Control of schistosomiasis in Guayama and Arroyo, Puerto Rico*

Bull. Org. mond. Santel 1970, 42, 151-156 Bull. Wld Hlth Org. Control of Schistosomiasis in Guayama and Arroyo, Puerto Rico * WILLIAM R. JOBIN,' FREDERICK F. FERGUSON 2 & JUAN R. PALMER 3 In 1953, a programme to control schistosomiasis mansoni was started in Guayama and Arroyo, Puerto Rico, employing, first, chemical and, later, both biological and chemical methods to control Biomphalaria glabrata, the snail host ofSchistosoma mansoni. Sodium pentachlorophenate was the molluscicide, and an ampullarid snail, Marisa cornuarietis, was used for biological control in ponds and reservoirs. In addition some chemotherapy was given to infected persons. The prevalence of intestinal schistosomiasis was measured annually, sampling about one-third of the 6-year-old population in Guayama and Arroyo and in Caguas, an untreated area. Costs of the programme and the results are discussed in relation to similar projects in other parts of Puerto Rico. In Guayama and Arroyo the prevalence of schistosomiasis reached zero in 6-year-olds by 1966 despite the persistence of the disease in a nearby untreated area. Although this decline appeared related to the control effort, it is noted that a large decline also occurred in the untreated area, suggesting the influence of other factors such as economic development or improvements in sanitation. Successful control of schistosomiasis mansoni has been achieved in Vieques Island and Patillas, Puerto Rico, and from these pioneering efforts it was pos- sible to predict the cost for an island-wide effort to control this parasitic disease (Ferguson, Palmer & Jobin, 1968; Palmer et al., 1969). Concurrent with the Vieques and Patillas projects, a control pro- gramme was started in 1953 in Guayama and Arroyo, two municipalities west of Patillas (Fig. 1). The purpose of the present report is to describe the control of the snail host, Biomphalaria glabrata, in Guayama and Arroyo and subsequent changes in the prevalence of schistosomiasis, and to assess the over-all significance of the programmes in Vieques, Patillas, Guayama, and Arroyo. Results from sub- sequent control projects in Aibonito and Naguabo and of a preventive campaign in the Lajas Valley (Fig. l) will be analysed later. * From the Bureau of Environmental Sanitation, Puerto Rico Department of Health, and the Tropical Disease Sec- tion, Ecological Investigations Program, National Commu- nicable Disease Center, Health Service and Mental Health Administration, Public Health Service, US Department of Health, Education, and Welfare, San Juan, Puerto Rico. 1 7 Philip Lane, Foxboro, Mass., USA. 2 Tropical Disease Section, Ecological Investigations Pro- gram, National Communicable Disease Center, Box 52, San Juan, Puerto Rico 00902. Requests for reprints should be sent to this address. 3Bureau of Environmental Sanitation, Puerto Rico Department of Health, Santurce, Puerto Rico. MATERIALS AND METHODS Guayama and Arroyo are municipalities on the south coast of Puerto Rico whose economies are based on cultivation of sugar cane (Tables 1 and 2). The flat coastal areas are irrigated by the Patillas and Guamani canals which originate from the Patillas and Carite reservoirs to the north (Fig. 2). Arroyo is much smaller than Guayama, and snail control in the two municipalities was carried out by a single crew consisting of a vector-control inspector, a foreman, and 5 labourers with a vehicle. The control method consisted at first of snail con- trol with sodium pentachlorophenate applied to flow- ing water at 6 mg/l for 24 hours and to standing water at 10 mg/l (Palmer et al., 1969). After 1956, the ampullarid predator snail Marisa cornuarietis was also put into the Patillas and Carite reservoirs and into the hundreds of night-storage reservoirs found throughout the cane-fields; these were seeded at loading rates of about 0.3 snail per m2 of habitat (Ruiz-Tiben, Palmer & Ferguson, 1969). In the final years after 1963, the control work consisted