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Pathogens from human feces are now being found alive and well in deep ocean water, where they survive for long periods of time at the low temperatures.
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One dinoflagellate, Pfiesteria piscicida (the “cell from hell”), has at least 24 life-forms and elaborates a neurotoxin that has caused neurocognitive deficits in fishermen and laboratory workers ( 3). Nutrient runoff into coastal waters is causing many more algal blooms (“red tides”) than ever before, some of which are frightening in their toxicity. Rivers and oceans play a prominent role in these new ecologies. New and unique ecologies are providing new opportunities for microbes. Air travel disseminates microbes and their vectors around the world overnight. Invasion of remote wilderness areas by large numbers of people provides exposure to pathogens previously confined to local habitats. Large distribution systems for water and food enable almost instantaneous spread of a pathogen to tens of thousands of people. Other contributing factors, discussed in an earlier review ( 2), include extreme crowding, widespread filth in developing countries, and worldwide mixing of people, microbes, vectors, and animal hosts on very short timescales. These children have no birth certificates and therefore no representation in world population estimates. This estimate is actually low, because-according to UNICEF data-about one third of all births (40 million children) go unregistered every year ( 1). One contributing factor is the human population explosion, now rocketing past the 6 billion mark, up from 2.5 billion in only half a century. Microbes are enjoying unprecedented opportunities for spread and passage across species barriers. The twin themes of genetic diversity and natural selection are explored in this review, with their relevance to viruses, the vertebrate immune system, virulence, and communicable disease epidemiology.
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Some are planktonic in the world's oceans, numbering 10 billion per liter of seawater some are planktonic in our blood some lie low inside cells some take over a cell's replication machinery and explode the cell with new copies of themselves and some splice their genes seamlessly into our chromosomes. They are mostly genes and have mastered the art of manipulating other genes. Viruses call for especially close watching. One of our most urgent challenges in public health is to understand the evolution and natural history of pathogens and parasites and how a sudden shift in virulence or in targeted host population may occur without warning. The threat of emerging infections grows with the swelling tide of the human population and the continued disregard for the health of the environment.