Seroprevalence of antibodies against Chikungunya, Dengue, and Rift Valley fever viruses after febrile illness outbreak, Madagascar

Abstract

In October 2009, two-3 months after an outbreak of a febrile disease with joint pain on the eastern coast of Madagascar, we assessed serologic markers for chikungunya virus (CHIKV), dengue virus (DENV), and Rift Valley fever virus (RVFV) in 1,244 pregnant women at 6 locations. In 2 eastern coast towns, IgG seroprevalence against CHIKV was 45% and 23%; IgM seroprevalence was 28% and 5%. IgG seroprevalence against DENV was 17% and 11%. No anti-DENV IgM was detected. At 4 locations, 450-1,300 m high, IgG seroprevalence against CHIKV was 0%-3%, suggesting CHIKV had not spread to higher inland-altitudes. Four women had IgG against RVFV, probably antibodies from a 2008 epidemic. Most (78%) women from coastal locations with CHIKV-specific IgG reported joint pain and stiffness; 21% reported no symptoms. CHIKV infection was significantly associated with high bodyweight. The outbreak was an isolated CHIKV epidemic without relevant DENV co-transmission.

Figure 1

Madagascar (gray shading in inset), showing the main roads, the capital of Antananarivo (square), the harbor city of Toamasina (white circle), and the locations of the 6 study sites (black circles) from which serologic samples from pregnant women were screened for IgG against chikungunya virus, dengue virus, and Rift Valley fever virus. The altitudes of the locations are as follows: Mananjary and Manakar, coastal; Ifanadiana, 466 m; Moramanga, 920 m; Tsiroanomandidy, 860 m; Ambositra, 1,280 m; Toamasina, coastal; Irondro, 40 m; Antananarivo, 1,300 m.

Figure 2

Images from immunofluorescence assays in Vero E6 cells for IgG against chikungunya virus (CHIKV), dengue virus (DENV), and Rift Valley fever virus (RVFV). Original magnification ×100 and ×200.

Figure 3

Images of immunofluorescence assays in Vero E6 cells for IgM against chikungunya virus (CHIKV) and dengue virus (DENV). For each of the viruses, a positive control, an example of a positive serum sample (if available), and a negative control are shown. Original magnification ×100 and × 200.