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Topic:Disease Outbreaks
Disease outbreaks in horses refer to the occurrence and spread of infectious diseases within equine populations. These outbreaks can be caused by various pathogens, including bacteria, viruses, and parasites, and can lead to significant health issues in affected horses. Common diseases that may result in outbreaks include equine influenza, equine herpesvirus, strangles, and equine infectious anemia. The transmission of these diseases can occur through direct contact, environmental exposure, or vectors such as insects. Disease outbreaks can have substantial impacts on horse health, welfare, and the equine industry as a whole. This page compiles peer-reviewed research studies and scholarly articles that explore the epidemiology, transmission dynamics, and management strategies associated with disease outbreaks in equine populations.
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...
Phylogenetic and phylogeographic analysis of equine influenza in Colombia. In 2022, Colombia experienced an outbreak of equine influenza (EI) that primarily affected competition horses. Despite the epidemiological relevance of equine influenza virus (EIV) in the country, no previous phylogenetic or phylogeographic analyses based on complete genomes have been reported. Objective: To perform phylogenetic and phylogeographic analyses of complete EIV genomes obtained from horses with clinical signs in two Colombian regions between 2020 and 2023. Methods: Molecular epidemiological study based on whole-genome sequencing and evolutionary analyses. Methods: Nasopharyngeal sa...
Factors associated with equine influenza during the 2025 outbreak in a draft horse population at the Obihiro Racecourse, Japan. In April 2025, equine influenza re-emerged in Japan for the first time in 17 years, resulting in an outbreak at a horse racecourse for Ban'ei racing, a unique form of horse racing in which draft horses pull heavy sleds. This study aimed to describe the epidemiological characteristics of the outbreak and identify individual- and management-level factors associated with equine influenza cases in order to develop improved control programs. A retrospective analysis was conducted using clinical records reported to the racecourse authority between April 21 and June 18, 2025. Cases were defined based...
Molecular detection of African horse sickness virus from selected areas in Ethiopia. Equines are vital to global economies and support millions of livelihoods. However, their productivity and welfare are severely hindered by infectious diseases such as African Horse Sickness, which causes major socio-economic losses in Ethiopia. A cross-sectional study was conducted from November 2022 to May 2023 to isolate and detect African horse sickness virus in equines across epidemic areas of Ethiopia. In total, 30 blood samples and 2 tissue representative specimens were aseptically collected from clinically sick and recently dead animals and transported under cold chain to the National ...
Longitudinal and spatial declines in equine Hendra virus vaccination despite continued risk. Hendra virus is an emerging zoonosis endemic to Australia with high fatality of infection in horses and humans. The role of infected domestic horses as amplifying bridge hosts for onward transmission to humans led to the creation of an equine vaccine as a One Health solution against spillover. Despite the risk this disease represents, previously reported equine vaccination rates were low. This study explored vaccination trends between 2012 and 2023 at fine spatial scales and identified demographic and ecological predictors of vaccination against emerging zoonoses. Over 1 million doses of Equiv...
Combined treatment with valacyclovir and heparin reduced the incidence of equine herpesvirus myeloencephalopathy and improved survival in naturally occurring equine herpesvirus-1 outbreaks. Describe the effects and outcomes of valacyclovir and heparin administration in equine herpesvirus-1 (EHV-1)-exposed horses. Unassigned: A multicenter retrospective study identified 111 horses naturally exposed to EHV-1 from August 2017 to March 2018. Equine herpesvirus-1 infection was confirmed via blood or nasal secretion PCR. Horses that developed neurologic signs were diagnosed with equine herpesvirus myeloencephalopathy (EHM). Clinical signs, treatment, and survival were reported. A subset of horses was treated with valacyclovir and heparin. Prophylactic medication administration was perf...
Detection of equine parapoxvirus in the stable environment during pastern dermatitis outbreak in Finland. Equine parapoxvirus (EqPPV) has emerged as a cause of recurring pastern dermatitis outbreaks in horses in Finland. First detected in 2013, EqPPV has since been associated with potentially hundreds of clinical cases and suspected zoonotic transmission. Based on serological data and field reports, EqPPV causes pastern dermatitis outbreaks in Finland every few years. This study aimed to investigate the environmental presence and plausible transmission dynamics of the virus to prepare for future outbreaks and give targeted guidelines to stable staff and veterinarians. Results: After a large-scale ...
Intermittent shedding dynamics of EHV-1 across biological matrices during a natural outbreak linked to international equestrian events. Equine herpesvirus type 1 (EHV-1) outbreaks associated with international equestrian events have demonstrated the capacity of this virus for rapid transboundary dissemination. However, detailed longitudinal data integrating viral shedding across multiple biological matrices within the same animals during naturally occurring outbreaks remain limited. In this study, ten horses hospitalized during a naturally occurring EHV-1 outbreak linked to an international jumping competition were monitored for 10-12 days, from which 306 nasal, ocular, urine and faecal samples were obtained and analysed by qu...
