Questions and Answers About Toxoplasmosis

A pregnant woman feeding a cat on a kitchen table

All of us are familiar with a crazy cat lady, whether it' s a relative or a fictional character from television. You have probably wondered at one time or another why some women are so attracted to cats. Recent studies done at Stanford University suggest that these unhealthy obsessions with felines may be developed as a result of being exposed to a common parasite known as Toxoplasma gondii. This organism is able to alter the human brain, resulting in behavior change. It is this alteration which is believed by some to create the deep attraction towards cats.

Toxoplasmosis is considered to be the third leading cause of death attributed to foodborne illness in the United States. More that 60 million men, women, and children in this country carry the Toxoplasma parasite, but very few have symptoms because the immune system usually keeps the parasite from causing illness. However, women newly infected with Toxoplasma during pregnancy and anyone with a compromised immune system should be aware that toxoplasmosis can have severe consequences for them.

Latent (mild with no symptoms) toxoplasmosis, characterized by the life-long presence of cysts of the parasite in different host tissues, including the nervous system, and by the presence of Toxoplasma IgG antibodies in blood, was long considered asymptomatic. In the past 20 years, several effects of this form of parasitosis on the human organism were described in the literature. For example, latent toxoplasmosis increases the risk of schizophrenia and Parkinson's disease influences human personality and behavior, impairs psychomotor performance, enhances the risk of suicide, of traffic accident and increases probability of the birth of male offspring.

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Can toxoplasmosis cause mental illness? There is an ongoing research whether chronic toxoplasmosis can affect reaction time, behavior and mental illness. Multiple studies have found a link between schizophrenia and bipolar disorder and the presence of antibodies to Toxoplasma. These studies have also documented that individuals with schizophrenia have had more exposure to cats than healthy ones.

Can toxoplasmosis make a person suicidal? A study of more than 45,000 women in Denmark, the largest of the kind, suggested that there could be a link between toxoplasmosis and suicides among women. In another report published by a group of researchers in Turkey (2010) confirmed the association between Toxoplasma antibodies and suicide attempts. It has been suggested that the infection with Toxoplasma parasite may elevate testosterone levels, and in turn that elevation in testosterone may lead to an increase in aggression. Testosterone has been linked to suppression of impulse control and emotional regulation. This can explain why the association between Toxoplasma and suicide is observed in older women, but not in younger women whose male hormones are balanced by estrogen and progesterone. Infected individuals may also wish to injure themselves, not just die. It should be noted, though, that not all those infected are at risk for suicide. Contributing risk factors include depression, impulsivity, aggression, arousal, and reduction of fear.

Are people with toxoplasmosis at increased risk of having traffic accidents? Yes. Toxoplasma has been associated with reflex impairment resulting in traffic accidents. Researchers from Czech Republic found the risk of a traffic accident in individuals with latent (the mildest form of infection) toxoplasmosis was 2.65 times higher than in the toxoplasmosis-free persons, especially in those with higher level of anti-Toxoplasma antibody titer. A high antibody titers may increase the risk of an accident by 16 times, representing a serious and highly underestimated economic and public health problem.

Can Toxoplasma parasite cause Alzheimer's disease? The link between toxoplasmosis and Alzheimer's disease is actively investigated. In a case control study about latent (mild, with no clinical symptoms) toxoplasmosis and Alzheimer's disease that was conducted in 2011 in Turkey, it was suggested that Toxoplasma infection may be involved in the pathogenic mechanisms of Alzheimer's disease, as the amount of Toxoplasma IgG antibodies among individuals with Alzheimer's disease was 44.1% higher than in AD-free individuals.

Can toxoplasmosis cause epilepsy? According to the research conducted in 17 countries to find a link between latent (without any clinical symptoms) toxoplasmosis and cryptogenic (of unknown cause) epilepsy, epilepsy is 4.8 times more frequent among Toxoplasma positive persons. In addition, the results showed a strong association between the frequency of epilepsy and Toxoplasma infection within the same region.

