The mode of transmission might be due to contact (physical contact, airborne inhalation) with an infected individual or secretion (sputum or other bodily fluids). Transmission can also occur by means of a vector (insects). Pneumonia, Tuberculosis, Diarrhoeal diseases, Malaria, Measles & more recently HIV/AIDS have been listed as mostly deadly infectious diseases. Although many epi-economic models have investigated the spread and transmission of infectious disease many aspects of it are still unclear.