Is flushable cat litter a public health hazard?

I had an interesting question today about the cat-associated parasite Toxoplasma gondii. It can cause serious infection in people that ingest it, particularly in immunocompromised individuals and pregnant women, but disease is rare. Since cats can pass one form of the parasite in their feces, the question was whether using flushable kitty litter is a bad idea, since it would result in Toxoplasma being discharged into the sewage system.

On one hand…

  • Water is a source of Toxoplasma exposure.
  • Food contaminated by Toxoplasma-contaminated water is a also a source of exposure.
  • Municipal water was determined to be a possible source of exposure in at least one Toxoplasma outbreak (Bowie et al. 1997).
  • The form of Toxoplasma in cat feces is hard to kill, so it could survive routine water treatment measures.

On the other hand….

  • Cats rarely shed Toxoplasma. They typically do so only for a short period of time after their first exposure (usually when they're quite young), so the vast, vast majority of household cats are not shedding the parasite.
  • There’s a massive dilutional effect when something goes down the drain. To constitute a risk, the parasite would have to come out of the cat, survive waste water treatment and be discharged into the environment, then either make it into a drinking water source (with more dilution and more treatment) or reach someone’s mouth through other routes such as on food or from contaminating the general environment (e.g. soil, recreational water bodies). Even if some Toxoplasma were present in cat feces in flushable litter, the odds that someone susceptible would encounter enough Toxoplasma from this source to cause disease is exceedingly remote.

I don’t think using flushable litter constitutes a public health risk.

More information about Toxoplasma is available on the Worms & Germs Resources - Pets page, as well as in our archives.

Why Finnegan's an indoor cat

I grew up with cats, and they were all indoor/outdoor. I never really thought about it since that was just the way things were done. Yet, as much as he’d like to convince us otherwise, our current cat Finnegan is an indoor cat. There are a lot of reasons for this.

One reason for keeping Finnegan in the house is zoonotic disease prevention. I was recently giving a talk about "Pets and immunocompromised owners" at the American College of Veterinary Internal Medicine forum, and a recurring theme for reducing the risks associated with cats was keeping them inside. (Want to reduce the risk of the cat being exposed to Toxoplasma? Keep it inside. Want to reduce the risk of Salmonella exposure? Keep the cat inside...).

Another important reason is the animal's own health:

  • Cat vs car rarely ends well for the cat, and untold thousands of cats meet their ends on roads every year.
  • Cat vs cat isn’t as bad but can lead to cat bite abscesses and transmission of a few different pathogens such as feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV).
  • When outside, cats can also be exposed to various insect borne pathogens that can be of concern. This kind of risk varies between regions, with areas such as those where there are ticks carrying Cytauxzoon felis (a parasite normally carried by bobcats) perhaps being the biggest concern.

Wildlife is another concern, in two ways. Just like with cars, cat vs larger critter such as a coyote rarely ends well for the cat. From an ecological standpoint though, greater problems occur from cats killing smaller wildlife. It’s been estimated that free-roaming domestic cats kill billions (yes, Billions) of birds and small mammals every year. I won’t go into all the details here, but there’s a good article on the Canadian Cooperative Wildlife Health Centre’s website about the impact such avid feline predators can have on local ecology.

Some people would argue that cats are better off going outside. Looking back at the cats with which I grew up, a lot died early because they were allowed to go outside. It’s hard for me to justify the risk to the cat, wildlife and public health for some anthropomorphic “he’d really enjoy being outside” argument.


"Human suicide parasite" in cats

I love my cats. But sometimes when Bonnie and Clyde are living up to their names, puking up hair balls twice a day, peeing on the guest bed (yes, contrary to popular belief even vets can't stop their own cats from doing this sometimes), caterwauling at 3 AM, or begging for food all afternoon, they do make me c-r-a-z-y crazy - but they're not making me suicidal.

In yet another example of how the media will present study results in the manner that will sell the most newspapers or magazines, rather than the way that helps people interpret the results in a logical manner, comes an article entitled "Is Your Cat Hosting a Human Suicide Parasite?" The article talks about a study recently published in the Archives of General Psychiatry (Pedersen et al. 2012) which looked at a cohort of 45 788 women in Denmark who gave birth between 1992-1995, and found a statistically significant association between self-directed violence (including suicide attempts) in these women and their antibody titre to Toxoplasma gondii at the time of birth.  The risk in seropositive women was 1.53 times greater than the risk in seronegative women.

