HSE is a type of infectious encephalitis that occurs when the herpes simplex virus (HSV) enters the brain. HSV can be of two types: HSV1 and HSV2. HSV1 is mainly associated with early mouth and throat infections often without symptoms, but lately it has also been associated with genital herpes. HSV2 is associated with genital herpes mainly in adolescents and adults as it is transmitted through sexual activity.

About 90% of adults are infected with HSV1 in their lifetime. The virus attaches and enters the sensory nerves of the throat and moves to nerve cells called "andia" (e.g., trigeminal ganglia). Here, the virus establishes a latent (hidden) and life-old infection. In some people, from time to time, the virus may reactivate to produce recognized lesions such as cold sores around the lips and nose.
The word limnology is derived from the Greek limne - marsh, pond and Latin limnaea - something related to a marsh. In other words, limnology is the study of the structural and functional relationships of indoor aquatic organisms, because their dynamic physical, chemical and biotic environments affect them.