by Amy Stewart
It must have shocked the medical team gathered around her in the operating room when, in the middle of the procedure, with her skull open and her brain exposed, the surgeon started laughing. He was just so relieved to find out that, rather than an intractable tumor, the woman had been suffering from tapeworms. Removing the worm was a simple affair, and the woman awoke from surgery to the remarkable news that she didn’t have a brain tumor after all.
An infestation of pork tapeworm begins when a person eats raw or undercooked pork laden with tapeworm larvae. Inside pigs, the larvae form fluid-filled cysts that don’t develop into adults unless they are ingested by humans. Once a person eats pork infested with those cysts, the larvae settle into the intestinal wall, where they mature and reach several meters in length. Adult tapeworms can occupy the intestine for twenty years, releasing thousands of eggs that get discharged from the body through feces. The adult tapeworm may exit the body on its own, or it can be killed with prescription medication.
The Arizona woman was most likely infected not through under-cooked pork, but through contact with feces impregnated with tape-worm eggs. One way this could happen is if food handlers infested with tapeworms don’t wash their hands after going to the bathroom, allowing tapeworm eggs from feces to remain on their hands when they prepare food. When people swallow the eggs rather than the larvae, a different kind of infestation occurs. The eggs, once swallowed, hatch into larvae that are initially far more mobile, preferring to explore the body rather than remain in the intestine. They can migrate to the lungs, the liver, or the brain.
Although pigs serve as hosts for tapeworms, allowing the eggs to develop into larvae, humans are the only known definitive host. That means that larvae can reach adulthood only in a human.
To the astonishment of the medical community, the talk show host Tyra Banks recently devoted an episode of her show to the so-called tapeworm diet, in which people willingly ingest tapeworm eggs to lose weight. In fact, tapeworms can cause severe digestive problems, anemia, and organ damage, and may actually cause people to gain weight, not lose it, making this a very dangerous diet plan.
Pork tapeworms are estimated to infest one in ten people worldwide, with the rate much higher in impoverished countries. The presence of tapeworms in the brain is now the leading cause of epilepsy worldwide—a tragedy that could easily be prevented with better sanitation.
LYMPHATIC FILARIASIS
Wuchereria bancrofti and Brugia malayi
Also known as elephantiasis, infestation with these parasitic worms causes thick, wrinkled skin and grotesque swelling of arms, legs, breasts, or genitals. Over 120 million people worldwide carry the parasite, with 40 million suffering the most severe symptoms. The parasites require both mosquitoes and humans to complete their life cycle: they can only develop from infants (called microfilariae in this case) to larvae while inside a mosquito, and those larvae can only reach adulthood inside a human. The offspring of the adult worms—the next generation of microfilariae—must find their way back into a mosquito to continue growing and repeat the process.
One bite from an infected mosquito probably won’t transmit the disease. It can take hundreds of bites for enough male and female larvae to enter the body, track each other down, and reproduce. Once established, however, the adult worms settle into the lymph system and build nestlike structures that block lymphatic fluid and cause the characteristic swelling. Adults live for five to seven years, mating and producing millions of offspring, which circulate in the blood in the hopes of eventually being extracted through mosquito bites to continue their life cycle.
This disease is found in the poorest parts of the world, including Africa, South America, parts of South Asia, the Pacific, and the Caribbean. Although a blood test can detect the presence of the microfilariae, a strange quirk in their behavior makes this an unreliable method: the tiny creatures only circulate through the bloodstream at night when mosquitoes are biting. During the day, they may not show up on a blood test at all. And treatment is even harder: there is no way to eliminate the adult worms, but an annual deworming pill called Mectizan will kill their offspring and stop further transmission of the disease.
But annual pill distributions are not easy in remote areas or countries torn apart by violence. Now public health officials are trying a new approach: adding the dewormer to table salt, at a cost of only twenty-six cents per bag. In China, the disease was eliminated after the government ordered people to use the salt.
While the idea of distributing medicated salt to the world’s poorest people may seem strange or disturbing, it has many benefits. Dewormers kill several other annoying parasites, including roundworms, lice, and scabies. A Centers for Disease Control official working to eradicate lymphatic filariasis called the drug “the poor man’s Viagra” because people look and feel so much better without the constant irritation of parasites that they once again find themselves in the mood for love, causing a little baby boom in communities that get the treatment. “I’ve heard of babies named Mectizan,” the health official told a reporter.
SNAIL FEVER
Schistosoma sp.
A freshwater snail is to blame for the transmission of this parasitic worm. The eggs of Schistosoma worms are excreted from infested people in feces or urine. If that waste goes into a river or lake, the eggs hatch and must then enter the body of a freshwater snail to develop into the next generation. They are then released from the snail, and they wait for a human to wade into the water so they can burrow into the skin and continue their life cycle.
This disease, called bilharzia or schistosomiasis, infects two hundred million people worldwide, primarily in Africa but also in the Middle East, East Asia, South America, and the Caribbean. People develop a rash, flulike symptoms, bloody urine, and damage to the intestines, bladder, liver, and lungs. A single pill called praziquantel, given once a year, treats the disease and prevents further transmission. The drug costs only eighteen cents per pill, and this—along with improved sanitation—may someday eliminate the disease.
