viruses as cause of disease Flashcards
what is a virus
an infectious, obligate intraceullar parasite
describe the genetic material or viruses
comprises genetic material (DNA or RNA) surrounded by a protein coat and/or a membrane
what organelles do viruses have
none
no cell wall either
are viruses dependent on the host cell
yes
whereas bacteria are not
viruses do not carry out metabolic reactions on their own – require the organelles and enzymes of a host to carry out such reactions
are viruses alive
no
whereas bacteria are
different shapes of viruses
helical
icosahedral
complex
different structures of viruses
non enveloped
enveloped
what is the only way viruses can replicate
Viruses can only replicate by exploiting the energy and reproductive machinery of cells of higher organisms.
describe process of viral replication
- Attachment: viral and cell receptors e.g. HIV
- Cell entry: only central viral core carrying the nucleic acid and some associated proteins enter host cell
- Interaction with host cells: use cell materials (enzymes, amino acids, nucleotides) for their replication
- Replication: may localize in nucleus, cytoplasm or both
- Assembly: occurs in nucleus, in cytoplasm or at cell membrane
- Release: bursting open of cell, or by leaking from the cell over a period of time
how do viruses cause disease
Damage by direct destruction of host cells e.g. HIV
Damage by modification of host cell structure or function e.g. rotaviruses
Damage involving over-reactivity of the host as a response to infection e.g. hepatitis B
Damage through cell proliferation and cell immortalization e.g. HPVs
Evasion of both extracellular and intracellular host defences
what does the immune response vary for
Viruses
Bacteria
Protozoa
Helminths
what are pathogens
micro-organisms capable of causing disease
key attributes of pathogens
infectivity
virulence
invasiveness
what is infectivity
the ability to become established in host, can involve adherence and immune escape
what is virulence
the ability to cause disease once established