Isolation and Identification of Emerging Equine Encephalosis Virus Serotype 6 in Israel, 2023. Equine encephalosis (EE) is an arthropod-borne viral disease resembling a mild form of African horse sickness disease, which affects all species of equids. Previously, only EEV serotype 4 (EEV-4) caused sporadic outbreaks of the disease in Israel. In the summer of 2023, EE was clinically diagnosed in horses and donkeys in Israel. For laboratory confirmation, tissue cultures were inoculated with whole-blood samples obtained from sick animals. Five EEV isolates were successfully recovered in tissue and confirmed by conventional RT-PCR and Sanger sequencing of several viral genes. BLAST analysis ...
An epizootic of equine viral arteritis at a Thoroughbred racetrack in Illinois: 223 cases. An epizootic of equine viral arteritis (EVA) occurred over an 8-wk period in the summer of 1993 at a midwestern Thoroughbred (TB) racetrack that ceased operations in 2021. Based on clinical signs, viral isolation, and serology, 223 horses (213 TBs, 10 lead ponies) were affected. Consistent clinical signs included fever (38.3-40.6°C; 101-105°F), depression, inappetence, and diffuse urticaria, including distal limb and preputial edema. Equine arteritis virus (EAV) was cultured from buffy coat samples from 24 of 28 acutely ill horses. Seventeen of 18 convalescent horses and 1 of 92 non-affected...
Risk assessment of West Nile fever in equines in Europe based on an ecological niche model. West Nile fever is a zoonotic viral disease transmitted by Culex mosquitoes, capable of causing severe neurological illness in humans, equines, and birds. Over the past dozen years, Europe has experienced numerous WNF outbreaks of varying severity, leading to significant public health and economic impacts. Consequently, WNF has emerged as a major concern for both public health and veterinary sectors. In this study, we employed spatiotemporal analysis techniques alongside an optimized ecological niche model to investigate the spatiotemporal distribution patterns of historical WNF outbreaks, pre...
First confirmed report of equine coital exanthema in Uruguayan horses. Equine Coital Exanthema (ECE) is a contagious venereal disease caused by Equid alphaherpesvirus 3 (EHV‑3). Although ECE is self-limiting, it causes significant economic losses to the global equine industry due to the temporary segregation of affected mares and stallions from breeding activities. This report describes the epidemiological, clinical, histological, and molecular findings from an outbreak of ECE in Uruguayan horses. Seven days following the introduction of a stallion, five mares developed extensive papular and vesicular dermatitis in the vaginal and perineal regions. The stallion...
Multivalent Disabled Infectious Single Animal (DISA)-DIVA vaccine for all nine serotypes of African horse sickness virus (AHSV) is broadly protective in IFNAR (-/-) mice. African horse sickness (AHS) is a highly severe, midge-borne disease of equids showing a mortality rate of > 90% in naive domestic horses. Outbreaks are caused by AHS virus (AHSV) and result in devastating economic losses in developing countries as equids play a crucial role in the agricultural industry and many households. The AHSV species encompasses nine serotypes showing no or limited cross protection, which is challenging regarding AHS vaccine development. Recently, and like bluetongue virus (BTV), the AHS Disabled Infectious Single Animal (DISA)-DIVA vaccine platform was developed...
Diagnosis and Surveillance of West Nile Virus Infection in Horses: Current Methods, Challenges, and Future Directions. West Nile virus (WNV) is a mosquito-borne flavivirus of growing importance for both human and equine health in Europe. Horses are highly susceptible to neurological disease and, because they share ecological exposure with humans, they represent valuable sentinels for detecting local viral circulation within a One Health framework. However, diagnosis of WNV infection in equines is complicated by the short and low-level viraemia, which limits the sensitivity of molecular assays, and by serological cross-reactivity with related flaviviruses and the confounding effects of vaccination. In this narr...
The 2025 outbreak of equine influenza among draft horses at Obihiro Racecourse, Hokkaido, Japan. In 2025, an outbreak of equine influenza occurred among draft horses at Obihiro Racecourse in Hokkaido, Japan. The number of horses showing clinical signs increased dramatically in April. The proportion affected was significantly higher in 2-year-olds than in older groups. The proportion that developed fever during the outbreak was significantly higher than that observed among Thoroughbreds during the 2007 outbreak. In non-epidemic periods, the geometric mean hemagglutination inhibition antibody titer of 2-year-old draft horses was significantly lower than that of 2-year-old Thoroughbreds. The...
