Epidemiology is the branch of medical science dealing with the transmission and control of disease. In other words, the study of spreading of disease with an effect to tracing down the cause. Epidemiology deals with only one population while infectious disease epidemiology refers to two or more populations which include human, infectious agents, vectors (mosquitoes are vectors of malaria), and animal population.

Infection is caused by an infectious agent it can be helminthes, bacteria, fungi, protozoa, viruses, prions. Infectivity in one person can be transmitted to others. A case can be an exposure (skin, sexual intercourse, water contact etc) and contact patterns. The cause is often known in infectious disease epidemiology. If an infectious agent is a necessary cause what is infectious epidemiology disease then used for?

• Identification of causes of new, emerging infections, e.g. HIV.
• Monitoring the behavior of persons that are infected.
• Identification of source of eruptions.
• Identification of routes of transmission.
• Study of natural history infections
• Identification of new innovations.

There are some terms that are used to classify infectious diseases.

Acute disease: a disease in which symptoms develop quickly.
Chronic disease: a disease with mild symptoms that develop slowly and last a long time.
Subacute disease: a disease with time line and symptoms between acute and chronic.
Communicable disease: disease transfer from one person to another.
Noncommunicable disease: disease originating from opportunistic pathogen.
Primary infection: initial infection within a given patient.
Secondary infection: infections that follow primary infection often by opportunistic pathogens.

We are incessantly being bare to infectious agents. Our immune system that protects our body against infections or foreign substances. The fortes for the safety from infectious disease are to cover up our coughs and sneezes while communicating with poeple which is the mainsail cause of cold, flu, tuberculosis. As routes of transmission are direct or indirect. A direct contact of skin to skin causes herpes type I, an indirect contact of food-borne cause food poisoning. Other factors also influence transmission of disease age, sex, genotype, behavior, nutritional status, health status, air quality, weather, food etc. We should conceal ourselves from these ambush snipes so that one may live healthy live.

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