When the University of Florida’s Emerging Pathogens Institute (EPI) released a report on April 28 ranking the microorganisms that cause the greatest burden to U.S. public health, many familiar names claimed spots in the top 10: Salmonella, Campylobacter and Listeria monocytogenes all enjoyed prominent ranking, while Clostridium perfringens and E. coli O157:H7 were not far behind.


The pathogen ranked as the second most burdensome, however, lacks comparable name recognition.

Toxoplasma gondii is a parasitic pathogen estimated to cost Americans nearly $3 billion in medical harm each year — outranked in costliness and annual deaths only by Salmonella — though it receives considerably less media attention than its illness-inducing counterparts.

While it’s most commonly known as a danger when handling the feces or litter of cats that eat wild animals, the parasite is also transmitted to humans via raw or undercooked meats — historically pork and beef.

The Centers for Disease Control and Prevention (CDC) estimates that 22.5 percent of the U.S. population over 12 years old has been infected with Toxoplasma at some point, with half of those infections coming from food. Most healthy individuals infected by the parasite never show symptoms, which typically appear in people with weakened immune systems or newborns whose mothers became infected during their pregnancy.

In developing fetuses, Toxoplasma can cause permanent mental and physical disabilities, and it’s linked to an average of 16 stillbirths and infant deaths each year. When otherwise healthy people show symptoms of infection, they usually arise as mild headaches, muscle aches and fevers, each of which can persist for weeks. People with compromised immune systems, such as those who are HIV positive, can suffer effects such as confusion, seizures and blurred vision.

The EPI report links Toxoplasma to an estimated 86,686 illnesses a year, resulting in 4,428 hospitalizations and 327 deaths. By comparison, Salmonella sickens 1,027,561 people annually, with 19,336 hospitalizations and 378 deaths. E. coli O157:H7 sickens 63,153, hospitalizes 2,138, and kills 20.


The data cited in the report does not measure the demographics of those who die from food poisoning, but individuals with severely compromised immune systems likely make up the vast majority of Toxoplasma deaths, said Michael Batz, Ph.D., lead author of the report and head of Food Safety Programs at the EPI.

Because Toxoplasma is a parasite as opposed to a virus or bacterium, it does not lead to outbreaks the way more prominent foodborne pathogens do, which could help explain why it receives less attention, Batz said

“The news media respond to large outbreaks, but those represent a comparably small number of foodborne illnesses,” he said. “If you were to actually compare the total number of illness cases to just the number of outbreak cases, you’d probably end up with an estimate of hundreds of illnesses out there for each outbreak case.”

Toxoplasma can remain latent in humans for years without developing into an illness, until their immune systems significantly weaken, or it can result in an unexpected miscarriage in pregnant women who don’t show symptoms. These low-profile impacts, Batz said, grant it a status as a “silent killer.”

In the EPI report’s list of the top 10 most burdensome food and pathogen combinations, Toxoplasma and pork ranked second behind Campylobacter and poultry, while Toxoplasma and beef tied for eighth place with Salmonella and produce. Toxoplasma has been linked to an estimated 41 percent of pork-related and 23 percent of beef-related illnesses.

Batz said he thinks the government and meat producers should direct more energy toward reducing the risk of Toxoplasma infections, starting by investing in studies that improve knowledge of the parasite’s sources and the full extent of its impact on public health. He also emphasized increasing education about Toxoplasma, particularly in regard to extra precautions during pregnancies.

“I don’t know how accurate the estimates of congenital Toxoplasma infections are, but for me the concern is: Is the necessary information out there?” Batz said. “Pregnant women hear about it in cats and cat litter, so should they also be hearing about it in regard to handling beef?”

In recent years, incidences of Toxoplasma in pork have declined while its presence has increased in other foods overall. The EPI report cited a 2009 CDC study that found the current leading foodborne risks for Toxoplasma to be raw ground beef, rare lamb and locally produced cured, dried or smoked meats. The study also linked Toxoplasma to drinking raw goat’s milk, eating raw shellfish and handling wild game.

To reduce the risk of Toxoplasma and other foodborne infections, the CDC recommends cooking meat to the recommended internal cooking temperatures, freezing meat to sub-zero temperatures before cooking, and washing hands and utensils with hot, soapy water after contact with raw meats and unwashed produce.

In addition, the Mayo Clinic recommends wearing gloves while gardening and avoiding raw milk.


Image of Toxoplasma gondii oocysts under UV fluorescence microscopy from CDC’s DPDx Image Library.

  • Doc Mudd

    The Mayo Clinic further recommends
    “Wash or peel all fruits and vegetables. If possible, use a vegetable soap to wash fruits and vegetables, especially if you’re eating them raw. Otherwise, scrub them carefully.”
    Toxoplasma organisms are voided from infected animals in feces.
    Manure used as soil amendment and manure deposited by grazing animals in organic farming is a potent source of toxoplasma, as is any residual dirt on vegetables.
    Toxoplasma is only one of a myriad of organisms, good and bad, populating soils managed organically – the mantra of organic is “living soil” teeming with every sort of organism…including toxoplasma. It poses a deadly risk to unborn children.
    Toxoplasmsis was ranked by the Florida study as the #2 food borne cause of death! Women of child bearing age can be dangerously exposed to toxoplasma from raw vegetables and leafy greens or by indirect contact with organic soils.

  • Kate

    Can one be tested for this parasite?

  • jandrews

    Kate: Yes, there are blood tests that can screen for antibodies to Toxoplasma. Here’s some information on it: http://www.mayoclinic.com/health/toxoplasmosis/DS00510/DSECTION=tests-and-diagnosis

  • Michael Bulger

    Toxoplasma was ranked #2 in this study in association with pork. Beef and toxoplasma ranked #8. Vegetables and leafy greens (produce) and toxoplasma did not rank in the top ten. Soil-borne toxoplasma was not studied.
    The experts estimated that toxoplasma transmitted via produce accounts for approx. 7% of toxoplasmosis cases. How many of these come from Organic produce and how many from conventional? They did not offer any estimates.
    Whatever the numbers are, they are too high. One illness is too many. This is one of the reasons the National Organic Program has controls that are designed to prevent pathogens from transferring to edible crops. In the case of compost, Organic standards require that the compost reach an internal temperature high enough, and for a long enough time, to kill human pathogens.
    I came across a study which asserted that toxoplasma might survive in soil longer than the 90-120 day period that the NOSB mandates between raw manure application and harvesting. But…Here’s the kicker:
    Conventional farmers also use lots of manure, and they lack the regulatory oversight for food safety that organic farmers are required to obtain.
    So certainly, a serious look has to be taken as to whether or not raw manure is contaminating produce in the field. However, it would be a grave mistake to overlook conventional agriculture and focus on organic. At least in theory, the 90-120 day period would make organic produce a safer bet than unregulated conventional produce.

  • James Andrews

    Kate: Yes, there are blood tests that can screen for antibodies to Toxoplasma. Here’s some information on it: http://www.mayoclinic.com/health/toxoplasmosis/DS00510/DSECTION=tests-and-diagnosis