Food-borne Illnesses Table: Parasitic Agents

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Incubation Period

Signs and Symptoms

Duration of Illness

Associated Foods

Laboratory Testing


Cryptosporidium parvum

7 days average (2-28 days)

Cramping, abdominal pain; watery diarrhea; fever and vomiting may be present and may be relapsing.

Days to weeks

Contaminated water supply, vegetables, fruits, unpasteurized milk.

Must be specifically requested. May need to examine water or food.

Supportive care, self-limited. If severe consider paromomycin for 7 days

Cyclospora cayetanensis

1-11 days

Fatigue, protracted diarrhea, often relapsing.

May be protracted (several weeks to several months)

Imported berries, contaminated water, lettuce.

Request specific examination of the stool for Cyclospora.   May need to examine water or food.

TMP-SMX for 7 days

Entoamoeba histolytica

2-3 days to 1-4 weeks

Bloody diarrhea, frequent bowel movements (looks like Shigella), lower abdominal pain.


Fecal-oral; may contaminate water and food.

Examination of stool for cysts and parasites – at least 3 samples. Serology for long-term infections.

Metronidazole and iodoquinol

Giardia lamblia

1-4 weeks

Acute or chronic diarrhea, flatulence, bloating.


Drinking water, other food sources.

Examination for ova and parasites – at least 3 samples.


Toxoplasma gondii

6-10 days

Generally asymptomatic, 20% may develop cervical lymphadenopathy and/or a flu-like illness.
In immunocompro-mized patients:  central nervous system (CNS) disease, myocarditis, or pneumonitis is often seen.


Accidental ingestion of contaminated substances (e.g.. putting hands in mouth after gardening or cleaning cat litter box); Raw or partly cooked pork, lamb, or venison.

Isolation of parasites from blood or other body fluids; observation of parasites in patient specimens, such as bronchoalveolar lavage material or lymph node biopsy. Detection of organisms is rare, but serology can be a useful adjunct in diagnosing toxoplasmosis. Toxoplasma-specific IgM antibodies should be confirmed by a reference laboratory. However, IgM antibodies may persist for 6-18 months and thus may not necessarily indicate recent infection.
For congenital infection:
  isolation of T. gondii from placenta, umbilical cord, or infant blood. PCR of white blood cells, CSF, or amniotic fluid (reference laboratory). IgM and IgA serology (reference laboratory).

Asymptomatic healthy, but infected, persons do not require treatment. Spiramycin or pyrimethamine plus sulfadiazine may be used for immunocompromized persons or pregnant women, in specific cases.

Toxoplasma gondii  (congenital infection)

In infants at birth

Treatment of the mother may reduce severity and/or incidence of congenital infection. Most infected infants have few symptoms at birth, but will generally develop signs of congenital toxoplasmosis (mental retardation, severely impaired eyesight, cerebral palsy, seizures) later, unless the infection is treated.

Passed from mother (who acquired acute infection during pregnancy) to child.

Trichinella spiralis

1-2 days to 2-8 weeks

Nausea, vomiting, diarrhea, abdominal discomfort followed by fever, myalgias, periorbital edema.


Raw or undercooked contaminated meat, usually pork or wild game meat, e.g., bear or moose.

Positive serology or demonstration of larvae via muscle biopsy. Increase in eosinophils.

Supportive care + mebendazole.


Incubation Period

Signs and Symptoms

Duration of Illness

Associated Foods

Laboratory Testing