Emerging Viruses: the Evolution of Viruses and Viral Diseases Author(S): Stephen S
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Emerging Viruses: The Evolution of Viruses and Viral Diseases Author(s): Stephen S. Morse and Ann Schluederberg Source: The Journal of Infectious Diseases, Vol. 162, No. 1 (Jul., 1990), pp. 1-7 Published by: Oxford University Press Stable URL: http://www.jstor.org/stable/30127833 Accessed: 18-08-2014 21:02 UTC Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Oxford University Press is collaborating with JSTOR to digitize, preserve and extend access to The Journal of Infectious Diseases. http://www.jstor.org This content downloaded from 155.58.212.160 on Mon, 18 Aug 2014 21:02:31 UTC All use subject to JSTOR Terms and Conditions 1 Fromthe NationalInstitute of Allergy and Infectious Diseases, the FogartyInternational Center of the National Institutesof Health, and the RockefellerUniversity Emerging Viruses: The Evolution of Viruses and Viral Diseases Stephen S. Morse and Ann Schluederberg From the Rockefeller University,New York,New York,and the National Institute of Allergy and InfectiousDiseases, National Institutesof Health, Bethesda, Maryland Challengedby the sudden appearanceof AIDS as a major rus and host can follow severalpossible lines, and pathogens public healthcrisis, the National Instituteof Allergy and In- may not always evolve towardslower virulence. In a model fectious Diseases and the FogartyInternational Center of the developed by Levin (describedin [3]), for example, a virus NationalInstitutes of Health(NIH), togetherwith The Rocke- strain that kills much faster will not be favoredover a less- feller University,jointly sponsoredthe conference "Emerg- virulent strainif it has a modest transmissionadvantage, but ing Viruses: The Evolution of Viruses and Viral Diseases" it will prevailif it is much more readily transmittedthan the held 1-3 May 1989 in Washington,DC. It was convened to less-virulentstrain. Examples such as myxomatosisin Aus- consider the mechanismsof viral emergence [1]and possible tralia supportthe notion that in the tradeoffbetween trans- strategiesfor anticipating,detecting, and preventing the emer- missibilityand virulence, many viruses evolve toward a middle gence of new viral diseases in the future. To providea broad course, favoringtransmissibility but allowing them to retain perspective,participants comprised virologists, infectious dis- some virulence. Viruses that are transmissibleover a long ease specialists, theoreticalbiologists, historians, epidemi- time (e.g., human immunodeficiencyvirus [HIV]) have a ologists, ecologists, and molecularbiologists (see below for selective advantageeven when their effective rates of trans- program and participants). mission are relatively low [5]. Although mathematicalapproaches offer useful insights, and Haase caution that models will often inade- Theoretical Considerations May prove quate in predicting outcomes because viral emergence and The enormity of the problem was outlined in the keynote host interactions are complex, being dependent on both address by Lederberg,who said that humankind'sonly real genetics of the host and externalconditions. For example,as competitorsfor dominionof the planetare viruses, which can discussed by Lovejoy, there are many examples of disease serve as both parasites and genetic elements in their hosts. emergenceprecipitated by environmentalchange, but it is im- Not only do theyhave considerable genetic plasticity, enabling possible at presentto predictor model accuratelyhow global them to evolve in new directions,but their genetic and meta- warmingor other possible environmentalchanges will affect bolic entanglementswith cells uniquelyposition them to medi- viral disease emergence. ate subtle, cumulativeevolutionary changes in their hosts as well. Their effectsare not alwaysso subtle, however;viruses Historical Lessons on Disease Emergence also can decimate a population. The fact that naturalselec- tion in the long run favorsmutualism offers only limited en- According to McNeill [6], the most striking examples of couragementto the human race, as too many people might emergenceof infectious diseases arose from new patternsof suffer as the result of viral mutation before an equilibrium human movement, leading to new contacts across what had could be reached. [2] previouslybeen geographicboundaries that containeda dis- Accordingto May and Anderson [3, 4], coevolutionof vi- ease. Examples are the introductionof smallpox into the Americas and of syphilis into Europe. Disease emergence resulting from expanded geographic Received 