Microbiology
Summary
The Varicella-Zoster virus (VZV), a member of the Herpesviridae family, is an enveloped virus with a double-stranded DNA genome. VZV is causative agent of both chickenpox in children and shingles in adults. The virus is transmitted via respiratory droplets or from ruptured vesicles, and induces a range of symptoms including a widespread rash, fever, and headache. The chickenpox rash is described as a "dewdrop on a rose" or a vesicular lesion with surrounding erythema. The lesions appear in different stages of healing, unlike smallpox which presents a rash of uniform stage. Major complications include pneumonia and encephalitis, particularly in adults and the immunocompromised.
Post chickenpox, the virus remains dormant in the dorsal root ganglia of nerves and may be reactivated in later life, particularly under stress or immunosuppression, causing shingles. Shingles rash exhibits a similar "dewdrop on a rose" appearance and is found within a dermatomal distribution, predominantly affecting the lumbar and thoracic dermatomes without crossing the midline. This rash causes intense pain which may persist post rash as postherpetic neuralgia. In rare cases, shingles may affect the trigeminal nerve potentially leading to loss of vision, a condition known as herpes zoster ophthalmicus. The varicella vaccine, a live attenuated vaccine, is given to prevent chickenpox. A live attenuated zoster vaccine is available for adults over 60 for preventing shingles. Treatment includes acyclovir, famciclovir, or valacyclovir. It is noteworthy that if a pregnant woman gets infected with VZV during the first two trimesters, it may lead to congenital varicella syndrome in the child causing limb hypoplasia, cutaneous scarring in a dermatomal pattern, and blindness.
Lesson Outline
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FAQs
The Varicella-Zoster virus (VZV) is a member of the Herpesviridae family. This family is characterized by viruses that stay in the body after the initial infection, and can reactivate later. VZV is responsible for two major diseases: chickenpox, which is the primary infection, and shingles, which is due to reactivation of the dormant virus.
The varicella vaccine is designed to prevent the diseases caused by the varicella-zoster virus. The primary one is chickenpox. Immunization by the vaccine helps the body to produce a strong immune response to the virus without causing the full-blown disease. This largely prevents the person from contracting chickenpox, and by extension, shingles later in life.
Acyclovir is an antiviral drug used for treating infections caused by the herpesvirus family, including the Varicella-Zoster virus. It helps to slow down the growth and spread of the virus. While it doesn't cure the diseases, it can decelerate their progression, alleviate symptoms, and help the healing process.
Dorsal root ganglia (clusters of nerve cells located near the spinal cord) play a key role in VZV infections. After the primary infection, which manifests as chickenpox, VZV remains dormant in the dorsal root ganglia. Later, under certain conditions such as weakened immunity, the virus can reactivate and travel along the nerves causing shingles, which is characterized by a painful rash typically on one side of the body.
