Bacterial and viral enterocolitis in horses: a review

Diagnostic approaches, aetiological agents and their associations with short-term survival and laminitis in horses with acute diarrhoea admitted to referral institutions

BACKGROUND

An international description of the diagnostic approaches used in different institutions to diagnose acute equine diarrhoea and the pathogens detected is lacking.

OBJECTIVES

To describe the diagnostic approach, aetiological agents, outcome, and development of laminitis for diarrhoeic horses worldwide.

STUDY DESIGN

Multicentre retrospective case series.

METHODS

Information from horses with acute diarrhoea presenting to participating institutions between 2016 and 2020, including diagnostic approaches, pathogens detected and their associations with outcomes, were compared between institutions or geographic regions.

RESULTS

One thousand four hundred and thirty-eight horses from 26 participating institutions from 4 continents were included. Overall, aetiological testing was limited (44% for Salmonella spp., 42% for Neorickettsia risticii [only North America], 40% for Clostridiodes difficile, and 29% for ECoV); however, 13% (81/633) of horses tested positive for Salmonella, 13% (35/262) for N. risticii, 9% (37/422) for ECoV, and 5% (27/578) for C. difficile. C. difficile positive cases had greater odds of non-survival than horses negative for C. difficile (OR: 2.69, 95%CI: 1.23-5.91). In addition, horses that were positive for N. risticii had greater odds of developing laminitis than negative horses (OR: 2.76, 95%CI: 1.12-6.81; p = 0.029).

MAIN LIMITATIONS

Due to the study's retrospective nature, there are missing data.

CONCLUSIONS

This study highlighted limited diagnostic investigations in cases of acute equine diarrhoea. Detection rates of pathogens are similar to previous reports. Non-survival and development of laminitis are related to certain detected pathogens.

Survival rates and factors associated with survival and laminitis of horses with acute diarrhoea admitted to referral institutions

BACKGROUND

Clinicopathological findings and their association with the outcome and development of laminitis in horses with acute diarrhoea has not been investigated in a multicentre study across different geographic regions.

OBJECTIVES

Describe and compare clinicopathologic findings of diarrhoeic horses between different geographic regions, survival rates and factors associated with non-survival and laminitis.

STUDY DESIGN

Multicentre retrospective case series.

METHODS

Information from horses with acute diarrhoea presenting to participating institutions between 2016 and 2020 was collected, and clinicopathological data were compared between surviving and non-surviving horses and horses that did and did not develop laminitis. Survival rates and seasonal and geographic differences were also investigated.

RESULTS

One thousand four hundred thirty-eight horses from 26 participating institutions from 4 continents were included; 76% survived to discharge with no differences identified between geographic regions. The survival proportion of horses with SIRS and creatinine concentrations > 159 μmol/L was 55% (154/279) compared with 81% (358/437) for those with SIRS and creatinine concentrations < 159 μmol/L (p < 0.001). The survival proportion of horses with SIRS that had an L-lactate concentration > 2.8 mmol/L was 59% (175/298) compared with 81% (240/296) in horses with SIRS and L-lactate concentration < 2.8 mmol/L (p < 0.001). The proportion of horses that developed laminitis was lower in Europe (4%, 19/479) compared with North America (8%, 52/619), Australia (8%, 12/138) and Latin America (11%, 16/146) (p < 0.05). More horses developed laminitis in the summer (46%, 39/85) compared with winter (18%, 15/85), spring (18%, 15/85) and fall (19%, 16/85) (p < 0.01). Horses with laminitis had greater odds of non-survival than those without laminitis (OR: 3.73, 95% CI: 2.47-5.65).

MAIN LIMITATIONS

Not all variables were available for all horses due to the retrospective nature.

CONCLUSIONS

Clinicopathological findings in horses with acute diarrhoea and their association with survival are similar across geographic regions. However, developing laminitis secondary to diarrhoea is less common in Europe. In addition, factors associated with non-survival were indicative of disease severity and subsequent cardiovascular compromise.

Antibacterial Evaluation of Gallic Acid and its Derivatives against a Panel of Multi-drug Resistant Bacteria

BACKGROUND

Infectious diseases are the second leading cause of deaths worldwide. Pathogenic bacteria have been developing tremendous resistance against antibiotics which has placed an additional burden on healthcare systems. Gallic acid belongs to a naturally occurring phenolic class of compounds and is known to possess a wide spectrum of antimicrobial activities.

AIMS & OBJECTIVES

In this study, we synthesized thirteen derivatives of gallic acid and evaluated their antibacterial potential against seven multi-drug resistant bacteria, as well as cytotoxic effects against human embryonic kidney cell line in vitro. Methods: 13 compounds were successfully synthesized with moderate to good yield and evaluated. Synthesized derivatives were characterized by using nuclear magnetic resonance spectroscopy, mass spectrometry, and Fourier transformation infrared spectroscopy. Antibacterial activity was determined using microdilution while cytotoxicyt was assessed using MTT assay.

