The physical space of the MSK Library is permanently closed to visitors as of Friday, May 17, 2024. Please visit this guide for more information.
The physical space of the MSK Library is permanently closed to visitors as of Friday, May 17, 2024. Please visit this guide for more information.
Lice are parasitic insects that can be found on people’s heads and bodies, including the pubic area. Human lice survive by feeding on human blood. Lice found on each area of the body are different from each other. The three types of lice that live on humans are: Pediculus humanus capitis (head louse), Pediculus humanus corporis (body louse, clothes louse), and Pthirus pubis (“crab” louse, pubic louse). Only the body louse is known to spread disease. Lice infestations (pediculosis and pthiriasis) are spread most commonly by close person-to-person contact. Dogs, cats, and other pets do not play a role in the transmission of human lice.
Human scabies is caused by an infestation of the skin by the human itch mite (Sarcoptes scabiei var. hominis). The microscopic scabies mite burrows into the upper layer of the skin where it lives and lays its eggs. The most common symptoms of scabies are intense itching and a pimple-like skin rash. The scabies mite usually is spread by direct, prolonged, skin-to-skin contact with a person who has scabies.Scabies occurs worldwide and affects people of all races and social classes. Scabies can spread rapidly under crowded conditions where close body contact is frequent. Institutions such as nursing homes, extended-care facilities, and prisons are often sites of scabies outbreaks.
Swimmer’s itch, also called cercarial dermatitis, appears as a skin rash caused by an allergic reaction to certain parasites that infect some birds and mammals. The adult parasite lives in the blood of infected animals such as ducks, geese, gulls, swans, and certain mammals such as muskrats and raccoons. The parasites produce eggs that are passed in the feces of infected birds or mammals. If the eggs land in or are washed into the water, the eggs hatch, releasing small, free-swimming microscopic larvae.
These larvae swim in the water in search of a certain species of aquatic snail. If the larvae find one of these snails, they infect the snail, multiply and undergo further development. Infected snails release a different type of microscopic larvae (or cercariae, hence the name cercarial dermatitis) into the water. This larval form then swims about searching for a suitable host (bird, muskrat) to continue the lifecycle.
Although humans are not suitable hosts, the microscopic larvae burrow into the swimmer’s skin, and may cause an allergic reaction and rash. Because these larvae cannot develop inside a human, they soon die.
Pinworm infection is caused by a small, thin, white roundworm called Enterobius vermicularis that sometimes lives in the colon and rectum of humans. Pinworm infection is spread by the fecal-oral route, that is by the transfer of infective pinworm eggs from the anus to someone’s mouth, either directly by hand or indirectly through contaminated clothing, bedding, food, or other articles.
Although pinworom infection can affect all people, it most commonly occurs among children, institutionalized persons, and household members of persons with pinworm infection.
While an infected person sleeps, female pinworms leave the intestine through the anus and deposit their eggs on the surrounding skin. Pinworm infection causes itching around the anus which can lead to difficulty sleeping and restlessness. Symptoms are caused by the female pinworm laying her eggs. Symptoms of pinworm infection usually are mild and some infected people have no symptoms.
Malaria is a serious and sometimes fatal disease caused by a parasite that commonly infects a specific type of mosquito (the Anopheles mosquito) which feeds on humans. Four kinds of malaria parasites infect humans: Plasmodium falciparum, P. vivax, P. ovale, and P. malariae.
Usually, people get malaria by being bitten by an infective female Anopheles mosquito. Only Anopheles mosquitoes can transmit malaria and they must have been infected through a previous blood meal taken from an infected person. When a mosquito bites an infected person, a small amount of blood is taken in which contains microscopic malaria parasites. About 1 week later, when the mosquito takes its next blood meal, these parasites mix with the mosquito’s saliva and are injected into the person being bitten.
Because the malaria parasite is found in red blood cells of an infected person, malaria can also be transmitted through blood transfusion, organ transplant, or the shared use of needles or syringes contaminated with blood. Malaria may also be transmitted from a mother to her unborn infant before or during delivery (“congenital” malaria).
An estimated 576-740 million people in the world are infected with hookworm. Hookworm was once widespread in the United States, particularly in the southeastern region, but improvements in living conditions have greatly reduced hookworm infections. Hookworms live in the small intestine. Hookworm eggs are passed in the feces of an infected person. The larvae mature into a form that can penetrate the skin of humans. Hookworm infection is mainly acquired by walking barefoot on contaminated soil.
Most people infected with hookworms have no symptoms. Some have gastrointestinal symptoms, especially persons who are infected for the first time. The most serious effects of hookworm infection are blood loss leading to anemia, in addition to protein loss.
An estimated 807 million–1.2 billion people in the world are infected with Ascaris lumbricoides (sometimes called just Ascaris or ascariasis). Ascariasis is now not common in the United States. Ascaris parasites live in the intestine. Ascaris eggs are passed in the feces of infected people. The worm eggs can then grow into a form of the parasite that can infect others. Ascariasis is caused by ingesting those worm eggs. This can happen when hands or fingers that have contaminated dirt on them are put in the mouth, or by eating vegetables or fruits that have not been carefully peeled, washed, or cooked.
Taeniasis in humans is a parasitic infection caused by the tapeworm species Taenia saginata (beef tapeworm), Taenia solium (pork tapeworm), and Taenia asiatica (Asian tapeworm). Humans can become infected with these tapeworms by eating raw or undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Infections with T. saginata occur wherever contaminated raw beef is eaten. Tapeworm infections due to T. solium are more prevalent in under-developed communities with poor sanitation and where people eat raw or under-cooked pork. Higher rates of illness have been seen in people in Latin America, Eastern Europe, sub-Saharan Africa, India, and Asia.
