What is Toxoplasma gondii?


Toxoplasma gondii.  What do we know about this parasite and the illness it causes?



In March, FSIS announce a proposed rule that in the words of FSIS “consolidate and streamline existing regulations in meat and poultry products.”  The title, Draft Compliance Guideline for the Prevention and Control of Trichinella and other Parasitic Hazards in Pork and Products Containing Pork.  Although this is just a proposal, with regards to trichinella, a clarification here is a welcome one.  Control of this parasite needs to be either by regulation or by the FSIS establishment addressing it their HACCP analysis.  This Draft Guidance proposes the latter.


The proposed rule focuses almost entirely on Trichinella.  At the end of the document the agency states that establishments in their hazard analysis must also consider other protozoan parasites.  The discussion at the end of the document regarding other parasites is almost entirely about Toxoplasma gondii.  What do we know about this parasite and the illness it causes?


According to Scallan, et.al., reviewing foodborne illness data covering the years 2000-2008, it was estimated that the foods consumed in the United States that were contaminated with 31 known agents of foodborne disease caused 9.4 million illnesses, 55,961 hospitalizations, and 1,351 deaths each year. Norovirus caused the most illnesses; nontyphoidal Salmonella spp., norovirus, Campylobacter spp., and T. gondii caused the most hospitalizations; and nontyphoidal Salmonella spp., T. gondii, L. monocytogenes, and norovirus caused the most deaths.  Scallon, et. al. used the U.S. population in 2006 (299 million persons) for its basis.


How do people get toxoplasmosis?


According to the CDC, a Toxoplasma infection occurs by:


·       Eating undercooked, contaminated meat (especially pork, lamb, and venison).


·       Accidental ingestion of undercooked, contaminated meat after handling it and not washing hands thoroughly (Toxoplasma cannot be absorbed through intact skin).


·       Eating food that was contaminated by knives, utensils, cutting boards and other foods that have had contact with raw, contaminated meat.


·       Drinking water contaminated with Toxoplasma gondii.


·       Accidentally swallowing the parasite through contact with cat feces that contain Toxoplasma. This might happen by


1.  cleaning a cat's litter box when the cat has shed Toxoplasma in its feces


2.  touching or ingesting anything that has come into contact with cat feces that contain Toxoplasma


3.  accidentally ingesting contaminated soil (e.g., not washing hands after gardening or eating unwashed fruits or vegetables from a garden)


·       Mother-to-child (congenital) transmission.


·       Receiving an infected organ transplant or infected blood via transfusion, though this is rare.


Who is at risk for developing severe toxoplasmosis?


People who are most likely to develop severe toxoplasmosis include:


·       Infants born to mothers who are newly infected with Toxoplasma gondii during or just before pregnancy.


·       Persons with severely weakened immune systems, such as individuals with AIDS, those taking certain types of chemotherapy, and those who have recently received an organ transplant.


How does this all relate to the meat industry and in particular FSIS inspected establishments and their HACCP plans?


Epidemiologic data suggest that most pigs become infected after birth, either from the ingestion of oocysts in feed and water contaminated with infected cat feces, or by eating tissue cysts from animals. Based on the existing information, it is reasonable to assume that pigs raised in total enclosed environmentally regulated buildings in the absence of cats are least likely to have T. gondii. However, risk factors for Toxoplasma infection in swine herds are not yet well defined. Until more definitive information becomes available, the following practices are recommended to reduce toxoplasmosis in swine:


  • Keep cats out of the swine barns, feed, and water.
  • Remove dead pigs immediately to prevent cannibalism.
  • Rodents should be controlled by rodenticides, not by cats.


·         Never feed uncooked garbage to pigs.




According to the Ontario ministry, food and rural affairs


Pre-slaughter (on-farm)


On-farm control is the first key step in toxoplasmosis prevention. Epidemiological data suggest that most pigs become infected after birth, either from ingesting oocysts in feed and water contaminated with infected cat feces, or by eating tissue cysts from rodents, wild animals and birds. Raising pigs that are free from T. gondii is possible if the following good production practices are followed.


  • Keep cats out of the swine facilities and ensure cat feces do not contaminate feed and water. If cats are kept on the farm, a stable, mature population might be safe. Currently, vaccines for T. gondii control are not commonly available.
  • Adopt an effective rodent control program to minimize mouse and rat populations.
  • Tighten biosecurity programs to keep wildlife, such as birds, skunks and raccoons, from accessing pigs and facilities. Pigs raised in hoop structures or outdoors are at high risk of infection due to the easy access to barns by wild animals and birds.
  • Never feed edible residual material (ERM) containing meat products.
  • Remove dead pigs immediately to prevent cannibalism.
  • Change or thoroughly wash boots before entering barns to avoid tracking in oocysts that have been shed by feral cats in the environment surrounding the barns.


Ensure proper procedures for any on-farm composting of dead pigs to ensure the activity does not attract cats or rodents.


For pork producers, keeping cats out of the swine facilities and strictly following biosecurity and rodent control programs are key measures to take for effective control of T. gondii.


According to the National Pork Board:


A survey of major commodity meats in the retail meat cases of a representative sample of major U.S. metropolitan areas found that viable Toxoplasma was present in 0.38% of pork samples.  No viable Toxoplasma was found in beef or chicken, but up to 1.3% of chickens were found to have been exposed to the parasite.  It is likely that freezing of chicken is responsible for inactivating the parasite before it reaches the consumer.  Given that consumers of fresh meat are provided with guidance on cooking, coupled with the low prevalence of viable Toxoplasma in retail pork, the risk to consumers from eating pork can be estimated to be quite low.


Furthermore, the National Pork Board reported a 6.02% prevalence of T. gondii in sows and in 2006 reported 2.6% in market hogs.


So, is this a hazard reasonably likely to occur in a pork processing establishment?  Since hazard analysis should always be specific to each operation, there is no definitive answer.  However, if in your HACCP plan you name Trichinella as reasonably likely to occur, it is probably prudent to do the same with Toxoplasma; since the same interventions are effective against each parasite.




Scallan E, Hoekstra RM, Angulo FJ, Tauxe RV, Widdowson M-A, Roy SL, et al. Foodborne illness acquired in the United States—major pathogens. Emerg Infect Dis [serial on the Internet]. 2011 Jan [date cited]. http://dx.doi.org/10.3201/eid1701.P11101


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