This paper examines the mechanisms by which infectious diseases spread from person to person, organized around a three-link chain of transmission. Beginning with the history of devastating epidemics, the paper outlines how direct and indirect contact, germ incubation within the body, and the immune system's response together form a cycle of infection. Drawing on Mayo Clinic and United Nations sources, the paper also identifies practical prevention measures — including handwashing, vaccination, and voluntary isolation — that correspond to each link in the transmission chain, arguing that understanding how diseases spread is essential to stopping them.
From the European plague to the smallpox that contributed to the destruction of thousands of Native Americans, infectious diseases have been among the deadliest forces in human history. Since science has learned to understand how infectious diseases are spread, however, people have been able to take steps to prevent disease from wreaking havoc on themselves and their communities. A personal knowledge of how infectious diseases spread — and how they can be prevented — is essential to ensuring that you and your family remain protected.
According to the Mayo Clinic, infectious diseases can spread from person to person through either direct or indirect contact ("Infectious Diseases" 2007). This means that while a person must come into contact with the germ responsible for spreading the disease in order to get sick, that person may or may not come into direct contact with someone who is already ill. Contact can be considered the first link in the chain of spreading infectious diseases.
The most common type of contact is person-to-person contact, in which one person coughs on, kisses, or exchanges bodily fluid with a sick person. In addition to person-to-person contact, several other transmission routes exist. Animal-to-person contact — in which a sick animal or animal waste passes a bacterium or virus to a human — and mother-to-unborn-child contact are two other methods of direct transmission. Infectious diseases can also be passed through indirect contact; touching the same pencil that a person with the flu has handled is one such example.
Two additional routes of transmission are airborne spread and contact through vehicles such as insect bites and stings ("Infectious Diseases" 2007). The United Nations has suggested that environmental changes may be releasing long-buried infectious diseases into the air ("Environmental Changes" 2005). Regardless of the specific route, the easiest way to prevent infectious diseases is to limit the person-to-person contact that most commonly spreads them.
Once a person has come into contact with an infectious disease, the second link in the transmission chain is the germ's incubation inside the body. Germs include bacteria, viruses, fungi, protozoa, and helminths — parasites most commonly associated with conditions such as ringworm. While most germs do not harm the body, some are dangerous. These harmful germs "are constantly mutating to breach your immune system's defenses" ("Germs" 2007). Once they breach the immune system, they begin to multiply, completing the second link in the chain. As germs multiply and overwhelm the immune system's initial defenses, a person becomes sick.
"Immune response and visible disease symptoms"
"Handwashing, vaccination, and self-isolation as defenses"
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