By HowStuffWorks.com for Animal Planet

The parasitic life is all about finding niches in the ecosystem and exploiting them for all they're worth. And after billions of years mucking their way through blood vessels and intestines, you better believe they've gotten rather good at it. Untold billions are clamoring for a chance to get inside you -- and it just so happens that the best way to do that is to stow away in your next meal.

In this article, we're going to take a look at a few menu items with a high probability for parasites. By no means does this mean you're guaranteed a belly full of worms with each one! It's essential to stress that proper food storage, fresh ingredients and sanitary food preparation conditions vastly decrease the chances for food contamination.

So get ready to tuck in your napkin -- and for goodness sake wash your hands -- because we're about to take a close look at what's for dinner.

5. Escargot

If you happen to find the prospect of consuming cooked snails repulsive, then their parasites aren't going to concern you. However, if you're in the opposite camp and can't think of a better conveyance for tasty garlic butter, then you might want to sit down before reading this. Did you know that snails themselves sometimes dine on decaying leaves, fecal matter and carrion? For this reason, one of the first steps in preparing a snail for the dinner table is to clean out its digestive system. Snail farmers often avoid a lot of potential toxicity by raising their livestock on ground cereal.

Think back to that diet -- not the ground cereal, the other stuff. Angiostrongylus cantonensis or rat lungworm frequently set up house in snails and other mollusks thanks to their indiscriminate palates. And since snails are both bottom feeders and tasty treats, they're perfect for transmitting these parasites. Enjoy some undercooked escargot and Angiostrongylus cantonensis might wind up in your brain, resulting in sickness, headache and even meningitis. Additionally, a poorly washed food snail can bring a number of other disease risks straight to your table.

To be fair, however, rat lungworm is common in a number of mollusks, including freshwater snails, slugs, shrimp and crabs. Frogs also play host. As always, the safest move is to err on the side of overcooking your creepy, crawly dinner choice.

4. Sushi and sashimi

The world's oceans are teaming with delicious life forms. The problem is that many of those life forms are home to parasites. You can eliminate the risk of infection by simply cooking your seafood thoroughly. Alternately, you can freeze the fish for a week or cure it in saturated salt brine for five to seven days.

Sadly, each of these techniques can leave sushi enthusiasts in the lurch. The whole point to sushi, after all, is to appreciate the taste and texture of fresh, raw seafood. The two problem worms to consider before dining on uncooked fruit of the sea are the Anisakidae nematode roundworms and the Diphyllobothrium tapeworm.

Of these, the roundworm is the most common. If ingested, you might not even notice it or suffer any symptoms. However, the worm can "tickle" your throat on the way down, and if it bores into your stomach lining, it can cause severe abdominal inflammation and pain within an hour of ingestion. Luckily, these pesky parasites don't survive longer than 10 days in the human digestive track.

The Diphyllobothrium tapeworm is common in salmon, as well as other saltwater fish that also frequent fresh water. These freeloaders can thrive in the human gut for years, causing abdominal pain, weakness, weight loss and anemia. Luckily, they can be eradicated through medical treatment.

To avoid risking a mouthful of spicy nematode roll or tapeworm sashimi, stick to reputable restaurants that follow food safety guidelines. If you're still feeling a bit paranoid, ask whether the fish has been previously frozen or stick to the many sushi options that use cooked or vegetarian ingredients.

3. Steak tartare

What's this, more raw meat? Do you see a pattern forming here? Naturally, steak or lamb tartare can offer an excellent risk for parasitic infection. Not only does the whole dish revolve around raw meat, but many recipes call for the addition of a raw egg as well. While a delectable treat in Asia, Eastern Europe and Ethiopia, all that raw meat serves up the risk for roundworms and the intracellular bacteria parasites salmonella, E. coli and Listeria monocytogenes.

