Ch 12 Infectious disease

Disease described as infectious (communicable) if

caused by invasion by a pathogen and can be transmitted from one host to another

pathogen

infectious agent that cause disease

host

organism infected with a pathogen

signs and symptoms result from

damage to tissues and organs of the host

Most common pathogen groups

Viruses (influenza, Ross River virus disease)

bacteria (tuberculosis, tetanus)

fungi (chytridiomycosis)

protists (malaria, phytophthora dieback)

Transmission

passing of an infectious disease from an infected host to another individual

Contagious

easily transmitted by close contact with an infected organism or their secretions (body fluids)

Zoonotic diseases

infectious disease - transmitted from one vertebrate group to another

e.g. avian (bird) or swine (pig) influenza virus can infect humans via direct contact, close contact and indirect contact

Ways of transmission

Direct contact with infected host’s saliva, mucus, faeces, blood or urine when handling bird or scratched

Close contact - airborne and inhaled (bird shake feathers)

Indirect contact - susceptible host comes into contact with area - infected animals live or roam - surfaces or objects contaminated

virulence

severity of the disease it causes

\-help pathogen invade a host, cause disease + evade host defences

susceptibility

likelihood of developing a disease;

\-if high = ability to resist disease ↓

\-depend on age, state of health, immune system

symptoms

effects the pathogen has on the body of the host

incubation period

time between infection and onset of symptoms

\-occur due to:

* pathogen dividing many times to reach numbers sufficient to cause disease
* take time to reach target tissues susceptible to particular pathogen

Disease often contagious before onset of symptoms

\-pathogen can be passed on before the person even knows they have it

\-incubation period = adaptation of the pathogen, allow it to be transmitted before host incapacitated by symptoms

Virus

\-non-cellular pathogens = no metabolic processes

\-consists one or more strands of nucleic acid (RNA/DNA) inside protein coat (capsid)

\-microscopic = 30-300nm

\-neither prokaryotic or eukaryotic

\-obligate parasite = cannot function outside a host cell

\-limited to infecting a specific host cell or organism = virus recognise and bind to receptors on cells (adenovirus infects epithelial cell in upper respiratory tract - cold)

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Example of diseases caused by viruses

Ross River disease

COVID-19

influenza

Viral replication in eukaryotic host