viral infections

viral infections 

A virus (from the Latin virus meaning toxin or poison) is a sub-microscopic infectious agent that is unable to grow or reproduce outside a host cell.”
Acute virus infection:
Following host entry the virus multiplies and spreads rapidily. and contact with the virus activates host immune responses. Hosts immune mechanisms overcome and eliminate virus. The hosts retains immunological virus and virus survival dependent on rapid dissemination and susceptible hosts aviabliliy.

Characteristics of actute virus disease:
-normally rapid onset.
-symptoms often corresponds with peak viral multiplication.
-often fever and mygalia (from activation of immune response)
-vary in servity from one individual to another.
-Resolve rapidly once the innate immune response develops.

Acute viral infections are serve public health problems.
-usually associated with epidemics
-short incubation period
-delay in indentifibile symptoms until the virus has already spread.
-Acute infections occur in crowded places e.g schools, militariy, nursing homes.

EXAMPLE OF ACUTE VIRAL INFECTION:
RHINOVIRUSES (INFLUENZA)
-common cold often caused by rhinoviruses more than 110 serological types. killed by gastric acid and replicated at 33'C.
-Bind to ICAM-1 on epithelial cell surface and are not easily removed by muco-ciliary secretions.
-enter host cells by translocation
-Lyse host cells after replication and spread to neighbouring cells leading to progressive and extensive damage.
Pathogenesis of the common cold:
-debris from lysed cells provokes a strong inflammatory response
-increased secretion of fluids from lamina propria leads to runny nose and sneezing.
-Phagocytes migrate to to site of infection.
-Release of inflammatory mediators leads to blocked nose and mild fever
-Symptoms are restricted to the upper part of the respiratory tract as these viruses multiply optimal at 33'C and less at 37'C.

Immunity to rhinoviruses
-Rhinoviruses recognises by immune system specific mucosal response -IgA ect rather than humoral response
-immune response quickly clears the infection leading to rapid recovery. (couple of days)
-Immune memory of the infection is retained but is not long lasting as for systematic virus infection.
-frequent reoccurrence of the common cold is due to the larger number >100 of serological distinct strains of rhinoviruses.
EXAMPLE OF ACUTE VIRAL INFECTION: ENTEROVIRUSES.  (MEASLES)

**REMEMBER TO STAY POSITIVE LIKE A PROTON!!**