Zika's viral odyssey finally revealed
The Montpellier Research Institute (CNRS/UM) has demonstrated the ability of the Zika virus to adopt a "Trojan horse" strategy to reach its host's brain. The findings were published in the highly selective journal Nature Communications.
In 2015, the major Zika epidemic that struck Brazil highlighted the role of this virus in the underdevelopment of the brains of babies born to infected mothers, as well as in the onset of neurological disorders—such as encephalitis—in adults. The migration of the virus into brain tissue remains a mystery to researchers. The brain has a cellular barrier, considered impenetrable, that protects it by ensuring a hermetic separation between the blood and the tissues. The mystery has now been solved thanks to Raphaël Gaudin's team atthe Montpellier Institute of Research (CNRS/UM). This work demonstrates, once again, that viruses definitely have more than one trick up their sleeve to achieve their goals.
The so-called "Trojan horse" strategy
Like Odysseus, hero of the Odyssey, who hid his soldiers in a large wooden horse to get them into the city of Troy and attack it, the Zika virus has found its own way through walls in a subtype of white blood cells. Hidden in what are known as monocytes, the virus takes control of these cells, which are initially designed to defend our immune system, and forces them to migrate to our brain, thus circumventing our famous blood-brain barrier.
Zebrafish and “mini-brains”
To demonstrate this clever stratagem, two experiments, in vivo and in vitro, were conducted. Human monocytes infected with the Zika virus were first injected into a zebrafish. This quasi-transparent animal had its blood vessels made fluorescent beforehand so that the virus's path could be tracked in real time and in 3D. The researchers were thus able to observe that the infected cells did indeed migrate out of the blood vessels and move toward the tissues much more quickly than cells not exposed to Zika.
The pursuit of this spinning inside the brain is carried out in vitro. Raphaël Gaudin's team collaborated with a Dutch laboratory specializing in the creation of "mini-brains" produced from embryonic stem cells. These organoids were exposed to infected monocytes as well as healthy monocytes and free virus. The researchers then observed greater dissemination of the virus in the brain by infected monocytes, confirming their hypothesis. This promising discovery could well become Zika's Achilles heel and pave the way for new therapeutic applications to combat the virus. Unless, of course, the virus has other tricks up its sleeve.
Zika in brief…
The Zika virus was discovered in the Zika Forest (Uganda) in 1947. The virus is mainly contracted through the bite of an Aedes mosquito or through sexual transmission and blood transfusions. While Zika symptoms are generally mild in adults, transmission from pregnant women to their fetuses can cause severe brain malformations in newborns, including microcephaly. In 2016, photographer Felipe Dana captured images of the terrible consequences of Zika in northeastern Brazil, a region hit hard by the epidemic.