Systemic Infections Virus Primary replication Secondary replication Enteroviruses Intestinal epithelium Lymphoid tissues cns Herpesviruses Oropharynx or lymphoid cells, GU tract CN.S
Systemic Infections Virus Primary Replication Secondary Replication Enteroviruses Intestinal epithelium Lymphoid tissues, C.N.S. Herpesviruses Oropharynx or Lymphoid cells, G.U.tract C.N.S
Spread Throughout the host Apart from direct cell-cell contact, there are 2 main mechanisms for spread throughout the host via the bloodstream via the nervous system
Spread Throughout the Host • Apart from direct cell-cell contact, there are 2 main mechanisms for spread throughout the host: • via the bloodstream • via the nervous system
via the bloodstream Virus may get into the bloodstream by direct inoculation-e.g Arthropod vectors, blood transfusion or LV. drug abuse. The virus may travel free in the plasma(Togaviruses, Enteroviruses),or in association with red cells (orbiviruses), platelets (HSV, lymphocytes(EBV, CMv or monocytes LEntiviruses). Primary viraemia usually proceeds and is necessary for spread to the blood stream, followed by more generalized, higher titre secondary viraemia as the virus reaches other target tissues or replicates directly in blood cells
via the bloodstream • Virus may get into the bloodstream by direct inoculation - e.g. Arthropod vectors, blood transfusion or I.V. drug abuse. The virus may travel free in the plasma (Togaviruses, Enteroviruses), or in association with red cells (Orbiviruses), platelets (HSV), lymphocytes (EBV, CMV) or monocytes (Lentiviruses). Primary viraemia usually proceeds and is necessary for spread to the blood stream, followed by more generalized, higher titre secondary viraemia as the virus reaches other target tissues or replicates directly in blood cells
via the nervous system spread to nervous system is preceded by primary viraemia. In some cases, spread occurs directly by contact with neurons at the primary site of infection, in other cases via the bloodstream. Once in peripheral nerves, the virus can spread to the CNs by axonal trans port along neurons [classic -HSW) Viruses can cross synaptic junctions since these frequently contain virus receptors allowing the virus to jump from one cell to another
via the nervous system • spread to nervous system is preceded by primary viraemia. In some cases, spread occurs directly by contact with neurons at the primary site of infection, in other cases via the bloodstream. Once in peripheral nerves, the virus can spread to the CNS by axonal transport along neurons (classic - HSV). Viruses can cross synaptic junctions since these frequently contain virus receptors, allowing the virus to jump from one cell to another
Cell/Tissue Tropism Tropism-the ability of a virus to replicate in particular cells or tissues -is controlled party by the route of infection but largely by the interaction of a virus attachment protein wAp]with a specific receptor molecule on the surface of a cell andhas considerable eifect on pathogenesis. Many VAP'sand virus receptors are now known
Cell/Tissue Tropism • Tropism - the ability of a virus to replicate in particular cells or tissues - is controlled partly by the route of infection but largely by the interaction of a virus attachment protein (V.A.P.) with a specific receptor molecule on the surface of a cell, and has considerable effect on pathogenesis. Many V.A.P.'s and virus receptors are now known