A few weeks ago, I was taking care of a patient in the intensive care unit who was using a ventilator when the resident on duty informed me that there was something in the breathing tube. Looking closely, there was a wriggling, flesh colored worm which we promptly fished out and sent to the laboratory. The laboratory identified the worm as Ascaris lumbricoides, a common roundworm that infects humans.

Worm or helminthic infections affect 25 percent of the world's population, mostly in subtropical and tropical areas in resource-limited settings. The Philippines has a significant worm burden disproportionately affecting children in slum areas and rural communities. Worms can cause malnutrition, stunting, and even death with severe infections. Worm infestations, especially those that are transmitted through eggs in the soil, are usually a marker of poor sanitation and hygiene, although even affluent communities can get infected if there are infectious carriers.

The most common worm infection in the world and in the Philippines is ascariasis, which is what my patient had. The worm in his breathing tube was an unusual manifestation that can occur in very sick patients when the worm leaves its usual spot in the large intestine and wanders into other parts of the body. Ascaris is a common worm in childhood and will occasionally show up in the stool. Poor sanitation and the use of human feces as fertilizer (night soil) introduce eggs into the soil where they become embryonated and infectious. It is then transmitted when people inadvertently ingest the worm egg on their dirty hands or in contaminated food.

Ascaris infection is usually asymptomatic, but chronic infections can rob children of nutrients and cause chronic diarrhea, stunting, and malnutrition. This has been shown to affect intelligence and can limit a person's economic prospects later in life. Heavy infestations can cause the worms to get tangled up into a ball, blocking the intestines. This can become a surgical emergency, and I have seen quite a few cases where the surgeon had to open up the abdomen, locate the ball of worms, cut into the intestine, and manually extract the worms one at a time. Ascaris can also go up into the small intestine, enter the common bile duct, and go up toward the liver and gallbladder. This can cause a severe infection known as ascending cholangitis, which can be fatal. An ascaris in the bile duct can also cause a backflow of enzymes into the pancreas (a large intra-abdominal gland that makes enzymes and insulin), causing pancreatitis.

Another common worm is whipworm, or Trichuris trichiura. Whipworm infection does not usually produce symptoms, but just like ascaris, it can cause diarrhea, stunting, and malnutrition in children. It is also transmitted by ingesting eggs that are found in contaminated soil. One consequence of heavy whipworm infestation is rectal prolapse, or the rectum turning inside out and coming out through the anus. This is disfiguring, and the prolapsed rectum can get infected and cause the patient to become septic.

Hookworm is another common worm that can be acquired when children walk barefoot on soil where the larvae have hatched from eggs. Unlike Ascaris or whipworm, where eggs are swallowed in order to get infected, hookworm larvae penetrate the skin, go through the bloodstream, and eventually end up in the large intestine, where they use hooks on their heads (hence the name) to attach to the intestinal wall and absorb nutrients and blood that leaks from the attachment site. This can cause significant anemia, especially in heavy infestations, and can also cause stunting and malnutrition.

Tapeworm can be acquired through ingestion of raw or inadequately cooked pork, beef, or fish containing the larva in its muscle tissue. These larvae eventually make their way into the intestines, where they absorb nutrients and can also cause malnutrition and stunting. Tapeworms can become very long, and egg-containing tapeworm segments called proglottids sometimes break off and show up in the stool as short wormlike segments that wriggle around. Pork tapeworm (Taenia solium) is particularly dangerous because, aside from being acquired from eating raw pork, the ingestion of eggs from contaminated soil can lead to pork tapeworm larvae in the brain. This condition, called neurocysticercosis, is the most common cause of seizures in developing countries. The worm larvae in the brain can block the flow of cerebrospinal fluid, causing increased brain pressure, strokes, and death.

One worm that is endemic to the Philippines, which has almost been eliminated in other countries, is Schistosoma japonicum. Schistosomiasis, or schisto for short, is acquired from wading in contaminated fresh water, such as that found in rice fields. Schisto eggs from stool hatch when they come in contact with fresh water and become larvae, which then infect a specific snail known as Oncomelania. Other schistosoma species (S. mansoni, S. haematobium, S. mekongi, S. intercalatum) use different snail species and have different target organs. Infected snails release a juvenile, free-swimming form of schistosoma called cercaria, which are able to penetrate human skin. Once in the bloodstream, the worms make their way to the blood vessels supplying specific organs – for S. japonicum, it happens to be the vessels leading up to the liver. While many worms are hermaphroditic (have both male and female reproductive parts in a single worm), S. japonicum has both male and female worms, and these intertwine mate for life near the liver and release millions of eggs in their lifetime. The eggs lodge in the liver, spleen, and intestines and cause cirrhosis or scarring of the liver. Sometimes the eggs end up in the lungs, where they cause shortness of breath. Occasionally, the eggs end up in the brain and cause seizures. Schistosomiasis in children can be deadly, and those who survive can have chronic health problems.

There are many other worms found in the Philippines, and these can cause significant suffering and malnutrition, especially among children. These include the filarial worms Wucheria and Brugia, pinworm (Enterobius), Capillaria, Strongyloides, as well as intestinal, liver, and lung flukes. Treatment of worms is usually straightforward with a single dose of albendazole or mebendazole working well for most roundworms, while praziquantel is needed for schistosomiasis, flukes, and tapeworms. Some complicated conditions, like neurocysticercosis, may require specialized care in the hospital. Some worms are so prevalent that elimination programs and mass drug administration are needed to control their spread. Worm infections are ultimately preventable if communities practice good hygiene and sanitation. These should be a priority for local government, especially since they impact children disproportionately.