They range in size from microscopic single-celled organisms known as protozoa to visible worms known as helminths. But, what they all have in common is that they derive their nourishment from other living organisms known as host organisms.
When the parasites live and reproduce in the tissues and organs of animal and human hosts they can then be excreted in feces and go on to infect other individuals. There is a hard shell covering to some varieties of protozoa that permit them to survive for lengthy periods of time in water waiting to infect another host.
Examples of protozoan parasites include Cyclospora, Giardia, and Cryptosporidium. A well-known foodborne helminth is Trichinella, an intestinal roundworm.
Giardiasis is a diarrheal disease caused by the microscopic parasite Giardia. A parasite is an organism that feeds off of another to survive. Once a person or animal (for example, cats, dogs, cattle, deer, and beavers) has been infected with Giardia, the parasite lives in the intestines and is passed in feces.
Once outside the body, Giardia can sometimes survive for weeks or months. Giardia can be found within every region of the U.S. and around the world.
How giardiasis is spread?
• Eating uncooked food that contains Giardia organisms
• Drinking water or using ice made from water sources where Giardia may live (for example, untreated or improperly treated water from lakes, streams, or wells)
• Swallowing water while swimming or playing in water where Giardia may live, especially in lakes, rivers, springs, ponds, and streams
• Swallowing Giardia picked up from surfaces (such as bathroom handles, changing tables, diaper pails, or toys) that contain stool from an infected person or animal
• Having contact with someone who is ill with giardiasis
• Traveling to countries where giardiasis is common
Anything that comes into contact with feces from infected humans or animals can become contaminated with the Giardia parasite. People become infected when they swallow the parasite. It is not possible to become infected through contact with blood.
Intestinal symptoms of giardia infection
• Gas or flatulence
• Greasy stool that can float
• Stomach or abdominal cramps
• Upset stomach or nausea
These symptoms may also lead to weight loss. Some people with Giardia infection have no symptoms at all.
Symptoms of giardiasis normally begin 1 to 3 weeks after becoming infected. In otherwise healthy people, symptoms of giardiasis may last 2 to 6 weeks. Occasionally, symptoms last longer. Medications can help decrease the amount of time symptoms last.
Risks of getting giardiasis – People more likely to become infected include:
• Children in child care settings, especially diaper-aged children
• Close contacts (for example, people living in the same household) or people who care for those sick with giardiasis
• People who drink water or use ice made from places where Giardia may live (for example, untreated or improperly treated water from lakes, streams, or wells)
• Backpackers, hikers, and campers who drink unsafe water or who do not practice good hygiene (for example, proper handwashing)
• People who swallow water while swimming and playing in recreational water where Giardia may live, especially in lakes, rivers, springs, ponds, and streams
• International travelers
If you think you have giardiasis contact your health care provider.
Diagnosing Giardia infection
Your health care provider will ask you to submit stool samples to see if you are infected. Because testing for giardiasis can be difficult, you may be asked to submit several stool specimens collected over several days.
Many prescription drugs are available to treat giardiasis. Although the Giardia parasite can infect all people, infants and pregnant women may be more likely to experience dehydration from the diarrhea caused by giardiasis. To prevent dehydration, infants and pregnant women should drink a lot of fluids while ill. Dehydration can be life threatening for infants, so it is especially important that parents talk to their health care providers about treatment options for their infants.
Preventing & Controlling Giardia infection
• Practice good hygiene
• Avoid water (drinking or recreational) that may be contaminated
• Avoid eating food that may be contaminated
Can I get giardiasis from my pet?
The risk of humans acquiring Giardia infection from dogs or cats is small. The exact type of Giardia that infects humans is usually not the same type that infects dogs and cats.
Photo courtesy of CDC/Dr. Stan Erlandsen; Dr. Carol Wells
Cyclosporiasis is an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis. Cyclospora cayetanensis is a parasite composed of one cell, too small to be seen without a microscope. People become infected by consuming food or water contaminated with the Cyclospora parasite.
How is Cyclospora spread?
Cyclospora is spread by people ingesting something – such as food or water – that was contaminated with feces (stool). Cyclospora needs time (days to weeks) after being passed in a bowel movement to become infectious for another person. Therefore, it is unlikely that Cyclospora is passed directly from one person to another.
Who is at risk for Cyclospora infection?
In the United States, foodborne outbreaks of cyclosporiasis have been linked to various types of imported fresh produce. People living or traveling in countries where cyclosporiasis is endemic may be at increased risk for infection.
What are the symptoms of Cyclospora infection?
Cyclospora infects the small intestine (bowel) and usually causes:
Less common symptoms include:
The time between becoming infected and becoming sick is usually about 1 week. Some people who are infected with Cyclospora do not have any symptoms.
