Feline Infectious Diseases

Feline Immunodeficiency Virus

The Feline Immunodeficiency Virus (FIV), often called the Feline AIDS Virus, is an important infectious disease of the cat. It is likened to the AIDS virus which affects humans because of the similarities in the two diseases which result. Fortunately, most viruses are species specific. This is the case with the human AIDS virus and with FIV. The AIDS virus affects only humans, and the FIV affects only cats.

Contributing Factors

The FIV is transmitted primarily through bite wounds from other cats that usually occur in fights. Other interactions of cats, such as sharing common food and water bowls or grooming each other, have not been shown to be significant in transmission.

Clinical Signs

An FIV infected cat will generally go through a prolonged period of viral dormancy before it becomes ill. This incubation period may last as long as 6 years. Thus, we generally do not diagnose FIV in sick cats who are relatively young.

When illness occurs, we can see a variety of severe, chronic illnesses. Because FIV suppresses the cat’s immune system, minor illnesses or wounds may take much longer to heal than in a healthy cat. The most common illness is a severe infection affecting the gums of the mouth. Abscesses from fight wounds, which would normally heal within a week or two, may remain active for several months. Respiratory infections may linger for weeks. The cat may lose weight and go through periods of not eating well; the hair coat may become unkempt. The cat may have episodes of treatment-resistant diarrhea. Ultimately, widespread organ failure occurs, and the cat dies.


Evidence of exposure to the FIV can be detected by a simple blood test. A positive test means the cat has been exposed to the virus and will likely be infected for the remainder of its life. A negative may mean that the cat has not been exposed; however, false negatives occur in two situations and usually involves adult cats:

Adult Cats

  1. From the time of initial virus inoculation into the cat, it may take up to two years for the test to turn positive. Therefore, for up to two years, the test is likely to be negative even though the virus is present in the cat.
  2. When some cats becomes terminally ill with FIV, the test may again turn negative. This occurs because antibodies (immune proteins) produced against the virus become attached and bound to the large amount of virus present. Since the test detects antibodies which are free in circulation, the test may be falsely negative. This is not the normal occurrence, but it does happen to some cats.


The vast majority of kittens under 4 months of age who test positive have not been exposed to the virus. Instead, the test is detecting the immunity (antibodies) that were passed from the mother to the kitten. These antibodies may persist until the kitten is about 6 months old. Therefore, the kitten should be retested at about 6 months of age. If it remains positive, the possibility of true infection is much greater. If the kitten tests negative, there is nothing to worry about.

If a kitten is bitten by an FIV-infected cat, it can develop a true infection. However, the test will usually not turn positive for many months. If a mother cat is infected with the FIV at the time she is pregnant or nursing, she can pass large quantities of the virus to her kittens. This means of transmission may result in a positive test result in just a few weeks.


No treatments are available to rid the cat of the FIV. Sometimes, the disease state can be treated, and the cat experiences a period of recovery and relatively good health. However, the virus will always remain in the cat and may become active at a later date. Therefore, the long term prognosis is unfavorable.

If you have a cat which tests FIV-positive but is not ill, euthanasia is not immediately necessary or recommended. As long as it does not fight with your other cats or those of your neighbors, transmission is not likely to occur. However, if it is prone to fight or if another cat often instigates fights with it, transmission is likely. In fairness to your neighbors, it is generally recommended to restrict an FIV-positive cat to your house. Owners of infected cats must be responsible so that the likelihood of transmission to someone else’s cat is minimized.


Although the virus is slow-acting, a cat’s immune system is severely weakened once the disease takes hold and this makes the cat susceptible to various secondary infections. Infected cats who receive supportive medical care and are kept in a stress-free, indoor environment can live relatively comfortable lives for years before the disease reaches its chronic stages.


Neutering of male cats and keeping cats indoors are the only available preventive measures which can be recommended. No vaccine is currently available to prevent infection with this virus.