Multi-state equine botulism outbreak in the United States linked to contaminated feed: an epidemiologic, clinicopathologic, and regulatory investigation. A multi-state outbreak of equine botulism occurred between December 2022 and March 2023 in the United States. Follow-up and testing were performed on 42 horses, including 24 that died or were euthanized in the outbreak that affected ~98 horses. Affected horses had all been exposed to the same commercial feed. Clinical signs included progressive muscle weakness and tremors, recumbency, and colic. No significant gross or microscopic abnormalities were observed on autopsy. Feces and gastrointestinal content were tested for various infectious agents, including botulinum toxin; fecal samples from 2...
When Vibrio is not Vibrio: misidentified Aeromonas sp. associated with equine abortions and neonatal death, revealed by MALDI-TOF and 16S rRNA sequencing. A retrospective review of equine necropsies performed at the Normandy Laboratory for Animal Health, French Agency for food, environmental and occupational health and safety (1996-2022) unexpectedly reported Vibrio alginolyticus, Vibrio parahaemolyticus and Vibrio vulnificus in equine samples using API 20NE, prompting a re-evaluation of bacterial identification. Of 27 strains, 25 were cultivable, and re-examined using API 20NE, API 20E, MALDI-TOF, 16S rRNA gene sequencing and Vibrio-specific PCR assays. API 20NE confirmed the original (erroneous) identifications; all Vibrio-specific PCR assays ...
Culicoides biting midges (Diptera: Ceratopogonidae) feeding on donkeys in the United Kingdom, with reference to the risk of transmission and persistence of African horse sickness virus. African horse sickness virus (AHSV: Sedoreoviridae; Orbivirus) causes a severe and often fatal disease in horses (African horse sickness: AHS) and is transmitted almost exclusively by Culicoides biting midges (Diptera: Ceratopogonidae). In recent years, unprecedented outbreaks of AHSV have occurred in new geographical foci in Thailand and other related Culicoides-borne viruses continue to emerge unexpectedly, causing disease outbreaks in northern Europe. This study investigated Culicoides abundance and diversity at a donkey (Equus asinus) sanctuary in southern England. The incidence and severi...
West Nile Virus in Europe: Epidemiology, Vector Ecology, Environmental Drivers, and the Role of Equine Sentinel Surveillance in a One Health Framework. West Nile virus (WNV) is a mosquito-borne flavivirus that remains an important public and veterinary health concern across Europe. Periodic outbreaks affecting humans, horses, and wildlife highlight the complex ecological interactions underlying viral circulation. This narrative review aims to synthesize current knowledge regarding WNV epidemiology, transmission dynamics, and surveillance strategies in Europe, with particular attention to the Romanian context. Available surveillance data indicate recurrent seasonal transmission in several European regions; however, reported case numbers may be...
Spatio-temporal analysis of anthrax in livestock at zonal level in Ethiopia, 2008-2020. Ethiopia has not only one of the largest livestock populations in Africa, but also a substantial growing human population, increasing the risk of zoonotic disease transmission. Anthrax is a priority zoonosis in Ethiopia due to its risks to both human and animal health. Utilising 13 years of retrospective data (2008-2020) from 92 zones, this study investigated the spatio-temporal distribution of livestock anthrax cases in Ethiopia. High variability in annual incidence was observed, with the lowest number of cases (n=2357, 3.73 %) in 2018 followed by the highest number of cases (n=8210, 12.98 %)...
Transmission of Salmonella clones between different animal species in a horse and cattle breeding region in Japan. Sequence type 34 (ST34) Salmonella enterica serovar Typhimurium and its monophasic variant (Salmonella 4,[5],12:i:-) are the most prevalent clones among humans and animals worldwide, including in Japan. Although cross-species transmission may have occurred in the background of global spread, the matter remains unresolved. Here, we conducted high-resolution phylogenetic analysis using whole-genome sequencing data of Salmonella Typhimurium and 4,[5],12:i:- obtained from a horse and cattle breeding district in Japan and identified cases of cross-species transmission of ST34 Salmonella 4,[5],12:i:...
What happened after the epidemic? Equine influenza surveillance sheds light on sources and seasonal risk in the United Kingdom. The epidemiology of equine influenza (EI) in the United Kingdom has not been systematically described since the 2019 epidemic. Objective: To summarise UK EI surveillance (2020-2024), quantify outbreak seasonality and assess movement-related sources. Methods: Retrospective observational analysis of national surveillance and horse importation data. Methods: Epidemiological data for laboratory-confirmed EI cases in the United Kingdom were collated. Outbreaks (EI-infected premises) were defined as one or more laboratory-confirmed cases on the same premises within a 4-week period. Monthly outbreak ...
