Within a herd
PPRV spreads rapidly within a herd, causing heavy losses for farmers.
Animals which survive PPR are protected for life against a new infection.
There are no chronic carriers of the virus. Once they reach the end of the viral excretion period, they no longer constitute a danger for their fellows. The disease will only reappear in a herd when the virus can maintain itself there again; meaning once a population of susceptible animals has been reconstituted. As on average one third of herds are replaced each year, this corresponds to a 3-year interval.
The age of the animals in a herd affects the seroprevalence level and the epizootic risk. Small ruminants which have been kept in a herd for more than 3 years have a higher probability of having been contaminated and immunized than younger animals. This is particularly true for females, which show higher seroprevalence. Used for reproduction and to provide milk for home consumption, females are kept for longer periods than males. The latter often are sold by the age of two to cover the family's financial needs. However, at the individual level, no difference in susceptibility between males and females of the same age has been demonstrated.
Fundamental :
Serological surveys in herds render it possible to establish a map of the epidemiological situation of PPR at the regional and national level, determine areas at risk, and describe the factors favouring the spread of the disease. Such surveys are crucial for setting up PPR surveillance and control strategies based on vaccination.