Toxoplasma gondii is a parasite that is shed in the feces of cats, which are the parasites definitive host.  Most house cats only ever shed significant amounts of the parasite the first time they're exposed to the parasite (typically when they're young).  Depending on where people live and various cultural practices, transmission of the parasite from scooping out litterboxes may actually be relatively uncommon compared to other possible sources including exposure from soil (e.g. working in the garden and then not washing one's hands), eating unwashed vegetables, or eating some types of undercooked meat.

The most glaring limitation of the Pedersen study is that they didn't control for any other factors that may have resulted in the women who committed acts of self-directed violence being more likely to be seropositive for Toxoplasma than others.  For example, women with mental illness may be less likely to practice good hand hygiene (one of the most important factors for reducing the risk of parasite transmission), and therefore more likely to be exposed to Toxoplasma, or there may be other factors about their health or their lifestyle that make them more prone to infection. The point is the authors only found an association in a specific subset of the population (Danish women who had given birth to at least on child).  This does not mean that the relationship is causative - they can't say that Toxoplasma infection makes people more prone to self-directed violence, only that women - in this particular group - who were seropositive for the parasite were also at increased risk for this kind of behaviour.  It's a somewhat subtle but very important difference.  The authors of the study clearly acknowledge the limitations of their work, but the news article does not do quite as good a job of pointing this out, until right at the very end where it does finally get mentioned.

Does Toxoplasma infection cause behavioural changes in rats that may make them more likely to wander into a cat's territory and be eaten?  According to an experimental study it can, and it does make a certain amount of ecological sense that the parasite could have an effect on its intermediate host (the rat) that makes it more likely to be able to continue its life cycle (via being eaten by a cat) by reducing fear in the rat. Could infection of the brain in humans cause subtle behavioural changes?  I can't deny the possibility, but humans are not rats and I would be very wary of extrapolating results from one species to the other. But is this parasite likely to "drive our brains off the highway" as the news article says?  I'm not ready to buy that, certainly not based on this study.  As the authors clearly state in the first line of the paper "Suicide is a tragic multifactorial outcome of mental illness, with complex biopsychosocial underpinning..."  There are so many things that contribute to such an unfortunate outcome that a lot more work is needed before anyone can justifiably blame a "suicide parasite" in cats.

Whether you believe Toxoplasma infection can result in behavioural changes in people or not, there are some very simple steps everyone can take to help decrease the risk of becoming infected with this parasite regardless.  These are particularly important for individuals who are immunosuppressed and women who are pregnant, because it is very well established that toxoplasmosis in these high-risk individuals certainly can have severe repercusions to either the individual or the unborn fetus.  However, it is by no means necessary for such individuals to get rid of their cats if they take these simple precautions:

  • Clean your cat’s litter box every day. The oocysts shed in cat feces usually take about 24 hours to become infective once they’ve been passed, so daily cleaning helps remove them before they reach this stage.
  • Always wash your hands with soap and water after cleaning your cat’s litter box, after working in the garden or in any soil, and after handling raw meat.
  • Keep your cat indoors. Outdoor cats are more likely to be exposed to Toxoplasma and shed oocysts in their stool. 
  • Keep sandboxes covered so outdoor cats don’t contaminate them with stool.
  • Cook all meat, especially pork, lamb, mutton and wild game, to an internal temperature of 67ºC/153ºF or higher.

More information about Toxoplasma can be found on the info sheet on the Worms & Germs Resources page.

Cats and pregnancy: Not-so-"expert" advice

A recent column by pediatrician Dr. T. Berry Brazelton has caused quite a stir. Dr. Brazleton is apparently a very well known syndicated columnist, and he answered a question from a reader about her pregnant daughter and her cats. The reader was concerned about the cats lying on the baby. However, Dr. Brazleton focused on the risks of toxoplasmosis, which we've covered in previous posts and in a fact sheet in the Worms & Germs Resources page. He points out some valid facts and concerns regarding toxoplasmosis and prevention of this disease. However, he strayed off the logical, evidence-based trail with the statement "It would be better for the baby if your daughter would rid herself of the cats."