11 December 1989; revised 18 January 1990. boundariesof viruses or their vectors was a recurringtheme Financial NationalFoundation for Infectious Hoffman-La support: Diseases, discussed in talks by Johnson, Monath, Evans, Shope, and Roche, Lilly ResearchLaboratories, and Merck Sharp8c Dohme Research Laboratories(for the conference);RR-03121 and RR-01180,National Insti- others. Yellow fever probablyemerged in the New Worldas tutes of Health (to S. S. M.). a result of the African slave trade, which broughtAedes ae- and Dr. S. Morse, the Rockefeller Reprints correspondence: Stephen gyptiin watercontainers of ships. Similarly,the rise of dengue University, 1230 YorkAve., Box 2, New York, NY 10021-6399. hemorrhagicfever in SoutheastAsia in the late 1940s is at- The Journalof InfectiousDiseases 1990;162:1-7 tributedto to cities with water ? 1990by The Universityof Chicago.All rightsreserved. rapidmigration open storage, 0022-1899/90/6201-0001501.00 which favoredproliferation of the mosquito or other suitable This content downloaded from 155.58.212.160 on Mon, 18 Aug 2014 21:02:31 UTC All use subject to JSTOR Terms and Conditions 2orse l chluederberg ID 990;162 July) Table 1. Some examples of "emerging"viruses. Symptoms Distribution Natural host Orthomyxoviridae(RNA, 8 segments) Influenza Respiratory Worldwide (from China) Fowl, pig Bunyaviridae(RNA, 3 segments) Hantaan, Seoul, and others Hemorrhagicfever with renal syndrome Asia, Europe, USA Rodent (e.g., Apodemus) Rift Valley fever* Fever, may also cause hemorrhage Africa Mosquito; ungulate M8SJ1(VirusOropouche* Fever Brazil, Trinidad, Panama Midge Togaviridae (Alpha) (RNA) O'nyong-nyong* Arthritis, rash Africa Mosquito Sindbis* Arthritis, rash Africa, Europe, Asia, Australia Mosquito; bird Flaviviridae (RNA) Yellow Fever* Fever, jaundice Africa, South America Mosquito; monkey Dengue* Fever, may also cause hemorrhage Asia, Africa, South America, Mosquito; human; Caribbean monkey Rocio* Encephalitis Brazil Mosquito; bird KyasanurForest* Encephalitis India Tick; rodent Arenaviridae (RNA, 2 segments) Junin (Argentine hemorrhagicfever) Fever, hemorrhage South America Calomys musculinus Machupo (Bolivian hemorrhagicfever) Fever, hemorrhage South America Calomys callosus Lassa fever Fever, hemorrhage West Africa Mastomys natalensis Filoviridae (RNA) Marburg, Ebola Fever, hemorrhage Africa Unknown Retroviridae(RNA + reverse transcriptase) Human immunodeficiency virus AIDS, AIDS-related complex Worldwide ? Primate Poxviridae (DNA) Monkeypox Smallpox-like Africa (rainforest) Squirrel NOTE. Boldface indicates viruses with greatest apparentpotential for emergence in the near future. * Transmittedby arthropodvector. vectors. Of currentconcern in the USA is the fact thatAedes Otheranimals, especially primates,are importantreservoirs albopictus, an aggressive and competent dengue virus vec- for transferby arthropods. tor, was broughtto Houston in used Asian tires and has es- Accordingto Monath,MOO of the ^20 knownarthropod- tablished itself in at least 17 states. Krause noted that with borne viruses (arboviruses)cause humandisease. At least 20 dengue hemorrhagicfever "lappingat our shores,"we have of these might fulfill the criteria for emerging viruses, ap- a potentially serious public health problem in the making. pearing in epidemic form at generally unpredictableinter- vals. Most arboviruseshave enzootic cycles involvinga vector (e.g., mosquitoes, ticks, or biting flies) and wild vertebrate Recent Examples of Emerging and Potentially hosts, most of which rarelymanifest overt disease. Many ar- Emergent Viruses boviruses can also be transmittedvertically within their vec- Table 1 lists some viruses that have been associated with tors, assuringsurvival over winters or dry seasons. Periodic "emergent"disease. Disease emergenceoften followsecologic amplificationoccurs when vector and susceptiblehost popu- changes caused by human activities, such as agricultureor lation densities and other factors favorrapid virus transmis- agriculturalchange, migration, urbanization,deforestation, sion, and it may be followed by epidemics in humans or or dam building. For example, Argentinehemorrhagic fever domestic animals. In such situations,arboviruses may enter increasedas agriculturalchanges favoredthe rodentthat car- into a second transmissioncycle involving one or more ar- ries this virus. thropodvector species differentfrom the enzootic vector spe- Surprisingly,most emergentviruses are zoonotic, with nat- cies and humansor domestic animals as viremic hosts. This ural animalreservoirs a more frequentsource of new viruses makes surveillancedifficult.