A consideration of the economic impact of schistosomiasis*

Bull. Org. mond. Sante 1197, 47, 559-566 Bull. Wld Hlth Org. A consideration of the economic impact of schistosomiasis* W. H. WRIGHT ' An attempt is made to estimate the economic effects of schistosomiasis, a disease known to be endemic in 71 countries or islands with a totalpopulation ofabout 1 362 million persons, of whom approximately 124 905 800 are infected. These data are based on pre- valence rates representing, for the most part, single stool or urine examinations; the actual number of cases is undoubtedly much greater. This analysis refers only to resource loss attributable to reduced productivity. The annual loss from complete and partial disability is estimated to be US $445 866 945 in Africa, US $755 480 in Mauritius, US $16 527 275 in South- West Asia, US $118 143 675 in South-East Asia, and US $60 496 755for the Americas. The total estimated annual world loss amounts to US $641 790 130 but this sum does not include the cost of public health programmes, medical care, or compensation for illness. Few attempts have been made in recent years to analyse the economic impact of disease and to correlate public health expenditure with those conditions that are mainly responsible for disability and a loss of working capacity. When economists have dealt with the problem they have been mainly concerned with the cost of medical care. As an example, in one of the latest studies Klarman (1965) scarcely mentions the economic consequences of disease, and in the bibliography containing 230 titles there are only two references to this subject. This lack of interest may be due to difficulties arising from the paucity of basic data. However, Weisbrod (1961) believes that it is important to attempt some quantification, even if it is imperfect, to illustrate what could be done to provide a basis for the allocation of resources in the health sector. The tropical diseases in particular have been greatly neglected; Wright et al. (1962) endeavoured to collect information of this kind but the data were few and mostly unauthoritative. Nevertheless, the infectious and parasitic diseases are mainly respon- sible for morbidity in the developing countries. Schistosomiasis has been selected as a model for * Presented at the Eighth International Congresses on Tropical Medicine and Malaria, Teheran, Iran, 1968. 'Former Chief, Laboratory of Tropical Diseases, Natio- nal Institutes of Health, Bethesda, Md., USA; Consultant, The Gorgas Memorial Institute of Tropical and Preventive Medicine, Washington, DC, USA. Present address: 6624 32nd Place, N.W., Washington, DC 20015, USA. the economic impact of a tropical disease. A number of estimates have been made of the losses resulting from this disease in localized areas. Farooq (1964), a pioneer in collecting baseline data, has presented a comprehensive review of the subject. In attempting to estimate the economic importance of schistosomiasis, one is immediately confronted with a varied array of factors for most of which there are no adequate measurements, Among these factors are geographical distribution, prevalence, intensity of infection, clinical gradients, morbidity and mortality, and transmission patterns, which are influenced by environmental conditions, the relative efficiency of the molluscan intermediate hosts, agricultural practices, and human behaviour. If facts were available, the economic impact of the disease could be estimated with some degree of accuracy in terms of the cost of medical care, public health programmes, the time lost from gainful occupation, and compensation for illness. At present, it is only possible to formulate reasonable projections on the basis of the conservative treatment of current data, such as they are. GEOGRAPHICAL DISTRIBUTION Schistosomiasis is known to be endemic in 71 countries or islands that have a total population of about 1 362 million people. The disease occurs in all countries of Africa with the exception of Lesotho 2933 - 559 3 560 W. H. WRIGHT (formerly Basutoland), in one of the Mascarene islands (Mauritius), in South-West Asia,1 in South- East Asia, and in the Americas. Former foci in Cyprus and Portugal have now disappeared. India is not in- cluded in the present summary, since it is believed that transmission has ceased in the single focus in Maharashtra State. PREVALENCE RATES AND TRANSMISSION PATTERNS Prevalence rates are exceedingly variable. Even in the same locality the rate in one village may be very different from that in a neighbouring village. In Zanzibar, for instance, Forsyth & Macdonald (1966) found that Schistosoma haematobium in- fections were highly focal, even in an apparently homogeneous population living within a short radius of one school. In a locality comprising 36 villages, 98.2% of the children in 9 neighbouring hamlets were infected while in the remaining 27 hamlets only 19.9% of the children were infected. In the delta area of Egypt, Farooq et al. (1966) found signi- ficant differences in the rates of infection with S. haematobium in different parts of a single village, fishermen, boatmen, farmers, and labourers having the highest rates. Variations in the infection rate