Amplification of the Sylvatic Cycle of Dengue Virus Type 2, Senegal, 1999–2000: Entomologic Findings and Epidemiologic Considerations

Abstract

After 8 years of silence, dengue virus serotype 2 (DENV-2) reemerged in southeastern Senegal in 1999. Sixty-four DENV-2 strains were isolated in 1999 and 9 strains in 2000 from mosquitoes captured in the forest gallery and surrounding villages. Isolates were obtained from previously described vectors, Aedes furcifer, Ae. taylori, Ae. luteocephalus, and—for the first time in Senegal—from Ae. aegypti and Ae. vittatus. A retrospective analysis of sylvatic DENV-2 outbreaks in Senegal during the last 28 years of entomologic investigations shows that amplifications are periodic, with intervening, silent intervals of 5–8 years. No correlation was found between sylvatic DENV-2 emergence and rainfall amount. For sylvatic DENV-2 vectors, rainfall seems to particularly affect virus amplification that occurs at the end of the rainy season, from October to November. Data obtained from investigation of preimaginal (i.e., nonadult) mosquitoes suggest a secondary transmission cycle involving mosquitoes other than those identified previously as vectors.

Impact of Climate and Mosquito Vector Abundance on Sylvatic Arbovirus Circulation Dynamics in Senegal

“…3,35 However, our data and this analysis have several limitations. The observed arbovirus dynamics may be heavily influenced by bias in the surveillance techniques used to generate the data.…”

“…Collection methods have been described previously. 2,3,13 Briefly, mosquitoes were collected at savanna and gallery forest sites surrounding Kedougou (12 11 W, 12 33 N) (Figure 2). The majority of mosquitoes were collected by human landing collection during the rainy season (generally June through October), with individuals collecting mosquitoes for 2 hours around dusk.…”

“…These sylvatic cycles have been confirmed by isolation of virus from mosquitoes captured in gallery forests 2 and detection of antiviral antibodies and isolation of sylvatic viruses from non-human primates and humans. 3 Routine surveillance for multiple mosquito-borne viruses, using mosquito capture by human landing collection in gallery forests as well as periodic and opportunistic capture of primates (Figure 1), has been conducted in southeast Senegal for over 50 years by the Institut Pasteur de Dakar. Virus isolations from mosquitoes and non-human primates have revealed interesting patterns in the periodicity and synchrony of DENV circulation, 4 but the drivers of these patterns are poorly understood.…”

Differential replication of dengue virus serotypes 2 and 3 in coinfections of C6/36 cells and Aedes aegypti mosquitoes

“…The development of severe disease forms is associated with multiple factors, some of which are related to the virus and the virulence of some strains, and others that are related to the host immune response [3]. Approximately 96 million cases of dengue infection are reported annually [4], mainly in the tropical and subtropical regions of the Asian [5,6], African [7], and American [8] continents. In other words, approximately half of the global population is at risk for DENV-associated diseases.…”

Genotyping of Dengue Virus 2 Using Restriction Site-Specific (Rss)-PCR

“…Dengue viruses consist of a single-stranded positive-sense RNA genome of approximately 10,700 bases in length, surrounded by a nucleocapsid and a lipid envelope (Santos et al 2002). In terms of illness and death, dengue is the most important viral disease transmitted to humans by mosquitoes (Diallo et al 2003). At the beginning of the 21 st century it is estimated that between 50 and 100 million cases of DF (dengue fever) and several hundred thousand cases of DHF (dengue hemorrhagic fever) occur each year, depending on epidemic activity (Gubler 2002).…”