An estimated 604-795 million people in the world are infected with whipworm. Whipworms live in the large intestine and whipworm eggs are passed in the feces of infected persons. Whipworm infection is caused by ingesting eggs. This can happen when hands or fingers that have contaminated dirt on them are put in the mouth or by consuming vegetables or fruits that have not been carefully cooked, washed or peeled.
People infected with whipworm can suffer light or heavy infections. People with light infections usually have no symptoms. People with heavy infections can experience frequent, painful bowel movements that contain a mixture of mucus, water, and blood. Rectal prolapse (when the rectum sags and comes out of the anus) can also occur.
Many kinds of lab tests are available to diagnose parasitic diseases. The kind of test(s) your health care provider will order will be based on your signs and symptoms, any other medical conditions you may have, and your travel history. Diagnosis may be difficult, so your health care provider may order more than one kind of test.
A fecal (stool) exam, also called an ova and parasite test (O&P)
This test is used to find parasites that cause diarrhea, loose or watery stools, cramping, flatulence (gas) and other abdominal illness. CDC recommends that three or more stool samples, collected on separate days, be examined. This test looks for ova (eggs) or the parasite.
Endoscopy/Colonoscopy
Endoscopy is used to find parasites that cause diarrhea, loose or watery stools, cramping, flatulence (gas) and other abdominal illness.This test is used when stool exams do not reveal the cause of your diarrhea.
Blood tests
Some, but not all, parasitic infections can be detected by testing your blood. Blood tests look for a specific parasite infection; there is no blood test that will look for all parasitic infections. There are two general kinds of blood tests that your doctor may order: These tests are used to look for some parasitic diseases that may cause lesions in the organs.
X-ray, Magnetic Resonance Imaging (MRI) scan, Computerized Axial Tomography scan (CAT)
These tests are used to look for some parasitic diseases that may cause lesions in the organs.
Parasitic infections are often associated with tropical areas. However, these infections are also present in the United States. Anyone can become infected although certain racial or ethnic minority groups, persons born outside the United States, and people with lower incomes appear to be most at risk.
The following parasitic diseases in the United States that are priorities for public health action are based on the number of people infected, severity of the illnesses, and, ability to prevent and treat them.
Chagas disease is caused by the parasite Trypanosoma cruzi, which is transmitted to animals and people by insect vectors and is found only in the Americas (mainly, in rural areas of Latin America where poverty is widespread). Chagas disease (T. cruzi infection) is also referred to as American trypanosomiasis.
It is estimated that as many as 8 million people in Mexico, Central America, and South America have Chagas disease, most of whom do not know they are infected. If untreated, infection is lifelong and can be life threatening.
Cyclosporiasis is an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis. People can become infected with Cyclospora by consuming food or water contaminated with the parasite. People living or traveling in tropical or subtropical regions of the world may be at increased risk for infection because cyclosporiasis is endemic in some countries in these zones. In the United States, foodborne outbreaks of cyclosporiasis have been linked to various types of imported fresh produce. People can get infected with Cyclospora more than once.
Cysticercosis is a parasitic tissue infection caused by larval cysts of the tapeworm Taenia solium. These larval cysts infect brain, muscle, or other tissue, and are a major cause of adult onset seizures in most low-income countries. Cysticercosis is the disease associated with the development of the larval form (cysticercus) of the pork tapeworm, Taenia solium, within an intermediate host (usually pigs). However, humans (the usual definitive host) can serve as accidental intermediate hosts following ingestion of infectious eggs.
Note that cysticercosis is only acquired from the fecal-oral route (ingestion of eggs), not via the ingestion of cysticerci in undercooked pork, which is associated with intestinal taeniasis.
Toxocariasis is an infection transmitted from animals to humans (zoonosis) caused by the parasitic roundworms commonly found in the intestine of dogs (T. canis) and cats (T. cati). While anyone can become infected with Toxocara, young children and owners of dogs or cats have a higher chance of becoming infected. Approximately 5% of the U.S. population has antibodies to Toxocara, which suggests that tens of millions of Americans may have been exposed to the Toxocara parasite.
The most common Toxocara parasite of concern to humans is T. canis, which puppies usually contract from their mother before birth or from her milk. The larvae mature rapidly in the puppy’s intestine; when the pup is 3 or 4 weeks old, the worms inside the puppy begin to produce large numbers of eggs that contaminate the environment through the puppy’s feces. After the eggs pass into the environment, it takes about 2 to 4 weeks for infective larvae to develop in the eggs. If a person ingests one of these infective eggs, then they can become infected with toxocariasis.
Toxoplasmosis is an infection caused by a single-celled parasite called Toxoplasma gondii. While the parasite is found throughout the world, more than 40 million people in the United States may be infected with the Toxoplasma parasite. The Toxoplasma parasite can persist for long periods of time in the bodies of humans (and other animals), possibly even for a lifetime. Of those who are infected however, very few have symptoms because a healthy person’s immune system usually keeps the parasite from causing illness. However, pregnant women and individuals who have compromised immune systems should be cautious; for them, a Toxoplasma infection could cause serious health problems.
Toxoplasmosis is considered to be a leading cause of death attributed to foodborne illness in the United States.
Trichomoniasis (or “trich”) is a very common STD caused by infection with Trichomonas vaginalis (a protozoan parasite). Although symptoms vary, most people who have trich cannot tell they have it. In the United States, CDC estimates that there were more than two million trichomoniasis infections in 2018. However, only about 30% develop any symptoms of trich. Infection is more common in women than in men. Older women are more likely than younger women to have the infection.