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Malaria. Dengue fever. West Nilevirus. Lyme disease. These and

other infectious diseases are on the rise inhumans. Is our interaction with Earth’senvironment somehow responsible?What factors are involved in the emer-gence and transmission of infectious dis-eases? How are climate change and otherenvironmental parameters involved?These complexities have created a tangledweb that scientists must soon unravel.

If biologists, climatologists, physicians,and other researchers work closely to-gether, said Richard O’Grady, executivedirector of the American Institute of Bi-o logical Sciences (AIBS), “we have the potential to predict disease outbreaksand to mitigate their effects. Acceleratingclimate change and threats to health arenow two [sides] of the same coin.”

Links among the environment and infectious diseases were demonstratedin many ways and for many locations by

AIBS conference speakers; they madeconnections between microbes, envi-ronmental events such as El Niño, anddisease incidence in people. Large-scaleenvironmental events—global climatechange, land-use change and habitat

destruction, and human populationgrowth and urbanization—alter the risksof viral, parasitic, and bacterial diseases.Agricultural intensification, deforesta-tion and reforestation, increased precip-itation, and ocean warming all play arole.

For example, in a case that might becalled “CSI: Infectious Diseases and Cli-mate Change,” otherwise healthy peoplebegan dying of a mysterious respiratorydisease in 1993 in the US Southwest. Testsyielded surprising results: The victimshad hantavirus pulmonary syndrome, aresult of a previously undetected type ofhantavirus.

Research by biologist Terry Yates ofthe University of New Mexico, honoredposthumously at this year’s meeting withthe AIBS Distinguished Scientist Award,showed that the outbreak was connectedto the El Niño climate phenomenon, apattern of changes in ocean circulation

Climate, Environment, and Infectious Diseases: A Report from the AIBS 2008 Annual Meeting

The American Institute of Biological Sciences dedicated this year’s annual

meeting to the challenge of Earth’s changing climate and its effects on the

environment, and the spread of infectious diseases. The conference, held in May

in Arlington, Virginia, attracted more than 250 biologists, climatologists, and

other scientists, as well as physicians and public health officials.

C H E RY L LY N D Y B A S

Urbanization, along with moderntransportation patterns, is behind the

global reemergence of denguehemorrhagic fever. Dengue viruses andtheir mosquito vector (Aedes aegypti)

have completely adapted to anurbanized lifestyle, needing only

humans to complete their life cycles.Photograph: US Department of

Agriculture.

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and atmospheric weather. Increased rain-fall led to more plants, more mice, andmore opportunities for people to comeinto contact with the rodents’ droppingsand urine, which contain the virus.Named for the Hantaan River in Korea,hantaviruses were known to spread frommice to humans in Asia and Europe, butuntil the 1993 outbreak, hantaviruseshad been seen only outside America.

“We can no longer discuss infectiousdiseases simply as those that affect the US,or that affect New York City, or Wash-ington, DC,” said scientist and choleraexpert Rita Colwell, of the University ofMaryland and Johns Hopkins Univer-sity Bloomberg School of Public Health.“Infectious diseases that arise in Africa orin Asia reach the United States, as evi-denced by the SARS [severe acute respi-ratory syndrome] episodes,” she said.“The connections to the environmentare very dramatic. For example, the ori-gin of SARS was tracked to bats in cavesin Asia.”

Colwell, who is also the president ofAIBS, spoke of cholera as a disease not just restricted to Bangladesh or Indiabut prevalent also in Latin America andAfrica. The environmental burden of dis-ease falls on those least prepared to deal

with it, she said. Countries in Africa andin Asia, where populations are large andpoverty is high, are particularly affected,as shown in studies by the Centers forDisease Control and Prevention (CDC)in Atlanta, Georgia. Dealing with the effects of climate change on infectiousdisease falls—so far—mostly on thesepopulations.