The key here is to order tartare only from a reputable establishment. If you're going to eat it raw, you're going to want a very fresh, certified cut of meat and you're going to want it prepared in a hygienic environment. Some chefs put an emphasis on the use of grass-fed livestock, as the bacteria in grain-fed animals become acclimatized to an acidic environment, preparing them for survival in the human gut. Also, freezing a cut of beef for 14 days should wipe out any parasitic risks.

Steak and lamb tartare dishes (as well as other raw meats) remain a delicacy throughout the world and there's no reason to cease your enjoyment of them. Just exercise a little caution when choosing where you order it.

2. Pink hamburger

Granted, not all hamburgers are created equal. On one end of the spectrum, you have the discs of gray mystery meat grill-flipped by the hundreds at your local fast-food joint. On the other end, you have fancy gourmet burgers ground to order. Somewhere in between, summertime grill masters put the sizzle on some serious beef patties.

But if steak tartare is the classy method of consuming raw beef, then a rare, pink hamburger is generally considered the low-rent option for risking a bun full of E. coli, Listeria monocytogenes or salmonella. Undercooked hamburgers are a major risk factor for E. coli, with the number of outbreaks typically doubling during summer months.

Again, cleanliness and freshness are everything. While you might invite the prospect of a pink center in a $30 gourmet burger, you should send that pinkish fast-food burger back. In addition, a 2008 study published in the Annals of Diagnostic Pathology examined the contents of eight fast-food hamburgers and discovered Sarcocystis parasites in two of them. Unlike other parasites that might be lurking in a pink hamburger, Sarcocystis is usually asymptomatic.

1. Ham and pork sandwiches

Interestingly enough, one of the more statistically risky menu items isn't even raw. The USDA, FDA and Centers for Disease Control and Prevention rank simple deli meat right at the top of their lists for Listeria monocytogenes infection. These meats often feature extended refrigerated storage times, during which L. monocytogenes has adequate time to thrive. The lesson here is to use fresh deli meat and only frequent sandwich shops that are going to do the same.

Pork poses a host of other parasitic risks as well if undercooked or poorly stored. Pork tapeworms pose a severe threat in that they sometimes spread to a host's eyes, spine or brain with potentially fatal results. A Trichinella worm infection offers a similar array of dire symptoms, ranging from nausea, diarrhea, vomiting, fatigue and fever to muscle pain, chills, heart problems and even death. So when considering that roadside barbecue purchase or vending machine ham sandwich, exercise a little caution. You might spare yourself a whole lot of parasites.

Again, you can't beat cleanliness and fresh ingredients when choosing a restaurant. When all else fails, order it well done.

Roundworm, also nematode, common name for any of a phylum of unsegmented terrestrial, freshwater, or marine worms. Roundworms are almost worldwide in distribution and are abundant in the surface layers of soils. Many of them are economically and medically harmful, living as parasites in plants and animals, including humans. Roundworm infections are common and frequently go unnoticed, but several species cause serious diseases.

Roundworms are cylindrical, tapering animals with simple bodies consisting of an interior gut and a muscular outer wall, separated by a fluid-filled cavity called a pseudocoel. The outer wall secretes an elastic cuticle that is molted four times during the animal's lifetime. Species range in size from microscopic to about 10 cm (about 4 in) long. Most species have separate sexes, but a few are hermaphroditic; fertilization is internal. The young roundworms, which resemble the adults, develop without metamorphosis.

Classification of the approximately 12,000 known species of roundworms—many thousands of unknown species are suspected—is a subject of some controversy among zoologists. Many include the Gordian worms (see Horsehair Worm) as a subclass, but others group them separately. Although numerous roundworms are free-living, the parasitic forms are of greatest economic interest. One important group, the ascaroid nematodes, includes the threadworms and the common worm of puppies. Another contains the eelworms, which produce root knot of cotton, and forms that produce earcockle of wheat. Other, medically significant forms of roundworm include the various genera known as hookworm; the filaria, which cause elephantiasis; the trichina worm, the cause of trichinosis; and the whipworm, which infests the human intestine.

