A new study shows there is even more reason to worry about the Zika and chikungunya viruses and the pests that spread them; increased risk of neurological diseases like stroke.

Aedes aegypti, the mosquito most commonly associated with spread of Zika and Chikungunya, are essentially ecologically useless disease vectors. Nothing they do in nature wouldn't be done by other creatures except transmit these diseases most often to humans.  Stroke occurs when one of the arteries supplying blood to the brain becomes blocked. The risk of stroke is known to be increased after some types of viral infection, like varicella zoster virus, which causes chickenpox and shingles, and HIV. Stroke is also being recognized increasingly as a complication of COVID-19. This has important implications for the investigation and management of patients with viral infection, as well as for understanding the mechanisms of disease. 

These viruses, which mostly circulate in the tropics, cause large outbreaks of rash and fever in places like Brazil and India. Zika is widely known to cause brain damage in babies following infection in pregnancy, but the new research shows it can also cause nervous system disease in adults.

The study of 201 adults with new onset neurological disease, treated in Brazil during the 2015Zika and 2016 chikungunya epidemics, is the largest of its kind to describe the neurological features of infection for several arboviruses circulating at the same time.

The new research shows that each virus can cause a range of neurological problems. Zika was especially likely to cause Guillain-Barre syndrome, in which the nerves in the arms and legs are damaged. Chikungunya was more likely to cause inflammation and swelling in the brain (encephalitis) and spinal cord (myelitis). However, stroke, which could be caused by either virus alone, was more likely to occur in patients infected with the two viruses together.

In total 1410 patients were screened and 201 recruited over a two-year period at Hospital da Restauração in Recife, Brazil. Comprehensive PCR and antibody testing for viruses was carried out in Fiocruz laboratories. Of the 201 patients admitted with suspected neurological disease linked to Zika, chikungunya or both, 148 had confirmation of infection on laboratory testing, around a third of whom had infection with more than one virus. The median age of patients was 48, and just over half the patients were female. Only around 10% patients had fully recovered at discharge, with many having ongoing issues like weakness, seizures, and problems in brain function.

Of the stroke patients, who were aged 67 on average, around two thirds had infection with more than one virus. Many of the people who had a stroke had other stroke risk factors, such as high blood pressure, indicating that stroke following Zika and chikungunya viral infection may most often be seen in those who are already high risk.