomalacia and porcine pulmonary oedema have been associated with the intake of feed heavily contaminated with fumonisins. In addition, high levels of fumonisins in the maize-based staple diets of certain populations have been linked to ...
Subconjunctival haemorrhages in neonatal thoroughbred foals. A survey of 169 neonatal thoroughbred foals revealed that 8.3 per cent had subconjunctival haemorrhages, but there was no indication of a relationship between retinal and subconjunctival haemorrhages. The haemorrhages were not related to any abnormality of the foals and there was no sex or eye predisposition. In most cases the haemorrhages were fresh and red, occurred mainly dorsally or dorsonasally and extended up to the limbus; they resolved completely within four to 10 days, depending on their initial severity and extent. They had no effect on the foals' vision in the short or long term. Th...
Determinants of the maximal change in pleural pressure during tidal breathing in COPD-affected horses. In six COPD-affected horses, we analysed the factors responsible for the changes in pleural pressure (delta Pplmax) that occur during tidal breathing. Four-hundred-and-sixty-eight measurements of each parameter: pulmonary resistance (RL), dynamic elastance (Edyn), air flow rates, and the timing of breathing, were gathered during a trial of the bronchodilator pirbuterol. Data were placed into seven ranks, based on the magnitude of delta Pplmax; rank 1: 5-15; rank 2: 15-25; rank 3: 25-35; rank 4: 35-45; rank 5: 45-55; rank 6: 55-65; and rank 7 > 65 cm H2O. Up to rank 4 (45 cm H2O), the increa...
Molecular epidemiological studies of veterinary arboviral encephalitides. Recent studies using molecular genetic approaches have made important contributions to our understanding of the epidemiology of veterinary arboviral encephalitides. Viruses utilizing avian enzootic hosts, such as Western equine encephalitis virus (WEEV) and North American Eastern equine encephalitis virus (EEEV), evolve as relatively few, highly conserved genotypes that extend over wide geographic regions; viruses utilizing mammalian hosts with more limited dispersal evolve within multiple genotypes, each geographically restricted. Similar findings have been reported for Australian alphaviruse...
Comparison of medical and surgical treatment for impaction of the small colon in horses: 84 cases (1986-1996). To characterize clinical findings and compare effects of treatment and outcome for horses treated medically or surgically for impaction of the small colon. Methods: Retrospective study. Methods: 84 horses with impaction of the small colon. Methods: Medical records were reviewed for history, physical examination findings, laboratory values, treatment, response to treatment, complications, out-come, and necropsy findings. Results: 47 horses were treated medically and 37 horses were treated surgically. Significant differences between groups were not identified for duration of clinical signs, phys...
Genetic divergence with emergence of novel phenotypic variants of equine arteritis virus during persistent infection of stallions. The persistently infected carrier stallion is the critical natural reservoir of equine arteritis virus (EAV), as venereal infection of mares frequently occurs after breeding to such stallions. Two Thoroughbred stallions that were infected during the 1984 outbreak of equine viral arteritis in central Kentucky subsequently became long-term EAV carriers. EAV genomes amplified from the semen of these two stallions were compared by sequence analysis of the six 3' open reading frames (ORFs 2 through 7), which encode the four known structural proteins and two uncharacterized glycoproteins. The major ...
Streptococcus equi but not Streptococcus zooepidemicus produces potent mitogenic responses from equine peripheral blood mononuclear cells. Streptococcus equi causes equine strangles. The acute disease has many of the hallmarks of an acute response including high fever, elevated plasma fibrinogen and neutrophilia, affects known to be mediated by proinflammatory cytokines. The objective of this study was to screen-culture supernatants from equine clinical isolates of S. equi and S. zooepidemicus for stimulation of mitogenic responses by horse peripheral blood mononuclear cells. Mitogenicity comparable to that of concanavalin A was detected in culture supernatants of S. equi strains but not in those of S. zooepidemicus. Mitogenicity...
