Toxoplasmosis in cats: background and an unusual case

A Toxoplasmosis organism in fluid from the respiratory tract

What is toxoplasmosis?

Toxoplasmosis is a disease caused by a one-celled parasite called Toxoplasma gondii, hereafter called the "toxo organism."  In humans, it may affect many different organs of the body, causing many different types of clinical signs.  The respiratory system is commonly involved and pneumonia may result.  The most common finding is a mild, flu-like illness that lasts a few days.  Most people recover uneventfully.  Even if the patient sees a physician, the illness may still be attributed to the flu unless special blood tests are run. There have been some recent studies of populations with a high rate of Toxoplasmosis infection that suggests that infection with the toxo organism may cause humans to be more likely to develop "guilt prone" neuroses and that there may be a link between Toxo and certain mental disorders such as OCD and schizophrenia. Many of the stories about this study have strongly exaggerated the strength of this link, and while there appears to be a correlation between the two, there is no evident cause.

Dirty Carrots - Image courtesy of dragonariaes

Additionally, Toxoplasmosis infection is much more likely to occur in humans due to ingestion of undercooked meat or eating or drinking substances contaminated with Toxo organisms, gardening, or eating unwashed fruits or vegetables from a garden than from infection due to sharing a home with a
cat.

How does it relate to pregnant women?

If a pregnant woman contracts toxoplasmosis just before or during pregnancy, it is possible for the toxo organism to affect the unborn baby.  It is this form of the disease that has the most dire consequences because the baby may be affected for life. Infections with Toxoplasmosis earlier in life should not cause problems with pregnancy, but any concern about this matter should be discussed with an obstetrician.

Pregnant women should not clean the litterbox if at all possible, but if they must, should wear gloves and a mask. If the litterbox is kept clean daily, the risk is lower as the Toxoplasmosis oocysts do not become infective for 1-5 days after being passed in the stool. Avoid feeding your cat raw meats, and keep your cat indoors to minimize exposure. While you do not have to get rid of your cat because you are pregnant, pregnant women should not bring new cats into the home or handle stray cats or kittens. Outdoor sandboxes should be kept covered, and any gardening should be done while wearing gloves. Avoid undercooked meats.

• From the CDC website, the definition of "cooked meats":
• For Whole Cuts of Meat (excluding poultry)
  • Cook to at least 145° F (63° C) as measured with a food thermometer placed in the thickest part of the meat, then allow the meat to rest* for three minutes before carving or consuming.
• For Ground Meat (excluding poultry)
  • Cook to at least 160° F (71° C); ground meats do not require a rest* time.
• For All Poultry (whole cuts and ground)
  • Cook to at least 165° F (74° C), and for whole poultry allow the meat to rest* for three minutes before carving or consuming.

How common is toxoplasmosis in adults?  And how common in cats?

Labwork helps diagnose Toxoplasmosis in cats and people

Exposure to the toxo organism will result in the production of antibodies.  Antibodies are the defense   The presence of antibodies means that the person or cat has been exposed; it does not necessarily mean that any disease occurred.  There are some estimates that about 50% of domestic cats in the United States have been exposed to toxoplasmosis. This does not mean that 50% of cats have an active infection with Toxoplasma. The presence of antibodies only means that exposure to the toxo organism has occurred in the past. However, the Companion Animal Parasite Council reports that the  prevalence of oocysts (infective shedding) in cats in the United States at a rate of approximately 1% In six surveys from different states in which more than 10 cats were included in all studies, oocyst shedding ranged from 0.0 to 6.6% (mean of 0.7%). In a study of over 200 cats, approximately 50 cats were infected and none of them were actively shedding infective Toxoplasmosis organisms. Positive antibody titers in cats in the U.S. range anywhere from 14% to 100% - these cats have been exposed but are non-infective.
agents of the immune system and are produced in response to immune system stimulation.

The CDC estimates that about 22.5% of the U.S. population 12 years and older have been infected with Toxoplasma. The Companion Animal Parasite Council reports that 11% of the U.S. population between the ages of 6 and 49 are seropositive (have antibodies to Toxoplasmosis). In France and Germany, approximately 80% of the population have been infected with Toxoplasmosis. In some regions of the world, particularly where the climate is hot and humid, up to 95% of the population has been infected with Toxoplasma.

