Toxoplasmosis

Toxoplasmosis is a parasitic disease caused by Toxoplasma gondii, an apicomplexan. Infections with toxoplasmosis are associated with a variety of neuropsychiatric and behavioral conditions. Occasionally, people may have a few weeks or months of mild, flu-like illness such as muscle aches and tender lymph nodes. In a small number of people, eye problems may develop. In those with a weakened immune system, severe symptoms such as seizures and poor coordination may occur. If a woman becomes infected during pregnancy, a condition known as congenital toxoplasmosis may affect the child. Toxoplasmosis is usually spread by eating poorly cooked food that contains cysts, by exposure to infected cat feces, or from an infected woman to her baby during pregnancy. Rarely, the disease may be spread by blood transfusion or other organ transplant. It is thought to not otherwise spread between people, but broader transmissibility remains a matter of scientific debate. Studies have reported the presence of T. gondii in human semen and have proposed sexual transmission as a possible route, though this has not been established as a primary mode of spread. The parasite is only known to reproduce sexually in the cat family. It can infect most types of warm-blooded animals, including humans. Diagnosis is typically by testing blood for antibodies or by testing the amniotic fluid in a pregnant patient for the parasite's DNA. Prevention is by properly preparing and cooking food. Pregnant women are also recommended not to clean cat litter boxes or, if they must, to wear gloves and wash their hands afterwards. Treatment of otherwise healthy people is usually not needed. During pregnancy, spiramycin or pyrimethamine/sulfadiazine and folinic acid may be used for treatment. Up to half of the world's population is infected by T. gondii, but have no symptoms. In the United States, approximately 11% of people have been infected, while in some areas of the world this is more than 60%. Approximately 200,000 cases of congenital toxoplasmosis occur yearly. Charles Nicolle and Louis Manceaux first described the organism in 1908. In 1941, transmission during pregnancy from a pregnant woman to her baby was confirmed. There is tentative evidence that otherwise asymptomatic infection may affect people's behavior.

Signs and symptoms Infection has three stages:

Acute Acute toxoplasmosis is often asymptomatic in healthy adults. However, symptoms may manifest and are often influenza-like: swollen lymph nodes, headaches, fever, and fatigue, or muscle aches and pains that last for a month or more. It is rare for a human with a fully functioning immune system to develop severe symptoms following infection. People with weakened immune systems are likely to experience headache, confusion, poor coordination, seizures, lung problems that may resemble tuberculosis or Pneumocystis jirovecii pneumonia (a common opportunistic infection that occurs in people with AIDS), or chorioretinitis caused by severe inflammation of the retina (ocular toxoplasmosis). Young children and immunocompromised people, such as those with HIV/AIDS, those taking certain types of chemotherapy, or those who have recently received an organ transplant, may develop severe toxoplasmosis. This can cause damage to the brain (encephalitis) or the eyes (necrotizing retinochoroiditis). Infants infected via placental transmission may be born with either of these problems, or with nasal malformations, although these complications are rare in newborns. The toxoplasmic trophozoites causing acute toxoplasmosis are referred to as tachyzoites, and are typically found in various tissues and body fluids, but rarely in blood or cerebrospinal fluid. Swollen lymph nodes are commonly found in the neck or under the chin, followed by the armpits and the groin. Swelling may occur at different times after the initial infection, persist, and recur for various times independently of antiparasitic treatment. It is usually found at single sites in adults, but in children, multiple sites may be more common. Enlarged lymph nodes will resolve within 1–2 months in 60% of cases. However, a quarter of those affected take 2–4 months to return to normal, and 8% take 4–6 months. A substantial number (6%) do not return to normal until much later.

Latent Due to the absence of obvious symptoms, hosts easily become infected with T. gondii and develop toxoplasmosis without knowing it. Although mild, flu-like symptoms occasionally occur during the first few weeks following exposure, infection with T. gondii produces no readily observable symptoms in healthy human adults. When the infection enters a latent phase, during which only bradyzoites (in tissue cysts) are present; these tissue cysts and even lesions can occur in the retinas, alveolar lining of the lungs (where an acute infection may mimic a Pneumocystis jirovecii infection), heart, skeletal muscle, and the central nervous system (CNS), including the brain. Cysts form in the CNS (brain tissue) upon infection with T. gondii and persist for the lifetime of the host. Most infants who are infected while in the womb have no symptoms at birth, but may develop symptoms later in life. Reviews of serological studies have estimated that 30–50% of the global population has been exposed to and may be chronically infected with latent toxoplasmosis, although infection rates differ significantly from country to country. This latent state of infection has recently been associated with numerous disease burdens, neural alterations, and subtle sex-dependent behavioral changes in immunocompetent humans, as well as an increased risk of motor vehicle collisions.

Skin While rare, skin lesions may occur in the acquired form of the disease, including roseola and erythema multiforme-like eruptions, prurigo-like nodules, urticaria, and maculopapular lesions. Newborns may have punctate macules, ecchymoses, or "blueberry muffin" lesions. Diagnosis of cutaneous toxoplasmosis is based on the tachyzoite form of T. gondii being found in the epidermis. It is found in all levels of the epidermis, is about 6 by 2 μm and bow-shaped, with the nucleus being one-third of its size. It can be identified by electron microscopy or by Giemsa staining tissue where the cytoplasm shows blue, the nucleus red.

Cause

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