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A Review on Theories and Models of Disease Causation for COVID-19

Epidemiology is a discipline that includes the study of all those conditions which influence the health of a community. It helps to describe the pattern of disease as a method of figuring out the potential preventive and controlling measures. The fundamental principal of epidemiology is that; a disease is sudden event. Every individual in a population has a specific set of characteristics and the exposure that determines his/her potentiality and susceptibility to a disease. It can be possible that firstly the non-pathogenic version of virus transmitted to an animal host such as pangolin and further directly to human or via any other intermediate like cat, Himalayan civets and dogs. After being transmitted to human, it could have evolved the pathogenic state. The aim of an epidemiological study is to analyses and avoid the potential outbreaks of any disease further. For occurrence of a disease, all three factors: agent-host-environment, play a crucial role. Previously, the SARS-CoV and MERS-CoV were also categorized under zoonotic disease. The novel coronavirus 2019-nCoV is from the same genera coronavirus. This virus is transmitted from human to human, affects the respiratory system. The newly emerged 2019-nCoV is fatal and life-threatening in comparison to SARS-CoV and MERS-CoV. The agent 2019-nCoV, host-human (susceptible human & infected human) and the favorable environmental condition allowed for occurrence of COVID-19. The viruses are transmitting between human through direct or indirect contact with infected patient.