Feline Leukemia Virus Disease

Feline leukemia virus infection was, until recently, the most common fatal disease of cats. Because we can now protect cats with a leukemia virus vaccine, we are seeing fewer cases of the disease. However, it still remains a major cause of death in cats.

“Leukemia” means cancer of the white blood cells. This was the first disease associated with the feline leukemia virus (FeLV) and, thus, the source of its name. We often use the term “leukemia” rather loosely to include all of the diseases associated with the virus, even though most are not cancers of the blood. This virus causes many other fatal diseases, in addition to leukemia.

Feline leukemia virus is classed as a retrovirus. The retroviruses are of particular importance because they have the ability to integrate into the genetic material, or DNA, of the host. For this reason, some call the
retroviruses “the ultimate genetic parasites.” There are three subtypes of the virus and the diseases caused are dependent upon the particular subtype involved. The feline immunodeficiency virus (FIV), discussed above, is another feline retrovirus.


In the total population of cats, the incidence of FeLV is only about 1-2%. Free-roaming adult cats that are FeLV-negative have usually acquired age-related resistance to the virus. The incidence is much higher in “exposure households,” or households where there is a FeLV-positive cat living among other cats. In this setting, 30% – 100% of the cats may be found to test positive.

Clinical Signs

There are three major disease categories associated with the FeLV:

  1. Leukemia is a cancer of the white blood cells.
  2. Lymphosarcoma (also called Lymphoma) is a cancer of many different organs but it begins in lymphoid tissue, such as a lymph node. Almost any tissue may be affected; organs commonly involved include lymph nodes, intestinal tract, kidneys, liver, spinal cord, brain, bone marrow and blood. In young cats, lymphoma often manifests as a mass within in the thoracic cavity; this is called “mediastinal lymphoma.”
  3. The Non-Cancerous Diseases include a variety of somewhat unrelated diseases. Anemia, abortion, arthritis, and immune suppression are examples. When the immune system is suppressed, the cat becomes susceptible to many diseases it would ordinarily resist and mild diseases, such as respiratory infections, may become fatal.


The main means of transmitting the virus is through cat fights. Because large quantities oftenFeLV are shed in cat saliva, puncture wounds associated with fighting result in injection of the virus into other cats. There are also large amounts of virus in respiratory secretions. Other less frequent routes of viral spread include sharing food and water bowls, cats grooming each other, and transmission from mother to kittens before birth.


The “leukemia test” is used to determine if a cat harbors the virus. Any of three different tests may be used to detect one particular virus protein in the cat. Some tests detect earlier stages of infection, whereas others are used to detect later (ie., irreversible) stages of infection.

  1. The blood ELISA test is performed on a blood sample and detects the FeLV at any stage of infection. This test turns positive within a few days of infection and, in some cases, may later turn negative if the cat’s immune system eliminates the infection.
  2. The IFA test is performed on a blood smear and turns positive only after the FeLV infection has progressed to a late stage of infection. Once positive, the IFA test usually means that the cat has a permanent infection. A cat that tests IFA positive is only rarely able to successfully eliminate the virus. The cat that is IFA positive is called “persistently positive” or “persistently viremic.”
  3. The tears/saliva ELISA test is performed on a sample of tears or saliva. It turns positive only in a late stage of infection; therefore, it may yield a false negative result in cats that are in the early stage of FeLV infection. It also has been associated with some false positive results due to inherent errors in the way the test is performed. Because of these problems, the tears and saliva tests are not used routinely.

