McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 1 3  Anthelmintic agents

Whipworm infections Whipworms are transmitted when eggs found in the soil are ingested. Whipworms attach to the wall of the colon. In large numbers, they cause colic and bloody diarrhoea. In severe cases, whipworm infestation may result in prolapse of the intestinal wall and anaemia related to blood loss. Threadworm infestation Threadworms can cause more damage to humans than most of the other helminths. Threadworms are trans- mitted as larvae found in the soil and inadvertently ingested. The larvae mature into worms, and, after burrowing into the wall of the small intestine, female worms lay eggs. These eggs hatch into larvae that invade many body tissues, including the lungs, liver and heart. In very severe cases, death may occur from pneumonia or from lung or liver abscesses that result from larval invasion. Ascaris Worldwide, Ascaris infection is the most prevalent hel- minthic infection. It may occur wherever sanitation is poor. Eggs in the soil are ingested with vegetables or other improperly washed foods. Many individuals are unaware that they have this infestation unless they see a worm in their stool. However, others become quite ill. Initially, the individual ingests fertilised roundworm eggs, which hatch in the small intestine and then make their way to the lungs, where they may cause cough, fever and other signs of a pulmonary infiltrate. The larvae then migrate back to the intestine, where they grow to adult size (i.e. about as long and as big around as an earthworm), causing abdominal distension and pain. In the most severe cases, intestinal obstruction by masses of worms can occur. Hookworm infections Hookworm eggs are found in the soil, where they hatch into a larva that moults and becomes infective to humans. The larvae penetrate the skin and then enter the blood and within about a week reach the intestine. Hookworms attach to the small intestine of infected individuals. The worms suck blood from the walls of the intestine, damaging the intestinal wall and leading to severe anaemia with lethargy, weakness and fatigue. Malabsorption problems may occur as the small intesti- nal mucosa is altered. Treatment for anaemia and fluid and electrolyte disturbances is an important part of the therapy for this infection. Infections caused by platyhelminths The platyhelminths (flatworms) include the cestodes (tapeworms) that live in the human intestine and the flukes (schistosomes) that live in the intestine and that

also invade other tissues as part of their life cycle. Because schistosomes invade tissues, they are dis- cussed in the following section on tissue-invading worm infections. Cestodes Cestodes are segmented flatworms with a head, or scolex, and a variable number of segments that grow from the head. Cestodes enter the body as larvae that are found in undercooked meat or fish; they sometimes form worms that are several metres long. Persons with a tapeworm may experience some abdominal discomfort and distension, as well as weight loss because the worm eats ingested nutrients. Many infected people require a great deal of psychological support when they excrete parts of the tapeworm or when the worm occasionally exits through the mouth or nose. TISSUE-INVADING WORM INFECTIONS Some of the worms that invade the body exist outside of the intestinal tract and can seriously damage the tissues they invade. Because of their location within healthy tissue, they can also be more difficult to treat. Trichinosis Trichinosis is the disease caused by ingestion of the encysted larvae of the roundworm, Trichinella spiralis , in undercooked pork. Once ingested, the larvae are deposited in the intestinal mucosa, pass into the blood- stream and are carried throughout the body. They can penetrate skeletal muscle and can cause an inflamma- tory reaction in cardiac muscle and in the brain. Fatal pneumonia, heart failure and encephalitis may occur. The best treatment for trichinosis is prevention. Because the larvae are ingested by humans in under- cooked pork, freezing pork meat, monitoring the food eaten by pigs and instructing individuals about properly cooking pork can be most beneficial. Filariasis Filariasis refers to infection of the blood and tissues of healthy individuals by worm embryos, which enter the body via insect bites. These thread-like embryos, or filariae, can overwhelm the lymphatic system and cause massive inflammatory reactions. This may lead to severe swelling of the hands, feet, legs, arms, scrotum or breast—a condition called elephantiasis. Schistosomiasis Schistosomiasis (see Figure 13.1) is a platyhelmin- thic infection by a fluke that is carried by a snail. This disease is a common problem in parts of Africa, Asia