Causes

Most cases of encephalitis are related to viruses, and the most common cause is herpes simplex virus-1 (HSV-1) in adults. HSV-2 is more common in neonates and may be transmitted from a mother infected with genital herpes during childbirth. Herpes encephalitis has a range of clinical presentations and can be transmitted during birth, through the blood, or by neuronal transmission. Neuronal transmission often occurs from the peripheral neuron in retrograde fashion to the brain. Arboviruses are also common causes of encephalitis; although most people bitten by arbovirus-infected insects do not develop the disease, approximately 10% do have overt symptoms. Transmission of arboviruses requires an insect vector and usually occurs in the Northern Hemisphere between June and October. The two most common arboviruses cause La Crosse encephalitis and St. Louis encephalitis. In the United States, most cases of nonepidemic encephalitis are caused by the La Crosse virus, are most common in rural areas of the Midwest, and affect children. Epidemics of both St. Louis encephalitis (found mostly in the East and Midwest) and western equine encephalitis (WEE; found across North America) have contributed a large number of the total cases since 1955. Many sources cite the St. Louis encephalitis virus as the most common form in this country, although many forms of the disease exist.

Although relatively uncommon, the deadliest arbovirus is the eastern equine encephalitis (EEE), which is mostly encountered in the New England region. Other viruses include the WEE (most common in rural communities west of the Mississippi River) and the Powassan (POW) virus, the only arbovirus known to be transmitted by ticks. Encephalitis has also been associated with many other diseases, including Creutzfeldt-Jakob disease, HSV (specifically HSV-1), kuru, malaria, mononucleosis, rabies, trichinosis, and typhus.

Pregnancy And Childbirth

Pregnancy And Childbirth

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