The Cat that Tests Positive – Possible Outcomes of FeLV-infection

When we are exposed to a virus, such as a flu virus, there are two possible outcomes. Either our immune system responds to the challenge and protects us, or it is unable to respond successfully and we develop the flu. A number of factors determine which outcome occurs and whether or not we will get sick:

  1. The amount of the virus (Did someone sneeze directly in your face?)
  2. The strain of the virus (Some strains are more potent than others.)
  3. The status of our immune system (Are immune suppressing drugs being taken?)
  4. Age (The very young and very old are more likely to become infected.)
  5. The presence of other infections which might cause debilitation

The behavior of the feline leukemia virus in the cat’s body cannot be predicted. Instead of the two possible outcomes described above (ie., we get sick or we get well), there are four possible outcomes for cats with FeLV. Understanding these allows one to more fully comprehend some of the unusual situations that may arise in cats.

OUTCOME 1: IMMUNITY The cat mounts an immune response, eliminating the infection.

This is the most desired outcome because it means that the cat will not become persistently infected with the virus. During this period of virus challenge, the cat may actually develop a mild form of illness. Fever, poor appetite, lethargy, and swollen glands (lymph nodes) in the neck may develop and last for 3 to 10 days. Outcome 1 occurs about 40% of the time after a cat is challenged by the FeLV. Immunity to the virus is more likely to develop in the adult cat than in the kitten.

OUTCOME 2: INFECTION The cat’s immune system is overwhelmed by the virus.

This is the least desired outcome because the cat is persistently infected with FeLV. All three of the FeLV tests will become positive and remain positive for the rest of the cat’s life.

Although the cat may be sick for a few days initially (as described above), it usually recovers and appears normal for weeks, months, or years. Ultimately, most of these cats die of FeLV-related disease, but as many as 50% will still be healthy after 2-3 years and 15% after 4 years. Vaccination of these cats will not cause any problems, but doesn’t help the cat, either.

Outcome 2 occurs about 30% of the time after a cat is challenged by FeLV. Although infection is more likely to occur in the kitten, many cats are persistently infected as adults. Although the main mode of viral transmission is through bite wounds (saliva), direct daily contact with a FeLV infected cat will often result in transmission of the virus. Non-infected exposed cats are at risk and should be vaccinated, although daily viral contact will result in vaccination failure of some cats.

OUTCOME 3: LATENCY The cat harbors the virus but we cannot easily detect it.

Unlike other viruses, the FeLV does not directly kill the cat’s cells or make them become cancerous. Instead, it inserts a copy of its own genetic material (called DNA) into the cat’s cells; these cells may later be transformed into cancer cells or cells which will no longer function normally. In Outcome 3, the genetic

change in the cat’s cells will remain undetected for an average of 2 1/2 years, during which time the cat will appear completely normal.

In the early stages of infection, the blood ELISA test will be positive, but it will turn negative about 2-4 weeks later. Following that, the blood ELISA and the IFA tests will remain consistently negative.

The prospect of latent infection presents us with a frustrating situation. Latency is estimated to occur about 30% of the time; it leaves the cat in a precarious situation. Some cats will ultimately reject the abnormal cells, and the state of latency will be terminated. In other cats these abnormal cells will result in the production of new FeLV which will result in Outcome 2. Outcome 2 generally leads to death due to a FeLV disease.

Latency is the state that explains the following situations:

  1. Latently infected cats will test negative on all of the FeLV tests. If they are vaccinated, they will not be protected. They may develop a fatal FeLV-related disease later, especially following some form of stress or the administration of steroids. Stressors that may activate latent infections include pregnancy and nursing, overcrowding, movement to a new environment, territorial conflicts, poor nutrition, and other diseases. Steroids are used commonly in cats because they are very beneficial for many feline diseases.
  2. Lymphosarcoma is the form of cancer normally caused by the FeLV. Cats some forms of lymphosarcoma normally test positive with any FeLV test. Latently infected cats may have lymphosarcoma and test negative on the FeLV tests. It is also thought that some cats successfully eliminate the virus but not before malignant transformation of cells has already occurred. This may be another explanation for FeLV-negative cats with lymphosarcoma.
  3. Latently infected pregnant cats may test FeLV negative (and even be vaccinated) but pass the FeLV to their kittens through nursing. These kittens often experience Outcome 2.

