Two studies out Monday show that the Zika virus may not be working alone in causing strange infections in South America. It may be getting help from dengue and chikungunya, too.
One team found that mosquitoes can be infected with Zika and chikungunya at the same time and could, in theory, infect people with both viruses in a single bite.
And a second team found a range of unusual symptoms in people in Brazil last year as Zika, chikungunya and dengue all swept through populations, often infecting people at the same time. One of the oddest is known as “dancing eyes-dancing feet syndrome.”
The findings, presented at a meeting of the American Society of Tropical Medicine and Hygiene, add to the growing list of mysterious and previously unsuspected damage that Zika virus causes.
Related: As Zika Spreads, GBS Cases Soar
“Our analysis shows that each of these viruses may have the potential to cause a range of neurological complications, some very severe, and patients should be monitored for symptoms,” said Dr. Isadora Siqueira of Brazil’s Oswaldo Cruz Foundation, who worked on one study.
“What’s very difficult to determine is whether having a co-infection with two of these viruses increases the risk of neurological problems. We are still looking closely at the case of the patient who was infected with both chikungunya and dengue.”
“Our analysis shows that each of these viruses may have the potential to cause a range of neurological complications, some very severe."
Dengue and Zika are closely related viruses called flaviviruses. Chikungunya is in a different family, called alphaviruses, but all three are spread by Aedes aegypti mosquitoes and they can cause similar symptoms: fever, headache and body aches. Zika causes severe birth defects; dengue can cause a deadly hemorrhagic fever and chikungunya causes racking pain.
They are not easy to tell apart and only with tests made available in recent months can doctors tell for sure which virus a patient has had.
All three can also cause rare neurological side-effects and doctors have wondered if people get sicker if they become infected with more than one at the same time, or one after the other.
The findings from northeastern Brazil suggest they may. They reported on 21 cases of neurological illnesses including Guillain-Barre syndrome, a strange, paralyzing condition that can be caused by a number of infections, including Zika.
Related: Man Dying From Zika Infected His Son
Most of the patients had classic Guillain-Barre, which usually clears up, although it can make patients seriously ill. Others had much more unusual conditions, including two with opsoclonus-myoclonue ataxia syndrome, commonly known as dancing eyes-dancing feet syndrome because of the strange, jerky movements it can cause.
It usually only affects about 1 in a million people, but both cases turned up in the same hospital during an epidemic affecting 18,000 people.
One of the two patients tested positive for both Zika and dengue, while the second had both chikungunya and dengue, Siqueira said.
"People bitten by this type of mosquito could be infected by both viruses at once."
None of the patients died but it can take weeks or even months to fully recover from these conditions. Zika has killed a handful of patients, as has chikungunya. Dengue comes in four strains and is much deadlier.
There’s a worry if the viruses work together to worsen illness. Brazilian doctors have been trying to determine if having two infections together or close together makes a pregnant woman more likely to have a baby with birth defects, for instance.
Related: See Full Zika Virus Coverage Here
A team at Colorado State University wanted to see if mosquitoes could pass along more than one of the viruses at once. They can.
Claudia Rückert and colleagues infected both Aedes aegypti and Ae. albopictus mosquitoes (Asian tiger mosquitoes) with Zika and chikungunya at the same time.
“Their saliva is clearly testing positive for both, which could mean that people bitten by this type of mosquito could be infected by both viruses at once,” Rückert said in a statement