An outbreak of abortion in mares associated with Salmonella abortusequi infection

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.

Serological investigation and isolation of Salmonella abortus equi in horses in Xinjiang

BACKGROUND

Salmonella enterica subspecies enterica serovar abortus equi (S. abortus equi) is one of the main pathogens that causes abortion in pregnant horses and donkeys, which was highly infectious and greatly restricts the healthy development of the horse industry.

OBJECTIVES

In order to investigate the prevalence and biological characteristics of S. abortus equi in different regions and breeds of horses in Xinjiang.

METHODS

This study conducted ELISA detection of S. abortus equi antibodies on serum samples of 971 horses collected from three large-scale horse farms and five free-range horse farms in Yili Prefecture and Bayingol Mongolian Autonomous Prefecture of Xinjiang from 2020 to 2023. On this basis, bacterial isolation, culture, identification, and drug sensitivity tests were conducted on 42 samples of aborted foal tissues and 23 mare vaginal swabs.

RESULTS

The results showed that the positive rate of S. abortus equi antibody was as high as 20.91% in 971 horse serum samples. Among them, the positive rate in the Ili region (29.09%) was significantly higher than that in the Bayingole region (11.24%), and the positive rate in mares (22.45%) was higher than that in stallions (14.05%). In terms of horse breeds, the positive rates of self-propagating thoroughbred horses, half-bred horses, Ili horses and Yanqi horses were 43.22%, 28.81%, 14.72% and 11.24% respectively. In addition, S. abortus equi was more susceptible to juvenile and elderly horses, with positive rates of 70.00%and 41.86%, respectively, both of which were significantly higher than young (10.97%) and adult (19.79%) horses. Further, 9 strains of S. abortus equi were obtained through bacterial isolation, culture and identification, which were resistant to five antibiotics (Clarithromycin, Clindamycin, penicillin, Sulfamethoxazole and Rifampicin), and sensitive to 13 antimicrobial agents (Amoxicillin, Ciprofloxacin and Gentamicin, et al.).

CONCLUSION

There was a high infection rate of S. abortus equi in Ili Prefecture and self-propagating thoroughbred horses, and juvenile or old mares were more susceptible, which will provide scientific basis for the prevention of S. abortus equi infection in different regions and breeds of horses in Xinjiang.

Development and application of a competitive ELISA for the detection of antibodies against Salmonella Abortusequi in equids

The high abortion rate associated with Salmonella Abortusequi (S. Abortusequi) infection in equids has re-emerged over the past 10 years and has caused serious economic losses to China. Our previous studies showed that the flagellin FljB gene could distinguish S. Abortusequi from most Salmonella serotypes. In this study, the flagellin antigen was used to develop a competitive enzyme-linked immunosorbent assay (cELISA) that could be used to detect both horse and donkey serum samples using a monoclonal antibody (MAb) that was found to bind to FljB. A cELISA was established using the purified MAb coating of the plate and incubation of the mixture of horseradish peroxidase (HRP)-conjugated FljB antigen with the undiluted serum sample. The performance of the cELISA and the tube agglutination test (TAT) assay was compared with respect to sensitivity and specificity, by testing a panel containing 660 S. Abortusequi-positive and 515 S. Abortusequi-negative serum samples, all of which had been characterized by Western blotting. Receiver operator characteristic (ROC) analyses were performed to determine the cutoff value and estimate the detection specificity (Sp) and sensitivity (Se). ROC analysis showed that the area under the ROC curve (AUC) values of cELISA [AUC = 0.9941; 95% confidence interval (CI), 0.9898-0.9984] were higher than those of TAT (AUC = 0.7705; 95% Cl, 0.7437-0.7972). A cutoff value of 39.5% was selected with Sp and Se values of 100 (95% Cl, 99.26-100.00) and 97.58 (95% Cl, 96.10-98.50), respectively. The cELISA has excellent futures compared with TAT, such as shortened detection time, no need for pre-treatment of sera, and easy interpretation of the results, and is more suitable for disease surveillance.

Bacteremia and Late-Term Abortion Secondary to Salmonellosis in a Dog

A 5 yr old, 54-day-pregnant whippet presented for hyperthermia, lethargy, and spontaneous abortion of multiple fetuses. Blood work and clinical signs raised concern for uterine sepsis; therefore, the dog underwent an emergency ovariohysterectomy. Blood and uterine samples cultured a Salmonella species. Following ovariohysterectomy and oral antibiotic therapy, the dog had no further systemic signs. Repeat blood cultures and Salmonella testing were negative. To the authors' knowledge, this is the first report of a Salmonella species causing bacteremia in conjunction with late-term abortion in a dog.