Comparison of the effects of halothane, isoflurane and methoxyflurane on the electroencephalogram of the horse. We have investigated in eight ponies the effects of three different end-tidal concentrations of halothane, isoflurane and methoxyflurane on median (F50) and 95% spectral edge (F95) frequencies of the EEG and the second differential (DD) of the middle latency auditory evoked potential (MLAEP). The three concentrations of each agent were chosen to represent approximately the minimum alveolar concentration (MAC), 1.25 MAC and 1.5 MAC for each agent. During halothane anaesthesia, F95 decreased progressively as halothane concentration increased, from mean 13.9 (SD 2.6) at 0.8% to 11.9 (1.1) at 1.2%...
The gamma2 late glycoprotein K promoter of equine herpesvirus 1 is differentially regulated by the IE and EICP0 proteins. The equine herpesvirus 1 immediate-early (IE) phosphoprotein is essential for the activation of transcription from viral early and late promoters and trans-represses its own promoter. Transient-transfection assays showed that the IE protein trans-represses the gamma2 late gK promoter. Gel shift and DNase I footprinting assays demonstrated that the IE protein binds to the gK promoter sequences from -42 to -26 and from -13 to +12 that overlap the transcription initiation site (+1). These results indicated that the IE protein binds to the transcription initiation site of the gK promoter sequences...
Hepatotoxicity associated with pyrrolizidine alkaloid (Crotalaria spp) ingestion in a horse on Easter Island. Since 1984, a significant number of privately owned and feral horses on Easter Island have died of a syndrome consisting of progressive anorexia, weight loss, obtundation, and other central nervous system abnormalities. A single horse experiencing clinical signs of the reported syndrome was identified, examined and necropsied. Clinical signs included inappetence, emaciation, ataxia and icterus. Gross necropsy findings included hepatic enlargement and mottling, ascites and gastric impaction. Histopathological lesions included hepatic hemorrhage and necrosis, periportal megalocytosis, portal fib...
The circumstances surrounding the outbreak and spread of equine influenza in South Africa. Equine-2 influenza A virus (H3N8) infection first occurred among naïve horses in South Africa in December 1986. The virus was introduced following the importation of six horses from the United States of America. While the release of in-contact horses from quarantine three days after the arrival of these six horses played a role in the rapid spread of the disease in South Africa, other outbreaks of disease were associated with viral introduction by personnel or contaminated instruments. The control measures and implications of the introduction of equine influenza to South Africa are also discu...
[HYPP: hyperkalemic periodic paralysis in the horse]. Hyperkalaemic periodic paralysis(HYPP) is characterized by intermittent episodes of muscular tremor, weakness, and collapse, and is probably caused by abnormal electrolyte transport in the muscle cell membrane. During an episode of HYPP, most animals are severely hyperkalaemic. HYPP is a hereditary disease and occurs only in American Quarter horses or crossbreds. Because these horses are now being imported into the Netherlands, HYPP should be included in the differential diagnosis of horses showing signs of muscle tremor, paresis, or paralysis. The present article reviews the literature on HYP...
Influence of site and age on biochemical characteristics of the collagen network of equine articular cartilage. To determine variations in biochemical characteristics of equine articular cartilage in relation to age and the degree of predisposition for osteochondral disease at a specific site. Methods: Articular cartilage specimens from 53 horses 4 to 30 years old. Methods: Healthy specimens were obtained from 2 locations on the proximal articular surface of the first phalanx that had different disease prevalences (site 1 at the mediodorsal margin and site 2 at the center of the medial cavity). Water, total collagen, and hydroxylysine contents and enzymatic (hydroxylysylpyridinoline [HP]) and nonenzymat...
Evaluation of temporal and spatial clustering of horses with Corynebacterium pseudotuberculosis infection. To determine whether horses with Corynebacterium pseudotuberculosis infections that were examined at a veterinary medical teaching hospital between July 1, 1992, and June 30, 1994 had patterns of temporal or spatial clustering. Methods: 134 case and 800 control horses randomly selected from all non-case horses admitted during the study period. Methods: Admission date and geographic location were determined. Scan, Cuzick & Edwards', and Knox tests were applied to determine whether case horses had patterns of temporal or spatial clustering. Results: For all windows > or = 3 days (134 case...
