BACKGROUND: Dengue viruses (DENV) are endemic in over 100 countries worldwide, and annually 50 to 100 million people are infected by one of the four DENV serotypes, whereas over 2.5 billion people are at risk for infection. West African countries lack the surveillance to determine the true incidence of dengue; hence, this disease is likely significantly underestimated. In Mali, approximately 14 million people are potentially at risk of acquiring a dengue infection. METHODS AND FINDINGS: A serosurvey for DENV was conducted on 95 human serum samples obtained from the Institute National de Recherche en Sante Publique in 2006. DENV-specific IgM and IgG enzyme-linked immunosorbent assays were performed on all samples, and a subset was tested using the plaque-reduction neutralization test against the DENV and yellow fever virus (YFV). Samples collected during the acute infection (0-5 days postonset of symptoms) were tested for dengue NS1 antigen and reverse-transcriptase polymerase chain reaction for Flaviviruses, Alphaviruses, and Bunyaviruses RNA. A total of 87 (93%) of samples were positive for anti-DENV IgG antibodies. Of a subset of 13 IgG positive samples, 2 samples neutralized monotypically against DENV-1 and -2, whereas 3 others neutralized broadly against YFV and multiple DENV. Although no polymerase chain reaction positives were found, DENV NS1 was detected in 1 of the 20 acute samples tested. CONCLUSIONS: Of the 93 human serum samples tested, the dengue prevalence based on dengue IgG enzyme-linked immunosorbent assay results was 93%. Three DENV specific positive samples and two YFV positives were identified by plaque-reduction neutralization test. Finally, one sample tested positive for dengue NS1, thus suggestive of an acute infection within 14 days of obtaining the sample from the patient. Based on these serological data from this study, YFV and DENV appear to be co-circulating in Mali.

After the isolation of West Nile virus (WNV) from humans, mosquitoes, and chickens in 2007, an analysis of animal surveillance involving multiple species (horses, monkeys, sheep, dogs, and birds) used to track WNV transmission from 2006 to 2008 was performed. During this period 13.4% of all the animal samples collected were seropositive by blocking ELISA for WNV. The most complete island-wide sampling was obtained from horses of which 22% were serologically positive and 96% were confirmed as WNV infections by plaque-reduction neutralization test. Our conclusion from this 3-year study is that animal surveillance is an early indicator of WNV activity before the identification of human cases. Additionally, the results indicated that horses have a greater geographical range and should be continued to be used as sentinels for passive surveillance in the tropics.

Annually, over 2.5 billion people are at risk for infection by dengue virus (DENV), while between 50 and 100 million people contract the disease. There is an urgent need for alternative diagnostic tools that can detect DENV during acute infection. Recent studies have shown that dengue nonstructural protein 1 (NS1) is detectable in the blood as early as the onset of symptoms and persist well into the convalescent phase of the infection. We evaluated the utility of the BioRad Platelia Dengue NS1 Antigen Capture(R) kit in combination with real time reverse transcriptase polymerase chain reaction (RT-PCR) and IgM antibody capture enzyme linked immunosorbent assay (MAC ELISA) for refining a new diagnostic algorithm for the diagnosis of an acute or convalescent DENV from a single clinical sample. We tested the BioRad kit in three panels of sera. These panels were designed to evaluate the sensitivity of the NS1 kit in (1) early convalescent samples, (2) PCR false negative acute samples, and (3) confirmed secondary dengue infections with IgM negative convalescent samples. Results show that the NS1 can be detected in 22% serum collected after 10 days post onset of illness and in 22% of samples that did not elicit an IgM response. Additionally, NS1 was detected in 37% of the PCR false negative acute samples tested suggesting that NS1 detection may be valuable in increasing the sensitivity of current acute phase diagnostics. These results will improve diagnosis in a single acute or early convalescent sample for disease surveillance and clinical diagnosis.