Therapeutic Efficacy of Phage PIZ SAE-01E2 against Abortion Caused by Salmonella enterica Serovar Abortusequi in Mice

Salmonella enterica subsp. enterica serovar Abortusequi is a frequently reported pathogen causing abortion in mares. In this study, the preventive and therapeutic effects of phage P_IZ SAE-01E2 against S Abortusequi in a mouse model of abortion were investigated. Phage P_IZ SAE-01E2 was stable at different temperatures (4 to 70°C) and pH values (pH 4 to 10) and could lyse the majority of the Salmonella serogroup O:4 and O:9 strains tested (25/28). There was no lysogeny-related, toxin, or antibiotic resistance-related gene in the genome of P_IZ SAE-01E2. All of these characteristics indicate that P_IZ SAE-01E2 has the potential for use in phage therapy. In in vivo experiments, 2 × 10³ CFU/mouse of S Abortusequi ATCC 9842 was sufficient to lead to murine abortion (gestational day 14.5) within 48 h. A single intraperitoneal inoculation of P_IZ SAE-01E2 (10⁸ PFU/mouse, multiplicity of infection = 10⁵) 1 h before or after S Abortusequi challenge provided effective protection to all pregnant mice (10/10). After 24 h of treatment with phage P_IZ SAE-01E2, the bacterial loads in both the placenta and the uterus of the infected mice were significantly decreased (<10² CFU/g) compared to those in the placenta and the uterus of the mice in the control group (>10⁶ CFU/g). In addition, the levels of inflammatory cytokines in the placenta and blood of the mice in the phage administration groups were significantly reduced (P < 0.05) compared to those in the placenta and blood of the mice in the control group. Altogether, these findings indicate that P_IZ SAE-01E2 shows the potential to block abortions induced by S Abortusequi in vivo IMPORTANCE S Abortusequi is an important pathogen that can induce abortions in mares. Although S Abortusequi has been well controlled in Europe and the United States due to strict breeding and health policies, it is still widespread in African and Asian countries and has proven difficult to control. In China, abortions caused by S Abortusequi have also been reported in donkeys. So far, there is no commercial vaccine. Thus, exploiting alternative efficient and safe strategies to control S Abortusequi infection is essential. In this study, a new lytic phage, P_IZ SAE-01E2, infecting S Abortusequi was isolated, and the characteristics of P_IZ SAE-01E2 indicated that it has the potential for use in phage therapy. A single intraperitoneal inoculation of P_IZ SAE-01E2 before or after S Abortusequi challenge provided effective protection to all pregnant mice. Thus, P_IZ SAE-01E2 showed the potential to block abortions induced by S Abortusequi in vivo.

Abortion in donkeys associated with Salmonella abortus equi infection

BACKGROUND

Salmonella enterica subspecies enterica serovar abortus equi (S. abortus equi) is well known as the aetiological agent of equine abortion. However, abortion caused by S. abortus equi has not been previously described in donkeys.

OBJECTIVES

To investigate whether S. abortus equi was correlated with an abortion outbreak consisting of 61 abortions.

STUDY DESIGN

Investigation of the clinical cases using pathoanatomical, bacteriological, serological and molecular approaches.

METHODS

Autopsies on nine aborted foetuses were performed. Tissue specimens from seven aborted foetuses and two mares were cultured and subjected to detection of equine herpesvirus 1 (EHV-1), equine herpesvirus 4 (EHV-4) and equine arteritis virus (EAV) by polymerase chain reaction. The isolates were serotyped according to the Kaufmann-White scheme and analysed by multi-locus sequence typing (MLST). Detection of EHV and EAV antibodies was performed in all pregnant mares.

RESULTS

No obvious gross lesions were observed in the foetuses. Nine Gram-negative isolates were obtained from all nine tissue samples and were identified as Salmonella spp. All of the isolates belonged to the B group, the O antigen epitope was 4, 12 and H antigen was not obtained. The isolates of Salmonella were characterised as sequence type (ST) 251. Detection of EHV-1, EHV-4 and EAV was negative.

MAIN LIMITATIONS

The mechanism that causes abortion in donkeys needs further study and the lack of histological examination.

CONCLUSION

Salmonella abortus equi was isolated as the single agent and was responsible for the abortions. Equine practitioners should be aware of S. abortus equi infection as a cause of abortion in donkeys.

