The Chikungunya virus, transmitted via mosquito bite, causes severe joint pain.
© Staras/iStock/Thinkstock
The strain of Chikungunya virus (CHIKV) that has traveled across the Americas in the last two years is potentially milder and caused less severe symptoms than the strain responsible for the major Indian Ocean outbreaks of 2004–06, according to new research from A*STAR scientists and their international collaborators.
CHIKV is transmitted to humans by mosquitoes and brings high fever, headache and serious joint pain. There is currently no vaccine or treatment. The disease was in the spotlight in 2004 following outbreaks in Africa, India and Southeast Asia. Almost 270,000 people were infected in 2005–06 on La Reunion — about a third of the Indian Ocean island’s population.
In late 2013 CHIKV arrived in the Americas, initially to the island of St Martin. Within a year more than a million people were infected across the Caribbean, South and Central America.
Three separate strains of the virus are known, originating from West Africa, East-Central-South African (ECSA) and Asia. French scientists led by Xavier de Lamballerie, of the Aix-Marseille University, identified the Caribbean CHIKV as being of the Asian strain rather than the ECSA genotype behind the Indian Ocean outbreaks.
In collaboration with the French team, Lisa Ng of the A*STAR Singapore Immunology Network and co-workers infected batches of connective tissue cells called fibroblasts taken from mice with two different CHIKV isolates to investigate the responses more closely.
Laboratory tests that measured the level of virus in the samples over a 24-hour period confirmed that the Asian-Caribbean strain replicates more slowly than the ECSA version.
Ng and colleagues also found that mice infected with Asian-Caribbean CHIKV had lower concentrations of virus in their blood and significantly less joint swelling.
“The results were very consistent,” says Ng. “We had no idea which would cause more severe swelling until we saw those first results.”
“This suggests the symptoms of patients with Asian-Caribbean CHIKV might be somewhat milder to those with the ECSA strain, and that therefore their clinical management might also be different.”
The A*STAR team that helped to characterize the milder form of CHIKV: Back row (L to R): Jason Kam, Yi-Hao Chan, Fok-Moon Lum, Wendy Lee and Jeslin Tan. Front row (L to R): Zhisheng Her, Lisa F. P. Ng, Teck-Hui Teo, and Laurent Renia.
© 2015 A*STAR Singapore Immunology Network
The researchers also found important differences in immune system reactions to infection, with ECSA CHIKV triggering greater responses from type 1 T helper (Th1) cells, which promote inflammation, and from natural killer cells, which target and kill infected cells.
“This suggests that if doctors could control the number of Th1 and NK cells, they could perhaps control the swelling and damage,” adds Ng.
The A*STAR-affiliated researchers contributing to this research are from the Singapore Immunology Network.