How common is it in babies?

The disease toxoplasmosis occurs in about 400 to 4000 births per year in the US. About 4 million babies are born, each year - a rate of 0.01% (as few as 1-10 births out of 10,000 will be infected). Although this is indeed a real disease with dire consequences, it should be noted that its incidence is very small, especially in light of how many people have Toxoplasma antibodies.

How is it transmitted?

Although several species may develop the disease toxoplasmosis, including humans and dogs, the organism can only complete its life cycle in the domestic cat.  This means that the cat may be infected with the toxo organism and transmit it to other cats or to other species, including humans.  However, in order for this to occur the following must happen:

Toxoplasmosis life cycle

1.        The cat must be infected with the toxo organism, and most cats are not.  In order for this to occur, the cat must eat something infected with it.  It is most commonly available to the cat by ingestion of infected mice or infected raw or undercooked meats, especially pork or mutton.

2.        The cat must be shedding the toxo organism in its feces.  This occurs for only about a 10 day period.  It usually only occurs once in the cat's lifetime.  (In a few situations, the cat may shed the organism again; however, if that occurs, the number of organisms that are shed are so small that transmission is very unlikely.)

3.        The toxo organism must "incubate" in the cat's feces for 1-5 days before it is infective to humans.  This "incubation" must occur after the feces leaves the cat's body and have access to oxygen (i.e. in the litter box or in soil).

4.        The toxo organism must be swallowed by the person being infected.  It is not spread to humans through the air.

Raw or undercooked meat is a common source of Toxoplasmosis infection

The toxo organism may also be transmitted to humans by eating raw or undercooked meats, especially pork or mutton.  Since many hamburgers from fast-food restaurants are made of beef diluted with pork, most authorities feel that human infection occurs much more frequently by this method than by association with cats.  The incidence of toxo antibodies in U.S. veterinarians is not different than that of the rest of the population. None of our staff members who have been tested for Toxoplasmosis have tested positive, and we probably clean more litterboxes than all of our clients, combined!

What is involved in testing for toxoplasmosis?

We are frequently asked to test a cat that belongs to a pregnant woman for toxoplasmosis.  Pregnant women should know the following concerning toxoplasmosis testing.

1.         A screening test for toxo antibodies can be performed on both the pregnant woman and the cat.  A negative result means that the woman (and/or the cat) has not been exposed to the toxo organism.  However, it does not infer that either the woman or the cat has any immunity to toxoplasmosis in the event of a future exposure.  In fact, it means just the opposite.  Both are susceptible to infection.

2.        A single antibody titer that is positive, performed on the woman and/or the cat, means that there has been exposure to the toxo organism in the past or that there is an active infection of toxoplasmosis in progress.  In order to know which situation exists, a second test must be run 2-4 weeks later. 

a.        If the two tests give similar results, there has been an infection in the past and a certain degree of immunity exists. 

b.       If the second test is significantly higher that the first, there is a strong possibility that an active case of toxoplasmosis is in progress. 

c.        It is very important that both tests be performed by the same testing laboratory in order to properly compare results.

3. The direct means of documenting the possibility of transmission of toxoplasmosis requires that we microscopically examine a fecal sample from the cat looking for the oocysts (eggs) of the toxo organism.  Because these oocysts are very tiny (even under a microscope) and because the cat may not be shedding oocysts today but may do so in the future, multiple examinations must be done during the course of pregnancy, preferably once weekly.  This is not a very high yield procedure, meaning that it can be difficult to detect the parasites, and they can be missed by this diagnostic technique.

