Over the years public health officials have had to deal with numerous emerging diseases; SARS, Lyme Disease, Ebola and most recently, Zika virus. While some of these diseases have been around for years, sometimes they cause a sudden increase in cases of illness that may have very serious complications. Last year the Ebola scare had people all around the world worried about the spread of a highly contagious and lethal disease. This year, it seems the news is all about the Zika virus as it has spread from Polynesia to Africa and Asia and finally into Central and South America.
Distribution of Zika Virus as of April 2016 (courtesy of the CDC)
The Zika virus is not a new virus, it was first noted as a unique infectious agent back in the 1940’s. Unlike Ebola which is has a high mortality rate if untreated, Zika infection has not resulted in any known fatality. Traditionally found in Africa and Asia, it has been known to cause mild symptoms such as fever, joint pain and a rash lasting around a week.
Zika has moved much higher in the ranks of diseases to be concerned about during recent outbreaks in South America. Here, infections have been linked to increased cases of Guillain-Barré syndrome and birth defects, notably microcephaly in newborns in northeast Brazil. This birth defect is the result of the brain failing to develop fully. The condition is noticeably apparent as the child’s head is smaller than normal. This apparent change from the African strain into something more like a pandemic virus may be due to an evolution of the previously mild virus into a more harmful form. Even for infants born without obvious complications, long term effects of Zika infection on brain development, while largely unknown, are cause for much concern. Recent reports suggest an increased incidence of encephalitis and meningitis in patients exposed to the Zika virus.
Image courtesy of the CDC
A new study provides a possible mechanism for how Zika virus infects skin cells. Zika virus attaches to the AXL protein found on the surface of skin cells. This allows the virus to infect the cells and cause a skin rash. Researchers hope to develop drugs that block this attachment and help prevent infection. These receptors are also present in neural stem cells providing a possible connection to the birth defects seen in newborns. Another new study shows that Zika virus readily infects stem cells that eventually develop into neurons of the brain cortex. In that study up to 90% of the infected cells were destroyed by the virus.
The virus is transmitted by the Aedes aegypti mosquito commonly found in Polynesia, South America and equatorial Africa. Interestingly, a few cases of infection have found to be caused by direct sexual contact with an infected partner. If confirmed, this would be the first example of an insect borne infection that was then passed person to person as happens in the case of an STI. While work is underway on a vaccine for this virus, current prevention focuses on control of, and reducing exposure to, virus carrying mosquitoes. A genetically engineered mosquito has been released that hopefully will interfere with the reproduction cycle of the insect. In many places women have been cautioned to forgo becoming pregnant at this time. The risk of birth defects is seen to be too high at this time.
The video below provides a nice overview of Zika and how to prevent infection when traveling to locations with the Aedes aegypti mosquito.
For More Information:
- Infographic: Zika Virus (Ricochet Science)
- Tang, Hengli, et al. “Zika virus infects human cortical neural progenitors and attenuates their growth.” Cell stem cell (2016).
- “Zika Virus Can Cause Birth Defects in Babies, CDC Confirms” – NPR, April 2016
- WHO overview of Zika
- CDC information page on the Zika virus
- “Study: Mechanism Between Zika Virus, Birth Defects” – WebMD, March 2016
Article by Michael Troyan. Michael has spent 20 years teaching non-majors biology and microbiology and currently works as an online instructor at Penn State University. He can be reached at [email protected]
Image Sources:
- Distribution Map, microcephaly art and Zika microscope image : CDC
- Animation: By Simpleshow foundation (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
- Microscope image of Zika Virus: 2016 Cynthia Goldsmith via the CDC
