Well Done or Frozen Venison Prevents Toxoplasmosis Infection

toxoplasmosis venison qdma lead

In the early 1980s, I was one of three South Carolina wildlife biologists who consumed freshly killed venison for dinner following a day of processing several deer. The venison was cooked rare, the way we liked it. Two of us ended up hospitalized for nine days with fevers peaking at 104 degrees daily. Strangely, there were no other symptoms, making it impossible for our doctors to reach an accurate diagnosis. Once our fevers subsided, however, we were discharged from the hospital. Months later, a curious physician from the state health department looked at our blood samples and closed our case with a diagnosis: toxoplasmosis.

Toxoplasmosis is a parasitic disease caused by a tiny organism called a protozoon. This parasite, known as Toxoplasma gondii, is one of the world’s most common parasites. It causes a broad scope of symptoms. They range from asymptomatic (no obvious symptoms), which is probably the most common, to a flu-like condition, and to more serious complications in pregnant women, infants born to infected mothers, and for people with weakened immune systems.

The Source: Cats

How does one “catch” this disease? Many wild and domestic animals can harbor this parasite, but it is the house cat (tame and feral) that is most often associated with human infections. Direct and indirect contact with cat feces provides the pathway for disease transmission. Consuming unwashed and/or undercooked vegetables from a garden frequented by cats is a common indirect method of contracting toxoplasmosis.

Results from a recent Ohio State University study in the metropolitan Cleveland, Ohio area revealed that 60 percent of more than 400 deer tested were infected with toxoplasmosis. This was three times higher than rates in suburban deer, likely due to a higher density of free-ranging or feral house cats in urban areas.

Preventing Infection

The concern with venison consumption from these urban and suburban areas is obvious, but it should be applied throughout the whitetail’s range. For venison lovers, there are several ways to minimize your chances of contracting this common disease. Once the meat has been processed, wash cutting boards, dishes, utensils, countertops, and hands with hot, soapy water. Avoid touching your mouth after handling raw meat.

If you insist on serving your venison with a pink center, make absolutely certain that the meat has been frozen prior to cooking.

It is a long-standing tradition for hunters at a deer camp to prepare fresh venison, especially backstraps and tenderloins, as a celebration meal following a successful hunt. To complicate matters, for many it is sacrilege to grill or pan-fry venison well-done. Therefore, any Toxoplasma parasites that are present will not be killed.

Here’s an important notice to venison lovers. If you insist on serving your venison with a pink center, make absolutely certain that the meat has been frozen prior to cooking. Otherwise, cook meat at a temperature of at least 145 degrees and allow a rest time of three minutes before carving and consuming. During the rest time, the temperature remains constant or continues to rise briefly, which destroys the toxoplasmosis pathogens.

Lifelong Complications

As for my two colleagues and me, none of us have had any complications from the disease since we initially recovered. It is unfortunate, though, that we are not allowed to give blood nor can we serve as organ donors. Toxoplasma antibodies generally persist for life and therefore may be present in one’s bloodstream as a result of either a current or previous infection. There are medications that can help reduce the severity of a toxoplasmosis infection, but the best approach is prevention. Deer hunters are encouraged to keep their hands clean, to always freeze their venison before it is cooked, or to cook it thoroughly. From this point on, no worries!

  • Bounty_Hunter

    This article is a little bit incomplete. Just freezing meats does not kill the parasite, it must be frozen to below a certain temperature (less than -20º F.) and for a 2-3+ week duration. This information was gleaned from an article I had read on some study of T. gondii and how it was able to overwinter in soils in northern climates. The researchers determined why it was able to survive winters in less-harsh climates even though the ground was frozen there. (I wish I could find that link now, but this was quite a few years ago.) Here’s a reprint of what I usually post on hunting and outdoorsmen forums (and cat-lickers’ forums, of course).

    For those who love a good game-meat jerky or sausage (some of my favorites), there are reports on the internet of how to destroy T. gondii. Much of the misinformation is being spread by cat-lickers who were born to lie. It’s not as easy as just freezing the meat for a few days. They have found that even washing your hands and garden-vegetables in bleach and hydrochloric acids and digestive enzymes will not destroy T. gondii oocysts. It’s one really tough bugger. It can even survive living in saltwater, this is why so many rare and endangered marine-mammals (all the way up to whales) are now dying-off along all coastlines around the world from contracting T. gondii in run-off from the lands.