I am unaware of any medical, veterinary or public health group that advocates removal of pets from households with pregnant women. In fact, the Centers for Disease Control and Prevention (CDC) specifically state that pregnant women do NOT need to get rid of their cats. Dr. Brazleton also stated "Some cats will seek out the infants' mouths and noses and lie on them to smother them." While Dr. Brazleton may be well-versed in pediatrics, he apparently didn't take the time to look into current evidence and recommendations in this regard. His statements are ill-informed and irresponsible.

One should never dismiss peoples' concerns about disease or injury to babies from pets. The health of babies far superceeds concerns about pets. However, there are positive social and emotional aspects of pet ownership that similarly must not be ignored. There is simply no evidence that removing cats from households with pregnant women or infants is useful or necessary. The key is to consider basic (often common sense) infection control measures and proper animal management/training to reduce the risk of any adverse events.

Pet columnists have picked this article up and made various responses. One of the best I've seen is from Steve Dale. It provides some good basic information about why Dr. Brazleton's advice is unsound.

Comprehensive information about toxoplasmosis, and reducing the risks of disease, can be found on the Worms & Gerns Resources page.

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Your mother was right! Wash your hands

You may notice a recurring theme in many of our posts and on virtually all of the information sheets on the Worms & Germs Resources page: an emphasis on handwashing. There is increasing emphasis on hand hygiene (i.e. hand washing and use of alcohol hand sanitizers) education in hospitals because the hands of healthcare workers are a major (if not the most important) means of disease transmission between patients. Despite hand hygiene being easy, cheap and effective, people rarely wash their hands as often as they should, and they often don't do it properly.

Most of the research about hand hygiene that has been published has focused on its use and impact in human hospitals, but this area is now also being studied more with regard to animals and veterinary medicine. A study published earlier this year in Veterinary Microbiology provided more evidence that hand hygiene is a critical infection control measure when dealing with animals. The study, coordinated by Dr. Maureen Anderson (of Worms&Germs fame) looked at MRSA carriage rate in veterinarians who work with horses. In addition to finding a high rate of MRSA carriage among these veterinarians (which was consistent with other reports indicating that equine vets are at higher than average risk for exposure to MRSA), the study looked at factors associated with MRSA carriage. Vets that reported routinely washing their hands between farms and those that reported washing their hands after contact with potentially infectious cases had a significantly lower rate of MRSA carriage. That should come as absolutely no surprise, but it's one more piece of evidence that we need to pay more attention to this routine infection control measure, in human hospitals, in veterinary environments and in households.

Remember, the 10 most important sources of infection are the fingers on your hands!

Click here for instructions on how to wash your hands properly.


If you are looking for an interesting website to play around with, you should try HealthMap. This is a website created by the Harvard-MIT Division of Health Sciences and Technology that maps infectious disease reports from various sources. You can search by region and see what disease problems have been reported recently, or select specific diseases and find out where they've been reported.   Some examples are shown below. The top image shows all disease reports worldwide (in the last 30 days), while the bottom image shows reports of Salmonella in North America during the same time period. The site relies on reports of diseases (many cases of various diseases occur but are never reported), so it focuses mainly on outbreaks or high profile cases , but it is still quite interesting.

Above: All reported disease outbreaks/cases worldwide in the last 30 days.
Below: Reported outbreaks/cases of Salmonella in North America in the last 30 days.
See the HealthMap site for more details.

Feline Immunodeficiency Virus - HIV/AIDS for Cats

Everyone is familiar with the human immunodeficiency virus (HIV) - the retrovirus that causes acquired immunodeficiency syndrome (AIDS) in people. Although HIV can only infect humans and some primates, cats can be infected by a very similar virus from the same genus (Lentivirus) with a similar name – feline immunodeficiency virus (FIV). The FIV virus is transmitted from cat to cat by contact with blood, usually through a cat bite.  In Canada and the USA, up to 3% of healthy cats may be infected with FIV.

