Veterinary Epidemiology and Zoonosis

MORBIDITY RATE AND PREVALENCE

Morbidity rate (amount of infection)

• Number of animals affected by a disease in a population (it indicates the level of disease, dynamics of disease spread, effects of existing managemental practices and losses due to various conditions in a population).

Morbidity Rate	=	No. of animals affected ————————————————————————————————————— Total no. of susceptible population at risk	x	100
Proportional Morbidity Rate	=	No. of animals with a specified disease ————————————————————————————————————— Total no. of diseased animals	x	100

Prevalence

• Prevalence is the number of diseased animals in the susceptible population over a period of time (time is defined), without distinction between old and new cases.
• It may be point prevalence or instantaneous prevalence and period prevalence.

Prevalence (P)

=

No. of individuals having a disease at particular point in time ————————————————————————————————————— No. of individuals in the population at risk at that point of time

Point prevalence

• If the time is not specified, that is the amount of disease in a population at a particular point in time (also called instantaneous prevalence rate, IPR) .

Point Prevalence Rate

=

No. of cases of a disease existing in a population at specified point of time —————————————————————————————————————  No. of animals in that population at that same point of time

x

10a

• (Note: Rate can be expressed in 10^a, where ‘a’ may be 2 to 6 )  

Period Prevalence

• If the time is specified i.e., number of cases that occurred during a specified period of time. Example, a year (annual prevalence).

Period Prevalence Rate

=

No. of affected animals during a period —————————————————————————————————————  No. of animals exposed to risk during that period

x

100