    For those of you who enjoy game-meat jerky or sausage , you CAN destroy the viable T. gondii parasites and cysts in the meat, but you MUST freeze the meat to temperatures below (MINUS) -20º F. The common home-freezer in a fridge/freezer-combo rarely goes down to below (PLUS) +15 F. You MUST use a freezer that is rated as a typical home “deep freezer” to attain the temperatures required to destroy this parasite (typically -20º F. or lower). And keep it frozen for several weeks at those temperatures.

    Then and only then can you feel relatively safe using game-meats infected with T. gondii for those foods that require raw meats for their production. If you make these foods yourself or receive any of these products from a hunting friend as a gift, or a store (or ANY meats intended for human consumption today); be sure to deep-freeze (-20º F.) them for at least 3 weeks before consumption, in-case the provider did not. Your brain will thank you. Alert everyone you know that hunts. They too will thank you.

    Thought you might like to know.

    And don’t forget to hygienically destroy and dispose of all free-roaming, invasive-species, community-vermin, house-cats to stop this.

    When ridding your lands and lives of these highly destructive man-made invasive-species vermin cats please do so in a manner where you can safely and sanitarily retrieve that useless carcass and dispose of it so no other life comes in contact with it. Your wildlife and neighbors will thank you. If using guns, I’d even advise against using a shotgun (the tool of choice in the past), too much disease-filled splatter. Make it clean as possible. Wear gloves while disposing of any cat-carcasses and even bury or burn those gloves too when the last cat in your area is finally gone. You need to dispose of that cat safely and hygienically so that wildlife won’t die from the deadly 3dozen+ diseases vermin cats spread even after their death.

    Leaving ANY cat out in nature, alive OR dead, is no better than intentionally poisoning your native wildlife to death. I know this. I fed some wildlife and their offspring that they had while under my care with one of the hundreds of shot-dead house-cats on my lands. Those native animals then promptly died from some disease in that invasive-species cat-meat. Cats truly are complete and total wastes-of-flesh. They can’t even be used to feed wildlife safely. And letting live cats roam free is absolutely NO different than throwing DDT on everyone’s property to outright kill any other living thing. It’s now time to put the cap back on every bottle of man-made environmental-poison labeled “CAT” and dispose of all of them too as environmentally safe as is humanely possible. Then make the production, ownership, and use-of any bottle labeled as “CAT” into a punishable fine, just like DDT was responsibly dealt with to end that similarly man-made environmental disaster.

  • Amelia

    Thank you for posting this and bringing awareness into this little known subject. I was infected a year ago by a bad scratch from my dog who had previously been in contact with feral cats. I am one of the few people who had the rare symptom of losing some of my eyesight in my right eye. It got as bad as 20/500 at one point and is now about 20/30 or 20/40. I used to be 20/10. I now have a permanent scar on my optic nerve causing a blind spot in the corner of my eye with the rest of the vision being very distorted with very muted colors. It will never be the same. Had I not been pregnant I may have not been effected. Thankfully it happened the night before a scheduled csection or my baby would have been very sick. I’m thankful he is a growing healthy boy but now I take it upon myself to educate everyone I can on this very serious disease!

    • Joe Hamilton

      Amelia, so sorry to hear about your vision problems, but thank goodness you have a healthy son. Thanks for sharing your story with us. Hopefully it will help others who read about toxoplasmosis. Take care!

  • Joe Hamilton


    Thanks for your very thorough discussion regarding the root of the problem with regard to cats. I would add to your comments that it is not so much the domestic house cat that we should be concerned with, it is the millions of feral house cats that have reached “plague” proportions throughout the urban and suburban areas of the country, AND, I’m sad to mention that college/university campuses are included as well. In too many instances, those compassionate cat lovers have established programs to catch these poor, homeless critters, go to the trouble and expense to have them neutered and then returned to the site of capture. This ensures the perpetual presence of toxoplasmosis in our woods and neighborhoods, AND in our human populations!

    Joe Hamilton
    QDMA Founder & Senior Advisor

    • JJ McKibbin

      Thank you Joe.