primarily in ditching to eliminate snail habitats and reseeding M. cornuarietis as needed to keep the reservoirs stocked. Although the programme was designed primarily for snail control, it was learned some years later that stibophen chemotherapy was given by physi- 2461 - 151 - W. R. JOBIN, F. F. FERGUSON & J. R. PALMER FIG. I AREAS WITHIN THE PUERTO RICO PROGRAMME FOR SCHISTOSOMIASIS CONTROL (SHADED) AND THE UNTREATED AREA, CAGUAS *A L A / C O C EA N CAR/IBB EA N S E A TABLE I HUMAN POPULATION CHARACTERISTICS FOR 7 MUNICIPALITIES IN PUERTO RICO DURING 1950 AND 1960 a Population Municipality 1091950 1960 Treated: Aibonito 18191 Arroyo 12 936 Guayama 32 807 Naguabo 21 019 Patillas 18 851 Vieques 9 228 Subtotal 113 032 Untreated: Caguas 60132 Puerto Rico c 2 200 000 18 360 13 315 33 678 17 195 17 106 7 210 106 864 65 098 2 300 000 Population change, 1950 to 1960 +0.9 % +2.9% +2.7% -18.2 % -9.3% -21.9 % -5.5 % +8.3 % +6.3% Population Median family density income in 1960 in 1960 (persons/kmi2) (US $) 229 963 343 861 200 1 140 128 890 138 527 54 b 921 157 433 265 1 491 1 268 a 0 ii CULEBRA VIEQ>UES a Data from the 1960 US census. b Vieques is the least densely populated municipality in Puerto Rico. c The estimated total population in 1969 was 2.7 million. - 152 SCHISTOSOMIASIS CONTROL PROGRAMME IN PUERTO RICO TABLE 2 GEOGRAPHICAL CHARACTERISTICS OF 7 MUNICIPALITIES IN PUERTO RICO Area Average ElevationMunici(pality rkin) annual aboverainfall a (cm) sea level b (m) Treated: Aibonito 80 152 600 Arroyo 39 152 10 Guayama 168 127 50 Naguabo 19 229 18 Patillas 122 203 22 Vieques 111 115 15 Untreated: Caguas 150 203 74 a Data from Bogart, Arnow & Crooks (1964). b Elevation at city hall. cians in many parts of Puerto Rico from 1954 until 1957, when its use was actively discouraged by the health authorities. Details of the treatment are not available, nor were the effects adequately assessed, although the results were generally considered unsatis- factory. As many as 300 persons may have been treated yearly in each of the municipalities men- tioned. The effect of the control programme on the pre- valence of schistosomiasis was measured by an annual examination of single faecal specimens from first-grade schoolchildren, using a formol-ether con- centration technique to find ova of Schistosoma man- soni (Ritchie et al., 1960); about one-third of the 6-year-old population was sampled. The prevalence of schistosomiasis in Caguas, an untreated municipa- lity in central Puerto Rico, was similarly measured. FIG. 2. GUAYAMA AND ARROYO, PUERTO RICO, SHOWING CONTOURS, WATERBODIES, AND TOWNS 1 24S 4 7KM C A R I B B E A N S E A WNO 91764 K . 153 W. R. JOBIN, F. F. FERGUSON & J. R. PALMER RESULTS An analysis of the cost of snail control during 1955, a typical year in the active phase of the pro- gramme before biological control was introduced, showed that the cost for molluscicide was US $880, about 11% of the annual project cost of $8298. Since most of the chemical was applied at 10 mg/l to standing water, then the cost for mollusciciding was about $7.80 per 100 m3 of treated water. Marisa cornuarietis was introduced to the area in 1956 and used as a biological control agent in the numerous night-storage ponds which were too large for the economical use of molluscicides. By 1960 the B. glabrata populations were reduced from their original wide distribution throughout Guayama and Arroyo to a single habitat in Puente de Jobos, west of the town of Guayama and close to the Caribbean. Because of the virtual disappear- ance of the snails the project was put on maintenance status in 1963, and the crew began to work part- time in other municipalities west of Guayama. The crew spent at least 2 days a week in Guayama and Arroyo inspecting for the reappearance ofB. glabrata. The prevalence of schistosomiasis among 6-year- olds in Guayama and Arroyo declined from a maxi- mum of 20% in Guayama and 8% in Arroyo during 1954, to nil in both projects by 1966 (Table 3). The prevalence in the untreated