RESULTS

The results of antibacterial assay showed that seven out of thirteen compounds exhibited antibacterial effects with compound 6 and 13 being most potent against Staphylococcus aureus (MIC 56 μg/mL) and Salmonella enterica (MIC 475 μg/mL) respectively. On the other hand, most of these compounds showed lower cytotoxicity against human embryonic kidney cells (HEK 293), with IC50 values ranging from over 700 μg/mL.

CONCLUSION

Notably, compound 13 was found to be non-toxic at concentrations as high as 5000 μg/mL. These findings suggest that the present synthetic derivatives of gallic acid hold potential for further studies in the development of potent antibacterial agents.

Relationship between the Cycle Threshold Value (Ct) of a Salmonella spp. qPCR Performed on Feces and Clinical Signs and Outcome in Horses

The objective of this retrospective study was to evaluate the clinical significance of fecal quantitative real-time polymerase chain reaction (qPCR) Salmonella results when taking the cycle threshold values (Ct) into account. The study included 120 Salmonella qPCR-positive fecal samples obtained from 88 hospitalized horses over a 2-year period. The mean Ct of the qPCR test was evaluated in regard to (1) clinical outcome and (2) systemic inflammatory response syndrome (SIRS) status (no SIRS, moderate SIRS, or severe SIRS) of the sampled horses. An ROC analysis was performed to establish the optimal cut-off Ct values associated with severe SIRS. The mean ± SD Ct value was significantly lower in samples (1) from horses with a fatal issue (27.87 ± 5.15 cycles) than in surviving horses (31.75 ± 3.60 cycles), and (2) from horses with severe SIRS (27.87 ± 2.78 cycles) than from horses with no (32.51 ± 3.59 cycles) or moderate (31.54 ± 3.02 cycles) SIRS. In the ROC analysis, the optimal cut-off value of Ct associated with a severe SIRS was 30.40 cycles, with an AUC value of 0.84 [95% confidence interval 0.76-0.91] and an OR of 0.64 [0.51-0.79]. Results suggest that including the Ct value in the interpretation of fecal qPCR results could improve the diagnostic value of this test for clinical salmonellosis in horses.

An Overview of Equine Enteric Clostridial Diseases

The understanding of the pathogenesis of equine enteric clostridial organisms is an active, evolving field. Advances will improve our knowledge both from the animal welfare and human health perspectives. The zoonotic nature of this group of diseases makes them relevant in the age of One health, as a significant amount of close human-equine interactions occurs for business and pleasure. Economic and welfare reasons prompt a better understanding of enteric clostridial pathogenesis, treatment, and control of the infection in horses and ongoing efforts are needed to advance clinical outcomes.

Potomac Horse Fever

Potomac horse fever (PHF) is a common cause of equine colitis in endemic areas. Until recently, the only causative agent known to cause PHF was Neorickettsia risticii. However, N. findlayensis has been isolated from affected horses. Horses typically become infected upon ingestion of Neorickettsia spp.-infected trematodes within aquatic insects. The most common clinical signs include diarrhea, fever, anorexia, lethargy and colic. The diagnostic test of choice for PHF is PCR of blood and feces. Tetracyclines remain an effective treatment. Supportive care, including fluid therapy, colloid administration, NSAID and anti-endotoxin medication, and digital cryotherapy, is also necessary in some cases.

Fecal prevalence of Clostridium innocuum DNA in healthy horses and horses with colitis

This study compared the prevalence of C. innocuum DNA in the feces of healthy horses and horses with acute colitis. C. innocuum was identified in 22% (15/68) of colitis cases and 18% (12/68) of healthy horses (p = 0.416).

Direct and culture-enriched 16S rRNA sequencing of cecal content of healthy horses and horses with typhlocolitis

Next generation sequencing has demonstrated that alpha diversity of the fecal microbiota is significantly altered in horses with typhlocolitis. The objective of this study was to evaluate the bacterial composition of the cecum content of horses with and without typhlocolitis through direct and culture-enriched 16S gene sequencing of six healthy horses and six horses with acute typhlocolitis; a case-control study design. Cecal content was collected after euthanasia. An aliquot was used for direct 16S gene sequencing. Another was serially diluted with brain heart infusion (BHI) and plated onto five different agar media. All culture medias, except for MacConkey, were incubated anaerobically. Bacterial colonies were harvested in bulk and used for DNA extraction, 16S PCR amplification, and sequenced using the Illumina MiSeq platform. Predominant phyla in healthy and diseased horses were Firmicutes, followed by Bacteroidetes in all cultured medias, except for MacConkey agar, in which Proteobacteria was the dominant phylum. Greater bacterial richness was identified in sequenced cecal contents as compared to cultured plates (P < 0.05). Culture-enriched molecular profiling combined with 16S rRNA gene sequencing offer an alternative method for the study of the gut microbiota of horses. For direct cecum content 16S gene amplification, the alpha diversity indices were lower in diarrheic horses compared to healthy horses (P < 0.05). A higher relative abundance of Fusobacteriota was found in 2/6 samples from diarrheic horses. The role of Fusobacteriota in equine colitis deserves investigation.

