“…Consequently, the mathematical modeling of diseases with multiple pathogen strains, such as dengue fever, HIV/AIDS, influenza, malaria and West Nile virus, has received considerable attention (see, for instance, [1,2,12,15,19,27,29,23,26,34,39] and some of the references therein). These studies have, in general, focussed on the determination of threshold condition(s) for the co-existence of the strains, as well as the evaluation of the role of cross-immunity (defined as a scenario where infection with one strain confers partial or complete protection against infection with another strain) in the transmission dynamics of the disease strains.…”