Undercooked Venison Can Cause Rare Blindness Disorder

With that task complete, the doctor at the Cole Eye Institute in Cleveland pushed a second needle deep into the back of Crockett’s eye, all the way to the retina. Stopping just short of the optic nerve, he injected a steroid.

After emptying the syringe and withdrawing the needle, the doctor grabbed a third needle, directed it into the same deep site, and injected an antibiotic.

It was February 2021 and the intent of those injections was to battle a microscopic parasite in Crockett’s right retina. The parasite and its surrounding cyst were building pressure on the optic nerve and shutting down the eye’s vision. The single-cell parasite—Toxoplasma gondii, or T. gondii, for short—had migrated there through Crockett’s bloodstream, attracted by the eye’s rich network of blood vessels.

The parasite’s journey to the far side of Crockett’s eye began after the 57-year-old hunter ate raw venison backstrap in October 2020, not realizing it was tainted with the common parasite. And why would Crockett have known or worried about toxoplasmosis, or his specific ailment, ocular toxoplasmosis? He and his northern Ohio hunting buddies had long made it their custom to clean and chunk raw backstrap after a kill, season it with salt and pepper, and eat it while butchering and packaging their deer. Nothing bad or disagreeable ever followed.

Until it did.

Blinding Booger Crockett said the first sign of trouble came on Oct. 18, 2020, while watching the Cleveland Browns play the Pittsburgh Steelers on TV at his niece’s home. He said it seemed like a “booger” was on the contact lens on his right eye, causing a shadow that obscured his vision in the 6 to 9 o’clock quadrant. He cleaned his contacts after returning home but the problem persisted. He went to the emergency room, but only stumped the doctors on duty.

“I saw six ophthalmologists over the next five days while losing vision in the eye,” Crockett told MeatEater. “The first five doctors didn’t know what was going on, and sent me to someone else. The sixth doctor perked up when I said I liked hunting deer. Then his ears really perked up when I said I liked rare venison. It didn’t take him long to settle on toxoplasmosis and how to treat it.”

The eye injections weren’t as bad as Crockett anticipated. “I got cold sweats and pictured Dr. Mengele and death-camp experiments,” he said, recalling the “Angel of Death” of Nazi Germany. “The needles are a lot longer than what actually goes into your eye. The doctor got me ready, numbed everything, told me to pick a spot on the ceiling that I liked, and said, ‘Don’t move.’ The next day, my eye looked like I’d lost a fistfight.”

Crockett said his vision has improved over the past 17 months, but it might never return to normal. He still has a shadow in the eye’s 6-9 quadrant and has taught himself to shoot left-handed, which required breaking 50 years of shooting habits.

“I have no choice but to shoot with my left eye because I lost the center of my vision in the right eye,” Crockett said. “I could no longer see the cross-hairs in my riflescope. I haven’t shot my bow since this started, and I shoot my muzzleloader with my left eye. I picked up a left-handed autoloader for duck hunting. Switching wasn’t easy, but at least I didn’t lose all my vision. I think of it as a first-world problem. I’m hoping it only gets better with time.”

Overlooked Threat Crockett was surprised when the eye specialist linked his vision loss to raw venison. Like most hunters, Crockett assumed food-borne illnesses seldom involved deer. Most hunters know about trichinellosis—trichinosis, for short—which is common in rare meat from bears or pigs. The most recent summary from the U.S. Centers for Disease Control and Prevention identified 80 trichinellosis cases nationwide from 2011 to 2015; 13 involving wild pigs, 18 from domestic pork, 26 from bears, and 23 from unidentified sources.

Most hunters have also heard about tularemia, or “rabbit fever,” which they can contract while gutting and skinning hares, rabbits, or muskrats; or from the bites of fleas, deerflies, dog ticks, wood ticks, and lone star ticks. The CDC recorded 2,108 tularemia cases from 2010 to 2019, with over half the cases (1,099) concentrated in the four-state region of Arkansas, 393 cases; Missouri, 259; Oklahoma, 226; and Kansas, 221.

Most hunters the past 20 years have also heard advice from the World Health Organization to not eat venison from deer infected with chronic wasting disease. There’s no verified case of CWD transmitting to humans from deer or elk, but CWD’s bovine version (mad cow disease) jumped from cattle to humans in the United Kingdom.

The ‘Neglected’ Parasite In contrast, venison-borne toxoplasmosis generates few warnings, press releases, and public-service ads aimed at hunters. The U.S. Centers for Disease Control and Prevention labels toxoplasmosis a “neglected” parasitic infection, even though it annually infects over 800,000 Americans, has infected 11% of the population 6 years and older, sends thousands to hospitals each year, and causes hundreds of deaths from foodborne illnesses.

