25 - Infection and Immunity What does a pathogen have to...

Info iconThis preview shows pages 1–14. Sign up to view the full content.

View Full Document Right Arrow Icon
Infection and Immunity
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
What does a pathogen have to do? Infect (infest) a host Reproduce (replicate) itself Ensure that its progeny are transmitted to another host
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Mechanisms of Transmission Aerosols - inhalation of droplets, e.g. Rhinoviruses , the 'Common Cold Virus' or Adenoviruses . Faecal-Oral - e.g. Astroviruses , Caliciviruses ; these viruses cause acute gastroenteritis. Vector-borne - e.g. in Arthropods such as mosquitos, ticks, fleas: Arboviruses . Close personal contact - especially exchange of bodily fluids: Sex; Blood, e.g. Herpesviruses
Background image of page 4
Entry into the Host Skin - dead cells, therefore cannot support virus replication. Most viruses which infect via the skin require a breach in the physical integrity of this effective barrier, e.g. cuts or abrasions. Many viruses employ vectors, e.g. ticks, mosquitos or vampire bats to breach the barrier. Respiratory tract - In contrast to skin, the respiratory tract and all other mucosal surfaces possess sophisticated immune defence mechanisms, as well as non-specific inhibitory mechanisms (cilliated epithelium, mucus secretion, lower temperature) which viruses must overcome.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Entry into the Host Gastrointestinal tract - a hostile environment; gastric acid, bile salts, etc Genitourinary tract - relatively less hostile than the above, but less frequently exposed to extraneous viruses (?) Conjunctiva - an exposed site and relatively unprotected
Background image of page 6
Sites of virus entry
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Transmission patterns Horizontal Transmission: Direct person- to-person spread. Vertical Transmission : Relies on PERSISTENCE of the agent to transfer infection from parents to offspring. Several forms of vertical transmission can be distinguished: 1.Neonatal infection at birth, e.g. gonorrhorea, AIDS. 2.Infection in utero e.g. syphilis, CMV, Rubella (CRS), AIDS. 3. Germ line infection - via ovum or sperm.
Background image of page 8
Primary Replication Having gained entry to a potential host, the virus must initiate an infection by entering a susceptible cell. This frequently determines whether the infection will remain localized at the site of entry or spread to become a systemic infection
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Localized Infections Viruses Primary Replication Rhinoviruses U.R.T. Rotaviruses Intestinal epithelium Papillomaviruses Epidermis
Background image of page 10
Sys temic 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.
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
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
Background image of page 12
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
Background image of page 13

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 14
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 68

25 - Infection and Immunity What does a pathogen have to...

This preview shows document pages 1 - 14. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online