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Brain Parasites, California’s Hidden Health Problem

The views expressed are those of the author and are not necessarily those of Scientific American.

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Sara Alvarez was afraid.

The doctors told her she needed surgery — brain surgery. Operations on such a complex organ are never simple, but this procedure was exceptionally difficult. There was a high risk of complications, of debilitation, of post-op problems. Alvarez might wake up paralyzed. She might wake up legally blind. Worse still, there was a chance she might not wake up at all.

Her mad dash to the emergency room had all begun with a walk in the park four days earlier. It was December 20, 2010, in Sunnyvale, Calif., a town that lives up to its name. The West Coast winter, not as long or as harsh as seasons in the East, gave her the opportunity to take her youngest child out for an afternoon stroll.

In the fading light of dusk, Alvarez, too, began to fade. She lost the feeling in her right leg. Her right foot followed suit. She couldn’t lift or move her right hand. She was weak, and her body was numb.

There was fear then, too.

At 10:15 p.m., Alvarez says her husband drove her to Redwood City. That night she became a patient at Kaiser Permanente Redwood City Hospital. She says the doctors batted diagnoses back and forth. It was a tumor. No, it was cancer.

It was Christmas, and Alvarez’s children cried and prayed, terrified that an unknown affliction would steal their mother away. Finally a CT scan revealed the malady. Alvarez had neurocysticercosis — a calcified tapeworm lodged in her brain.

Neurocysticercosis, which is common around the world but is not recognized as a major health concern in the U.S., has taken root in California, some health officials say. The disease is easy to prevent and relatively inexpensive to treat if caught early on. But once in the advanced stages, these brain parasites are costly to both patient and government.

The problem is that, due to a lack of education, most of the population doesn’t know that there’s a parasite wriggling within them, says Patricia Wilkins, a scientist with the Center for Disease Control and Prevention (CDC). Latinos, the community most afflicted by the disease, do not receive outreach or education about how to avoid or treat the potentially life-threatening organism, Wilkins adds.

Neurocysticercosis “primarily exists in marginalized populations, Hispanic immigrants,” Wilkins adds.

The National Institutes of Health classifies neurocysticercosis as the leading cause of epilepsy worldwide, and the World Health Organization (WHO) estimates that tapeworms infect 50 million people globally. The CDC says an estimated 1,900 people are diagnosed with neurocysticercosis within the United States yearly.

According to a January 2012 study in PLOS Neglected Tropical Diseases, California bears much of the burden with 304 hospitalized cases in 2009, the most recent year for which statistics exist. Eighty-five percent of patients in California were identified as Latino, and 72 percent were reported in the southern half of the state.

The high percentage of Latino cases is not surprising. Neurocysticercosis is common within third-world countries in Asia, Africa and Latin America. The disease’s telltale symptoms of paralysis, extreme headaches and chronic seizures present themselves in mass form. Individuals contract neurocysticercosis after becoming infected by tapeworm carriers. Immigrants traveling between countries, such as migrant workers, are often unwitting tapeworm hosts, transporting the disease across borders in their guts.

Scientists aren’t quite sure how it works, but tapeworm larvae seem to have developed a chemical secretion that keeps the human body’s immune system from barging in on their banquet. People can live for decades without any symptoms of neurocysticercosis because the tapeworm larvae break down natural defenses. Unfortunately, tapeworm larvae can’t live forever.

“While it’s alive, it’s a problem, but when it starts to die it’s a bigger problem,” Despommier says.

When the larvae die, the chemical balance is restored, and the immune system begins to attack, causing headaches, seizures and paralysis. Alvarez says she experienced debilitating headaches for 20 years before her diagnosis, but she probably consumed tapeworm eggs much earlier than that. When Alvarez immigrated to the United States in
the late 1980s she complained to American doctors of a pain so absolute it blinded her and made her vomit.

They gave her Tylenol.

“That’s a very typical story,” says Darvin Scott Smith, chief of infectious disease at the Kaiser Hospital.

Many physicians, even those in highly populated areas sizable immigrant populations, are unaware of the disease and how to diagnose it, he adds. Even many of the health organizations that target Latinos had never heard of neurocysticercosis and said their institutions were not funding research or community outreach.

Nobody cares about this disease, and they should, if not from a humanitarian point of view than from a fiscal aspect, says Wilkins, a scientist with the CDC.

