Research Article: An Outbreak of Chikungunya in Rural Bangladesh, 2011

Date Published: July 10, 2015

Publisher: Public Library of Science

Author(s): Selina Khatun, Apurba Chakraborty, Mahmudur Rahman, Nuzhat Nasreen Banu, Mohammad Mostafizur Rahman, S. M. Murshid Hasan, Stephen P. Luby, Emily S. Gurley, Andrea Bingham. http://doi.org/10.1371/journal.pntd.0003907

Abstract: BackgroundThe first identified Chikungunya outbreak occurred in Bangladesh in 2008. In late October 2011, a local health official from Dohar Sub-district, Dhaka District, reported an outbreak of undiagnosed fever and joint pain. We investigated the outbreak to confirm the etiology, describe the clinical presentation, and identify associated vectors.MethodologyDuring November 2–21, 2011, we conducted house-to-house surveys to identify suspected cases, defined as any inhabitant of Char Kushai village with fever followed by joint pain in the extremities with onset since August 15, 2011. We collected blood specimens and clinical histories from self-selected suspected cases using a structured questionnaire. Blood samples were tested for IgM antibodies against Chikungunya virus. The village was divided into nine segments and we collected mosquito larvae from water containers in seven randomly selected houses in each segment. We calculated the Breteau index for the village and identified the mosquito species.ResultsThe attack rate was 29% (1105/3840) and 29% of households surveyed had at least one suspected case: 15% had ≥3. The attack rate was 38% (606/1589) in adult women and 25% in adult men (320/1287). Among the 1105 suspected case-patients, 245 self-selected for testing and 80% of those (196/245) had IgM antibodies. In addition to fever and joint pain, 76% (148/196) of confirmed cases had rash and 38%(75/196) had long-lasting joint pain. The village Breteau index was 35 per 100 and 89%(449/504) of hatched mosquitoes were Aedes albopictus.ConclusionThe evidence suggests that this outbreak was due to Chikungunya. The high attack rate suggests that the infection was new to this area, and the increased risk among adult women suggests that risk of transmission may have been higher around households. Chikungunya is an emerging infection in Bangladesh and current surveillance and prevention strategies are insufficient to mount an effective public health response.

Partial Text: Chikungunya is an arthropod-borne disease caused by Chikungunya virus (Alphavirus family, Togaviridae family) which was initially identified in Tanzania in 1952 [1]. Chikungunya outbreaks likely happened before the virus was identified because there were many verifiable depictions of epidemic fevers with remarkable arthralgia [2]. Humans can be a reservoir for Chikungunya virus during epidemics. In the past 50 years, Chikungunya has re-emerged in several occasions in both Africa and Asia [3]. Rapid and local transmission of Chikungunya occurred in the Caribbean and the Americas within 9 months during 2013–2014 [4].Aedes mosquitoes transmit Chikungunya virus. Aedes aegypti mosquitoes are responsible for transmission of both Chikungunya and dengue [5]and in Asia, have been identified as the primary vector in most urban dengue epidemics [6].Aedes albopictus was identified as the vector in the 2006 Chikungunya outbreak in La Reunion (an island in the Indian Ocean). This newly identified vector caused effective replication and spread the infection beyond previously endemic areas [6].A.albopictus can prosper in both rural and urban environments [7] and breed in artificial water containers [8].

We focused the investigation in Char Kushai village because a review of the log books from the local public hospital showed that 70% of the inpatients and outpatients who sought care for fever and joint pain during May—October 2011 were from that village. We conducted house-to-house surveys to identify and enlist suspected cases, defined as any inhabitant of Char Kushai village who reported fever followed by joint pain in the extremities with onset since August 15, 2011. Local authorities reported that the outbreak had been ongoing since May, but we limited our suspected case finding efforts to those occurring since August due to concerns about the ability of residents to reliably recall illnesses for more than a few months.

Data collectors surveyed all 897 households in the village and collected information regarding symptoms for all 3,840 residents; 1105 (29%) of household members met the suspected case definition. There were no differences in attack rates by gender among children <10 years of age; however, females were more likely to report illness than males for every other age group and the differences were greatest among residents aged 31–40 years (28% of males vs 50% of females) and 41–50 years (29% vs 53%) (Table 1). Sixty-four percent of households had at least one suspected case, while 15% had three or more (Table 2). Laboratory findings confirmed that Chikungunya virus caused this outbreak and the clinical features were consistent with previously described outbreaks [17, 18]. This investigation provides further evidence that Chikungunya virus has become an emerging public health problem in Bangladesh [11]. Though no recent community seroprevalence studies of Chikungunya have been published from Bangladesh or nearby countries, a 1995 cross-sectional survey carried out in Kolkata, which is approximately 250 km from Dhaka, indicated that the level of previous exposure to Chikungunya infection in that city was low [19]. Chikungunya infection gives life-long immunity [20], so the consistently high attack rates by age group in our investigation suggest that Chikungunya was new to this geographic area. An abundance of a particular species of mosquitoes during an outbreak is an important condition for determining the vector responsible for transmission [21] and the fact that A.albopictus hatched from 89% of the larvae collected in the village suggests that this vector was likely responsible for transmission during this outbreak. As A. albopictus has a tendency to breed in water compartments close to homes and to feed during the day [22], persons who are at home during the day time could be at increased risk due to prolonged exposure to these mosquitoes. Adult women, most of whom spend the majority of their day at or very near the home, experienced the highest attack rates in this outbreak. This finding is similar to outbreaks of Chikungunya in rural areas in other countries where higher risk among women was also reported [23, 24]. Source: http://doi.org/10.1371/journal.pntd.0003907

 

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