Cultivation and Isolation of Viruses

Herpesviruses

• Cytomegalovirus (CMV) (HSV-5) is a ubiquitous herpesvirus that can cause infectious mononucleosis (heterophil-negative) and congenital defects
• CMV replicates in epithelial cells of the respiratory tract, salivary glands, and kidneys, and persists in lymphocytes
• Incubation period: 4-8 weeks
• Properties of the virus: largest genetic content of human herpesviruses (HHV)

Transmission and Pathogenesis

• CMV can be transmitted from person to person through close contact with virus-bearing material
• Primary CMV infections in immunosuppressed hosts are more severe than in normal hosts, with pneumonia as a frequent complication
• Cytopathology: multinucleated giant cells indicate herpesvirus (HSV-1, HSV-2, or varicella-zoster) presence
• Serology: antibodies appear 4-7 days after infection, peaking in 2-4 weeks, detected by neutralization, immunofluorescence, and enzyme-linked immunosorbent assay

Treatment and Diagnosis

• Several antiviral drugs are effective against HSV infections, including Acyclovir, Valacyclovir, and Vidarabine
• Laboratory diagnosis: polymerase chain reaction (PCR), isolation and identification of virus, cytopathology, and serology

Herpes Simplex Virus (HSV)

• HSV-1 and HSV-2 are widespread in the human population, with HSV-1 spread by contact and HSV-2 transmitted sexually or from a maternal genital infection to a newborn
• HSV growth cycle: rapid, requiring 8-16 hours for completion
• Clinical findings: primary infections may be clinically inapparent, but result in antibody production and establishment of latent infections in sensory ganglia
• Recurrent lesions are common

Varicella-Zoster Virus (HSV-3)

• Varicella-zoster virus (VZV) causes varicella (chickenpox), a mild, highly contagious disease characterized by a generalized malaise, fever, and vesicular eruption of the skin and mucous membranes
• Incubation period: 10-21 days
• Cases of congenital varicella syndrome can occur after maternal cases of chickenpox during pregnancy
• Varicella pneumonia is rare in healthy children but is the most common complication in neonates, adults, and immunocompromised patients

Human Herpesvirus 8 (HHV-8)

• HHV-8 is also known as Kaposi sarcoma-associated herpesvirus (KSHV)
• It was first detected in 1994 in Kaposi sarcoma specimens
• HHV-8 is lymphotropic and causes Kaposi sarcomas, vascular tumors occurring in AIDS patients, and multicentric Castleman disease

Poxviruses

• Poxviruses are the largest and most complex of viruses infecting humans, resistant to inactivation
• They have linear ds DNA and own RNA polymerase
• Infections are characterized by a rash, with lesions induced by some members of the family being markedly proliferative
• The group includes vaccinia virus, variola virus, and parapoxvirus
• Edward Jenner introduced vaccination with live cowpox virus in 1798

Hepatitis Viruses

• Hepatitis viruses are caused by one of the following five agents: hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D (HDV), and hepatitis E virus (HEV)
• All Hepatitis viruses are ss RNA, except HBV which is ds DNA
• HAV and HEV are nonenveloped viruses, while HBV, HCV, and HDV are enveloped viruses
• Hepatitis viruses produce acute inflammation of the liver, resulting in a clinical illness characterized by fever, gastrointestinal symptoms, and jaundice

Parvoviruses

• Parvovirus B19 is pathogenic for humans and has a tropism for erythroid (RBC) progenitor cells