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

Cuterebra infection: Not really that cute...

Gryffin

Meet Gryffin, a tiny little kitten found wedged between the wall of a gas station and the ice machine. He weighed less than two pounds, and had a wound on his leg. Upon examination by the doctor, it appeared to be a run-of-the mill bite-wound abscess. Once under anesthesia, we were able to take a closer look - clipping up the hair and scrubbing the wound with antiseptic scrub. Bite wound abscesses have a tendency to become infected, so Dr. Brooks removed the scab and flushed the wound. As would be expected, the wound was infected. After cleaning it out, the doctor gently probed the wound and determined that it was clean. We treated Gryffin with pain medication and antibiotics.

But, Gryffin didn't get better. His wound still seemed to bother him, and we examined him again. The wound was free from infection - what could it be? Dr. Brooks commented that it was a remote possibility that it was a Cuterebra breathing pore, but no Cuterebra was found in the wound, and the pores do not scab over while the larvae are inside. It was also an unusual site for a Cuterebra infection, since Cuterebra larvae generally infect the head and neck regions of cats. She decided to satisfy her curiosity non-invasively, by placing the ultrasound probe on Gryffin's leg. This is what she saw:

Ultrasound image of a cuterebra larva

Deep within the wound, far from the scabbed opening, a dead Cuterebra lay - acting essentially like a sliver under the skin, causing irritation and infection and pain. Dr. Brooks was now able to locate the larva and remove it, much to Gryffin's relief! We measured the Cuterebra once it was removed, and determined that it was the biggest one we had ever seen, at 4cm in length.

Cuterebra larva after removal

Cuterebra. It doesn't sound too bad, and usually, they don't cause too much trouble, but Cuterebra larval infection can cause problems for cats.

The Cuterebra larvae are immature bot flies - a large bumblebee sized fly. The adult flies are harmless - in fact, they live for such a short time, they do not even have mouth parts for eating!

Adult Cuterebra

They lay thousands of eggs in the environment (blades of grass, wood chips - areas near rodent burrows) or on other insects (such as mosquitoes), or even directly on the host (such as horses) - usually in clusters of 5-15 eggs. Cats and dogs are not the normal host of the Cuterebra, but can become infected if they spend time in areas where the eggs have been deposited. The eggs tend to hatch quickly when exposed to the warmth of a nearby body. Most of the time, cats will become infected by coming into contact with a newly-hatched Cuterebra larva with the nose or mouth, but the Cuterebra can also enter the body through open wounds.

Once in the body, the larva forms a small cyst under the skin - most commonly near the face and neck. These lumps are usually very easy to distinguish from a cancerous lump by the 2-4mm breathing pore that the larva creates. Often, the larva can be seen moving towards and away from the pore to breathe. These lumps are called "warbles". It is most common to see the warbles in late

August and September. Some years, we see a lot, other years, we see none. In the Waterford area, kittens tend to be most commonly affected, but any cat that goes outside could come into contact with a Cuterebra larva.

Sometimes, a sneezing cat may have a Cuterebra infection in its nose. On some rare occasions, a Cuterebra infection may occur in or near the eye or spinal cord. These situations are very rare. Cats that develop eye infections may or may not have damage to the eye. Neurologic signs of Cuterebra infection may include "head pressing", circling in one direction, or other behavioral changes. Cats that develop spinal cord infections may fully recover once the Cuterebra larva is removed.

The most effective treatment for Cuterebra infection (called "cuterebriasis") is surgical removal of the larva. In some situations, this can be quite complicated, depending on the location of the larva. It is important to be able to remove the entire larva, and not to break the larva while it is inside the cat, or a severe allergic-type reaction can occur (called "anaphylaxis"). 



It is important to remember that you can NOT get a Cuterebra infection from an infected cat, but you may have Cuterebra present in your yard.

Two weeks after removing Gryffin's parasite, he looks great!

In Michigan, late summer and early fall is the time of year that Cuterebra infections become evident. The larvae are very difficult to see until they become large, due to the fur coat your cat wears. Some years, we do not see any cats with Cuterebra infections, other years we see quite a few. This year, we saw a cluster of 4 cats with Cuterebra infection, all in a row at the end of August and early September. Two of the cats had Cuterebra larvae in the neck region, Gryffin had his infection in a hind leg, and one Cuterebra was located up a cat's nose! He had a "chronic upper respiratory infection" that would get only a little better with antibiotics. Some might have written that off as a viral infection (viruses do not respond to antibiotic treatment), but Dr. Brooks took a look up the cat's nose and there was the source of the chronic sneezing! Once the Cuterebra was removed from the cat's nose, he fully recovered.

These days, Gryffin is doing much better, without his creepy-crawly passenger!

EDIT: 11/4/14 Gryffin came in for a recheck and had gained almost a pound since his last visit. His wound is healed and he is looking and feeling great!


For more information:
Article on Cuterebra from the American Association of Veterinary Parasitologists