Modelling the time-dependent transmission rate for porcine circovirus type 2(PCV2)in pigs using data from serial transmission experiments

摘要

Six successive transmission trials were carried out from 4 to 39 days post inoculation(DPI)to determine the features of the infectious period for PCV2-infected pigs.The infectiousness of inoculated pigs,assessed from the frequency of occurrence of infected pigs in susceptible groups in each contact trial,increased from 4 to 18 DPI(0,7 and 8 infected pigs at 4,11 and 18 DPI,respectively)and then decreased slowly until 39 days post infection(4,2 and 1 pigs infected at 25,32 and 39 DPI,respectively).The estimated time-dependent infectiousness was fitted to three unimodal function shapes(gamma,Weibull and lognormal)for comparison.The absence of infected pigs at 4 DPI revealed a latency period between 4 and 10 DPI.A sensitivity analysis was performed to test whether the parametric shape of the transmission function influenced the estimations.The estimated time-dependent transmission rate was implemented in a deterministic SEIR model and validated by comparing the model prediction with external data.The lognormal-like function shape evidenced the best quality of fit,leading to a latency period of 8 days,an estimated basic reproduction ratio of 5.9[1.8,10.1]and a mean disease generation time of 18.4 days[18.2,18.5].