Chikungunya virus: epidemiology, replication, disease mechanisms, and prospective intervention strategies

Like that of the ECSA lineage, the geographical range of the Asian lineage has also recently expanded.Since 2011, when the virus was first detected in the Pacific Island region of New Caledonia (50), CHIKV has caused outbreaks on 10 of the 22 countries and territories of the Pacific Islands, with strains from the Asian lineage being responsible for the majority of these outbreaks (51, 52).Beginning in 2012, islands in Oceania were bombarded with not only CHIKV outbreaks, but also epidemics of Dengue virus and Zika virus (50, 53, 54).As with CHIKV, infected travelers are thought to be the main source of Dengue and Zika virus outbreaks in the Pacific.Strains from the Asian and ECSA lineages, including the IOL subgroup, continue to cocirculate and spread within the Indian subcontinent, Southeast Asia, and Oceania (Figure 1 and refs.41, 47, 55-60).With such high rates of virus importation by infected travelers, the introduction of CHIKV into the Western Hemisphere seemed inevitable.In December 2013, the first local transmission of CHIKV in the Western Hemisphere in modern history was reported, with autochthonous cases identified in the Caribbean island of French St. Martin (61).The emergence of CHIKV in the Western Hemisphere was remarkable in that the virus spread rapidly to immunologically naive populations in the Caribbean as well as Central, South, and North America.Since the 2013 introduction of CHIKV in the Americas, over 2 million suspected cases caused by endemic transmission have occurred in almost 50 countries, including 12 cases of autochthonous transmission in the United States (Figure 1 and ref. 51).The initial outbreak of CHIKV in the Americas was first attributed to a variant from the Asian lineage.However, the introduction of an ECSA strain into Brazil in 2014 (62) raises a concern for vector adaptation in the Americas and spread of CHIKV to more temperate regions, such as the United States, where A. albopictus has a greater range (Figure 1 and ref.63).Because of globalization and the expansion and year-round presence of relevant vectors, especially in densely populated urban centers (63), the risk that the virus will become endemic in tropical regions of the Americas remains high.Establishment of CHIKV in the Americas, as well as repeated introduction events, suggests that the virus will continue to spread and that the sporadic and explosive outbreaks of CHIKV observed in Africa and Asia also will likely occur in the Western Hemisphere.