Chikungunya virus spreads in and around homes
Outbreaks of the mosquito-borne disease chikungunya appear to be driven by infections centered in and around the home, with women significantly more likely to become ill, suggests new research from the Johns Hopkins Bloomberg School of Public Health, the Institut Pasteur in Paris and icddr,b.
The recently published findings in the Proceedings of the National Academy of Sciences offer key insights into how health officials can combat other diseases that spread the same way, including Zika.
The research focuses on a small rural village in Bangladesh, but offer a new path for investigating and responding to outbreaks large and small for a variety of diseases transmitted via the Aedes mosquito, which also includes dengue and yellow fever.
Typically when there is an outbreak, we study who is sick and try to understand why, says the first author Henrik Salje, a post-doctoral fellow in the Department of Epidemiology at Johns Hopkins Bloomberg School of Public Health and a visiting scientist at Institut Pasteur. 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 to help us determine the best way to intervene.
For the study, researchers investigated a 2012 chikungunya outbreak in Palpara, a village 60 miles outside the Bangladeshi capital of Dhaka. The team visited every household in the village and interviewed 1,933 individuals from 460 households. A total of 364 people (18 percent) reported having symptoms consistent with chikungunya (fever with severe joint pain or rash) between May 29 and Dec. 1, 2012.
Even though chikungunya is transmitted via mosquito and not by coming into close contact with someone who is ill the researchers found that more than a quarter of human infections spread within the same household and that half of infections occurred in households less than 200 meters away. This was an unexpected finding, the researchers say.
Meanwhile, 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 during the day at home while men spend 45 percent at home. Coupled with the tendency of infected mosquitoes not to travel far, this made being at home an important determinant for becoming infected during the chikungunya outbreak.
We had good reason to suspect that women in Bangladesh spend a lot more time at home than men Emily Gurley, co-senior author and director of the emerging pathogens program at icddr,b says.
However, this study allowed us to quantify exactly how big this difference is and to demonstrate how this could be responsible for increased risk of infection by some mosquito-borne pathogens. Outbreaks of viruses such as dengue and Zika that are spread by the same mosquito as chikungunya are likely to disproportionately affect women in such communities, too.
Overall, the researchers found that women in Palpara were 1.5 times more likely to develop chikungunya than men. The researchers also found that coils designed to repel mosquitoes did not work to prevent transmission in this region.
The researchers used advanced statistical methods to disentangle the many competing factors that determine how an outbreak spreads and who gets infected. This study demonstrates how we can combine carefully collected data with computational tools to understand the spread of a pathogen says Simon Cauchemez, head of the mathematical modelling of infectious diseases unit at Institut Pasteur and co-senior author.
By collecting information on the wider community and not just counting the people that got sick, future outbreak investigations will be able to better understand how an epidemic is progressing and ultimately help control it.
How social structures, space, and behaviors shape the spread of infectious diseases: chikungunya as a case study was authored by Henrik Salje, Justin Lessler, Kishor Kumar Paul, Andrew S. Azman, M. Waliur Rahman, Mahmudur Rahman, Derek Cummings, Emily Gurley and Simon Cauchemez.
The researchers are from the Institut Pasteur in Paris, icddr,b, Institute of Epidemiology Disease Control Research in Bangladesh (IEDCR) and the University of Florida.
Source: icddr,b web
