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In biology, a pathogen (Greek: πάθος, pathos "suffering", "passion" and -γενής, -genēs "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. [1] The term pathogen came into use in the 1880s.
A human pathogen is a pathogen (microbe or microorganism such as a virus, bacterium, prion, or fungus) that causes disease in humans. The human physiological defense against common pathogens (such as Pneumocystis ) is mainly the responsibility of the immune system with help by some of the body's normal microbiota .
For example, certain cancers arise from dysfunction of the immune system (skin tumors and lymphoma after a renal transplant, which requires immunosuppression), Streptococcus pneumoniae is spread through contact with respiratory secretions, such as saliva, mucus, or cough droplets from an infected person and colonizes the upper respiratory tract ...
A mixed infection is an infection that is caused by two or more pathogens. An example of this is appendicitis, which is caused by Bacteroides fragilis and Escherichia coli. The second is an iatrogenic infection. This type of infection is one that is transmitted from a health care worker to a patient.
Bacterial pathogens also require access to carbon and energy sources for growth. To avoid competition with host cells for glucose which is the main energy source used by human cells, many pathogens including the respiratory pathogen Haemophilus influenzae specialise in using other carbon sources such as lactate that are abundant in the human ...
In 2022 the World Health Organization (WHO) published a list of fungal pathogens which should be a priority for public health action. [4] Markedly more fungi are known to be pathogenic to plant life than those of the animal kingdom. [5] The study of fungi and other organisms pathogenic to plants is called plant pathology.
Research on pathogens is inherently risky: If handled incorrectly, pathogens can escape the lab, for example, or researchers may unintentionally make a pathogen more lethal by modifying it ...
No clear examples of archaean pathogens are known, [111] although a relationship has been proposed between the presence of some archaean methanogens and human periodontal disease. [112] Numerous microbial pathogens are capable of sexual processes that appear to facilitate their survival in their infected host.