Emerging infectious diseases

WorldHeolth r 50thYeor, No. I, Jonuorv-Februoryl99i Emerging infertious diseqses Dovid Heymonn The emergtunce or re- emr;rgence of infectious diseoses slemsfrom the inueosing world populofion, ropid internotionoltrovel on o large xole, ond inueosed r,xposure of humon beings to diseose vecfors in nofure. j,. , report published by the United '. , States Institute of Medicine in '' ' 1 1992 called attention to signs that the fight against infectious diseases was far from won, despite great advances in the development of antibiotics and vaccines. The report cited emerging or newly identified infectious diseases as evidence for this and also highlighted re-emerging or resurgent infectious diseases hitherto thought to have been over- come. It is now clear that the emergence or re-emergence of infectious dis- eases is partly the result of a shift of resources away from infectious disease control, public health and sanitation. It is aggravated by the fact that antibiotics which were once effective against some of the most common human infections have gradually become ineffective. In addition, changes to the environment may bring the animals and insects that carry disease into closer contact with human beings. During the past 20 years, more than 30 new micro- organisms have emerged, some of which cause dramatic and lethal disease in localized outbreaks or over great distances, at the cost ofenor- mous suffering and expense to soci- ety. Meanwhile many common diseases have re-emerged and spread rapidly after periods when they were Mtnguinhos fovelo in Rio de Joneuo. S/ums ore fertile breeding grounds for tnfectious dlseoses. Phofo: Keyst'one o. no longer considered to be a problem. The term "emerging infections" refers to newly identified and previ- ously unknown infectious diseases which cause public health problems, either locally or internationally. They include: a fatal respiratory disease caused by a virus called sin nombre ; a variant Creutzfeldt-Jakob disease which is suspected, though not proven, to be associated with a similar disease in cattle called bovine spongiform encephalopathy; HIV infection, which is now a worldwide cause of human suffering and death and a heavy economic burden; and some rare but equally devastating diseases such as Ebola haemorrhagic fever. These diseases may be new in human beings, or may have been present for a long time but not recog- nized. But many emerging diseases are thought to be the result of people coming into closer contact with natural reservoirs of disease in the environment, which has permitted a jump of the infectious agent across the species barrier from animal to human being. Other examples of new or newly detected infectious diseases of global concem include Legionnaires' disease, haemolytic uraemic syndrome caused by E sche richia c oli Ol57 :H7, Lyme disease, hepatitis C and E, and a new form of cholera caused by Vibrio cholerae 0139. WorldHeolth I 50lhYeor, No. 1, Jonuory-Februory1997 Re-emerging infectious diseases are infections that have been known about for some time but had fallen to such low levels that they were no longer considered a public health problem. They often reappear in epidemic proportions. Well-known examples are: tuberculosis, which is increasing worldwide partly owing to its close association with HIV infec- tion; cholera, which has been reintro- duced into countries where water and sanitation systems have deteriorated; and dengue or "breakbone" fever, which has occurred in urban areas where mosquito control has broken down. Drug resistonre Resistance to antibiotics is a phe- nomenon common to both emerging and re-emerging infections. Many well-known antibiotics are no longer effective against common inf-ections such as pneumonia, gonorrhoea and tuberculosis. At the same time, fewer new antibiotics are being released on the market, partly be- cause of the high cost of developing and licensing them and partly be- cause they have a potentially short life because of the development of resistance. Ifthe arsenal ofdrugs against infectious diseases loses its power, the future for patients with even a common local infection will become bleak. Several factors contribute to the emergence and re-emergence of infectious diseases, but most can be linked with the increase in the num- ber of people and in population movements, rapid intemational travel, overcrowding in cities with poor sanitation, changes in the han- dling and processing of large quanti- ties of food, and increased exposure of human beings to the carriers and natural reservoirs of disease. Other factors include a deteriorating public health infrastructure which is unable to cope with population demands, and the emergence of resistance to antibiotics resulting from their in- WHO ensures thot int'ernotional ropid response teoms con be mobilized in cose of epidemtc threots. Phofo: WHO/G. Rodier. creased misuse. Travel has always been a means by which disease has spread across the world. In the 14th century in the city-state of Venice it resulted in protective legislation which has evolved, over the centuries, into the current International Health Regulations. Today, well over 50 million people use international air The lnternofionol Heolt'h Regulations require cetoin infect'ious dlseoses to be reponed. This imponoil bol for slopprng the spreod of epidemics ocross boundories ts now being revised io mole tt more opplicable to infection conlrol in lhe 2l sl centurv lnternotionol Heolth Regulotions The first recorded quorontine regulotion wos written in Venice in 1377 to protect the cily-stote from diseoses corrled by shipborne rots. Neorly five centuries loter, in I B5l , the first lniernotionol Sonitory Conference loid down certoin principles for proteciion ogoinsl diseose, but onoiher century elopsed before o wide voriety of meosures were forged inlo the lnternotionol Sonitory Regulotions of I 951 . ln I 969, the lnter- notionol Heolth Reguloiions (lHR) were odopted, oimed ot ensuring moximum securiiy ogoinst the internotionol spreod of diseose. The officiol reporting of three communicoble diseoses - choiero, plogue ond yellow fever - is required under the lHR, bui no internotionol body - not even WHO - hos ihe mondote to enforce this reporting. Consequently some outbreoks go unreported when o country believes its economic interesls might be odversely offected. When Peru wos hit by cholero in I 99 I , ond when lndio suffered on outbreok of pneumonic plogue three yeors loter, both countries prompily reported the foct. Their trode ond trovel losses were estimoted ot US$ ZOO million ond $ I 200 million respectively. Todoy, new ond re-emerging infectious diseoses not deolt with under the IHR