Zoonotic Diseases from Horses: A Systematic Review

Investigation of the seroprevalence to equine coronavirus and SARS-CoV-2 in healthy adult horses recently imported to the United States

Adult horses are susceptible to equine coronavirus (ECoV) and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), although, only ECoV has been linked to clinical disease. Little information is available regarding the seroprevalence against ECoV and SARS-CoV-2 in adult healthy horses. The goal of the present study was to determine the seroprevalence against two coronaviruses known to infect horses using convenience samples collected from horses recently imported from Europe to the United States from 2019 to 2023. A total of 385 banked serum samples were tested against ECoV and SARS-CoV-2 using previously validated ELISA assays. Prevalence factors including date of arrival in the United States, signalment and country of origin were available for the majority of the horses. A total of 9/385 (2.3%) and 4/385 (1.0%) horses tested seropositive for ECoV and SARS-CoV-2, respectively. The ECoV seropositive horses were all mares, ages 4 to 26 years (median 9 years) and originated from Germany, the Netherlands, Ireland, Belgium and Italy. These mares were predominantly imported during the summer and fall months. All SARS-CoV-2 seropositive horses were mares ages 5 to 10 years (median 7.5 years) imported from the Netherlands and the United Kingdom. The majority of the SARS-CoV-2 seropositive horses were imported during the colder months of the year. The study results support the presence of ECoV in Europe and report on the first SARS-CoV-2 seropositive healthy adult horses outside the United States. Commingling for movements by air and close contact to humans may predispose transmission with ECoV and SARS-CoV-2, respectively.

Detection of Gastrointestinal Pathogens with Zoonotic Potential in Horses Used in Free-Riding Activities during a Countrywide Study in Greece

The objectives of this study were (a) to detect zoonotic gastrointestinal pathogens in faecal samples of horses using the FilmArray® GI Panel and (b) to identify variables potentially associated with their presence. Faecal samples collected from 224 horses obtained during a countrywide study in Greece were tested by means of the BioFire® FilmArray® Gastrointestinal (GI) Panel, which uses multiplex-PCR technology for the detection of 22 pathogens. Gastrointestinal pathogens were detected in the faecal samples obtained from 97 horses (43.3%). Zoonotic pathogens were detected more frequently in samples from horses in courtyard housing (56.0%) than in samples from horses in other housing types (39.7%) (p = 0.040). The most frequently detected zoonotic pathogens were enteropathogenic Escherichia coli (19.2% of horses) and Shiga-like toxin-producing E. coli stx1/stx2 (13.8%). During multivariable analysis, two variables emerged as significant predictors for the outcome 'detection of at least one zoonotic pathogen in the faecal sample from an animal': (a) the decreasing age of horses (p = 0.0001) and (b) the presence of livestock at the same premises as the horses (p = 0.013). As a significant predictor for the outcome 'detection of two zoonotic pathogens concurrently in the faecal sample from an animal', only the season of sampling of animals (autumn) emerged as significant in the multivariable analysis (p = 0.049). The results indicated a diversity of gastrointestinal pathogens with zoonotic potential in horses and provided evidence for predictors for the infections; also, they can serve to inform horse owners and handlers regarding the possible risk of transmission of pathogens with zoonotic potential. In addition, our findings highlight the importance of continuous surveillance for zoonotic pathogens in domestic animals.

Antimicrobial Resistance in Equines: A Growing Threat to Horse Health and Beyond-A Comprehensive Review

The equine industry holds substantial economic importance not only in the USA but worldwide. The occurrence of various infectious bacterial diseases in horses can lead to severe health issues, economic losses, and restrictions on horse movement and trade. Effective management and control of these diseases are therefore crucial for the growth and sustainability of the equine industry. While antibiotics constitute the primary treatment strategy for any bacterial infections in horses, developing resistance to clinically important antibiotics poses significant challenges to equine health and welfare. The adverse effects of antimicrobial overuse and the escalating threat of resistance underscore the critical importance of antimicrobial stewardship within the equine industry. There is limited information on the epidemiology of antimicrobial-resistant bacterial infections in horses. In this comprehensive review, we focus on the history and types of antimicrobials used in horses and provide recommendations for combating drug-resistant bacterial infections in horses. This review also highlights the epidemiology of antimicrobial resistance (AMR) in horses, emphasizing the public health significance and transmission dynamics between horses and other animals within a One Health framework. By fostering responsible practices and innovative control measures, we can better help the equine industry combat the pressing threat of AMR and thus safeguard equine as well as public health.

