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Birth, immigration in South Pacific may promote spread of dengue
The 2013 reappearance of the dengue virus type 3 in the South Pacific islands suggests that birth and immigration rates in this region may promote the recurrence of epidemics every 4 to 5 years, according to recent findings.
In the study, researchers investigated an outbreak of the dengue virus serotype 3 (DENV-3) at the National Referral Hospital in Honiara, Solomon Islands, in January 2013, after an 18-year absence. By July 2013, more than 6,000 suspected cases and seven deaths were reported.
After screening serum samples from 3,141 patients for DENV nonstructural protein (NS1) and immunoglobulin M against DENV, the researchers found that 1,220 (39%) of the samples tested positive. Reverse transcription PCR analysis revealed NS1 positivity in 10 additional samples.
In March 2013, DENV-3 also was reported in French Polynesia in two family members. One of these family members had recently traveled to Cayenne, French Guiana, and returned with a fever. By July 2013, French Polynesia had 1,326 suspected cases of dengue, of which 258 were confirmed by lab testing. Serotype testing identified 170 DENV-1 infections, 73 DENV-3 infections and one case of coinfection with both serotypes.
A phylogenetic analysis indicated that the Solomon Islands outbreak was the result of the introduction of a strain from Indonesia. This strain might have been circulating in Papua, New Guinea, for 4 to 5 years and went unidentified. Prior reappearance of DENV-4 into the Pacific Islands may have originated with the introduction of a strain from India into the Solomon Islands.
Conversely, the researchers found that based on epidemiologic and phylogenetic evidence, the outbreak of DENV-3 infection in French Polynesia was due to a strain carried from South America.
Before 1990, most outbreaks of DENV in the South Pacific were transmitted from Latin America. However, the current study determined that since that time, Southeast Asia is the main source of outbreaks.
According to the researchers, births and immigration rates (1.2% and 1.1%, respectively in French Polynesia in 2010) in these regions offered enough susceptible hosts to generate a DENV epidemic every 4 to 5 years and for one of the DENV serotypes to re-emerge every 12 to 15 years.
“Moreover, the finding that recent DENV-3 outbreaks were caused by multiple genotypes supports observations made during outbreaks of DENV-1 infection in 2001-2004,” the researchers wrote. “These observations also suggest that the principal determinant of DENV reemergence in the South Pacific Islands is herd immunity, rather than the genotype of DENV being introduced.”
Disclosure: The researchers report no relevant financial disclosures.