When I was six years old, parasites took over my body. I lay in bed for three months, immobile, grey, skinny, unwilling to eat and, worst of all, barely able to breathe. Doctors diagnosed me with bronchitis, and treated me with antibiotics. I got marginally better, and when they took me off the antibiotics I got a whole lot worse. They put me on and took me off antibiotics twice more, and by the end I was so thin and wheezy my mother thought I was dying. She took me to another health practitioner for a second opinion. The woman took one look at me, knew I was riddled with parasites, and gave me an anti-parasitic plant extract. A week later I burst with parasites from both ends, screaming with terror-I could breathe again.
The worms I was infected with are called pin worms, and they are estimated to infect roughly 400 million people worldwide (10 per cent of all humans), primarily children. They normally live in the colon, but in my case it seems that they had colonized my lungs (or possibly my stomach, eliciting an allergic reaction), making it near impossible for me to breathe. Whatever the cause, it was absolutely terrifying for my family and I.
My experience was by no means a common one-Dr. Jay Keystone, parasitologist and specialist in tropical diseases at Toronto General Hospital said he has never seen pin worms infect somebody like that. Severe parasitic infections are relatively uncommon in cold, northern, developed countries.
Worldwide however, “Human parasitic infections, worms and protozoa, are one of the major causes of human morbidity and mortality,” said Dr. Keystone. Nearly one half of the world’s population is infected with a parasitic worm. The single-celled parasite plasmodium, the source of malaria, causes between 300 million and 500 million acute illnesses a year, and kills one African child every 30 seconds. Blood flukes infect about 200 million people worldwide; a million people this year will die from them.
But while the statistics (and photographs) can be shocking, Dr. Keystone stresses that most parasitic infections are relatively harmless. “Many people develop a degree of immunity to their parasites, so they can quite happily walk around with no symptoms at all. People freak out when I tell them they have parasites, and I simply tell them, ‘Look, humans would not be humans if we did not have parasites.’ We all have them. From birth we get infected with fungi, viruses, bacteria, worms, all sorts of parasites.” A parasite is defined as any creature that spends part of its life cycle living off the energy of another creature. There are in fact 342 species that parasitize humans. “So I don’t treat a parasite just because it’s a parasite, it has to be potentially harmful. In most cases the psychological impact of the parasite is much greater than the pathological impact.”
Although severe parasitic infections are relatively uncommon in Canada, Dr. Keystone sees worms crawling out of people’s skin, squirming in their bowels and feeding on their blood pretty much every day at Toronto General. Most of the cases he sees are in travelers and in new Canadians, recent arrivals from the tropics, but other sectors of Toronto’s population are highly infested. At least 20 per cent of children in day care have some kind of parasite, mostly pin worms and single celled organisms. Dr. Keystone found that as much as 70 per cent of the male gay community is infected with parasites due to direct oral-anal contact. So while you can’t live your life in fear of parasitic infections, be aware that these creatures are around and would have no qualms with taking up residency in your warm, cozy colon.
In the interest of educating other potential parasitic hosts, we present a handful of the world’s most famous parasites.
HOOKWORMS
The hookworms Ancylostoma duodenale and Necator americanus affect about 800 million people worldwide. They aren’t as big as roundworms, averaging about only a centimeter in length. They get their name from the characteristic shape of their mouths. Hookworms attach to the walls of the small intestine where they feed on their host’s blood, which can cause severe aenemia (especially in children). Eggs are passed in the feces, and a new host is infected when the eggs penetrate the skin. Larva of this parasite can also get into you through your skin, where they can crawl around just beneath the surface for months, causing a condition known as “creeping eruption.” Be careful not to let your dog lick your face-hookworms (and many other worms) are commonly spread to humans by their pets.
ROUNDWORMS
Ascaris lumbricoides is the most common parasitic worm found in humans, infecting about 25 per cent of the world’s population, one and a half billion people. Adults live in the small intestine and can grow up to 18 inches long. This parasite is spread when eggs are passed in the feces and then spread by unsanitary conditions. Eggs are ingested and then flow down to the small intestine where they hatch. The larva then burst through the intestinal walls, travel through the circulatory system, penetrate the lungs, crawl up through the air passages, down through the esophagus, and then end up back in the small intestine where they live out the rest of their lives. Nobody knows why this worm travels all the way through the body only to end up right back where it started, but larval migration can be fatal if they rupture blood vessels in the lungs. The worms can also kill you if they continue to move around once they reach adulthood-it is not unknown for ascarid worms to clog up the colon, block bile ducts, or rupture the intestine and fall into the body cavity.
PIN WORMS
Pin worms, Enterobius vermicularis, are estimated to infect 400 million people, roughly 10 per cent of all humans. Unlike most worms, these are found primarily in Europe and North America, mostly in children. Measuring about a centimeter long, colonies of adults live in the colon. Females emerge from this lair at nighttime and crawl outside to the perianal region, where they lay their eggs (up to 10,000 at a time). If you want to see if your kid has pin worms, simply apply scotch tape to their bum while they sleep, rip it off, and look for eggs on the sticky side. Be careful though-pin worms are incredibly contagious, and they are spread when people breathe in the eggs. If you shake out a infected child’s sheets on laundry day, chances are the entire house will get the worms as well. They are relatively harmless though, usually just resulting in mild stomach upset, irritability and insomnia in small children.