Pattern of prescriptions and prudent use of antimicrobial in horse practice at a Veterinary Teaching Hospital

Antimicrobial prescriptions of the University of Pisa and their compliance with prudent use recommendations were investigated over 11 years (2011-2021). At least one antimicrobial was always prescribed in surgical prophylaxis for the suture of wounds and in 33% of horses with signs of disease of a body system. Antimicrobials were administered in monotherapy (48%) in fixed dose combinations (21%) and empirical combinations (31%). Antimicrobials were mostly (63%) administered by parenteral route, while oral and topical antimicrobials accounted for 14% and 23% of prescriptions, respectively. Gentamicin, benzylpenicillin and ceftiofur were the most prescribed antimicrobials; aminoglycosides, penicillins and cephalosporins were the most common class of antimicrobial prescribed. Protected antimicrobials (WHO HPCIA and rifampicin) represented 24% of antimicrobial dispensations. The pattern of classes of antimicrobial used by body system was broad and included up to eight different pharmaceutical classes. The heterogeneity of antimicrobial use was confirmed by the estimate of the prescription diversity index. Antimicrobial prescriptions were in compliance with prudent use recommendations in terms of availability of diagnosis, respect of the dose range and duration of treatment On the contrary, principles of appropriate antimicrobial use have only been partially observed in relation to off-label use, use of antimicrobials in empirical combination, use of antimicrobial susceptibility tests and use of protected antimicrobials, suggesting that additional interventions are required to improve the responsible use of antimicrobials use in our equine practice.

Gut microbiota changes in horses with Chlamydia

BACKGROUND

Zoonotic diseases pose a significant threat to public health. Chlamydia, as an intracellular pathogen, can colonize the intestinal tract of humans and animals, changing the gut microbiota. However, only a few studies have evaluated alterations in the gut microbiota of horses infected with Chlamydia. Therefore, this study aimed to investigate gut microbiota and serum biochemical indicators in horses with Chlamydial infection (IG) and healthy horses (HG). Fecal and blood samples were collected from 16 horses (IG: 10; HG: 6) before morning feeding for the determination of gut microbiota and serum biochemical parameters.

RESULTS

The results showed that total globulin (GLB), alanine aminotransferase (ALT), and creatine kinase (CK) levels were significantly increased in IG compared with HG. Notably, the gut microbial diversity increased in IG compared with HG. Furthermore, Moraxellaceae and Akkermanisa abundance decreased in IG, while Streptococcus, Treponema, Prevotella, and Paraprevotella abundances (13 genera of bacterial species) increased. Compared with HG, carbohydrate metabolism increased in IG while amino acid metabolism decreased. In addition, the abundance of 18 genera of bacteria was associated with the level of five serum biochemical indicators.

CONCLUSIONS

In summary, this study elucidated the influence of Chlamydia infection in horses on the gut microbiota, unraveling consequential alterations in its composition and metabolic profile. Therefore, this study improves the understanding of Chlamydia-induced intestinal infections.

Understanding the divergent evolution and epidemiology of H3N8 influenza viruses in dogs and horses

Cross-species virus transmission events can lead to dire public health emergencies in the form of epidemics and pandemics. One example in animals is the emergence of the H3N8 equine influenza virus (EIV), first isolated in 1963 in Miami, FL, USA, after emerging among horses in South America. In the early 21st century, the American lineage of EIV diverged into two 'Florida' clades that persist today, while an EIV transferred to dogs around 1999 and gave rise to the H3N8 canine influenza virus (CIV), first reported in 2004. Here, we compare CIV in dogs and EIV in horses to reveal their host-specific evolution, to determine the sources and connections between significant outbreaks, and to gain insight into the factors controlling their different evolutionary fates. H3N8 CIV only circulated in North America, was geographically restricted after the first few years, and went extinct in 2016. Of the two EIV Florida clades, clade 1 circulates widely and shows frequent transfers between the USA and South America, Europe and elsewhere, while clade 2 was globally distributed early after it emerged, but since about 2018 has only been detected in Central Asia. Any potential zoonotic threat of these viruses to humans can only be determined with an understanding of its natural history and evolution. Our comparative analysis of these three viral lineages reveals distinct patterns and rates of sequence variation yet with similar overall evolution between clades, suggesting epidemiological intervention strategies for possible eradication of H3N8 EIV.

