Scientists determine why second dengue infection is worse than first

There is now strong evidence to prove that a second dengue infection can be more severe than the first, according to a study which was published on Thursday (November 2^nd) in the journal Science.

Aedes aegypti mosquitoes are seen at the Laboratory of Entomology and Ecology of the Dengue Branch of the U.S. Centers for Disease Control and Prevention in San Juan, Puerto Rico, March 6^th, 2016. (REUTERS/Alvin Baez/File Photo)

The study was conducted between August 2004 and April 2016 with 6,684 children aged between two and 14. More than 41,000 blood samples were analysed to determine why some children developed severe diseases such as dengue hemorrhagic fever and dengue shock syndrome when they had a second infection.

According to the journal, a person infected for a second time is at risk of a more severe case of dengue because antibodies have fallen to a specific low range giving rise to antibody-dependent enhancement, or ADE.

"In sum, we verify enhancement of dengue disease in humans and show that the level of pre-existing anti-DENV antibodies is directly associated with the severity of secondary dengue disease in humans.

"We also show that the immune correlate for enhanced severe dengue disease is distinct from that for protection. These observations are important for future dengue and Zika vaccine trial design and evaluation, as well as for further studies on the mechanisms of ADE in relation to severe dengue and Zika disease," scientists said in the report.

“This paper, what it does, it shows for the first time the narrow range of antibody concentrations … that actually produces enhancement of disease in vivo,” said Nikos Vasilakis, an associate professor of pathology at the University of Texas Medical Branch in an interview with health news website, STAT.

Another expert, Dr. Scott Halstead told the site that although this was not the first proof of ADE, it was the largest study to prove the effect.

Senior author Eva Harris, a professor of infectious diseases and immunology at the University of California, stressed that the finding does not explain all cases of severe dengue disease.

“This is definitely not like there’s only one explanation,” Harris told STAT. “It’s just saying that this particular explanation seems to be valid in humans.”

VNF/CNA