Zika virus infection – what we know so far

I am frequently asked, when next am I visiting home. My answer is always, no time soon. My home is Antigua, an island in the Eastern Caribbean. The truth is, since news of the Zika virus outbreak in the Caribbean and Latin America last year, and particularly the suspected link between Zika virus infection and devastating birth defects, I knew I would have to put any trip to the Caribbean on hold for sometime. I do not have children yet, but am hoping to do so eventually. When that does happen, I cannot imagine the worry that my husband and I would experience, if there was a chance that I got infected with Zika virus during pregnancy.

This week, I am on vacation, and as an “island girl” I longed for a tropical setting for my vacation. My husband and I settled on Pensacola, Florida. However, given the recent reports of Zika virus transmission in an area just outside of Miami, I have to admit that there was transient hesitancy in going to Pensacola. We got insect repellant for the trip, just in case.

I am happy to have choices about being in an area where Zika virus transmission is likely. But what about all those persons living in the heart of the Zika epidemic? How does one deal with this situation, protect them-self, and protect their unborn baby? Well, as with every other situation, knowledge is power. The more you know about a situation, the better able you are to protect yourself.

Below, I outline what we have learnt about Zika virus disease, since the onset of the outbreak in Brazil last year, and subsequent spread through many other countries throughout Latin America and the Caribbean. I will also summarize the recommendations from World Health Organization (WHO) and Center for Disease Control (CDC) regarding prevention. Finally, I will mention some unanswered questions.

Related post: What’s that ‘new’ virus going around?

– As noted in a previous blog post, only ~20% of persons infected with the Zika virus actually develop symptoms of infection, and those symptoms include headache, rash, painful joints, and fever.
– The current outbreak taught us that Zika virus has a particular affinity for nervous tissue. Evidence for this is the association with serious complications involving the nervous system. These complications include Guillain-Barre syndrome (paralysis from damage to the nerves), meningoencephalitis (inflammation of the lining of the brain and of the brain tissue itself), and myelitis (inflammation of the spinal cord causing muscle weakness or paralysis).

ZIKA VIRUS INFECTION IN PREGNANCY
– An association between Zika virus infection in pregnancy and the development of fetal microcephaly, has been shown. I will admit that at the start of the epidemic I was very skeptical about this link, but human observational studies, as well as animal studies, have supported this association.
– Apart from microcephaly, other complications have been seen in fetuses of pregnant women infected with Zika virus, including restricted growth of the fetus, ocular (eye) abnormalities, and fetal death.
– Fetal death has been reported in women infected with Zika virus from as early as the 6th week, to as late as the 32nd week of pregnancy.
– Miscarriage has been reported in some pregnant women with Zika virus infection.
– Zika virus can be transmitted to a fetus, even if the mother never had symptoms of infection.
– Not all fetuses of women infected with Zika virus during pregnancy, will develop abnormalities. A study in Brazil showed that abnormalities were detected in 29% of cases, and of those, 17% had microcephaly, cerebral atrophy (small brain in normal sized skull) or brain calcifications.
– The risk for microcephaly is highest in the first trimester, but can happen with Zika virus infection occurring well into the second trimester, up to the 20 week point of pregnancy. However, even though microcephaly may not be an issue with infection in late pregnancy, other complications such as fetal death and miscarriage have occurred late in the third trimester.

WHERE IN THE BODY CAN ZIKA VIRUS BE FOUND?
– Zika virus has been detected in numerous body fluids including blood, amniotic fluid, urine, saliva, semen, and breast milk.
– Generally, Zika virus can be detected in the blood for at least a week after onset of symptoms. However, in pregnant women, virus may be present in the blood for up to 10 weeks. This is probably not from ongoing infection of the mother, but from ongoing viral replication in the fetus or placental tissue.
– Zika virus can be detected in urine for at least 14 days from onset of symptoms.
– Zika virus can be detected in semen for at least 3 months

TRANSMISSION OF ZIKA VIRUS
– Even though Zika virus has been detected in numerous body fluids, transmission has not been shown to occur from kissing, breastfeeding, or contact with urine from an infected person.
– The proven modes of transmission of Zika virus are a bite from an infected mosquito (Aedes species), from mother to unborn child, and sexually (from male to female and male to male).
– Only this week in the NEJM, a letter to the editor described 2 patients in Brazil who acquired Zika virus infection after platelet transfusion in January 2016. Currently, it is standard practice to test all donated blood for Zika virus, therefore blood transfusion is felt to be an unlikely way to acquire infection now.

Related post: It’s (almost) impossible to avoid mosquito bites if you live in the tropics

PREVENTING ZIKA VIRUS INFECTION IN WOMEN WHO MAY BECOME PREGNANT
– Women should avoid getting pregnant for at least 8 weeks after possible exposure to Zika virus, even if they don’t have symptoms.
– A woman who has had symptoms of Zika virus infection, should wait 6 months before trying to get pregnant.
– Men returning from an area with active Zika virus transmission, should adopt safe sex practices (use of condoms) for at least 8 weeks after their return, even if asymptomatic.
– If men experience symptoms of Zika virus infection, they should adopt safer sexual practices or consider abstinence for at least 6 months, to prevent sexual transmission of the virus.
– Women living in areas with active Zika virus transmission, may consider delaying pregnancy. However, this may be unrealistic for many persons, therefore standard measures to prevent mosquito bites should be adopted.

UNANSWERED QUESTIONS
– Is there some cofactor, such as a co-infection, which makes microcephaly and severe neurologic complications more common with Zika virus infection, compared to other mosquito borne flavivirus infections?
– Why is it that not all pregnant women who get Zika virus infection, develop fetal or pregnancy complications?
– At what point in pregnancy is infection with Zika virus most likely to cause fetal complications?
– Exactly how long is the risk for sexual transmission, after onset of Zika virus infection?

It is hoped that answers to these questions will arise, as research into this remarkable virus continues.