In what way does Toxoplasma parasite affect the brain in persons with schizophrenia? The T. gondii genome contains two enzymes (amino acid hydroxylases) that potentially could directly affect dopamine and serotonin synthesis. Dopamine is an important neurotransmitter which plays various roles in origin of neuropsychological disorders including schizophrenia and other neurological diseases such as depression, Alzheimer's disease and Parkinson disease. Dopamine levels are also often increased in schizophrenia patients and decreased in patients with Alzheimer's disease, Parkinson's disease and major depression. There are also evidences that inflammatory reactions to infections may contribute to developing schizophrenia and related psychotic disorders (increased maternal levels of the inflammatory cytokine IL-8 and TNFα during pregnancy are associated with an increased risk for schizophrenia and psychotic illness among children). Graey matter volume in the cortical regions, hippocampus and in the caudate is reduced in schizophrenia patients compared with Toxoplasma-free persons.

Can toxoplasmosis change a person's character? Latent toxoplasmosis is a common infection affecting 20–60% of the population, but there is growing evidence of its effects on human behavior. Different studies have shown that infected men were more likely to disregard rules and were more expedient, suspicious, jealous, dogmatic, while infected women more likely warm hearted, outgoing, conscientious, persistent, and moralistic. In one study soldiers were tested during their entrance examination for a voluntary participation in an international military mission. Toxoplasma-infected soldiers expressed stronger tendency to mask any negative property when responding to questions in questionnaires. Several studies have shown Toxoplasma-infected men are expedient, nonconforming, disregards rules, dogmatic; self-indulgent; these factors are associated with substance abuse, anxiety, and personality disorders. These men are also characterized by higher suspiciousness, they are vigilant, suspicious, skeptical, distrustful and oppositional. Both men and women were found to be more apprehensive compared with uninfected persons.

Can toxoplasmosis cause blistering skin disease? Yes, although skin (cutaneous) toxoplasmosis is quite rare and mostly affects persons with compromised immune system or serious systemic diseases. A 60-year-old woman with aplastic anemia developed vesicular varicella-like skin condition on her face, arms, legs, back and abdomen that was similar to herpetic infection but turned out to be an infection with Toxoplasma. Cutaneous toxoplasmosis might mimic other infectious diseases.

How do people get infected with Toxoplasma besides handling cat litter? Undercooked meat, especially pork, lamb, and wild game meat, and soil contaminated with cat feces on raw fruits and vegetables are the major sources of food borne transmission of Toxoplasma parasite to humans. The new trend in the production of free-range organically raised meat could increase the risk of Toxoplasma contamination of meat. Adequate cooking of meat, washing of raw fruits and vegetables and good sanitation in the kitchen can prevent this infection. In the United States, a recent study showed an elevated risk for infection in persons eating rare lamb, eating locally produced cured, dried, or smoked meat, or working with meat.

What are the most common signs and symptoms of Toxoplasma infection? Most cases of toxoplasmosis are asymptomatic (do not produce symptoms), but 10 percent of infected persons may have a mononucleosis-like or flue-like illness of variable severity. Most common symptoms are fatigue (this can last over 1 month), fever, muscle pain, headache, diarrhea, dizziness, abdominal pain and enlarged lymph nodes.

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Can I die from toxoplasmosis? While life-threatening toxoplasmosis is generally seen in immunosuppressed persons, there have been a number of case reports in immunocompetent individuals. Complications include systemic disease, bronchiolitis, pneumonitis, pneumonia in a pregnant women, fatal myocarditis, pericarditis, simultaneous myocarditis and polymyositis, enlarged liver and hepatitis, encephalitis, encephalitis with paralysis and chorioretinitis, and Guillain-Barré syndrome.

Which countries have the highest infection rate? It is generally assumed that approximately 25 to 30% of the world's human population is infected by Toxoplasma. Actually, the infection rate vary widely between countries (from 10 to 80%) and often within a given country or between different communities in the same region. Low infection rate (10 to 30%) have been found in North America, in South East Asia, in Northern Europe, and in Sahelian countries of Africa. Moderate prevalence (30 to 50%) have been found in countries of Central and Southern Europe, France, United Kingdom, and high infection rate have been found Latin America and in tropical African countries.

What is the most effective way to kill the parasite in food? Tissue cysts remain infectious in refrigerated carcasses or minced meat for up to 3 weeks. Freezing alone is not a reliable means of rendering all tissue cysts noninfective: cysts have remained viable for >11 days at −7°C. However, the deep-freezing of meat at −12°C or lower for at least 3 days is usually efficacious to kill cysts, although it may depend on the thickness of the piece of meat. Tissue cysts are usually killed immediately by heating to 152 F. The survival of tissue cysts at lower temperatures depends on the duration of cooking. Tissue cysts remain viable at 140 F for about 4 min and at 122 F for about 10 min. Cooking for a prolonged period of time may be necessary under household conditions to achieve the temperatures that are required to kill all tissue cysts of Toxoplasma in all parts of the meat. Some tissue cysts will remain infectious after cooking in a microwave oven, possibly due to an uneven heating of the meat.

