News Scan for Apr 28, 2014

More Caribbean chikungunya
;
Origin of 1918 pandemic flu virus

Chikungunya cases in the Caribbean top 33,000

The Caribbean chikungunya outbreak grew by 3,499 cases in the past week, reaching 33,260 suspected, probable, or confirmed cases, according to an update today from the European Centre for Disease Prevention and Control (ECDC). The case count is up from 29,761 in the agency's Apr 22 report.

Martinique continues to report the largest numbers, with 17,630 suspected (up from 16,000) and 1,515 confirmed or probable cases, the ECDC said. Guadeloupe reported the second-most cases, with 6,000 suspected and 1,328 confirmed or probable cases. The French side of St. Martin is third, with 3,030 suspected and 793 confirmed or probable cases.

Also reporting cases are Dominica, 1,063 suspected and 98 confirmed cases; the Dominican Republic, 767 suspected and 17 confirmed cases; St. Barthelemy, 480 suspected and 135 confirmed or probable cases; the Dutch side of St. Martin, 301 confirmed cases; French Guiana, 36 confirmed locally acquired and 18 imported cases; Anguilla, 33 locally acquired confirmed cases and 1 likely imported; British Virgin Islands, 9 confirmed cases; St. Vincent and the Grenadines, 3 cases; and Aruba, St. Lucia, and St. Kitts and Nevis, each with 1 confirmed case.

The chikungunya outbreak is the first known in the Americas and began in December 2013 on the French side of St. Martin. So far 6 outbreak deaths have been confirmed, 3 on the French side of St. Martin, 2 on Martinique, and 1 on Guadeloupe.
Apr 28 ECDC update

 

Scientists propose alternate origins for 1918 pandemic flu virus

The 1918 H1N1 pandemic influenza virus may have originated from reassortment between a human flu virus lineage and an avian flu virus, researchers speculate today after conducting a phylogenetic evolutionary analysis. The findings run contrary to previous estimates of the virus's evolution.

US and UK researchers analyzed full-length gene sequences from human, bird, and swine viruses over the years involving H1, H2, H5, and N1 subtypes, according to their study in Proceedings of the National Academy of Sciences.

Their results indicate that human H1 (the "H" is for the hemagglutinin [HA] protein) emerged from an avian source well before 1918 but after 1895. They also noted that the classic swine flu lineage is nested completely within the 1918 genetic diversity of human H1 but the seasonal human H1 HA line is only distantly related to the pandemic 1918 HA.

"This pattern indicates that the swine influenza lineage emerged directly from the human pandemic virus but that postpandemic seasonal H1N1 did not," they write. "Rather, there is strong phylogenetic evidence that it descended from a distinct H1 lineage that shared a common ancestor with the 1918 pandemic ~1907."

"These results are consistent with an avian-to-human movement of H1 in the first decade of the 20th century," the authors conclude. They say their theory fits with the age-related pattern of extensive morality in 20- to 40-year-olds, because people that age would have been primarily exposed to an H3N8 virus, which would afford little cross-immunity.

Previously, predictions that the 1918 strain was of avian origin and did not reassort with a human strain have predominated.
Apr 28 Proc Natl Acad Sci abstract
CIDRAP overview on pandemic influenza, which includes 1918-origin theories

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