Introduction to Herpes Simplex Viruses (HSV):
Herpes simplex viruses (HSV) are extremely widespread in human population. They can multiply in a wide variety of cells and infect a wide range of animals, demonstrating their wide host range.
Gingivostomatitis, keratoconjunctivitis, encephalitis, genital disease, and infections in neonates are among the many illnesses caused by the herpes simplex viruses. In nerve cells, the herpes simplex viruses cause latent infections that frequently recur.
Types of HSV: HSV-1 and HSV-2
Type 1 and type 2 herpes simplex viruses (also known as HSV-1 and HSV-2) are different in how they spread; HSV-1 is spread by contact, typically through contaminated saliva, whereas HSV-2 is spread through sexual contact or from a maternal vaginal infection to a newborn.
This results in different clinical features of human infections
Pathogenesis and clinical course:
Because HSV causes cytolytic infections, pathologic changes are due to necrosis of infected cells together with the inflammatory response. Lesions induced in the skin and mucous membranes by HSV-1 and HSV-2 are the same. Changes induced by HSV are similar for primary and recurrent infections but vary in degree, reflecting the extent of viral cytopathology.
Fig: Herpes Virus: Immune Evasion by Latency
HSVs spread when a susceptible person comes into contact with an excreting virus; for an infection to start, the virus needs to come into contact with mucosal surfaces or broken skin.
The virus is disseminated via respiratory droplets or direct contact with infected saliva, and HSV-1 infections are often restricted to the oropharynx. The majority of primary HSV infections are asymptomatic and typically moderate. When an immunocompromised host is unable to control viral replication, viremia can develop, which can lead to widespread organ involvement.
Clinical Manifestations of HSV Infections:
Oropharyngeal and Oral HSV Infections
Usually, primary HSV-1 infections don’t cause any symptoms. Symptomatic illness affects the buccal and gingival mucosa of the mouth and is more common in young children (1–5 years old). Clinical disease lasts for two to three weeks, and the incubation period is brief (about three to five days, with a range of two to twelve days).
Symptoms include fever, sore throat, vesicular and ulcerative lesions, gingiva-stomatitis, and malaise. Gingivitis (swollen, tender gums) is the most striking and common lesion. Primary infections in adults commonly cause pharyngitis and tonsillitis. Localized lymphadenopathy may occur.
Keratoconjunctivitis and Ocular Herpes
Severe keratoconjunctivitis can result from HSV-1 infections in the eye.
Recurrent eye lesions are common and manifest as vesicles on the eyelids, corneal ulcers, or dendritic keratitis. The corneal stroma may gradually get involved in recurrent keratitis, resulting in blindness and permanent opacification. Infections with HSV-1 are the second leading cause of corneal blindness in the United States, after trauma.
Fig: Herpes Simplex Virus Disease Syndromes
Cutaneous infections are frequently severe and sometimes fatal when they affect people who have skin conditions like burns or eczema that allow for widespread local viral multiplication and spread. In a person with chronic eczema, eczema herpeticum is a primary infection, typically caused by HSV-1. Rarely, the disease could be lethal.
Encephalitis and Neurological Complications
Herpesviruses can induce a severe form of encephalitis. Infections with HSV-1 are thought to be the most frequent cause of spontaneous, deadly encephalitis in the US. Those who survive the disease frequently have lasting neurologic abnormalities, and the disease has a high fatality rate.
The majority of patients with HSV encephalitis seem to have recurrent infections, whereas about half seem to have original infections.
Genital Herpes and Reproductive Health
HSV-2 is often spread through vaginal channels, and the infection site is where viral replication starts. After invading local nerve endings, the virus travels to the dorsal root ganglia via retrograde axonal flow, where it replicates further and establishes latency. While vaginal HSV-2 infections cause latently infected sacral ganglia, oropharyngeal HSV-1 infections cause latent infections in the trigeminal ganglia. Although HSV-1 can occasionally result in clinical bouts of genital herpes, HSV-2 is typically the source of genital illness. Serious primary genital herpes infections can linger for roughly three weeks. Vesiculo-ulcerative lesions of the male penis or the female cervix, vulva, vagina, and perineum are the hallmarks of genital herpes.
The lesions are very painful and may be associated with fever, malaise, dysuria, and inguinal lymphadenopathy (swollen lymph nodes in the groin area). Aseptic meningitis (about 10% of cases) and extra-genital lesions (approximately 20% of cases) are among the complications. The duration of viral excretion is around three weeks. Some protection against heterotypic infection is provided by preexisting immunity due to the antigenic cross-reactivity between HSV-1 and HSV-2. Genital herpes virus recurrences are frequent and typically moderate, and an initial HSV-2 infection in an individual already immune to HSV-1 is typically less severe.
In healthy individuals, cutaneous HSV infections are rare because intact skin is resistant to the virus. Abrasions that become infected with the virus might develop localized lesions produced by HSV-1 or HSV-2 (traumatic herpes). These lesions are found on wrestlers’ bodies (herpes gladiatorum) and on the fingertips of dentists and medical staff (herpetic whitlow). a newborn may contract HSV from infected mother during pregnancy (intrauterine), during delivery, or after birth.
Treatment and Management:
Acyclovir and valacyclovir are two antiviral medications that have shown promise in treating HSV infections. Acyclovir is currently the standard therapy. They are the inhibitors of the synthesis of viral DNA. The HSV thymidine kinase monophosphorylates the nucleoside analog acyclovir, which cellular kinases then transform into the triphosphate form. The medications may decrease genital herpes recurrences, shorten the healing period, and suppress clinical signs.