As with HIV in people, FIV attacks a cat’s immune system, which can leave the animal susceptible to many different infections that a healthy cat could normally fight off. Some of these infections, like toxoplasmosis, are similar to those that occur in AIDS patients. (More information on toxoplasmosis and Toxoplasma is available on the Worms & Germs Resources page). Depending on a number of factors, an FIV-positive cat may remain healthy for years, but once the animal begins to show signs of a weakened immune system, it will often develop chronic or recurrent health problems. The infection is life-long – there is no “cure” for FIV.

Some key points to remember:

  • Cats cannot get HIV. People cannot get FIV. They are related but different viruses.
  • Keeping your cat indoors will prevent fighting with other cats and decrease the risk of your cat contracting FIV.
  • There is a vaccine available for FIV, but it remains uncertain if the vaccine can protect cats from all strains of the virus.  The vaccine also interferes with tests for FIV infection.  Therefore, preventing exposure to the virus is still the best way to prevent FIV infection.
  • If your cat already has FIV, it is important to keep it indoors to decrease exposure to pathogens that could make your cat sick, and to prevent your cat from spreading the virus to other cats.

More information about FIV can be found on the Cornell Feline Health Center website.


Are pregnancy and cats compatible?

There is a degree of risk of disease transmission from any contact with an animal, just as there is from any contact with another person.  Some of the diseases involved are minor or even insignificant, while others are potentially devastating.  And the risk can change in certain situations, such as pregnancy. A developing fetus is more susceptible to some diseases that may typically have little to no effect on an adult.  Toxoplasmosis is one disease that gets a lot of attention from pregnant women.

Toxoplasmosis is caused by the protozoal parasite Toxoplasma gondii.  Infection of a pregnant woman with Toxoplasma can cause birth defects or even miscarriage. But the real risk occurs when a woman who has not been previously exposed to Toxoplasma becomes infected during pregnancy. Pregnant women who were exposed to Toxoplamsa before they became pregnant, and therefore already have antibodies against the parasite, are not at risk.

Cats are the only animal species that can spread Toxoplasma in their stool. Only a very small percentage of cats are shedding Toxoplasma at any one time, but the proportion can be higher among cats that go outside, hunt or are fed raw meat. It takes 24 hours or more for Toxoplasma in cat stool to become infectious - a person cannot be infected with Toxoplasma from fresh stool. This key point can greatly reduce the risk of transmission from a cat, if the cat's litter box is cleaned out on a daily basis.

Any infection that can potentially have devastating effects on a fetus needs to be taken seriously. While it appears to be rare these days, some women are still advised to get rid of their cats if they are pregnant. Pregnant women do not need to give up their cats!  A few basic measures can greatly reduce the risk of transmission of Toxoplasma from cats to pregnant women:

  • Pregnant women should not have contact with litter boxes (or any cat feces) if possible - preferably another person should do the litter box cleaning.
    • If a pregnant woman must clean the litter box, it should be done daily so that Toxoplasma does not have enough time to become infectious.
  • Litter boxes should be regularly scrubbed and cleaned with scalding water (see the Worms & Germs Resources page for more information on Litter Boxes).
  • Keep your cat's fur free of stool contamination.  This is especially  important in longhaired cats that might get stool on the fur around their hind end, or sick/old/obese cats that have difficulty grooming themselves properly.
  • Keep your cat indoors. Outdoor cats are more likely to be exposed to Toxoplasma and spread the infection.
  • Do not feed your cat raw meat.
  • Wash your hands thoroughly after cleaning the litter box, handling raw fruit and vegetables, and working with soil (for example, in the garden).
  • Cook all meat completely to recommended temperatures, and practice safe meat handling to prevent spread of contamination from raw meat to kitchen surfaces and other food.

More information about Toxoplasma and zoonotic diesases associated with Cats can be found on the Woms & Germs Resources page.

