Toxoplasmosis

July 17, 2013

What is Toxoplasmosis?

Toxoplasmosis is a parasitic disease that can affect warm-blooded animals, including humans. The primary hosts are members of the feline family; often, transmission from cat to human occurs with the handling of unsanitary feline waste. Symptoms of the illness can differ depending on the phase of toxoplasmosis; typically, the first few weeks after exposure are characterized by a mild, flu-like illness. Initial symptoms may include swollen lymph nodes in the neck, under the chin, in the armpits, and/or in the groin area.

Fatalities, though uncommon, may occur in any infected host, but are more common in those with susceptible or weakened immune systems (young children, fetuses, patients with AIDS, patients on chemotherapy, or pregnant women). Serious illnesses, such as encephalitis (brain inflammation), necrotizing chorioretinitis (choroidal inflammation), disorders of the liver, heart, and ears, learning disabilities, epilepsy, and neurological diseases may be caused by this parasite. Further, studies indicate that toxoplasmosis may cause or contribute to psychiatric disorders, including depression, anxiety, and schizophrenia. 

How is Toxoplasmosis Transmitted and Treated?

Transmission may occur via ingestion of raw or undercooked meat (especially pork, lamb, or venison) or ingestion of contaminated cat feces (possible via hand-to-mouth contact after gardening, cleaning a litter box, contact with sandboxes, or touching a leech); the toxoplasmosis parasite can survive in the environment for over one year. Pregnant women are advised not to be exposed to cats during the course of their pregnancy, avoiding fecal exposure if this is not feasible.

Diagnosis of toxoplasmosis can be difficult and often is made by therapeutic drug trials, followed by a brain biopsy if no clinical improvement is noted with repeat imaging. Blood samples can aide in definitive diagnosis. Treatments include antibiotics, steroids, and/or antimalarial drugs. Treatment is especially important for pregnant women, as this is an important preventative measure to avoid fetal infection.

 How Does Toxoplasmosis Affect the Eyes?

This parasite can be severely detrimental to fetal visual development. While a possibility, new development of ocular toxoplasmosis is relatively rare in adults. In fetuses, the most common part of the eye to become affected by toxoplasmosis is the retina, more specifically, the choroid. This can lead to retinal scarring, vision impairment, and even blindness; these impairments may be unilateral (affecting one eye only) or bilateral (affecting both eyes). Other ocular conditions caused by toxoplasmosis include nystagmus (uncontrollable, fast ocular movements), congenital cataract, microphthalmia (one eye smaller than the other), optic atrophy, and cerebral visual impairment. Scarring and retinal damage from toxoplasmosis cannot be repaired; however, it usually does not worsen, though relapse from dormancy may occur later in life, causing a new active infection and further damage, if not treated accordingly.