Re-emergence of equine glanders in Mongolia based on region-wide serosurveillance. Glanders, a zoonotic disease caused by , has re-emerged in Mongolia after decades of control. We conducted nationwide serosurveillance from 2021 to 2024 to assess the prevalence and geographic distribution of glanders. Using random 3-stage cluster sampling, we collected 3,001 horse serum samples from 332 herds. Those herds were in 46 soums (administrative districts equivalent to counties) in 13 provinces and in 3 districts in Ulaanbaatar. Sera were tested using the complement fixation test, and positive results were confirmed by immunoblotting and ELISA. Overall seroprevalence was 1.03% (95% C...
Rocio virus sustained circulation in Brazil: first infection case in a horse highlights the need for enhanced arbovirus surveillance. Rocio virus (ROCV), a neurotropic arbovirus of the genus, caused Brazil’s largest encephalitis outbreak in the 1970s but has since been rarely detected. We report the first ROCV encephalitis clinical case after nearly 40 years and isolated and sequenced the virus from CNS tissue of a horse. Metatranscriptomics enabled full-genome sequencing, revealing divergence from the reference sequence at an evolutionary rate of 5.8–7.0 × 10⁻⁴, consistent with . Thirty-one non-synonymous substitutions were identified, with the envelope protein most affected. Findings indicate ROCV cryptic circula...
Pulmonary fibrosis in horses associated with spontaneous Crotalaria juncea intoxication. We report an outbreak of Crotalaria juncea intoxication in horses exhibiting progressive weight loss and respiratory distress in northeastern Brazil. Necropsy revealed firm, non-collapsed lungs with extensive interstitial fibrosis, bronchiolar epithelial hyperplasia with club cells proliferation, and marked pulmonary arterial remodeling. Hepatic lesions consisted primarily of centrilobular necrosis, probably resulting from hypoxic injury related to anemia and prolonged agonic death. Pasture inspection identified significant invasion by shrubs of C. juncea in various phenological stages.
Characterisation of Salmonella Typhimurium from a fatal equine nosocomial outbreak and retrospective analysis of equine clinic salmonellosis cases (2010-2025). In 2024, a highly fatal outbreak of equine salmonellosis occurred in a Hungarian equine referral hospital, resulting in the death or euthanasia of four out of five affected horses. () subsp. serovar Typhimurium was identified as the primary causative agent from equine faecal, reflux, and post-mortem intestinal content samples, while one case involved Coeln. Extensive environmental sampling during the outbreak also yielded multiple serovars. Whole-genome sequencing revealed a high degree of genetic relatedness among the Typhimurium isolates, confirming nosocomial transmission. The source ...
Molecular characterization and phylogeography of equine influenza virus H3N8 detected in donkeys in Nigeria 2022-2023. Equine influenza virus (EIV) H3N8 is a highly contagious respiratory pathogen that poses significant health and economic risks to equids globally. In southeastern Nigeria where equids are sold and slaughtered, limited data exist on EIV epidemiology and circulating lineages. Methods: To address this gap, an active surveillance was conducted between January 2022 and October 2023. A total of 400 nasal swabs were collected from horses and donkeys at slaughterhouses and animal markets. The swabs were screened for equine influenza virus (EIV) using quantitative Reverse-Transcription Polymerase Chain...
Identifying Host-Characteristics and Management Risk Factors in a California Equine Herpesvirus Myeloencephalopathy (EHM) Outbreak. Equine alphaherpesvirus-1 (EHV-1) is a highly contagious virus that can cause the neurological form, equine herpesvirus myeloencephalopathy (EHM). Understanding transmission-related risk factors is crucial for improving prevention strategies and guiding effective control measures. In this study, we collected data from 63 horses that had previously participated in the February 2022 winter horse show season at the Desert International Horse Park (DIHP) (26 cases and 37 controls) to identify host and management factors associated with EHV-1 infection and/or EHM development during the February 202...
Antibody responses to equine parapoxvirus reveal a re-emerging pattern. Parapoxviruses (PPV) cause skin and mucous membrane signs to several animal species and humans worldwide. Equine parapoxvirus (EqPPV) was first detected in a sick horse in Finland in 2013. It is potentially zoonotic, and a similar virus has been detected in humans in the USA. In winter 2021–2022, EqPPV caused a large-scale pastern dermatitis epidemic in racehorses all over Finland. Field reports suggest that similar epidemics of unverified cause have also occurred in 2015 and 2019. The aim of this study was to develop a serological test and study the immune response, seroprevalence, and hist...
Biosecurity perspectives of equestrian competition organizers in Ontario, Canada. Biosecurity plays an important role in the prevention and control of infectious disease outbreaks in the equine population. With competition organizers responsible for implementing and upholding biosecurity requirements at competitions, it is important to understand the biosecurity landscape at these locations where Ontario horses commonly travel and interact in large group settings. Unassigned: The objective of this study was to describe the perspectives, challenges and experiences of competition organizers of both sanctioned and unsanctioned events in Ontario, Canada regarding implementing e...