How long will it be before the rest ofthe world follows suit? That depends,Colwell believes, on decisions we makenow about our environmental future.Climate change poses risks to ecosystemsand the life support they provide to peo-ple, and to all animals and plants onEarth. The bottom line, AIBS meetingparticipants agreed, is that to safeguard

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Bluetongue disease in sheep is an example of the impact of climate change on thespread of a disease. Warmer temperatures allowed the midge that is the African

vector (Culicoides imicola) to persist in southern Europe; the pathogen then shiftedto new, palearctic vectors (Culicoides obsoletus and Culicoides pulicaris) and

spread through Europe. Graphic: European Commission.

Terry Maple (left) is president of the Palm Beach Zoo and coauthor of A Contractwith the Earth. James Hansen (right) is director of the NASA Goddard Institute for

Space Studies. Photographs: Carroll Photography.

Rita Colwell is AIBS President and a professor at the University of

Maryland–College Park and at Johns Hopkins University BloombergSchool of Public Health. Photograph:

Carroll Photography.

794 BioScience • October 2008 / Vol. 58 No. 9 www.biosciencemag.org

human health, we must live within ourplanet’s environmental limits.

The environmental century: A world beyond fossil fuels?Terry Maple, president of the Palm BeachZoo in Florida, spoke of the premise ofthe book A Contract with the Earth, whichhe wrote with Newt Gingrich. Maplecalled ours “the environmental century.”Green investments are growing, he said,and we need to address what he called theoverwhelming issues facing life on Earthin the near future. Through their book,Maple and Gingrich hope to appeal to thepublic to open up dialogues and debateissues.

Looking at innovation as a solutionto climate change is a promising path,Maple said. “If we get serious about in-novation, we’re going down the roadAmerica is good at. We’ll be selling thistechnology to the people we’re now buy-ing oil from.” For example, he discov-ered that almost no solar power projectsexist in the state of Florida. Through hisefforts, the Palm Beach Zoo is joiningwith Florida Power and Light to build afacility that’s nearly half solar powered.

An engaged and informed populaceand finding new energy sources are theonly answers to the challenges we face,Maple and Gingrich believe. Answers willcome not a moment too soon, many atthe meeting said. Global warming, sayclimate and health scientists, is begin-

ning to set off a worldwide “domino effect.”

“In the story of Earth’s recent climate,we have all the characteristics of ‘the perfect storm,’” said climatologist JamesHansen, director of the NASA GoddardInstitute for Space Studies. “Among themis that the primary greenhouse gas we’reputting into the atmosphere by burningfossil fuels, carbon dioxide, lasts a verylong time. A large fraction will stay inthe air for several centuries.”

What level of carbon dioxide is an im-minent threat to life on Earth? “The dan-gerous amount of carbon dioxide is lessthan what’s there now,” Hansen said.“We’ve increased carbon dioxide to 385parts per million. We’re going to have toreduce it to at least 350 parts per million.”

A third of the warming in the last cen-tury has occurred over the past 30 years.Isotherms are moving forward at a rate ofsome 60 kilometers with each passingdecade. If we continue business as usual,Hansen believes, that rate will double inthe next century. “The most importantthing in the short term,” Hansen said, “isto deal with coal, the biggest source of car-bon dioxide. I think if we addressed this,and got the process going in the rightdirection, there would be positive feed-backs in the social system that could, in fact, take us to a world beyond fossil fuels.” We can’t double or triple theamount of carbon dioxide in the atmo -

sphere, he said, “or we’re going to producea completely different planet.”

Infectious disease risks and publichealth: The climate factor“Unlike directly transmissible disease be-tween humans, zoonotic and vectorbornediseases are very much dependent on theenvironment, especially climate,” said bi-ologist Durland Fish, director of the YaleUniversity Center for EcoEpidemiology.Fish focused on Lyme disease as an ex-ample.