were related to differences in religion, educational attain- ment, and domestic habits. In a 3-year study of 4 communities in the State of Pernambuco, Brazil, Barbosa (1965, 1966) found marked differences in the types of exposure, vector efficiency, prevalence rates, intensity of infection as measured by egg counts, and clinical involvement. The disease was most severe when transmission factors were at optimum levels. THE DISTRIBUTION OF SCHISTOSOMIASIS AND POPULATIONS EXPOSEX) COMPARED WITH POPULATIONS INFECTED Wright (1968) previously estimated the propor- tions of the population exposed and infected in most of the 71 countries where the disease occurs. In- fection rates were based on data compiled from various urine and stool surveys carried out mainly during the period 1955 64.2 In a few instances, the results of surveys made prior to 1955 were included. New material has been added, and the estimates have 1 As used in this article, the term " South-West Asia " refers to Democratic Yemen, Iran, Iraq, Israel, Lebanon, Saudi Arabia, Syria, Turkey, and Yemen. ' Wright, W. H. et al. (1966), unpublished WHO docu- ments Bilh/WP/66.3A and Bilh/WP/66.3B. been reevaluated critically in the light of more recent information. In no instance have infection rates been based on the results of immunological tests. Population estimates are for mid-year 1965, and were compiled by the United Nations (1966). The author is aware of the errors inherent in any attempt to derive an average rate of infection for any country. Available data for most countries comprise results of surveys conducted by many investigators employing different methods of exami- nation at different times. In many countries, pre- valence rates are virtually unknown and in other countries the data are extremely limited. Complete coverage exists in only a very few instances. In collating the data, a conservative approach has been adopted. Some comment should be made about the esti- mates for certain countries. For Egypt as a whole no infection rates have been published since those of Scott (1937). The geographical areas used by Scott have been taken as a basis and more recent pre- valence and population data have been applied to them.This procedure indicates a total of 13 852 916 infected persons in Egypt out of a population of 30083 419 in 1967 (United Arab Republic, 1967). This number is close to the estimate of Farooq (1967) of 14 million cases. Here, as for other coun- tries in Africa and parts of South-West Asia, the number of persons exposed and the number infected with S. haematobium and S. mansoni have been estimated separately but the numbers have been combined. S. mattheei has not been included in the compilation because it is usually concomitant with S. haematobium. Cases infected with S. inter- calatum have been omitted because of the relative rarity of this schistosome. In the almost complete absence of recent reports, it is impossible to arrive at any valid estimate of the number of cases of schistosomiasis in China. Wright (1950) estimated the total number of cases to be 32 777 630 on the basis of certain prevalence rates in the infected provinces and on census data for 1947. Maegraith (1958) stated that recent surveys had revealed over 11 million persons infected, with local infection rates ranging from 10% to 70%, and indicated that the working capacity of affected individuals was well below half the normal capacity. Hertwig & Oberdoerster (1960) stated that the official estimate indicated that 100 million persons were exposed and 10 million were infected. Until recently, late population data for the in- fected provinces were not available. Their population ECONOMIC IMPACT OF SCHISTOSOMIASIS56 in mid-year 1965 was estimated to be 335 252 000, as developed from 1957 census returns (US Congress Joint Economic Committee, 1967). Since 1947, there has been an increase of 35 % in the population of the endemic areas. In estimating a total of 24 741 000 cases, a generous allowance has been made for the results of the control campaign. The current estimates are 24% below those made by the present author (Wright, 1950), and are considered to be conservative from the view of the population increase of 35% since 1947. Schistosomiasis is no longer a public health problem in Japan. It was estimated by Komiya (personal communication, 1966) that in 1966 there were no more than 20 000 cases in that country. The extent of the disease in Laos, Cambodia, and Thailand is unknown. It appears to be more wide- spread than present evidence indicates but it is impossible at this time to estimate the number of infected persons in those countries. Data relating to the total population of the 71 countries in which schistosomiasis is endemic, together with the population exposed or infected, are given in Table 1. The total population of those countries is over 1 362 million persons, of whom over 592 million are exposed to the disease and over 124 million infected. Considering that this estimate is based mainly on prevalence rates derived from single stool or urine examinations, the total number of cases is probably much greater. The data are somewhat at variance with those previously presented by