In slightly more than a year, the Americas have seen more than 1.24 million cases of chikungunya virus, a mosquito-borne disease that causes high fever and debilitating joint pain. The tropical virus was rare in North, Central, and South America until December 2013, when investigation of suspected dengue virus in the Caribbean island of St. Martin turned up 26 cases of chikungunya, without any sign they had been imported from elsewhere. As of the end of February 2015, that handful of cases had exploded to 1,247,400 suspected and confirmed cases, affecting almost every country in the hemisphere, according to the Pan-American Health Organization. Until the end of 2013, chikungunya in the Americas was almost entirely imported from countries in Africa or Asia where the tropical virus was endemic. In the U.S., most cases are still imported — a cumulative total of some 2,542 since 2013, according to the PAHO, with an additional 11 cases, all in Florida, blamed on local transmission. But most of that transmission now comes from the epidemics raging elsewhere in the region. The U.S. numbers might be an underestimate. They’re based on reports to the ArboNET, a national arboviral surveillance system managed by the CDC and state health departments. But until this year, the virus was not a nationally notifiable disease, so some cases might have been missed. There is no specific treatment for the virus and no vaccine, but its dramatic spread has re-focused the attention of vaccine researchers. Online in Lancet Infectious Diseases this week, investigators are reporting that a recombinant candidate based on a measles vaccine had promising immunogenicity in a phase I dose-finding trial.
Regardless of dose, a single shot of the vaccine produced neutralizing antibodies to chikungunya, according to Bernd Jilma, MD, of the Medical University of Vienna in Austria, and colleagues. A second dose, either 28 or 90 days after the first led to seroconversion in all participants, Jilma and colleagues reported. And last summer, investigators led by Julie Ledgerwood, DO, of the National Institute of Allergy and Infectious Diseases, reported that a virus-like particle vaccine produced immunogenic reactions in a study of 25 volunteers. The endpoint of the study was the presence of neutralizing anti-chikungunya antibodies on day 28 — a mark that was reached by 44% in the lowdose group, 92% in the medium-dose group, and 90% in the high-dose group.