Can birds transmit Toxoplasma infection? Yes, T. gondii infection is common in some avian species such as thrushes, nuthatches, robins, American crows, doves, sparrows, starlings, owls, pigeons, ducks, vultures, hawks, turkeys, gulls, terns, jays and other species. Affected pigeons are usually dull, emaciated, and have conjuctivitis. Some species or breeds of pigeons appear to be more susceptible to clinical toxoplasmosis than others. For example, severe toxoplasmosis has occurred in crown pigeons, ornamental pigeons, and pigeons from Australia and New Zealand. Outbreaks of toxoplasmosis in aviary yellow canaries have been reported in several countries including Australian, UK and USA (Michigan). Affected birds died from severe encephalitis.

Can toxoplasmosis cause brain cancer? Yes, several epidemiological studies reported associations of brain cancer and toxoplasmosis. T. gondii may increase the risk of brain cancer because it is a long-lived parasite that encysts in the brain, where it provokes inflammation that results in increased mutation rates and prevents infected cells from programmed death (apoptosis) causing tomors. In addition, cell pathogens may disrupt traditional cell barriers to cancer, allowing cancer-causing mutations to accumulate through time. In general, persons with toxoplasmosis develop brain cancer twice as often than those who are not infected.

Can toxoplasmosis increase anxiety level? According to researchers from Karolinska Institutet in Sweden, it is possible. In one laboratory experiment, human brain (dendritic) cells were infected with Toxoplasma. After infection, the cells, which are a key component of the immune defense, started secreting the signal substance GABA. In another experiment on live mice, the team was able to trace the movement of infected dendritic cells in the body after introducing the parasite into the brain, from where it spread and continued to affect the GABA system. GABA is a signal substance that, among other effects, inhibits the sensation of fear and anxiety. Disturbances of the GABA system are seen in people with depression, schizophrenia, bipolar diseases, anxiety syndrome and other mental diseases.

Is there a vaccine to prevent toxoplasmosis? No drugs or vaccines currently exist to treat or prevent the chronic stage of the disease. The parasites may remain invisible to the immune system for years and then reactivate when immunity wanes, boosting the risk for recurrent disease.

What medications are used to treat toxoplasmosis? Pyrimethamine (the most effective anti-Toxoplasma agent available) plus sulfadiazine (with folinic acid). Adverse effects include decrease in the ability of the bone marrow to produce blood cells (myelosuppression), which can be improved with folinic acid), abdominal pain, rash, and headaches. Pyrimethamine is combined with sulfadiazine, another folate antagonist. In addition to rash and myelosuppression, sulfadiazine can cause crystal-induced kidney disease. Trimethoprim-sulfamethoxazole (TMP-SMX) has similar to pyrimethamine-sulfadiazine for toxoplasmic encephalitis and chorioretinitis; however, unlike pyrimethamine-sulfadiazine, it is also available intravenously. Pyrimethamine plus clindamycin is also effective. If none of these drugs can be used, clarithromycin, azithromycin, atovaquone, and dapsone are alternatives.


  1. Latent Toxoplasmosis and Human. A Dalimi, A Abdoli
  2. Toxoplasma on the Brain: Understanding Host-Pathogen Interactions in Chronic CNS Infection. Sushrut Kamerkar, Paul H. Davis
  3. Varicella-like cutaneous toxoplasmosis in a patient with aplastic anemia. Stefan Zimmermanna et al.
  4. Foodborne Toxoplasmosis. Patricia M. Griffin, Section Editor, Jeffrey L. Jones, J. P. Dubey
  5. Acute Primary Toxoplasmosis in Travelers Returning From Endemic Countries. Rahul Anand MD et al.
  6. Epidemiology of and Diagnostic Strategies for Toxoplasmosis. Florence Robert-Gangneuxa, Marie-Laure Dardé

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Because there are no animal protection laws in China and Pakistan, and no measures have been taken to eradicate inhumane customs and savagery, Go Pets America urges you to boycott goods produced in China Pakistan!

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