      My use of the term “domestic house-cat” is meant to include both pet cats that are allowed to free-roam, and feral cats, as they are the exact same species (Pet cats that are kept exclusively indoors and are not fed raw meat are at much lower risk of contracting toxoplasmosis. And if their litter-box contents are properly disposed of, they won’t be contaminating the environment with oocysts even if they do happen to become infected).

      You are absolutely correct: Feral cats are a plague. It’s more than toxoplasmosis (although that alone is enough). It’s also rabies, hookworm, bartonella, fleas, and even the actual plague disease. It is bird and wildlife decimation on a massive and unsustainable scale. It is an infringement of private property rights when trap-neuter-return (tnr) programs make it impossible for property owners to remove cats from their own property.

      Colleges, towns, cities, and even entire counties have been duped, bribed, or bullied into establishing these tnr programs (trap-neuter-redump would be a more accurate name). Many of them have been at it for a decade or more, even though there is little evidence it even stabilizes feral cat populations, let alone reduces them. There is no town, city, or county anywhere in the country that can state that it has fewer feral cats on the streets now than it did when it started tnr. It is far past time to take serious meaningful steps to significantly reduce the population.

      Best regards,
      JJ McKibbin

      • Joe Hamilton

        JJ, I’m on your side on this one. Thanks for your response.

  • JJ McKibbin

    Thank you for this article.

    Toxoplasmosis infections are common. 60 million Americans are infected and another million become newly infected each year. As you pointed out, a high percentage of deer may be infected, and in fact many game animals are infected. Unfortunately, infected meat is not limited to game animals. Many animals raised for human consumption are also infected. You are also correct to identify the source of toxoplasmosis infections as domestic house-cats.

    Toxoplasma gondii can only complete its life cycle in the intestine of a member of the cat family. Only cats. The cat then sheds the oocysts (eggs) by the tens of millions in its feces. Again, only cats. No other animal sheds the oocysts. The oocysts are very durable and can remain viable in soil or water for 18 months or more. In dry conditions they can become aerosolized and inhaled. Oocysts can also be spread by insects or rodents or even the wind from feces to food sources. Water sources can become contaminated when rain washes the oocysts into them. The reason the soil, water, or plant material is contaminated with oocysts is because cats are shedding them. There would not be environmental contamination of oocysts if the cats weren’t there to shed them by the tens of millions. Recent research now indicates that cats can become reinfected a second time and go through a second oocyst shedding cycle. Yes, any warmblooded animal, including humans, can become infected by ingesting oocysts from contaminated food or water sources, or even by inhaling them in dry areas where they have become aerosolized. But none of these other warmblooded animals can shed more oocysts.

    Humans and animals can also become infected by eating the undercooked meat of infected animals. But those infected meat animals became infected by ingesting oocysts shed by cats. No matter how humans or animals become infected, the original source is cats. Now, it is true that any member of the cat family can shed oocysts, and this includes native cats such as bobcat, mountain lion, and lynx. But since the population of all of these native species combined comprises only 2% of the total number of cats nationwide, and since most human populated areas have almost zero native cats living among people, the source of oocyst contamination is almost exclusively domestic house-cats.

    Environmental contamination of oocysts from cats is so pervasive in areas with high concentrations of cats that scientists fear toxoplasmosis infection may become almost impossible to avoid. 60 million Americans are already infected. Besides the proven health issues of blindness, birth defects, and fatal infections in the immuno-compromised, toxoplasmosis is now being linked to Alzheimers, schizophrenia, autism, depression, suicide, obsessive/compulsive disorder, and more. There is no vaccine and no cure for toxoplasmosis. Once you have it, you have it for life. We really don’t know at this point what all issues this parasite presents in humans. The potential problems from this parasite should not be minimized. To do so is irresponsible.

    For more information go to the “files” section of the toxoplasma gondii facebook page and read the 2013 Torrey and Yolken study entitled “Toxo Oocysts Public Health”.

    • Bounty_Hunter

      Recent research proves that the oocysts can even survive up to 4.5 YEARS in any waters. That 18-months limit was just for viability in soils. Thought you might find that “interesting”.

      • JJ McKibbin

        Thank you. Can you please give me a link to the study showing viability of 4.5 years?