Current and Future Advances in the Detection and Surveillance of Biosecurity-Relevant Equine Bacterial Diseases Using Loop-Mediated Isothermal Amplification (LAMP)

Horses play an important role throughout the world, whether for work, culture, or leisure, providing an ever-growing significant contribution to the economy. The increase in importation and movement of horses, both nationally and internationally, has inevitably allowed for the global equine industry to grow. Subsequently, however, the potential for transmission of fatal equine bacterial diseases has also escalated, and devasting outbreaks continue to occur. To prevent such events, disease surveillance and diagnosis must be heightened throughout the industry. Current common, or "gold-standard" techniques, have shown to be inadequate at times, thus requiring newer technology to impede outbreaks. Loop-mediated isothermal amplification (LAMP) has proven to be a reliable, rapid, and accessible tool in both diagnostics and surveillance. This review will discuss equine bacterial diseases of biosecurity relevance and their current diagnostic approaches, as well as their respective LAMP assay developments. Additionally, we will provide insight regarding newer technology and advancements associated with this technique and their potential use for the outlined diseases.

Interactions of Equine Viruses with the Host Kinase Machinery and Implications for One Health and Human Disease

Zoonotic pathogens that are vector-transmitted have and continue to contribute to several emerging infections globally. In recent years, spillover events of such zoonotic pathogens have increased in frequency as a result of direct contact with livestock, wildlife, and urbanization, forcing animals from their natural habitats. Equines serve as reservoir hosts for vector-transmitted zoonotic viruses that are also capable of infecting humans and causing disease. From a One Health perspective, equine viruses, therefore, pose major concerns for periodic outbreaks globally. Several equine viruses have spread out of their indigenous regions, such as West Nile virus (WNV) and equine encephalitis viruses (EEVs), making them of paramount concern to public health. Viruses have evolved many mechanisms to support the establishment of productive infection and to avoid host defense mechanisms, including promoting or decreasing inflammatory responses and regulating host machinery for protein synthesis. Viral interactions with the host enzymatic machinery, specifically kinases, can support the viral infectious process and downplay innate immune mechanisms, cumulatively leading to a more severe course of the disease. In this review, we will focus on how select equine viruses interact with host kinases to support viral multiplication.

Willingness to adopt personal biosecurity strategies on thoroughbred breeding farms: Findings from a multi-site pilot study in Australia's Hunter Valley

There are almost 9,500 full-time employees in Australia's thoroughbred horse breeding industry. During foaling, they can be exposed to bodily fluids and mucous membranes which may present risks for zoonotic disease. These risks can be mitigated through personal biosecurity strategies. The aim of this study was to identify which personal biosecurity strategies were more or less likely to be adopted by workers. Seventeen participants representing 14 thoroughbred breeding farms and three equine veterinary practices in Australia's largest thoroughbred breeding region trialed up to 16 stakeholder-nominated personal biosecurity strategies over the 2021 foaling season. The strategies encompassed personal protective equipment (PPE), zoonotic disease awareness, policies and protocols, supportive environments, and leadership. Strategy adoption was monitored through three repeated self-audit surveys designed around the Transtheoretical Model of change (TTM) and findings were reviewed in exit interviews. For all survey waves in aggregate, 13 strategies were practiced by at least 50.0% of participants. Participants were most likely to use a ready-made foaling box (98.0%), communicate the message that PPE usage is a personal responsibility (94.1%) and use ready-made PPE kits (88.2%). However, 31.4% had no intention of doing practice sessions and/or dummy runs for PPE use and 27.5% had no intention of using a buddy system on farm/practice to check use of PPE. Whilst these rates indicate workers' willingness to adopt and maintain personal biosecurity strategies, they also indicate capacity for more practices to be implemented more often. Overall, the findings highlight the need for personal biosecurity interventions to be sensitive to the demands of the annual thoroughbred breeding calendar, the size of the breeding operation and the availability of skilled staff.

