What are the different levels of causes of diseases? Explain with an example.

Disease: Any discomfort, dysfunction, or disorder in the normal functioning of the body tissues, organs, or any parts that cause physical, mental, or social difficulty is termed a disease.

There are three levels of causes of disease. These are as follows:

1. The primary cause of the disease: This includes the direct or main cause of the disease, i.e. the causal agent or pathogen that gains entry into the body and infects it. Various pathogens like bacteria, viruses, fungi, protozoans, parasitic worms, and insects fall under this category.
2. The secondary cause of the disease: This includes the indirect cause that facilitates the entry of the pathogen into the body and allows infection. These include the various vectors of diseases.
3. The tertiary cause of the disease: This includes the environmental conditions or surrounding that allows the disease to occur in it. This includes poor sanitation and poverty-stricken conditions.

Thus, for example,

1. In the occurrence of Cholera, the primary cause is the bacteria, Vibrio cholerae which is the causal agent.
2. The secondary cause is contaminated food or water that enters the body through the fecal-oral route and provides an entrance route to the bacteria.
3. Unhygienic water and poor sanitation form the tertiary cause.