The risk of contracting the brain parasite toxoplasma from kitty litter vs. meat.
How to Prevent Toxoplasmosis
Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.
The brain parasite toxoplasma “is responsible for considerable disease and death in the United States.” It is the second leading cause of foodborne-related death in the U.S., after Salmonella. It can invade through the placenta, so can be especially devastating during pregnancy, leading to miscarriages, or blindness, or developmental delay. It can impair cognitive function in adults too, which explains why those who are infected appear to be at increased risk for getting into things like traffic accidents. “Multiple lines of evidence indicate that chronic [toxoplasma] infections “are likely associated with certain psychiatric disorders.” It may even increase the risk of developing leukemia. Okay, okay; how do you prevent it?
Well, the parasite can get into the muscles. So, from food-animals, people can get it “through meat consumption.” But in “a non-food animal like a cat,” you get infected through contact with feces. Thankfully, in cats, the “danger of infection exists only when the animal is actively shedding [the parasite.]” They get it from eating infected rodents. And so, cats that are kept indoors, that don’t hunt, and are not fed raw meat shouldn’t pose a threat—though if feral cats are turning your local playground sandbox into a litter box, that could be a problem. As many as 6 percent of stray cats or those with outdoor access may be actively infected at any one time. They only shed the parasite for a few weeks, though. So, if you adopt a cat at a shelter, it should be safe as long as they didn’t just come in.
Many women have heard about the cat connection, but may be less aware of the risk of foodborne infection. “Only [about one in three] may be aware that [toxoplasma] may be found in raw or undercooked meat. Nevertheless, a high percentage of women indicated that they do…[try to] practice good [hygiene]…such as washing their hands after handling raw meat, gardening [where cats may be pooping,] or changing cat litter.”
What’s the riskiest type of meat? “Cattle are not considered important hosts for [the parasite;]” it’s more pigs and poultry, as well as sheep and goats. The prevalence of infection among factory-farmed pigs varies from 0 to over 90 percent, though, ironically, the likelihood of toxo infection in organic meat may be higher because the animals have outdoor access.
Who undercooks pork and poultry, though? Surprisingly, about one in three Americans may undercook meat across the board, in terms of reaching necessary pathogen-killing temperatures, and a single slice of ham can end up with more than a thousand parasites per slice.
Current meat inspection at the slaughterhouse can’t detect them. There are tests you can do, but there is no widespread testing. The risk from a single serving of meat, though, is really small. The average probability of infection per serving of lamb, for example, was estimated to be 1 in like 67,000. The reason there are 16 times the number of cases attributed to pork is not because pigs are more affected; in the U.S., we just happen to eat a lot more pork chops than lamb chops.
Is there anything we can do if we’re one of the approximately one in four Americans already infected? Well, one of the problems with having these parasites in our brain is accelerated cognitive decline as we age. This study evaluated older adults every year for five years, and the executive function of those testing positive for toxoplasma seemed to drop quicker over time, as did a measure of their overall mental status.
Another thing that’s associated with cognitive decline is reduced folate availability, and the two may actually be related, as recent evidence suggests that toxoplasma may harvest folate directly from our nerve cells, sucking up folate from our brain. So, beyond dopamine production, which is why we think toxo increases the risk of schizophrenia, the parasite may be sucking folate out of our brain. But enough to affect our cognitive functioning? Perhaps so. Here’s a measure of cognitive function across a range of folate concentrations. Among those uninfected, it doesn’t seem to matter whether they have lots of folate or little. They obviously have enough either way. But those who are infected have worse scores at lower levels (higher is worse on this test). The same thing with vitamin B12. So, it’s important to get enough B12 and folate. For B12, the official recommendation is that all people aged 50 or over start taking a vitamin B12 supplement, or eat vitamin B12-fortified foods every day. And, anyone on a plant-based diet should start taking that advice at any age. And folate is found concentrated in beans and greens. So, following my Daily Dozen recommendations will get you more than enough, as, for example, a half-cup of cooked lentils gets you half the way there, as does three-quarters of a cup of cooked spinach.
Please consider volunteering to help out on the site.
- Jones JL, Kruszon-moran D, Wilson M, Mcquillan G, Navin T, Mcauley JB. Toxoplasma gondii infection in the United States: seroprevalence and risk factors. Am J Epidemiol. 2001;154(4):357-65.