High mortality in foals associated with Salmonella enterica subsp. enterica Abortusequi infection in Italy

Salmonella enterica subsp. enterica serovar Abortusequi is frequently reported as a cause of abortion in mares and neonatal septicemia and polyarthritis in Asian and African countries, but only sporadically in Europe and the United States. We report an outbreak of S. Abortusequi in foals in Italy, characterized by high mortality. In a herd of Murgese horses, 10 of 34 newborns died at birth and a further 7 died, after developing severe clinical signs, during the first 10 d of life. Tissue specimens from different organs of 2 dead foals, synovial fluids from 4 sick foals, and vaginal and rectal swabs from their dams were cultured. A total of 16 isolates, all as pure cultures, were obtained and identified as Salmonella. The isolates exhibited the same antimicrobial resistance pattern and the same sequence type, ST251, a type that has been associated with S. Abortusequi. Six of 16 isolates were serotyped and found to be S. Abortusequi 4,12:-:e,n,x. Equine practitioners should be aware of S. Abortusequi infection as a cause of neonatal mortality in foals.

Aneurysm of the cranial mesenteric artery as a site of carriage of Salmonella enterica subsp. enterica serovar Abortusequi in the horse

Salmonella enterica subsp. enterica serovar Abortusequi is a pathogen restricted to horses. Our investigation targeted 4 draft horses (9-10 months old) kept on a Japanese farm that had suffered an outbreak of S. Abortusequi abortion. The 4 horses were suspected to be carriers of the bacterium owing to their high agglutination titers (≥1:2,560) in tube agglutination testing. The owners' on-farm observations confirmed that the horses had no apparent abnormalities, and S. Abortusequi was not isolated from their blood, rectal swabs, or sternal bone marrow fluid at antemortem investigation. However, at autopsy, all horses displayed the following: suppurative aneurysm of the cranial mesenteric artery with heavy infection with Strongylus vulgaris larvae; heavy intestinal parasitic infection with Gasterophilus intestinalis, Parascaris equorum, Anoplocephala perfoliata, and S. vulgaris; and enlargement of the systemic lymph nodes. In each case, large numbers of S. Abortusequi were isolated from the anterior mesenteric artery thrombus. The thrombus isolates harbored a single virulence plasmid, and the pulsed-field gel electrophoresis profiles of the isolates were identical not only to each other but also to those of Japanese enzootic strains of S. Abortusequi. These results reveal that parasitic aneurysms of the cranial mesenteric artery should be considered an important possible site of carriage of S. Abortusequi in horses. The results also suggest high clonality of the isolated serovar in the horse population in Japan.

A racing start in life? The hurdles of equine feto-placental pathology

Significant progress has been made in understanding and monitoring the causes of equine abortion over past decades. However, not all in utero pathology results in abortion. It has long been recognised that some in utero pathology, such as twinning or chronic placentitis, can result in the birth of live but growth-retarded foals and there is historical evidence that birth weight may influence future athletic performance. Clinical experience (e.g. from twins) and experimental studies (pony-Thoroughbred embryo transfer) have highlighted the importance of reduced functional placental area in limiting growth in utero in horses. Many other nonfatal in utero pathologies (e.g. umbilical cord-related circulatory compromise) can potentially affect either placental function or other organ systems. Their influence on the short- and long-term health of the foal and its future athletic performance is in many cases poorly documented or understood. This review summarises the main causes of in utero pathology and reflects on how these may potentially affect the foal if born alive, highlighting the need for long-term studies on this important subject.

Animal contact as a source of human non-typhoidal salmonellosis

Non-typhoidal Salmonella represents an important human and animal pathogen world-wide. Most human salmonellosis cases are foodborne, but each year infections are also acquired through direct or indirect animal contact in homes, veterinary clinics, zoological gardens, farm environments or other public, professional or private settings. Clinically affected animals may exhibit a higher prevalence of shedding than apparently healthy animals, but both can shed Salmonella over long periods of time. In addition, environmental contamination and indirect transmission through contaminated food and water may complicate control efforts. The public health risk varies by animal species, age group, husbandry practice and health status, and certain human subpopulations are at a heightened risk of infection due to biological or behavioral risk factors. Some serotypes such as Salmonella Dublin are adapted to individual host species, while others, for instance Salmonella Typhimurium, readily infect a broad range of host species, but the potential implications for human health are currently unclear. Basic hygiene practices and the implementation of scientifically based management strategies can efficiently mitigate the risks associated with animal contacts. However, the general public is frequently unaware of the specific disease risks involved, and high-risk behaviors are common. Here we describe the epidemiology and serotype distribution of Salmonella in a variety of host species. In addition, we review our current understanding of the public health risks associated with different types of contacts between humans and animals in public, professional or private settings, and, where appropriate, discuss potential risk mitigation strategies.

