Parasitic Diseases



Parasitic Diseases 2333
Photo by: Jubal Harshaw

Parasitic diseases are illnesses caused by infestation (infection) with parasites such as protozoa (one-celled animals), worms, or insects. These diseases are widespread in Africa, southern Asia, and Central and South America, especially among children. They include malaria and schistosomiasis, the world's most common serious infectious diseases.

KEYWORDS

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Cestodes

Flukes

Food borne diseases

Infection

Infestation

Nematodes

Protozoa

Trematodes

Tropical diseases

Waterborne diseases

Tickborne diseases

Vectors

Most of the world's 6 billion people are infected with parasites, which are primitive animals that live in or on the bodies of humans, animals, or insects. Often the parasites do little damage, and people may be unaware they are infected. But in any given year, more than a billion people, many of them children, fall sick with parasitic diseases, and millions of them die.

Where Do Parasitic Illnesses Occur?

Parasites live everywhere, but they particularly thrive in warm, moist climates. So they are most common in sub-Saharan Africa, the Indian subcontinent, southeastern Asia, and Central and South America. Some nations in these areas are too poor to take measures that could prevent parasitic infections—such as building water and sewage treatment plants, controlling mosquitoes, or providing adequate medical care. At the same time, in some places, parasitic diseases make so many people weak, ill, and unable to work that they slow economic development and help keep regions impoverished.

Some parasites are found worldwide, even in cooler climates and in wealthier nations, including the United States. These include pinworms, whipworms, and such protozoa as Giardia lamblia (which causes intestinal problems), Babesia (which is spread by ticks and causes fever and chills), Trichomonas vaginalis (which infects the genital tract of men and women), and Cryptosporidium parvum (which has caused outbreaks of diarrheal illness in some cities of the United States).

The Giardia lamblia protozoan.
The Giardia lamblia protozoan.

What Are the Most Common Parasitic Diseases?

The intestinal roundworm Ascaris lumbricoides causes ascariasis, estimated to infect 1 billion people, although it often does little damage. More important in its impact is malaria, which is estimated to cause 300 million to 500 million illnesses a year and about 2 million deaths. About half of those deaths occur in children under age 5. Schistosoma blood flukes cause schistosomiasis (shis-to-so-MY-a-sis), which is estimated to cause 120 million illnesses, 20 million of them severe.

Other parasitic diseases that are estimated to cause a million or more cases of illness are filariasis, amebiasis, Chagas' disease, leishmaniasis, and African sleeping sickness (trypanosomiasis).

Ectoparasites

"Ecto-" means "outer." Ectoparasites live on the outer surface of humans. They include lice and the mites that cause scabies (SKAY-beez).

How Do Parasitic Diseases Spread?

In most cases, people get a parasitic infection by bathing in, swimming in, or drinking water that contains parasites; by eating food that has not been cooked thoroughly; or by coming into contact with untreated sewage. That commonly can happen when human waste is used to fertilize fields. It also can happen if people who handle food do not wash their hands thoroughly after a bowel movement.

Leishmaniasis (leesh-ma-NY-a-sis) occurs in tropical and some temperate areas. Protozoa (single-celled parasites) in the genus Leishmania cause the disease, which is transmitted by the bite of infected sandflies. Forms of the disease include (1) cutaneous (ku-TAY-nee-us) leishmaniasis, which causes a painless but unsightly skin ulcer that often heals on its own, leaving a depressed scar; (2) muco-cutaneous (myoo-ko-ku-TAY-nee-us) leishmaniasis, which eats away at the tissues inside the nose and mouth; and (3) kala-azar (ka-la-a-ZAR), which affects the lymph nodes, spleen, liver, and bone marrow and can be fatal. The Leishmania donovani parasite, seen here under an electron microscope, can cause the form of leishmaniasis called kala-azar. © Manfred Kage/Peter Arnold, Inc.
Leishmaniasis (leesh-ma-NY-a-sis) occurs in tropical and some temperate areas. Protozoa (single-celled parasites) in the genus Leishmania cause the disease, which is transmitted by the bite of infected sandflies. Forms of the disease include (1) cutaneous (ku-TAY-nee-us) leishmaniasis, which causes a painless but unsightly skin ulcer that often heals on its own, leaving a depressed scar; (2) muco-cutaneous (myoo-ko-ku-TAY-nee-us) leishmaniasis, which eats away at the tissues inside the nose and mouth; and (3) kala-azar (ka-la-a-ZAR), which affects the lymph nodes, spleen, liver, and bone marrow and can be fatal. The Leishmania donovani parasite, seen here under an electron microscope, can cause the form of leishmaniasis called kala-azar.
© Manfred Kage/Peter Arnold, Inc.

Many impoverished nations are undergoing rapid urbanization, meaning many people are crowded together into fast-growing cities that may lack sewage treatment facilities. Raw (untreated) sewage may be dumped into rivers whose water is also used for drinking, bathing, washing, and cooking. Parasitic diseases spread easily in such conditions.

Insects and animals spread some parasitic diseases. Mosquitoes, for instance, spread malaria. Tsetse flies spread African trypanosomiasis (tripan-o-so-MY-a-sis), also called African sleeping sickness. Domestic animals spread beef and pork tapeworms.

This young man has a skin rash on his upper arm caused by hookworm larvae. St. Bartholomews Hospital/Science Photo Library/Photo Researchers, Inc.
This young man has a skin rash on his upper arm caused by hookworm larvae.
St. Bartholomews Hospital/Science Photo Library/Photo Researchers, Inc.

What Happens When People Get Parasitic Diseases?

