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# Lethal & Infectious Dose 50

By Levi Clancy for Student Reader on
updated

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Virulence can be measured via LD50 (Lethal Dose 50) and ID50 (Infectious Dose 50), which is the dose required to kill or infect 50% of the test population, respectively.

`	|100%   -|				 __		 __	|				|  |		|  |	|				|  |		|  |	|				|  |		|  |	|				|  |		|  |	|				|  |		|  |50%    -|		 __		|  |		|  |	|		|  |		|  |		|  |	|		|  |		|  |		|  |	|		|  |		|  |		|  |	|   __		|  |		|  |		|  |	|__|__|_________|__|____________|__|____________|__|____________	    10		 50		0150		0200			    # bacteriay-axis: % mice killedx-axis: # bacteria`

Two bacterial pathogens were used to infect mice separately at the indicated dosages and the resulting morbidity and mortality was scored (see tables below, with pathogen, outcome, and CFU of the dose). What are the approximate ID50 and LD50 values for both pathogens?

PathogenOutcome101102103104105

Pathogen A

Morbidity

10%

100%

100%

100%

100%

Pathogen A

Mortality

0%

0%

10%

40%

100%

Pathogen B

Morbidity

0%

1%

15%

60%

100%

Pathogen B

Mortality

0%

0%

10%

40%

100%

Pathogen A: 10 < ID50 105

Pathogen B: 103 < ID50 < 104 and 104 < LD50 < 105

Provide a hypothesis explaining why the patterns of morbidity and mortality differ between these two pathogens.

A is highly infectious and readily causes disease, but does not efficiently kill the host. B is not as infectious but readily causes death if and when infection is established.