Lyme disease was discovered in theearly 1970s in Lyme, Connecticut, but itoccurs throughout much of the UnitedStates and in Europe and Asia. Lyme dis-ease risk remains highest in northeasternUS states like Connecticut and RhodeIsland. “There‘s been a lot of speculationabout what’s going to happen with Lymedisease and climate change,” Fish said.“We could have more severe disease atmore northerly latitudes.”

Environmental change and reforesta-tion have resulted in the epidemic ofLyme disease, scientists believe. A centuryago, there were no deer—nor was thereLyme disease—in southern New Eng-land. In the absence of deer, deer tickscan’t survive. It’s only since reforestationand the subsequent proliferation of deer,Fish said, “that Lyme disease has beenable to expand its range.” The changingenvironment, he said, has everything todo with changing human disease risk.

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Durland Fish (left) is an epidemiologist at Yale University. Howard Frumkin (center) is an internistand environmental and occupational health specialist at the Centers for Disease Control

and Prevention. David Rogers (right) is an ecologist at the University of Oxford. Photographs: Carroll Photography.

“We’re witnessing the emergence of adifferent world than the one in whichour grandparents grew up,”saidHowardFrumkin, a physician and director of theNational Center for EnvironmentalHealth at the CDC.“Theworld is chang-ing almost before our eyes, including thehealth burden of climate.”

Heat waves in cities, said Frumkin,have become more common as the cli-mate warms. “We know who in cities isthe most vulnerable: the elderly, peoplewho are shut-ins, people who live onupper floors, people without air condi-tioning, people on certain medicationsthat impair the ability to dissipate heat.”Heat waves are an example of a publichealth problem related to climate changethat physicians know how to handle.Through simple buddy systems, peopleare brought to safety in refuge centers.

Infectious diseases are much harderto deal with.As tropical climates expandtheir ranges, tropical diseasesmaymarchalong in lockstep.“Sometimes this is pre-dictable,” Frumkin said,“and sometimesnot.”He cited dengue fever as an exam-ple of predictability. Climate modelinghas been used to forecast an extension ofdengue fever in various parts of theworld.“Sure enough, a decade after thatclimate model was run,” Frumkin said,“we’re seeing headlines about the ex-pansion of dengue fever.”

Scientists need to take existingmodelsthat describe climate system changes and

Earth system changes, then scale downand extend them so they can forecasthealth outcomes and implications of cli-mate change, Frumkin believes. “Thenwe need to develop plans to protect thepublic, test those plans using researchprotocols so we know what works best,and ultimately implement steps to pro-tect public health.”

“If everything is connected,” askedecologist David Rogers, of the Univer-sity of Oxford, “how can we sort outcause and effect?...How many ‘inconve-nient truths’ are there? Is there some-thing elsewe should knowabout?”Rogersquestionedwhether climate changemay

already have had an effect on some dis-eases. For that, he said, the disease musthave changed “in the right place, at theright time, and in the right direction, ac-cording to our understanding of the re-lationship between climate and disease.”In the case of malaria in East Africa, hebelieves, most highland areas will be-come climatically suitable for the diseasein the near future. Evidence exists thatsome of those regions already harbor it.

Rogers also cited a rise in the numberof human cases of tickborne encephali-tis in the Baltic states from 1970 to 2005.“Are they due to global warming?” heasked. The answer lies in many complexvariables, he believes, not in climatechange alone. In Lithuania, for example,economic changes in total employment,agricultural changes in number of cattle,environmental changes in tick abun-dance, and other factors play an impor-tant role.We have a distance to go,Rogerssaid, in understanding the factors in-volved in the spread of infectious dis-eases. Only when we do can we say howmuchof that advance is a result of climatechange.

The challenge ahead: Predictingthe emergence of infectiousdiseasesEcological changes are important for pro-viding new opportunities for pathogensto reach the human population or tocross species, said scientist StephenMorse

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Stephen Morse (left) is an epidemiologist at Columbia University Mailman School of Public Health.Andrew Dobson (center) is an ecologist at Princeton University. Duane Gubler (right) is a tropical

disease specialist at the University of Hawaii. Photographs: Carroll Photography.