An unusual case of Toxoplasmosis

 In most cases of Toxoplasmosis, the cat is mildly ill and may not even produce symptoms worrisome enough for an owner to call the veterinarian. A few years ago, however, we saw a very unusual case involving Toxoplasmosis. A previously healthy, 4 year old male cat came to see us 9 months after he had a wellness exam with no concerns. He was an indoor-outdoor cat, and had previously had roundworms, so his owners brought in stool samples for checking very regularly. Most of the time, they were negative. In November, they brought T.C. to us as an emergency. He had been eating poorly and had been lethargic for a few days, but they had just found him collapsed and struggling to breathe. When they arrived at the hospital, he was unable to stand and his color was blue-gray instead of a healthy pink. His chest sounded as though it were full of fluid. He was immediately placed in an oxygen cage. He recovered enough for us to take him to the x-ray room and take one x-ray before he needed to return to the oxygen cage. His x-ray showed fluid in the chest, an enlarged heart and

Toxoplasmosis organisms inside a cell

other signs similar to congestive heart failure. Since his breathing was so labored, we were limited as to what we could do to him - he was too critical to remove from the oxygen cage for very long, even when offered an oxygen mask. Placing an oxygen mask caused him to struggle and breathe with even more difficulty. We gave him medications to try to ease his breathing and eliminate the fluid from his chest, however despite treatment, two hours after he entered the hospital, he stopped breathing and could not be resuscitated. Upon post-mortem examination, we found that he had Toxoplasmosis organisms infesting many of his major organs - heart, lungs, and kidneys. His stool sample was negative for Toxoplasmosis.

How can toxoplasmosis be prevented?

There are several practical means of preventing the transmission of toxoplasmosis. To review:

1.         Do not allow your cat to eat mice or poorly-cooked meat.  Feeding a commercial cat food and not allowing your cat outdoors virtually eliminates any possibility of the cat becoming infected.

2.         Clean all feces from your cat's litter box daily.  Even if the cat's feces is infected with toxo oocysts, they must incubate for 1-5 days before becoming infectious.  To be extra safe, do not let a pregnant woman clean the litter box.

3.         When working in soil (flower beds) that cats might use for defecation, wear gloves to keep from getting oocysts on your hands.

4.         Avoid eating raw or poorly-cooked meats.  Be especially careful of fast-food hamburgers.  Since this is probably more of a threat to your baby than your cat, special attention should be paid here.

5.         Keep children's sandboxes covered.  Outdoor cats will frequently use the sandbox for defecation.  Even if the feces are scooped out, the sandbox may remain contaminated with parasites.

SUMMARY

1.        Toxoplasmosis that affects babies is quite rare. (Incidence in the United States is 0.028% of all births.)   It is frequently referred to as "A Ladies Home Journal Disease."   (This magazine was the first widely-read publication to link toxoplasmosis and cats.)

2.        Feeding commercial cat food and keeping your cat indoors so it cannot catch mice will prevent spread of toxoplasmosis by your cat.

3.        Having someone other than a pregnant woman clean out the litter box daily will prevent spread of toxoplasmosis by your cat.

4.        Transmission from your cat to you requires that you swallow the toxo oocysts that have incubated in your cat's feces for 1-5 days.  Reasonable personal hygiene should be adequate to prevent that from occurring.

5.        Toxoplasmosis is transmitted more commonly in the United States via poorly cooked meat than by cats.

6.        Testing your cat's blood for toxoplasma antibodies is only meaningful if a positive test is followed 2-4 weeks later with another test.

Weekly testing of your cat's feces will more directly detect a cat that is capable of transmitting toxoplasmosis.

Additional resources:
Cat Parasite Affects Human Culture 
Latent Toxoplasmosis and Human 
Prevalence of Toxoplasma gondii Infection in Feral Cats in Seoul, Korea 
Companion Animal Parasite Council Recommendations for Toxoplasma  
Toxoplasmosis in the Fetus and Newborn
CDC information on Toxoplasmosis and Pregnancy
Preventing Congenital Toxoplasmosis
Cornell Feline Health Center Information on Toxoplasmosis
International Cat Care Information on Toxoplasmosi

Mr. May’s Musings

Boomer

 (Interview transcribed by Boomer's personal assistant)

Age: Just turned 1 year old

Weight: Great body condition (although Dr. Bailey calls me “fat cat”) 10.4 lbs.

Gender: neutered male

Demeanor at the vet’s office: Curious, but well behaved.

