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Parasites and Foodborne Illness
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Parasites may be present in food or in water and can cause disease. Ranging in size from tiny, single-celled
organisms to worms visible to the naked eye, parasites are more and more frequently being identified as causes
of foodborne illness in the United States. The illnesses they can cause range from mild discomfort to debilitating
illness and possibly death.
What are parasites?
Parasites are organisms that derive nourishment and protection from other living organisms known as
hosts. They may be transmitted from animals to humans, from humans to humans, or from humans to animals.
Several parasites have emerged as significant causes of foodborne and waterborne disease. These organisms live
and reproduce within the tissues and organs of infected human and animal hosts, and are often excreted in feces.
How are they transmitted?
They may be transmitted from host to host through consumption of contaminated food and water, or by putting
anything into your mouth that has touched the stool (feces) of an infected person or animal.
How do they vary?
Parasites are of different types and range in size from tiny, single-celled, microscopic organisms (protozoa) to
larger, multi-cellular worms (helminths) that may be seen without a microscope.
What are some common parasites?
Some common parasites are Giardia duodenalis, Cryptosporidium parvum, Cyclospora cayetanensis,
Toxoplasma gondii, Trichinella spiralis, Taenia saginata (beef tapeworm), and Taenia solium
(pork tapeworm).
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Giardia duodenalis (formerly called G. lamblia)
Giardia duodenalis, cause of giardiasis (GEE-are-DYE-uh-sis), is a one-celled, microscopic parasite that
can live in the intestines of animals and people. It is found in every region throughout the world and has become
recognized as one of the most common causes of waterborne (and occasionally foodborne) illness.
How do people get giardiasis?
People get giardiasis the following ways:
- By consuming food or water contaminated with G. duodenalis cysts (the infective stage of the organism).
- By putting anything into your mouth that has touched the stool of a person or animal with giardiasis.
Symptoms of giardiasis
Diarrhea, abdominal cramps, and nausea are the most common symptoms. Some cases may be without symptoms.
When will symptoms appear? What is the duration?
Symptoms will usually appear 1 to 2 weeks after ingestion of a G. duodenalis cyst. They may last 4 to 6
weeks in otherwise healthy persons, but there are cases of chronic illnesses lasting months or even years.
Who is at risk for contracting giardiasis?
Those at risk include:
- persons working in child daycare centers and children attending daycare centers;
- international travelers (traveler's diarrhea);
- hikers, campers, or any other persons who may drink from untreated water supplies; and
- persons with weakened immune systems including those with HIV/AIDS infection, organ transplant recipients, or those individuals undergoing chemotherapy.
How to prevent giardiasis
- Wash hands with hot, soapy water before handling foods and eating, and after using the toilet, diapering young children, and handling animals.
- Make sure infected individuals wash their hands frequently to reduce the spread of infection.
- Drink water only from treated municipal water supplies.
- When hiking, camping, or traveling to countries where the water supply may be unsafe to drink, either avoid drinking the water or boil it for 1 minute to kill the parasite. Drinking bottled beverages or hot coffee and tea are safe alternatives.
- Do not swallow water while swimming.
- Do not swim in community pools if you or your child has giardiasis.
- Drink only pasteurized milk, juices, or cider.
- Wash, peel, or cook raw fruits and vegetables before eating.
- Do not use untreated manure to fertilize fruits and vegetables.
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Cryptosporidium parvum
Cryptosporidium parvum, cause of the disease cryptosporidiosis (KRIP-toe-spo-RID-e-O-sis), is a
one-celled, microscopic parasite, and a significant cause of waterborne illness worldwide. It is found in the
intestines of many herd animals including cows, sheep, goats, deer, and elk.
How do people get cryptosporidiosis?
People get cryptosporidiosis the following ways:
- By consuming food or water contaminated with C. parvum oocysts (infective stage of the parasite). The oocysts are the environmentally resistant stage of the organism and are shed in the feces of a host (human or animal).
- By putting anything into your mouth that has touched the stool of a person or animal with cryptosporidiosis.
Symptoms of cryptosporidiosis
Symptoms include watery diarrhea, stomach cramps, upset stomach, and slight fever. Some cases may be without symptoms.