ROUNDWORM
Ascaris lumbricoides
Ascaris lumbricoides needs no help from a mosquito or a snail to find its way into the human digestive tract. At over a foot long, and roughly the diameter of a pencil, it is perfectly capable of taking care of itself. Roundworms settle into the small intestine, where they live for up to two years. Females can lay up to two hundred thousand eggs per day. Those eggs pass from the body in the stool. Once on the ground, they develop into tiny larvae that may find their way back into the human body. This is more likely to happen in areas with poor sanitation, where children may play on the ground near areas used as a latrine, or in communities that use improperly treated human waste for fertilizer on crops that they then eat without proper washing.
Once back inside the body, the worms spend about two weeks in the lungs, then move into the throat, where they are swallowed so that they can reach the small intestine and grow into an adult. In the worst cases, people can harbor several hundred adult roundworms in their intestines. Oddly, the worms are greatly troubled by general anesthesia, and have been known to flee the body via the nose or mouth on the operating table. In areas where roundworm infestations are common, surgeons have learned to administer deworming medications before surgery to prevent startled roundworms from blocking intubation tubes as they attempt to exit the body.
Although some people experience only mild abdominal symptoms, a serious case of roundworm infestation (called ascariasis) can lead to respiratory problems, nutritional deficiencies, organ damage, and severe allergic reactions. An estimated 1.5 billion people—up to one-quarter of the world’s population—are infested with roundworms. Most of those are children. Roundworms kill an estimated sixty thousand people per year, mainly through intestinal blockages. Infestations are found in tropical and subtropical regions around the world and sometimes in southern regions of the United States. Prescription medications can kill the worms and a soil bacterium called Bt (Bacillus
thuringiensis), which is used to control nematodes in soil, shows promise in treating people as well. But improved sanitation is the only sure way to eliminate the disease.
GUINEA WORM
Dracunculus medinensis
President Jimmy Carter saw Guinea worm infestations firsthand in 1988, when he was visiting a village in Ghana as part of the Carter Center’s humanitarian work. Over half of the people in the village were debilitated by the worms. He told reporters: “My most vivid memory was of a beautiful young 19-year-old-or-so woman with a worm emerging from her breast. Later we heard that she had eleven more come out that season.”
Dracunculiasis, more commonly known as Guinea worm disease, is an ancient affliction that has been found in Egyptian mummies. It is transmitted by a tiny freshwater crustacean called a copepod that people swallow when they drink from ponds or other unclean water sources. Once they swallow it, the copepod dies but the guinea worms inhabiting it move into the small intestine to grow and mate. The male dies, but the female eventually reaches two to three feet in length, resembling a long strand of spaghetti. She burrows into connective tissue, around joints, or alongside the bones of the arms and legs.
Guinea worm disease is an ancient affliction that has been found in Egyptian mummies.
A person might not know they were infested until a year had passed. At that point, the female decides she is ready to leave, and moves near the skin, creating blisters that rupture after a few days. Soaking the wound in cool water brings some relief from the burning pain—which is exactly what the worm is counting on. As soon as her victim drops an arm or leg in the water, she emerges slightly from the skin and releases millions of larvae, thus perpetuating the life cycle. Worst of all, she takes her time exiting the body, and any attempts to grab her or cut her into pieces will only result in the worm retreating back into her hole and emerging later somewhere else.
Treating people is not easy, as there is no medication that works against the worm. Instead, people have to wait for the parasite to show herself, then gingerly wrap a piece of gauze or tie a stick around the bit that emerges from the skin so that she cannot retreat inside again. Every day, inch by inch, the visible part of the worm is wrapped up until, after about a month, she has slithered out entirely.
The fight against Guinea worm disease is remarkable in that it has been so effective. Twenty years ago there were 3.5 million cases in twenty countries throughout Africa and Asia, and now only 3,500 cases remain, primarily in Ghana, the Sudan, and Ethiopia. To stop the disease, people learned to filter their water through mesh cloths or straws that they could carry with them.
If current efforts to fight the parasite continue, Guinea worm disease will become the first parasitic disease to be eliminated completely and the first human disease of any kind to be wiped out without any assistance from vaccines or medications.
DEADLY
Oriental Rat Flea
XENOPSYLLA CHEOPIS
On an autumn day in 1907, two boys in San Francisco found a dead rat in the cellar. Inspired by their father, an undertaker, they decided to find a coffin for the rat and give it a proper funeral. This occupied them for one happy afternoon—perhaps the last such carefree day of their youth. When they ran home for dinner that night, they brought along a souvenir of their adventures: bloodthirsty, plague-infested fleas, starved for a meal after their host had died.
The rat flea would prefer to leave humans, cats, dogs, and chickens alone, but when rat populations experience a massive die-off—as they do during epidemics of the plague—the fleas have no choice but to turn to other warm-blooded creatures for their food. This is exactly what happened to those two unfortunate boys. Within a month the plague had claimed their parents but spared the boys, leaving them orphans.