Wound swabs versus biopsies to detect methicillin resistant Staphylococcus aureus in experimental equine wounds

OBJECTIVE

To compare: (1) the load and diversity of cultivatable bacterial species isolated from tissue biopsies with cultures from surface swabs, and (2) the ability of each technique to detect methicillin-resistant Staphylococcus aureus (MRSA) in a model of MRSA-infected equine wounds.

STUDY DESIGN

Experimental in vivo study.

ANIMALS

Three light-breed adult horses.

METHODS

Four 2.5 × 2.5 cm full-thickness skin wounds were created on the dorsolateral aspect of each forelimb. Five days later, each wound was inoculated with a pure culture of MRSA (ATCC 43300). One hundred microlitres of 0, 5 × 108 , 5 × 109 or 5 × 1010 colony forming units (CFU)/ml was used to inoculate each wound. Surface swabs (Levine technique) and tissue biopsy samples (3 mm punch biopsy) were obtained at 2, 7, 14, and 21 days after inoculation. Quantitative aerobic culture was performed using routine clinical techniques.

RESULTS

A similar bacterial profile was identified from the culture of each wound-sampling technique and there was moderate correlation (R = 0.49, P < .001) between the bacterial bioburdens. Agreement was fair (κ = 0.31; 95% CI, 0.129-0.505) between the sampling techniques in identification of MRSA. Methicillin-resistant Staphylococcus aureus was isolated more frequently (P = .016) from cultures of tissue biopsies (79%; 76/96) than from surface swabs (62%; 60/96).

CONCLUSION

Bacterial load and diversity did not differ between sampling techniques but MRSA was detected more often from the cultures of tissue biopsies.

CLINICAL SIGNIFICANCE

Tissue biopsy should be preferred to culture swab in wounds where MRSA is suspected.

Risk factors and diseases associated with failure of natural passive immunization in foals

ABSTRACT This study aimed to report the prevalence of diseases in foals, patients at the Hospital Veterinário de Grandes Animais, Universidade Federal de Lavras (HVGA-UFLA), and its association with deaths and possible failures in the transfer of passive immunity (FTIP) via colostrum. Data were obtained from clinical records of horses aged between 0 and 3 months, admitted to the HVGA between January/2014 and December/2018. Descriptive analyzes of the diseases and organ systems affected were performed, as well as univariate analyzes with chi-square or Fisher's exact tests, identifying possible associations between FTIP, infectious diseases and other factors. No significant relationships were found between FTIP and infectious disease, meconium retention, sepsis, or death. However, it was shown that animals weighing between 10 and 30kg were 29.333 times more likely (95% confidence interval 1.734 - 505.951) to die than those weighing between 30.1 and 130kg. Therefore, it can be concluded that low weight is a very relevant risk factor, which may be related to the failure of postural reflexes and, consequently, to the inability to ingest colostrum, impairing the ability to respond to infectious agents.

Clostridium haemolyticum, a review of beta toxin and insights into the antigen design for vaccine development

Phospholipases C (PLCs) represent an important group of lethal toxins produced by pathogenic bacteria of the Clostridium genus, including the beta toxin of C. haemolyticum. Bacillary hemoglobinuria in cattle and sheep is the main disease caused by this pathogen and its incidence can be reduced by annual vaccination of herds. Currently, widely used vaccines depend on cultivating the pathogen and obtaining high concentrations of the toxin, disadvantages that can be overcome with the use of recombinant vaccines. In the development of this new generation of immunizing agents, identifying and understanding the structural and immunological aspects of the antigen are crucial steps, but despite this, the beta toxin is poorly characterized. Fortunately, the time and resources required for these investigations can be reduced using immunoinformatics. To advance the development of recombinant vaccines, in addition to a brief review of the structural and immunological aspects of beta toxin, this work provides in silico mapping of immunodominant regions to guide future vaccinology studies against C. haemolyticum. A review of alternatives to overcome the limitations of beta toxin vaccines (conventional or recombinant) is also proposed.

