By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University
Dr. Deresinski reports no financial relationships relevant to this field of study.
SYNOPSIS: An outbreak of autochthonously acquired chikungunya infection has affected 298 individuals as of early October 2017, while a small outbreak also has occurred in southeastern France.
On Sept. 7, Italian public health authorities reported the identification of three locally acquired cases of chikungunya virus infection in Anzio, a seaside town approximately 60 km south of Rome and the site of a famous World War II battle. A week later, six cases from within Rome itself were reported. Cases continued to occur in nearby areas as well as from the more distant Calabria region, the “toe of the Italian boot.” As of Oct. 4, the total number of reported cases was 298. Further investigation suggested that autochthonous transmission actually had started in June and perhaps earlier.
Meanwhile, on Aug. 11, France reported an outbreak of chikungunya in the commune of Cannet-des-Maures, in the Provence-Alpes-Cote d’Azur region in the southeastern part of the country. Two clusters of additional cases were reported, reaching a total of 17 cases as of Oct. 3.
The viruses causing infection in Italy and France are distinct. The virus detected in Anzio belongs to the East/Central/South African (ECSA) lineage with homology to strains recovered in India and Pakistan in 2016. Of note is that it does not carry the E1-A226V mutation previously reported to facilitate transmission by Aedes albopictus, the tiger mosquito, which was introduced in Italy prior to the only previous outbreak of autochthonous cases in 2007, with the infection first introduced by a traveler from India. That outbreak accounted for 205 cases and one death, all in the province of Ravenna. The French virus, in contrast, belongs to a sublineage of ECSA that is known to include virus from central Africa and does contain the E1-A226V mutation. France experienced small outbreaks of locally acquired cases in 2010 and 2014, with two and 11 cases, respectively.
Aedes albopictus maintains activity throughout the year in tropical and subtropical regions, peaking in summer and autumn. Furthermore, there is evidence that cold adaptation of this aggressive mosquito is occurring in central Italy. It breeds in both natural and man-made collections of water. An outdoor mosquito (although apparently also adapting to indoor environments), it bites throughout the day, with peak activity in the early morning and late afternoon. The E1-A226V envelope mutation detected in the virus in France increases the transmissibility of the virus by Aedes albopictus. One can hope that its absence in the virus causing the current infections in Italy will limit transmissibility, ameliorating the outbreak. The major vector of chikungunya virus in the world is not Aedes albopictus, but Aedes aegypti, which is present in Europe, albeit limited to date to the Black Sea region and Madeira. Both of these mosquitoes are present in areas of the United States, and local transmission of chikungunya has occurred in Florida, as well as in Puerto Rico and the U.S. Virgin Islands. As many have suggested, many people in the United States as well as residents and travelers to Europe may encounter this virus.
Just to add to the woes in Italy, the CDC just reported that four cases of locally acquired malaria due to Plasmodium falciparum have occurred in migrant workers in Ginosa (which is in the “instep” of the Italian boot).1 The isolated nature of the outbreak, however, would appear to represent little threat outside that community.