OUTCOME 4: IMMUNE CARRIER The cat becomes an immune carrier.

The FeLV becomes hidden in some of the cat’s epithelial cells. Although the FeLV is multiplying, it is not able to get out of these cells because the cat is producing antibodies against the virus. The cat will appear normal in every way, except for its test results. The immune carrier will have a positive blood ELISA test and a negative IFA test.

This situation is unlikely to happen; it is estimated to occur 1-2% of the time. These cats may revert to an active FeLV infection (Outcome 2) or may develop a latent infection (Outcome 3). The main reason for understanding this situation is that it explains conflicting FeLV test results. Otherwise, there is not a specific test to detect it.


  • Leukemia. Some forms of leukemia (blood cancer) are unresponsive to all available forms of cancer treatment. Other types of leukemia may respond to chemotherapy, though most of these have an average survival time of less than one year. Because the virus is not affected by treatment, the cat will always remain infected with FeLV. Also, relapse of leukemia is possible (and expected). These factors cause us to recommend treatment of leukemia in very few situations.
  • Lymphosarcoma. Lymphosarcoma is treatable, but not curable. Research has shown that cats with lymphoma who are FeLV-positive do not respond to treatment as well as FeLV-negative cats.
  • Secondary infections. Depending upon the type of infection involved and the general state of the cat’s health, the prognosis may range from favorable to guarded. For example, bacterial infections may respond well to antibiotic therapy. Other types of infections, such as certain fungal infections, may not respond well because of the FeLV-induced weakness of the cat’s immune system.

The healthy FeLV-positive cat. Healthy infected cats may remain apparently unaffected by the virus for several years. With good supportive care and prompt attention to all potential medical problems, these cats may live for a number of years. Bear in mind that these cats should be considered infectious and potentially dangerous to other cats. Such cats should be isolated from non-infected cats to prevent spread of infection. Many people find this undesirable or impossible and elect euthanasia to protect non-infected cats.


The prognosis is dependent upon many factors. In general, 80% of all persistently positive cats (IFA positive) succumb within three years, most of these deaths occurring within the first six months of detection. The cat who is transiently positive may expect a normal lifespan, or may become ill if latent virus in the body is reactivated.

Transmission to Humans

Extensive tests have been conducted for over 15 years to determine if the FeLV can be transmitted to humans. To date, no conclusive evidence has demonstrated any FeLV-related disease in humans or other animal species, including the dog. However, persons with compromised immune systems are of concern to many researchers. Newborn babies, persons on chemotherapy, AIDS patients or transplant recipients on anti-rejection drugs should probably not be unnecessarily exposed to this or any other virus.


A vaccine is available to protect cats from the FeLV. Although not 100% of cats are totally protected, the vaccine is strongly recommended for cats who are exposed to open populations of cats, (ie., outdoor cats). We have seen a definite decline in the incidence of feline leukemia virus infection and related diseases since vaccine use became widespread. We strongly recommend it for cats at risk of exposure. If your cat stays indoors at all times and is not in contact with another cat that goes outdoors, the vaccine is generally not recommended. Many owners have concern that the vaccine will cause a cat to test positive for the virus, but this is not true. While the history of vaccination is important for us to know, it does not alter our ability to interpret the feline leukemia virus test.

Testing Prior to Vaccination

Cats that are already infected with the FeLV will not be helped by the vaccine. (They will not be hurt by it, either). We recommend pre-vaccination testing for the FeLV in these particular situations:
1) Cats with a history of cat fights or fight wounds (ie., abscesses) 2) Cats exposed to FeLV-infected cats 3) Cats from unknown backgrounds (particularly animal shelters, humane societies, or pet shops) 4) Routine health care, especially in multicat households

