Treatment of parasitic diseases

Definition

Parasites are organisms that depend on hosts, including humans, for their food source and survival. Treatment for parasitic disease involves drugs and other therapies to manage the three types of parasites: protozoan, helminthic, and ectoparasitic.

Protozoa

Protozoa (living, single-cell, parasitic, eukaryotic organisms) may or may not produce disease in a host. Some of these diseases are asymptomatic. However, some protozoa can prove uncomfortable and even deadly for the host. Common protozoan diseases include malaria, amebiasis, toxoplasmosis, and trichomoniasis.

Malaria is a global disease that kills more than one million people each year. Spread by the female Anopheles mosquito, malaria has a triad of antimalarial treatment options. The first option is chemoprophylaxis. Using the principle of prevention, persons who travel to highly infested, at-risk areas are prescribed medications to decrease the chance of contracting the disease. Chemoprophylaxis medications are given for one week before the person travels, during the trip, and for one to four weeks after return home. Chloroquine is most commonly prescribed for chemoprophylaxis. However, if the traveler cannot take this drug for some reason, other drugs, such as atovaquone-proguanil, primaquine, doxycycline, and mefloquine (for use in pregnant women), may be combined for preventive therapy.

The second treatment option for malaria is for an acute attack. The drug of choice is chloroquine, which works by interrupting the erthocyctic stage of the infection and by limiting the life cycle of malaria protozoa. If the infected person is resistant to chloroquine, then he or she can use primiquine, quine sulfate, mefloquine, or atovaquone-proguanil. Sometimes, combination antibiotics are prescribed, including doxycycline, clindamycine, and tetracycline (not used in pregnant women). Certain side effects occur, so caution should be observed with the use of these antimalarial drugs.

Amebiasis is a protozoan disease that results from ingesting Entamoeba histolytica. Amebiasis is usually treated with metronidazole and an opioid to control diarrhea. Antibiotics such as chloroquine and tetracycline are sometimes used with paromomycin and iodoquinol for intestinal infections.

Toxoplasmosis, caused by Toxoplasma gondii, transfers to humans through feces (such as feces in the litter boxes of cats), soil, or contaminated vegetables. Treatment includes four or five weeks of pyrimethamine in combination with sulfadiazine.

Trichomoniasis, commonly known as trich, is a sexually transmitted disease caused by T. vaginalis. A single dose of metronidazole (Flagyl) is prescribed to both the infected person and his or her sexual partner or partners.

Helminths

Helminths (multicelled parasitic worms) can often be seen with the naked eye. They usually enter humans through the skin or through the digestive tract and attach to the intestines. The most common helminths are roundworms (nematodes), tapeworms (cestodes), and flukes (trematodes). Medications used to treat helminth disease are known as anthelmintics.

The most common roundworm, Ascaris lumbricoides, causes ascariasis in Latin America and Asia, usually in children. To treat ascariasis, oral mebendazole (Vermox) is prescribed for three days. If the infected person is unable to take mebendazole, they can be treated with albendazole or pyrantel pamoate.

A common helminth found in the United States is the pinworm, a roundworm caused by Enterobius vermicularis. Treatment for this helminth, a single dose of mebendazole, albendazole, or pyrantel, usually provides relief, but the dose may be repeated if needed. Pinworms can cause anal itching, so antipruritic creams may be prescribed for local irritation. Hookworms are often acquired by walking barefoot on contaminated dirt. Treatment for hookworms includes albendazole and mebendazole, given for three days.

Tapeworms are usually contracted by humans by eating raw or undercooked meat contaminated with tapeworm cysts or larvae. Tapeworms can grow quite large, some as long as two to six feet (seven to twenty-five meters). Tapeworm infection is treated with a single dose of praziquantel with a laxative, given to excrete the worm and any eggs.

Flukes are flat worms that may infect the intestine. Some forty to fifty million people worldwide are infected with one of about seventy varieties of flukes. Praziquantel (Biltricide) is the treatment of choice.

Ectoparasites

Ectoparasites attach themselves to the skin or to the hair follicles of the host. Ticks, lice, leeches, bedbugs, and mites are all ectoparasites. Treatment is based on the type of ectoparasite involved. Ticks must be carefully removed from the host's skin, and the area must be treated with alcohol. Head lice can be removed by using a shampoo medication, such as Nix, that contains permethrin. After shampooing, the nits, or lice eggs, should be removed using a small-tooth comb. A second shampoo treatment is usually recommended for use seven days after the first shampoo treatment.

Impact

Parasitic disease causes devastating illness and even death. Protozoan diseases, such as malaria, kill more than one million people annually, primarily in Africa. Globally, some fifty million people each year are afflicted with amebiasis alone, resulting in forty thousand or more deaths. Trichomoniasis infects about 15 percent of women in the United States, with some 2.5 to 3 million cases seen in clinics treating sexually transmitted diseases. Each year, an estimated four hundred to four thousand cases of congenital toxoplasmosis are reported in the United States, resulting in mental retardation, blindness, epilepsy, and, occasionally, stillbirth and abortion. Helminths infect more than two billion people each year worldwide. Ascariasis, which is found in Latin America and Asia, affects some four million people and causes about sixty thousand deaths annually, primarily in children. In the United States, about forty million people, mostly children, have pinworms, while hookworms infect almost one billion people each year.

Parasitic diseases are expensive to diagnose and treat, and they lead to reduced economic growth. Infected workers experience lost productivity and increased use of limited healthcare resources. Prevention and treatment of parasitic disease is a primary goal for the improvement of global health.

Bibliography

Adams, Michael P., and Robert W. Koch. “Pharmacotherapy of Protozoan and Helminthic Infections.” In Pharmacology: Connections to Nursing Practice. Upper Saddle River, NJ: Pearson Prentice Hall, 2010.

"Clinical Overview of Parasitic Diseases." Centers for Disease Control and Prevention (CDC), 28 Oct. 2024, www.cdc.gov/parasites/hcp/clinical-overview/index.html. Accessed 4 Feb. 2025.

"Mass Drug Administration for Control of Parasitic Infections." UpToDate, 31 Aug. 2023, www.uptodate.com/contents/mass-drug-administration-for-control-of-parasitic-infections. Accessed 4 Feb. 2025.

Molyneux, David, ed. Control of Human Parasitic Disease. Vol. 61 in Advances in Parasitology, edited by J. R. Baker, R. Muller, and D. Rollinson. London: Academic Press, 2006.