Via Emerging Infectious Diseases, a remarkable report: Transcontinental Movement of Asian Genotype Chikungunya Virus. Excerpt:
In agreement with findings in a recent report characterizing the 2013 CHIKV detected on St. Martin Island (6), the phylogenetic tree generated from our sequence data showed that the 2014 CHIKV from BVI is within the Asian genotype and is closely related to strains recently isolated in China and the Philippines.
This finding supports the idea that a single CHIKV strain of the Asian genotype was recently introduced into the Caribbean and is currently moving throughout the region. The 2 CHIKVs isolated in Yap in 2013 are most closely related to the CHIKV from BVI, differing by only 18–19 nt.
The tree also demonstrates that the CHIKV strains from Yap, BVI, China, and the Philippines form a strongly supported clade (bootstrap of 1,000) within the Asian genotype (Figure). Within this clade, the CHIKVs detected in 2012 in Zhejiang Province, China, and the Philippines are nearly identical, differing by only 4 nt in the entire genome.
However, there is some ambiguity regarding the exact origins of these 2 strains. The 2012 CHIKV from the Philippines is described in GenBank (www.ncbi.nlm.nih.gov/nuccore/KC352904.1) as an “imported Chikungunya fever case in Ningbo port”; the virus was isolated and identified in Ningbo, China, but was detected in samples from a traveler from the Philippines (GenBank accession nos. KC352904.1 and KC488650.1). The 2012 Zhejiang CHIKV was detected and characterized in Zhejiang Province, but the virus was from a sailor who traveled around Southeast Asia; therefore, the exact origin of this virus is also unknown (7).
The striking similarity between the 2012 CHIKVs from the Philippines and Zhejiang Province suggests a common origin, perhaps the Philippines, where CHIKV transmission was documented in 2012 and 2013. Regardless of the exact origins of these 2 strains, it is clear that the CHIKV strain currently moving throughout the Caribbean originated from a CHIKV strain that was recently circulating between China, the Philippines, and Yap in Southeast Asia.