A model for the emergence of drug resistance in the presence of asymptomatic infections

An analysis of a mathematical model, which describes the dynamics of an aerially transmitted disease, and the effects of the emergence of drug resistance after the introduction of treatment as an intervention strategy is presented. Under explicit consideration of asymptomatic and symptomatic infective individuals for the basic model without intervention the analysis shows that the dynamics of the epidemic is determined by a basic reproduction number [Formula: see text]. A disease-free and an endemic equilibrium exist and are locally asymptotically stable when [Formula: see text] and [Formula: see text] respectively. When treatment is included the system has a basic reproduction number, which is the largest of the two reproduction numbers that characterise the drug-sensitive ([Formula: see text]) or resistant ([Formula: see text]) strains of the infectious agent. The system has a disease-free equilibrium, which is stable when both [Formula: see text] and [Formula: see text] are less than unity. Two endemic equilibria also exist and are associated with treatment and the development of drug resistance. An endemic equilibrium where only the drug-resistant strain persists exists and is stable when [Formula: see text] and [Formula: see text]. A second endemic equilibrium exists when [Formula: see text] and [Formula: see text] and both drug-sensitive and drug-resistant strains are present. The analysis of the system provides insights about the conditions under which the infection will persist and whether sensitive and resistant strains will coexist or not.