HSV is a double-stranded linear DNA genome that exists in both circular and linear forms in the body of the virus. HSV-1 is mainly found in the skin and mucous membranes above the face and waist and in the central nervous system, and occasionally in the external genitalia; HSV-2 is mainly found in the genitalia and in the skin and mucous membranes below the waist and occasionally in the oral cavity. The important feature of HSV infection is that the virus can exist in the body for a long time. Clinical manifestations Clinical manifestations can be divided into two types: primary and recurrent. Primary herpes simplex has an incubation period of 2 to 12 days, with an average of 6 days, and occurs mostly in infants or children, often as an insidious infection with occasional symptoms. The virus is latent in the ganglia after infection and often recurs when stimulated by certain factors such as fever, sun exposure, menstruation, emotional stress, surgery, application of adrenocorticotropic hormones and certain infections such as lobar pneumonia, epidemic meningomyelitis, malaria, influenza and the common cold. Primary herpes simplex skin mucosal damage often takes 2 to 3 weeks to heal, while most of the lesions of recurrent herpes simplex disappear within 1 week. Clinically, there are local and systemic infections. 1) Localized infections 1) Cutaneous herpes is mostly seen as recurrent herpes or adult primary herpes. It can occur in any part of the body, and it is usually found at the junction of the skin and mucous membranes, with the lip margin, corners of the mouth, and around the nostrils. Initially, localized itching, burning or tingling of the skin is followed by congestion and redness, followed by the appearance of pinhead or rice-grain-sized clusters of blisters with a slightly red base, which do not fuse with each other but can appear in multiple clusters at the same time. The blisters are thin-walled, with clear, clear fluid, which breaks down on its own for a short period of time, vesicles, and oozes, and then dries and crusts after 2 to 10 days, leaving no scar after debridement. (2) Oral herpes is characterized by large blisters on the oral mucosa, tongue, gums, pharynx and even esophagus, which then turn into ulcers. The patient has localized pain, refusal to eat, salivation, and may be accompanied by fever and swelling of submandibular and/or cervical lymph nodes. It is most commonly seen in children and in adults who have oral sex. (3) Genital herpes is mainly due to HSV-II infection. The genital, perineal, peri-vulvar, femoral and buttock skin can be involved, with herpes, ulcers and punctate erosions. In males, the herpes occurs on the glans, foreskin, coronal sulcus, penis, and also scrotum; in females, it occurs on the labia, clitoris, vagina, cervix, and also on the urethra and surrounding skin. A history of anal sex in homosexuals can lead to herpetic proctitis, followed by perianal and rectal purulent infections or inguinal lymphadenitis. A few patients develop sacral radiculitis leading to neuralgia, urinary retention or constipation. (4) Ocular herpes manifests as herpetic keratitis and conjunctivitis, mostly unilateral, often accompanied by herpes or edema of the affected eyelid and enlarged preauricular lymph nodes. Repeated episodes can lead to corneal ulceration, clouding, and even perforation leading to blindness. In neonates and patients with systemic disseminated infections such as AIDS, chorioretinitis or acute necrotizing retinitis can occur, often leading to blindness. (5) HSV in herpetic nail infected fingers is a complication of primary oral or genital herpes. The virus can enter through a break in the epithelium of the finger or directly into the epidermis of the finger for occupational and other reasons. Herpes lesions often occur in the terminal phalanges and penetrate deep into the nail bed to form cellular necrosis; therefore, local pain is severe and throbbing-like, often accompanied by fever, elbow fossa and axillary lymphadenitis. Dentists and nurses who often touch herpes patients with bare hands are at risk of developing this disease. (6) Neonatal herpes is caused by HSV-II in 70% of neonatal HSV infections, all due to exposure to genital tract secretions at birth; congenital infections are often caused by intrauterine fetal infections in mothers with primary HSV infection during pregnancy. Fetuses with intrauterine infection may be born prematurely, with congenital malformations, or with impaired mental development. HSV infection in newborns may present as asymptomatic occult infection or may cause different forms or degrees of clinical manifestations. In mild cases, only oral, skin and eye herpes, but in severe cases, central nervous system infection or even generalized infection. (7) Central nervous system infections More than 70% of HSV infections in newborns are central nervous system infections, while they are rare in older children and adults. Primary HSV encephalitis is rare, except for neonates with primary HSV-2 infection. It is mostly caused by the activation of HSV-1 latent in the trigeminal ganglion or autonomic roots and then spreads to the central nervous system. The infection mainly involves the frontal and temporal lobes and is dominated by hemorrhagic necrotizing encephalitis. The clinical manifestations of HSV encephalitis vary by type, with HSV-1 causing mainly focal encephalitis and HSV-2 tending toward meningoencephalitis. The prodromal symptoms may include fever (up to 40°C), general malaise, headache, myalgia, drowsiness, abdominal pain, and diarrhea. 1/4 of the patients have a history of orofacial herpes. 2-5 days later, symptoms of central nervous system damage may appear, such as headache, vomiting, mental changes, neurological symptoms, and psychiatric symptoms. 2/3 of the patients may have local and general convulsions and meningeal irritation signs. In the extreme stage of the disease, death is caused by increased intracranial pressure due to cerebral edema and brain parenchymal necrosis, and even brain herniation. Among them, convulsions, impaired consciousness and mental abnormalities are the characteristics of the disease. 8) Herpes simplex hepatitis is mainly seen in primary and secondary immunocompromised patients and is prone to acute liver failure. The main manifestations are fever, increased liver enzymes, marked leukopenia, and may not appear herpetic dermatosis. (2) Systemic infection (1) Systemic disseminated herpes simplex infection disseminated HSV infection is most common in children aged 6 months to 3 years, and can also be seen in primary or secondary immunocompromised patients, especially in those with low cellular immunity, such as AIDS patients and organ transplant patients. The clinical presentation is severe, with multi-organ involvement. The initial presentation may be severe herpetic gingivitis, esophagitis, vulvovaginitis, high fever and even convulsions, followed by widespread blistering throughout the body with a concave top of the umbilicus, and viremia, causing herpetic hepatitis, encephalitis, pneumonia, gastroenteritis, adrenal gland dysfunction and other visceral damage. The death rate is as high as 70%. (2) Eczema-like herpes is caused by the sudden onset of HSV virus infection in and around the skin of chronic eczema and dermatitis, resulting in rapid progression of the disease, extensive lesions, and bleeding fusion, hemorrhage or transformation into impetigo, and occasionally hematogenous dissemination or secondary bacterial infection, involving other important organs and causing further deterioration of the disease, easily misdiagnosed as an aggravation of the original eczema.