Asymptomatic dengue-infected humans can transmit the virus to mosquitoes

A drawing of a female Aedes aegypti mosquito (Credit: E.A. Goeldi)

An estimated 3.9 billion people in 128 countries are at risk of dengue virus infection. Of the estimated 390 million dengue infections that occur each year, 96 million will manifest clinically with flu-like symptoms including fever, headache, nausea and muscle and joint pain. Unlike the flu virus, dengue virus cannot be transmitted directly from person to person. It instead relies on an insect vector, the mosquito Aedes aegypti. Female mosquitoes contract the virus when they bite and feed on an infected human. After a period of four to ten days, the virus disseminates to various tissues in the mosquito, where it remains for the rest of the mosquito’s life. At this point, the mosquito is infectious and can transmit the virus through its saliva and bite.

Earlier studies showed that the time during which dengue virus-infected humans can transmit the virus to mosquitoes coincides with the onset of clinical symptoms and an increase in viral load in their blood. These observations led to the assumption that infected, asymptomatic humans are so-called “dead-end hosts” for the virus because their viral levels are so low as to make them noninfectious to mosquitoes, essentially breaking the transmission chain.

In a new paper published last week in the Proceedings of the National Academy of Sciences, an international group of researchers challenged a long-held assumption that asymptomatic patients infected with the dengue virus are not infectious. The team sought to experimentally test the assumption that asymptomatic people are noninfectious and to determine how human-to-mosquito transmission varied with timing of symptom onset. Continue reading


Hold your breath: carbon dioxide triggers exploratory behaviour in mosquitoes to help find hosts

A female mosquito feeding on a hapless victim.
A female mosquito feeding on a hapless victim.


The tranquility of a lakeside sunset, disturbed by my attempts to stop bloodthirsty mosquitos from eating me as supper. I don’t know why mosquitoes think I’m a more appetizing meal than my camping companions but thanks to a new study, I now have a better understanding of how they hone in on targets such as myself.

Mosquitoes rely on a number of different cues to find their hosts. These include the heat and scents we emit, the humidity generated when our sweat evaporates and the carbon dioxide that we breathe out. What is less well known is how these different cues interact with and influence one another. For example, does sensing one cue help a mosquito pick up on other cues? That’s the question Dr. Michael Dickinson at the California Institute of Technology tried to answer. Together with colleagues at the University of Washington, his team showed that carbon dioxide triggers mosquitoes to explore visual elements in their environment, which in turn guides them to potential hosts.

Continue reading