Mosquitoes are major disease vectors; many people consider them to be the world's deadliest animal because they cause serious illnesses including malaria, dengue, and Zika virus, and kill around 725,000 people a year. New research reported in The Lancet Neurology has suggested that a combination of two viruses spread by mosquitoes: Zika, and chikungunya, may increase the risk of stroke. These viruses both cause fever and rashes and are endemic to the tropics, and when Zika virus infects a pregnant woman, her fetus is at risk for developmental disorders affecting the brain. Zika and chikungunya may also cause neurological complications in kids and adults.
In this study, the researchers followed 201 adults that were treated for a new neurological disorder in Brazil during a 2015 Zika epidemic and a 2016 chikungunya epidemic. The work showed that each virus may cause a variety of neurological problems. Zika was associated with a higher risk of Guillain-Barre syndrome, which is characterized by damage in the nerves of the arms and legs. Chikungunya was linked to inflammation in the brain, and swelling in the spinal cord and brain.
Strokes happen when there is a blockage in an artery that supplies the brain with blood. Some viral infections are known to increase the risk of stroke. While a stroke might happen because of or during infections with either virus, this work found that patients that had been infected with both Zika and Chikungunya had a higher risk of stroke than people with either virus alone.
"Our study highlights the potential effects of viral infection on the brain, with complications like stroke," said study author Dr. Suzannah Lant, a Clinical Research Fellow at the University of Liverpool. "This is relevant to Zika and chikungunya, but also to our understanding of other viruses, such as COVID-19, which is increasingly being linked to neurological complications."
Over two years, 1,410 patients were screened for this study to identify the 201 patients that were suspected to have a neurological disease linked to either Zika, chikungunya, or both. Lab tests confirmed infection in about one-third of these patients, while about one-third of them were infected with more than one virus. Only about ten percent of the patients had recovered fully by the time they were discharged. Ongoing problems including weakness, seizures, and impaired brain function were reported.
"Zika infection most often causes a syndrome of rash and fever without many long-term consequences, but these neurological complications - although rare - can require intensive care support in hospital, often result in disability, and may cause death," said the leader of the Brazilian team, Dr. Maria Lúcia Brito Ferreira, neurologist and department head at Hospital da Restauração.
"Although the world's attention is currently focused on COVID-19, other viruses that recently emerged, such as Zika and chikungunya, are continuing to circulate and cause problems. We need to understand more about why some viruses trigger stroke so that we can try and prevent this happening in the future," noted senior study author Professor Tom Solomon, Director of the National Institute for Health Research Health Protection Research Unit in Emerging and Zoonotic Infections at the University of Liverpool.