Perhaps you have seen the recent headlines about cats and suicides. The study behind it, performed in Denmark, made the national news this month. Upon reading it, I had flashbacks to a Ladies’ Home Journal article published in the 1970s that linked toxoplasmosis to cats. The article resulted in pet cat abandonment and wild and irresponsible recommendations from obstetricians regarding pregnant women and cats.
Yes, the parasite Toxoplasma gondii can cause disease (toxoplasmosis) in cats, unborn babies and adults. The disease in cats is probably the least important because it is so rare. I have treated cats for 40 years and only seen two confirmed cases in which T. gondii actually caused clinical disease in a cat. If a pregnant woman becomes infected, a real threat to her unborn baby exists. In addition to mild to severe damage to the liver, kidney and lungs, this parasite may cause ocular involvement resulting in permanent impaired vision or even blindness. As reported in this new article, infections in the brain have been associated with increased risk of suicide.
All of this is true. What is misleading in the recent article, however, is the automatic link from suicide to cats and litterboxes. This demands that we examine some important facts about T. gondii and its modes of transmission.
If You Read One Thing About the Recent Toxo Study, Read This
What are the take-home messages from this new article about toxoplasmosis and suicide?
1. It appears from one study that T. gondii can infect the brains of humans increasing the risk for suicide.
2. Cats can be a source of toxoplasmosis for humans, but uncooked or poorly cooked meat consumed by humans far more likely causes it.
3. To be infected by a cat, a human must swallow infective oocysts that are found in cat stool after the stool has been in the litterbox for one to five days.
4. Reasonable hygiene is enough to protect humans from cat transmission.
5. Don’t forget that the cat must be infected to be a source of T. gondii. Keeping the cat indoors and feeding it only cooked meat or processed cat food will do that. (Keep rodents out of the reach of your cats, too.)
Read on for information to support this.
How Toxoplasmosis Spreads
T. gondii is a protozoal (one-celled) organism that infects most warm-blooded animals. Domestic and wild cats, however, are the only hosts in which the entire life cycle can be completed. Most cats become infected when they ingest bradyzoites, the slow growing phase of the organism that resides in tissue cysts of an intermediate host, most commonly rodents. The bradyzoites are released from the tissue cysts when the tissues of the intermediate host are digested. They penetrate the walls of the small intestine and mature into oocysts (similar to eggs of other parasites) that pass in the cat’s stool. After one to five days from shedding from the cat, they change into the infective form that can pass the disease to another warm-blooded animal, such as a human.
To be infected, the next animal or human must swallow these infective oocysts. This is where the cat becomes an unlikely part of the life cycle. In order for a human to be infected by a cat, the cat must pass infective oocysts in its stool, the stool must lie in the litterbox or soil for one to five days, a person must get the oocysts on his or her hands then lick his or her hands or handle food about to be consumed so the oocysts can be swallowed.
How to Prevent T. gondii Transmission
You can stop the spread of T. gondii from cats to humans. To begin with, keep cats from getting infected in the first place. Keeping the cat indoors and feeding it only cooked or processed cat food is effective. Cleaning out the litterbox every day is effective. And, washing one’s hands after cleaning out the litterbox is effective. In fact, just doing one of these three things will effectively prevent transmission from cats to humans.
An estimated 50% of humans have been infected with T. gondii. Because fewer than 50% of the U.S. population owns cats, what is the source of most cases of toxoplasmosis? Simple: Uncooked meat and meat cooked rare. The tissue cysts containing T. gondii are easily killed with normal cooking; however, poorly cooked meat (rare) or uncooked meat (sashimi) is consumed by many Americans.
More Facts on the Toxoplasmosis Transmission
Kittens 6 to 14 weeks of age are much more likely to shed oocysts than cats 4 months of age or older. Infected cats only shed significant numbers of T. gondii for one to two weeks, and this shedding occurs only once in their lifetimes. In the unusual situations in which shedding occurs again, the number of oocysts are so low that the likelihood of transmission to humans is greatly reduced.
The new article on T. gondii and suicide is great science. The journalistic sensationalism that followed, however, does a great disservice to the cat. It also does a great disservice to humans by not addressing the most common source of the organism in humans. A crusade to remove cats from households without also banning the human consumption of raw or poorly cooked meat harms the cat and the public. I suggest you keep your cats indoors, feed them cooked meat or processed cat food, use reasonable hygiene (hand washing) after cleaning out the litterbox and don’t eat raw or poorly cooked meat.