Dengue fever in travellers and risk of local spreading: case reports from Southern Italy and literature update

Dengue fever (DF), an arbovirosis caused by Dengue viruses (DV, serotypes 1-4), is responsible for an increasing number of travel-related acute febrile illnesses due to population growth, climate changes, spreading by viremic travellers, and improved laboratory diagnosis. The presence of efficient vectors (mosquito Aedes albopictus) has also been described in temperate regions including Italy which is considered the most heavily infected European country. Normally characterized by non-specific signs and symptoms, DF incidence is probably underestimated, especially in non-endemic countries, but the risk of severe forms is substantial. Between August and November 2013, five DF patients (4 males, age 23-38) were observed in the Infectious Disease Clinic (University of Bari, Southern Italy). All had just returned from DF endemic areas (2 French Polynesia, 3 Dominican Republic); 4/5 were hospitalized. Common clinical features included acute febrile syndrome, headache (2 with retro-orbital pain), rash (all patients), two with bleeding manifestations and one with gum bleeding. Laboratory tests demonstrated leukopenia (4 patients), elevated liver enzymes (3 patients), and thrombocytopenia (1 patient). Serum samples for DV antibodies and RNA detection were analyzed by the Regional Arbovirosis Reference Laboratory. Viral RNA was identified in 2/5 patients (DV-4) and seroconversion in the remaining cases. All patients made a complete recovery. Recent literature was reviewed, focusing on epidemiology and vector distribution (especially European and Italian territories), pathogenesis, clinical features, diagnosis, and treatment including vaccine strategies. The occurrence of 5 DF cases during the period of highest vector activity (June-November) in Italy emphasizes the risk of local outbreaks in temperate regions. This paper highlights the importance of clinical alert for dengue also in non-endemic countries.