Bradfordville Animal Hospital
Toxoplasmosis Information

Toxoplasmosis, a disease most commonly associated with cats, is caused by the protozoal parasite Toxoplasma gondii.  Cats are the only known definitive hosts for this organism, though dogs and humans may also become infected. Approximately 30 % of cats and 50 % of humans are serologically positive for the parasite; however, clinical disease is uncommon.

Transmission

Cats may become infected with Toxo in one of three ways:

1. infection of kittens from the mother cat prior to birth
2. ingestion of cysts from contaminated feces
3. ingestion of birds, fish, reptiles, small mammals or other types of raw meat which contain cysts

After ingestion, these cysts may be shed in the feces of the infected cat for 7-10 days. Once released from the cat back into the environment, these cysts must be exposed to the proper conditions for 1-5 days before they can become infectious. In the cat, the cysts also travel from the intestines to other parts of the body such as the eyes, heart and central nervous system where they may remain inactive for the life of the cat, or in a small number of cases, may cause actual disease.

Clinical Signs and Diagnosis

Clinical signs of infected, sick cats may vary depending on the organ involved. Anorexia, weight loss, lameness, fever, lethargy, difficulty breathing, coughing, jaundice, enlarged lymph nodes, seizures and eye problems are some of the signs that may be seen. Toxo may also be seen in cats infected with feline leukemia virus or feline immunodeficiency virus (feline AIDS) because these viruses cause the cat's immune system to malfunction and consequently, it is easier for the Toxo organism to cause clinical disease.

The most common way of diagnosing Toxo is by a special blood test which demonstrates an antibody response to the organism. This response, called a titer, may be measured based on two types of antibodies. Measuring these titers helps differentiate if a cat had had a recent exposure to Toxo (i.e. within the past 4 months) or if the exposure occurred sometime in the past (i.e. within the past several years). In either case, a positive titer does not necessarily mean that a cat is "sick" with Toxo. The results of these titers are combined with other blood test results, radiographs and clinical signs to determine the diagnosis. Toxoplasmosis can be treated with a specific antibiotic, though response times vary depending on which body systems are affected. Very young kittens and immunosuppressed cats typically do not respond well to treatment. It is also important to know that if a cat has shed oocysts at some point in the past, it is extremely unlikely that shedding would ever occur again.

Human Infection

Toxoplasmosis can also pose a serious health risk to humans, most notably those in an immunocompromised state (i.e. those undergoing chemotherapy or infected with AIDS) and a pregnant woman's unborn baby. Toxoplasmosis infections in normal, healthy people often cause no signs at all or possibly mild, flu-like symptoms. The organism may then encyst in tissues throughout the body where it lies dormant. If an infected individual becomes immunocompromised, the Toxo may then become active again and cause a life-threatening brain infection. In a pregnant woman, the parasite can also cross the placenta to infect the fetus. If this happens, miscarriage or premature birth may occur or the baby could be born with neurological problems, including permanent brain damage. It is important to note however, that the chance of a pregnant woman contracting Toxo from eating undercooked meat is higher than contracting it from her cat. Likewise, in HIV-infected individuals, no correlation has been shown between owning a cat and testing positive for Toxo antibodies. The bottom line to this is that neither pregnant women nor HI V-infected persons have to give up their cats.

Unfortunately, the cat has borne the brunt of responsibility for human infection, while less attention has been placed on other, equally important modes of infection. For example, it is more likely to contract Toxo from ingestion of contaminated soil or water than from contact with a cat! Methods of infection with Toxo are discussed below.

Cats

Humans can only become infected from cats by handling contaminated fecal material which contains sporulated oocysts. CONTACT WITH FRESH FECES CANNOT CAUSE INFECTION! Cats cannot transmit Toxo by licking a person and due to the nature of healthy cats to groom themselves frequently, cysts are not found on their fur. A healthy cat which has a positive titer for Toxo essentially poses no danger to its owner. Susceptible individuals should exercise caution when their cat has no titer at all and other factors are present which make it possible for the cat to be infected.

Soil and Water

Soil and water may be contaminated from fecal material of cats which has been deposited and subsequently sporulated. Gardening, therefore, poses a hazard as does drinking water from any unreliable source. Outdoor sandboxes should also be considered a source of potential infection.

Meat

Raw meat is a very common source of Toxoplasma. Approximately 25 % of pork is infected but any raw meat should be considered suspect. Freezing meat at -20 degrees Centigrade for several days will greatly reduce the viability of tissue cysts and cooking meat to 150 degrees Fahrenheit for 20 minutes will kill the cysts.

The following is a list of suggestions which can greatly reduce the chances of infection from Toxoplasmosis:

• prevent cats from hunting, when possible
• use a litter box liner and change it daily
• have the litter box cleaned daily, with any feces flushed. If another person is not available to do this, wear gloves and wash hands immediately after cleaning.

• boil water prior to drinking if the source is unknown or unreliable
• wear gloves when gardening or working with soil
• wash vegetables prior to eating
• cover sandboxes to prevent cats from defecating in them
• WASH HANDS, WASH HANDS, WASH HANDS!

• avoid eating raw or undercooked meat
• DO NOT feed raw meat to cats
• wash hands, cutting boards, utensils and other contaminated surfaces after contact with raw meat

By following these suggestions and using common sense, there is little reason that cats and susceptible individuals cannot share the same home and lavish attention on each other in that unique way that makes the cat/owner relationship so special!

Points to remember

1. Toxo oocysts are not infectious when they are first passed from the cat- they must sporulate first, which takes 1-5 days
2. A positive Toxo titer in a cat does not mean that the cat is sick because of Toxo
3. Cats usually only shed oocysts 1 time- recurrent shedding does not usually occur
4. Cats are only 1 source of potential infection of Toxo and are one of the least likely sources overall. Soil, water and meat are also very important routes of infection.
5. It is as important for a susceptible individual to have a Toxo titer checked as it is his/her cat.
6. Washing hands is the single- most important factor in preventing Toxoplasmosis.