Seroprevalence of Antibodies against Chikungunya, Dengue, and Rift Valley Fever Viruses after Febrile Illness Outbreak, Madagascar - - Emerging Infectious Disease journal - CDC
Seroprevalence of Antibodies against Chikungunya, Dengue, and Rift Valley Fever Viruses after Febrile Illness Outbreak, Madagascar
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In October 2009, the sentinel surveillance system for early outbreak detection in Madagascar (1) reported an increase of cases of fever with joint pain on the eastern coast. At the beginning of February 2010, chikungunya virus (CHIKV) infection was diagnosed in a patient from the Mananjary district. The International Federation of Red Cross and Red Crescent Societies reported 702 clinically diagnosed cases of chikungunya during February 9–February 15, 2010. Six hundred occurred in the coastal city of Mananjary, and 96 occurred in the small village of Irondro at the crossroads between the towns of Mananjary, Manakara, and Ifanadiana, indicating that the area was a focal point of the epidemic (Figure 1) (2).
AbstractIn 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.
Arthropod-borne viruses (arboviruses) such as CHIKV (3), dengue virus (DENV), and Rift Valley fever virus (RVFV) (4,5) are emerging pathogens in the southwestern Indian Ocean region. In 2005–2006, CHIKV caused outbreaks and epidemics on La Réunion, Mauritius, Mayotte, and the Seychelles (6), which caused considerable illness and death (7). Chikungunya appears to occur as an epidemic and an endemic disease in this region. The endemic disease affects mainly populations with high levels of IgG against CHIKV who live in rural areas in Africa (8). The epidemic disease occurs in Asia and the Indian Ocean region in populations in which herd immunity is weak, often in urban areas where Aedes aegypti and Ae. albopictus mosquitoes are the main transmission vectors. During epidemics, humans are the primary reservoirs. Monkeys, rodents, birds, and cattle have been identified as animal reservoirs (9–11). The onset of chikungunya epidemics is acute with high attack rates as seen in 2005–2006 on La Réunion (12). Concurrent epidemics of dengue and chikungunya have been reported from Asia (13) and Africa (14). In 2006, a combined outbreak of dengue fever and chikungunya fever occurred near the Madagascan city of Toamasina (15), but the rest of the country remained unaffected by this epidemic. An increased number of RVFV infections was noticed in Madagascar during the rainy seasons of 2008 and 2009 with 476 (19 fatal) and 236 (7 fatal) suspected cases, respectively (4).
The sudden emergence of chikungunya in the Mananjary area indicated a lack of herd immunity in the affected population. The previous outbreak of CHIKV infection in Madagascar in 2006 in the Toamasina region occurred in conjunction with DENV infection. Because of the recent reports of RVFV infections in animals and humans, our investigation of the recent outbreak in Madagascar included assessment of serologic parameters against CHIKV, DENV, and RVFV.
Approximately 2–3 months after the peak and 1–2 months after the decline of the outbreak of chikungunya, we retrospectively assessed the serologic markers and reported clinical features of women who came for routine pregnancy follow-up visits at 6 geographic locations. By focusing on pregnant women, we could reduce the need to stratify for age and sex and thus minimize the fragmentation of data. The focus could then to be placed on 1) assessing a possible inward spread of the epidemic, 2) evaluating whether the epidemic was limited to CHIKV or due to a simultaneous occurrence of DENV or RVFV infections, and 3) detecting factors associated with an increased risk of CHIKV infection.