I would say that pathogenicity is the characteristic of a microorganism that
describes its capacity to harm a specific host under specific conditions.
Thus pathogenicity depends on 3 factors:
1. The microorganism's virulence (intrinsic characteristics -virulence
factors- which render it potentially pathogenic, depending on 2 and 3).
Virulence may be measured by the number of microorganisms needed to cause
the death of 50% of a given host (the Lethal Dose 50 or LD50). The higher
the LD50 the less virulent the microorganism. Statistical methods have
replaced nowadays the necessity to cause the death of laboratory animals to
calculate the LD50.
2. The host: given microorganism may cause harm to some hosts and not to
others (for example anthrax will be pathogenic for cattle but not to
3. Environmental conditions such as stress, antibacterial therapy or other
microorganisms: given microorganism may or may not cause harm to same host
under different conditions (for example Mannheimia haemolytica will be
pathogenic for cattle after transport, causing Shipping Fever, but not to
cattle under adequate management). These conditions are Risk Factors or
I hope this helps
"Joanne" <joann3remove at remove.tm.net,my> wrote in message
news:3e7ba214_1 at news.tm.net.my...
> hi. i'm taking basic microbiology this semester, and i'm wondering if any
> you can clear up something for me. what do you mean by pathogenicity of a
> virus? the dictionary states it as the ability of the virus to cause
> disease. but how do i describe it? for example, if i were asked to
> the pathogenicity of equine herpesvirus type 1, what am i supposed to say?
> i'm very confused. thanks