Viral Infectious Agents Overview

Viral Infectious Agents

• Viral pathogenesis often involves latent periods, like in herpes simplex viruses
• Herpes simplex viruses (HSV) type 1, transmitted through direct contact, cause primary infection, usually in children
• Primary HSV-1 infection commonly presents as acute gingivostomatitis, characterized by vesicles on the gums, which rupture and form healing crusts
• Latency of HSV-1 resides in the trigeminal ganglion, a cluster of sensory nerve cell bodies near the spinal cord
• Reactivation of HSV-1 can occur every few years, triggered by stress or compromised immune function, causing recurrent herpes labialis (cold sores) or reactivation of primary gingivostomatitis
• Varicella-zoster virus (VZV) presents in two forms: primary varicella (chickenpox), characterized by a generalized rash, and reactivation zoster (shingles), presenting as a localized rash
• Chickenpox infection typically affects children aged 4-10 years
• Adults reactivating latent varicella infection experience shingles, usually in the dermatome which gets reactivated
• Rash of varicella begins on trunk and spreads to limbs, whereas shingles remains limited to a single dermatome
• Vesicles, pustules, and ulcers develop during the course of varicella
• Diagnostic laboratories use smears of vesicular lesions with direct virus detection or serology to confirm the specific VZV antibodies (IgM or rising IgG titre). This is achieved by ELISA
• The poxvirus family is the largest of all the viruses, distinguished by their large size (300nm), brick-shaped morphology, enveloped structure, and double-stranded DNA.
• Smallpox, a member of this family, no longer exists

Hepatitis B Virus (HBV)

• HBV is a DNA virus belonging to the Hepadnaviridae family, causing serum hepatitis
• The complete virus, called the Dane particle, is spherical or tubular shaped, identifiable by the hepatitis B surface antigen
• HBV transmission occurs through sexual contact, exposure to contaminated blood products, percutaneous exposures (tattoos, piercings), and perinatally from infected mothers to newborns.
• Diagnosis involves detecting the hepatitis B surface antigen or antibodies in the blood serum, viral DNA (using PCR), and liver function tests (e.g., ALT, bilirubin)

HIV

• HIV is an enveloped virus that requires direct blood-to-blood contact for infection
• The HIV envelope contains glycoproteins (gp120 and gp41), essential for attachment and entry into host CD4+ T cells
• The HIV genome consists of two identical copies of positive-sense single-stranded RNA, associated with reverse transcriptase
• HIV transmission routes include sexual contact, blood and blood products (e.g., contaminated needles), and vertical transmission (mother to child during pregnancy or breastfeeding)
• Diagnosing HIV involves detecting HIV-specific antibodies in blood serum (using ELISA), followed by confirmatory Western blot if the ELISA is positive
• Additional tests for HIV diagnosis include nucleic acid tests (NAT) for measuring HIV DNA or RNA (e.g., PCR) and CD4 count to establish diagnosis of AIDS (if the CD4 count is below 200 cells/mm3 or CD4/CD8 ratio is less than 1)