Zika Virus: An Introduction

Before November of this year, Zika virus was a relatively unknown viral pathogen, generating minimal attention compared to this year’s infectious disease all-stars such as the MERS coronavirus, influenza, and of course Ebola. Typical symptoms of infection are a rash, fever, joint pain, and red eyes and less commonly, muscle pain, vomiting, and headaches.[1] The infection lasts for about a week, and symptoms occur in 20% of cases. Management of patients is supportive, as there is no Zika specific therapeutic or vaccine available.[2] Transmitted by the Aedes aegypti mosquito, Zika virus causes a notably mild infection compared to other arboviral pathogens like dengue and chikungunya which cause more severe joint pain and, in the case of dengue, a high fever.[3-5] The mildness of the symptoms and, until recently, low incidence, have allowed this virus to slip under the radar, but there are now two factors which have promoted the Zika virus to an unprecedented position of fame.

It’s spreading quickly. First described in Uganda in 1968, Zika virus was only reported in a few African nations, the South Pacific, and parts of Asia prior to its first big outbreak on Yap Island, Micronesia in 2007. Prior to this outbreak, there had only been 14-15 cases ever recorded.[2] In October of 2013, Zika showed up in French Polynesia, affecting roughly 11 percent of the population and spreading to nearby islands such as Cook Islands, New Caledonia, and Easter Island. The virus was first detected on Easter Island off the coast of Chile in February of 2014, and made its way to Brazil by May of 2015.[1]

Zika virus continues to spread at an unprecedented rate with presence in 14 Brazilian states and 10 countries in South and Central America, including Mexico and most recently Panama. Following in the footsteps of dengue and chikungunya, which are also transmitted by the Aedes aegypti mosquito, Zika is demonstrating that diseases that rely on mosquitos for transmission can expand rapidly.[6-8]

It has a suspected link to congenital birth defects. Both French Polynesia and Brazil have experienced an alarming surge in reported cases of congenital brain and spine malformation, particularly microcephaly.[2] Infants born with microcephaly in infants have a smaller and underdeveloped brain which usually causes developmental complications and can be lethal. The malformation can be caused by several different types of viral infections, but has never before been linked to Zika virus. As of December 8th, Brazil has had 1,761 cases of microcephaly this year, compared to 59 total recorded cases in 2014.[9] This is almost 30 times more cases than was reported last year. Though the recent introduction of Zika virus to the Brazilian population parallels the shockingly high number of infants born with microcephaly, data directly linking the two is limited. On November 28th, a newborn who died shortly after birth from microcephaly tested positive for Zika virus.[7] The discovery brought the recent surge in media attention to Zika virus and the outbreak in Brazil. Besides this case, there have only been two cases in which the virus was found in the amniotic fluid of expecting mothers with microcephalic babies.[3,10]

Similarly, in French Polynesia and Brazil, health care officials have reported an increase in central nervous system (CNS) disorders coinciding with the arrival of Zika virus. The most commonly observed CNS disorder is the neuro-degenerative Guillain-Barre syndrome (GBS). Again, definitive evidence to support this connection is lacking, and more research is needed. However, of the 42 Brazilian cases of GBS diagnosed this year, 62 percent were found to have symptoms consistent with Zika virus infection.[10] 

Judging from the recent increase in media mentions, it’s safe to say that the infectious disease world is starting to focus on this rapidly spreading disease. The next few months will be very telling not only as we watch to see where the virus will show up next, but also as researchers gather data and determine if Zika truly is the cause of the observed congenital birth defects and complications. Moving forward, both the Pan American Health Organization and the World Health Organization have released statements advising countries bordering endemic nations to watch for Zika virus infection symptoms and those in endemic areas, particularly expecting mothers, to take precautions to avoid mosquito bites.[10] The Brazilian Ministry of Health even goes as far as to encourage women to hold off on getting pregnant until Zika’s effect on prenatal development is fully understood.[12]

As is true of many arboviral pathogens, the best prevention strategy is to control or eliminate the vector population. Dengue, chikungunya and Zika virus have all been spreading quickly, and outbreaks of dengue have been reported in the US, making mosquito control an issue of international importance.[13,14] Because Aedes aegypti mosquitoes reproduce in stagnant water, ensuring that ponds and large puddles are filled in, and water collection devices are covered or empty, is critical for limiting the size of mosquito populations.2 Furthermore, limiting interaction with mosquitoes through repellents, screened windows, and long-sleeved clothing will help to decrease the likelihood of infection. Since the outbreak of the virus, the Brazilian army has been an active participant in draining unnecessary water barrels and other catchment devices for Zika prevention.[3] A proactive approach would benefit every country faced with this newly emerged disease.

 

  1. Zika Virus: Symptoms and Treatment http://www.cdc.gov/zika/symptoms/index.html. Accessed December 09, 2015.
  2. Belluz J. The Zika virus is spreading across Latin America. Here's what we know. Vox. 2015.
  3. McKenna M. Mosquitoes Bring Disease, Maybe Birth Defects, To US Border. Phenomena: National Geographic; 2015.
  4. Chikungunya Virus: Symptoms, Diagnosis, & Treatment http://www.cdc.gov/chikungunya/symptoms/index.html. Accessed December 09, 2015.
  5. Dengue Fever http://www.webmd.com/a-to-z-guides/dengue-fever-reference. Accessed December 08, 2015.
  6. Fox M. This Virus You Never Heard of May Be Causing Birth Defects in Brazil. NBC News; 2015.
  7. Dias T. This is the current state of microcephaly epidemic caused by zika virus in Brazil. Nexo Journal 2015.
  8. Zika virus infection – Panama. Disease Outbreak News. December 05, 2015.
  9. Herriman R. Brazil microcephaly update: Nearly 1800 suspected cases, Zika virus related microcephaly protocol published. Outbreak News Today. December 08, 2015.
  10. Epidemiological Alert: Neurological syndrome, congenital malformations, and Zika virus infection. Implications for public health in the Americas. Pan American Health Organization, World Health Orgnization; December 01, 2015.
  11. Freire LF, Coutinho R. Zika virus can cause miscarriages. Folhape 2015.
  12. Zika Virus Causes Pregnancy Scare – Brazil Women Warned Not to Get Pregnant As Virus Linked to Rare Birth Defect. The Gleaner; 2015.
  13. Dengue fever, Chikungunya and Zika virus in the Pacific Islands. Safe Travel  https://www.safetravel.govt.nz/news/dengue-fever-chikungunya-and-zika-virus-pacific-islands. Accessed December 08, 2015
  14. Maron DF. Dengue Fever Makes Inroads into the U.S. Scientific American. 2013.