Date Published: January 11, 2016
Publisher: Public Library of Science
Author(s): Beatriz Galatas, Sowath Ly, Veasna Duong, Kathy Baisley, Kunthy Nguon, Siam Chan, Rekol Huy, Sovann Ly, Sopheak Sorn, Leakhann Som, Philippe Buchy, Arnaud Tarantola, Scott B Halstead. http://doi.org/10.1371/journal.pntd.0004281
Abstract: The East/Central/South African genotype of Chikungunya virus with the E1-A226V mutation emerged in 2011 in Cambodia and spread in 2012. An outbreak of 190 cases was documented in Trapeang Roka, a rural village. We surveyed 425 village residents within 3–4 weeks after the outbreak, and determined the sensitivity and specificity of case definitions and factors associated with infection by CHIKV. Self-reported clinical presentation consisted mostly of fever, rash and arthralgia. The presence of all three clinical signs or symptoms was identified as the most sensitive (67%) and specific (84%) self-reported diagnostic clinical indicator compared to biological confirmation by MAC-ELISA or RT-PCR used as a reference. Having an indoor occupation was associated with lower odds of infection compared with people who remained at home (adjOR 0.32, 95%CI 0.12–0.82). In contrast with findings from outbreaks in other settings, persons aged above 40 years were less at risk of CHIKV infection, likely reflecting immune protection acquired when Chikungunya circulated in Cambodia before the Khmer Rouge regime in 1975. In view of the very particular history of Cambodia, our epidemiological data from Trapeang Roka are the first to support the persistence of CHIKV antibodies over a period of 40 years.
Partial Text: Chikugunya is caused by an alphavirus transmitted by the bite of Aedes mosquitoes. In humans, it is mostly a self-limiting illness marked with debilitating joint pains but severe illness occurs in about 1 clinical case in 1000 . Although it may have circulated since the late 1800s , the chikungunya virus (CHIKV) was first detected in Africa in 1952 . The Asian strain spread through Asia in the 1960s causing a series of outbreaks throughout the region, including Cambodia. After several decades of absence, CHIKV re-emerged in the early 2000s [3–5], with large outbreaks of significant public health concern in Asia and Africa. In 2005, a major epidemic in La Réunion island  displayed different epidemiological characteristics than previous outbreaks, with a higher attack rate and causing a number of deaths. Genetic analysis attributed this outbreak to a mutated strain of the East/Central/South African (ECSA) strain of CHIKV bearing the E1-A226V and other mutations on the E2 glycoprotein gene [7,8], termed the Indian Ocean Lineage (IOL) strain . Subsequently, outbreaks of the IOL strain have been recorded in the Indian Ocean [9–11], South- , Southeast- [13–17] and East Asia  and the Pacific . The first outbreak in a temperate country was recorded in 2007 , and cases have been detected in Arabia [21,22]. In 2013, another CHIKV strain, this time of Asian lineage  stormed through the Americas, causing over 1.5 million suspected or confirmed cases to date [24–27]. That outbreak is still ongoing. Chikungunya poses a real and imminent threat to all yet unaffected areas where Aedes aegypti or Aedes albopictus are present, including various regions of Europe , the USA , Brazil  or Australia .
In March 2012, Trapeang Roka consisted of 134 households with 695 inhabitants, mainly rice field workers and factory workers. All persons who were available on the day of the outbreak investigation were approached to be interviewed; there were no refusals. In total, 425 participants (61.1% of the village) from 98 households (73.1%) were surveyed. The global attack rate was 44.7% (190/425) based on IgM (n = 188) or PCR (n = 2) testing.
Our findings show that in a country such as Cambodia that is highly endemic for dengue, the most sensitive and specific way of clinically diagnosing CHIKV infection based on patients’ self-reported signs is with the simultaneous presentation of fever, joint pain and rash. This clinical case definition of CHIKV can be used to detect outbreaks, especially in age groups not usually affected by dengue, and for surveillance of epidemic trends. It cannot, however, guide individual patient management of severe cases or help precisely measure caseload, and may be of limited use in a setting with seasonal dengue outbreaks. Access to laboratory confirmation is therefore essential for patient management, for intermittent human and virological surveillance, and to confirm the beginning and end of an outbreak.