Injection Site Sarcomas

In recent years, a disturbing phenomenon has been identified by veterinary researchers. A relationship has been found between feline leukemia virus vaccine (as well as rabies vaccine) and the development of very aggressive tumors at the injection site. The numbers of cats who have developed these tumors is very small compared to the total number of vaccinations given (1-3 per 10,000), but the outcome is devastating for cats that do get these cancers. Several veterinary schools are actively researching this problem. It remains unclear exactly why some cats develop tumors in response to vaccination; a genetic predisposition is thought to be part of the problem. At this time, feline specialists are recommending that leukemia vaccination be reserved for cats that are at risk for exposure to the virus. Strictly indoor cats generally do not need vaccination against FeLV. We can advise you about exceptions to the routine vaccination protocols.

Feline Infectious Peritonitis

Feline Infectious Peritonitis (FIP) is a progressive, almost always fatal, viral disease of domestic cats. It affects some exotic cats, with the cheetah being particularly susceptible. It does not affect non-feline species, such as dogs.

Cause and Transmission

FIP is caused by a virus in the coronavirus family. The feline infectious peritonitis virus (FIPV) and the feline enteric coronavirus (FECV) are the main coronaviruses of cats.

Disease caused by FECV is usually self-limiting and involves diarrhea in young kittens. Infection with the FIPV is serious and usually has fatal consequences.

Transmission of FIPV between cats is most likely by the fecal-oral route; a susceptible cat is infected by coming in contact with fecal material from an infected cat. The virus is swallowed and begins to reproduce in the lining of the intestine. Once certain blood cells become infected with the virus, they transport it throughout the body. Also, it is considered possible that the virus can be transmitted between cats through nasal, salivary and urinary secretions.

Contributing Factors

Exposure to the virus does not necessarily equate with infection and progression to death. A strong, healthy immune system is important for recognition of the virus and preventing its reproduction in the cat’s body. Some cats are able to completely eliminate the virus, whereas others are infected but show minimal or no signs of infection. These cats may eventually eliminate the virus or continue to harbor a small amount of virus in the body. They may or may not become ill with FIP at a later time. Cats who are unable to eliminate the virus may show signs of serious illness in a matter of a few weeks.

Environmental stresses are important factors in transmission of the disease. Crowding of many cats together leads to stress, suppression of the immune system, and sharing of the virus. This scenario is most common in overcrowded catteries where cats come in close contact with one another. Concurrent infection with immune-suppressing viruses, such as the feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV), also predisposes cats to infection with FIPV.


Male and female cats are affected equally. There are two main age groupings for FIPV: kittens less than a year of age have the highest incidence, followed by geriatric cats over 13 years of age. It is relatively less common in young adult and middle aged cats. Because of its transmission in cattery situations, it is more common in purebred cats.

Because FIP is difficult to diagnose, studies which evaluate its overall prevalence in cats provide only an estimate. In infected catteries, 80-90% of the cats may test positive for exposure to one of the coronaviruses.

Clinical Signs

Cats with FIP may initially only show vague, nonspecific signs, such as poor appetite, fever, and weight loss. Virtually any organ system may be affected, so a variety of signs are possible.
In general, we consider that there are two forms of FIP: the dry (non-effusive) form and the wet (effusive) form. The wet form is characterized by the accumulation of large quantities of fluid in the chest and/or abdomen. If it occurs in the chest, the cat will experience difficulty breathing. When it occurs in the abdomen, a large, bloated appearance will result. The dry form affects the target organs in a similar fashion, but no fluid is produced. At different times during the disease process, the cat may pass from one form to the other. Because the type of fluid which is produced with wet FIP is very unusual, it is easier to diagnose than the dry form, where signs may be more vague.


Diagnosis of FIP may be difficult and frustrating. There are no specific tests which are reliable in all cases. Biopsy of an affected organ provides the only definitive diagnosis; this provides the pathologist with a small sample of tissue for study. Recovery of such tissue from an already sick cat involves a certain amount of risk. One of the most difficult aspects of FIP is that there is no simple diagnostic test. The ELISA, IFA, and virus-neutralization tests detect the presence of coronavirus antibodies in a cat, but these tests cannot differentiate between the various strains of feline coronavirus. A positive result means only that the cat has had a prior exposure to coronavirus, but not necessarily one that causes FIP.

