From Wikipedia
A pathogen, (from Greek: πάθος pathos "suffering, passion", and γἰγνομαι (γεν-) gignomai (gen-) "I give birth to") an infectious agent, or more commonly germ, is a biological agent such as a virus, bacteria, prion, or fungus that causes disease to its host.[1][2] There are several substrates including pathways whereby pathogens can invade a host; the principal pathways have different episodic time frames, but soil contamination has the longest or most persistent potential for harboring a pathogen.
Potency
One hypothesis regarding pathogens states that the longer a pathogen can survive outside of the body, the more dangerous it can be to a potential host. In countries that have higher sanitation standards, pathogens cannot survive for as long outside of the human. This is seen as encouragement to mutations to the pathogen which would make it less deadly, as such mutations would allow the pathogen to survive in the host for longer periods of time
Transmission
One of the primary pathways by which food or water become contaminated is from the release of untreated sewage into a drinking water supply or onto cropland, with the result that people who eat or drink contaminated sources become infected. In developing countries most sewage is discharged into the environment or on cropland; even in developed countries there are periodic system failures resulting in a sanitary sewer overflow.
Pathogens can enter marine waters via untreated or partially treated human sewage. Humans may encounter pathogens through direct contact with contaminated water, ingestion of contaminated water, or consumption of raw or partially cooked shellfish harvested from contaminated waters. Pathogen inputs to the Klein River Estuary are a concern because of the potential human health risks and the economic losses associated with the possible closure of Abalone farming and beaches in Hermanus.
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