Investigation of the Blood Microbiome in Horses With Fever of Unknown Origin - PubMed (original) (raw)

Y Tina Yu 1, Ximena Olarte Castillo 1, Renee Anderson 1, Minghui Wang 2, Qi Sun 2, Rebecca Tallmadge 1, Kelly Sams 1, Guillaume Reboul 1, Jordan Zehr 1, Joel Brown 1, Xiyu Wang 1, Nicholas Marra 3, Bryce Stanhope 1, Jennifer Grenier 2, Nicola Pusterla 4, Thomas Divers 1, Linda Mittel 1, Laura B Goodman 1 4

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Investigation of the Blood Microbiome in Horses With Fever of Unknown Origin

Yining Sun et al. Vet Med Sci. 2025 Mar.

Abstract

Background: Fever of unknown origin (FUO) without a respiratory component is a frequent clinical presentation in horses. Multiple pathogens, both tick-borne and enteric, can be involved as etiologic agents. An additional potential mechanism is intestinal barrier dysfunction.

Objectives: This case-control study aimed to detect and associate microbial taxa in blood with disease state.

Study design: Areas known for a high prevalence of tick-borne diseases in humans were chosen to survey horses with FUO, which was defined as fever of 101.5°F or higher with no signs of respiratory illness or other recognisable diseases. Blood samples and clinical parameters were obtained from 52 FUO cases and also from matched controls from the same farms. An additional 23 febrile horses without matched controls were included.

Methods: Broadly targeted polymerase chain reaction (PCR) amplification directed at conserved sequence regions of bacterial 16S rRNA, parasite 18S rRNA, coronavirus RdRp and parvovirus NS1 was performed, followed by deep sequencing. To control for contamination and identify taxa unique to the cases, metagenomic sequences from the controls were subtracted from those of the cases, and additional targeted molecular testing was performed. Sera were also tested for antibodies to equine coronavirus.

Results: Over 60% of cases had intestinal microbial DNA circulating in the blood. Nineteen percent of cases were attributed to infection with Anaplasma phagocytophilum, of which two were subtyped as human-associated strains. A novel Erythroparvovirus was detected in two cases and two controls. Serum titres for equine coronavirus were elevated in some cases but not statistically different overall between the cases and controls.

Main limitations: Not all pathogens are expected to circulate in blood, which was the sole focus of this study.

Conclusions: The presence of commensal gut microbes in blood of equine FUO cases is consistent with a compromised intestinal barrier, which is highlighted as a direction for future study.

Keywords: microbiome; molecular diagnostics; pathogen discovery; tick‐borne disease.

© 2025 The Author(s). Veterinary Medicine and Science published by John Wiley & Sons Ltd.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

FIGURE 1

FIGURE 1

Violin plot of clinical signs observed in fever of unknown origin (FUO) cases. Medians and quartiles are plotted as dashed lines. A score of 1 represents least severe and 4 represents most severe. Letters indicate statistically similar results (p > 0.05).

FIGURE 2

FIGURE 2

Body temperatures of all cases with fever of unknown origin, all matched controls, only cases positive for A. phagocytophilum, and their matched controls. Each data point represents one horse; medians and interquartile ranges are shown as lines.

FIGURE 3

FIGURE 3

Aggregate analysis of all microbiome data with control sequences subtracted from cases. The percent of cases for which different sequences were detected is plotted for each taxon.

FIGURE 4

FIGURE 4

Codon‐aware phylogeny of Parvovirus NS1 with amino acid sequences of the four blood samples from this study and 32 sequences from other genera of viruses in the family Parvoviridae using PhyML method with 100 Bootstrap resamplings. Bootstrap values are indicated at each node, and the scale bar indicates genetic distance. Horse icons are placed next to sequences from equines.

FIGURE 5

FIGURE 5

Serum titres for equine coronavirus (ECoV). Individual animals are plotted with medians (solid bars) and the 1.958 OD450 nm cut‐off value (dashed line).

References

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