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In other cases, a virus could protect you from a different pathogen.

Other research is underway examining other types of air pollution from the Tijuana River, including bacteria and other pathogens from sewage.

High concentrations of these bacteria indicate the presence of pathogens that could be harmful to beachgoers.

Even before the fire, few septic tanks and leach fields probably met current standards, which require substantially enhanced removal of pathogens.

Each human and mammalian infection gives the virus an opportunity to mutate and evolve better ways of transmitting from person to person — a key benchmark for what makes a pathogen a pandemic-level threat.