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Flashcards in Viral Pathogenesis Deck (16)

How do viruses make us sick

-how do viruses get into our bodies
-why are viral infections so miserable
-how exactly do viruses damage the host
-what do we know about how viruses cause disease


where do we encounter viruses

-food and water


mechanisms of viral transmission

-respiratory: aerosols
-fecal-oral: food, water, dirty hands
-contact- lesions, saliva, fomites
-zoonoses- animals, insects
-blood- direct contact, blood products, organ transplants
-sexual- mucous membranes, blood
-maternal-neonatal- birth, breastmilk
-genetic- prions, retroviruses


Susceptibility and severity of viral disease depend on

-the nature of exposure- route- aerosol vs scratch
-the viral dose- more virions increases risk of disease
-the status of person- age, general health, immune status
-the virus-host interactions- unique genetic features of each


Routes of entry, disemination and shedding in host example: smallpox

-acquired through respiratory tract, disseminates in blood and sheds from postules on the skin


Virus sites of enry

-in and out of conjunctiva
-in and out of respiratory tract
-in of alimentary tract
-in and out of urinogenital tract and anus
-scratch injury
-arthropod (bug)


Sites of virus entry in the respiratory host

-turbinate baffles
-tonsillar lymphoid tissues
-cervical lymph node
-bronchial lymph node


Virus entry into M cells in GI tract

-M cell sample the gut contents and present it to underlying immune cells
-viruses can infect M cells and easily reach the blood stream
-Reovirus attach to M cells


Virus Dissemination

-virus may spread from the surface of the body to lymph nodes and the blood stream
-primary viremia leads to
-replication in internal organs
-may occur without symptoms (incubation stage)
-secondary viremia disseminates the virus to organs where it is shed
-transmission may be by direct contact or through the environment (air, water, objects)
-exposure to infected blood is now a common route of transmission


Excretion of HIV-1

-HIV was measured by PCR
-most virus was in blood plasma and lymphocytes and in CSF
-sperm had less virus than semen
-in ear wax- weird


Virus Host interactions

-virus infection may be unnoticed, cause illness, induce autoimmunity, be persistent, or be lethal
-a successful virus will avoid destruction by the immune system and avoid destroying the host before replication is finished


General patterns of infection

-acute- common cold


Injury induced by viruses

-symptoms of viral disease (fever, tissue damage, rash, aches, pains, nausea) are mainly caused by the host response to infection
-virus replication -> cell injury <-host response
-cell injury is caused directly by viruses and indirectly by the host
-direct effects: cell lysis


Direct effect of virus: cell inactivation

-virus infection may halt essential cell functions
-infected cells are susceptible to apoptosis
-loss of cell functions can lead to organ damage or failure


Indirect effects of immunopathology

-the host immune response to a virus may be the sole cause of disease
-immune pathology usually caused by T cells and antibody complexes
-caution: vaccination can make some viral infections worse
-corneal scarring caused by immune response to chronic HSV reactivation


Factors that contribute to a viral infection

-Host: immune status, route of exposure, age, habits, barriers to dissemination, contagiousness
-Virus: antigenic diversity, infectious dose, cell killing or inactivation, pattern of infection, ability to diseeminate, shedding