Toxoplasmosis - Why Your Cat Shouldn't Get the Blame or the Boot

Toxoplasma gondii is one of the most widespread zoonotic pathogens in the world. Toxoplasma is a protozoal parasite that can infect almost any warm-blooded animal, including humans. In most people and animals, infection doesn’t cause any illness at all, and after the initial infection, the body usually produces strong immunity which protects it from subsequent Toxoplasma infection. Problems arise when infection occurs in a person with a weakened immune system. For example, toxoplasmosis (i.e. illness due to Toxoplasma) has been a major problem in HIV/AIDS patients, although better HIV treatments have decrased the incidence of the disease in this group in recent years. Toxoplasma can also cause problems when a woman is infected for the first time, before her body has developed immunity to the parasite, while she is pregnant. In these cases, the parasite can infect the fetus. This may result in birth defects or loss of the pregnancy altogether.

Our friendly feline companions have the unfortunate distinction of being what is called the “definitive host” of Toxoplasma. This means that even though the parasite can infect many species of animals, cats are the only species that shed the parasite “eggs” (which are called oocysts in this case) in their stool after they’re infected. But what most people don’t realize is that the number of cats that are shedding oocysts at any one time is very small – usually less than 1 in 100. And after the first time a cat is infected, it usually doesn’t shed oocysts again, and if it does it sheds them in very low numbers.

Depending on individual lifestyle and eating habits, a person is just as likely or more likely to be exposed to Toxoplasma from working in the garden or eating undercooked meat (particularly free-range pork or wild game). People who are pregnant or who have a weakened immune system do NOT need to get rid of their cats because of Toxoplasma, but they DO need to take steps to avoid exposure to Toxoplasma from all sources.  This includes avoiding contact with cat stool and kitty litter by asking someone else to clean their cat’s litter box for them if possible, or wearing rubber gloves and being very careful to wash their hand very well afterwards if they need to clean the box themselves. Here are a few more tips that can help reduce their risk of exposure to Toxoplasma:
  • Clean your cat’s litter box every day. The oocysts usually take about 24 hours to become infective once they’ve been passed in your cat’s stool, so daily cleaning helps remove them before they reach this stage.
  • Always wash your hands with soap and water after cleaning your cat’s litter box, after working in the garden or in any soil, and after handling raw meat.
  • Cook all meat, especially pork, lamb, mutton and wild game, to an internal temperature of 67ºC/153ºF or higher.
  • Keep sandboxes covered so outdoor cats don’t contaminate them with stool.
  • Keep your cat indoors. Outdoor cats are more likely to be exposed to Toxoplasma and shed oocysts in their stool.
You can find more information about Toxoplasma on the Worms & Germs Resources page.

Information Sheets for Pet Owners

INFORMATION SHEETS specifically for KIDS, for VETERINARIANS, for PHYSICIANS and for PUBLIC HEALTH PERSONNEL are also available on the Worms & Germs RESOURCES page!

Click on the highlighted topics below for information sheets. Topics that are not highlighted are in development and coming soon. Sheets for other animal species and diseases are also under development and will be added when they are available.

Diseases Other
Dogs Rabies Litter Boxes
Cats Giardia Sandboxes
Turtles Toxoplasma Cat Bites
Hamsters Leptospira Raw Meat
Rabbits Clostridium difficile Petting Zoos
Pet Birds Cryptosporidium Needlestick Injuries
African Dwarf Frogs MRSA  
Reptiles MRSP  
  MRSP (Deutsch)  
  MRSP (Francais)  
  Rat Bite Fever  
  Cat Scratch Disease  
  Lyme Disease & Ticks  


Please Remember:

  • Your veterinarian and physician are your ultimate resource for information about the health of your pets or your family.
  • Information provided here is accurate to the best of our knowledge, but infectious diseases can be unpredictable and these sheets are for general information purposes only.
  • There can be great variation in disease risks in different geographic areas. The information provided was developed for Ontario, Canada, but most of the information is relevant for other regions as well.

Research Posters

2012 International Clostridium difficile Symposium

2012 International Conference on Equine Infectious Diseases IX

2011 ASM-ESCMID Conference on Methicillin-resistant staphylococci in animals

2011 University of Guelph Centre for Public Health and Zoonoses Symposium

2011 Canadian Animal Health Laboratorians Conference

2011 Canadian Association of Clinical Microbiology and Infectious Diseases

Coming soon

  • 2011 American College of Veterinary Internal Medicine Forum, June
  • 2011 ASM-ESCMID conference on methicillin-resistant staphylococci in animals, Sept