Toxoplasmosis is an infection caused by a single-celled parasite called Toxoplasma gondii. While many infected individuals experience no symptoms or only mild, flu-like illness, the infection can lead to serious health issues for infants and people with weakened immune systems.
Common Transmission Pathways
One of the most common ways humans contract toxoplasmosis is by consuming undercooked meat that contains Toxoplasma gondii tissue cysts. Pork, lamb, and venison are particularly known carriers of the parasite. If meat is not cooked to an adequate internal temperature, the parasites within these cysts can remain viable and cause infection upon ingestion.
Accidental ingestion of oocysts from contaminated soil or produce also represents a frequent transmission route. Cats are the primary hosts where Toxoplasma gondii completes its life cycle and sheds millions of microscopic oocysts in their feces. These oocysts can contaminate soil in gardens or sandboxes, and if hands are not properly washed after contact, the parasite can be transferred to the mouth.
Produce, such as unwashed fruits and vegetables grown in contaminated soil, can also harbor these oocysts. Eating such produce without thorough washing can lead to infection. Drinking water contaminated with Toxoplasma gondii oocysts is another way the parasite can spread, particularly in areas where water treatment is insufficient.
Less Frequent Transmission Routes
Toxoplasmosis can also spread through congenital transmission, meaning from a mother to her unborn child during pregnancy. If a woman acquires a Toxoplasma gondii infection for the first time during or just before pregnancy, the parasite can cross the placenta and infect the fetus. This can lead to severe health problems for the baby, including vision issues, developmental delays, and, in some cases, miscarriage or stillbirth.
Transmission through organ transplantation or blood transfusion from an infected donor is rare but has been reported. In organ transplantation, the risk is highest when a recipient who has never been exposed to the parasite receives an organ from a donor who has the infection. The parasite can be present in the donated organ or blood products, particularly in individuals who are immunosuppressed due to their medical condition or medications.
Preventing Transmission
Preventing toxoplasmosis involves several practical measures, particularly focusing on food hygiene and managing exposure to cat feces. Thoroughly cooking meat is an important step; meat, especially pork, lamb, and venison, should be cooked to an internal temperature of at least 160°F (70°C) until it is no longer pink in the center and the juices run clear.
Washing fruits and vegetables meticulously under running water before consumption is also important, particularly for produce grown in gardens where cats may roam. Good hand hygiene is important; hands should be washed thoroughly with soap and water after gardening, handling raw meat, or touching anything that might have come into contact with cat feces. Avoiding cross-contamination in the kitchen by washing cutting boards, knives, and utensils after contact with raw meat is also recommended.
For cat owners, responsible litter box management significantly reduces the risk of transmission. The parasite’s oocysts do not become infectious until 1 to 5 days after being shed in cat feces, so cleaning the litter box daily can prevent them from reaching an infective stage. Pregnant individuals or those with weakened immune systems should ideally have someone else handle litter box duties.