Parasites and Foodborne Illness

USDA Meat & Poultry Hotline

1-888-MPHotline

(1-888-674-6854)

The Food Safety and Inspection Service (FSIS) is the public health agency 

in the U.S. Department of Agriculture responsible for ensuring that the nation’s commercial supply of meat, poultry, and egg products is safe, wholesome, and correctly labeled and packaged.

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 illness. These organisms live and 

reproduce within the tissues and organs of infected human and animal hosts, and 

are often excreted in feces.

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. 

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. The size ranges from 1 to 2 μm (micrometers) 

to 2 meters long. 

Examples of parasites are Giardia duodenalis, Cryptosporidium parvum, Cyclospora 

cayetanensis, Toxoplasma gondii, Trichinella spiralis, Taenia saginata (beef 

tapeworm), and Taenia solium (pork tapeworm). 

Food Safety Information

United States Department of Agriculture

Food Safety and Inspection Service

Parasites may be present in food or in water and can be identified as causes of foodborne or waterborne illness in the United States. They range in size, from tiny single-celled organisms to worms visible to the naked eye. 

Their lifecycle may also vary. While some parasites use a permanent host, others go through a series of developmental phases using different animal or human hosts. The illnesses they can cause range from mild discomfort to 

debilitating illness and possibly death. 

What are parasites?

How are they 

transmitted?

How do they vary?

What are some 

common parasites?
Food Safety Information 2

Parasites and Foodborne Illness

People get giardiasis the following ways: 

•	 Giardiasis is frequently associated with drinking contaminated water, 

but some people might get infected by consuming uncooked meat 

also contaminated with G. duodenalis cysts (the infective stage of the 

organism). 

•	 By putting anything into your mouth that has touched contaminated 

surfaces or the stool of a person or animal with giardiasis. 

Diarrhea, abdominal cramps, gas, and nausea are the most common 

symptoms. Chronic infection might lead to dehydration and severe weight 

loss. Some cases may be without symptoms. 

Symptoms will usually appear 1 to 2 weeks after ingestion of a G. duodenalis 

cyst. They may last 2 to 6 weeks in otherwise healthy persons, but there are 

cases of chronic illnesses lasting months or even years. 

Those at risk include:

•	 Day care providers and children attending daycare centers; 

•	 International travelers (traveler’s diarrhea); 

•	 Hikers, campers, or any other persons who may drink from untreated 

or contaminated water supplies, including while swimming in lakes or 

rivers; and 

•	 Young children, pregnant women, older adults, and persons with 

weakened immune systems including those with HIV/AIDS infection, 

cancer, diabetes, kidney disease, and transplant patients, or those 

individuals undergoing chemotherapy.

•	 Wash hands with warm water and soap before handling foods and 

eating, and after going to the bathroom, changing diapers, 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 can be a 

safe alternative. 

•	 Do not swallow water while swimming. 

•	 Do not swim in community pools if you or your child has giardiasis.

•	 Always cook your food to a safe internal temperature. Safe 

temperatures can be found at:

www.fsis.usda.gov/Fact_Sheets/index.asp

•	 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. 

Watering untreated manure can spread the organism.

Who is at risk 

for contracting 

giardiasis?

How to Prevent 

Giardiasis

Giardia duodenalis or intestinalis (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 in the United States. 

How do people get 

giardiasis?

Symptoms of 

Giardiasis

When will symptoms 

appear? What is the 

duration?
Food Safety for Persons with AIDS

Food Safety Focus Food Safety Information 33

Parasites and Foodborne Illness

This parasite can be found in soil, food, water, or surfaces that have have been 

contaminated with feces from infected humans or animals.

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 include watery diarrhea, stomach cramps, upset stomach, and slight 

fever. Some cases may be without symptoms. 

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. For healthy people, symptoms may last up to 2 weeks. For individuals with weakened immune 

systems, cryptosporidiosis can be serious, long-lasting, and sometimes fatal.

Those at risk include:

•	 Day care providers and children attending daycare centers; 

•	 Young children, pregnant women, older adults, and persons with 

weakened immune systems, including those with HIV/AIDS infection, 

cancer, diabetes, kidney disease, and transplant patients, or those 

individuals undergoing chemotherapy. 

•	 International travelers (traveler’s diarrhea); and 

•	 Hikers, campers, or any other persons who may drink from untreated 

water supplies.

•	 Wash hands with warm water and soap before handling foods and 

eating, and after going to the bathroom, changing diapers, and handling 

animals. 

•	 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 can be a safe 

alternative. 

•	 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. Watering 

untreated manure can spread the organism.

Cryptosporidium parvum

Cryptosporidium parvum, cause of the disease cryptosporidiosis (KRIP-toe-spo-RID-e-O-sis) also called “Crypto,” 

is a one-celled, microscopic shelled parasite and a significant cause of waterborne and foodborne illness worldwide. 

It is found in the intestines of many herd animals including cows, sheep, goats, deer, and elk. The illness could be 

intestinal, tracheal, or pulmonary. 

How do people 

get intestinal 

cryptosporidiosis?

Symptoms of intestinal 

cryptosporidiosis

When will symptoms 

appear? What is the 

duration?

Who is at risk 

for contracting 

cryptosporidiosis?

How to Prevent 

Cryptosporidiosis
Food Safety Information 4

Parasites and Foodborne Illness

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 include watery diarrhea (sometimes explosive), loss of appetite, 

bloating, 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.

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. 

Persons of all ages are at risk for infection. 

