Pathogens are transported into the ocean through variety of ways. The three main ways pathogens spread through the ocean are: untreated municipal sewage, sewage from ships, and livestock and animal waste. Human sewage is the most common source of pathogen pollution, particularly in South America, Asia, and Africa. Countries that are “poverty-stricken, war-torn, or politically unstable are generally more susceptible to pathogenic diseases because of poor infrastructure, lower standards of sanitation or hygiene, and inadequate maintenance of water supplies.” Waste from recreational and commercial vessels, particularly cruise ships, also introduce pathogens to ocean waters. Lastly, discharge of waste from farm, domestic, or wild animals can introduce bacteria, viruses, and parasites into local water systems and coastal waters.
In the ocean, different species of marine life are susceptible to varying types of diseases and pathogens. Different pathogens and diseases may either affect a wide variety of species or specialize on a few.
Marine mammals are known to be susceptible to nearly the entire range of marine pathogens. Pneumonia and botulism have both been reported in wild and captive species of marine mammals. Brucellosis, which can trigger abortions, has been noted with potential zoonotic capabilities. Erysipelas, also known as Diamond Skin Disease, is a disease affecting terrestrial mammals as well as fish. Lesions tend to form on marine mammals affected by Diamond Skin Disease. A much larger portion of marine pathogens and bacteria exist to affect the marine mammal population, with massive fatal outbreaks having occurred in the past.
Just as many, if not more, pathogens and diseases affect the planet's fish populations. The most commonly noted infections include "pop eye" and "fin rot" (both caused by gram-negative bacteria). Fish tuberculosis is a common condition as well that carries safety implications; fish tuberculosis is known to be zoonotic.