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Patterns of chikungunya virus observed over 60 years in Philippines
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An age-specific seroprevalence analysis demonstrated a sporadic pattern of chikungunya virus transmission over a 60-year duration in the Philippines and suggested that more than half of the population remains susceptible to infection.
“Individuals who become infected by [chikungunya virus (CHIKV)] develop specific antibodies to the virus that can be detected years later using plaque reduction neutralization assays (PRNTs),” Henrik Salje, PhD, from the epidemiology department at Johns Hopkins School of Public Health, and colleagues wrote. “Seroprevalence studies can therefore be used to characterize the proportion of the population that has been exposed to the virus at some point in their life.”
Henrik Salje
The researchers examined data from two serological studies conducted in 1973 and 2012 in Cebu, Philippines, to estimate the historical incidence of CHIKV in the region from 1952 to 2012.
In the earlier analysis, age-specific and seroprevalence data were available for 150 participants, 33 of whom were seropositive for CHIKV. Positive results ranged from 6% in participants aged younger than 10 years to 42% in those aged 40 to 49 years.
In the 2012 study, data on baseline neutralizing antibody titers were available for 853 participants. Overall, 28% had baseline PRNT titers, suggesting a history of CHIKV infection. There were no detectible titers reported in children aged younger than 14 years, indicating an insignificant circulation of the virus, according to the researchers.
The researchers combined the results and estimated that 3.1 outbreaks (95% CI, 3-4) occurred between 1952 and 2012. Fifty-five percent of model iterations suggested an outbreak occurred in 1968 or 1969, 100% iterations identified an outbreak in 1986, and 72% of iterations identified an outbreak in 1993.
“These patterns are consistent with re-emergence driven by reintroduction of virus rather than continuous low levels of undetected human infection,” the researchers wrote.
The mean probability of infection among susceptible participants was 23% (95% CI, 16%-37%) per outbreak. More than 50% of the entire population were susceptible to infection throughout the duration of the study.
Twelve percent of participants seroconverted between 2012 and 2013, and were 2.2 times (95% CI, 1.5-3.1) more likely to be living within 50 meters of each other compared with other participants, the researchers wrote. A substantial spatial dependence was observed up to 230 meters, indicating small-scale focal transmission.
Sustained multiyear transmission was not associated with large-scale chikungunya outbreaks. The researchers estimated that more than 350,000 cases were unidentified despite implementation of surveillance systems.
“This study highlights the utility of age-specific seroprevalence studies in efforts to understand the long-term epidemiology of pathogens, such as CHIKV, especially in settings where surveillance systems may not be able to reliably capture cases,” the researchers wrote. “Incorporating systematic serological investigations into health systems could allow improved disease surveillance.” – by Jen Byrne
Disclosure: The researchers report no relevant financial disclosures.
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