A Scoping Review of the Global Distribution of Causes and Syndromes Associated with Mid- to Late-Term Pregnancy Loss in Horses between 1960 and 2020

Equine pregnancy loss is frustrating and costly for horse breeders. The reproductive efficiency of mares has significant implications for a breeding operation’s economic success, and widespread losses can have a trickle-down effect on those communities that rely on equine breeding operations. Understanding the causes and risks of equine pregnancy loss is essential for developing prevention and management strategies to reduce the occurrence and impact on the horse breeding industry. This PRISMA-guided scoping review identified 514 records on equine pregnancy loss and described the global spatiotemporal distribution of reported causes and syndromes. The multiple correspondence analysis identified seven clusters that grouped causes, syndromes, locations and pathology. Reasons for clustering should be the focus of future research as they might indicate undescribed risk factors associated with equine pregnancy loss. People engaged in the equine breeding industry work closely with horses and encounter equine bodily fluids, placental membranes, aborted foetuses, and stillborn foals. This close contact increases the risk of zoonotic disease transmission. Based on this review, research is required on equine abortion caused by zoonotic bacteria, including Chlamydia psittaci, Coxiella burnetii and Leptospira spp., because of the severe illness that can occur in people who become infected.

Molecular Identification of Infectious Enteropathogens in Faeces of Healthy Horses

Zoogenic faecal contamination of the environment is one of the indices included in the evaluation of ecological threats, health hazards and adverse impacts on various ecosystems. The risks and environmental concerns are associated with the fact that faeces of wild and domesticated animals constitute the largest source of environmental loading of enteropathogens associated with transmission of zoonotic diseases (enteric zoonoses). Although sick animals are more likely to transmit pathogens, healthy ones can also be the carriers and defecate them into the environment. This is of particular importance given the close human-animal interactions and health effects resulting from human and ecological exposures to faecal hazards from companion and farm animals. We have therefore set out to investigate whether healthy equines can carry and defecate human infectious pathogens. For this purpose, we set up a pilot study to examine the faecal DNA of horses using culture-independent molecular diagnostics – fluorescent probe-based quantitative real-time PCR. Our results revealed that among a total of 23 horses, 6 were found to carry Campylobacter jejuni (C. jejuni), and 5 had Salmonella enterica serovar Typhimurium (S. Typhimurium). Moreover, Enterococcus faecalis (E. faecalis) was found in 14 horses, while 19 were positive for Clostridium perfringens (C. perfringens). Furthermore, the frequently reported protozoan parasites in livestock, Cryptosporidium parvum (C. parvum) and Giardia lamblia (G. lamblia), were discovered in 8 and 7 samples, respectively. This pilot study shed new light on the phenomenon of healthy horses carrying C. jejuni and other human-health-related enteropathogens.

Isothermal Nucleic Acid Amplification Technologies for the Detection of Equine Viral Pathogens

Simple Summary

Equine viral diseases remain a prominent concern for human and equine health globally. Many of these viruses are of primary biosecurity concern to countries that import equines where these viruses are not present. In addition, several equine viruses are zoonotic, which can have a significant impact on human health. Current diagnostic techniques are both time consuming and laboratory-based. The ability to accurately detect diseases will lead to better management, treatment strategies, and health outcomes. This review outlines the current modern isothermal techniques for diagnostics, such as loop-mediated isothermal amplification and insulated isothermal polymerase chain reaction, and their application as point-of-care diagnostics for the equine industry.

Abstract

The global equine industry provides significant economic contributions worldwide, producing approximately USD $300 billion annually. However, with the continuous national and international movement and importation of horses, there is an ongoing threat of a viral outbreak causing large epidemics and subsequent significant economic losses. Additionally, horses serve as a host for several zoonotic diseases that could cause significant human health problems. The ability to rapidly diagnose equine viral diseases early could lead to better management, treatment, and biosecurity strategies. Current serological and molecular methods cannot be field-deployable and are not suitable for resource-poor laboratories due to the requirement of expensive equipment and trained personnel. Recently, isothermal nucleic acid amplification technologies, such as loop-mediated isothermal amplification (LAMP) and insulated isothermal polymerase chain reaction (iiPCR), have been developed to be utilized in-field, and provide rapid results within an hour. We will review current isothermal diagnostic techniques available to diagnose equine viruses of biosecurity and zoonotic concern and provide insight into their potential for in-field deployment.