Other tests have been developed that can detect parts of the virus itself. The immunoperoxidase test detects virus-infected cells in the tissue, but a biopsy of affected tissue is necessary for evaluation. Another antigen test uses polymerase chain reaction (PCR) to detect viral genetic material in tissue or body fluid. Although this test shows promise, PCR is presently only capable of detecting coronaviruses in general, not necessarily those that cause FIP.

To date, there is no way to screen healthy cats for the risk of developing FIP, and the only way to definitively diagnose FIP is by biopsy, or examination of tissues at autopsy. Generally, veterinarians may rely on a presumptive diagnosis, which can be made with a relatively high degree of confidence by evaluation of the cat’s history, presenting symptoms, examination of fluid if it is present, and the results of supporting laboratory tests including a positive coronavirus antibody titer.


Many treatments have been tried for cats with FIP, but none have been consistently successful. Apparently, an occasional cat will recover, but this is the exception rather than the rule. Removing fluid from the chest or abdomen in cats with the wet form will make them comfortable for a short while, and a few drugs will make some of them feel better. Some of the available antiviral drugs have been tried alone and in various combinations. Human interferon has had some effect in prolonging the lifespan. Some of the other antiviral drugs are toxic and cannot be given to cats. There is no known curative treatment available.

  • Prognosis – The prognosis for a cat with FIP is very poor. Once a reasonably reliable presumptive diagnosis has been made, euthanasia is often the most appropriate course of action.
  • Prevention – The coronavirus may live for up to 3 weeks in the environment. If viral shedding into the environment seems likely, a l:30 mixture of household bleach and water (ie., 1 cup of bleach in a gallon of water) should be used to disinfect food and water bowls, litter pans, cages, bedding material, and items that will not be adversely affected by household bleach. A preventive vaccine against FIP is available, but most veterinarians do not recommend that the vaccine be given routinely to all cats. The vaccine is generally recommended for cats in contact with free-roaming cats or for those living in households that have had a cat with FIP. Initially, two doses are given at a 2-4 week interval. An annual booster is needed to maintain immunity. For cats already infected with FIPV, the vaccine is of no known benefit.


Toxoplasmosis is an infectious disease caused by a one-celled parasite called Toxoplasma gondii. It is a prevalent parasite of cats throughout the world, although other species, such as humans, can become infected. The cat is unique in that it is the definitive host of the parasite, meaning that the organism must pass through the cat to complete all stages of it’s life cycle.

Contributing Factors

Cats usually become infected by feeding on rodents, some types of insects, and by ingestion of undercooked meat. Although cats who go outdoors are at somewhat increased risk of becoming infected, indoor cats mayalso contract the disease.


Once the immune system has been exposed to the toxo organism, antibodies will be produced. Antibodies (also called globulins) play a protective role in the immune system. However, detection of antibodies against toxo only means that the person or cat has been exposed; it does not mean that active toxoplasmosis is present.

The scientific literature reports that in the United States, between 30% and 50% of cats have antibodies to toxoplasmosis. About 1/3 of humans are thought to have been exposed. However, those statistics do not mean that antibody-positive cats and humans have toxoplasmosis. The presence of antibodies only means that exposure to the Toxo organism has occurred in the past.

Clinical Signs

In humans, clinical signs are rarely apparent when the immune system is normal. If signs of illness arepresent, they are usually self-limiting and nonspecific. The majority of clinical signs result from replication of the organism within tissues.

The respiratory system may be involved, giving the impression of a flu-like illness. In other cases, it may appear similar to mononucleosis, with fever and swollen lymph nodes. In humans with weakened immune systems (such as with AIDS or patients receiving chemotherapy), the consequences of toxoplasmosis can be devastating, eventually leading to death of the individual.

