According to the basic host–pathogen model, if the combined death and recovery rate from a disease doubles, and the effectiveness of the disease to spread from infected to uninfected individuals remains the same, the threshold density should

A. decrease by half.
B. stay the same.
C. double.
D. decrease by a factor of four.

A. decrease by half.

B. stay the same.

C. double.

Explanation:

Host-pathogen models resembels the host-parasite models and predator-prey which is used to evaluate the evolutionary strategies of pathogens.

The host-vector-pathogen system can be demonstarted as a change in the number of 4 types of people: healthy hosts, uninfected vectors, infected hosts, and infected vectors.

The threshold density should decrease by half, stay the same, or double, according to the standard host-pathogen model, if the combined death and recovery rate from a disease doubles, and the ability of the disease to spread from infected to uninfected persons.

Hence, the correct options are A. decrease by half, B. stay the same, and C. double.

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