- Lilly EL, Wortham CD. High prevalence of Toxoplasma gondii oocyst shedding in stray and pet cats (Felis catus) in Virginia, United States. Parasit Vectors. 2013;6:266.
- Jones JL, Ogunmodede F, Scheftel J, et al. Toxoplasmosis-related knowledge and practices among pregnant women in the United States. Infect Dis Obstet Gynecol. 2003;11(3):139-45.
- Huang Y, Huang Y, Chang A, Wang J, Zeng X, Wu J. Is Toxoplasma Gondii Infection a Risk Factor for Leukemia? An Evidence-Based Meta-Analysis. Med Sci Monit. 2016;22:1547-52.
- Jones JL, Parise ME, Fiore AE. Neglected parasitic infections in the United States: toxoplasmosis. Am J Trop Med Hyg. 2014;90(5):794-9.
- Herrero L, Gracia MJ, Pérez-arquillué C, Lázaro R, Herrera A, Bayarri S. Toxoplasma gondii in raw and dry-cured ham: The influence of the curing process. Food Microbiol. 2017;65:213-220.
- Guo M, Mishra A, Buchanan RL, et al. A Systematic Meta-Analysis of Toxoplasma gondii Prevalence in Food Animals in the United States. Foodborne Pathog Dis. 2016;13(3):109-18.
- Yan C, Liang LJ, Zheng KY, Zhu XQ. Impact of environmental factors on the emergence, transmission and distribution of Toxoplasma gondii. Parasit Vectors. 2016;9:137.
- Purslow P. Parasitic zoonoses present some risks with low-temperature cooking of pork. Meat Sci. 2016;119:14-5.
- Hussain MA, Stitt V, Szabo EA, Nelan B. Toxoplasma gondii in the Food Supply. Pathogens. 2017;6(2).
- Guo M, Dubey JP, Hill D, et al. Prevalence and risk factors for Toxoplasma gondii infection in meat animals and meat products destined for human consumption. J Food Prot. 2015;78(2):457-76.
- Guo M, Buchanan RL, Dubey JP, et al. Qualitative Assessment for Toxoplasma gondii Exposure Risk Associated with Meat Products in the United States. J Food Prot. 2015;78(12):2207-19.
- Guo M, Mishra A, Buchanan RL, et al. Quantifying the Risk of Human Toxoplasma gondii Infection Due to Consumption of Domestically Produced Lamb in the United States. J Food Prot. 2016;79(7):1181-7.
- Herrero L, Gracia MJ, Pérez-arquillué C, et al. Toxoplasma gondii: Pig seroprevalence, associated risk factors and viability in fresh pork meat. Vet Parasitol. 2016;224:52-59.
- Berrett AN, Gale SD, Erickson LD, Brown BL, Hedges DW. Toxoplasma Gondii Moderates the Association between Multiple Folate-Cycle Factors and Cognitive Function in U.S. Adults. Nutrients. 2017;9(6).
- Nimgaonkar VL, Yolken RH, Wang T, et al. Temporal Cognitive Decline Associated With Exposure to Infectious Agents in a Population-based, Aging Cohort. Alzheimer Dis Assoc Disord. 2016;30(3):216-22.
- Flegr J. Influence of latent Toxoplasma infection on human personality, physiology and morphology: pros and cons of the Toxoplasma-human model in studying the manipulation hypothesis. J Exp Biol. 2013;216(Pt 1):127-33.
- 9: Vitamin B12. In: Dietary Reference Intakes For Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, And Choline. Washington, D.C.: National Academies Press; 1998.
- Arora N, Sadovsky Y, Dermody TS, Coyne CB. Microbial Vertical Transmission during Human Pregnancy. Cell Host Microbe. 2017;21(5):561-567.
Image credit: Herk3 via wikimedia. Image has been modified.
Motion graphics by Avocado Video
Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.
The brain parasite toxoplasma “is responsible for considerable disease and death in the United States.” It is the second leading cause of foodborne-related death in the U.S., after Salmonella. It can invade through the placenta, so can be especially devastating during pregnancy, leading to miscarriages, or blindness, or developmental delay. It can impair cognitive function in adults too, which explains why those who are infected appear to be at increased risk for getting into things like traffic accidents. “Multiple lines of evidence indicate that chronic [toxoplasma] infections “are likely associated with certain psychiatric disorders.” It may even increase the risk of developing leukemia. Okay, okay; how do you prevent it?
