As a microbiologist, people have been asking me recently about the Zika virus that is receiving so much attention in the news. Sensationalized media coverage has understandably caused some fear and confusion about this latest outbreak. But I think it has been further intensified by our vivid memories of the deadly Ebola crisis in western Africa last year. My goal in this article is to help you understand the Zika virus and the threat, if any, that it poses to you and your loved ones.
What is Zika?
Zika is a virus, a type of germ that is much smaller than your own cells or even bacteria. Consider this: human cells, like the ones making up your skin, might be around 50-100 micrometers in width, or about 0.05-0.1 millimeters. Bacteria, like E. coli, are a tenth this size, in the 5-10 micrometer range. The Zika virus, however, is only about 40 nanometers, equivalent to 0.04 micrometers, or 0.00004 millimeters. Not only are these viruses ridiculously small, they aren’t even alive! To replicate themselves, they have to hijack your cells and turn them into little factories for making more of themselves. And in the process of this hostile takeover, we get sick. The illness caused by the Zika virus is variably called Zika, Zika fever, or Zika virus disease.
Yellow Fever Virus, a close relative of the Zika virus, in the family Flavivirus. (Wikipedia)
What are the symptoms of ZVD?
Zika virus disease, or ZVD, is generally mild with symptoms resolving on their own within a week. Common symptoms include fever, rash, conjunctivitis (red eyes), headache, muscle pain, and joint pain.
Rarely, ZVD may result in an episode of Guillain-Barré syndrome (GBS). GBS is a neurological disorder caused by your own immune system attacking your nerve cells (autoimmunity). The result can be muscle weakness and paralysis that can last up to several months. GBS is rare, and death from GBS is rarer still.
The greatest danger posed by Zika is that of microcephaly in a newborn whose mother had ZVD during pregnancy. Microcephaly results in a smaller than normal head and brain, leading to severe developmental disabilities. The connection between Zika virus disease in a woman and microcephaly in her newborn child is not well understood, but the correlation appears to be strong, especially in Brazil.
This Brazilian infant has microcephaly. His mother was sick with Zika virus at some point in her pregnancy. (BBC)
How can someone catch the Zika virus?
Zika is not typically transmitted directly from one person to another. Instead, it requires that a specific type of mosquito (Aedes aegypti or Aedes albopictus) act as a vector, or shuttle, between people. The mosquito bites an infected person, consumes his or her blood along with the Zika viruses in it, and then proceeds to bite another person, accidentally introducing the virus into that person’s blood. It is estimated that only 20% of people infected with Zika virus actually get sick.
As mentioned above, it appears that a pregnant mother can pass Zika viruses to her unborn child during pregnancy, a situation that may lead to a birth defect known as microcephaly.
In Brazil, Zika has reportedly been transmitted via blood transfusions.
There have also been three verified cases of sexually-transmitted Zika.
Where can Zika be found and is it spreading?
Over the past few decades, Zika virus outbreaks have been documented in Africa, Southeast Asia, and the Pacific Islands. It had not been recognized in the western hemisphere until 2015 and has since exploded across most of Latin America. Brazil has thus far been the hardest hit.
It is expected that Zika virus can, and eventually will, be transmitted anywhere the Aedes mosquito vectors thrive, which includes parts of the southern United States. No local transmission of Zika has been documented in the continental US (in other words, no one has caught the virus from mosquitos on the US mainland), but some US Territories (Puerto Rico, US Virgin Islands, and American Samoa) have reported local Zika virus transmission via mosquitos (10 cases), and some travellers (91 cases) have brought it back to mainland US from South or Central America.
The most recent 9 cases in the US were pregnant women (not that pregnant women are more susceptible to Zika, but they are being monitored for it more closely). Of these 9, one gave birth to a child with microcephaly, two miscarried, and two had abortions after ultrasounds showed signs of microcephaly. Two others gave birth to healthy babies and the remaining two are still pregnant. Clearly, Zika has brought to light some complicated ethical and moral considerations in addition to the public health concerns.
Antibiotics are useless against Zika. Antibiotics target molecules in living cells, which viruses are not. While there are a few antiviral drugs on the market for a limited number of viral infections (e.g., HIV, Hepatitis C), there are none to combat Zika virus disease. Viral infections are often best combatted with vaccines, however no Zika vaccine currently exists. Since symptoms are generally mild (see above), comfort measures such as Tylenol for fever and body aches, rest, and adequate hydration are all that is needed. Precautions include removing mosquito breeding sites, fumigating with pesticides, and personal application of mosquito repellant.
Is Zika a new virus?
While Zika virus has undoubtedly been on Planet Earth for a very long time, mankind only became aware of it in the past century. During a monitoring survey of yellow fever in rhesus monkeys in the Ugandan Zika Forest in the 1940s, scientists discovered a new virus that was causing mild fever in some of the animals. It was identified as a close relative of the yellow fever virus, in the family Flavivirus. The Flaviviruses include yellow fever virus, dengue virus, West Nile virus, and now Zika virus.
A Rhesus Macaque. (Wikipedia)
Footnote on Zika in Costa Rica
(I am leading a class trip to Costa Rica in May and added this section for my students and their parents.) The first case presumed to have originated in Costa Rica was a male traveller from the US who had visited the Guanacaste Province in December. The Tico Times and The Costa Rica Star report that 2 Costa Ricans have been infected with Zika virus from local mosquitos, both in the Guanacaste Province. Two more Ticos have tested positive for Zika, but they had travelled to Colombia and Honduras where they likely encountered the virus. Compared to the 72,000 suspected cases in Brazil, resulting in over 4,000 cases of microcephaly, the risks in Costa Rica appear to be negligible.
In conclusion, Zika virus is a rapidly spreading germ that is very common in South America and increasing in frequency in Central America. It is spread primarily by mosquitos. Symptoms are generally mild, although Guillain-Barré syndrome has been reported. Zika poses the greatest threat to pregnant women and their unborn children.
I hope this short article has helped you to understand the risks posed by Zika viruses here in the US and abroad. If you leave your questions and comments below, I’ll do my best to respond quickly.