Nature Vol. 293 17 September 1981 181 Agricultural production and malaria resurgence in Central America and India Georganne Chapin* & Robert Wasserstromt AMONG the inhabitants of Asia, Latin which mosquitoes of the Anopheles for a short time on the inside walls of America and tropical Africa malaria subfamily transmit Plasmodium parasites human houses after biting their victims. By remains a major cause for alarm. Yet only a to human beings. After reproducing in spraying walls with DDT, WHO officials few years ago, health officials in a dozen astronomical numbers, these parasites reasoned they could reduce the vector developing countries (capitalizing on the transform their human hosts into a popUlation to manageable levels. Simul­ discoveries of British parasitologist Ronald reservoir of illness which may be spread to taneously, they proposed to treat everyone Ross half a century earlier) pointed uninfected individuals. affected by the disease with chloroquine or triumphantly at their efforts to eradicate In 1907, Dr William Gorgas, an other anti-Plasmodium drugs so as to entirely this mosquito-borne scourgel - 5 . American Army surgeon in the Panama destroy the reservoir of disease. If these Following World Health Organization Canal Zone, set out to break this cycle by conditions could be maintained for three or (WHO) guidelines, for example, Indian draining swamps, emptying, covering or four years, they calculated, malaria trans­ authorities instituted a programme of oiling pools of standing water and mission might be broken forever. More­ medical treatment and pesticide appli­ screening human habitations. Although he over, projects of this sort could be carried cation in 1952 which within a single decade was unable to eradicate the disease com­ out without altering political arrangements reduced the number of cases from over 100 pletely, within two years the death rate or patterns of land tenure. million to 50,000 (ref. 6). Ten years later, from malaria among canal company using the same methods, health workers in employees had fallen to 8.86 per thousand Complications Sri Lanka cut the annual incidence of - a decrease of 80 per cent. More or less Despite the simplicity of the plan, WHO malaria from three million cases to fewer simultaneously an Italian physician, Dr officials were aware that a worldwide than 25. Angelo Celli, noticed that in southern campaign to eradicate malaria would face By 1970, however, it had become clear Europe the disease tended to attack people nearly insurmountable obstacles. In many regions, control programmes were A few years ago the battle against malaria seemed to have been won. However virtually non-existent, and even those that now, despite vigorous anti-malaria campaigns, the disease has made a did exist suffered from a lack of funds, comeback. The resurgence of malaria in Central America and India seems to technical expertise and administrative have been paralleled by intensified agriculture in these countries and the efficiency. But there was another obstacle associated increased use of pesticides. which experts at WHO were more reluctant to engage: as early as 1953, they obtained that malaria eradication had run into who were either poor or landless, par­ conclusive evidence that Anopheles severe difficulties. Instead of dwindling to ticularly those who worked as seasonal mosquitoes, like many insect pests, sooner insignificance, the number of infected indi­ labourers on certain large farms. He or later became resistant to DDT and other viduals rose again to distressing pro­ reasoned that transmission depended to a pesticides. Within a few years, in fact, such portions. In India, which had served as a considerable degree on the flow of fresh resistance had been reported in Greece and showplace for WHO policies, five million human blood into malarious zones just as Italy (where insecticides were used both in people were soon infected; in Sri Lanka, the A nopheles population began its annual public health and in agriculture) as well as two million people became sick again explosion. Not only sanitary measures and in the Lebanon, Iran, Saudi Arabia and almost overnight; and in Central America medical treatment, then, but land reform Nigeria. In some cases a single application infection rates grew to previously unknown and other social programmes might playa was sufficient to reduce mortality (that is, in­ levels 7 . Moreover, unlike earlier out­ substantial part in conquering the disease. crease resistance) among mosquitoes by 80 breaks, this new plague was often carried By the end of the Second World War, percentl8. Accordingly, WHOmalariologists by mosquitoes which had become resistant however, it