The impact of brain infections on early human development
Alex Si
Early brain development is a critical period in a foetus’ development given how quickly the brain grows, forming around 250,000 new neurones every minute in the womb. Infections in the brain at this time or shortly after birth can be very dangerous due to foetus’s/ baby’s immature immune system and can lead to damage that could lead to lifelong defects. Infections of the brain have multiple causes: viruses, fungi, bacteria, and sometimes parasites. Additionally, infections of the brain can often spread to other areas of the central nervous system (CNS), namely, the spinal cord, leading to serious complications. The brain may either be directly infected (encephalitis) or the membrane layer that surrounds the brain and spinal cord, called the meninges, can be infected (meningitis). When both are simultaneously infected, it is referred to as meningoencephalitis – often infections of the meninges will spread to the brain itself. Owing to the potentially extremely severe consequences of such infections, it is of critical importance that these infections are prevented as far as possible through early diagnoses and subsequent intervention. The two periods in which brain infections may be most damaging to humans in early life are before the baby is born or just after. Frequently occurring congenital brain infections include cytomegalovirus (CMV) - the most common one to occur, zika virus, and toxoplasmosis. There are a few modes in which infections can reach a developing embryo, with the most common being horizontal transmission – which involves a pathogen spreading across the placenta from the mother to the child; the foetus is most vulnerable to infection in this manner during early pregnancy. Foetuses may also be infected via vertical transmission, when pathogens in the vaginal canal arise through the cervix leading to congenital infection. Finally, while somewhat rare, infections also may occur when spread during a medical procedure which involves the uterine environment. CMV was first discovered in 1881 by Hugo Ribbert. While it is generally harmless in infected adults, it can cause serious developmental issues in growing foetuses and newborn babies. At birth, around 90% of babies that have congenital CMV are asymptomatic and generally develop in the same way as any healthy human. However, around 10% of asymptomatics may develop hearing loss throughout development into adulthood. Additionally, a very small proportion of those with asymptomatic CMV may develop vision problems. However, the 10% of those with congenital CMV that are symptomatic are likely to be born with more severe defects. Hearing loss is very common for those with congenital CMV as well as learning disabilities due to brain calcifications. In more extreme cases, the child may develop motor function issues, chiefly cerebral palsy. In the most severe cases, stillbirth may occur, or death within the first year of life. The ways in which CMV causes specific defects have various mechanisms. CMV hearing loss is believed to be a result of virally induced labyrinthitis, where the labyrinth – a membranous region in the inner ear – inflames. CMV can cause damage to vision through inducing chorioretinitis, an inflammation of the choroid and retina, or through damaging tissue in the eye causing scarring in the macular region, as well as damage it may cause to the optic nerve. Other symptoms of CMV caused by damage to the developing brain, including learning disabilities or cerebral
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