SIZE:
Up to 4 mm
FAMILY:
Pulicidae
HABITAT:
Found near rats, their
primary food source
DISTRIBUTION:
Worldwide, particularly tropical and subtropical climates, but some temperate zones as well
This particular rat had died during an outbreak of the Black Death that began just after the turn of the century when a steamer called the Australia left Honolulu and passed through the Golden Gate with its load of passengers, mail, and plague-ridden rats. The rats made their way through the city, which was, at that time, not a particularly clean place: garbage piled up, and makeshift sewers allowed germs and rodents to proliferate. The rats felt right at home. Soon, a few people in Chinatown exhibited the dreaded symptoms: severe fever and chills, headaches and body pain, and telltale red lumps the size of boiled eggs in the armpits and groins. Before long, hemorrhages would give way to enormous black bruises, and death would not be far behind.
The flea’s role in this dreaded disease had been discovered in the late 1800s, but the exact mechanism was still a mystery. It was not until 1914 that scientists realized that the gut of the flea held clues as to how it managed to spread the plague so swiftly and efficiently. What they discovered was a remarkable phenomenon called blocking, in which the plague bacteria, Yersinia pestis, builds up in the gut of a flea to such an extent that the flea can barely swallow. Instead it is only able to draw the host’s blood into the esophagus, where it mingles with live plague bacteria. Unable to swallow because it is so full of plague itself, it regurgitates the blood and the bacteria back into the host’s bloodstream. Flea vomit is the true culprit in a plague epidemic.
But that’s not all: the fleas are so hungry because of their inability to digest a blood meal that they feed voraciously, moving from host to host in a desperate attempt to fill their bellies. Ultimately the fleas die of starvation and exhaustion, if the plague itself doesn’t kill them first.
The Oriental rat flea is just one of over eighty species of fleas that transmit the plague. The disease would have killed many more in San Francisco during the so-called Barbary Plague except for one lucky fact: Oriental rat fleas were in the minority during this outbreak. The species most often found during the San Francisco plague were less prone to blocking and less likely to regurgitate plague bacteria.
Within a month the plague had claimed their parents, but spared the boys, leaving them orphans.
The plague appears to have evolved from a more benign gastrointestinal bug about twenty thousand years ago, and it has run its destructive course through human civilization several times, killing more people than every war combined. An African and European pandemic in the sixth century known as Justinian’s Plague killed about forty million people, which represented about a fifth of the world’s population at that time. When it reappeared in Europe in the Middle Ages it was called the Black Death. For two centuries it ravaged Europe, killing another one-third to one-half of Europe’s population.
Doctors at the time believed that the plague circulated in the air. They ordered patients to keep the windows closed and refrain from bathing, which they believed would expose the skin to the sickening air. Keeping the windows closed wouldn’t stop the plague, but it might have stopped the smell. The stench of the dead and the dying must have been overpowering: in large cities like London there was no choice but to pile bodies in thinly covered mass graves. The rat population thrived in such a horrific mess. Ironically, cats were believed to be consorts of witches in those days, so they were killed. Persecution of cats during the Middle Ages nearly eliminated populations of the rat’s natural predator, just when Europeans could have used the cats’ hunting skills the most.
The plague then moved from China to India to the United States in the early twentieth century. Today, cases of plague still occur from time to time in the American Southwest, but modern antibiotics can usually treat a case that is caught early.
Meet the Relatives The cat flea, Ctenocephalides felis, is a relative, as is the dog flea Ctenocephalides canis—but in the United States, it is primarily the cat flea that preys on both cats and dogs. They are known to transmit tapeworms.
/> Flea vomit is the true culprit in a plague epidemic.
PAINFUL
Paederus Beetle
PAEDERUS SP.
Heavy El Niño rains brought more than floods to Nairobi in 1998: the wet weather created an explosion of Paederus beetles, also called Nairobi flies for their long association with the region. The beetles creep into schools and homes, attracted to the lights. They don’t bite and they don’t sting, so their presence would only be a minor irritant, if not for the fact that when the lights go out, the bugs tend to let go of the lamps and land on whoever might be sitting, or sleeping, below them. The natural tendency is to swat at the bug when it lands, but crushing this beetle releases a surprisingly toxic poison called pederin.
SIZE:
6–7 mm
FAMILY:
Staphylinidae
HABITAT:
Damp environments, including woods, meadows, and aquatic areas
DISTRIBUTION:
Found almost worldwide, particularly in India, Southeast Asia, China, Japan, the Middle East, Europe, Africa, and Australia
Nothing much happens when the poison first hits the skin. But the next day a rash develops, and a few days after that blisters appear. It takes a couple of weeks for the raw, exposed skin to begin to heal, and during that time people may develop infections if they don’t keep the wounds clean. A single beetle can raise a welt the size of a quarter on the skin. A drop of its poison, rubbed into the eye, brings on excruciating pain and temporary blindness, a condition called “Nairobi eye.” The problem in Kenya grew so severe that the ministry of health issued warnings urging citizens to keep lights turned off at night, sleep under mosquito nets, and get in the habit of blowing the insects off their skin rather than swatting them. Health officials call this strategy “brush, don’t crush.”