Microbiology
Summary
Herpes simplex viruses (HSV) consist of two main types: HSV-1 and HSV-2. Both belong to the Herpesviridae family, a group of enveloped viruses with double-stranded DNA genomes. HSV-1 tends to lie dormant in the trigeminal ganglia. On the other hand, HSV-2 remains latent in the sacral ganglia. Both types can be transmitted vertically, classifying them under the TORCHeS infections.
HSV-1 is predominantly linked to orofacial infections, such as gingivostomatitis, herpes labialis (cold sores), and keratoconjunctivitis. It's the primary cause of sporadic encephalitis in the US, and can result in hemorrhagic temporal lobe encephalitis. HSV-2 typically associates with genital infections and can manifest as painful inguinal lymphadenopathy and aseptic meningitis. Various clinical presentations such as herpetic whitlow, erythema multiforme, and the hallmark Òdew drop on a rose petalÓ appearance of HSV lesions further characterize these viruses. Diagnostically, intranuclear inclusions called Cowdry bodies are notable in infected cells. The Tzanck smear has been used historically to spot multinucleated giant cells indicative of HSV infection. Furthermore, both viruses can be managed with antiviral agents like valacyclovir and acyclovir to suppress outbreaks.
Lesson Outline
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FAQs
HSV-1 primarily causes oral herpes and is typically transmitted during childhood via non-sexual contact. It is characterized by cold sores or fever blisters around the mouth. HSV-2, on the other hand, causes genital herpes, and is mainly sexually transmitted. It leads to sores or blisters on the genitals, rectum or mouth. However, it's important to note that both types can infect both areas, although this is less common.
Cowdry bodies are intranuclear inclusion bodies that appear in cells infected with certain types of viruses, including the herpes simplex virus. These are usually composed of nucleic acid and protein. In the context of a HSV infection, the presence of Cowdry type A bodies typically indicates cellular changes that result from viral replication.
Herpetic whitlow is a painful infection of the fingertip caused by the herpes simplex virus. It generally occurs when the skin on the finger comes into direct contact with HSV-1 or HSV-2. ItÕs most commonly seen in healthcare workers who come in contact with the virus when they donÕt use gloves or proper protection. There are also occurrences in children when they suck their thumbs or fingers when they have a herpes infection of the lips or mouth.
A Tzanck smear is a diagnostic test where cells are scraped from a blister or sore and examined under a microscope. It was historically used to detect viral changes in herpes infections, but due to limited accuracy and inability to distinguish herpesvirus types, modern methods like PCR and viral culture are now preferred for HSV diagnosis.
