Much left to learn about Zika
Q. What do I need to know about the Zika virus so I am well informed for questions from patients?
A. Zika virus infection is primarily a mosquito-borne disease transmitted by Aedes aegypti and potentially Aedes albopictus mosquitoes, which also transmit dengue, chikungunya and yellow fever virus infections.
At present, there is no antiviral treatment for Zika virus infection, which is considered a mild illness that generally resolves within two to seven days; about 75-80 per cent of people infected with the virus do not display symptoms.
Of particular concern is the link between Zika virus infection and neurological conditions. The World Health Organization stated that based on research to date, there is scientific agreement that Zika virus infection is causally linked with microcephaly (due to incomplete brain development) in fetuses/newborns and with Guillain-Barré syndrome.
Key to avoiding infection for Canadians planning to travel to areas with ongoing Zika virus transmission is that they protect themselves from mosquito bites. That includes assessing whether their destination is implementing control measures (such as fogging or larvicide use to control mosquito populations) and practising personal protection measures (such as using insect repellent on exposed skin, wearing light-coloured pants, long-sleeved shirts and hats, and using screens and nets to prevent entry of mosquitoes into living and sleeping areas).
Zika virus infection can also be transmitted through sexual contact. There are documented cases of transmission from symptomatic males to their sexual partners; however, there have been no documented transmissions from women to their sexual contacts. Recent reports from Brazil have found Zika virus in saliva, urine and breast milk, but there have been no documented transmissions from these body fluids. Zika virus replicates in the blood of infected patients and clears from the bloodstream by seven days after symptom onset. Unofficial reports of transmission through blood transfusion in Brazil are under investigation. Potential blood donors who have travelled to Zika risk areas must wait 21 days after returning to Canada before donating blood.
Pregnant women should avoid travelling to Zika endemic countries. If travel is necessary, they should practise stringent personal protection measures to avoid mosquito bites. Current guidelines suggest that women considering pregnancy should avoid becoming pregnant during such travel and for two months after their return.
After a male partner returns from a risk area, women should delay trying to become pregnant for six months, as the virus has been shown to persist in semen longer than in other body fluids. Men returning home to a pregnant partner should use condoms for the duration of the pregnancy.
Based on current information, the likelihood of local transmission of Zika virus by mosquitoes in Canada is exceedingly low. Other Aedes species are not known to transmit Zika virus, and the Aedes aegypti and Aedes albopictus mosquitoes are not native to our country.
Today, researchers are attempting to answer some key questions:
- What additional species of mosquitoes can potentially transmit Zika virus?
- What is the risk of fetal infection following maternal infection at different stages of pregnancy?
- What is the mechanism of the neurological injuries caused by Zika virus infection?
- What is the risk of Guillain-Barré and other neurological syndromes after Zika virus infection?
- Can Zika virus be transmitted sexually by women, and following asymptomatic infection?
It is clear that our understanding of the clinical features of Zika virus is far from complete. The best advice we can offer to patients and the general public is to make themselves aware of Zika endemic areas and to practise personal protection measures during any travels there.