Antimicrobial prescribing patterns in equine ambulatory practice

Antimicrobial resistance is one of the most important public health risks facing our world today. Antimicrobials are commonly prescribed in equine veterinary medicine, but limited information exists documenting their use in practice. The goal of this study was to investigate antimicrobial prescription patterns in regards to prescription frequency, duration, drug class, clinician and affected body system in an equine ambulatory setting via retrospective analysis of billing and electronic medical records. Risk factors associated with antimicrobial prescription including the nature of the visit, submission of a culture, body system affected and clinician were assessed using multivariable regression. We found that antimicrobials were prescribed in 8.5 % of visits with a median number of 3.5 (IQR 0.8-12.2) animal-defined daily doses (ADD), defined as the number of daily doses of all antimicrobials prescribed to a patient at a single visit. Aminoglycosides were the most common class of antimicrobials prescribed and trimethoprim sulfamethoxazole was the most common drug prescribed overall. Amikacin was primarily used for patients presenting with musculoskeletal signs, and the median number of ADDs for visits where amikacin was prescribed was 1 (IQR 0.9-1.9), while the median number of antimicrobial ADDs for all other visits was 4.4 (IQR 0-14.1). Statistically significant differences in antimicrobial use patterns existed across clinicians, months, years and affected body systems. Horses presenting with ocular (OR 1199; 95 % CI 204-7,037; p < 0.001) and integumentary (OR 365; 95 % CI 87.2-1532; p < 0.001) signs were most likely to be prescribed an antimicrobial. Emergency visits (OR 5.61; 95 % CI 3.19-9.89; p < 0.001) and submission of a bacterial culture (OR 3.58; 95 % CI 2.11-6.09; p < 0.001) were associated with an increased likelihood of an antimicrobial prescription. This observational study was the first to quantitatively characterize antimicrobial use patterns in equine ambulatory practice in the United States, which is an important step needed to determine appropriateness of use and develop and evaluate antimicrobial stewardship guidelines.

Antimicrobial resistance in clinical bacterial isolates from horses in the UK

BACKGROUND

Surveillance of antimicrobial resistance (AMR) in horses is important to aid empirical treatment decisions and highlight emerging AMR threats.

OBJECTIVE

To describe the AMR patterns of common groups of bacteria from clinical submissions from horses in the UK during 2018, and to determine how this varies by sample site and type of submitting veterinary practice.

STUDY DESIGN

Prospective observational study.

METHODS

All data on bacterial culture and subsequent antimicrobial susceptibility testing (AST) collected in 2018 from six large equine diagnostic laboratories were included. Resistance patterns were analysed including resistance to 1 or 2 antimicrobial classes, multidrug resistance (MDR), extensively drug resistant (XDR), resistance to highest priority critically important antimicrobials and isolates where there was no readily available treatment for adult horses in the UK. Submitting practices were classified according to whether they treated referral cases or not (first opinion). Comparisons between proportions and resistance for each bacterial group and sample site was performed using Chi-squared (or Fisher's exact test).

RESULTS

A total of 6,018 bacterial isolates from 4,038 diagnostic submissions were included from respiratory (n = 1555), urogenital (n = 1,010), skin/hair/wound/abscess (n = 753), surgical site infection (SSI) /catheter-related-infection (CRI) /orthopaedic infections (n = 347) and unknown/'other' submissions (n = 373). There were 2,711 Gram-negative isolates and 3,307 Gram-positive isolates. Prevalence of MDR for E. coli was 31.7%, Staphylococcus spp. 25.3% and > 25% for the majority of bacterial isolates from SSI/CRI/orthopaedic submissions. For Enterococcus spp. there was no readily available treatment for adult horses in the UK in 30.2% of positive submissions. MDR was significantly higher from referral hospital than first opinion submissions for the majority of pathogens (except Actinobacillus spp. and Pasteurella spp. and β-haemolytic Streptococcus spp.).

MAIN LIMITATIONS

Since culture and susceptibility results are not systematic analyses based on harmonised methods, selection bias could impact the findings.

CONCLUSIONS

Ongoing surveillance is essential to understand emerging patterns of resistance. MDR is high in SSI/CRI/orthopaedic infections, which is important for hospital biosecurity and guiding treatment decisions. Harmonisation of diagnostic procedures and interpretation of results amongst veterinary laboratories will improve AMR surveillance and data comparison among laboratories.