Toxoplasmosis is an infection caused by the Toxoplasma gondii parasite. This microscopic parasite can infect most warm-blooded organisms, but felines such as domestic cats are the only known definitive hosts in which the parasite can reproduce. In humans and other animals, toxoplasmosis can have some serious effects.
How do people get toxoplasmosis?
People can get toxoplasmosis by:
- Eating undercooked, contaminated meat: Especially pork, lamb, or venison.
- Ingesting contaminated soil or water: Cat feces in the environment can spread T. gondii oocysts, which can remain infectious in soil for over a year.
- Eating unwashed fruits and vegetables: That have been in contact with contaminated soil.
- Accidental ingestion of contaminated cat feces: Cats can shed T. gondii in their feces for up to 2 weeks after infection.
- Mother-to-child transmission: If a woman is infected with toxoplasmosis during pregnancy, she can pass the parasite on to her unborn child via the placenta.
Consuming raw or undercooked meat and produce appears to be the most common route of transmission. Cats only shed the parasite for a short period of time but can re-shed oocysts after reinfection. Indoor cats are less likely to be infected than outdoor cats that hunt.
What are the symptoms of toxoplasmosis?
Most healthy people who become infected with toxoplasmosis do not have any symptoms because their immune system usually keeps the parasite from causing illness. Some individuals may experience ‘flu-like symptoms for a few days, such as:
- Swollen lymph nodes
- Muscle aches
- Sore throat
Typically these symptoms resolve on their own without treatment. However, toxoplasmosis can cause more serious symptoms in people with weakened immune systems, such as those with HIV/AIDS, cancer patients receiving chemotherapy, and organ transplant recipients taking immunosuppressant medications.
How does toxoplasmosis affect immunocompromised people?
When a person’s immune system is weakened, T. gondii can cause significant illness. Symptoms may include:
- Confusion or altered mental status
- Severe headaches
- Poor coordination
- Lung problems causing cough and shortness of breath
- Blurred or lost vision
- Skin lesions
Without treatment, toxoplasmosis can be fatal in immunocompromised individuals as the parasite spreads to organs throughout the body, including the central nervous system and brain. Even with treatment, toxoplasmosis can cause lasting damage.
How does toxoplasmosis affect pregnant women?
If a pregnant woman becomes infected with toxoplasmosis for the first time during gestation or just before pregnancy, she can transmit the parasite to the developing fetus via the placenta. The likelihood of transmission depends on when during pregnancy the mother becomes infected:
- Early in pregnancy – highest risk of transmission to the fetus
- Late in pregnancy – lower risk of transmission
The earlier in pregnancy the transmission occurs, the more severe the effects on the fetus may be. Congenital toxoplasmosis can cause the following complications:
- Premature birth
- Enlarged liver or spleen
- Eye damage – including blindness
- Cerebral calcifications
- Cognitive deficits
Fortunately, if a pregnant woman is diagnosed with acute toxoplasmosis, antibiotics can often minimize transmission and reduce severity of fetal infection. However, early detection is key.
Does toxoplasmosis cause problems later in life?
Most otherwise healthy people who acquire toxoplasmosis usually remain asymptomatic after their initial mild, flu-like illness resolves. But some research indicates toxoplasmosis infection may have subtle, long-term effects even in people who seemed to fully recover, including:
- Increased risk for mental health disorders like schizophrenia, bipolar disorder, depression, and anxiety later in life.
- Impaired vision and hearing
- Reduced IQ and cognitive function
- Greater likelihood of being involved in a traffic accident
- Changes in personality and behavior
Exactly why and how toxoplasmosis causes these effects is not fully understood. Some experts theorize the parasite may directly damage certain neurons or indirectly manipulate neurotransmitters that affect mood, personality, cognition, and behavior.
Toxoplasmosis and mental health
Several studies show a correlation between toxoplasmosis infection and increased rates of mental illness like schizophrenia and bipolar disorder. However, a direct causative link is difficult to prove and findings have been mixed. Some key points from the research:
- Individuals diagnosed with schizophrenia or bipolar disorder have higher rates of T. gondii antibodies compared to the general population.
- People with schizophrenia are 2-3 times more likely to have been exposed to T. gondii.
- Toxoplasmosis patients show brain abnormalities similar to schizophrenia patients.
- T. gondii may contribute to schizophrenia by altering neurotransmitters like dopamine.
While more research is needed, these associations suggest toxoplasmosis may at least be a contributing factor in some mental illness cases. It’s unlikely to be a sole cause. Genetics, brain physiology, and environmental factors are also involved in psychiatric disorders.
Toxoplasmosis and personality/behavior changes
The T. gondii parasite forms cysts in brain tissue and produces an enzyme called tyrosine hydroxylase. This enzyme affects dopamine levels in the brain, which helps regulate mood, sociability, decision-making, and potential risk-taking behavior. Some personality and behavioral shifts associated with toxoplasmosis infection include:
- Increased impulsivity
- Reduced fear/aversion to threats
- Greater extroversion and sociability
- Higher neuroticism
- Reduced conscientiousness
In rodent studies, T. gondii-infected mice show evidence of similar behavioral alterations, including less cautious behavior and attraction to feline urine despite the inherent risk. The parasite may manipulate host behavior to support transmission between intermediate hosts and feline definitive hosts.
