Human Parvovirus B19 and Herpes Simplex Virus

Human Parvovirus B19 (Erythema Infectiosum)

• A single-stranded DNA (ssDNA) non-enveloped virus belonging to the Parvoviridae family.
• Parvovirus B19 is the only species within the Parvoviridae family that is pathogenic to humans.
• Infects immature red blood cells in the erythroid lineage.
• Transmission occurs through respiratory droplets, blood transfusions, and vertical transmission from mother to fetus.

Herpes Simplex Virus (HSV) 1 and 2

• A member of the Herpesviridae family, belonging to the alpha group.
• Characterized by a double-stranded DNA (dsDNA) enveloped icosahedral structure.
• Transmitted by direct contact with infected secretions.
• HSV-1 is typically associated with oropharyngeal lesions (cold sores, fever blisters), while HSV-2 is associated with genital herpes and neonatal herpes.
• HSV-1 and HSV-2 share substantial sequence homology but can be distinguished by sequence analysis or restriction enzyme analysis of viral DNA.
• HSV-1 and HSV-2 can cross-react serologically, but each type has unique proteins.
• Transmission patterns of HSV are evolving, with new species emerging through genetic recombination.

Modes of Vertical HSV Transmission

• Placental transmission during pregnancy.
• Neonatal herpes is most commonly caused by HSV-2.
• Neonatal herpes can be acquired in utero, during birth, or after birth.
• The most common route of infection is during birth through contact with herpetic lesions in the birth canal.
• Cesarean section is used in pregnant women with genital herpes lesions to prevent infection.

HSV Pathology

• Infection requires contact with mucosal surfaces or broken skin; unbroken skin is resistant.
• Viral replication initially occurs at the site of infection.
• The virus invades local nerve endings and is transported by retrograde axonal flow to dorsal root ganglia.
• Latency is established after further replication.
• Over 80% of humans carry latent HSV-1, but not all experience recurrences.
• The reason for reactivation in some individuals is unknown.

Monkeypox

• An Orthopoxvirus belonging to the Poxviridae family.
• A zoonotic disease, with the primary reservoir host unknown.
• Squirrels, rabbits, and rodents can be infected.
• Commonly found in Central and West Africa.
• Transmission occurs through direct contact with infected persons, animals, or contaminated materials.
• Incubation period is 5-21 days.
• Symptoms include fever, intense headache, lymphadenopathy, back pain, and myalgia.
• A prominent feature of monkeypox is pronounced lymphadenopathy, which is not observed in smallpox or chickenpox.
• Skin rash appears 1-3 days after fever onset, typically on the face, palms, soles, oral mucosa, and genitalia.
• Rash progresses from macules to papules to vesicles to pustules, ultimately forming crusts/scabs that dry up and fall off.
• Monkeypox is a self-limited disease, lasting 2-4 weeks.
• Complications are common and serious, including pulmonary distress, secondary bacterial infections, and encephalitis.
• Vaccination with vaccinia can protect against monkeypox or reduce the severity of the disease.

Variola Virus

• Has a narrow host range, limited to humans and monkeys.
• Primary infection occurs through the mucous membranes of the upper respiratory tract.
• Viral replication occurs in the following stages:
  • Primary multiplication in the lymphoid tissue draining the site of entry.
  • Transient viremia and infection of reticuloendothelial cells throughout the body.
  • A secondary phase of multiplication in these cells, leading to a secondary, more intense viremia.
  • Clinical disease presentation.

Variola Virus Clinical Findings

• Incubation period is 10-14 days.
• Lesions in the mouth ulcerate and discharge virus by the 6th-9th day.