Bilateral testicular leiomyosarcoma in a stallion. No abstract available
Amylopectinosis in fetal and neonatal Quarter Horses. Three Quarter Horses, a stillborn filly (horse No. 1), a female fetus aborted at approximately 6 months of gestation (horse No. 2), and a 1-month-old colt that had been weak at birth (horse No. 3), had myopathy characterized histologically by large spherical or ovoid inclusions in skeletal and cardiac myofibers. Smaller inclusions were also found in brain and spinal cord and in some cells of all other tissues examined. These inclusions were basophilic, red-purple after staining with periodic acid-Schiff (both before and after digestion with diastase), and moderately dark blue after staining wi...
Infection with equine herpesvirus 1 (EHV-1) strain HVS25A in pregnant mice. The abortigenic effects of equine herpesvirus 1 (EHV-1) strain HVS25A, given intranasally, were assessed in pregnant BALB/c, C57BL/6J and Quakenbush mice at day 16 of pregnancy. All EHV-1-infected BALB/c mice showed clinical signs typical of EHV-1-induced disease, together with evidence of abortion. However, although there were fetal and neonatal deaths in some C57BL/6J and Quakenbush litters, the respiratory and systemic effects of EHV-1 infection in the dams were inconsistent. BALB/c dams were then inoculated at day 15 of pregnancy with either EHV-1 or rabbit kidney (RK) cell lysate (control...
Long terminal repeat sequences of equine infectious anaemia virus are a major determinant of cell tropism. The Wyoming strain of equine infectious anaemia virus (EIAV) is a highly virulent field strain that replicates to high titre in vitro only in primary equine monocyte-derived macrophages. In contrast, Wyoming-derived fibroblast-adapted EIAV strains (Malmquist virus) replicate in primary foetal equine kidney and equine dermis cells as well as in the cell lines FEA and Cf2Th. Wyoming and Malmquist viruses differ extensively both in long terminal repeat (LTR) and envelope region sequences. We have compared the promoter activities of the Wyoming LTR with those of LTRs derived from fibroblast-adapte...
Transmissibility from horses to humans of a novel paramyxovirus, equine morbillivirus (EMV). Determination of potential infectivity of a new paramyxovirus equine morbillivirus (EMV) from horses to humans and humans to humans as a result of two outbreaks in Queensland which involved 23 horses and three humans. Methods: Seroepidemiological testing using neutralizing and immunofluorescing antibodies on people with variable levels of exposure to infected horses and humans. Results: All serological testing on a total of 298 individual contacts was negative. Conclusions: While the three human cases of EMV were probably infected as a result of very close contact with horses, these data sugge...
Increased interleukin-6 activity in the serum of ponies acutely infected with equine infectious anaemia virus. 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...
Studies on equine lipid metabolism. 2. Lipolytic activities of plasma and tissue lipases in large horses and ponies. The enzymatic fundamentals of lipid metabolism of equine have not been thoroughly investigated at this point in time. It is still unclear why ponies in contrast to horses may become hyperlipaemic when coming negative energy balance. In this study, the activities of the triglyceride-cleaving key enzymes of ponies are large bred horses were investigated in order to obtain insight into the aetiology of the syndrome. The objective of the study was to measure the activities of hormone-sensitive lipase (HSL), lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) in ponies and horses in ex ...
Mediators of anaphylaxis but not activated neutrophils augment cholinergic responses of equine small airways. Neutrophilic inflammation in small airways (SA) and bronchospasm mediated via muscarinic receptors are features of chronic obstructive pulmonary disease in horses (COPD). Histamine, serotonin, and leukotrienes (LTs) are reported to be involved in the exacerbation of COPD, and currently, histamine has been shown to increase tension response to electrical field simulation (EFS) in equine SA. We tested the effects of these mediators and the effects of activated neutrophils on the cholinergic responses in SA. Histamine, serotonin, and LTD4 had a synergistic effect on EFS responses and only an addi...
