Simmons, G. (1972). Differential equations with applications and historical notes. New York.
Cvjetanović, B., Grab, B., & Uemura, K. (2014). Epidemiological model of typhoid fever and its use in the planning and evaluation of antityphoid immunization and sanitation programmes. Bulletin of the World Health Organization, 45(1), 53.
Hyman, J. M. (2006). Differential susceptibility and infectivity epidemic models. Mathematical Biosciences and Engineering, 3, 88-100.
Gottlieb, D., & Orszag, S. A. (1977). Numerical analysis of spectral methods: theory and applications (Vol. 26). Siam.
Moatlhodl, K., & Gosaamang, K. R. (2017). Mathematical Analysis of Typhoid Infection with Treatment. Journal of Mathematical Sciences: Advances and Applications, 40, 75-91