Drugs such as Ablendazole and certain steroids, which are used to treat tapeworms and brain swelling, are relatively inexpensive — a maximum of a few hundred dollars. Wait until it’s a serious problem, though, and the dollar amount rises dramatically.

The CDC reports the average cost of neurocysticercosis at $37,600 per hospitalization.

The most common form of payment is Medicaid, a tax-funded public service. In Los Angeles County, the economic impact is even more pronounced, costing $66,000 on average, the increase likely due to the high cost of health care in the state, says Frank Sorvillo, a University of Los Angeles professor of epidemiology.

Despite a marked decrease in immigration over the past few years, the number of neurocysticercosis cases has remained relatively constant since 2001, when there were 386 recorded hospitalizations in California. This suggests that the parasite has taken hold in the U.S., Sorvillo says.

These numbers are likely underestimated. Only five states — New York, California, Texas, Oregon and Illinois — report the disease, and the data is inconsistent. Oftentimes, departments rely on each other to deal with paperwork, and the numbers are never recorded, Smith says. As a result, not much is known about tapeworm outbreaks in the U.S. — or the parasites themselves. Scientists still consider much of their life cycle a mystery.

Pork tapeworms, or Taenia solium, are complex organisms. They exist in three life stages: egg, larvae and adult, but their growth is not a straight progression from one form to the next. Tapeworm larvae enter the body when humans eat contaminated pork.

The babies, about the size of peas, fight their way into the small intestine and attach, using rows of grappling hook-like teeth to make tiny slices into the soft flesh of the intestinal walls. The parasites cling to the slippery surfaces of their new homes and begin draining nutrients from their host. If all goes well, adults can grow up to 20 feet long.

It sounds unpleasant, but if you’re going to contract a tapeworm, dealing with 20 feet of invertebrate is really the way to go. Researchers say that adult Taenia solium is relatively harmless and asymptomatic. The real trouble starts when they begin to reproduce within their human host.

Tapeworm adults are made up of hundreds of segments called proglottids. The parasite grows like a fingernail, the newest addition at the head and old material at the tip. The senior proglottids contain eggs — thousands of them. During the course of a natural lifecycle, the proglottids are discarded through their host’s anus. A family member, friend or restaurant cook infected with an adult tapeworm can secrete tens of thousands of tapeworm eggs daily, which can be easily ingested by others.

Being infected with the eggs, however, doesn’t result in an adult tapeworm. The eggs just develop into larvae—and grow no further. According to parasitologist Judy Sakanari at the University of California, San Francisco, no one really knows why. Unlike most animals whose lifecycle follows a child-adolescent-adult pattern, these eggs will never mature into adulthood. Their development is stunted at the larvae stage, which allows them to ride the bloodstream. They use their hooks to rip apart tissue and gain access to nutrient-rich hotspots. Some of these miniature reapers ultimately find their way into the brain. That’s where the trouble starts — and stops.

While alive, the larvae are not as dangerous as they are when they’re dead. The brain calcifies the dead larvae, and, oftentimes, surgery is necessary to remove them. This ramps up costs for the hospital and drains Medicaid funds. The State of California is not responding to the issue, Wilkins says, because there isn’t enough funding to tackle every bug that infiltrates a community. Health officials must pick and choose which diseases require the most resources. So far, neurocysticercosis has not been one of them.

In a 2000 proposal filed by the WHO, doctors called for international monitoring of neurocysticercosis. They argued that surveillance was key to eradication, that statistics were paramount if governments across the globe had any hope of reducing epilepsy and increasing quality of life. So far, the petition has not experienced much success.

In early January 2011, Dr. Smith of Redwood City, Calif. celebrated his birthday in the operating room of Kaiser Hospital, observing Sara Alvarez’s brain surgery. Medical professionals trimmed Sara’s hair, gingerly peeled away layers of skin and cut through a portion of her skull. Hours later, the chief of infectious disease watched as a neurosurgeon plucked a calcified tapeworm larvae from Sara’s head.

Before she was diagnosed, Alvarez had never heard of neurocysticercosis, and she still isn’t sure who gave her the eggs. It could have been a chance encounter, or one of her loved ones might be a carrier. She’ll never know for sure. The host may remain undetected and contagious, spreading the disease — thousands of eggs at a time.

