As if the common symptoms associated with mosquito-borne viral infections weren’t bad enough, a new study from investigators at the University of Liverpool has found that dual infections with Zika and chikungunya viruses may be a trigger for stroke. These viruses, which mostly circulate in the tropics, cause large outbreaks of rash and fever in 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.

Findings from the new study were published recently in The Lancet Neurology through an article titled, “Neurological disease in adults with Zika and chikungunya virus infection in Northeast Brazil: a prospective observational study.”

“Our study highlights the potential effects of viral infection on the brain, with complications like stroke,” noted co-senior study author Suzannah Lant, MBChB, 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.”

In the current study, 201 adults with new-onset neurological disease, treated in Brazil during the 2015 Zika 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.

Interestingly, the new findings show 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.

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.

In total, 1,410 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 were carried out in Fiocruz laboratories.

“We recruited adults aged 18 years or older referred to Hospital da Restauração, a secondary-level, and tertiary-level hospital, with suspected acute neurological disease and a history of suspected arboviral infection,” the authors wrote. “We looked for evidence of Zika, chikungunya, or dengue infection by viral RNA or specific IgM antibodies in serum or CSF. We grouped patients according to their arbovirus laboratory diagnosis and then compared demographic and clinical characteristics.”

Amazingly, of the stroke patients, 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.

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,” concluded co-senior study investigator, Tom Solomon, FRCP, director of the National Institute for Health Research Health Protection Research Unit in Emerging and Zoonotic Infections at the University of Liverpool. “We need to understand more about why some viruses trigger stroke so that we can try and prevent this from happening in the future.”

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