At the end of October, we attended Columbia University's annual Presidential Lecture. Rita R. Colwell gave a speech entitled “Climate, Oceans, Infectious Disease, and Human Health: The Saga of Cholera.” She began her hour-long integration of forces great and creatures small by quoting Gro Harlem Brundtland, former Prime Minister of Norway and former Director General of the World Health Organization: “A single microbial sea washes over all humankind.”

Dr. Colwell is chairman of Canon US Life Sciences, a Distinguished University Professor at both the University of Maryland and Johns Hopkins, former director of the National Science Foundation, former president of the American Association for the Advancement of Science, and the holder of altogether too many distinctions to list. She is also a longtime friend and a current BioTechniques Editorial Board member.

On the agenda was an exhilarating sweep of analysis from the molecular to the planetary. Her purpose was to shake us with an understanding of how changing climates may make life not just warmer, but qualitatively different, as perturbations resonate through every level of scale: from the gene, to the organ, to the organism, to the community, to the ecosystem, to the environment as a whole.

Hantavirus

Consider, for a moment, the case of Hantavirus, which seemed to appear out of nowhere in the US Southwest in the early 1990s, with a shocking 70% mortality rate. But it was far from a new disease; Hantavirus had long been endemic to the Four Corners region, particularly in the area of the Canyon del Muerto. Even the canyon's name, Colwell speculated, might reflect the prevalence of pathogen.

Interestingly, Hantavirus's stunning reemergence owed less to the pathogen itself than to South Pacific Ocean. An El Niño event in the preceding years increased rainfall in the usually desert area, causing populations of deer mice—a Hantavirus host—to skyrocket. The return of drought drove the mice out of their usual habitats and sent them foraging into human habitations and outbuildings. The mice voided virus in their urine, which dried and concentrated. Humans subsequently stirred up and inhaled virus-laden dust, fell ill, and died.

Cholera

Hantavirus, though, affects relatively small populations. Cholera has been so prevalent for so long that it may be among the small number of organisms that have actually influenced human evolution. Colwell discounted the time-honored belief that cholera originated in South Asia, corrected the idea that it is a freshwater disease, and exhaustively refuted the notion that human beings are the main reservoir of infection.

Vibrio cholerae is, in fact, a nearly ubiquitous sea-going organism that requires a saline environment. It is present in almost all warm near-shore waters, where it lives commensally with a number of small zooplankton, notably copepods. It subsists on the host organisms’ chitin (and, to some extent, nutrients leaking from their joints) and colonizes their guts. Moreover, Vibrio seems to have adapted to assist its hosts in some way, possibly by helping in egg release and hatching. It appears, Colwell noted, that the genes that have developed to benefit their hosts are also responsible for the organism's pathogenicity in humans.

Indeed, the life cycles of Vibrio and their crustacean hosts are so closely linked that computer models of zooplankton blooms (as a function of sea surface temperature) can accurately forecast the timing and intensity of cholera disease outbreaks. (When waters cool, copepods go dormant. This may explain, Colwell said, why the Gram-negative V. cholerae enters a once-controversial “viable but non-culturable” stage.)

A rising tide lifts all pathogens

And here is the connection between cholera and the environment: As the average sea surface temperatures increase, so will V. cholerae's range. Fluctuations in sea-surface height—from tides, warming-driven storm surges, or melting ice caps—will drive the near-shore zooplankton farther and farther up freshwater estuaries, contaminating more water sources and reaching new human populations.

And so, in a world where no point on the globe is more than a few hours away from any other, a barrel of oil burned in Detroit or Beijing or Essen could mean an additional case of cholera in Abidjan in Cote d'Ivoire or Dacca in Bangladesh or Punta Arenas in Chile. Meeting these potential threats requires a mastery of science on every scale, effort from every country, and contributions from every discipline.