Poxviruses. Virus Variolae

Question 1

Classification

Answer 1

Family: Poxviridae

Genus: Orthopoxvirus

Species: variola virus

(Small pox virus)

Question 2

Characteristics

Answer 2

• poxviruses&raquo_space;> largest known DNA virus
• enveloped virus —> self made (has all its own machinery)
• linear, dsDNA
• Dumbbell-shaped core
• completely replicates in the cytoplasm —> forms type B inclusion bodies = Guarnierni bodies
  »> DNA-dependent RNA polymerase in virion
• one serotype

Question 3

Transmission

Answer 3

• by respiratory droplets

- by direct contact with the virus from skin lesions

Question 4

Pathogenesis

Answer 4

• the virus infects the mucosal cells of the upper respiratory tract, then spreads to the local lymph nodes and by viremia to the liver and spleen and later the skin
• skin lesions progress in the following order: macule, papule, vesicle, pustule, crust

M P V P C

Question 5

Disease

Answer 5

Variola (smallpox)

(The lesions are all the same age compared with chickenpox — distinguishing fact)

It has been eradicated from the world by use of vaccine

The last known case was in 1977 in Somalia

Question 6

Microbiological diagnosis

Answer 6

• detection&raquo_space;» CPE in cell culture or “pocks” on chorioallantoic membrane

> > > cytoplasmic inclusions seen in light microscopy = Guarnierni bodies

• detection&raquo_space;> Viral antigens in the vesicle fluid In precipitin test
• diagnosis&raquo_space;> A four-fold or greater rise in antibody titer in the convalescent-phase serum

Question 7

Treatment and prevention

Answer 7

Treatment: none

Prevention:

• live attenuated cowpox virus vaccine
• vaccine is no longer used except by the military, because the disease has been eradicated