Feline friends: As of last month, I have a new brother named Bandit – 8 months old

How I found my home:  My family likes to think they chose me…but I chose them.  I was born under the front porch of their home and lived there undetected for about a month.  When my sibling and I became a bit more adventurous, they saw us playing under the watchful eye of our mother on the sidewalk.  At that time, they did not know that they were “closet cat lovers” – so they just watched us through the front window as we played.  We were irresistible!  They watched until our mom got scared and moved us to a new section of the ‘hood.  I didn’t like it there and two weeks later, I found my way back HOME.  I stood on the back of a chair on the front porch and looked in the window until my human dad noticed me.  He called my human mom and the kids.  The rest as they say…is history!  

How I got my name: My human parents decided to let the kids name me. Before they discovered I was a male, they wanted to name me Kitty Perry.  One of the kids thought I should be named Professor Kitty Pants!  While everyone thought those were pretty funny names, thankfully, my human mom refused to introduce me to the vet that way!  After much deliberation, they all landed on the name Boomer – likely from the thunderstorms that made them decide to take me in. 

Favorite food:  I love to eat both wet and dry food…and treats whenever I can get them.  I especially love the dry food – but I’m currently working on portion control at the advice of my doctor and with the unsolicited help of my brother, Bandit.  He is a much faster eater than me.  When he is done with the food in his dish, he pushes me out of the way and dives into my bowl!  I try my best to scoop some food out onto the floor with my paw – but I’m not too successful! 

Standout moment of my first year:  The day after Christmas, I became very sick.  The initial diagnosis was scary for everyone…FIP*.  My family was really sad and brought me to see Dr. Bailey.  He came up with a treatment protocol that had me taking lots of medicine and everyone watched me carefully.  I’m happy to report that I’m 100% again!   After this ‘Cat’astrophe, Dr. Bailey thought I needed a friend and so my parents rescued the newest addition to our family, Bandit! 

My favorite sleeping spots:  I really don’t require a lot of sleep and am always ready for fun! I’ve carved a little spot for myself under a bed in my human brother’s room.  He’s away at medical school and will be married soon – so the spot is available!  It’s pretty nice because he put a warm fleece blanket under there and there is a dust ruffle that keeps me hidden.  My little brother seems to like this spot, too.  My other favorite spot is on my parent’s bed nestled right up against my mom.  She thinks I’m better than an electric blanket! 

My favorite things to do:  Before I had a little brother, my favorite thing to do was follow my humans around the house – especially when they would play hide and seek with me.  I also liked to relax on the top level of my kitty condo and look down at everyone else.  Sitting in a sunny spot near an open door or window is also a favorite way to pass the time.   Since my brother arrived, my new favorite thing to do is to chase him.  When I catch him, we either rough house or groom each other.  It depends on our mood!  No kitten…it’s all true!

* Note from Dr. Bailey: Boomer was initially seen at an Emergency Hospital in December for possible ingestion of a lily. His family did the right thing in rushing him to the ER immediately since lily poisoning is a true emergency. Fortunately, lily ingestion was not the source of his illness. 

It was suspected, due to the "anterior uveitis" (a painful inflammation of the front portion of the eye that makes the eye look red and cloudy) noted in his eyes (see photo below) and the fact that he had a fever, that he may have had FIP, or Toxoplasmosis, but thankfully, further testing and favorable response to treatment suggest that neither of these diseases were the cause. Unfortunately, about 6 out of every 10 cases of uveitis cannot be linked to a specific cause, despite extensive testing. Chronic, untreated uveitis is very painful to the cat and can lead to blindness.  

Fortunately, most cases of uveitis respond very quickly to prompt treatment, as was the case with Boomer. 

Boomer with anterior uveitis (red cloudy areas) in both eyes.

Does An Apple a Day Keep the Veterinarian Away? - Feline Health Myths, Part 1

Historically, cats have been the subject of a variety of myths, both positive and negative, so it comes as no surprise that their health is a subject of myth as well.

Cats should drink milk.

Some cats don't tolerate milk, some do

Reality: While most cats do love dairy products, most cats are lactose-intolerant because they lack the certain enzyme needed to digest it. Too much milk in your cat's diet can actually cause vomiting. In the wild, cat species do drink their mother's milk until they are weaned - around 6-8 weeks of age - and then never touch a drop of milk again. This myth likely started because farmers would put out saucers of milk for young kittens as they transitioned from a milk-only diet to a diet of barn rats and mice - a diet that is a bit rougher of a transition than to that of the highly palatable and readily available commercial diets of today's typical indoor kitty.

