Fast track — ArticlesInfection with chikungunya virus in Italy: an outbreak in a temperate region
Introduction
Chikungunya virus (CHIKV) is an arthropod-borne virus transmitted to human beings by Aedes spp mosquitoes. After the isolation of the virus in Tanzania in 1953,1 sporadic cases and a number of outbreaks of infection with CHIKV have been reported in several African countries, on the Indian subcontinent, and in southeast Asia.2 In the past few years, a series of outbreaks have been reported over a large geographical area that includes African islands in the Indian Ocean and the Indian subcontinent. The first of the outbreaks occurred in Kenya in 2004, followed by outbreaks on the Comoros Islands, the island of La Réunion, and other islands in the southwest Indian Ocean in early 2005, and by a large outbreak in India in 2005–06.3, 4 According to the molecular analysis of the strains isolated on islands in the Indian Ocean and in India, the epidemic was caused by a variant of the central/east African genotype of CHIKV.5
During the outbreak on islands in the Indian Ocean, a large number of travellers from industrialised countries with a temperate climate became infected with CHIKV and were still infected on returning home.6, 7, 8, 9 In some of these industrialised countries, Aedes albopictus—a vector of CHIKV—was introduced a number of years ago and is now widespread,10 with an especially high population density in Italy.11 This situation is particularly threatening because it has been suggested that the strain of CHIKV in the Indian Ocean has better adapted to A albopictus than it has to other Aedes spp.4 Nonetheless, to date, no outbreaks due to the local transmission of CHIKV have been reported in these countries. Here, we report on a large outbreak of CHIKV infection that occurred in two neighbouring villages in Italy.12
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Patients
In July and August, 2007, the local health unit of the province of Ravenna (region of Emilia Romagna, northeastern Italy) detected an unusually high number of cases of febrile illness in Castiglione di Cervia and Castiglione di Ravenna, two small villages divided by a river. In the second week of August, the local health unit implemented an active surveillance system to identify, both prospectively and retrospectively, all individuals with febrile illness, on the basis of reports provided by
Results
205 cases of CHIKV infection occurred between July 4 to Sept 27, 2007, in Ravenna (figure 1). There were several waves of cases, with the number peaking in the third week of August. Up to the time of this peak, most cases had occurred in Castiglione di Cervia and Castiglione di Ravenna. Afterwards, and after the first mosquito control measures in the area that was mainly affected had been implemented (on Aug 18), a new wave of cases was observed, most of which occurred outside the two villages.
Discussion
This outbreak of CHIKV infection, outside a tropical country, was probably begun by a man from India, who developed a febrile syndrome 2 days after his arrival in Italy. He had high titres of antibodies against CHIKV at the time of examination (early September) and was probably highly viraemic when visiting his relatives (late June) in the village where the epidemic began. The phylogenetic analysis showed that the strain that caused this outbreak was similar to the strains detected on the
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