The Zika Virus: What Have We Learned So Far?

From the llecture series: An Introduction to Infectious Diseases

By Barry C. Fox, MD, University of Wisconsin

“Zika is a major emerging viral infectious disease problem that has no simple or easy solution.”

Zika virus concept showing a crying baby and Aedes Aegypti mosquito in the background
(Image: airdone/Shutterstock)

Although the Zika virus existed in central Africa decades ago, the sudden and rapid spread of the virus around the world in a couple of years was significant, but not unprecedented. Other viral diseases, including the Dengue and Chikungunya virus which have the same mosquito vector of transmission, had a similar spread over just a few years. In the case of Zika, approximately 50 countries have been affected.

What is it, and How is it Spreading?

Image of Zica virus carrier aedes aegypti mosquito on human skin
Zika virus is spread by Aedes aegypti mosquito species. (Image: Tacio Philip Sansonovski/Shutterstock)

Zika is officially classified as a flavivirus and is closely related to Dengue and West Nile viruses. It is spread by Aedes aegypti mosquito species. Unlike most mosquitos in the US which tend to bite at dusk and dawn, Aedes can be aggressive daytime biters. They can also reproduce in a container of water as small as a bottlecap. This characteristic makes mosquito control measures much less likely to be successful. The best way to prevent Zika is to prevent mosquito bites. A. aegypti mosquitoes have a limited geographic range in the southern US. Both southern Florida and Texas have been affected so far in the US, but the A. aegypti mosquito also has a worldwide range.

This is a transcript from the video series An Introduction to Infectious Diseases. Watch it now, on The Great Courses Plus.

Illustration of a newborn baby with Microcephaly disease caused by Zika virus
Microcephaly is the most common abnormality caused by Zika virus. (Image: Luciano Cosmo/Shutterstock)

Much of the worldwide attention for the Zika virus is from its link to congenital neurological abnormalities in pregnant women. Microcephaly is the most common abnormality, leading to incomplete brain development. Children born with this condition not only struggle to survive but represent an ongoing healthcare burden, often in nations that already have limited healthcare resources. Miscarriage, and/or stillbirths are also attributed to the infection.

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What are The Symptoms of the Virus?

A great concern to the continental US would be a broader spread of Zika and a larger impact on pregnant women here. Of additional concern is another species of Aedes which could potentially harbor the Zika virus: A. albopictus. This species has a much larger geographic range throughout most of the US.

One of the unique features of this virus is that infection in males leads to contamination of sperm for up to 90 days, hence, Zika has also become a sexually- transmitted disease, estimated to be 5-10 % of total cases. Men who have traveled to or lived in Zika endemic areas need to take special precautions with sexual relations with their partners, especially if they are in the family planning mode.

Of those humans bitten by an infected mosquito, only one in five will have symptomatic disease. These include several days of mild symptoms including fever, chills, muscle aches, and a rash. These symptoms are also milder than infections with Chikungunya or Dengue virus, and milder than influenza infections. The asymptomatic nature of most infections complicates the diagnosis and potential identification in women of childbearing age. There have also been reports of Guillain-Barré syndrome, an uncommon neurological disorder with loss of ability to control and sense one’s arms and legs, that may be tied to the virus.

During the first week of infection, the Zika virus can be found in the bloodstream and can transfer from an infected person back to another uninfected mosquito via mosquito bites. The newly infected mosquito can then transfer the virus to other people in a vicious cycle. There are reliable blood and urine tests available to establish a diagnosis of Zika infection, but there are no effective anti-viral treatments for infection, nor will there likely be in the near future.

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Pregnant women can be tested for Zika infection, and they can also have prenatal care to assess the developing baby’s risk of congenital infection, including ultrasound exams, possible amniocentesis, or sampling of the fluid in the amniotic sac.

Where Is The Disease Now?

Originally Zika infections were confined outside the continental United States, and cases in the US were all “imported”. There is a significant burden of Zika infections in Puerto Rico. Also, cases have now been transmitted locally by mosquitoes to humans in south Florida and Texas. Despite local community efforts at mosquito control, the prevailing health authority opinion is that Zika will likely remain in these and other regional geographic areas.

Pregnant women have been advised by the Center for Disease Control not to travel to areas of the US or other areas of the world with known Zika virus cases. The local tourist bureau should not be your source of information if you are thinking of traveling abroad; rather, check the CDC site for information.

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The World Health Organization has issued a global response plan in 2016, available for review at http://www.who.int/emergencies/zika-virus/en/.

Map of Zika Virus transmission
Map produced by the US Centers for Disease Control of active Zika Virus transmission as of April 13, 2016. (Image: By NIAID (Zika Virus)/Public domain)

One of the more pressing global needs regarding Zika, since it’s most likely here to stay, is a vaccine for prevention. There are several types of vaccines simultaneously being investigated. A federal ethics panel, however, has recently declined to allow humans to be deliberately infected with the Zika virus. Although there are established rules of vaccine development, the rules may need reconsideration under the current world need for a vaccine.

In summary, Zika is a major emerging viral infectious disease problem that has no simple or easy solution. It is hoped that the virus will remain limited in its transmission areas in the United States. Pregnant women need to understand the risk of Zika in local areas, and if they are considering any travel outside the US, avoid Zika infected areas.

Common Questions About the Zika Virus

Q: How does one contract the Zika virus?

One primarily contracts Zika through mosquito bites. The most dangerous mosquitos are the species Aedes aegypti and Aedes albopictus.

Q: What are the top countries that harbor Zika?

The top countries harboring Zika include Cambodia, Colombia, Belize, Cayman Islands, Costa Rica, India, and Jamaica.

Q: Does Zika kill you or let up?

Most people do not experience symptoms, but some Zika victims report nausea, abdominal pain, and occasionally diarrhea. These symptoms appear 2-12 weeks after a bite. Truthfully, they tend to go away within a week. However, extreme symptoms can last weeks or months. Zika does not usually kill those who are afflicted with the virus, but it can harm the unborn fetus of a pregnant woman who contracts the virus.

Q: Is Zika still a threat in Mexico in 2019?

Zika no longer poses as big of a threat in Mexico or neighboring countries in 2019 as it has in the past few years, or at least not as many people are reporting it. That said, pregnant women should still take precautions when traveling to Mexico and Central/South American countries as well as the Caribbean islands.

This article was updated on November 18, 2020

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