**1. Introduction**

Mammalian brain and spinal cords are covered by three membranous tissue layers pia mater, arachnoid mater, and dura mater (from inner to outer) forming meninges. Infection in these layers is known as meningitis. An inflammation or infection in the brain tissue is known as encephalitis [1]. The infection in the brain and meninges together is known as meningoencephalitis or encephalomeningitis. This can be caused by either of the bacteria, fungi, viruses, or protozoans. Viral or aseptic meningoencephalitis, caused by herpes simplex

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virus type 1 (HSV 1) and 2 (HSV 2), is known as herpes meningoencephalitis (HME) [2]. The direct infection in the brain or meninges is called primary HME, whereas if it spreads from other parts to the brain, then it is called secondary HME. Both the male and female are affected at an equal ratio with a higher mortality and morbidity rate (∼50%) for infants. Like a communicable infection, spread through air, water, or close contact [3], the viruses after entering the patient through mouth, nose, or genital tract reach to the brain‐crossing blood‐brain barrier and cause infection.

The symptoms of this infection are a combinatorial effect of both the meningitis and encephalitis insisting the physicians to suspect meningoencephalitis [4]. Symptoms resemble to the common viral infections but may vary among the children and adults. Some of the typical symptoms of HME are nuchal rigidity, blurred vision, and purple body rashes. The infection can spread among people through droplets, foods, air, or close contact. There is always a need for early diagnosis of the infection followed by treatment. The disease can be suspected initially on the basis of the specific symptoms of the patients. This can be further confirmed by several laboratory‐based, imaging, or advanced techniques [5]. Although the prevention of HME is not possible through vaccination, but proper precaution measures can reduce the risk of spreading and relapsing of the disease. Abstain or safety measures during sexual intercourse and proper management during pregnancy lessen the risk of contamination.

Mild infected persons may recover in few weeks but a severely infected person requires longer time and intense care. Early treatment of the patients with antiviral drugs may hugely reduce the risk of the contamination and death. Anticonvulsants or diuretics can minimize the inflammation, cranial pressure, or pain. In this chapter, we have discussed in detail about the symptoms, causes, diagnosis, prevention, and treatment of HME.