When will symptoms appear? What is the duration?
Symptoms appear 2 to 10 days after ingestion of C. parvum oocysts. The illness usually goes away without
medical intervention in 3 to 4 days, but in some outbreaks in daycare centers, diarrhea has lasted 1 to 4 weeks.
In people with AIDS and other individuals with weakened immune systems, cryptosporidiosis can be serious,
long-lasting, and sometimes fatal.
Who is at risk for contracting cryptosporidiosis?
Those at risk include:
- persons working in child daycare centers and children attending daycare centers;
- persons with weakened immune systems including those with HIV/AIDS infection, organ transplant recipients, or those individuals undergoing chemotherapy;
- international travelers (traveler's diarrhea); and
- hikers, campers, or any other persons who may drink from untreated water supplies.
How to prevent cryptosporidiosis
- Wash hands with hot, soapy water before handling foods and eating, and after using the toilet, diapering young children, and handling animals.
- Make sure infected individuals wash their hands frequently to reduce the spread of infection.
- Drink water only from treated municipal water supplies.
- When hiking, camping, or traveling to countries where the water supply may be unsafe to drink, either avoid drinking the water or boil it for 1 minute to kill the parasite. Drinking bottled beverages or hot coffee and tea are safe alternatives.
- Do not swallow water while swimming.
- Do not swim in community swimming pools if you or your child has cryptosporidiosis.
- Drink only pasteurized milk, juices, or cider.
- Wash, peel, or cook raw fruits and vegetables before eating.
- Do not use untreated manure to fertilize fruits and vegetables.
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Cyclospora cayetanensis
Cyclospora cayetanensis (SIGH-clo-SPOR-uh KYE-uh-tuh-NEN-sis), cause of cyclosporiasis, is a one-celled,
microscopic parasite. Currently little is known about this organism, although cases of cyclosporiasis are being
reported from various countries with increasing frequency.
How do people get cyclosporiasis?
People get cyclosporiasis the following ways:
- By consuming food or water contaminated with C. cayetanensis oocysts (the infective stage of the organism).
- By putting anything into your mouth that has touched the stool of a person or animal with cyclosporiasis.
Symptoms of cyclosporiasis
Symptoms include watery diarrhea (sometimes explosive), stomach cramps, nausea, vomiting, muscle aches,
low-grade fever, and fatigue. Some cases are without symptoms. Symptoms are more severe in persons with weakened
immune systems.
When will symptoms appear? What is the duration?
Symptoms typically appear about 1 week after ingestion of C. cayetanensis oocysts. If untreated, the
symptoms may last a week to more than a month. Symptoms may return.
Who is at risk for contracting cyclosporiasis?
Persons of all ages are at risk for infection.
Persons with weakened immune systems including those with HIV/AIDS infection, organ transplant recipients, or
those individuals undergoing chemotherapy may be at greater risk for infection.
How to prevent cyclosporiasis
- Wash hands with hot, soapy water before handling foods and eating, and after using the toilet, diapering young children, and handling animals.
- Make sure infected individuals wash their hands frequently to reduce the spread of infection.
- Drink water only from treated municipal water supplies.
- When hiking, camping, or traveling to countries where the water supply may be unsafe to drink, either avoid drinking the water or boil the water for 1 minute to kill the parasite. Drinking bottled beverages or hot coffee and tea are safe alternatives.
- Do not swallow water while swimming.
- Do not swim in community swimming pools if you or your child has cyclosporiasis.
- Wash, peel, or cook raw fruits and vegetables before eating.
- Do not use untreated manure to fertilize fruits and vegetables.
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Toxoplasma gondii
Toxoplasma gondii, cause of the disease, toxoplasmosis (TOX-o-plaz-MO-sis), is a single-celled,
microscopic parasite found throughout the world. It is interesting to note that these organisms can only carry
out their reproductive cycle within members of the cat family. In this parasite-host relationship, the cat is the
definitive host. The infective stage (oocyst) develops in the gut of the cat. The oocysts are
then shed into the environment with cat feces.
How do people get toxoplasmosis?
