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Asymptomatic carriers have furthered the spread of many infectious diseases. A common principle in epidemiology, the 80–20 rule, speculates that 80% of the disease transmission is conducted by only 20% of people in a population. [15]
An infectious disease agent can be transmitted in two ways: as horizontal disease agent transmission from one individual to another in the same generation (peers in the same age group) [3] by either direct contact (licking, touching, biting), or indirect contact through air – cough or sneeze (vectors or fomites that allow the transmission of the agent causing the disease without physical ...
Under disease invasion, when a parasite invades a new host species, it may become pathogenic in the new host. [104] Several human activities have led to the emergence of zoonotic human pathogens, including viruses, bacteria, protozoa, and rickettsia, [105] and spread of vector-borne diseases, [104] see also globalization and disease and ...
Pathogenicity is the potential disease-causing capacity of pathogens, involving a combination of infectivity (pathogen's ability to infect hosts) and virulence (severity of host disease). Koch's postulates are used to establish causal relationships between microbial pathogens and diseases.
Relevant microbes may be viruses, bacteria, or fungi, and they may be spread through breathing, talking, coughing, sneezing, spraying of liquids, toilet flushing or any activities which generate aerosol particles or droplets or generate fomites, such as raising of dust. [13] [14]
Widespread non-communicable diseases such as cardiovascular disease and cancer are not included. An epidemic is the rapid spread of disease to a large number of people in a given population within a short period of time; in meningococcal infections , an attack rate in excess of 15 cases per 100,000 people for two consecutive weeks is considered ...
Bacteremia can travel through the blood stream to distant sites in the body and cause infection (hematogenous spread). Hematogenous spread of bacteria is part of the pathophysiology of certain infections of the heart ( endocarditis ), structures around the brain ( meningitis ), and tuberculosis of the spine ( Pott's disease ).
Lyme disease; Plague; West Nile virus; Many factors affect the incidence of vector-borne diseases. These factors include animals hosting the disease, vectors, and people. [21] Humans can also be vectors for some diseases, such as Tobacco mosaic virus, physically transmitting the virus with their hands from plant to plant. [citation needed]