Well, the parasite can get into the muscles. So, from food-animals, people can get it “through meat consumption.” But in “a non-food animal like a cat,” you get infected through contact with feces. Thankfully, in cats, the “danger of infection exists only when the animal is actively shedding [the parasite.]” They get it from eating infected rodents. And so, cats that are kept indoors, that don’t hunt, and are not fed raw meat shouldn’t pose a threat—though if feral cats are turning your local playground sandbox into a litter box, that could be a problem. As many as 6 percent of stray cats or those with outdoor access may be actively infected at any one time. They only shed the parasite for a few weeks, though. So, if you adopt a cat at a shelter, it should be safe as long as they didn’t just come in.
Many women have heard about the cat connection, but may be less aware of the risk of foodborne infection. “Only [about one in three] may be aware that [toxoplasma] may be found in raw or undercooked meat. Nevertheless, a high percentage of women indicated that they do…[try to] practice good [hygiene]…such as washing their hands after handling raw meat, gardening [where cats may be pooping,] or changing cat litter.”
What’s the riskiest type of meat? “Cattle are not considered important hosts for [the parasite;]” it’s more pigs and poultry, as well as sheep and goats. The prevalence of infection among factory-farmed pigs varies from 0 to over 90 percent, though, ironically, the likelihood of toxo infection in organic meat may be higher because the animals have outdoor access.
Who undercooks pork and poultry, though? Surprisingly, about one in three Americans may undercook meat across the board, in terms of reaching necessary pathogen-killing temperatures, and a single slice of ham can end up with more than a thousand parasites per slice.
Current meat inspection at the slaughterhouse can’t detect them. There are tests you can do, but there is no widespread testing. The risk from a single serving of meat, though, is really small. The average probability of infection per serving of lamb, for example, was estimated to be 1 in like 67,000. The reason there are 16 times the number of cases attributed to pork is not because pigs are more affected; in the U.S., we just happen to eat a lot more pork chops than lamb chops.
Is there anything we can do if we’re one of the approximately one in four Americans already infected? Well, one of the problems with having these parasites in our brain is accelerated cognitive decline as we age. This study evaluated older adults every year for five years, and the executive function of those testing positive for toxoplasma seemed to drop quicker over time, as did a measure of their overall mental status.
Another thing that’s associated with cognitive decline is reduced folate availability, and the two may actually be related, as recent evidence suggests that toxoplasma may harvest folate directly from our nerve cells, sucking up folate from our brain. So, beyond dopamine production, which is why we think toxo increases the risk of schizophrenia, the parasite may be sucking folate out of our brain. But enough to affect our cognitive functioning? Perhaps so. Here’s a measure of cognitive function across a range of folate concentrations. Among those uninfected, it doesn’t seem to matter whether they have lots of folate or little. They obviously have enough either way. But those who are infected have worse scores at lower levels (higher is worse on this test). The same thing with vitamin B12. So, it’s important to get enough B12 and folate. For B12, the official recommendation is that all people aged 50 or over start taking a vitamin B12 supplement, or eat vitamin B12-fortified foods every day. And, anyone on a plant-based diet should start taking that advice at any age. And folate is found concentrated in beans and greens. So, following my Daily Dozen recommendations will get you more than enough, as, for example, a half-cup of cooked lentils gets you half the way there, as does three-quarters of a cup of cooked spinach.
Please consider volunteering to help out on the site.
- Jones JL, Kruszon-moran D, Wilson M, Mcquillan G, Navin T, Mcauley JB. Toxoplasma gondii infection in the United States: seroprevalence and risk factors. Am J Epidemiol. 2001;154(4):357-65.
- Lilly EL, Wortham CD. High prevalence of Toxoplasma gondii oocyst shedding in stray and pet cats (Felis catus) in Virginia, United States. Parasit Vectors. 2013;6:266.
- Jones JL, Ogunmodede F, Scheftel J, et al. Toxoplasmosis-related knowledge and practices among pregnant women in the United States. Infect Dis Obstet Gynecol. 2003;11(3):139-45.
- Huang Y, Huang Y, Chang A, Wang J, Zeng X, Wu J. Is Toxoplasma Gondii Infection a Risk Factor for Leukemia? An Evidence-Based Meta-Analysis. Med Sci Monit. 2016;22:1547-52.