Story and images by permission of Sara Alvarez and Dr. Darvin Scott Smith

Watch the video:

Mollie Bloudoff-Indelicato About the Author: Mollie Bloudoff-Indelicato is an environmental reporting fellow at E&E Publishing, covering the impact of climate change on everything from the international chocolate industry to methane hydrates in Antarctica. She has a master's degree from the Columbia University Graduate School of Journalism with concentrations in science journalism and radio reporting. She is searching for a full-time position with a science-oriented publication that is interested in developing their social media presence and expanding their multimedia department. Contact her at, and follow her on Twitter at @mbloudoff. Follow on Twitter @mbloudoff.

The views expressed are those of the author and are not necessarily those of Scientific American.

Comments 21 Comments

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  1. 1. sapbucket 10:35 am 09/6/2012

    How does an adult get produced if the larvae never grows in to an adult? This seems like a paradox to me. Would anyone like to explain?

    Link to this
  2. 2. mbloudoff 11:00 am 09/6/2012

    @sapbucket: If you ingest a tapeworm larva, it’ll latch onto your intestinal wall and turn into a tapeworm adult.

    If you ingest a tapeworm egg, it’ll turn into a larva and could end up in your brain. However, it’ll never mature into an adult.

    Scientists aren’t sure why the life cycle doesn’t follow the child-adolescent-adult pattern. It’s one of the world’s many mysteries.

    Link to this
  3. 3. David Marjanović 12:13 pm 09/6/2012

    How does an adult get produced if the larvae never grows in to an adult?

    They do grow into adults if a pig, as opposed to a human, ingests an egg. That’s why it’s called the pork tapeworm, as the article correctly mentions.

    There are other species: beef, dog, fox tapeworm… Most tapeworm species have two hosts, the “intermediate host” that ingests the eggs, hosts the larvae, and is then eaten by the “terminal host” where the larvae develop into adults as correctly described in the article.

    What the article doesn’t get right is Latin grammar. One larva, two larvae; completely regular A-declension word.

    Scientists aren’t sure why the life cycle doesn’t follow the child-adolescent-adult pattern. It’s one of the world’s many mysteries.

    “Mystery”? Humans simply aren’t the correct intermediate host for a pork tapeworm. We don’t provide the same environment; something is wrong in it.

    Link to this
  4. 4. bucove 3:18 pm 09/6/2012

    If I may proffer a possible solution to a certain conundrum expressed in the article?

    a) Science does not understand the tapeworm life cycle.
    b) Empiric observation suggests tapeworms require an intermediate host (pigs? oh, come on! THINK!).

    I’d like to stimulate thought by asking two questions:

    a) (microbiology dept) How long an evolutionary history does this particular species of tapeworm have?

    b) (everyone) How long has cannibalism among humans been relegated to nightmares and cognitive avoidance?

    Link to this
  5. 5. bucove 3:22 pm 09/6/2012

    it doesn’t need two hosts, it only needs two trips though a host to complete the life cycle

    Link to this
  6. 6. CherryBombSim 7:39 pm 09/6/2012

    If David were correct and humans are the intermediate hosts, then we would need to be eaten by pigs to complete the life cycle? This does not sounds good.

    Link to this
  7. 7. kienhua68 8:15 pm 09/6/2012

    The real message here is be careful or be sorry.

    Link to this
  8. 8. d'abord-jahrstorfer 7:41 am 09/7/2012

    How common is that neurocysticercosis is susceptible of surgical therapy? How frequent is that the worm inside the brain is just a single one? How common are other parasitic diseases of the brain?

    Link to this
  9. 9. ironjustice 10:10 am 09/7/2012

    “Has taken root in California”
    “Public nudity pushes acceptable limits in San Francisco”
    “The proglottids are discarded through their host’s anus”

    Link to this
  10. 10. Imp... 10:52 am 09/7/2012

    My understanding is that humans CAN be both the initial (egg to larva) and the second (larva to adult) host, just not the same person. We can intake the eggs which then hatch into larva or intake the larva which grow into adults (and produce eggs).

    Link to this
  11. 11. lgao965 3:02 pm 09/7/2012

    Could someone clarify this?

    if what she had was the larvae that got into her brain, which can’t grow into adult size, that means Alvares could never have been spreading the disease to others? assuming that larvae can’t produce eggs?