Wright (1968). The exposed population shows an increase of 238 000, and that infected an increase of 7 000. The differences are accounted for by the availability of new data for the populations of certain endemic areas, including the governates of Egypt, provinces of China, and states of Brazil and Venezuela. MORBIDITY AND) MORTALITY Reliable data on morbidity and mortality are almost completely lacking and those that are avail- able are therefore of no value in an analysis of the costs of disease. In 1963, schistosomiasis was notifiable in 39 countries, in 11 of which the disease is not endemic (World Health Organization, 1963a). Even in those countries that require reports, the data, when available, are far from complete and do not indicate the true morbidity and mortality rates. Table 2 shows regional morbidity and mortality data for 1957, as taken from the US National Academy of Sciences survey of tropical health Table 2. Schistosomiasis morbidity and mortality rates in certain regions in 1957 a Region Morbidity rate Mortality rateper 100 000 persons per 100000 persons Africa 64.1 1 South-West Asia 75.96 South Central and J 00.44 South-East Asia 0.71 the Americas 0.78 a Adapted from Wright et al (11962) and based on country public health reports and limited data from WHO. Table 1. World distribution of schistosomiasis: total regional population, population exposed, and population infected Region ~~Total Population Population ~~~population exposed infected Africa 308 021 000 226 102 740 91 200310 Mascarene Islands (Mauritius) 741 000 370 500 66 690 South-West Asia 87003000 10745050 2271 020 South-East Asia 868 531 000 337 051 500 25 223 650 the Americas 98339000 18199750 6 144130 totals 1 362635000 592469540 124905800 561 W. H. WRIGHT (Wright et al., 1962). The figures are based on the limited WHO data available at that time, supple- mented by information from the annual public health reports from many countries. The inade- quacy of these figures is shown by the fact that if they were applied to the total population of the 71 countries, there would be less than 600 deaths from schistosomiasis in the whole world in any one year. Further evidence of the inadequacy of reporting is provided by the fact that in 1966 only 3 127 cases of schistosomiasis were notified to the Pan American Health Organization (unpublished data). More cases were reported from New York City than from the whole of Brazil. ECONOMIC CONSEQUENCES Mushkin & Collings (1959) have divided the economic consequences of disease into 3 cate- gories-viz., resource use, resource transfer, and resource loss. Resource use represents costs that are a share of the nation's resources of manpower and materials for providing health services and the materials used by the services. Resource transfer includes costs represented by the transfer of income from the healthy to the sick in public and private efforts to mitigate the burdens of illness. Resource loss represents costs reflected in reduced national production of all goods and services. It is not possible at this time to estimate the cost of total resource use attributable to schistoso- miasis. Few countries have control programmes whose direct cost might be determined, but even with this information, the portion of the health services cost attributable to schistosomiasis could probably not be estimated. It is equally difficult to obtain data on the costs involved in resource transfer. While the costs of medical care in certain countries could no doubt be obtained, it would not be possible to separate the portion of such costs attributable to schistoso- miasis cases alone. In 16 countries in Africa for various years from 1955 to 1960 there was a total of 1 593 940 hospitali- zations for all causes (World Health Organization, 1963b). Reports were made mainly by government hospitals and in many instances are obviously in- complete. Only 11 159 (0.7%) of the hospitalizations were for schistosomiasis but the 16 countries are estimated to have had a total of 43.6 million infected individuals. These data are probably representative of the paucity of medical care data for schistoso- miasis. Estimates of resource transfer costs could be calculated with some degree of validity if social security coverage with compensation for illness applied to countries in which schistosomiasis is endemic. In fact, some such coverage is available in 52 of the 71 countries in which the disease occurs (US Social Security Administration, 1967). How- ever, adequate protection is provided only in South Africa and Japan and there is partial coverage in the Philippines. In most African countries, agri- cultural workers, i.e., those most frequently exposed to the disease, are excluded. Since it is impossible at present to estimate the costs of public health services and medical care in relation to schistosomiasis, only resource loss is left to be evaluated for the economic consequences of schistosomiasis. Even here, however, the data are tenuous and subject to misinterpretation and -miscalculation. Estimation of degree of disability For estimates of total and partial disability incurred as a result of schistosome infection, autho- ritative calculations have