Young children, pregnant women, older adults, and persons with weakened 

immune systems including those with HIV/AIDS infection, cancer, diabetes, 

kidney disease, and transplant patients, or those individuals undergoing 

chemotherapy may be at greater risk for infection.

•	 Wash hands with warm water and soap before handling foods and 

eating, and after going to the bathroom, changing diapers, 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 

can be a safe alternative. 

•	 Do not swim in community swimming pools if you or your child has 

cyclosporiasis. 

•	 Wash, peel, or cook raw fruits and vegetables before eating. 

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. 

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?

Symptoms of 

Cyclosporiasis

When will symptoms 

appear? What is the 

duration?

Who is at risk 

for contracting 

cyclosporiasis?

How to Prevent 

Cyclosporiasis

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 the third leading cause of death from foodborne disease. 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?
Food Safety Information 5

Parasites and Foodborne Illness

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 non-infective 

parasites can remain in the infected individual for life. An unborn child may 

contract the parasite congenitally resulting in severe outcomes including miscarriage or stillbirth.

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. 

The time that symptoms appear varies, but generally symptoms will appear 1 

week to 1 month after consuming the parasite. 

Infants infected while still in the womb may show no symptoms at birth, but 

develop symptoms later in life. 

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. 

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. 

•	 If you are pregnant or planning to become 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 some-one 

who is healthy, and not pregnant, handle the meats for you. 

•	 Cook all raw beef, pork, lamb and veal steaks, chops, and roasts to 

a minimum internal temperature of 145 °F as measured with a food 

thermometer before removing meat from the heat source. For safety 

and quality, allow meat to rest for at least three minutes before 

carving or consuming. For reasons of personal preference, consumers 

may choose to cook meat to higher temperatures.

•	 Cook all raw ground beef, pork, lamb, and veal to an internal 

temperature of 160 °F as measured with a food thermometer.

•	 Cook all poultry to a safe minumum internal temperature of 165 °F as 

measured with a food thermometer. •	 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 warm water and soap after handling 

cats, cleaning 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. 

Symptoms of 

Toxoplasmosis and 

Severe Toxoplasmosis

When will symptoms 

appear? What is the 

duration?

Who is at risk for 

contracting severe 

toxoplasmosis?

How to Prevent 

Toxoplasmosis
Food Safety Information 6

Parasites and Foodborne Illness

People get trichinellosis (trichinosis) by consuming raw or undercooked meats 

such as pork, wild boar, bear, bobcat, cougar, fox, wolf, dog, horse, seal, or 

walrus infected with Trichinella larvae. 

The illness is not spread directly from person to person. 

The first symptoms are nausea, diarrhea, vomiting, fever, fatigue, 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. 

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. Symptoms may last for months.

Persons consuming raw or undercooked 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. 

•	 Wash your hands with warm water and soap after handling raw

meat. 

•	 Cook all raw pork steaks, chops, and roasts to a minimum internal 

temperature of 145 °F as measured with a food thermometer before 

removing meat from the heat source. For safety and quality, allow 

meat to rest for at least three minutes before carving or consuming. 

For reasons of personal preference, consumers may choose to cook 

meat to higher temperatures.

•	 Clean meat grinders thoroughly each time you grind meat at home.

People get Taeniasis by consuming raw or undercooked infected beef or pork.

Most cases of infection with adult worms are without symptoms. Some 

persons may experience abdominal pain, weight loss, digestive disturbances, 

and possible intestinal obstruction.

Trichinella spiralis

Trichinella spiralis, cause of trichinellosis (also known as 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 

trichinellosis?

Symptoms of 

Trichinellosis

When will symptoms 

appear? What is the 

duration?

Who is at risk 

for contracting 

How to Prevent 

Trichinellosis

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?

Symptoms of Taeniasis
Food Safety Information 7

Parasites and Foodborne Illness

Irritation of the peri-anal area can occur, caused by worms or worm segments 

exiting the anus. 

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. 

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. 

Cook all raw beef and pork steaks, chops, and roasts to a minimum internal 

temperature of 145 °F as measured with a food thermometer before removing meat from the heat source. For safety and quality, allow meat to rest for 

at least three minutes before carving or consuming. For reasons of personal 

preference, consumers may choose to cook meat to higher temperatures

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 may vary depending on the organ or organ system involved. For 

example, in muscles, lumps under the skin may result. Cysticercosis can 

cause blurred vision in the eyes. An individual with cysticercosis involving the 

central nervous system (neurocysticercosis) may exhibit neurological symptoms such as psychiatric problems or epileptic seizures. Death is common. 

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. 

Persons traveling to countries where sanitation may be substandard and the 

water supply may be unsafe. 

Young children, pregnant women, older adults, and persons with weakened 

immune systems including those with HIV/AIDS infection, cancer, diabetes, 

kidney disease, and transplant patients, or those individuals undergoing chemotherapy may be at greater risk for infection.

When will symptoms 

appear? What is the 

duration?

Who is at risk for 

contracting Taeniasis?

How to Prevent 

Taeniasis

How do people get 

cysticercosis?

Symptoms of 

Cysticercosis

When will symptoms 

appear? What is the 

duration?

Who is at risk 

for contracting 

cysticercosis?
Food Safety Questions?

Food Safety for Persons with AIDS

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Revised June 2011

Parasites and Foodborne Illness

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How to Prevent 

Cysticercosis

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•	 Drink water only from treated municipal water supplies.

• Do not eat undercooked pork or other meat.

•	 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. 

Avoid ice in those same areas. 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.

ety Information