Maybe the CDC considers toxoplasmosis neglected because 40 million Americans are carrying it around unknowingly. It’s often asymptomatic. A fetus can contract toxoplasmosis from the mother—often with dire birth defects—but most people get it by eating raw or undercooked lamb, pork, venison, vegetables, or milk products; or by touching cat-infected litterboxes or sandboxes.

In fact, most folks only associate toxoplasmosis with felines. Although cats are the only known “definitive” host of T. gondii—meaning only felines support the parasite during its reproductive cycle—many warm-blooded animals carry and spread it after picking it up in dirt infected by felines.

People who experience the infection’s common flu-like symptoms—aches, fever, fatigue, and swollen lymph nodes—typically recover without seeing a doctor. Others get misdiagnosed as having HIV, Lyme disease, or a common virus. A healthy person’s immune system usually neutralizes the parasites and their surrounding cyst, which can remain inactive in the body indefinitely. Their presence can provide lifelong immunity against another toxoplasmosis infection, unless certain medications or another disease like HIV or cancer compromises their immune system.

Deer are a Common Carrier But if any group should learn about toxoplasmosis and its risks, it’s hunters. Recent research shows deer often carry T. gondii tissue cysts, which are found in virtually all edible portions of infected deer, bears, and wild pigs. As with humans, the parasites can survive in game animals for years.

The T. gondii parasite, however, seldom shows up in commercially raised and sold beef, pork, or poultry, especially if it’s been frozen, which kills the organism. In contrast, researchers have found viable T. gondii parasites in about half the deer tested. Surveys on whitetail deer found toxoplasmosis rates ranging from 15% to 76%, including 53% (2009) in Iowa; 73% (2012) and 76% (2013) in Ohio; and 15% (2008), 28% (2009), and 25% (2010) in Minnesota studies. Ohio’s high rates might have resulted from the study’s urban setting, which likely had more cats than the other test sites, which were more rural or suburban.

Farther west, a 2005 study in Nebraska found T. gondii in 31 of 89 (35%) mule deer. A 2008 study of mule deer and blacktail deer in Washington, meanwhile, reported T. gondii antibodies in 14 blacktails but no muleys.

Infections are even higher in black bears and raccoons. One U.S. study found 80% of black bears were infected with toxoplasmosis, as were about 60% of raccoons. The researchers wrote, “Because raccoons and bears scavenge for their food, infection in these animals is a good indicator of the prevalence of T. gondii in the environment.”

As doctors learned of high toxoplasmosis rates in deer, they’ve increasingly looked for it when struggling to diagnose sick patients. Joe Hamilton—founder of the Quality Deer Management Association (now the National Deer Association)—was one of the first deer hunters diagnosed with the infection 40 years ago. Hours after he and three South Carolina colleagues finished processing deer one day, they ate some fresh venison after cooking it rare, “just the way we liked it.” Hamilton and his friend Gerald Moore started feeling bad days later.

“We ended up in the hospital for nine days with fevers peaking at 104 degrees in the afternoon,” Hamilton said. “We’d wake up feeling fine each morning and thinking it had passed, but by early afternoon we’d go downhill again. We were freezing to death in our hunting vests. The doctors didn’t know what we had. When we felt good enough to leave, they just sent us home.”

Months later, a researcher at South Carolina’s health department in Columbia grew curious about their case and took blood samples. The doctor later called with his findings: toxoplasmosis.

“He closed our case,” Hamilton said. “He said there’s nothing more to do. We’ve never had any more complications from it, but we can’t give blood or donate our organs because toxoplasma antibodies generally persist for life in your system.”

Documented Cases Since then, researchers have documented toxoplasmosis several times in deer hunters. In 2001, for example, five young Michigan men sought medical help after developing flu-like symptoms and severe vision problems. The men told doctors they were hunters and regularly ate raw or lightly cooked venison. All tested positive for toxoplasmosis.

An October 2017 outbreak in Wisconsin’s Jackson County hit 11 of 12 men who ate undercooked venison barbecue. Two of the 11 never developed symptoms, but the other nine suffered sweats, chills, fatigue, fever, rash, body aches, headaches, and dark urine. Three of the men developed ocular toxoplasmosis.

A year later, six of 10 deer hunters from Quebec, Canada, returned home from a late November/early December hunt in Illinois complaining of fever, muscle aches, and severe headaches. One man ended up in the hospital, three consulted a doctor, and two didn’t seek help. Tests identified toxoplasmosis, and investigators traced it to a meal on Nov. 30 where five of the men ate rare venison steaks, and a sixth ate a steak cooked medium. Follow-up tests on 12 frozen venison samples found no T. gondii present.

That investigation also summarized a major toxoplasmosis outbreak in 1995 in Victoria, British Columbia, that affected hundreds of people. Investigators at the time suspect the outbreak’s source was an infected cougar that defecated into a watershed. The T. gondii cysts then likely flowed into a reservoir that provided the residents’ drinking water.