seemed that a technology had urged their local counterparts to conduct to pesticides like DDT and dieldrin and finally been devised that could eliminate "time-limited" spraying operations - to could not be controlled by conventional malaria in much of the non-Western world: complete the "attack" phase as quickly as means8-- 15 • The origins of this major chemical pesticides. Insecticides like DDT possible. ecological disaster must be sought as much and dieldrin were not only cheap and easy Thus, anti-malaria teams were directed in the unwitting actions of international to use, but they also remained active for to treat the interior walls of all human organizations as in hapless nature. several months after each applicationl ? For habitations and shelters within the target this reason, they appeared to be ideally zone on a regular schedule - a gargantuan A seeming success suited for the task of killing Anopheles task under the best of circumstances. It is worth noting that early programmes mosquitoes, which characteristically rested Meanwhile, by organizing an elaborate to contain parasitic diseases - primarily malaria and yellow fever - achieved Table 1 Prevalence of malaria in Central America, 1965-1977 remarkable success without recourse to sophisticated technologies 16 • Efforts to No. of cases (thousands) overcome malaria before the Second World War concentrated on the ways in Country 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 Costa Rica 0.6 0.3 0.3 0.2 0.2 0.2 EI Salvador 34.2 68.6 83.0 35 .8 25.3 45.4 46.8 38.3 35.1 67.0 83.1 83.3 32.2 'Division of Sociomedical Sciences, School of Public Guatemala 14.3 22.0 21.2 11.0 10.6 10.9 8.3 9.3 1.0 1.0 9.6 Health, Columbia University, New York, New York 10032, USA. Honduras 6.9 17.1 16.1 15.7 29.6 34.5 48.4 18.6 8.8 7.5 30.3 48.8 39.4 tDepartment of Anthropology, and Division ofSocio­ Nicaragua 8.3 15.6 7.1 16.0 28.5 23.3 9.6 4.2 12.2 24.7 26.2 11.6 medical Sciences, Columbia University. New York. New York 10027, USA. Source: WHO, World Health Statistics Annual, Geneva, 1966-/9. 0028-0836/ 81 / 380184·05.01.00 e 1981 Macmillan Journals Lid 182 Nature Vol. 293 17 September 1981 system of regional laboratories and clinics, public health officials were supposed to Table :z Land Ienure in India, 1970 administer chemotherapy and monitor the campaign's progress. In areas where these Size of holding No. of holdings lifo Of rural Area "10 Of total area tactics proved to be successful, where the (hectares) (thousands) properties (millions of number of active cases diminished to zero, hectares) attack gave way to consolidation. And if no <0.5 23,178 32.9 5.4 3.4 new illness occurred during the following three years, consolidation was in turn 0.5- 1.0 12,504 17.7 9.1 5.6 replaced by maintenance, the constant vigil 1.0- 1.9 13,432 against a recurrence of infection. This 19.1 19.3 11.9 strategy was adopted in 1954 by the Pan 2.0- 2.9 6,722 9.5 16.4 10.0 American Health Organization (P AHO) and subsequently by the entire inter­ 3.0-- 3.9 3,959 5.6 13.6 8.4 national community. 4.0- 4.9 2,684 3.8 11.9 7.4 Initially, at least, it seemed that WHO's campaign enjoyed almost unmitigated 5.0- 9.9 5,248 7.4 36.3 22.4 success. In India, after ten years of struggle 10.0-19.9 2,135 3.0 28.5 27 .6 against malaria (1961), only 50,000 cases of the disease were uncovered by government 20.0-29.9 401 0.6 9.3 5.8 inspectors and a number of regions had passed from attack to consolidation or 30.0-39.9 120 0.2 4.2 2.6 maintenance. Similar triumphs were 40.0-49.9 45 0.1 2.1 J.3 registered in Pakistan, Sri Lanka, Paraguay, Venezuela, Mexico and Central >50 65 0.1 6.0 3.1 America. In ten other countries, Total 70,493 100.0 162.1 100.0 Plasmodium infection was completely overcome. Source: Ministry of Planning, Government of India, Statistical Abstract, India, 1977, New Delhi, 1978. Malaria re-emerges had reached alarming proportions among even measures of this kind might serve at Within a short time, however, the cam­ Anopheles mosquitoes - just as WHO best only as temporary expedients: vectors paign began to falter. Between 1961 officials had originally feared27•28 • which became resistant to one compound and 1966, disease rates in India increased The case of El Salvador is illuminating. frequently enjoyed mysterious immunity threefold; by 1970, half a million people In 1958 a group of entomologists reported to other unrelated poisons, and in any case caught malaria each year - many in areas that the local vector, Anopheles it was only a matter of time before natural where health authorities had recently albimanus, had lost its susceptibility to all selection favoured those insects which scored impressive victories.