Poxviridae and Smallpox (Variola Virus)

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Questions and Answers

Why was the eradication of smallpox achievable with a single, stable serotype of the variola virus?

  • A single serotype facilitated the creation of a universally effective vaccine, eliminating the need for multiple strain-specific vaccines. (correct)
  • A single serotype allowed for the development of antiviral drugs with broad-spectrum efficacy.
  • A single serotype reduced the virus's mutation rate, preventing the emergence of resistant strains.
  • A single serotype meant that natural immunity was highly effective and long-lasting.

How does the replication strategy of poxviruses, specifically their independence from host cell RNA polymerase, influence their method of infection and disease progression?

  • It allows the virus to replicate in the nucleus, leading to faster integration with the host genome and chronic infection.
  • It enables the virus to replicate within the cytoplasm, delaying immune detection and promoting efficient spread. (correct)
  • It restricts the virus to infecting only cells with active RNA polymerase, limiting the scope of infection.
  • It forces the virus to rely on specific host transcription factors, making it highly tissue-specific.

Considering the pathogenesis of smallpox, what is the most critical implication of the secondary viremia stage in the development of the disease?

  • It signifies the initial infection of the upper respiratory tract and marks the beginning of the incubation period.
  • It involves the infection of internal organs, causing severe systemic symptoms and potential organ failure.
  • It indicates the virus's entry into the lymph nodes, triggering an immediate and localized immune response.
  • It represents the widespread dissemination of the virus to the skin, leading to the characteristic rash of smallpox. (correct)

What is the primary immunological mechanism responsible for the skin damage observed in smallpox infections?

<p>Cytotoxic T cell-mediated killing of virus-infected cells, resulting in localized tissue destruction. (B)</p> Signup and view all the answers

How does the clinical presentation of smallpox rash, particularly its centrifugal distribution, aid in differentiating it from other vesicular diseases?

<p>The rash being more pronounced on the face and extremities helps distinguish it from chickenpox, where lesions are more concentrated on the trunk. (A)</p> Signup and view all the answers

Given the similarities and differences between M-pox and smallpox, what is the most critical factor that contributes to the lower mortality rate associated with M-pox?

<p>M-pox has a milder virulence profile, resulting in less severe systemic symptoms and complications. (A)</p> Signup and view all the answers

In the context of M-pox transmission and potential reservoirs, why is the focus on African rodents and non-human primates significant for public health strategies?

<p>These animals are frequently in close contact with humans, increasing the risk of zoonotic transmission. (C)</p> Signup and view all the answers

What specific attribute of the live attenuated vaccine virus contributed most to the global eradication of smallpox, and why was this strategy deemed safe enough for widespread use?

<p>Its similarity to smallpox virus, providing cross-protection, combined with a reduced capacity to cause severe disease. (D)</p> Signup and view all the answers

For molluscum contagiosum, what is the most critical factor determining the persistence and severity of lesions in affected individuals?

<p>The individual's immune status, with lesions being more extensive and persistent in immunocompromised individuals. (C)</p> Signup and view all the answers

Why is the physical removal of molluscum contagiosum lesions, such as through curettage or liquid nitrogen, often recommended despite the self-limited nature of the infection in immunocompetent individuals?

<p>These methods prevent viral shedding, thus reducing/preventing the risk of disease transmission and autoinoculation. (D)</p> Signup and view all the answers

Flashcards

Variola Virus

The agent of smallpox, a disease eradicated globally due to a single, stable serotype.

Poxviruses

Brick-shaped viruses with linear, double-stranded DNA, replicating in the cytoplasm and containing a DNA-dependent RNA polymerase.

Poxvirus Transmission

Respiratory aerosols, direct contact with skin lesions, or fomites like bedding.

Smallpox Infection Path

Infects upper respiratory tract/lymph nodes, enters blood (viremia), infects organs, re-enters blood (secondary viremia), spreads to skin to replicate, leads to rash due to cytotoxic T cells.

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Smallpox Clinical Symptoms

Fever and malaise followed by a rash concentrated on the face and extremities, progressing through macules, papules, vesicles, pustules, and crusts.

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M-pox

Disease caused by the M-pox virus with symptoms similar to smallpox but milder; transmitted from African rodents/primates to people.

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Smallpox Prevention

Vaccine containing live attenuated vaccine virus to prevent smallpox. Routine vaccination was discontinued after eradication.

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Molluscum Contagiosum Virus

Poxvirus transmitted by close personal contact, causing small flesh-colored papules with a central umbilicated crater.

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Molluscum Contagiosum Lesions

Small, 2-5 mm flesh-colored papules with a cup-shaped crater, often found around the eye and trunk in children or the genital area in adults.

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Molluscum Risk Groups

Children, people with AIDS, and immunocompromised individuals. Self-limited in immunocompetent patients but may persist for months.

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Study Notes

  • Poxviridae includes smallpox (variola virus), M-pox, and molluscum contagiosum virus.

Variola Virus

  • Variola virus is the causative agent of smallpox, the only human disease eradicated worldwide.
  • Eradication was possible due to a single, stable serotype.
  • Poxviruses are brick-shaped, containing linear, double-stranded DNA and a lipoprotein envelope.
  • The virion has a disc-shaped core within a double membrane and contains DNA-dependent RNA polymerase.
  • Replication occurs in the cytoplasm, necessitating its own RNA polymerase due to inaccessibility of host cell RNA polymerase.
  • Transmission occurs through respiratory aerosols and direct contact with the virus from skin lesions or fomites.
  • The virus infects the upper respiratory tract and lymph nodes initially, leading to primary viremia, then internal organs

Smallpox development

  • Secondary viremia follows, spreading to the skin for replication.
  • The rash is a result of virus replication in the skin and cytotoxic T cells attacking infected cells.
  • Incubation period lasts 7–14 days, with no symptoms.
  • Initial symptoms include fever and malaise, followed by a rash more pronounced on the face and extremities (centrifugal distribution).
  • The rash progresses through stages: macules, papules, vesicles, pustules, and crusts over 2–3 weeks.
  • All stages of lesions do not appear simultaneously, unlike varicella infection.
  • Diagnosis involves virus culture in cells or chick embryos, or detection of viral antigens in vesicular fluid using immunofluorescence.
  • Prevention was achieved through global vaccination using a live attenuated vaccine virus.
  • Routine civilian vaccination has been discontinued.

M-pox

  • M-pox, formerly known as monkeypox virus, is a rare infection caused by the M-pox virus.
  • Symptoms resemble smallpox but are milder, and the disease is rarely fatal.
  • African rodents and non-human primates may serve as reservoirs for the virus.
  • The mortality rate is approximately 11%.
  • Severely immunocompromised individuals, children under one year, those with eczema history, and pregnant or breastfeeding individuals are at higher risk of severe illness or death.

Molluscum Contagiosum Virus

  • Molluscum contagiosum virus is a member of the poxvirus family, distinct from smallpox and vaccinia viruses.
  • Transmission occurs via close personal contact, including sexual contact.
  • Common in children, lesions often appear around the eye and on the trunk.
  • Lesions are small, 2-5 mm flesh-colored papules on the skin or mucous membrane, painless, non-itchy, and non-inflamed with a white core.
  • They feature a characteristic cup-shaped or umbilicated crater
  • Adults often present lesions in the genital area.
  • In immunocompetent patients, lesions are self-limited but can persist for months.
  • Risk groups include children, people with AIDS, and immunocompetent individuals.
  • Immunocompromised patients (e.g., AIDS patients) may develop large and numerous lesions.
  • Removal of lesions by curettage or liquid nitrogen is often effective.

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