author(s)
S Balakrishnan and V Bhanu Rekha

abstract
Immunity is the resistance shown by the animals or human beings against infectious pathogens such as virus, bacteria, parasites, rickettsia, protozoa, fungi, moulds, etc. whereas, ‘herd immunity’ means resistance shown by the proportionate amount of population, preferably 80% of the population. Herd immunity may be innate and acquired, and can be well achieved by mass vaccination. This may be affected by the frequent exposures to the infectious pathogens in the endemic environment, and clinically and subclinically infected population, contiguous and widespread movement nature of the population, irregular pattern of vaccination, basic reproduction number (R_o) of infectious pathogens, import of animals, etc. Hence, prevention and control of infectious diseases is paramount important for sustainable livestock production. Maintaining the herd immunity is the only way to keep disease prevalence at minimum level at which no epidemics, no spread of diseases and insignificant economic loss to the farming community being achieved. This paper reviewed some of the basic concepts on herd immunity and its understanding to implement in the field in the process of eradication of infectious diseases from livestock population.