Case Report
Reemergence of Dourine in Italy: Clinical Cases in Some Positive Horses

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Abstract

In 2011, Trypanosoma equiperdum reemerged in Italy, almost 10 years after its last appearance. A total of eight infected horses have been observed to date. Six horses were affected by natural outbreaks of the disease, whereas two were infected experimentally. The aim of this study was to offer a recent perspective on clinical cases of dourine in Europe. Investigation of the clinical aspects confirmed the three stages reported in the literature: stage 1 (genital lesions), stage 2 (cutaneous signs), and stage 3 (nervous signs). The most common signs in the horses under study were notable weight loss, edematous skin eruptions and oedemas of the abdomen, mammary glands and hind legs. Three animals presented neurological signs (lip ptosis of lower lip and ataxia). Infections were paucisymptomatic or asymptomatic in some animals. Hyperthermia was not reported in infected animals and considerable anemia was observed. High antibody titers did not always correspond to clinical signs. Positive polymerase chain reaction test results of blood or tissue (skin, eye swab) often correspond to an advanced stage of the disease. Dourine is a variable disease; owing to its low prevalence and chronic manifestation, it can be difficult to make a quick diagnosis when facing a Dourine-positive horse.

Introduction

Dourine is a parasitic venereal disease of equines caused by a flagellate protozoan of the species Trypanosoma equiperdum. It is the only trypanosomiasis that is not transmitted by blood-feeding vectors. Dourine can affect horses, mules and donkeys. The latter are generally more resistant and often remain asymptomatic carriers. The infection is endemic in many areas of Asia, Africa, Russia, Middle East and Eastern Europe (World Organisation for Animal Health [OIE] data). Its course and clinical signs vary considerably depending on the virulence of the strain concerned, as described in the literature on this topic. The course of the disease in horses is chronic, varying from a few months to 1-2 years. A number of authors have broken the course down into three stages: stage 1 (genital lesions), stage 2 (cutaneous signs) and stage 3 (nervous signs) [1], [2]. Stage 1 involves genital edema and swelling, manifesting 1-2 weeks after infection. In stage 2, typical cutaneous plaques (“silver dollar” plaques) appear, with thickening of the skin, considered pathognomonic by some authors [1], [3], [4]. Stage 3 is characterized by progressive anemia, neurological disorders and paresis of the hindquarters, often ending in death. Mortality rate is high, at around 50% [3].

Before the recent epidemic, the last case notified in Italy was in 1998, when an asymptomatic stallion in the province of Padova tested positive with a titer of 1:6 on complement fixation (CF) testing. The last reported cases of Dourine-positive horses with clinical signs date back to the epidemic of the 1970s [5]. On May 19, 2011, a stallion undergoing routine serological testing in the province of Catania for stud purposes tested positive on CF. The epidemiological investigation that followed resulted in the identification of other holdings epidemiologically linked with the infected animals in southern Italy. The Italian Ministry of Health emanated an ad hoc surveillance plan with mandatory testing of all equines of reproductive age in Italy. This plan has so far led to the identification of seven outbreaks involving 20 positive animals.

Five positive animals previously destined for slaughter were transferred to the Istituto Zooprofilattico Sperimentale dell’Abruzzo e del Molise “G. Caporale” (Istituto G. Caporale) for inclusion in a study to investigate the pathogenesis and attempt the isolation of T. equiperdum, which is very difficult, as demonstrated by the low number of isolates in the past decades [3], [6].

The long period of the disease’s absence—from the epidemic in the 1970s to that of 2011—has resulted in a knowledge gap in generations of veterinarians. The literature on this topic is generally old and lacking in graphic evidence, as this disease is not generally present in developed countries. Moreover, Dourine is a chronic disease whose signs are not constantly present and whose pathogenicity can vary, depending on the strain concerned. Therefore, the aim of this study was to describe and provide graphic evidence of the signs observed during the recent outbreaks of Dourine.

Section snippets

Animals

Eight horses were observed (Table 1, Table 2, Table 3). One was studied at the holding concerned, whereas five naturally infected and two experimentally infected horses were observed at the Istituto G. Caporale. Experimental infection was carried out by blood transfusion from infected horses with clear signs of Dourine.

The age range of the horses in the study was 4-16 years. Most of them were half-breeds used for meat production. There were six mares and two stallions. The seven animals studied

Results

In Table 4, a value (0 or 1) is attributed to a given sign in each horse on the basis of its presence or absence. In this way, it is possible to establish which signs were most common and which horse presented the most signs at the same time.

Genital Edema

Slight oedema of the sheath was seen in one stallion. In one mare, oedema of the vulva was accompanied by ulcers along the rim of the vulva. The severity of these genital oedemas varied considerably. They were not observed in the animals infected experimentally (Fig. 2).

Edematous Cutaneous Wheals and Plaques

Wheals or plaques were found on the skin of both naturally and experimentally infected animals. The wheals varied in shape (roundish, oval or irregular) and size (from a few millimeters to a few centimeters) and were found on the trunk, neck, chest and shoulders. Numerous wheals appeared contemporaneously, developing quickly and suddenly. They were seen for a few hours to a few days and then disappeared, often reappearing in a different area. A “silver dollar” plaque was seen in just one

Nervous Signs

Three animals (Table 4) presented stiffness, weakness, lameness in one or more hind legs, staggering, lack of coordination, inability to stand upright after prolonged sternal or lateral recumbency and ataxia. When standing, animals often stood with the legs well splayed, especially the hind legs. The left hind leg of one animal often dragged on the ground, causing deformation of the hoof wall. As the disease progressed, the difficulties in movement became ever more evident and the affected

Increased Synovial Fluid

Increased synovial fluid and consequent joint ectasia were found in 50% of the symptomatic horses (Table 4). The joints affected were as follows: pastern, hock and carpus, with synovial fluid testing positive on PCR. In one animal the parasite could be seen on microscopic examination of synovial fluid from the hock joint.

Fever

No animal presented significant fever during the observation period.

Eye Lesions: Conjunctivitis and Keratitis

Mild corneal opacity was observed in just one experimentally infected animal. PCR of the conjunctival swab

Discussion

Data collected in this study demonstrate that most of the signs observed coincide with those reported in the few available literature studies. The stages of the disease described in the past and related to pathogenesis also occur in the same order today. The horses observed can be divided into three main groups: naturally infected mares (group 1), naturally infected stallions (group 2), and experimentally infected mares (group 3).

No rise in body temperature was observed in any of the infected

Conclusion

Given the extreme variability of signs in infected animals, difficulties in clinical diagnosis, and the lack of Europe-wide active surveillance plans, it is important to observe and report new cases of Dourine. Difficulties regarding the isolation of the T. equiperdum should stimulate more interest in the experts’ community.

References (16)

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