Spaying or neutering a cat will cause it to gain weight.
Reality: When spaying or neutering occurs around 6 months of age, it coincides with a cat's natural decrease in metabolism. This is the time that cat owners should switch from kitten food to a quality adult food. Making sure that your cat is balancing dry food with 3-6oz daily canned food will help with weight control, as canned food contains about 80% water. Your cat will feel full while taking in fewer calories than if she were eating a dry-food-only diet of highly concentrated calories. Think about it this way: eating a bowl of salad or hearty soup is often more filling than an calorie-equivalent serving of potato chips or cookies.

The other factor in feline weight gain is usually inactivity. As a cat matures, he tends to play less frequently and less vigorously - possibly as much due to how we interact with our cats as due to their age. We must often come up with ways to keep our mature cats active and interested in activity, such as food puzzles, scheduled "play times", and training sessions with a portion of the daily kibble as a reward. Yes, you can teach an old cat new tricks!

Pregnant women should not own cats.
Reality: It is true that some cats are infected with the parasite Toxoplasma gondii which can cause a disease called toxoplasmosis. It is possible for this disease to be contracted through the cleaning of the litterbox. However, this disease can also be contracted through the eating of undercooked meat (50% of cases), eating unwashed produce or through gardening without gloves, so cats are not the only culprit.

Instead of thinking of re-homing your cat, have other people empty the litter box daily. Toxoplasma oocysts (eggs) aren't infectious for the first 24 hours after they're excreted, so daily cleaning (which your cat prefers, anyway) will decrease the risk of tranmission even further.If no one else can clean the litter, wear gloves and a mask to clean and wash your hands thoroughly afterwards. Don't plan to get a kitten while pregnant, and try to limit your cat's hunting. If you feed a raw diet, it would be best to discontinue doing so while pregnant, both to decrease the risk to your cat, and also to limit the handling of raw meat while pregnant.

Cats are nocturnal.

Glowing tapetum lucidum

Reality: While cats can see in 1/6th the light that humans can, making it appear that they can see in total darkness, they do need some light to see. The tapetum lucidum ("bright tapestry") is a shiny cover across the back of the retina that helps reflect and enhance ambient light, which increases the cat's ability to see in low light. It is also what makes cats' eyes "glow" in the dark, or in flash photography.  In actuality, most cats are highly active in the early morning and early evening, making them "crepuscular" animals rather than "nocturnal".

Garlic is a good, natural flea repellant for my cat.
Reality:  Whether or not garlic is a good flea repellant, all members of the genus Allium (onion, garlic, leek, chives, shallots, and scallions) can be poisonous to both dogs and cats. Toxicity can cause damage to the red blood cells (RBC), resulting in Heinz body anemia. In particular, cats are 2 to 3 times more susceptible to RBC damage from these components than other species. While specific studies have not been done with garlic as to the safe levels of ingestions, acute onion toxicosis occurs in animals that eat more than 0.5% of their body weight at one time (less than 2 Tbsp. for a 10lb. cat). However, smaller doses given regularly over a period of time will cause the same problem.

Dietary ash and magnesium are what cause feline urinary crystals.

Struvite crystals in urine

Reality: While this was thought to be the main cause of crystals in the urine ("crystalluria") in the past, many pet food manufacturers responded to these concerns by decreasing the amount of ash (and phosphorous) and magnesium in their diets. What we know now is that maintaining a more dilute urine and more neutral pH by feeding primarily canned foods is the best way to prevent cats from developing urinary crystals. In addition, thoughtful litterbox husbandry - making sure the litterbox is a pleasant place for your cat so that he visits regularly to empty his bladder instead of holding his urine, and providing sufficient quantities of fresh water and encouraging your cat to drink by adding ice cubes or providing a pet fountain will help as well.

There are many more myths out there, so stay tuned for Part Two! Are there any myths you have heard that you want us to address?