What Are Parasitic Diseases?
A parasite is any organism that lives on or inside another organism (the host) and benefits at the host’s expense. They can enter the body through the mouth to reside in the intestines or even burrow through the intestinal wall to infect other organs. Parasites can bore directly through the skin or can enter via the bites of insects. Some can enter the soles of the feet while barefoot or through skin from water that has parasites.
In developed areas, parasites occur in immigrants, returning travelers, and those who have immunosuppression.
Parasites can cause signs and symptoms ranging from skin irritations to serious life-threatening illnesses, including sepsis, blood disorders, lung and gastrointestinal illness, and central nervous system infections.
Categories of Parasites Include
- Worms (helminths)
Protozoans are microscopic one-celled organisms which can cause a serious infection with just one organism. Route of transmission is fecal-oral (contaminated food or person-to-person contact). They can pass from person to person via mosquitoes or sand flies.
- Ameba: Such as Entamoeba
- Flagellates: Such as Giardia and Leishmania
- Ciliates: Such as Balantidium
- Sporozoa: Such as Plasmodium
Helminths are large organisms visible to the naked eye as adults.
- Flatworms: Tapeworms and flukes can live in the gastrointestinal tract
- Thorny-headed worms: Live in the gastrointestinal tract
- Roundworms (nematodes) such as segmented worms, leeches: They can live in the gastrointestinal tract, blood, lymphatic or subcutaneous tissues
Ectoparasites are typically blood-sucking parasites.
How Are Parasitic Diseases Diagnosed?
For diagnosis and subsequent treatment of parasitic infections, a thorough history for onset, signs and symptoms, travel, etc., is explored in addition to a careful physical exam that can identify rashes, bite marks, entrance sites, or eruptions.
Diagnosis of parasitic infections is initially prompted by signs and symptoms:
Gastrointestinal: Weight loss, anorexia, nausea/vomiting, abdominal pain and bloating, rectal itching, and bloody or unremitting diarrhea with dehydration.
Stool exam for eggs, larva, and actual organisms or worms to identify helminths or protozoa, including Giardia, Cryptosporidium, E. histolytica, and Blastocystis hominis.
Pulmonary: pneumonitis, persistent cough, or breathing difficulties, such as from Toxoplasmosis.
Serologic tests for the IgG, IgM, IgA, and IgE immunoglobulins that test for Toxoplasma gondii exposure and infection. Bronchoscopy may be necessary.
Dermatological: skin rashes, eruptions, itching, and swelling of superficial lymph nodes, as well as secondary bacterial infections of bites.
Neurological: cognitive impairments due to central nervous system parasites, such as Angiostrongylus cantonensis, Gnathostomiasis, Baylisascariasis, toxocariasis, trichinellosis, and others.
Blood tests can identify anemia or eosinophilia (a type of white blood cell elevation often occurring in parasitic infections). Examination of red blood cells can identify malaria and other blood disorders.
Management and treatment for a parasitic infection depends on the type of parasite, once identified. Some require no treatment at all, being self-limited in immunocompetent individuals.
- Balantidium coli (balantidiasis): volume and electrolyte replacement and antibiotics (tetracycline, metronidazole, or iodoquinol).
- Dientamoeba fragilis: Aggressive fluid and electrolyte replacement and an antibiotic such as albendazole or metronidazole.
- Giardia lamblia (giardiasis): Aggressive fluid and electrolyte replacement plus administration of an antimicrobial agent such as albendazole or metronidazole.
- Entamoeba histolytica (amebiasis): If asymptomatic, iodoquinol or paromomycin; if symptomatic, metronidazole or tinidazole, followed by administration of iodoquinol or paromomycin. Extraintestinal abscesses, if present, are drained and metronidazole or tinidazole is added.
- C. hominis or C. parvum (cryptosporidiosis): Since the diarrhea is self-limited (4 weeks), symptomatic treatment via fluids, nutritional support, and antispasmodic (anti-diarrheal) agents. For children or the immunosuppressed, nitazoxanide will shorten the duration of diarrhea.
Treatment for most helminth infections (pinworms, hookworms, trematodes, etc.) is via anthelmintic medications, such as praziquantel, niclosamide, or albendazole.
- Pinworms (ascariasis): A single dose of albendazole, mebendazole, or ivermectin.
- Hookworms (Ancylostoma or Necator): A single dose of albendazole or mebendazole, or one dose daily of pyrantel pamoate for 3 days.
- Flukes (trematodes): Three doses of praziquantel over 24 hours.
Prevention of Parasitic Diseases
Prevention of parasitic infections is simply by placing barriers between the parasites and the potential hosts, which is by avoiding exposure.
Protozoan (amebiasis, flagellates, ciliates, sporozoa, etc.) and helminth (intestinal worms) are most often encountered by fecal-oral routes, contaminated foods, or person-person contact. Prudent adherence to the following will limit exposure and infection:
- Hand-washing, using soap and hot water before and after using the toilet, after changing diapers, and before preparing or eating foods. Be wary of establishments in which you suspect hand-washing for employees is not strictly enforced.
- Avoid frequent hand-shaking.
- Cooking fruits and vegetables with boiled or purified water before eating.
- Wash, peel, or cook all raw fruits and vegetables.
- Thoroughly cook meat.
- Cook at temperatures of at least 145°F (62.8°C) for whole cuts of beef and pork, and 160°F (71°C) for ground meat and poultry.
- Avoid raw fish and meat.
- Avoid soil or water contact which may be contaminated with human or animal feces.
- Avoid walking barefoot, playing in sandboxes, swimming with open sores or swallowing swimming water in natural settings such as streams, ponds, or small lakes.