been accepted when they are available. Elsewhere, a careful study has been made of current data concerning clinical gradients, and estimates have been derived from such material. For Egypt and certain other countries in Africa, the data of Farooq et al. (1966) have been used; i.e., severe clinical involvement in 2.1 % of cases and moderate involvement in 30.5 % for both S. haema- tobium and S. mansoni. For S. haematobium alone the rates were 2.5% and 35.3 %, and for S. mansoni 1.4% and 13.5 %, respectively. For other countries in Africa, where the intensity of infection appears to be lower than in the Nile Delta area, a compensatory arbitrary reduction has been made in the above- mentioned rates. These standards are not completely realistic since Farooq et al. (1966) have noted that the majority of cases with irreversible effects, and therefore those in the severest category, cannot usually be detected without recourse to detailed clinical, pathological, and radiological techniques. However, the lack of such data does not invalidate the standards employed but only emphasizes their conservative nature. For South-West Asia, the above standards have been modified in some instances, particularly for Syria and Iran, where S. haematobium infections are less severe. In Iraq, where the severity of S. haemato- 562 ECONOMIC IMPACT OF SCHISTOSOMIASIS 563 bium infections is more marked than in other coun- tries of the region, it is estimated that 5% of infected persons are totally disabled and 50% moderately disabled. In S. japonicum infections in South-East Asia,1 the standards employed for China were 3% totally dis- abled and 25% partially disabled and for Japan 0.5% totally disabled and 10% partially disabled; for the Philippines, 4% of symptomatic cases were classified as severe or very severe and 39% as moderate, in accordance with the findings of Persigan et al. (1958). For S. mansoni infections in the Americas, clini- cal gradient data for Brazil have been derived from the findings of Kloetzel (1964), Cheever (1968), and Barbosa (personal communication, 1968), which indi- cate that 2% of cases are totally disabled and 25% partially disabled. The disease is less severe in other parts of the Americas, and the standards used for other countries are accordingly lower. In all instances, severe cases are considered to be completely incapacitated or soon to become so. In any one year such patients are considered to have contributed nothing to the gross national product (GNP). The moderately severe cases are considered to have a reduced productive capacity of 10%. The economic effect of deaths from schistosomiasis is not considered, since one cannot assign a mone- tary value to a human life. However, death during the active years deprives the economy of a productive asset. If a patient dies early in his productive career, the nation loses the net amount of material contribution for much of the patient's theoretical lifespan. In certain countries, schistosomiasis occurs in such limited areas or in such a mild form that it is obvious that little or no disability results from the disease. Countries in this category include Antigua, Israel, Lebanon, St Lucia, and Turkey. Countries for which estimates of economic loss cannot be made because of insufficient data are Cambodia, Celebes, Laos, St Martin, and Thailand. Estimation ofeconomic lossfrom decreased productive capacity In order to make a worldwide estimate of eco- nomic loss from the decreased capacity for pro- duction, some common denominator must be used. For this purpose, the per caput Gross National Product (GNP) in US dollars, as published in the 1 As used in this article, the term " South-East Asia " refers to Cambodia, Celebes, China, Japan, Laos, the Phi- lippines, and Thailand. World Bank Atlas (1967), has been employed. The GNP represents the sum of incomes accruing to factors of production after the deduction of direct taxation. National income represents the sum of incomes before the deduction of taxation. In an international study of health expenditure, Abel- Smith (1967) preferred to employ GNP; his pro- cedure has been followed here. Estimations of GNP entail certain margins of error. The income and output data in many countries leave much to be desired, and problems of inter- pretation arise. The conversion of sums in various national currencies into US dollars is also liable to distortion. This is particularly so for China, where the convertibility of the yuan into US dol- lar values has no fixed basis, and China's GNP has fluctuated widely within the past 15 years. Estimates of the extent of disability caused by schistosomiasis in the various geographical areas are given in Table 3. The total number of persons considered to be totally incapacitated is 2 650 260, and the total number believed to be partially dis- abled is 24 782 805. Table 4 shows that the esti- mated annual loss from total disability amounts to US $270 794 100 and that the annual loss from partial disability is US $370 996 030. The total annual economic loss from reduced productivity throughout the world is estimated to be US $641 790 130. Since this sum is based on minimum prevalence rates, the real loss is