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A Zika epidemic has been rampaging through the Americas. A mosquito-borne virus causes the disease, and has caused few symptoms in most of its adult victims. Its big threat, this year, seemed to be the risk that it posed to babies developing in the womb. It could limit the size of their heads and result in intellectual impairments. But now a new symptom has emerged. The virus can kill stem cells and limit their numbers in the brains of adults — at least in adult mice.
These new data suggest the virus may cause unknown — and potentially long-term — damage to adult minds. Scientists described their new finding August 18 in the journal Cell Stem Cell.
Most adults infected with Zika show few if any signs. Some may develop a headache, fever, rash and mild flu-like symptoms. These may last up to a week. In rare cases, things can be far worse. People may become paralyzed for days to a month or more. This syndrome is known as Guillain-Barré (Gee-YAHN bur-RAY). It typically causes weakness or tingling in the legs. But in severe cases, people may become totally paralyzed. Until they recover, these patients may breathe only with the help of a ventilator in a hospital’s intensive care unit.
But the main reason public health officials have been concerned about Zika’s spread is that it might be picked up by pregnant women. If the virus lodges in the brain of a fetus, it could kill some of the baby’s developing brain cells. And that may have happened already in more than 1,000 babies to date. Many of them were born with unusually small heads and brains. This condition, which can be caused by a number of infections, is known as microcephaly (My-kro-SEFF-uh-lee). It can limit a child’s brain development, with impacts that last a lifetime.
But the latest study finds that babies’ brains may not be the only ones at risk. Stem cells are unusual cells. What makes them special is that they aren’t special at all. Bone cells are different from nerve cells, which are different from skin cells. One of these specialized cells can’t take the place of another. But stem cells can. They can mature into many types — sometimes any types — of cells that the body may need.
If Zika targets newborn brain cells, it might do the same in adults. Or at least that’s what Joseph Gleeson had worried. Gleeson is a neuroscientist of Rockefeller University in New York City. Parts of the forebrain and the hippocampus play a major role in learning and memory. Both areas in the adult brain continue to make nerve cells. So Gleeson and his team decided to investigate whether those stem cells might be vulnerable to Zika.
And they were in the adult mice that they infected with Zika. The virus hit these brain regions hard. Nerve cells died. And in the forebrain and hippocampus, fewer new stem cells emerged. How few? The affected parts of the brain in these mice made just half to one-fifth as many new cells as did those areas in healthy mice.
It’s possible that people may not react the same way. One reason: The test mice were special. They had been genetically engineered to have weak immune systems. And that made them especially likely to pick up a Zika infection.
But Zika could potentially harm people who already have an impaired immune system, the authors say. It’s even possible that healthy people may be affected as the mice were. Clearly, more research is needed.
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cell The smallest structural and functional unit of an organism. Typically too small to see with the naked eye, it consists of watery fluid surrounded by a membrane or wall. Animals are made of anywhere from thousands to trillions of cells, depending on their size. Some organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
development (v. develop) In biology, the growth of an organism from conception through adulthood, often undergoing changes in chemistry, size and sometimes even shape.
epidemic A widespread outbreak of an infectious disease that sickens many people (or other organisms) in a community at the same time. The term also may be applied to non-infectious diseases or conditions that have spread in a similar way.
fetus (adj. fetal ) The term for a mammal during its later-stages of development in the womb. For humans, this term is usually applied after the eighth week of development.
flu Short for influenza. A highly contagious viral infection of the respiratory passages causing fever and severe aching. It often occurs as an epidemic.
Guillain-Barré Pronounced Gee-YAHN Bur-RAY. A rare condition that begins as the body’s immune system attacks peripheral nerves, causing weakness or tingling in the lower extremities. In severe cases, total paralysis can result. Three to 5 percent of people with Guillain-Barré die from complications, scientists estimate. The syndrome is thought to be a complication of several infectious diseases, including HIV, dengue, influenza and Zika.
hippocampus A seahorse-shaped region of the brain. It is thought to be the center of emotion, memory and the involuntary nervous system.
immune system The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.
infection A disease that can spread from one organism to another. It’s usually caused by some sort of germ.
journal (in science) A publication in which scientists share their research findings with the public. Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send out all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.
mature (verb) The process of growth and development that occurs as an individual moves toward adulthood.
microcephaly A condition that leaves babies with abnormally small heads and partially developed brains.
nerve A long, delicate fiber that communicates signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold, pain.
neuroscience Science that deals with the structure or function of the brain and other parts of the nervous system. Researchers in this field are known as neuroscientists.
risk The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.
STEM An acronym (abbreviation made using the first letters of a term) for science, technology, engineering and math.
stem cell A “blank slate” cell that can give rise to other types of cells in the body. Stem cells play an important role in tissue regeneration and repair.
symptom A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.
syndrome Two or more symptoms that together characterize a particular disease, disorder or social condition.
ventilator (in medicine) A device used to help a person breathe — take in oxygen and exhale carbon dioxide — when the body cannot easily do that on its own.
virus Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.
womb Another name for the uterus, the organ in mammals in which a fetus grows and matures in preparation for birth.
Zika A viral disease that can be transmitted to humans via mosquitoes. About 20 percent of infected people get sick. Symptoms include a slight fever, rash and pinkeye and usually fade quickly. A growing body of evidence suggests that the virus could also cause a devastating birth defect — microcephaly. Evidence suggests it may also cause neurological conditions such as Guillain-Barré syndrome.