Parasites and Viruses

Bacteria cause most foodborne illness. However, parasites and viruses—other tiny organisms that contaminate food—are culprits, too. Parasites such as Trichinella spiralis, Toxoplasma gondii, Cryptosporidium parvum, Entamoeba histolytica, and Giardia lamblia survive by drawing on the nutrients of a living host. Viruses such as hepatitis A and Calcivirus, or Norwalk-like virus, act like parasites. Through the food chain, parasites and viruses can infect humans.

Trichinosis is contracted by consuming under-cooked pork or game that has been infested with trichina larvae. With careful controls in the food industry, trichinosis is much less common today. However, still cook pork, game, and other meat to the recommended internal temperature to destroy any live trichina larvae. See "Safe Internal Temperatures."

Toxoplasmosis is caused by a parasite indirectly linked to raw and undercooked meat or poultry, unwashed fruits and vegetables, and contaminated water. It's also directly transferred to humans from cat feces. Pregnant women are at special risk because they can pass the parasite to their unborn baby. The disease can severely affect the central nervous system, causing mental impairment and visual disorders. To combat this parasite, cook meat, especially pork, lamb, and poultry, thoroughly. For pregnant women, avoid handling a cat's litter box; have it cleaned daily. Keep your cat indoors. If you do handle cats, wash your hands well with soap and water.

Cryptosporidium, traditionally linked to travelers' diarrhea in developing nations, has become a more common parasitic illness in the United States. It enters

  • if you need to be concerned about "red tide"? No, unless you harvest your own shellfish. "Red tide" happens when marine algae are in a time of excessive growth. That's when they produce shellfish toxins that may cause illness. These areas are carefully monitored to protect the shellfish supply. Heed "red tide" warnings issued by local authorities if you harvest your own shellfish.
  • if mercury in seafood is risky? Mercury is naturally present in all living things as well as in soil, air, and water. Pollution also releases into the air mercury that falls into water or on land, then washes into lakes, rivers, and oceans. Bacteria in water change mercury to methyl mercury, which is toxic. Over time methyl mercury can build up in long-lived larger fish.

Because methyl mercury is a potential risk to the developing nervous system of the fetus or the child, the U.S. Food and Drug Administration (FDA) and the Environmental Protection Agency advise: Women who are pregnant or who might become pregnant and nursing mothers should avoid eating shark, swordfish, king mackerel, and tilefish. Eat up to 12 ounces (2 average meals) a week of a variety of fish, lower in mercury (for example, shrimp, canned light tuna, salmon, pollock, and catfish), that can include up to 6 ounces of albacore ("white") tuna. Check local fishing advisories about fish you catch. No advice? You can eat up to 6 ounces of locally caught fish, if that's all the fish you eat that week. This advice also applies to young children, but serve smaller portions. Note: Fish in fish sticks and "fast-food" sandwiches are usually made with fish that is low in mercury.

. . . if your food is safe from "mad cow disease" and "foot-and-mouth" disease? These are different diseases. Although foot-and-mouth disease (FMD) is highly contagious among livestock and is economically disastrous, it poses no human risk, and FMD hasn't been found in U.S. livestock for about 75 years. Because travelers who visit agricultural areas can bring it back, the government prohibits import of agricultural products by people entering the United States who've been on a farm abroad or in contact with livestock abroad, and inspects their baggage. Before returning to the United States from FMD-infected areas, the U.S. Department of Agriculture (USDA) advises: Avoid agricultural areas five days before returning to the United States; clean and disinfect footwear with detergent and bleach; wash or dry-clean clothing; and avoid contact with livestock or wildlife for five days after returning to the United States. As other safety measures, the USDA regularly monitors U.S. cattle herds and has banned animals and animal products from infected areas. Note: FMD is different from hand, foot, and mouth disease (HFMD), common among infants and children.

"Mad cow disease," or bovine spongiform encephalopathy (BSE), affects the nervous system in cattle; it may be linked to a brain-wasting illness in humans known as Creutzfeldt-Jakob disease. To protect the U.S. food supply, government regulations have imposed import bans to make sure no live cattle or products from these animals are imported from areas where BSE is known to exist or is at risk, a ban on most mammalian protein in cattle feed, and a USDA surveillance program. Since 2004, FDA and, similarly, USDA regulations exclude potentially risky cattle products from human food, dietary supplements, and cosmetics. No research indicates that BSE is transmitted to cow milk. If you travel to Europe, where BSE is known to exist, your risk for getting this disease is very small, according to the National Institutes of Health. If you're concerned, however, avoid beef or beef products, or eat only solid pieces of meat rather than ground-beef products such as burgers or sausage when you travel there.

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