New causes for new diseases

t2 WoddHeolth r 50thYeor, No. l, lonuory-februory l997 New couses for new diseoses lohn t.lost Noturol chonges in the world's ecosystems ore now being loined by humon-induced chonges os the triggers for oufbreoks of emerging ond r e-e m er gi n g i nf e cti o ns. or better or worse, the risk of many infectious diseases is influenced by human alteration of local, regional or global ecosys- tems. Death rates from gastrointesti- nal disease declined in industrial nations early in the 20th century in part because of the invention of the internal combustion engine. Cars replaced horses as the main means of getting about; and cars didn't leave heaps of manure as breeding places for disease-carrying fl ies. Conversely, in the tropics and sub- tropics, dams to store water for irrigation and hydroelectric power have introduced water-borne diseases such as schistosomiasis to communi- ties where they previously did not exist. Day-care centres are popular in an age of small families and working mothers. They are also an ideal setting for transmitting infections among infants and toddlers, who are naturally affectionate so they touch, hug and kiss one another but are not yet trained in personal hygiene. The common cold, diarrhoeal diseases and more serious infections can spread like wildfire and - taken home by the children - they infect parents and other children in the house. Air-conditioning is widely used in hotels and hospitals in warm countries. But dilapidated air-condi- tioning units accumulate many kinds of moulds and microbes, including the microorganisms responsible for "Legionnaires' disease" (a dangerous form of pneumonia) or some forms of meningitis. International trade carries many "passengers" along with the articles transported between the nations of the earth. Consignments of used tyres imported into the United States in the 1980s, for instance, contained small pools of water in which Aedes albopictus, a variety of mosquito not native to the Americas, found an ideal environment to lay its eggs. These insects are able to transmit dengue fever. which now occurs in the southern USA as well as in Central and South America. Globolworming The greenhouse effect, mainly due to fossil fuel combustion, is changing the world's climate. Mosquitos that carry malaria, yellow feveq dengue and viral encephalitis are extending their range into temperate zones, higher altitudes of tropical regions and large cities like Nairobi and Harare. By the middle of the 21st century there may be several hun- dred million more cases of malaria each year as a result, many of them in regions now free of malaria. Not all ecological changes are caused by human activities. The tropical Pacific Ocean current El Niflo undergoes periodic warming. In the early 1990s, such a change was accompanied by the prolifera- tion in coastal waters of South America of blue-green algae. These harbour the cholera vibrio which can survive for lengthy periods in vari- ous forms of plankton. The flight of landless peasants from rural areas in developing coun- tries means that by the year 2000 over half the world's population will live in big cities. Many will live in slums which favour the transmission of infectious diseases like tuberculo- sis and HIV/AIDS. Tuberculosis has always flourished in conditions of poverty, overcrowding, poor nutri- tion and illiteracy; HIV infection spreads when women must resort to prostitution in order to survive, and when intravenous drug abuse with needle-sharing occurs. Finally, there have been several recent cases of a variant of Creutzfeld-Jakob disease, a progres- sive and fatal degenerative brain Stored waler permils irrigotion ond elechic power. However, il moy introduce diseoses /ike schislosomiosis info communities where lhey prevtously did not exisf . Photo. WHO/AKF/J.-1. Roy WoildHeolth r 50thYeor, No. 1, lonuory-Februoryl997 disease of cattle - is thought to be caused by the agent of scrapie. a TSE of sheep. Sheep's offal has been used to prepare protein supple- ments fed to cattle. Although not yet proven, the circumstantial evidence is persuasive and worrying: the inf'ectious agent seems to have passed from sheep to cattle to human beings. This may be an example of the consequences of human interfer- ence with natural processes - in this instance feeding animal protein to a vegetarian species. I A day-care centre tn Albonto. lnfecttous diseoses con spreod roptdly among young chrldren. Photo: WHO. disease, in the United Kingdom and France. These cases are thought to be due to exposure to an unconven- tional infectious agent belonging to the group responsible for transmissi- ble spongiform encephalopathies (TSE). One of these. bovine spongi- form encephalopathy (BSE) - a Dr.lohn M. Lost is Emerilus Professor of Eptdem iology o nd Con n u nity Med ici ne Unrversit'y of Ot't'owo, 45I Smyth Rood, affawa, Onlorio KIH BM5. Conctda. A sole woler pump tn Zimbobwe. Counlrtes lhol ensure minimum heolthy living condittons hove o good chonce of wiping out cholero. Photo:WHO 1$P Hubley Cleoning up dirty woter ond keeping it deon In mony ports of the developing world, drinking-woter is collected from sources outside lhe home. lt moy be contominoied ot the source or during storoge. Slrotegies to reduce wqterborne dlseose tronsmission musl sofeguord ogoinst both possibilities. New products ollow fomilles to disinfect drinking'woter immediotely ofter collection, ond newly designed norrow-mouthed, closed storo ge vessels prevent reconlo m i notion. This Mo-component prevenlion strotegy is o prociicol ond inexpensive woy for households ond communities thot Lock sofe woier to protect themselves ogoinst o voriely of woterborne pothogens, ond con progressively decreose woterborne diorrhoeol diseoses. The method hos been tested in vorlous ports of Bolivio by the United Stotes Deportment of Heolth, the US Centers for Diseose Control ond Prevention, the Pon Americon Heolth Orgonizotion ond the United Stotes Agency for Inlernotionol Development. Well occepted, it hos significontly improved the quolity of stored woter ond brought obout o decreose in diorrhoeol diseoses, especioliy omong infonts under one yeor. The method could be on effective tool ogoinst woterborne diseoses such os typhoid fever ond cholero ln such seitings os doy core centres ond old people's homes, ond could be used dur,ng feslivols Cllnlcs, schools ond even street vendors ore ottroctive potentiol torgets for this intervention, which encouroges the woshing of honds, foods ond kitchen utensils in Woter should be kepl in norrow'mouthed vesse/s rn order t'o minimize exlernol contominolion. Phofo: WHO/H Anenden. order to reduce diseoses tronsmitted by personol contoci or contominoted food. The next generolion of vessels, currently being pilot- iested omong Guotemolon street vendors, will hove o built-in soop dish to promote hond-woshing With the commitment of communities, ministries of heolth, United Notions ogencies, nongovernmentol orgonizotions ond privote industry, this low-cost, effective intervention could be implemented on o brooder scole. Adopted fron o conlribution of fhe lJnited Stotes Cenfers for Diseose Confrol ond Prevention to the World Heolth Repon 1996, p.44 rsee p. ? I of rhis i>sue for fu,rhe, details o{ the Report]