        • Bounty_Hunter

          Luckily, I read about this just in the last month, so backtracking to the source was still easily brain-lobe retrievable. 🙂 Here’s a link that was shared to me by Hajj Frederick Minshall (I think you know that name :-).

          “Detection of Toxoplasma gondii in environmental matrices (water, soil, fruits and vegetables”


          I still wish I could run across that study again that showed cats can become reinfected many times, and that a cat even having a high antibody count didn’t prevent them from becoming reinfected. It was some study in New Zealand or Australia in the mid-late 1990’s that was done for their sheep-ranchers. (Those livestock animals being the most susceptible to dead-offspring from a T. gondii infection. If gestating sheep aren’t producing viable offspring look no further than the nearest cat to the cause. All rural vets know this and advise all people who keep sheep to kill and safely dispose of all cats for miles around.) That article i had read was so many years ago that the source got buried in some 14,000 kitty-licker links I have in my bookmark archives. Finding it again just by web-page title alone hasn’t worked so far.

          • Bounty_Hunter

            Whoo hoo! I found it. I thought back to what article/discussion I had first posted about reinfection of T. gondii, it was that old article about “How Your Cat Is Making You Crazy” on The Atlantic Magazine. I went back into my archives and found the article and discussion. There, buried in 890 comments (no lie), I found the link I had shared with the quoted text.


            (Sadly, that link can no longer reach the original article.)

            “… in light of a startling discovery by Dubey and his research team. It was previously believed that once a cat had been infected with T. gondii and shed oocysts, that cat would not become re-infected and shed more oocysts.

            Dubey’s team has found that’s probably wishful thinking. They have shown that cats infected years earlier and that shed millions of oocysts then could be reinfected 6 years later and begin shedding oocysts again.

            That wasn’t the only surprise. The same study showed that cats could have very high levels of antibodies against T. gondii in their blood years after a previous infection and still become reinfected. “So you can’t use high levels of antibodies as an indicator of immunity,'” says Dubey.”

            Though I don’t understand how, if even a high antibody count could prevent reinfection, so why would there be a 6 year delay? Perhaps those were the only cats they studied 6 years later? My memory just logged that as a cat can become reinfected at any time again — there now being no reasonable immunological contradiction to frequent reinfection anymore.

            Ah-hah, I searched usda’s archives and found the article: https://agresearchmag.ars.usda.gov/1996/feb/toxo/

            I at least had the time period right (mid 1990’s), but this was about piggies, not sheep. I must have ran across that article from New Zealand/Australia and protecting their sheep during the same time period as I did this one. No wonder I couldn’t relocate the local bookmark and article for the last 4.5 years. 🙂

          • Bounty_Hunter

            An odd contradiction in that article. “Dubey says, the oocysts can survive freezing and thawing, allowing them to linger in the environment for years.”

            Then later states, “‘Freezing the meal for a single day in a domestic freezer is very
            effective for killing the tissue cysts, which are the form of the
            parasite that’s in meat,’ Dubey points out. ‘Also, cooking the meat to
            an internal temperature of 153° F will kill them. Tissue cysts are much
            more vulnerable than the oocysts.'”

            Ah, now I know where my memory logged the confusion. You must freeze the oocysts to BELOW minus-20º F. for several weeks to kill them. But the tissue cysts can be killed at higher freezing temperatures. Since game-animals (likely herbivores) have picked-up the disease from oocysts on the land (or in waters), and it has been documented that fur (especially cat-fur) is a very common carrier of the oocysts, I still say the likelihood of any game-meats having an oocyst or two on them (after field-dressing) could still be a likely source of infection. Yep, I’m going to still go with the advice to freeze to below minus-20º F. for several weeks — better safe than sorry!

          • Wen

            And here I though I was a little safer from the blasted things spreading this disease because the high desert freezes every winter. Thanks for sharing this.

About Joe Hamilton

Joe Hamilton is a wildlife biologist and the founder of the Quality Deer Management Association (QDMA). During his nearly 20 years with the South Carolina Department of Natural Resources, Joe helped implement QDM practices on more than 2 million acres. In 2000, he was awarded the Deer Management Career Achievement Award from The Wildlife Society. In 2011, he was named Conservationist of the Year by Budweiser Outdoors. He currently serves as Senior Advisor for QDMA.