- Jones JL, Parise ME, Fiore AE. Neglected parasitic infections in the United States: toxoplasmosis. Am J Trop Med Hyg. 2014;90(5):794-9.
- Herrero L, Gracia MJ, Pérez-arquillué C, Lázaro R, Herrera A, Bayarri S. Toxoplasma gondii in raw and dry-cured ham: The influence of the curing process. Food Microbiol. 2017;65:213-220.
- Guo M, Mishra A, Buchanan RL, et al. A Systematic Meta-Analysis of Toxoplasma gondii Prevalence in Food Animals in the United States. Foodborne Pathog Dis. 2016;13(3):109-18.
- Yan C, Liang LJ, Zheng KY, Zhu XQ. Impact of environmental factors on the emergence, transmission and distribution of Toxoplasma gondii. Parasit Vectors. 2016;9:137.
- Purslow P. Parasitic zoonoses present some risks with low-temperature cooking of pork. Meat Sci. 2016;119:14-5.
- Hussain MA, Stitt V, Szabo EA, Nelan B. Toxoplasma gondii in the Food Supply. Pathogens. 2017;6(2).
- Guo M, Dubey JP, Hill D, et al. Prevalence and risk factors for Toxoplasma gondii infection in meat animals and meat products destined for human consumption. J Food Prot. 2015;78(2):457-76.
- Guo M, Buchanan RL, Dubey JP, et al. Qualitative Assessment for Toxoplasma gondii Exposure Risk Associated with Meat Products in the United States. J Food Prot. 2015;78(12):2207-19.
- Guo M, Mishra A, Buchanan RL, et al. Quantifying the Risk of Human Toxoplasma gondii Infection Due to Consumption of Domestically Produced Lamb in the United States. J Food Prot. 2016;79(7):1181-7.
- Herrero L, Gracia MJ, Pérez-arquillué C, et al. Toxoplasma gondii: Pig seroprevalence, associated risk factors and viability in fresh pork meat. Vet Parasitol. 2016;224:52-59.
- Berrett AN, Gale SD, Erickson LD, Brown BL, Hedges DW. Toxoplasma Gondii Moderates the Association between Multiple Folate-Cycle Factors and Cognitive Function in U.S. Adults. Nutrients. 2017;9(6).
- Nimgaonkar VL, Yolken RH, Wang T, et al. Temporal Cognitive Decline Associated With Exposure to Infectious Agents in a Population-based, Aging Cohort. Alzheimer Dis Assoc Disord. 2016;30(3):216-22.
- Flegr J. Influence of latent Toxoplasma infection on human personality, physiology and morphology: pros and cons of the Toxoplasma-human model in studying the manipulation hypothesis. J Exp Biol. 2013;216(Pt 1):127-33.
- 9: Vitamin B12. In: Dietary Reference Intakes For Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, And Choline. Washington, D.C.: National Academies Press; 1998.
- Arora N, Sadovsky Y, Dermody TS, Coyne CB. Microbial Vertical Transmission during Human Pregnancy. Cell Host Microbe. 2017;21(5):561-567.
Image credit: Herk3 via wikimedia. Image has been modified.
Motion graphics by Avocado Video
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How to Prevent Toxoplasmosis
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Content URLDoctor's Note
Here’s the “daily dozen” thing I mentioned: Dr. Greger’s Daily Dozen Checklist
Of course, this is not the only reason to make sure you get enough vitamin B12. See, for example, Vitamin B12 Necessary for Arterial Health. I recommend 2,500 micrograms once a week of a cyanocobalamin supplement, though there’s also a toothpaste that appears to work!
This is the last in a four-video series. To catch up, check out Toxoplasmosis: A Manipulative Foodborne Brain Parasite, Long-Term Effects of Toxoplasmosis Brain Infection, and Does Toxoplasmosis Cause Schizophrenia?
For videos on more boring foodborne illnesses, see:
- Superbugs in Conventional vs. Organic Chicken
- Norovirus Food Poisoning from Pesticides
- Foster Farms Responds to Chicken Salmonella Outbreaks
- Chicken Salmonella Thanks to Meat Industry Lawsuit
- Is Meat Glue Safe?
- MRSA Superbugs in Meat
- Ciguatera Poisoning & Chronic Fatigue Syndrome
- C. difficile Superbugs in Meat
- How to Shop for, Handle, & Store Chicken
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