How long can the symptoms last?
If not treated, the illness may last from a few days to a month or longer. Symptoms may seem to go away and then return one or more times (relapse). It’s common to feel very tired. If you think you’ve been infected with Cyclospora see your health care provider.
Diagnosing Cyclospora infection
Your health care provider will ask you to submit stool specimens to see if you are infected. You might be asked to submit more than one specimen from different days. Identification of this parasite in stool requires special laboratory tests that are not routinely done. Therefore, if indicated, your health care provider should specifically request testing for Cyclospora. In addition, your health care provider might have your stool checked for other organisms that can cause similar symptoms.
Treatment for Cyclosporiasis
The recommended treatment is a combination of two antibiotics, trimethoprim-sulfamethoxazole, also known as Bactrim*, Septra*, or Cotrim*. People who have diarrhea should also rest and drink plenty of fluids. If a person ill with cyclosporiasis is not treated, symptoms can persist for several weeks to a month or more. Some symptoms, such as diarrhea, can return; and some symptoms, such as muscle aches and fatigue, may continue after the gastrointestinal symptoms have gone away. The infection usually is not life threatening.
I am allergic to sulfa drugs; is there another drug I can take?
No highly effective alternative drugs have been identified yet for people with Cyclospora infection who are unable to take sulfa drugs. See your health care provider to discuss potential options.
Avoiding food or water that might have been contaminated with stool may help prevent Cyclospora infection. People who have previously been infected with Cyclospora can become infected again. In the United States, foodborne outbreaks of cyclosporiasis since the mid-1990s have been linked to various types of imported fresh produce, including raspberries, basil, snow peas, and mesclun lettuce; no commercially frozen or canned produce has been implicated.
On the basis of the currently available information, avoiding food or water that may have been contaminated with feces is the best way to prevent cyclosporiasis. Treatment with chlorine or iodine is unlikely to kill Cyclospora oocysts. No vaccine for cyclosporiasis is available. CDC monitors the occurrence of cyclosporiasis in the United States and helps state health departments identify and investigate cyclosporiasis outbreaks to prevent additional cases of illness.
Cryptosporidiosis is a diarrheal disease caused by microscopic parasites, Cryptosporidium, that can live in the intestine of humans and animals and is passed in the stool of an infected person or animal. The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very resistant to chlorine-based disinfectants.
During the past 2 decades, Cryptosporidium has become recognized as one of the most common causes of waterborne disease (recreational water and drinking water) in humans in the United States. The parasite is found in every region of the United States and throughout the world.
Both the disease and the parasite are commonly known as “Crypto.”
How is crypto spread?
You can become infected after accidentally swallowing the parasite. Cryptosporidium may be found in soil, food, water, or surfaces that have been contaminated with the feces from infected humans or animals. Crypto is not spread by contact with blood.
Crypto can be spread by:
Common symptoms of crypto include:
Some people with Crypto will have no symptoms at all. While the small intestine is the site most commonly affected, Crypto infections could possibly affect other areas of the digestive tract or the respiratory tract.
Symptoms of crypto generally begin 2 to 10 days (average 7 days) after becoming infected with the parasite. In persons with healthy immune systems, symptoms usually last about 1 to 2 weeks. The symptoms may go in cycles in which you may seem to get better for a few days, then feel worse again before the illness ends.
Who is most at risk for infection with crypto?
Contaminated water may include water that has not been boiled or filtered, as well as contaminated recreational water sources (e.g., swimming pools, lakes, rivers, ponds, and streams). Several community-wide outbreaks of cryptosporidiosis have been linked to drinking municipal water or recreational water contaminated with Cryptosporidium.
Although crypto can infect all people, some groups are likely to develop more serious illness.
To avoid spreading the disease to others, infected individuals should wash their hands frequently with soap and water, especially after using the toilet, or changing diapers, and before eating or preparing food. If you think you may have crypto see your health care provider. Thoroughly wash with clear, clean (uncontaminated) water, all vegetables and fruits you plan to eat raw.
Your health care provider will ask you to submit stool samples to see if you are infected. Because testing for Crypto can be difficult, you may be asked to submit several stool specimens over several days. Tests for Crypto are not routinely done in most laboratories. Therefore, your health care provider should specifically request testing for the parasite.
What is the treatment for cryptosporidiosis?
Nitazoxanide has been FDA-approved for treatment of diarrhea caused by Cryptosporidium in people with healthy immune systems and is available by prescription. Consult with your health care provider for more information.