hove the some potentiol for spreoding ocross notionol boundories. The 1995 outbreok of Ebolo hoemorrhogic fever in Zolre wos fortunotely contoined before it could spreod beyond the frontiers. Simllorly, the 1993 oulbreok of hontovirus pulmonory syndrome in the United Stotes provoked notionol olorm obout the possibility of cross-border tronsmission, but ogoin the IHR were not opplicoble. Following o World Heolth Assembly resolution in 1995, WHO is now revising ond updoting the IHR to moke them more opplicoble to infection control in the 21st century They will cover "defined syndromes representing diseose occurrence of internotionol importonce" ond will set out the meosures notionol heolth outhorities should instrtute to protect their territorles from infectious diseoses. *ffiixtff#:* hho4Ne^6&fu WorldHeolth r 50thYeor, No. 1, Jonuory-Februoryl997 transport each year. The concerns expressed in Venice related to cholera, plague and smallpox which were transmitted from one continent to another by ship. Now it is not only possible but quite likely that a disease will appear days after the arrival of an infected traveller rather than during the voyage. Emerging and re-emerging infec- tions reflect the constant struggle of microorganisms to survive. primar- ily by finding breaks in the barriers which normally protect human beings from infection. Such breaks may result from high-risk human behaviour" failure of disease detec- tion systems, failure to control mosquitos and other carriers of disease. breakdown of water and sanitation systems, and deforestation which forces forest animals closer to human settlements in search of food. These breaks have developed rapidly in just a few decades, at the same time as interest in inf'ectious diseases has waned and resources for their detection and control have decreased. Because such diseases appeared to pose a declining threat, funds for their control were chan- nelled to efforts against other prob- lems. Experts on infectious disease retired or left the field and students turned to more rewarding subjects than viruses and bacteria - in short. the infrastructure for control of communicable disease began to crumble. WH0t response Since 1992 the alarm over emerging and re-emerging diseases has echoed around the world. Great concern was expressed by the Member States of WHO in a resolution of the World Health Assembly in 1995, which urged all countries to strengthen surveillance for infectious diseases in order to promptly detect re- emerging diseases and identify new ones. The success ofthis resolution depends on the ability to obtain information about infectious dis- eases and a willingness to communi- cate this information nationally and internationally. WHO therefore established the Division of Emerging and other Communicable Diseases Surveillance and Control (EMC), which is charged with strengthening national and interna- tional surveillance and control of communicable diseases, including lhose that represent new. emerging and re-emerging public health prob- lems, for which it must ensure a timely and effective response. One of the main functions of WHO, through EMC, is to provide technical assistance and training in communicable disease surveillance and control, and in public health laboratory support. EMC has also set up mechanisms for timely ex- change of information on the current communicable disease situation worldwide and on the experiences of countries in disease surveillance and control. This infbrmation may be obtained from printed WHO publi- cations and through the EMC World Wide Web site on http://www.who. ch,,iprogrammes/emc. WHO's col- Iaborating centres, linked electroni- cally with WHO headquarters and regional oflices, form a worldwide network for infectious disease moni- toring and early alert of outbreaks. The International Health Regula- tions are being revised and adapted to the scale of international traffic and trade expected in the 2 I st century. Another crucial role of WHO is to assist countries to respond to epidemic emergencies. EMC en- sures that it is possible to mobilize international rapid response teams of WHO statT and other experts in response to epidemic threats. in collaboration with the Division of Emergency and Humanitarian Action. WHO, through EMC and in partnerships with other bodies, will provide the key to cost-effective action for a world which is on the alert and able to contain infectious diseases. I Dr Dovid Heymann is Dtrector of the Division of Emerging ond other Communtcoble Dlseoses Survetllance and Conlrol, World Heolth Orgonizotion, l2I I Geneva 27, Swilzerlond. A globol portnership A worldwide portnership of coun tries, NGOs, internotionol orgoni- zolions ond individuols is required to respond odequotely to the threot of emerging diseoses. The logo se- lected for this yeor's World Heolth Doy (see bock cover) tries to show how this portnershlp ensures lheir ropid detection ond effective con- toinmenl. As one of the portners in this globol effort, WHC is strength- ening three globol monitoring systems. These bring together spe- ciolized loborotories ond diseose surveillqnce systems from oll coun- tries, ond feed informotion electron- icolly to lhe World Wide Web ond other internotionol electronic ond print medio. The first is the WHC system of colloboroting cenires, speciolized oborotories ond institutions wilh ex- pertise in the diognosis ond epi- demiolooy of infectious diseose. During recent epidemics it hos be- come cleor thoi some loborotory centres hove not kepi up with chonges in technology, while oth ers hove foiled to develop expertise in some of the newer infectious dis- eose chollenges. 1n strengthening this sysiem of colloboroting centres, WHO is urging governments to pro- vide the resources to keep the cen- tres up io dote, to increose the number of centres in developing couniries ond to ensure thot o I cen- tres ore linked electronicolly The second system consists of Mo WHC networks: WHONET for monilori ng ontimicrobiol resistonce, ond ihe progromme for moniloring gonococcol oniibiotic susceptibil' ity Through these, WHO regu orly obtoins stondordized ond quolity- ensured informotion on the currenl stote of ontlmicrobiol resistonce, ond helps countries to use this infor- motion for sound notionol drug poli cies. The third system is the Iniernotionol Heolth Regulotions (lHR), currently the only internotionol public heolth legislotion which re- quires reporting of infectious dis- eoses (see box on poge 5) WHO is revising the lHR, ond it is foreseen thot the regulotlons will eventuolly require reporting of clinico syn' dromes of potentiol worldwide im' portonce so thot there con be on immediote ond oppropriote inler- nolionol response.