Zika Virus Distribution as of 2015 (Image: Discover Magazine)
Several months ago I began receiving PROMed updates featuring cases of the little-discussed Zika virus in Brazil. Curious, I thought at the time, given that Zika is typically seen in Southeast Asia and Sub-Saharan Africa, but not yet anything to panic about. Since that time, this story has gained traction as the virus has clearly established itself in South and Central America, and is rapidly working toward that point in the Caribbean. The United States Centers for Disease Control and Prevention recently took the step of recommending that pregnant women avoid travel to regions affected by this outbreak, and the Brazilian government took the unprecedented step of recommending that women avoid becoming pregnant for the next two years. All of this has brought a degree of attention to the Zika outbreak perhaps not seen since the 2014 Ebola epidemic. That said, in recent days I have been asked about Zika several times, and thus decided to share twelve of the most common questions -and their answers- with you all.
1.) What is this Zika virus I keep hearing about? Zika is a flavivirus, or a close relative of West Nile virus, dengue virus, yellow fever virus, chikungunya virus, Japanese encephalitis virus, and others. It is primarily transmitted by mosquitoes (more on this in Question 4), and causes a mild, flu-like illness in infected persons. Patients usually present with fever, chills, and joint pain, but rarely if ever die of the infection. Zika is a mild illness for both children and adults. That said, there seems to be a potentially devastating pregnancy complication that certainly deserves attention (more on this in Questions 6 and 7).
2.) Why are we hearing about it all of a sudden?
Zika is not new; it has been circulating in Asia and Africa for decades. That said, it is newly emerging in the Americas which is why news outlets in the United States are paying close attention to it. Zika was introduced into Brazil , and was able to establish itself in Latin America because conditions were favorable for it to do so (again, more on this in Question 4).
3.) Zika is in South and Central America and is heading north. How long before there are cases in the United States?
I hate to break it to you friends, but there have already been cases in the US. All but one were in travelers returning from overseas.The one case that was “locally” transmitted was that of an infant born to a mother who was living in Brazil during part of her pregnancy.Will there be locally transmitted cases, where persons who have not travelled overseas become infected? Possibly.
4.) Will Zika become widespread in the US?
We now know that there have been cases of Zika in the US. Have they spread? WILL they spread? How can we know for sure what the threat level is? My response is somewhat conflicted here. For starters, Zika is what we call an “arbo”, or “arthropod-borne”, virus, meaning that its primary mode of transmission is by an insect vector. Mosquitoes suck blood containing Zika virus particles from an infected person, and they then deposit the viruses into the next person they bite. Here's where it gets complicated.
The thing about mosquitoes is that they are extremely diverse. It turns out that saying “mosquito” is a bit like saying “bird”: there are eagles, which are not the same as hummingbirds, which are not the same as flamingos, which are not the same as cardinals. Most mosquitoes are not able to effectively transmit Zika, but a few are. What matters is where these mosquitoes live.The principal mosquito implicated in Zika transmission, Aedes aegypti, is found at high levels in Central and South America and the Caribbean, but is less common in the continental US. Do we have this mosquito? Yes. It is easily found along the Gulf Coast. Is it everywhere? No. The reason I am conflicted in this particular question, however, is Zika’s interaction with the closely related mosquito Aedes albopictus. Multiple studies show that this species is quite capable of transmitting Zika, and this is of great concern. Why? Because is not only wider spread than its cousin; it is more aggressive as well. In other words a person is far more likely to be bitten by A. albopictus than A. aegypti, and if we assume that A. aegypti is the only bug doing the transmitting we will undoubtedly underestimate transmission potential in the US.
5.) How do I know if I have it?
As discussed above, symptoms of Zika are quite generic. A small number of patients experience fever, aches, malaise, and possibly a rash (as I would call it in class, a “general ick syndrome”), and the majority of patients experience no symptoms at all. As of now, being diagnosed with Zika in the US is quite a process. There is no available test that a standard laboratory can run in the US. If you have suspect you may be infected with Zika, your physician would have to send a sample of your blood to your state health department, which would then refer it to the Centers for Disease Control and Prevention.
6.) If anyone can be infected, why is there a travel ban only for pregnant women?
The Western Hemisphere Zika outbreak began last spring in Brazil. In the past few months, Brazil has seen greater than a 3,000% increase of a condition called microcephaly in newborn babies. Suspecting a connection, health officials began screening the mothers of these infants and found that a majority had been infected with Zika during their pregnancies. While we do not yet know why or how often, Zika in pregnant women seems tightly correlated with microcephaly of their babies.
Elison W. holds his baby brother Jose, who was born with microcephaly following Zika infection of their mother [Image: Felipe Dana/Associated Press]
7.) What is microcephaly?
Microcephaly literally means “small head”, and is an inborn condition wherein the skull and brain of a fetus do not grow to the appropriate size and level of development. Infants born with microcephaly have far higher rates of stillbirth and early/childhood death, and surviving infants almost invariably have severe cognitive disabilities. Such individuals require lifelong care and are at far higher risk for numerous health problems. While Zika is not a particularly frightening infection to an individual, a 3,000% increase in infants born with microcephaly has enourmous consequences both for families and medical systems.
8.) I recently travelled to Latin America. If I was infected with Zika can I spread it to other people in the US?
Potentially, in one of a few ways. If you live in an area infested with Aedes mosquitoes and are infected, a mosquito that bites you may ingest Zika virus particles and then transmit them to another person. This is the main
method of transmission. The other options, although rare and potentially speculative, involve body fluids. Like all arboviruses, Zika is found in blood and is therefore a potential bloodborne pathogen. The likelihood of Zika spreading via blood or tissue donations is very low, given that recent travel excludes you as a donor. The final discussed mechanism is sexual transmission. Zika virus particles have been detected in the semen of two different male patients, but it is not clear how common this phenomenon is. Notably, both patients had a condition called hematospermia, which features trace amounts of blood in the semen. Does this make them Zika transmitters? It is simply an unknown at this point.
9.) Is there a Zika vaccine?
No. Until the connection to microcephaly was realized very recently, there was no pressing need for a vaccine against a virus that causes a very mild disease. However, funds are now being redirected for vaccine development. Success seems likely, given that Zika has some close relatives (notably yellow fever, Japanese encephalitis virus, dengue fever virus, and chikungunya virus) with effective vaccines in existence or in the end stages of development.
10.) Is Zika going to become more common due to immigration?
Immigrants are no more or less likely to import Zika cases than travelers repatriating from affected countries. Zika is not a chronic, lifelong infection, meaning a person who has been in Brazil for 2 weeks or 20 years has precisely the same chance of coming to US shores infected with Zika.
11.) Is Zika another Ebola?
The only commonality between these two infections is that both are caused by viruses. Their clinical presentations, methods of transmission, associated dangers, prevention strategies, and long-term outcomes simply can’t be compared-they are too different.
12.) Boil it down for me: Should I be worried?
The persons who should be worried are expectant parents. If you are a non-expectant adult, you should not be worried. If you have small children or elderly family members, you should not be worried. If you are a pet owner, you should not be worried. If you are a man who has been potentially exposed, be cautious for sexual transmission to a partner for 2-4 weeks. After that, you should not be worried. If you are a woman of child-bearing age that is unlikely to become pregnant, you should not be worried. If you are pregnant or attempting to become pregnant, you should be judiciously cautious about your exposure to Aedes mosquitoes if there have been cases in your area (i.e., keep skin covered, use mosquito repellant, and stay indoors in air-conditioned spaces to the extent possible). Hopefully everyone finds themselves in one of those categories and can decide how much concern to give Zika accordingly.