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Terms & Synonyms

Official WHO Definition

The dominant member of a symbiotic relationship; a man or animal in which a parasite lives and from which it obtains food (WHO 1992).

Other Definitions


Interpretations and Explanations

Viruses and protozoan parasites are obligate parasites and they need a human or animal host to multiply. The probability of infection, the ability of the pathogen to establish and multiply within the host, depends on the level of exposure to the organisms in food, water or other environmental factors. The infective dose for human hosts is likely to be reached only if large accumulations occur within system deposits.In order for a pathogen to persist, it must reproduce in sufficient numbers within a given host in order to allow for the infection of another host. After leaving the body of their host, most pathogens gradually lose viability and the ability to infect.The specific journey a pathogen takes from host to host defines the transmission pathway and this may include non-human hosts. Diseases that are maintained within an animal population and sporadically introduced to human hosts are referred to as enzootic (c.f. endemic – upon people). For environmentally mediated pathogens, these pathways are often characterised by a significant time period outside the host. The transmission pathways increase in complexity when there are animal hosts that a pathogen can infect (WHO 1992).


Franceys R (1992)  A guide to the development of on-site sanitation

WHO Lexicon page (translations and examples)

See also

External Resources


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