Diversity and phylogeny of the tick-borne bacterial genus Candidatus Allocryptoplasma (Anaplasmataceae)

The family Anaplasmataceae includes tick-borne bacteria of major public and veterinary health interest, as best illustrated by members of the genera Anaplasma and Ehrlichia. Recent epidemiological surveys have also reported on the presence of a novel putative genus in the Anaplasmataceae, Candidatus Allocryptoplasma, previously described as Candidatus Cryptoplasma in the western black-legged tick, Ixodes pacificus. However, the genetic diversity of Ca. Allocryptoplasma and its phylogenetic relationship with other Anaplasmataceae remain unclear. In this study, we developed a multi-locus sequence typing approach, examining the DNA sequence variation at five genes of Ca. Allocryptoplasma found in ticks. Combining this multi-locus sequence typing and genetic data available on public databases, we found that substantial genetic diversity of Ca. Allocryptoplasma is present in Ixodes, Amblyomma and Haemaphysalis spp. ticks on most continents. Further analyses confirmed that the Ca. Allocryptoplasma of ticks, the Ca. Allocryptoplasma of lizards and some Anaplasma-like bacteria of wild mice cluster into a monophyletic genus, divergent from all other genera of the family Anaplasmataceae. Candidatus Allocryptoplasma appears as a sister genus of Anaplasma and, with the genera Ehrlichia and Neoehrlichia, they form a monophyletic subgroup of Anaplasmataceae associated with tick-borne diseases. The detection of genetically distinct Ca. Allocryptoplasma in ticks of significant medical or veterinary interest supports the hypothesis that it is an emergent genus of tick-borne pathogens of general concern.

The fecal bacterial microbiota of healthy and sick newborn foals

BACKGROUND

The fecal bacterial microbiota of normal foals and foals with enterocolitis has been characterized using next-generation sequencing technology; however, there are no reports investigating the gut microbiota in foals hospitalized for other perinatal diseases.

OBJECTIVE

To describe and compare the fecal bacterial microbiota in healthy and sick foals using next-generation sequencing techniques.

ANIMALS

Hospitalized (17) and healthy foals (21).

METHODS

Case-control study. Fecal samples were collected from healthy and sick foals on admission. Sick foals were further divided into sick nonseptic (SNS, n = 9) and septic (n = 8) foals. After extraction of DNA, the V4 region of the 16 S rRNA gene was amplified using a PCR assay, and the final product was sequenced with an Illumina MiSeq.

RESULTS

Diversity was significantly lower in healthy than sick foals (P < .05). The bacterial membership (Jaccard index) and structure (Yue & Clayton index) of the fecal microbiota of healthy, septic, and SNS foals were similar (AMOVA, P > .05). Bacterial membership (AMOVA, P = .06) and structure (AMOVA, P = .33) were not different between healthy and sick foals. Enterobacteriaceae, Enterococcus, and Streptococcus were among the 5 more abundant taxa identified in both groups.

CONCLUSION AND CLINICAL IMPORTANCE

Higher fecal microbiota diversity in sick than healthy foals might suggest a high exposure to environmental microorganisms or an unstable colonic microbiota. The presence of microorganisms causing bacteremia in foals in a high relative abundance in the feces of foals suggests the intestine might play an essential role in the causation of bacteremia in foals.

Fecal microbiota of horses with colitis and its association with laminitis and survival during hospitalization

BACKGROUND

The association of microbiota with clinical outcomes and the taxa associated with colitis in horses remains generally unknown.

OBJECTIVES

Describe the fecal microbiota of horses with colitis and investigate the association of the fecal microbiota with the development of laminitis and survival.

ANIMALS

Thirty-six healthy and 55 colitis horses subdivided into laminitis (n = 15) and non-laminitis (n = 39, 1 horse with chronic laminitis was removed from this comparison) and survivors (n = 27) and nonsurvivors (n = 28).

METHODS

Unmatched case-control study. The Illumina MiSeq platform targeting the V4 region of the 16S ribosomal RNA gene was used to assess the microbiota.

