Abstract
In the Lao PDR (Laos), urban dengue is an increasingly recognised public health problem. We describe a dengue-1 virus outbreak in a rural northwestern Lao forest village during the cool season of 2008. The isolated strain was genotypically “endemic” and not “sylvatic,” belonging to the genotype 1, Asia 3 clade. Phylogenetic analyses of 37 other dengue-1 sequences from diverse areas of Laos between 2007 and 2010 showed that the geographic distribution of some strains remained focal overtime while others were dispersed throughout the country. Evidence that dengue viruses have broad circulation in the region, crossing country borders, was also obtained. Whether the outbreak arose from dengue importation from an urban centre into a dengue-naïve community or crossed into the village from a forest cycle is unknown. More epidemiological and entomological investigations are required to understand dengue epidemiology and the importance of rural and forest dengue dynamics in Laos.
Highlights
Dengue is endemic in more than 100 countries in Asia, Africa and the Americas, but 70% of those currently at risk live in South-East Asia and the Western Pacific
High IgM and IgG titres against both O. tsutsugamushi and R. typhi can be detected in healthy rural Lao farmers, presumably reflecting repeated infections in endemic areas (LOMWRU, unpublished data)
Detection of such high titres may be a consequence of repeated or recent rickettsial infections rather than suggesting that O. tsutsugamushi and/or R. typhi were responsible for the outbreak
Summary
Dengue is endemic in more than 100 countries in Asia, Africa and the Americas, but 70% of those currently at risk live in South-East Asia and the Western Pacific. WHO estimates that 50–100 million people are infected by dengue globally every year [1]. Dengue infections may be asymptomatic or symptomatic, classified as dengue fever (DF), dengue haemorrhagic fever (DHF), and dengue shock syndrome (DSS) [2] or more recently as dengue, dengue with warning signs and severe dengue [3]. Dengue viruses (DENV) are single stranded RNA viruses from the family Flaviviridae, transmitted by Aedes spp. mosquitoes, which are predominantly urban. Sylvatic dengue has been described in humans in SE Asian and West African forests [4,5,6,7,8,9,10,11] but has only been associated with one outbreak [5]. There is evidence of interactions between urban and sylvatic dengue, their importance for dengue epidemiology and public health is not well understood [11]
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