Studies on the clinical relevance of microscopically demonstrable eperythrozoon-like structures on horse-erythrocytes.Original Title Untersuchungen zur klinischen Relevanz mikroskopisch nachweisbarer Eperythrozoon-ahnlicher Strukturen auf Pferde-Erythrozyten.

摘要

Hemotrophic mycoplasmas (Haemobartonella and Eperythrozoon species) are widely spread bacteria parasiting red blood cells. The disease is known as haemobartonellosis and eperythrozoonosis. Infections with hemotrophic mycoplasmas are described in detail in pigs, sheep, goats, cattle, cats and dogs. Infection in immunocompetent animals frequently is latent and considered to be a multifactorial disease. Typically acute disease is seen in immunosuppressed animals and can be provoked by splenectomy. The most important symptom in acute disease is hemolytic anemia. Clinical signs of disease in chronic infections are not specific symptoms, include weakness, weight loss, poor hair coat, slight anemia and, in live stock, decreased production. In acute disease great numbers of organisms can be observed as structures on the red blood cells in peripheral blood smears by light microscopic examination. Only in this acute stage can the diagnosis be made from the clinical signs and a blood smear. After the acute stage of disease infection can be diagnosed by direct detection by PCR or indirect detection by blood titers. The gold standard for diagnosing chronic latent infections is the microscopic detection of bacteriemia after splenectomy of a suspected animal or after the inoculation of suspected blood in a splenectomised laboratory animal. Hemotrophic mycoplasmas have not been grown in culture successfully. In the scientific literature, no publications are to be found dealing with systemic research considering the existence of hemotrophic mycoplasmas in horses. Since several years diagnosis and treatment of suspected eperythrozoonosis in horses are reported from the field in Germany. According to those reports detection of the parasite is done by microscopic examination of peripheral blood smears. In this study 108 horses were examined, partially with symptoms of suspected eperythrozoonosis (n=32). The other healthy horses composed a control group (n=76). After taking the anamnesis and performing a clinical examination to detect present symptoms peripheral blood was collected from every proband to run a hematology and prepare blood smears. The blood smear was blindly evaluated by three qualified examiners for the detection of eperythrozoon-like structures. As well as in symptomatic horses (27, 22 and 7 positiv smears) and in control animals (55, 50 and 14 positiv smears), suspected structures were observed regularly on the red blood cells. In the literature poor sensitivity and specificity are described for the light microscopic examination diagnosing hemotrophic mycoplasmas. Among other things the identification of artefacts as the structures looked for, can markedly raise the amount of false positive results. In this study the assessment of one examiner with only 21 positive diagnoses was significantly different than the two other examiners (each 72 and 82 positive diagnoses). Also the total correspondence of the three examiners was very low ( kappa values of 0.0225 and -0.0148). Comparing the hematological parameter, both groups did not show any relevant differences. No evidence was found confirming higher incidence of anemia in symptomatic horses. According to the knowledge about hemotrophic mycoplasmas in different species and the obtained results from this study, an infection with hemotrophic mycoplasmas in horses showing signs of chronic non-specific disease, where suspected structures in the blood smear are observed, cannot be just assumed. Only after the demonstration of hemotrophic mycoplasmas in the horse following phylogenetic analysis and the development of a specific PCR assay, an accurate diagnosis of infection with this pathogen can be made in the horse. The results of this study do not allow for the assumption of any causality between eperythrozoon-like structures on horse erythrocytes and any clinical symptoms.