Outbreaks of the mosquito-borne disease chikungunya appear to be driven by infections occurring mostly in and around homes, making women significantly more likely to get sick.
The findings may help health officials combat the virus and other diseases spread by mosquito, including Zika, dengue, and yellow fever.
Published in the Proceedings of the National Academy of Sciences, the study conducted in a small rural village in Bangladesh found that women there were 1.5 times more likely than men to develop chikungunya in a 2012 outbreak.
“Typically when there is an outbreak, we study who is sick and try to understand why,” says study leader Henrik Salje, a postdoctoral fellow in epidemiology at the Bloomberg School of Public Health at Johns Hopkins University and a visiting scientist at Institut Pasteur in Paris.
“In this case, we not only studied those who became infected with chikungunya, but also those who avoided illness. This allowed us to determine what factors may impact who comes down with a disease—and who does not—and [will] help us determine the best way to intervene.”
“We not only studied those who became infected with chikungunya, but also those who avoided illness.”
Chikungunya causes fever and debilitating joint pain along with muscle pain, headache, nausea, fatigue, and rash, the World Health Organization says. Most patients recover, but in some cases joint pain lasts for months or years. The disease has been found in Asia, Africa, Europe and, recently, the Caribbean and the Americas.
Researchers investigated chikungunya cases in Palpara, a village 60 miles outside the Bangladesh capital of Dhaka.
The team visited every house in the village and interviewed 1,933 individuals from 460 households. A total of 364 people (18 percent) reported having symptoms consistent with chikungunya between May 29 and Dec. 1, 2012.
Even though chikungunya is transmitted via Aedes mosquitoes—not by close contact with someone who is ill—more than a quarter of human cases spread within households and half of infections occurred in households less than 200 meters apart, creating small clusters of disease. This was an unexpected finding, the researchers say.
The researchers also looked at the movement habits of the wider Bangladeshi population and learned that women in the country spend 66 percent of their time between 8 a.m. and 8 p.m. at home while men spend 45 percent at home. Aedes mosquitoes only bite during daytime. Coupled with the tendency of infected mosquitoes not to travel far, this suggests why women were more likely to become infected.
“It appears that mosquitoes are very lazy. The extra time women spend in and around their home means they are at increased risk of getting sick.”
“It appears that mosquitoes are very lazy,” Salje says. “They bite someone in a household and get infected with a virus and then hang around to bite someone else in the same home or very nearby. The extra time women spend in and around their home means they are at increased risk of getting sick.”
Ideally, knowing where outbreaks are likely to be clustered could help in slowing them, but in the case of chikungunya, Zika, and several other diseases spread by the same types of mosquitoes, there is no vaccine. Mosquito control in developing countries tends to be poor and very little treatment is available. Also hampering response in places like rural Bangladesh: Few people visit doctors and authorities often don’t know about an outbreak until it is over.
“We don’t yet have a very good toolbox for fighting these diseases,” Salje says. “But once we do, this research tells us how we could trigger a response and tailor our interventions—particularly in rural communities—to those at the greatest risk, and those people are the ones who spend the most time in and around their homes.”
Other researchers from Johns Hopkins and from Institut Pasteur, the International Centre for Diarrhoeal Disease Research, and the University of Florida are coauthors of the study, which was funded by the Centers for Disease Control and Prevention and by the National Institute of Allergy and Infectious Diseases.
Source: Johns Hopkins University