People get toxoplasmosis the following ways:
- By consuming foods (such as raw or undercooked meats, especially pork, lamb, or wild game) or drinking untreated water (from rivers or ponds) that may contain the parasite.
- Fecal-oral: Touching your hands to your mouth after gardening, handling cats, cleaning a cat's litter box, or anything that has come into contact with cat feces.
- Mother-to-fetus (if mother is pregnant when first infected with T. gondii).
- Through organ transplants or blood transfusions, although these modes are rare.
Symptoms of toxoplasmosis and severe toxoplasmosis
Toxoplasmosis is relatively harmless to most people, although some may develop "flu-like" symptoms such
as swollen lymph glands and/or muscle aches and pains. In otherwise healthy individuals, the disease is usually
mild and goes away without medical treatment. However, dormant tissue stages can remain in the infected individual
for life.
However, persons with weakened immune systems such as those with HIV/AIDS infection, organ transplant recipients,
individuals undergoing chemotherapy, and infants may develop severe toxoplasmosis. Severe
toxoplasmosis may result in damage to the eyes or brain. Infants becoming infected before birth can be born
retarded or with other mental or physical problems.
When will symptoms appear? What is the duration?
The time that symptoms appear varies, but generally symptoms will appear 1 week to 1 month after consuming the parasite.
The duration of the illness depends on the health and immune status of the host. Persons with weakened immune
systems may experience illnesses of long duration, possibly resulting in death.
Who is at risk for contracting severe toxoplasmosis?
Those at risk include:
- Persons with weakened immune systems including those with HIV/AIDS infection, organ transplant recipients, or those individuals undergoing chemotherapy.
- Infants born to mothers who become infected with T. gondii shortly before becoming pregnant or during pregnancy. Those mothers exposed to T. gondii longer than 6 months before becoming pregnant rarely transmit toxoplasmosis to their infants.
How to prevent toxoplasmosis
- If you are pregnant or if you have a weakened immune system, you should discuss your risk of contracting toxoplasmosis with your health care provider.
- Wear clean latex gloves when handling raw meats, or have someone who is healthy, and not pregnant, handle the meats for you.
- Cook all meats thoroughly to 160 °F.
- Wash hands, cutting boards, and other utensils thoroughly with hot, soapy water after handling raw meats.
- Clean cat litter boxes daily because cat feces more than a day old can contain mature parasites.
- Wash hands thoroughly with hot, soapy water after handling cats, cleaning and cat litter boxes, especially before you handle or eat food.
- Wear gloves when you handle garden soil or sandboxes. Cats may use gardens or sandboxes as litter boxes.
- Cover sandboxes to prevent cats from using them as litter boxes.
- Help prevent cats from becoming infected with T. gondii by discouraging them from hunting and scavenging.
- Feed cats commercially made cat foods or cook their food.
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Trichinella spiralis
Trichinella spiralis, cause of trichinosis (TRICK-a-NO-sis) is an intestinal roundworm whose larvae may
migrate from the digestive tract and form cysts in various muscles of the body. Infections occur worldwide, but are most prevalent
in regions where pork or wild game is consumed raw or undercooked. The incidence of trichinosis has declined in the United
States due to changes in hog feeding practices. Presently, most cases in this country are caused by consumption of raw or
undercooked wild game.
How do people get trichinosis?
People get trichinosis by consuming raw or undercooked meats such as pork, wild boar, bear, bobcat, cougar, fox,
wolf, dog, horse, seal, or walrus containing Trichinella larvae.
The illness is not spread directly from person to person.
Symptoms of trichinosis
The first symptoms are nausea, diarrhea, vomiting, fever, and abdominal pain, followed by headaches, eye swelling,
aching joints and muscles, weakness, and itchy skin. In severe infections, persons may experience difficulty with
coordination and have heart and breathing problems. Death may occur in severe cases.
When will symptoms appear? What is the duration?
Abdominal symptoms may appear within 1 to 2 days after eating contaminated meat. Further symptoms (eye swelling
and aching muscles and joints) may begin 2 to 8 weeks after infection. Mild cases may assumed to be flu.