There are many co-benefits to adaptingto climate change. This parent walkingher children to school helps reduce airpollution by not driving, and all threebenefit from the physical activity, the

reduced risk of injuries from carcrashes, the social capital of greeting

neighbors, and more. Graphic courtesyof Howard Frumkin, CDC/ATSDR.

of Columbia University’s MailmanSchool of Public Health. “A problem thathas bedeviled all people who attempt topredict the effect of changing climate oninfectious diseases,” he said, “is that thespecific scenarios—what diseases willmove where—depend greatly on exactchanges in climate.”

Avian flu, Morse said, may or may notbe the next pandemic strain, but it’s ofconcern because there have been humancases and limited human-to-humantransmission, almost all of them associ-ated with domestic poultry. What effectsmight climate have on avian influenza?Migratory birds that interact with in-fected poultry follow age-old flyways fornow, but will these birds continue to usethose flyways when climate changes? Orwill they change their pattern? “I suspectthey will adapt,” Morse said, “just likeother living things, to find their ‘com-fort zone.’”

To answer questions about climateand disease, he said, “we need to under-stand a great deal more about seasonal-ity and related factors. Specific prediction

will depend on knowing specific condi-tions.”

As the world gets wetter or warmer,how is that going to affect disease pre-dictions? asked biologist Andrew Dobson,of Princeton University. “For most dis-eases, there is likely to be a seasonal driver.” It gets complicated, Dobson said,“because seasonal cycles interact withthe natural dynamics of disease.”

Cholera and malaria are the posterchildren for looking at the effects of cli-mate change on disease, he said. “Withcholera, we can develop models showingthat climate variability, particularly ElNiño, drives cholera dynamics inBangladesh.” If scientists ignore El Niño,he continued, they won’t do a very goodjob of predicting diseases; if they includeit, they still may miscalculate becausethey forgot to include all the details of immunity. “Unless you know how manysusceptible people are out there, you don’tknow how the population will respond.”

Scientists looking at climate andmalaria in Africa have noted a smallchange in temperature from 1950 to

2000, an increase of about 3 percent. “Ifyou use that temperature change to drivea model for the dynamics of the [mos-quito] vectors, then that 3 percent changeresults in a 30 percent increase in thenumber of vectors,” Dobson said. “A 30percent increase in vector density is likelyto give you a significant increase inmalaria.”

More than one variable needs to beconsidered, he believes. There’s the evo-lution of drug resistance. There’s bio -diversity. “The more biodiversity, themore it’s protecting us from, for example,mosquito-transmitted diseases,” Dobsonsaid. “That’s relevant to climate change,because as you go from the tropics tothe temperate zone, you have less andless biodiversity, which means that dis-eases can focus more on humans.”

The dynamics of all these interactionsare complex mathematical problems. “It’snot rocket science,” Dobson said. “It’smuch harder.”

And it all started long ago. Sometimein the past, “humans working in the forest brought the dengue virus into

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Will migratory birds continue to follow traditional flyways as the climate changes, or will they adapt and perhaps in the process transport avian influenza to new locations? Graphic: UN Food and Agriculture Organization.

villages, where epidemics first began,”said scientist Duane Gubler, of the Uni-versity of Hawaii John A. Burns School ofMedicine. But because human popu -lations were small then, the epidemicsdidn’t persist. “The viruses burnedthrough the villages and disappeared,”Gubler said. Then as port cities aroundthe world developed, and as mosquitoeswere transported and infested those portcities, an urban epidemic cycle began.

The mosquito Aedes aegypti is theprincipal vector of this disease. It’s a“highly domesticated mosquito,” Gublersaid. “It prefers to feed on humans. Itprefers to live in houses with humans—and not anywhere else.”

