What is Congenital Toxoplasmosis?
Congenital toxoplasmosis is an infection that occurs when the Toxoplasma gondii parasite is passed from a pregnant person to their baby during pregnancy. This transmission typically happens when the mother acquires a new infection, or in rare cases, when a previous infection reactivates because of a severely weakened immune system.
The timing of the maternal infection is a critical factor. An infection early in pregnancy is less likely to be transmitted to the fetus, but if it is, the consequences can be severe, sometimes leading to miscarriage or significant birth defects. Conversely, an infection in the third trimester has a much higher transmission rate, with some studies showing it can exceed 60%. Most babies infected this late in pregnancy, however, appear healthy at birth.
This creates a dangerous challenge: the absence of immediate symptoms does not mean the baby is unaffected. Without diagnosis and treatment, these children can develop serious complications, such as vision loss or learning disabilities, months or even years later. Understanding the potential long-term risks is crucial for ensuring proper care.
Neurological Complications: The Impact on the Brain
The Toxoplasma gondii parasite has a strong affinity for the central nervous system, making the developing brain a primary target. The infection can disrupt the brain's normal development and lead to some of the most significant and lasting complications of the condition.
Hydrocephalus and Structural Brain Damage
The infection can cause inflammation of the brain's ventricles, the chambers that produce and circulate cerebrospinal fluid. This inflammation can block the normal flow of fluid, causing it to build up and create dangerous pressure inside the skull, a condition known as hydrocephalus. The resulting pressure can damage surrounding brain tissue and cause an enlarged head (macrocephaly). In some severe cases, widespread tissue destruction can lead to the opposite effect—a smaller-than-normal head (microcephaly).
Cerebral Calcifications
As the immune system responds to the parasite in the brain, it can cause areas of tissue death. During the healing process, the body may deposit calcium in these damaged spots, creating small, hardened lesions known as cerebral calcifications. These calcifications, which are a hallmark sign of congenital toxoplasmosis, can be seen on brain scans like CT or ultrasound. They serve as permanent markers of injury and can disrupt the function of the brain regions where they are located.
Seizures and Motor Impairment
The structural damage from hydrocephalus and calcifications can disrupt the brain's normal electrical activity, often leading to seizures. Furthermore, injury to the parts of the brain that control movement can cause significant motor impairments. Depending on the location and extent of the damage, a child may develop conditions like cerebral palsy, affecting their muscle tone, posture, and ability to meet developmental milestones like sitting, crawling, and walking.
Sensory Complications: Vision and Hearing
The parasite frequently targets the delicate structures of the eyes and can also damage the auditory system, leading to permanent sensory deficits. These problems can be present at birth or emerge unexpectedly years later.
Chorioretinitis: A Lifelong Threat to Vision
The most common complication of congenital toxoplasmosis is chorioretinitis, an inflammation of the retina and the underlying blood vessel layer, the choroid. The parasite forms dormant cysts in the retinal tissue. These cysts can reactivate at any time—often years later—triggering an aggressive inflammatory response that destroys retinal cells and leaves permanent scars. If these scars form on the macula, the part of the retina responsible for sharp central vision, it can cause severe and irreversible vision loss. Each recurrence causes further damage, leading to a progressive decline in sight.
Other Ocular Problems
Beyond chorioretinitis, the infection can cause other eye conditions. Strabismus ("crossed eyes") can occur when poor vision in one eye prevents the brain from aligning both eyes correctly. Nystagmus, characterized by rapid, involuntary eye movements, can result from poor visual input or direct neurological damage. In severe cases, the infection can interfere with the physical development of the eye itself, leading to microphthalmia (abnormally small eyes) or cataracts (clouding of the lens).
Sensorineural Hearing Loss
Neurological damage can extend to the auditory system, causing sensorineural hearing loss. This means the problem lies with the inner ear or the nerve pathways that carry sound information to the brain. The impairment is often permanent and can be present at birth or develop gradually over time. If left unaddressed, even mild hearing loss can significantly impact a child’s speech, language development, and academic performance.
Systemic and Broader Developmental Consequences
Beyond the brain and eyes, congenital toxoplasmosis can affect multiple organ systems, leading to a range of complications that are often present in newborns and can influence a child's overall health and growth.
Organ Enlargement and Blood Disorders
The infection can disrupt fetal growth, causing babies to be born small for their gestational age. The parasite can also invade the liver and spleen, causing them to become enlarged (hepatosplenomegaly). This inflammation impairs organ function, often leading to jaundice—a yellowing of the skin and eyes from the buildup of bilirubin. The infection can also impact the bone marrow, leading to anemia (low red blood cell count) and thrombocytopenia (low platelet count), which can cause easy bruising or tiny, pinpoint red spots on the skin known as petechiae.
Long-Term Developmental Challenges
Even in the absence of severe neurological signs at birth, the infection can cause microscopic brain damage that affects higher-level functions later in life. These subtle impairments often do not become apparent until a child reaches school age. As academic and social demands increase, these children may struggle with learning disabilities, attention deficits, or problems with executive functions like planning and memory. Without a known diagnosis, these challenges can be mistaken for other conditions, delaying access to proper support.
Endocrine System Disruption
In some instances, the infection can damage the hypothalamus and pituitary gland, the brain’s control center for the body's hormonal systems. The consequences may not appear for years, often becoming evident during puberty. This can lead to endocrine abnormalities such as delayed or precocious (early) puberty, growth hormone deficiencies resulting in short stature, or other metabolic imbalances.
