Canine filarioid infections in an area of North-West Italy (Liguria) traditionally considered free from the disease

INTRODUCTION: Canine filarioid infections are widespread throughout the world and steadily increasing despite prophylaxis. New cases in dogs and in humans have occurred in many countries and regions that were previously considered to be free or for which epidemiological data were not available. The aim of this work is to report the presence of different species of filarioid nematodes in dogs in an area of north-west Italy (Liguria), traditionally considered free from the disease and where prophylaxis is not implemented. METHODS: Between 2009 and 2012 blood samples were collected from 365 dogs living in rural areas of Liguria (in the provinces of Savona and Imperia) and submitted to Knott’s test, histochemical staining, PCR targeting part of the 5.8S-ITS2-28S gene, and ELISA for Dirofilaria immitis antigens (Dirocheck, Synbiotics®). In addition serological data were analysed for D. immitis antigens that had been collected by the Istituto Zooprofilattico Sperimentale (IZS, section of Imperia) between 2004 and 2013 during the annual control for leishmaniosis. An average of 1285 dogs/year (range 417-2089) from the four Ligurian provinces (Imperia, Savona, Genoa, La Spezia) had been tested. RESULTS: Thirty-five dogs were positive to Knott's test for microfilariae (prevalence 9.6%, 95% Confidence Interval: 6.6-12.6%): Acanthocheilonema reconditum was the most common species (8.0%), while Dirofilaria repens (1.4%) and D. immitis (0.6%) were less common. Co-infection by D. repens and A. reconditum was observed in one dog. All morphological identifications were confirmed by histochemical staining and PCR followed by sequencing. Five dogs out of 365 (prevalence 1.4%, 95% CI: 0.2-2.6%) were positive to the ELISA test for antigens of D. immitis. Of these, two dogs were positive to Knott's test for microfilariae of D. immitis, while the other three did not present circulating microfilariae (occult filarioidosis). Analysis of the IZS data showed an average annual serological prevalence of 0.6% for D. immitis in the whole region. DISCUSSION AND CONCLUSION: The results of this study confirm that canine filarioid infections are increasing in Italy in areas that were once free, as is happening in many other countries worldwide, in particular in Central and Eastern Europe and South America. Prior to the present study, in our study area there had been only a few reports of cases of unidentified microfilaremia in 1986 and of one case of D. repens in a dog in Genoa in 1995.This study contributes to the epidemiological map of filarioid infections in Italy, and suggests the need for prophylaxis in this region. In addition, the widespread presence of different species of filarioid nematodes in the provinces of Imperia and Savona suggests the need to enlarge the study using Knott’s test and PCR also in dogs living in the other districts for which only preliminary serological data concerning D. immitis are available. The zoonotic potential of these parasites must also be considered in relation to tourism in the area, which attracts many visitors from other European countries, often travelling with dogs.