Possibilities and limits of serological diagnosis in pig stocks in the case of Mycoplasma hyopneumoniae infection
Nathues, H.; Strutzberg Minder, K.; Kreienbrock, L.; Beilage, E.G.
Deutsche Tierärztliche Wochenschrift 113(12): 448-452
2006
ISSN/ISBN: 0341-6593 PMID: 17233280 Document Number: 600772
When conducting their investigations to diagnose infectious diseases in pigs, practitioners are often forced to use smaller number of animals in order to minimize costs for the farmers. A cross-sectional study was conducted approximating such field conditions to show the limits of interpretation with reduced sample sizes in case of enzootic pneumonia. When compared with other respiratory pathogens, Mycoplasma hyopneumoniae, the aetiologic agent of enzootic pneumonia, spreads very slowly mainly when animals are in direct contact with each other. Furthermore, the interpretation of serological results is difficult because serological reactions occurred in several weeks time. Serological testing is normally used to confirm a clinical diagnosis by detecting an increase in antibodies against the aetiologic agent. Samples are collected at the beginning of the disease and then at four to six weeks later. An increasing number of serologically positive animals in a herd is usually interpreted as spread of infection. The true prevalence we observed in our investigation was used to make a statistical analysis describing the probability of detecting an increasing prevalence from 0.07 to 0.33 with a reduced sample size. We showed that the probability of detecting an increase in two seropositive animals was 44% when five samples per group were analysed. When only three samples were analysed per group, this probability decreased to 21%. A compromise must be found between epidemiological necessity and financial acceptability sample size and this could be a minimum of 10 samples/age group.