How worried should you be about Zika virus?

U-M virologist offers perspective on brain-affecting infection

Zika virus

Seen through a microscope, Zika virus particles (like the one at the tip of the arrow) don’t look too dangerous. But they’re suspected of causing lasting harm in a growing number of infants and others. Image courtesy of CDC

It seemed to burst onto the scene overnight, with tragic pictures of babies born with small heads and damaged brains. Now, the world’s health authorities have shifted into high gear to deal with Zika virus.

How does this virus compare to others, and what will it take to detect or defeat it? U-M virologist Katherine Spindler, Ph.D., offers some key information and a dose of perspective. She’s a member of a national team that hosts a weekly podcast on viruses, aimed at the general public, called This Week in Virology.

Dr. Spindler and her laboratory team in the U-M Medical School study how viruses cross a protective barrier to the brain and what viruses do once they’re there. They also look at how some viruses can cause mild illness in most people – but in immunocompromised individuals, cause serious damage. Working with scientists in Brazil, Spindler’s lab team studies other viruses that can cause brain problems.

Q: What is Zika virus and how does it spread?


Katherine Spindler, Ph.D., professor of Microbiology and Immunology at the U-M Medical School

Dr. Spindler: It’s a member of a family of viruses called flaviviruses, which also include the viruses that cause dengue fever, yellow fever and West Nile fever. It’s also part of a group of viruses that we called arboviruses, because they are carried by insects. The word “arbovirus” comes from “arthropod borne” – and insects are part of a group of animals called arthropods. At U-M, both my lab and that of Dr. Andrew Tai are studying some of these related viruses.

Like many arboviruses, Zika is spread by mosquitoes. When they bite a human or animal to get blood for food, mosquitoes can also pick up the virus if it’s present in high enough levels in the human blood. Then, the virus can escape from the mosquito’s blood reserve and get into the bloodstream of the next person – or animal – that the mosquito bites.

Fortunately, arboviruses do not spread like the common cold or influenza virus, through the air or tiny droplets that come out when someone sneezes or coughs. But Zika is believed to be spread from a pregnant woman to the fetus she carries – and possibly through direct exposure to an infected person’s blood. There is also some evidence of sexual transmission in a very few case reports, though there is only one report of Zika virus in semen.

Q: Do we know for sure what Zika virus is doing to people?

Countries where Zika virus infections are reported, according to the CDC, as of early 2016

Countries where Zika virus infections are reported, according to the CDC, as of early 2016

Dr. Spindler: We don’t yet know for certain that the cases of microcephaly – abnormally small heads and brain damage in infants – seen in Brazil and elsewhere are caused by Zika virus, or even caused by Zika virus working together with some other virus or other environmental factors.

Right now, we know that the two things are associated, and that there is a strong suspicion of a direct link. Health authorities are acting on that understanding, so that is why you have heard of warnings to pregnant women to avoid traveling to areas where Zika virus is spreading. Some countries affected by Zika are even advising women not to become pregnant at this time, and some countries are recommending avoiding unprotected sex after Zika infection.

There’s also a growing understanding that there may be an association between Zika virus infection and a nerve condition called Guillain-Barré Syndrome, which can leave someone paralyzed temporarily or even permanently.

For most people, though, a Zika virus infection is not a big deal – it causes a rash, a mild fever, or headache. In addition, 80% of people that get infected show no signs of disease. But it’s the growing suspicion of rare but serious side effects in newborn babies and some others that has launched it into the world spotlight.

Q: How does Zika compare with other viruses that can affect the brain?

Dr. Spindler: The condition seen in Brazilian babies is called microcephaly, which literally means tiny head. American babies can also be born with microcephaly, though it is rare. Many cases of microcephaly result from genetic errors. By far the largest number of cases in the U.S. of microcephaly that can be blamed on a virus are caused by cytomegalovirus, known as CMV.

CMV is a virus in the same family as the virus that causes herpes. Besides microcephaly, CMV can also cause other problems for babies born to women who were infected with it during pregnancy. There’s no vaccine, and about 5,000 babies born in the US every year have some lasting problem due to CMV.  It’s thought that CMV may actually attack the stem cells in the developing fetus that are crucial to growing a normal brain.

Another virus that can cause brain-related problems in fetuses and newborns is rubella, also known as German measles. If a pregnant woman catches it, her baby may suffer lasting damage to the brain, affecting hearing, vision or intelligence. Fortunately, we have a vaccine against that. It’s part of the MMR, or measles, mumps, rubella triple vaccine. And that’s why it’s so important for people of all ages to have a current MMR vaccination.

HIV, the virus that causes AIDS, can also affect the brains of babies after they are born, if their mothers and they are infected.

Mosquito sucking blood

Mosquito sucking blood

Another mosquito-borne virus that has been widespread in recent years in Latin America, called chikungunya, can also affect the brain. So can a disease called toxoplasmosis, which is caused by a one-celled animal that acts as a parasite, Toxoplasma gondii. This parasite is being actively researched by my Microbiology & Immunology colleague, Dr. Vernon Carruthers.

We really don’t know much about how viruses and parasites manage to cause damage and cross the barriers that protect the brain.

That’s what my lab and others are trying to understand at the most basic level, because it happens in many virus families. Once they have breached the protective barrier, replicating viruses may disrupt brain cell growth during development that leads to microcephaly and brain damage.

We’re studying crossing of this protective brain barrier by two other viruses that are common in Brazil and other parts of Latin America: dengue virus and Oropouche virus. We’re also studying it in a version of the virus that causes some cases of the common cold, adenovirus.

Q: So how can Zika virus be defeated?

Dr. Spindler: It would take a long time to develop a vaccine against it, or new antiviral drugs. It’s hard to even test to make sure someone has Zika – this requires specialized testing that’s not available in most areas where Zika is spreading.

The usual testing method, checking a person’s blood for antibodies that the body produces in response to a new infection, doesn’t work because Zika is so closely related to dengue virus, which is also circulating in the same areas.

Current tests for Zika antibodies probably wouldn’t be useful here in the United States because West Nile virus, another related virus that also spreads via mosquito bites and which is present in the US, is reported to also cross-react with antibodies to Zika virus.

Once there are good tests for Zika and they are used routinely, scientists can start to get good data about the mode of action of this virus, which will be an important step in defeating it.

Public health strategies will need to primarily reduce biting from mosquitoes, by controlling mosquito populations, and encourage personal protection against mosquito bites. Fortunately, that will reduce the risk of all arboviruses that spread via mosquitoes, not just Zika virus.

Scientists are working on breeding new varieties of mosquitoes that have slightly altered DNA, which has shown promise in preventing the spread of malaria. Perhaps that could be a weapon against Zika virus as well.

CDC guidance for preventing mosquito bites that can transmit multiple diseases.

CDC guidance for preventing mosquito bites that can transmit multiple diseases. (Click the image to see it larger)

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