More recently, eight hunters developed “toxoplasmic retinochoroiditis” (where the infection enters the retina of the eye) after handling raw or undercooked meat from seven deer and one bear. Five developed the disease after eating undercooked meat, while three developed it after cleaning some of the animals.

In other words, even though severe vision loss like Adam Crockett’s isn’t common, neither is it a fluke. A 2005 nationwide survey of ophthalmologists estimated 250,000 visits for active or inactive ocular toxoplasmosis during a two-year period. Further, the CDC estimates that every year 3,600 Americans suffer vision loss after contracting eye infections from T. gondii.

The CDC also estimates about 2% of those contracting toxoplasmosis develop eye lesions that scar the retina. Fortunately, even though ocular toxoplasmosis can cause pain, blurry vision, permanent damage, and even blindness, it usually attacks the retina, scars it, and fades away without symptoms. In fact, it’s the world’s most common cause of eye inflammation, according to the National Institutes of Health and the U.S. Department of Health and Human Services.

Personal Accounts Some hunters suffer far worse problems, however. Roger LaPointe, 67, of Louisville, Kentucky, recalls eating fresh venison poppers with three friends while deer hunting before Thanksgiving in November 2020. They felt fine after eating the rare to medium-rare treats, but LaPointe soon fell sick and went straight to bed when returning home. He didn’t get out of bed until after Thanksgiving. Three separate blood tests didn’t pinpoint the problem, and he ended up in the hospital for four days after Christmas. Another blood test revealed toxoplasmosis.

LaPointe was also battling a starburst-like light in his right eye. An infectious disease specialist diagnosed it as ocular toxoplasmosis, and LaPointe’s eye doctor put him on a strong antibacterial drug. Fifteen months later, LaPointe remains weak and his joints still ache. He’s also lost 40 pounds and feels only “somewhat better” than he did a year ago.

Brad Onstad, 52, of Champlin, Minnesota, said he ate fresh heart and tenderloin from a young buck his brother, Darren, killed the day before on opening day of the November 2009 season. They refrigerated the meat overnight in milk, cooked it medium-rare late the next morning, and ate it while watching a Minnesota Vikings football game on TV with a friend in their cabin near Hackensack in north-central Minnesota.

Three weeks later Brad Onstad fell ill with the worst “flu” he’d ever known. Night sweats forced him to sleep atop towels, and his legs felt like he’d run 20 miles. Different doctors diagnosed HIV, Lyme, and cat-scratch disease. He battled the illness for three weeks into mid-December, typically feeling good in the morning but miserable the rest of the day. It finally passed with no definite diagnosis.

When shoveling snow off his driveway in early February 2010, however, Onstad noticed a large, gray blind spot with blurry edges in his right eye. To imagine it, hold a softball at arm’s length and try seeing around it. The blind spot in his shooting eye baffled doctors until Onstad, a trained microbiologist, went online and found the 2001 research paper about the five Michigan deer hunters with flu-like symptoms followed by ocular toxoplasmosis.

His doctors confirmed by late February 2010 that Onstad had a “raging toxoplasmosis infection.” They put him on anti-parasitic drugs, steroids, and eye drops for four months, which eventually shrunk the blind spot in half. “A day or so after I started those drugs, the pressure in my right eye made it feel like it was going to pop out of my head,” he said.

Now 12 years later, the blind spot remains the same size and will likely never disappear. Further, Onstad can’t drive at night because of poor depth perception, and he switched long ago to left-handed shooting.

Not coincidentally, Onstad’s brother developed a similar blind spot in his right eye in October 2018. Although Darren Onstad never felt ill after eating the heart and tenderloin from his 2009 buck, the T. gondii cysts likely sat dormant nine years before damaging the eye’s retina. He, too, now shoots left-handed.

Conclusion The Onstads, LaPointe, Crockett, and Hamilton have long since frozen all venison before eating it. The CDC recommends freezing meat for several days at sub-zero temperatures to kill T. gondii parasites but warns that freezing won’t reliably kill certain trichinella or bacteria.

The CDC also urges hunters to cook their venison more thoroughly. They recommend cooking steaks and other whole cuts to at least 145 degrees at the center and letting it rest three minutes before carving and eating to ensure the heat kills all parasites. Ground venison should be cooked to at least 160 degrees. The CDC also recommends wearing gloves when field dressing and processing deer, and when digging or gardening where cats, deer, and other potential carriers live.

LaPointe considers those precautions minor. “I used to gut deer bare-handed while eating baloney sandwiches,” he said. “I’ll never do that again, and I never eat anything fresh off the deer anymore.”

Crockett said the experience taught him to be more careful not just with venison, but also with lamb, pork, and beef. “You basically risk exposure if you eat anything raw or rare,” he said. “I used to order my steaks ‘blue rare’ so they were cold in the middle. I liked to just take the chill off the meat. I now cook meat a bit more, but I won’t go to well-done, or eat what’s left on someone else’s plate.”