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
what is invasiveness
the capacity to penetrate mucosal surfaces to reach normally sterile sites
what are virulence factord
microbial factors that cause disease
do viral infections need fast or slwo cell entry
fast
components of humoral resonse
Antibody (IgA) – blocks binding
Opsonisation
Complement
components of cell mediated response
Antiviral action
Kill infected cells
Macrophages
d
descrive viral evasion
Interfere with specific or non-specific defence
Influenza changes coat antigen
what is Antigenic drift
spontaneous mutations, occur gradually giving minor changes in haemaglutinin and neuraminidase. Epidemics
what is antigenic shift
sudden emergence of new subtype different to that of preceding virus. Pandemics
how can bacteria enter host
Respiratory tract
Gastrointestinal tract
Genitourinary tract
Skin break
what does Low number or virulence indicate
phagocytes active
what does high number of virulence indicate
immune response
how do mycobacterium evade
escape from phagolysosome, live in cytoplasm
how does m.avium evade
block phagosome
what dows immune response for protozoa depend on
location of parasite in host
Blood stage – humoral immunity
Tissue stage – cell mediated immunity
Plasmodium fulciparium (malaria) – anopheles mosquito bite
describe protozoan evasion
Surface antigen variation
Intracellular phase
Outer coat sloughing
describe worm infection
Do not multiply in humans
Not intracellular
Few parasites carried
Poor immune response
Immune response not sufficient to kill
describe worm evasion
Decreased antigen expression by adult
Glycolipid/ glycoprotein coat (host derived)
what is passive immunity
preformed antibody transferred
3 types of passive immunity
Transplacental transfer
Colostrum
Inject preformed antibody
2 types of active immunity
Elicitis – protective immunity – immunological memory
Achieved by natural infection – vaccine administration
4 types of vaccines
Inactivated (killed)
Attenuated (avirulent)
Bacteria or viruses
Toxoid vaccines (inactivated toxins)