Tapeworm, common name for intestinal parasite of vertebrate animals (see Parasite). Tapeworms are flattened worms ranging in length from about 13 mm (about 0.5 in) to about 9 m (about 30 ft). The adult tapeworm is characterized by the presence of a head, or scolex, equipped with a crown of hooklets for attachment to the intestinal lining of its host. At the rear end of the scolex is a narrow neck, from which body segments, or proglottids, are budded off asexually. Tapeworms may have as few as three or as many as several thousand proglottids. The proglottids contain organs of sexual reproduction, each with both testes and ovaries; the segments farthest from the head mature most rapidly and, when ripe, separate from the main body of the worm and pass out with the feces of the host animal. These newly detached proglottids contain numerous eggs, and each egg contains an embryonic tapeworm.

When the living segment is ingested by another primary host, the proglottids regenerate a new scolex, which attaches itself to the intestinal wall, and the tapeworm resumes its growth by budding. When eggs are ingested, they hatch in the intestinal tract and release larval forms, which burrow into the tissues of the host and form cysts (see Cyst). These encysted forms are known by such names as bladder worms, cycticerci, hydatids, and measles; the host harboring this stage is known as an intermediate host, in contrast to the primary host, in which the tapeworm seeks the alimentary canal and develops there. The larvae often exhibit specific selection of tissues in encysting; for example, one species attacks the liver in humans and dogs, whereas another attacks the brain in sheep, causing the disease known as gid or staggers. When larvae are ingested by a primary host, usually in the form of encysted meat of the intermediate host, they are stimulated by the gastric juice to develop into adult tapeworms. The adults attach themselves to the intestinal wall and absorb partially digested food through their body surface; tapeworms have no mouths or digestive canals.

Several vermifuges, poisonous worm-killing substances, are effective in proper dosages in treating tapeworm infestation. Unless the scolex is dislodged, the worm is not eradicated.

Scientific classification: Tapeworms make up the class Cestoda. The tapeworm larva that attacks the liver in humans and dogs is classified as Taenia echinococcus. The tapeworm larva that attacks the brain in sheep is classified as Taenia coenurus.

Salmonella, genus of infectious bacteria, named for the American veterinarian Daniel Elmer Salmon, who first isolated it in 1885. The organism is transmitted through contaminated poultry, eggs, and certain other foods. Three species are recognized: Salmonella typhi;S. choleraesuis; and S. enteriditis, which has more than 1400 antigenically distinct serotypes. S. typhi produces typhoid fever. S. typhimurium, a serotype of S. enteriditis, causes salmonella gastroenteritis, a type of food poisoning characterized by abdominal pain, fever, nausea and vomiting, and diarrhea. The incubation period is 8 to 48 hours, and an attack may last from three to seven days. Mild cases usually are treated with antidiarrheal remedies; more severe cases require antibiotics. Careful cleaning and thorough cooking of food prevent salmonella infections.

Escherichia coli, commonly known as E. coli, is a species of bacteria normally present in human intestines. One strain, E. coli 0157:H7, produces high levels of toxins that can cause kidney damage, as well as septicemia, or blood poisoning. Symptoms can include diarrhea, chills, headaches, and high fever, and in some cases the infection can lead to death, even with medical intervention. Illness from E. coli may develop from consuming undercooked beef, unpasteurized milk, or from handling food without washing hands after changing diapers. Although E. coli is normally present in the human intestines, the variant E. coli O157:H7 produces toxins that cause bloody diarrhea and, in some cases, far more severe problems, including kidney failure and death. A person can become infected by eating contaminated meat. Thorough cooking kills the bacteria.

Listeria monocytogenes, which can cause septicemia, meningitis, and stillbirth, kills up to one-third of the people infected and most often results from unsanitary commercial processing of dairy, poultry, and meat products—including pizza toppings.

Trichinosis, common name applied to a disease of rats, swine, bears, cats, dogs, and humans, caused by infection with the larvae of a parasitic nematode roundworm, the trichina worm, Trichinella spiralis. The minute trichina worm is almost worldwide in distribution.

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