New findings on the dynamics of HIV and TB coinfection models

•HIV and TB coinfection model. Fractional and integer order model.•Treatment for both diseases and vertical transmission for HIV.•Fast transients in the fractional model.•The order of the fractional derivative behaves as a bifurcation parameter of the model.

In this paper we study a model for HIV and TB coinfection. We consider the integer order and the fractional order versions of the model. Let α∈[0.78,1.0]α∈[0.78,1.0] be the order of the fractional derivative, then the integer order model is obtained for α=1.0α=1.0. The model includes vertical transmission for HIV and treatment for both diseases. We compute the reproduction number of the integer order model and HIV and TB submodels, and the stability of the disease free equilibrium. We sketch the bifurcation diagrams of the integer order model, for variation of the average number of sexual partners per person and per unit time, and the tuberculosis transmission rate. We analyze numerical results of the fractional order model for different values of αα, including α=1α=1. The results show distinct types of transients, for variation of αα. Moreover, we speculate, from observation of the numerical results, that the order of the fractional derivative may behave as a bifurcation parameter for the model. We conclude that the dynamics of the integer and the fractional order versions of the model are very rich and that together these versions may provide a better understanding of the dynamics of HIV and TB coinfection.