RESULTS

The community membership (Jaccard index) and structure (Yue and Clayton index) were different (analysis of molecular variance [AMOVA]; P < .001) between healthy and colitis horses. The linear discriminant analysis effect size (LEfSe; linear discriminant analysis [LDA] >3; P < .05) and random forest analyses found Enterobacteriaceae, Lactobacillus, Streptococcus, and Enterococcus enriched in colitis horses, whereas Treponema, Faecalibacterium, Ruminococcaceae, and Lachnospiraceae were enriched in healthy horses. The community membership and structure of colitis horses with or without laminitis was (AMOVA; P > .05). Enterobacteriaceae, Streptococcus, and Lactobacillus were enriched in horses with laminitis (LDA > 3; P < .05). The community membership (AMOVA; P = .008) of surviving and nonsurviving horses was different. Nonsurviving horses had an enrichment of Enterobacteriaceae, Pseudomonas, Streptococcus, and Enterococcus (LDA >3; P < .05).

CONCLUSION AND CLINICAL IMPORTANCE

Differences in the microbiota of horses with colitis that survive or do not survive are minor and, similarly, the microbiota differences in horses with colitis that do or do not develop laminitis are minor.

Effects of Intravenous Antimicrobial Drugs on the Equine Fecal Microbiome

Alterations in the gastrointestinal microbiota after antimicrobial therapy in horses can result in loss of colonization resistance and changes in bacterial metabolic function. It is hypothesized that these changes facilitate gastrointestinal inflammation, pathogen expansion and the development of diarrhea. The objectives of this study were to determine the effect of intravenous administration of antimicrobial drugs (ceftiofur, enrofloxacin, oxytetracycline) on equine fecal bacterial communities over time, to investigate whether those changes are detectable after 5 days of treatment and whether they persist over time (30 days). Sixteen horses were randomly assigned into 4 treatment groups: group 1 (enrofloxacin, n = 4); group 2 (ceftiofur sodium, n = 4); group 3 (oxytetracycline, n = 4); group 4 (0.9% saline solution, placebo, n = 4). Antimicrobial therapy was administered for 5 days. Fecal samples were obtained before (day 0) and at 3, 5 and 30 days of the study period. Bacterial DNA was amplified using specific primers to the hypervariable region V1−V3 of the 16S rRNA gene using a 454 FLX-Titanium pyrosequencer. Antimicrobial therapy failed to cause any changes in physical examination parameters, behavior, appetite or fecal output or consistency throughout the study in any horse. There was a significant effect of treatment on alpha diversity indices (richness) over the treatment interval for ceftiofur on days 0 vs. 3 (p < 0.05), but not for other antimicrobials (p > 0.05). Microbial composition was significantly different (p < 0.05) across treatment group and day, but not for interactions between treatment and day, regardless of taxonomic level and beta-diversity distance metric. The most significant antimicrobial effects on relative abundance were noted after intravenous administration of ceftiofur and enrofloxacin. The relative abundance of Fibrobacteres was markedly lower on day 3 compared to other days in the ceftiofur and enrofloxacin treatment groups. There was an increase in Clostridia and Lachnospiraceae from day 0 to days 3 and 5 in ceftiofur and enrofloxacin treated groups. These findings showed the negative effect of antimicrobial drugs on bacterial communities associated with gut health (Fibrobacteres and Lachnospiraceae) and indicate that changes in specific taxa could predispose horses to gastrointestinal inflammation and the development of diarrhea.

Clostridial Diseases of Horses: A Review

The clostridial diseases of horses can be divided into three major groups: enteric/enterotoxic, histotoxic, and neurotoxic. The main enteric/enterotoxic diseases include those produced by Clostridium perfringens type C and Clostridioides difficile, both of which are characterized by enterocolitis. The main histotoxic diseases are gas gangrene, Tyzzer disease, and infectious necrotic hepatitis. Gas gangrene is produced by one or more of the following microorganisms: C. perfringens type A, Clostridium septicum, Paeniclostridium sordellii, and Clostridium novyi type A, and it is characterized by necrotizing cellulitis and/or myositis. Tyzzer disease is produced by Clostridium piliforme and is mainly characterized by multifocal necrotizing hepatitis. Infectious necrotic hepatitis is produced by Clostridium novyi type B and is characterized by focal necrotizing hepatitis. The main neurotoxic clostridial diseases are tetanus and botulism, which are produced by Clostridium tetani and Clostridium botulinum, respectively. Tetanus is characterized by spastic paralysis and botulism by flaccid paralysis. Neither disease present with specific gross or microscopic lesions. The pathogenesis of clostridial diseases involves the production of toxins. Confirming a diagnosis of some of the clostridial diseases of horses is sometimes difficult, mainly because some agents can be present in tissues of normal animals. This paper reviews the main clostridial diseases of horses.