# Absence of Host-Specific Hemotropic Mycoplasmas in Horses and Donkeys from Croatia: First Systematic Survey in Southeastern Europe

## TL;DR

This study found very low infection rates of blood-borne bacteria in horses and donkeys in Croatia, suggesting they are not natural hosts for these bacteria.

## Contribution

The first systematic survey of hemoplasmas in equids from southeastern Europe, revealing extremely low prevalence and no host-specific species.

## Key findings

- Only one horse out of 843 tested positive for Mycoplasma wenyonii, a hemoplasma typically found in cattle.
- No donkeys were infected, and the prevalence in horses was the lowest reported in any study.
- The findings suggest equids do not host hemoplasma species specifically adapted to them.

## Abstract

We studied a group of bacteria called hemoplasmas that live on the surface of red blood cells and can sometimes cause anemia. These bacteria are found in many animals, but very little is known about them in horses and donkeys. In Croatia, we tested 843 (817 horses and 26 donkeys) animals and found only one infected horse. The bacteria detected (Mycoplasma wenyonii) usually infect cattle, not horses. This shows that horses and donkeys are not natural hosts for these bacteria, but can sometimes become infected from other animals. Our study provides the first data of this kind from southeastern Europe.

Hemotropic mycoplasmas (hemoplasmas) are uncultivable, cell wall-less bacteria that parasitizeon the surface of red blood cells of mammals, potentially causing anemia and other systemic signs. While widely distributed among domestic and wild animals, their occurrence in equids remains poorly understood, and no species has been identified as host-specific to horses or donkeys. This study presents the first systematic survey of hemoplasmas in equids from southeastern Europe and only the second molecularly confirmed case in horses in Europe. A total of 843 equids (817 horses and 26 donkeys) from different regions of Croatia, representing various ages, uses, and husbandry systems, were screened for hemoplasmas by PCR targeting the 16S rRNA gene. Only one horse tested positive, identified as Mycoplasma wenyonii, a hemoplasma typically associated with cattle. The estimated prevalence was 0.12% (95% CI: 0.003–0.68%). No donkeys were infected. The extremely low prevalence observed here—the lowest reported in any study detecting hemoplasma-positive horses—supports the hypothesis that equids do not harbor host-specific hemoplasma species and may only sporadically acquire infections from other hosts via spillover. This finding underscores the apparent absence of persistent hemoplasma lineages adapted to equids and highlights the need for further research on their epidemiology, host specificity, and transmission dynamics.