In the early 1980s, scientists saw a dra-matic geographic expansion of both theviruses and the vectors. “As we go into the21st century,” Gubler said, “dengue hasbecome one of the most importantemerging tropical diseases.”

The combination of urbanization,modern transportation, and general globalization, along with increased move-ment of people, animals, and commodi-ties, is perfect for moving these pathogensaround, Gubler said. “Our single biggestchallenge is to do something about themovement of vectors and pathogens bymodern transportation. And we need abetter understanding of disease ecologybecause most of these diseases won’t havea drug or a vaccine.”

New approaches for a different worldThe malaria world is changing dramati-cally and rapidly, said Stephen Hoffman,chief executive officer of Sanaria, Inc., inRockville, Maryland. Hoffman is a physi-cian and tropical infectious disease spe-cialist who, with colleagues at Sanaria, isworking to develop the first successfulmalaria vaccine.

“We go to work every day with onedream and one dream only: to develop amalaria vaccine to prevent millions ofdeaths from malaria,” Hoffman said.“Malaria is responsible for more deathsin children than any other infectiousagent. More than 300 million people willsuffer clinical attacks of malaria duringthe next year. I’ve heard estimates re-cently that it’s up to one billion.” At least70 percent of the illnesses will occur insub-Saharan Africa, where 90 percent ofmalaria-related deaths occur, most ofwhich are children under five years old.

“Malaria not only has a huge healthimpact,” Hoffman said, “it also has a hugeeconomic impact. It’s the leading health-care expenditure in most of Africa. It’s amajor cause of poverty, and poverty en-hances disease. It’s been estimated that atleast 10 [billion] to 12 billion dollars arelost annually to malaria in Africa.”

Malaria is not only a disease of childrenin remote villages in Africa. Tens of mil-lions of travelers from North America,Europe, Australia, the Middle East, andEast Asia visit areas of the world withmalaria every year; some 30,000 contractthe disease. “Five to ten million Americantravelers are at serious risk annually, withequivalent numbers for Europe,” Hoff-man said.

Sanaria was formed five years ago withthe mission to develop, license, and re-lease a vaccine based on an attenuatedversion of the malaria-causing parasitePlasmodium falciparum. “The vaccine,we hope, will prevent infection with thisparasite in greater than 90 percent of the recipients for at least six months,” Hoff-man said.

The vaccine development method atSanaria is different from other ap-proaches. The company is using a live, at-tenuated, whole-organism vaccine; otherefforts have been “subunit recombinant”

(a subunit apart from the entire infectiousagent is used, and the vaccine is made re-combinantly in the laboratory). Sanariais now in the process of manufacturingits malaria vaccine for clinical trials, firstin the United States, then in Africa.

“The road to success has lots of po-tential potholes,” Hoffman said, but hebelieves that there will be a vaccine formalaria in five years. “I can hear foot-steps behind me, so we all work everyday to try to prevent the 3000 childrenwho are dying from malaria today fromdying.”

In her AIBS annual meeting closing re-marks, Colwell stated: “Interdisciplinaryapproaches will be required to addressthese critical problems of the 21st century.They’re international, in that we will needto work together to develop a global un-derstanding of these diseases, and alsoof global public health measures to betaken in a time of climate change and ofsocietal change.”

Billions of people are depending on theanswers.

Cheryl Lyn Dybas (e-mail: cldybas@

nasw.org) is a biologist and science

journalist who specializes in the

environment and health.

doi:10.1641/B580903Include this information when citing this material.

www.biosciencemag.org October 2008 / Vol. 58 No. 9 • BioScience 797

Stephen Hoffman is founder and chiefexecutive officer of Sanaria, Inc.

Photograph: Carroll Photography.

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Visit the AIBS Media Library at www.aibs.org/media-library for videos and audiorecordings of presentations made at AIBS annual meetings from 2000 onward.