undoubtedly much higher. The estimates for Africa are some 75 million below the figure previously given by Wright (1968). In the former estimates the average GNP for Africa (except Egypt) was employed. The present Table 3. The number of persons estimated to be totally disabled and partially disabled by schistosomiasis No. of persons No. of personsRegion totally disabled partially disabled Africa 1 735 983 16 327 200 Mascarene Islands (Mauritius) 1 400 20304 South-West Asia 43 622 639 406 South-East Asia 749 930 6 261 350 the Americas 119 325 1 534 545 totals 2 650 260 24 782 805 W. H. WRIGHT Table 4. Estimated annual costs of schistosomiasis resulting from lowered productivity in totally and partially disabled infected persons Estimated loss from Estimated loss from Total lstimated Region total disability partial disability economic lossdfrom (US $) (US $) (US $) Africa 173 037 570 272 829 375 445 866 945 Mascarene Islands (Mauritius) 308 000 447 480 755 480 South-West Asia 6 711 930 9 815 345 16 527 275 South-East Asia 64 305 550 53 838 125 118 143 675 the Americas 26 431 050 34 065 705 60 496 755 totals 270 794 100 370 996 030 641 790 130 compilations are derived from the use of the GNP for each country and are therefore more accurate. An average GNP obviously introduces certain dis- tortions in the net result. It should be emphasized that the estimates quoted here are based on available data, and that these data are markedly inadequate; for this reason, the calculations are believed to be on the conserva- tive side. It is hoped that this attempt to provide a partial quantification of the economic impact of a tropical disease will inspire investigators to obtain data that may eventually provide the basis for more accurate evaluations of economic losses caused by disease. R]SUMm EXAMEN DES REPERCUSSIONS tCONOMIQUES DE LA SCHISTOSOMIASE En depit des pertes colossales occasionnees par les maladies, on s'est peu pr6occupe dans les dernieres annees d'6valuer l'importance de ce fardeau 6conomique. Le cas des maladies tropicales, notamment, n'a guere retenu l'attention et pourtant les maladies infectieuses et para- sitaires sont la cause principale de morbidite dans les pays en voie de developpement. On a choisi la schistosomiase comme modele pour l'etude des consequences economiques d'une maladie tropicale. Endemique dans 71 pays ou territoires comptant une population totale d'environ 1 milliard 362 millions d'habitants, cette affection atteint approximativement 125 millions d'individus. Ce chiffre, obtenu apres un examen approfondi de toutes les donnees disponibles, est bas6 sur les taux de prevalence 6tablis le plus souvent a la suite d'un examen unique de selles ou d'urine. Le nombre reel des cas est sans nul doute beaucoup plus 6lev6. Les cons6quences 6conomiques de la maladie peuvent etre class6es en trois categories. On ne tient pas compte ici des frais de fonctionnement des services medicaux relatifs a la lutte contre la schistosomiase ni des sommes depens6es pour les traitements. Seules sont prises en consideration les pertes &conomiques resultant d'une pro- duction diminu6e de biens et de services. Pour estimer l'invalidit6 totale ou partielle caus6e par la schistosomiase, on a utilise, lorsqu'ils existaient, les taux provenant de sources dignes de foi. Ailleurs, on s'est fond6 sur les donnees cliniques pour 6valuer les pourcentages d'incapacite. Dans tous les cas, les infec- tions graves sont consider&es comme provoquant une inaptitude complete au travail, effective ou probable a breve echeance. Les personnes qui en sont atteintes n'apportent aucune contribution it l'conomie de leur pays. Les sujets souffrant d'une infection plus l6gere sont consideres comme ayant une capacit6 de production r6duite de 10%. On estime que, dans le monde, 2 650 260 personnes sont atteintes d'une incapacit6 totale et 24 782 805 d'une incapacit6 partielle. Dans certains pays, I'affection n'est pas d'une gravit6 telle qu'elle diminue l'aptitude du malade au travail. Pour calculer les pertes economiques imputables a la schistosomiase, on a utilis6 un commun denominateur, c'est-i-dire le produit national brut par habitant (1967) exprim6 en US dollars. Le montant annuel du manque it gagner r6sultant d'une productivit6 diminu6e des per- 564 ECONOMIC IMPACT OF SCHISTOSOMIASIS 565 sonnes atteintes d'une incapacite totale ou partielle est estime a S445 866 945 pour l'Afrique, S755 480 pour Maurice, 516 527 275 pour l'Asie du Sud-Ouest, 118 143 675 pour l'Asie du Sud-Est et 560 496 755 pour les Ameriques. Le total mondial est de $641 790 130. Ces chiffres sont evidemment tres au-dessous des pertes econo- miques reelles puisqu'ils n'incluent ni les sommes dipen- s&es pour 1'execution des programmes de sante publique et les soins medicaux ni les indemnit6s pour maladie. L'auteur souligne qu'il s'agit Ra d'une evaluation prudente basee sur des donnees qui sont loin d'etre completes. REFERENCES Abcl-Smith, B. (1967) An international study of health expenditure and its relevancefor healthplanning, Geneva, World Health Organization (Public Health Papers, No. 32) Barbosa, F. A. S. (1965) Morbidade na esquisotossomose. 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