On the dynamics of HIV-AIDS and cryptosporidiosis K. O. Okosun, M. A. Khan, E. Bonyah and S. T. Ogunlade Eur. Phys. J. Plus, 132 8 (2017) 363 Published online: 25 August 2017 DOI: 10.1140/epjp/i2017-11625-3