In cats, the most common signs are related to inflammatory changes in the eyes. The respiratory system, liver and central nervous system may also be involved, with signs of pneumonia, jaundice, or seizures.


Owners worried that they have been infected with toxoplasmosis should seek consultation with their physician about testing.

Veterinarians 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 pet cat. A negative result means that the woman (and/or the cat) has not been exposed to the toxo organism.
  2. A single antibody titer that is positive, performed on the woman and/or the pet cat, means that there has been exposure to the toxo organism at some time. In order to determine whether there is active infection, a second test must be run 2-4 weeks later. Be aware that no test is available to determine that infection has been acquired by contact with cats.
  • If the two tests give similar results, there has been an infection in the past and a certain degree of immunity exists.
  • If the second test is significantly higher that the first, there is a strong possibility that an active case of toxoplasmosis is in progress.
  • It is very important that both tests be performed by the same testing laboratory in order to properly compare results.


Clindamycin hydrochloride is the drug of choice for treating cats with toxoplasmosis. There is no evidence to indicate that the drug is able to completely remove the organism from the cat’s body, although most cats improve within 2-3 days of starting the drug. Infections that involve the eyes or central nervous system are more difficult to treat. In general, better results are achieved if the cat is treated for four weeks or longer.


Cats who respond to clindamycin therapy and are negative for feline leukemia virus and feline immunodeficiency virus have a good prognosis. Those with weakened immune systems, advanced stages of the disease, or infections of the nervous system have a guarded prognosis for full recovery.

Transmission to Humans

As stated above, several species may develop the disease toxoplasmosis, including humans and dogs, but 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. Owners should be aware that human infection resulting from direct contact with infected cats is extremely unlikely. In order for this to occur, the following must happen:

  1. The cat must be infected with the toxo organism. This usually occurs as a consequence of carnivorous feeding on mice or ingestion of undercooked meats, such as pork or mutton. Other sources of infection for cats include cockroaches and earthworms.
  2. The cat must be shedding the organism in its feces. This occurs for only about a 10 day period. It usually only occurs once in the cat’s lifetime.
  3. Organisms in the cat’s feces must have 1-5 days to sporulate (“incubate”). This “incubation” must occur after the feces leaves the cat’s body. Therefore, fresh cats feces cannot cause transmission of the infection to humans.
  4. The toxo organism must be swallowed by the person being infected. It is not spread to humans through the air.

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.

Although this is indeed a real disease with dire consequences, it should be noted that toxoplasmosis occursinfrequently, especially in consideration of the numbers of people with Toxoplasma antibodies. In AIDS patients with toxoplasmosis, the disease is generally considered to arise from reactivation of a prior infection rather than establishment of a new infection. For this reason, it is often not necessary to remove cats from the household of HIV-infected people.


At this time, researchers are investigating the utility of a mutant strain of toxo as a potential vaccine source. Until such time as a vaccine would be widely used, prevention of infection is indicated. Practical means of preventing infection include:

  1. Do not allow your cat to eat mice or poorly-cooked meat. Feeding a commercial cat food and not allowing your cat outdoors reduces the 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, pregnant women should not clean the litter box.
  3. When working in soil (flower beds) where cats might defecate, 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. Wash hands thoroughly after handling raw meat. Clean cutting boards, knives and all utensils involved in preparation of raw meat.
    Wash all fruits and vegetables prior to eating.
  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.


  1. Toxoplasmosis that affects babies is quite rare. The incidence in the United States is 0.028% of all births.
  2. Feed commercial cat food and keep your cat indoors.
  3. Clean the litter box of all feces daily. Pregnant women should not clean the box.
  4. Wash your hands following cleaning of the litterbox and handling of soil after gardening.
  5. Do not eat undercooked meats.