Toxoplasmosis and cognitive function
Some studies link chronic toxoplasmosis infection to subtle declines in certain cognitive functions, like:
- Reduced memory and lower IQ
- Slower reaction times
- Impaired concentration
One analysis of over 85,000 questionnaire responses found toxoplasmosis patients scored significantly lower on memory and IQ tests. slowed reaction times. T. gondii infection may impair cognition by damaging neurons or altering neurotransmitter levels.
Toxoplasmosis and vision/hearing loss
Case studies indicate toxoplasmosis can, in rare cases, cause inflammation of the retina and optic nerve, potentially leading to vision impairment or blindness. Hearing loss may also occur in some patients. More research is needed to determine the mechanisms behind these sensory effects.
Toxoplasmosis and traffic accidents
Interestingly, some studies have noted increased rates of traffic accidents associated with chronic toxoplasmosis infection. Infected individuals may have slower reaction times and be at higher risk of reckless driving behaviors. One analysis estimated toxoplasmosis patients were 2-3 times more likely to be involved in car accidents compared to non-infected drivers.
How is toxoplasmosis diagnosed?
Diagnosing toxoplasmosis requires a healthcare provider to check for T. gondii antibodies or DNA in blood, body fluids, or tissue samples. Diagnostic tests may include:
- Blood tests: To look for IgM and IgG antibodies produced by the immune system in response to toxoplasmosis. IgM indicates recent or acute infection while IgG signifies past infection.
- PCR test: This polymerase chain reaction test detects T. gondii DNA in blood or cerebrospinal fluid.
- Microscopic examination: Looking for tachyzoites or tissue cysts under the microscope can confirm toxoplasmosis, often performed on lymph node or spinal fluid samples.
- Congenital toxoplasmosis screening: Pregnant women can be tested via blood test, amniocentesis, or fetal ultrasounds to check for congenital infection.
For suspected ocular toxoplasmosis, an ophthalmologist may examine the eyes for inflammation and take a sample of fluid from the eye to test for the parasite’s DNA. Neuroimaging and CT scans can also help identify brain and organ damage associated with toxoplasmosis.
How is toxoplasmosis treated?
Toxoplasmosis is treated using antiparasitic medications including:
- Pyrimethamine – inhibits parasite growth
- Sulfadiazine – limits parasite reproduction
- Spiramycin – used in pregnancy to reduce transmission
- Azithromycin or clarithromycin
A combination of pyrimethamine and sulfadiazine is most commonly used to treat severe toxoplasmosis. For pregnant women or people with allergies, other antibiotic combinations may be prescribed instead. Treatment duration varies based on disease severity and immune function.
People with weakened immune systems may require longer treatment to prevent reactivation. Lifelong suppressive antibiotic therapy may be necessary in AIDS or transplant patients until their immune function improves. Congenital toxoplasmosis in newborns is treated for 12 months or longer.
What complications can occur with toxoplasmosis?
Without treatment, severe toxoplasmosis can lead to serious complications and permanent damage, especially in those with compromised immunity. Potential complications include:
- Loss of vision or hearing due to ocular or ear inflammation
- Seizures and epilepsy
- Obstructive hydrocephalus due to cysts blocking cerebrospinal fluid flow
- Permanent cognitive or motor deficits
- Respiratory failure if lungs are affected
- Coma or death if the infection spreads to the brain
Congenital toxoplasmosis can also cause lasting complications like seizures, developmental delays, blindness and cognitive impairment in children. Prompt treatment helps reduce the risk of permanent damage.
How can toxoplasmosis be prevented?
Preventing toxoplasmosis involves limiting exposure to possible sources of T. gondii infection through the following measures:
- Cook meat thoroughly, especially pork and lamb. Freeze meat for several days to help kill any parasites.
- Wash hands before and after handling raw meat.
- Wash all fruits and vegetables thoroughly.
- Clean cooking surfaces and utensils after they touch raw meat.
- Wear gloves when gardening or working with soil.
- Change cat litter daily. Have someone else change litter if pregnant or immunocompromised.
- Keep cats indoors and feed them commercial dry or canned cat food instead of raw meat or rodents.
- Avoid drinking untreated water.
- Control rodent and cat populations to limit environmental oocyst contamination.
Pregnant women not previously exposed to T. gondii should take precautions to avoid toxoplasmosis infection as it can readily pass to the fetus. Some doctors may recommend blood tests or prophylactic medication.
Toxoplasmosis is a fairly common parasitic infection that can have mild flu-like symptoms at first. However, it may have subtle, long-term neurological and psychiatric effects in some people. Severe, life-threatening toxoplasmosis can develop in those with weakened immunity or congenitally infected infants.
While many infections cause no initial symptoms, toxoplasmosis should be treated in high-risk groups to prevent complications. Following preventive measures can reduce the risk of contracting this stealthy parasite. Prompt diagnosis allows early treatment to minimize any lasting impairment from toxoplasmosis.