    Link to this
  12. 12. ispeak 3:55 am 09/8/2012

    I had an episode of numbness and jerk in the left leg and was diagnosed with the same in the year was a single one that manifested in the frontal right lobe.I took topomax for 6 months and then in the scan that followed later it showed no traces of the calcified monster..I have since then been on regular pills and now tapering off. yeah during my course i had dancing fingers (tremors)and needle like pricks on some parts of my body but bearable.I am from India and i think in us since the disease is not well understood and researched the best option advised is surgery which has major side effect..i want to understand how a human carrier infect the others..I have small children and a point in this blog has worried me a lot

    Link to this
  13. 13. JamesSavik 4:37 pm 09/8/2012

    This explains so much.

    Link to this
  14. 14. ivanbpaul 3:06 am 09/9/2012

    Its unusual that one has to resort to surgery for something that has been treated with medications since the last 10 years at least! This is common in India and South America and surgical treatment has been long given up as an option as one doesn’t require surgery for Neurocysticercosis. Wonder what the indication was?!

    Link to this
  15. 15. Roger J 9:50 am 09/9/2012

    Based on what I just read this justifies a much stronger defense of our boarders especially along the southern parts. I also believe that all immigrants entering the U.S. should have a full and complete physical before they are aloud to go freely walking our streets.

    Link to this
  16. 16. SalCanz 10:57 am 09/9/2012

    Actually, what you just read does not justify stronger defense of our borders, especially along the Southern parts. The disease is found in Africa, India, and South America. Immigrants from these parts of the world generally enter the US on airplanes or ships, not by crossing our Southern border. Moreover, any illness can be brought into the country by visitors from other countries or by Americans who have travelled abroad.

    By your logic, EVERYONE crossing a border into the US would have to have a complete physical before going beyond passport control. Obviously, that would be extraordinarily expensive & not cost-effective.

    Info in the article and comments shows that some simple, inexpensive measures would be effective in responding to this and other diseases: 1) educate the public about the importance of washing their hands thoroughly every time they use the toilet; 2) urge establishments preparing/serving food to make use of machines dispensing alcohol based cleansers; (cruise ships have everyone going into dining areas use these); and 3) having the CDC get info on diseases like this out to American MDs. From the comments, it sounds like MDs in countries where the disease is established, know more about it than our doctors do, so it makes sense to benefit from their expertise.

    The big point is to recognize that diseases and paracites do not recognize political boundaries. The goal of our government’s policies should be to (as much as possible) stop illnesses at our borders. Stopping particular groups of people will not promote that goal.

    Link to this
  17. 17. 2:53 pm 09/11/2012

    “A family member, friend or restaurant cook infected with an adult tapeworm can secrete tens of thousands of tapeworm eggs daily, which can be easily ingested by others.”

    How are the eggs secreted by the human host?

    Link to this
  18. 18. SalCanz 10:29 am 09/12/2012

    The eggs are secreted in feces. Which is why one of the most important ways of preventing the spread of the disease is for people to wash their hands thoroughly after using the toilet or changing diapers. See the CDC info on the disease at Also, look at the linked article on hand washing.

    These tape worms are endemic in some parts of the world, and people get them from eating infected pork. However, since the end of WWII, pigs in developed countries have been raised in conditions where they cannot ingest infected feces or water. So cases of the disease in the US are imported by people who have gotten infected abroad, either when traveling or living there.

    The CDC info page gives info on what you can do to avoid infection when traveling in areas where the worms are endemic.

    But the big takeaway message — as with preventing the spread of so many illnesses — is that people should THROUGHLY wash their hands — FREQUENTLY.

    Link to this
  19. 19. dgjohnsonstein 1:47 am 09/14/2012

    The article talked about recognizing the symptoms, but they did a poor job of informing us readers how to do so. Do a better job next time.

    Link to this
  20. 20. Sundaydiver 1:09 am 09/19/2012

    I’m shocked that even the parasite expert quoted here doesn’t seem to know what I learned as a biology undergrad: The “mystery” of the tapeworm larvae never maturing into adults is no mystery at all. It all makes sense considering that to a tapeworm, humans are what’s called a “false host.” The worm’s lifecycle evolved in the wild, independently of human presence. Eggs are ingested by say, a rodent, which is in turn eaten by a predator, the “true host” the worm is going for. The larvae stay arrested in their development until they are being consumed. Then they will develop into mature worms and complete the cycle. The reason for the “mystery” is that humans don’t tend to get eaten these days…

    Link to this
  21. 21. Charles12 12:02 am 11/11/2014

    Even I had this surgery.I had to buy tramadol Online to overcome the little pain.I had brought cheap tramadol 100mg.

    Link to this

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