Symptoms

The symptoms vary widely, but many parasitic infections cause fever, fatigue, or intestinal problems such as diarrhea or bowel obstruction (blockage of the intestines).

Diagnosis

Parasitic diseases can be difficult to diagnose because many parasites do not show up on the routine blood tests that doctors perform. In addition, people with parasites are prone to get bacterial infections as well, which may fool doctors into thinking that the bacteria alone are the cause of the illness.

Special blood tests, however, sometimes help with diagnosis. In addition, parasites sometimes can be seen if samples of stool or blood are examined under a microscope.

Treatment

Although most parasites can be killed by proper medication, some cannot.

How Can Parasitic Diseases Be Prevented?

Public authorities that build sewage and water treatment systems play a major part in preventing these diseases. Controlling the insects that spread some parasitic diseases also is important. So is teaching people always to wash their hands thoroughly after using the bathroom and before handling food.

Sleeping Sickness

African trypanosomiasis (tripan-o-so-MY-a-sis) is also called African sleeping sickness. Protozoa (single-cell animals) of the genus Trypanosoma cause the disease. African trypanosomiasis is found only in Africa and is transmitted by the bite of an infected Tsetse (TZEET-ze) fly. Treatment for African trypanosomiasis involves a number of drugs administered under a doctor's care over a period of weeks. Left untreated, death eventually occurs.

See also
Ascariasis
Babesiosis
Chagas' Disease
Cyclosporiasis and Cryptosporidiosis
Elephantiasis
Lice
Malaria
Pinworm
Schistosomiasis
Toxoplasmosis

Resources

The U.S. Centers for Disease Control and Prevention (CDC) has a Division of Parasitic Diseases (DPD) that posts fact sheets about many different parasitic infections at its website.
http://www.cdc.gov/ncidod/dpd/p_diseas.htm

The U.S. Food and Drug Administration's Center for Food Safety and Applied Nutrition posts a Bad Bug Book at its website with links to many different fact sheets about parasitic protozoa and worms.
http://www.vm.cfsan.fda.gov/~mow/intro.html

The World Health Organization (WHO) posts a fact sheet about parasitic diseases at its website.
http://www.who.int/ctd/html/intest/html

User Contributions:

Jakob
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Jul 23, 2012 @ 9:21 pm
Hello, my name is Jakob and I live in Ontario. My sister is very ill and yet to be diagnosed. In October of 2011, my mom, sister and I went out for ice cream at a local McDonalds. That night, she had very aggressive vomiting and crippling stomach/intestinal pain. Constipation, diarrhea, bilious vomiting and severe abdominal pain persisted for the months following and still continues. In the summer of 2011, we volunteered and built a sort of filter for a private creek, and we most definitely consumed some of the water(unintentionally, of course). She has had a number of tests done, with extremely conflicting results(e.g. one test said she has a yeast infection, another said vaginosis, another said nothing was wrong). In February 2012, she was prescribed amoxicillin for a URT infection. Around that time, she had an ear, eye, nose and throat infection. She was given Clarithromycin at some point aswell. She had every single symptom of H. Pylori at some point. He prescribed Omeprazole 20mg, and phoned every day for the first week. It did work, and it did help, but when we got the second batch they exacerbated her initial symptoms, to the point that she was forced to stop. Endoscopy revealed a Hiatal hernia and a number of ulcers. Omeprazole dose was tripled. She was tested for H. Pylori and came back negative, but I'm worried that due to the PPIs and antibiotics it was incorrect. She's lost 30 pounds in 1.5 months, and she's in daily pain. My family and I ended up doing alot of research because no one would tell us anything. I read testimonials, blogs, and studies, and I also researched the triple therapy regimen. We put her on Mastic gum, Probiotics and Oregano Oil. It worked absolute wonders and her symptoms no longer disrupted her sleep. She used to sleep for 3 hour periods, awakened by her pain. She has had a persistent lower problem for over 7 weeks, with nothing done! My aunt(a nurse) suggested that we take her off the Oil and everything, because it could be affecting the test's accuracy. We did. Last night she woke up twice within 4 hours, something that didn't happen for atleast a month. The doctors are insisting it's IBS, yet it happened overnight, she has ulcers and the H. Pylori meds helped. She also has way more symptoms than those associated with IBS. I'm honestly getting scared, her joints hurt constantly, she can barely eat, and she's in daily pain. She often also gets chills or shakes, and general body aches. She's exhausted after almost no physical activity. My main question is, is it plausible that she is carrying H. Pylori along with another parasite/bacteria? The natural regimen worked wonders on her, but the symptoms are coming back and evolving. I'm worried that its antibiotic resistant and helping other unwanted bugs to grow. CT scan said her adrenals, pancreas, kidneys, gallbladder and biliary system are normal. Liver and spleen, small and large bowel, mesentery are all unremarkable. Blood work appeared to be normal. No antibodies were found. Pus cells present in cervical swab. To date, no stool test of any kind was done!! I really need some sort of an outside opinion on this, they insist it's mere stress or IBS but I KNOW it's far more than that. She's only 17 and this has drastically affected her quality of life. She failed grade 12, missed out on a Punta Cana trip and doesn't go farther than a couple blocks away. All tests revealed essentially nothing, but everyone here knows there's something very wrong. She recently lost 3 teeth, and for a long time she had a very persistent bad breath, that smelled very similar to that described in H. Pylori infected people. Generally speaking, she is a very healthy eater and quite sanitary. Her diet has been limited to white rice, broccoli and shrimp, and we're slowly trying to introduce other foods. Any advice or response would be greatly appreciated.

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