A safe vaccine (DV-STM-07) against Salmonella infection prevents abortion and confers protective immunity to the pregnant and new born mice

Pregnancy is a transient immuno-compromised condition which has evolved to avoid the immune rejection of the fetus by the maternal immune system. The altered immune response of the pregnant female leads to increased susceptibility to invading pathogens, resulting in abortion and congenital defects of the fetus and a subnormal response to vaccination. Active vaccination during pregnancy may lead to abortion induced by heightened cell mediated immune response. In this study, we have administered the highly attenuated vaccine strain ΔpmrG-HM-D (DV-STM-07) in female mice before the onset of pregnancy and followed the immune reaction against challenge with virulent S. Typhimurium in pregnant mice. Here we demonstrate that DV-STM-07 vaccine gives protection against Salmonella in pregnant mice and also prevents Salmonella induced abortion. This protection is conferred by directing the immune response towards Th2 activation and Th1 suppression. The low Th1 response prevents abortion. The use of live attenuated vaccine just before pregnancy carries the risk of transmission to the fetus. We have shown that this vaccine is safe as the vaccine strain is quickly eliminated from the mother and is not transmitted to the fetus. This vaccine also confers immunity to the new born mice of vaccinated mothers. Since there is no evidence of the vaccine candidate reaching the new born mice, we hypothesize that it may be due to trans-colostral transfer of protective anti-Salmonella antibodies. These results suggest that our vaccine DV-STM-07 can be very useful in preventing abortion in the pregnant individuals and confer immunity to the new born. Since there are no such vaccine candidates which can be given to the new born and to the pregnant women, this vaccine holds a very bright future to combat Salmonella induced pregnancy loss.

Infectious causes of embryonic and fetal mortality

The purpose of this review is to summarize bacterial, fungal, protozoan, and viral causes of reproductive dysgenesis in cattle, sheep, goats, pigs, horses, dogs, and cats. The clinical presentations of disease due to reproductive pathogens are emphasized, with a focus on assisting development of complete lists of causes that result in abortion and infertility in these species. Clinicians are encouraged to assess clinical presentation, create complete lists of differential diagnoses, obtain appropriate diagnostic samples, maximize diagnostic laboratory support, and avoid zoonotic infections resulting from reproductive pathogens of animals. The foundation of an accurate diagnosis of reproductive loss due to infectious pathogens facilitates the prudent use of immunization and biosecurity to minimize reproductive losses.

Salmonella sepsis and miscarriage

We present a case of a miscarriage at 16 weeks of gestation due to infection and transplacental passage of Salmonella group C. This was identified as being Salmonella Virchow from genital tract swab culture, and placental Gram-staining revealed numerous colonies of Gram-negative bacilli within the fibrin between the placental villi, confirming a true villitis associated with a hematogenous infection. Based on the patient's history, it was suggested that she had contracted the salmonella infection from eating undercooked eggs. Treatment of salmonella infection in pregnancy is controversial, and antibiotic therapy should be reserved for cases of invasive disease, using amoxicillin or a cephalosporin.

Comparison of Salmonella enterica serovar Abortusequi isolates of equine origin by pulsed-field gel electrophoresis and fluorescent amplified-fragment length polymorphism fingerprinting

Equine paratyphoid is caused by Salmonella enterica serovar Abortusequi, and manifests mainly as abortion in the mare. We compared S. Abortusequi strains isolated in Japan and other countries using pulsed-field gel electrophoresis (PFGE) and fluorescent amplified-fragment length polymorphism (FAFLP) analysis. PFGE analysis of S. Abortusequi strains gave 21-27 fragments ranging in size from 33 to 602kb. Although two PFGE profiles were observed among the 20 S. Abortusequi isolates in Japan, the restriction fragments originating from the chromosome were common between the two profiles. The similarity index of the two profiles was 90.9%, while those between Japanese and five other S. Abortusequi strains were 29.8-37.5%. On the other hand, FAFLP analysis of S. Abortusequi strains generated 64-67 amplified fragments ranging in size from 100 to 400bp. One polymorphic fragment was observed among the 20 S. Abortusequi isolates in Japan. These data indicate the close relation of this agent in Japan. S. Abortusequi strains sharing a common ancestry might have been conserved in Japan.