Since the first epidemic modelling by D. Bernoulli for smallpox disease (criticized and improved by J. d'Alembert) some improvements have been done by R. Ross for malaria modelling, then by his coworker J. McKendrick, who combined BDP (Birth and Death process) and ODI (Ordinary Differential Equation) approaches. Present approaches use both continuous PDI (Partial Differential Equation) models and discrete tools on the frontiers between IBM (Individual Based Modelling), ARIMA (Autoregressive Integrated Moving Average) and BDP models. We give as application example some results concerning the present Covid-19 outbreak modelling.