Summer Buzz

Polyxeni Potter

Author affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia, USA

Reemergence of Chikungunya Virus in Bo, Sierra Leone

Rashid Ansumana, Kathryn H. Jacobsen

, Tomasz A. Leski, Andrea L. Covington, Umaru Bangura, Mary H. Hodges, Baochuan Lin, Alfred S. Bockarie, Joseph M. Lamin, Moses J. Bockarie, and David A. Stenger

Author affiliations: Njala University, Bo, Sierra Leone (R. Ansumana, A.S. Bockarie); Mercy Hospital Bo (R. Ansumana, A.L. Covington, U. Bangura, A.S. Bockarie, J.M. Lamin); Liverpool School of Tropical Medicine, Liverpool, United Kingdom (R. Ansumana, M.H. Hodges, M.J. Bockarie); George Mason University, Fairfax, Virginia, USA (K.H. Jacobsen); US Naval Research Laboratory, Washington, DC, USA (T.A. Leski, B. Lin, D.A. Stenger)

Abstract

We diagnosed 400 possible IgM-positive cases of chikungunya virus in Bo, Sierra Leone, during July 2012–January 2013 by using lateral flow immunoassays. Cases detected likely represent only a small fraction of total cases. Further laboratory testing is required to confirm this outbreak and characterize the virus.

Outbreaks of infection with chikungunya virus (CHIKV), an alphavirus that is transmitted by bites of infected Aedes spp. mosquitoes, were frequent in sub-Saharan Africa and southern and Southeast Asia during the 1950s–1970s, but the infection largely disappeared in the 1980s; only sporadic cases were observed (1). The virus reemerged in the early 2000s; major outbreaks were reported in Kenya, some island nations in the Indian Ocean, and several countries in Asia (2,3).
The primary symptoms of CHIKV infection are high fever (>38.5°C [102°F]) and severe pain in the distal joints of the extremities or the lumbar spine. A maculopapular rash, sensorineural impairment, severe headache, and other nonspecific symptoms may also occur. Symptoms usually resolve within 1–2 weeks after onset of fever, but for a sizeable proportion of patients, arthralgia and arthritis become chronic and pain persists for years (2,3).
A nationwide serosurvey in Sierra Leone in 1972 detected cases of CHIKV infection throughout the country (4), but we are not aware of any cases reported since the mid-1970s. Two recent developments made reemergence appear imminent. First, outbreaks of reemerging CHIKV have been reported in neighboring Guinea (5) and in Senegal (6). Second, recent yellow fever cases in Sierra Leone have shown that Aedes spp. mosquito–borne infections are common (7). Thus, it was not surprising when we initiated an infectious disease surveillance study in July 2012 in the city of Bo, in Southern Province, Sierra Leone, that we detected possible chikungunya virus infections. We report initial results of our investigation.

The Study

On July 7, 2012, the Mercy Hospital Research Laboratory (MHRL) in Bo, Sierra Leone, initiated a 1-year infectious disease surveillance program to identify the diversity of pathogens causing febrile illness in the city. A tiered analysis approach was used. First, all specimens from febrile study participants were tested for ≈12 infections with various pathogens, including CHIKV, by commercially available test kits. Specimens that showed negative results in this first round of testing were further tested by using cultures, multiplex PCR, and resequencing pathogen microarrays. The research protocol was approved by Njala University, George Mason University, the Liverpool School of Tropical Medicine, the US Naval Research Laboratory, and the Sierra Leone Ethics and Scientific Review Committee.