Below are 2 articles on parasites found in foods - fruits/vegetables and meats. The study on the fruits & vegetables is limited; regardless, the amount of parasites found should be considered as a good gauge on the prevalence of parasites. We know that Toxoplasma parasites are a huge problem with people who own cats, but  in the below meat article they have been found in raw meats. This suggests to me that people are getting infected by raw foods far more than previously thought, particularly by T. gondii.

DD

http://findarticles.com/p/articles/mi_m0887/is_8_19/ai_64714678

Isolation Of Parasites From Fruits And Vegetables - Brief Article - Statistical Data Included

 August, 2000  by L.J. Robertson,  B. Gjerde

Raw fruits and vegetables are common vehicles for the transmission of parasites. Giardia, Cryptosporidium, Cyclospora, and Ascaris are the most common cause of foodborne infections from fruits and vegetables. This problem is becoming an increasing concern because of the expanding number of susceptible people (i.e., the elderly and the immunocompromised), more extensive produce trade across international borders, and changes in national and international policies concerning food safety.

Despite this problem, published methods on the isolation of parasites from fruits and vegetables are inadequate. With this in mind, two Norwegian researchers recently described a method for isolating Giardia, Cryptosporidium, and Ascaris from various fruits and vegetables, based upon the conventional methods of helminth extraction and the immunomagnetic separation (IMS).

Strawberries, bean sprouts, Chinese leaves, iceberg and green lollo lettuce, and a pre-prepared autumn salad mix were used in the study. Parasite suspensions were added to the fruits and vegetables and subsequently isolated with a washing procedure, and sonication and immunomagnetic separation for Giardia and Cryptosporidium. Immunofluorescence for Giradia and Cryptosporidium and brightfield microscopy for Ascaris was used for identification.

Recovery efficiencies from lettuce, Chinese leaves, and strawberries were found to be approximately 67% for Giardia, 42% for Cryptosporidium, and 72% for Ascaris. The recovery efficiency from bean sprouts was more variable and lower, especially for Giardia cysts. During the longer washing process with larger amounts of debris and cells being removed, there were lower recoveries. Parasites were not detected in any of the control samples that had not been seeded.

This improved technique for recovering parasites from fruits and vegetables exhibited higher recovery efficiencies than previous reported procedures. The improved recovery efficiency for Ascaris eggs is probably due to the washing procedure, while the authors believe that both the washing and the IMS assisted in the improved recovery efficiencies for Giardia and Cryptosporidium. As noted in these results, bean sprouts are a difficult substance to work with as shown by the variable recovery efficiencies. Even though polymerase chain reactions and fluorescent in situ hybridizations are available for use against these parasites, they can not be applied to fruits and vegetables. Therefore, the procedure described could be a useful tool in investigating foodborne outbreaks of parasitic infection.

http://findarticles.com/p/articles/mi_m3741/is_5_50/ai_86506273
 

Defining risk from meatborne parasites - Toxoplasma gondii analysis - Brief Article

Agricultural Research,  May, 2002  by Judy McBride

A single-celled parasite called Toxoplasma gondii likely infects more than 60 million people in the United States, according to the Centers for Disease Control and Prevention. While most of the infected don't have any symptoms, the parasite can cause serious damage in developing fetuses, people with AIDS, and others with compromised immune systems.

A common route of infection is exposure to egglike oocysts in the feces of infected cats. But T. gondii can infect tissues of domestic and wild animals, and people can ingest the parasite by eating or handling raw or undercooked meats, including pork, lamb, or venison. According to rough estimates, about 3 percent of U.S. market-age pigs have T. gondii tissue cysts. But improvements in how swine are fed and housed are reducing exposure.

Still, "it looks like foodborne infection is a major route," says Benjamin M. Rosenthal with the Agricultural Research Service in Beltsville, Maryland. He notes that members of a vegetarian religious denomination living in suburban Maryland were one-half to one-tenth as likely to have been exposed to T. gondii as their neighbors. And a large European study attributed between one- and two-thirds of toxoplasmosis-related birth defects to consumption of undercooked or inadequately cured pork, lamb, or beef. Thorough cooking--to 160-170 [degrees] F--can prevent transmission.

Toxoplasma parasites have close relatives that can also form cysts in the muscles of domesticated animals and primates. These include parasites belonging to the genera Neospora, Hammondia, Besnoitia, and Sarcocystis.

"We know far less about their actual or potential public health risk," says Rosenthal. "These other cyst-forming parasites may contribute to the estimated 86 percent of U.S. foodborne illnesses that currently go undiagnosed." There are many reports of Sarcocystis infection in humans worldwide, he adds, but the animal sources of those infections are poorly defined.

That's why Rosenthal, a molecular systematist, joined ARS' Parasite Biology, Epidemiology, and Systematics Laboratory nearly 3 years ago. He is defining the distribution of these cyst-forming parasites in domestic and wild animals and in people. And he's doing it by looking for variations in their genes.

"You have to know who's who before you can make effective risk assessments," he says.

Until recently, for example, researchers didn't have sensitive tests to diagnose or distinguish Neospora caninum infections from those caused by T. gondii.

"Many of these other parasites also cause miscarriages in cattle, goats, sheep, and nonhuman primates," Rosenthal says. "Do they pose a direct risk to human health? To begin to answer the question, we first have to tell them apart and determine how many species exist. Learning how they are related to one another will help us assess their potential to infect people and cause disease."

Genetic comparisons may also shed light on the evolutionary age of these parasites and the conditions that let them flourish. For instance, there are only three main genotypes of T. gondii worldwide. And there's very little genetic variation within each genotype, which is unusual for such an especially abundant organism.

These facts suggest that T. gondii may have relatively recent evolutionary origins, says Rosenthal, and may have taken advantage of opportunities for transmission that came with the domestication of animals.

"Parasite adaptations to particular agricultural practices may explain why infection with T. gondii is so common in our cats and in certain food animals," he says.

But such a conclusion will rest on a better understanding of the genetic variation of other, related parasites, says Rosenthal. A recent study led by Stanford University scientists may help explain T. gondii's success. The team reported strong evidence that the most virulent of the three genotypes appears to be the offspring of a sexual recombination between the other two.

In this case, it looks like Mother Nature selected a whole new strain rather than selecting by individual gene mutations, says Rosenthal.

With Toxoplasma, he says, "every gene you look at exists in only one or two forms. Is the genetic uniformity of T. gondii extreme when compared to its closest parasitic relatives?"

Rosenthal's research will help answer that question while developing the diagnostic tools necessary to evaluate any food-safety risks posed by these "poorly understood but intriguing parasites and their relatives."

This research is part of Food Safety, an ARS National Program (#108) described on the World Wide Web at http://www.nps.ars.usda.gov.

Benjamin M. Rosenthal is with the USDA-ARS Parasite Biology, Epidemiology, and Systematics Laboratory, Bldg. 1180, 10300 Baltimore Ave., Beltsville, MD 20705-2350; phone (301) 504-5408, fax (301) 504-8979, e-mail brosenth@ anri.barc.usda.gov.

COPYRIGHT 2002 U.S. Government Printing Office
COPYRIGHT 2002 Gale Group