Who is at risk for contracting trichinosis?
Persons consuming raw or under cooked pork or wild game.
Persons with weakened immune systems including those with HIV/AIDS infection, organ transplant recipients, or
those individuals undergoing chemotherapy may be at a greater risk for infection.
How to prevent trichinosis
Cook pork and wild game to 160 °F to kill any Trichinella larvae that may be present.
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Taenia saginata/Taenia solium (Tapeworms)
Taenia saginata (beef tapeworm) and Taenia solium (pork tapeworm) are parasitic worms (helminths).
Taeniasis is the name of the intestinal infection caused by adult-stage tapeworms (beef or pork
tapeworms). Cysticercosis is the name of the tissue (other than intestinal) infection caused by
the larval-stage of the pork tapeworm only.
It is interesting to note that humans are the definitive hosts of both organisms. This means that
the reproductive cycle, and thus egg production by the organisms, occurs only within humans. Eggs are passed in
human feces and they may be shed into the environment for as long as the worms remain in the intestines (for as
long as 30 years). In addition, the eggs may remain viable in the environment for many months.
These diseases are more prevalent in underdeveloped countries where sanitation practices may be substandard and
in areas where pork and beef are consumed raw or undercooked. They are relatively uncommon in the U.S., although
travelers and immigrants are occasionally infected.
How do people get Taeniasis?
People get Taeniasis by consuming infected beef or pork (raw or undercooked).
Symptoms of Taeniasis
Most cases of infection with adult worms are without symptoms. Some persons may experience abdominal pain, weight
loss, digestive disturbances, and possible intestinal obstruction.
Irritation of the peri-anal area can occur, caused by worms or worm segments exiting the anus.
When will symptoms appear? What is the duration?
T. saginata (beef tapeworm) infections appear within 10 to 14 weeks. T. solium (pork tapeworm)
infections appear within 8 to 12 weeks.
Taeniasis may last many years without medical treatment.
Who is at risk for contracting Taeniasis?
Anyone consuming infected beef or pork (raw or
undercooked).
Persons with weakened immune systems including those with HIV/AIDS infection, organ transplant recipients, or
those individuals undergoing chemotherapy may be at a greater risk for infection.
How to prevent Taeniasis
Cook beef and pork to 160 °F to kill encysted tapeworm larvae that may be present.
How do people get cysticercosis?
People get cysticercosis the following ways:
- By consuming food or water contaminated with the eggs of T. solium (pork tapeworm). Worm eggs hatch and
the larvae then migrate to various parts of the body and form cysts called cysticerci. This can be a serious or fatal disease if it involves organs such as the central nervous system, heart, or eyes.
- By putting anything into your mouth that has touched the stool of a person infected with T. solium.
- Some persons with intestinal tapeworms may infect themselves with eggs from their own feces as a result of poor personal hygiene.
Symptoms of cysticercosis
Symptoms may vary depending on the organ or organ system involved. For example, an individual with cysticercocis
involving the central nervous system (neurocysticercosis) may exhibit neurological symptoms such as psychiatric
problems or epileptic seizures. Death is common.
When will symptoms appear? What is the duration?
Symptoms usually appear from several weeks to several years after becoming infected with the eggs of the pork
tapeworm (T. solium). Symptoms may last for many years if medical treatment is not received.
Who is at risk for contracting cysticercosis?
Persons traveling to countries where sanitation may be substandard and the water supply may be unsafe.
Persons with weakened immune systems including those with HIV/AIDS infection, organ transplant recipients, or
those individuals undergoing chemotherapy may be at a greater risk for infection.
How to prevent cysticercosis
- Drink water only from treated municipal water supplies.
- When traveling to countries where the water supply may be unsafe, either avoid the water or boil it for 1 minute to kill parasite eggs. Drinking bottled beverages or hot coffee and tea are safe alternatives.
- Do not swallow water while swimming.
- Do not swim in community swimming pools if you or your child are infected with tapeworms.
- Wash, peel, or cook raw fruits and vegetables before eating.
- Make sure that infected individuals wash their hands frequently to reduce the spread of infection.
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Last Modified:
May 2001 |
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