WHIPWORMS
More than a billion people worldwide are infected with the whipworm Trichuris trichiura. This species gets its name from the shape of their heads, which they embed in the lining of the large intestine where they can live for several years. Eggs are passed in the feces, whereupon they are passed to other hosts if the eggs are ingested. Most infections do not cause any serious symptoms, but over years one person can become infected repeatedly and develop a large worm burden, resulting in anemia, diarrhea and dysentery. Heavy worm burdens in children can result in mental and physical retardation.
GUINEA WORM
Dracunculus medinensis is also known as the “fiery serpent,” and was featured in the writings of Greek, Roman, and Arabian scholars. Adult female worms are only two millimeters in diameter but can grow to a meter in length. They live just under the skin for about a year, usually in the legs and feet. When pregnant females release their eggs into the host, an intense and painful allergic reaction results, hence the name “fiery serpent.” The skin eventually breaks open and victims typically rush to wash the ulcer, releasing the eggs into rivers and streams where they can continue their life cycle. Eggs infect small crustaceans called copepods-humans contract the worm when these copepods are swallowed in contaminated water. What happens to the female that just released those eggs, you ask? She can only be removed by tying the exposed end of the worm to a stick, and then twirling the parasite out like a string of spaghetti. Even worse, one person could get Guinea worm over and over again if local drinking water is not cleansed of the parasite. Fortunately, the WHO estimates that this worm will be eradicated from human populations within five to ten years.
EYE WORM
Loa loa can be found in the tissue just beneath the skin in any part of the human body, including just below the surface of the eye, hence the common name “eye worm.” Adult worms measure up to about seven centimeters in length, and infect some 13 million people worldwide. Although they don’t tend to cause serious health problems this parasite can cause hosts quite a shock when they notice it crawling beneath their skin or across their eyeball. This worm is generally found only in equatorial Africa.
TAPEWORMS
Probably the most famous of parasites, tapeworms can indeed reach spectacular sizes in human hosts. Diphyllobothrium latum, the broadfish tapeworm, can grow up to 30 feet in length; this parasite is especially common in Scandinavia and the Great Lakes region, as humans become infected by eating raw or undercooked fish (watch out for cheap sushi). Humans can also get the beef tapeworm Taenia saginata and the pork tapeworm T. solium by eathing contaminated meat. Together these three species infect about 90 million people worldwide. Tapeworms do not normally cause severe health problems. The animals are segmented, and sometimes individual subunits of the worms, called proglottids, can give the owner quite a shock. “I’ve actually seen segments crawl out of somebody’s butt, into their underwear and fall on the floor,” said Dr. Keystone, who sees a tapeworm every few months here in Toronto. Tapeworms can sometimes cause painful and even fatal infections during the juvenile stage of their life cycle. Immature tapeworms can penetrate the intestine and travel to virtually any area of the body. If they settle in the muscle tissue they may cause little or no harm, short of terrifying hosts and doctors who commonly misdiagnose such lumps as tumours. If the juvenile worms settle somewhere more delicate however, like the eye or spinal cord, they can cause blindness, paralysis, and even death.
RIVER BLINDNESS
The parasite Onchocerca volvulus is the cause of the tropical disease “river blindness.” Adults grow up to 50 centimeters long and live just beneath the host’s skin. The body attempts to control the parasite by enclosing it in a fibrous capsule. Adults cannot move, but females can release embryos, or microfilariae, into the rest of the rest of the body. Often these embryos end up in the eye, where they die, accumulate, and result in blindness. The disease is spread when mosquitos feed on an infected human and transfer the embryos to another host. In areas where the mosquitos are rampant as much as 40 per cent of the adult population is blind as a result of this disease.
BLOOD FLUKES
Approximately 200 million people worldwide, mainly in Africa, southeast Asia, the Caribbean and South America, are infected with the blood flukes Schistosoma mansoni, S. haematobium, and S. japonicum, resulting in an estimated one million deaths every year. The flukes average about a centimeter in length, live in the veins of the abdomen, and can live for up to 30 years in one host. Eggs are passed in the urine or feces, infect aquatic snails, hatch as larvae, and then burrow into the skin of humans when they bathe in infected water. The movement of eggs through the human body can result in severe tissue damage, noticeable as blood in the urine. If the eggs are not passed in feces or urine they end up in the liver, where the body attempts to deal with them by encapsulating then in a fibrous ball. The damage to the liver, intestine and bladder can eventually result in death.
ELEPHANTIASIS
This crippling disease is caused by the worms Wuchereria bancrofti and Brugia malayi, which are spread like malaria via mosquitoes. About 107 million people are infected. Adult worms live in human lymph nodes where they can block the lymph nodes and ducts, causing intense and debilitating swelling. The worms particularly enjoy living in the lymph nodes of the lower abdominal cavity, legs, and genitals. Although not pictured here for obvious reasons, one can find a multitude of images of men with severely deformed testicles on parasitological web sites. Note that elephantiasis is not “elephant man disease.”
HYATID DISEASE
The tiny tapeworm Echinococcus granulosus measures only six millimeters in length at the most, yet can cause cysts in human hosts the size of basketballs. The worm normally lives in the small intestine of canines, but when eggs are passed in a dog’s feces humans can inhale the eggs and contract the parasite. The eggs hatch in the small intestine, then break through the gut wall, travel through the circulatory system, and then find a home in some soft, comfortable tissue, usually the liver. The larva then produce single celled offspring, called protoscolices, that result in the growth of a cyst; a large cyst can contain tens of thousands of protoscolices. Cysts can be fatal if they grow in a vital tissue like the lungs, liver or brain. About three million people worldwide are infected, including a number being treated at Toronto General.