Most people who have healthy immune systems will recover without treatment. Diarrhea can be managed by drinking plenty of fluids to prevent dehydration. Young children and pregnant women may be more susceptible to dehydration. Rapid loss of fluids from diarrhea may be especially life threatening to babies.
Therefore, parents should talk to their health care provider about fluid replacement therapy options for infants. Anti-diarrheal medicine may help slow down diarrhea, but a health care provider should be consulted before such medicine is taken.
People who are in poor health or who have weakened immune systems are at higher risk for more severe and more prolonged illness. The effectiveness of Nitazoxanide in immunosuppressed individuals is unclear. HIV-positive individuals who suspect they have Crypto should contact their health care provider. For persons with AIDS, anti-retroviral therapy that improves immune status will also decrease or eliminate symptoms of Crypto. However, even if symptoms disappear, cryptosporidiosis is often not curable and the symptoms may return if the immune status worsens.
A single-celled parasite called Toxoplasma gondii causes a disease known as toxoplasmosis.
While the parasite is found throughout the world, more than 60 million people in the United States may be infected with the Toxoplasma parasite. Of those who are infected, 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.
How Toxoplasma infection occurs
More about toxoplasmosis
Higher risk for severe toxoplasmosis
What should I do if I think I am at risk for severe toxoplasmosis?
Precautions to take to avoid infection
There are several general sanitation and food safety steps you can take to reduce your chances of becoming infected with Toxoplasma gondii:
What should I do if I think I may have toxoplasmosis?
If you suspect that you may have toxoplasmosis, talk to your health care provider. Your provider may order one or more varieties of blood tests specific for toxoplasmosis. The results from the different tests can help your provider determine if you have a Toxoplasma gondii infection and whether it is a recent (acute) infection.
What is the treatment for toxoplasmosis?
In an otherwise healthy person who is not pregnant, treatment usually is not needed. If symptoms occur, they typically go away within a few weeks to months. For pregnant women or persons who have weakened immune systems, medications are available to treat toxoplasmosis.
The signs, symptoms, severity and duration of trichinellosis vary. Nausea, diarrhea, vomiting, fatigue, fever, and abdominal discomfort are often the first symptoms of trichinellosis.
Headaches, fevers, chills, cough, swelling of the face and eyes, aching joints and muscle pains, itchy skin, diarrhea, or constipation may follow the first symptoms. If the infection is heavy, patients may experience difficulty coordinating movements, and have heart and breathing problems. In severe cases, death can occur.
For mild to moderate infections, most symptoms subside within a few months. Fatigue, weakness, muscle pain, and diarrhea may last for months.
Symptoms of trichinosis
Abdominal symptoms can occur 1-2 days after infection. Further symptoms usually start 2-8 weeks after eating contaminated meat. Symptoms may range from very mild to severe and relate to the number of infectious worms consumed in meat.
Often, mild cases of trichinellosis are never specifically diagnosed and are assumed to be the flu or other common illnesses.
Am I at risk for trichinellosis?
If you eat raw or undercooked meats particularly bear, pork, wild feline (such as a cougar), fox, dog, wolf, horse, seal, or walrus, you are at risk for trichinellosis.
Infection can only occur by eating raw or undercooked meat containing Trichinella worms. It cannot be passed to others.
If you think you have trichinellosis, see your health care provider who can order tests and treat symptoms of trichinellosis infection. If you have eaten raw or undercooked meat, you should tell your health care provider.
Diagnosis & Treatment
A blood test or muscle biopsy can show if you have trichinellosis.
Several safe and effective prescription drugs are available to treat trichinellosis. Treatment should begin as soon as possible and the decision to treat is based upon symptoms, exposure to raw or undercooked meat, and laboratory test results.
Is trichinosis common in the United States?
Infection used to be more common and was usually caused by ingestion of undercooked pork. However, infection is now relatively rare. During 2008–2010, 20 cases were reported per year on average.
The number of cases decreased beginning in the mid-20th century because of legislation prohibiting the feeding of raw-meat garbage to hogs, commercial and home freezing of pork, and the public awareness of the danger of eating raw or undercooked pork products.
Cases are less commonly associated with pork products and more often associated with eating raw or undercooked wild game meats.
The best way to prevent trichinellosis is to cook meat to safe temperatures. A food thermometer should be used to measure the internal temperature of cooked meat. Do not sample meat until it is cooked.
USDA recommends the following for meat preparation:
Foods are fully cooked when they reach these minimum internal temperatures
*Letting whole cuts of meat “rest” refers to the amount of time the product remains at the final temperature, after it has been removed from a grill, oven, or other heat source. When meat is removed from the heat source, for 3 minutes its temperature remains constant, or continues to rise, which destroys pathogens.