area, Caguas, declined from 11% in 1954 to 0.5% by 1965 but increased again to 1.2% in 1966. Some of the reasons for the improvement in Caguas can be inferred from the population changes (Tables 1 and 3). Caguas was rapidly becoming urbanized and was improving economically to a level above the average for Puerto Rico, while the situation in Guayama and Arroyo remained relatively unchanged and the incomes were below the Puerto Rican average (Table 1). Other factors such as the unregulated use of stibophen for chemotherapy and fluctuations in snail populations cannot be quantified but may have been important (Ritchie, Radke & Ferguson, 1962). DISCUSSION The cost for applications of molluscicide in Guayama and Arroyo was slightly lower than the costs in Vieques or Patillas, probably because of TABLE 3 PREVALENCE OF SCHISTOSOMIASIS AMONG 6-YEAR-OLDS IN GUAYAMA, ARROYO, AND CAGUAS, PUERTO RICO, 1953-66 a Guayama Arroyo Caguas Positive No. % 16.2 20.1 8.7 3.5 6.2 6.5 2.6 1.7 1.6 1.8 0.9 1.3 1.0 0.0 No. tested 0 124 106 66 111 137 145 123 158 238 226 201 238 260 Positive No. tested - No. % 0 10 2 4 2 2 2 5 2 1 3 0 0 8.1 1.9 6.1 1.8 1.5 1.4 4.1 0.6 0.8 0.4 1.5 0.0 0.0 94 274 288 504 590 525 246 663 727 831 1 079 1 147 1 302 1 425 Positive No. 9 31 19 31 32 26 10 21 16 13 14 6 17 9.6 11.3 6.6 6.2 5.4 5.0 4.1 3.2 2.2 1.6 1.3 0.5 0.5 1.2 a Results are for single faecal examinations for Schistosoma mansoni ova. The populations of 6-year-olds in Guayama, Arroyo, and Caguas in 1960 were 1056, 417, and 1728, respectively. Year 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 No. tested 308 249 298 256 321 399 495 352 506 498 572 555 519 704 50 50 26 9 20 26 13 6 8 9 5 7 5 0 154 SCHISTOSOMIASIS CONTROL PROGRAMME IN PUERTO RICO better roads (Palmer et al., 1969; Ferguson, Palmer & Jobin, 1968). The experience with biological con- trol showed that it is much cheaper than chemical control. M. cornuarietis displaced B. glabrata in the main reservoirs and in almost 100 night-storage ponds at a yearly cost per pond of $5.47 for har- vesting adult snails from natural habitats and seeding them in the ponds (Ruiz-Tiben, Palmer & Ferguson, 1969). Since the average pond contained 5000 m3 of water, this works out at a yearly cost of $0.11 per 100 m3 for biological control, compared with $7.80 per 100 m3 for 1 chemical application per year. These cost figures represent the cost for control of the snails, not for control of the disease, since many socio-economic changes and some epidemio- logical changes undoubtedly occurred in the 3 muni- cipalities over the 14 years of the programme. Such changes were difficult to monitor and impossible to control. The over-all significance of the control programme in Puerto Rico can be assessed by summarizing the prevalence data from Guayama and Arroyo with data from Vieques Island and Patillas, and compar- ing these with the data from Caguas, the untreated municipality (Fig. 1). The combined summary shows that the rate in 1954 among 6-year-olds was the same in the 4 treated areas taken together as in Caguas, the untreated area (as may be calculated from Table 4). However, by 1960 the over-all preva- lence in the treated areas was appreciably lower than in Caguas, and by 1966 it came close to zero. It cannot be concluded that the success of the programme was due to snail control alone, since improvements in sanitation and economic develop- ment undoubtedly played a part in the decline of the disease. Furthermore, the control programme might have taken much longer to achieve a significant reduction in prevalence if other conditions in Puerto Rico had not been favourable. None the less, the experience proved that the disease could be controlled by simple methods and at a cost within the budgetary possibilities of the TABLE 4 PREVALENCE OF SCHISTOSOMIASIS AMONG 6-YEAR-OLDS IN 4 TREATED MUNICIPALITIES AND AN UNTREATED MUNICIPALITY, PUERTO RICO a Municipality 1954 1960 1966 Treated: Arroyo 10/124 5/123 0/260 Guayama 50/249 6/352 0/704 Patillas b 13/203 1/227 2/405 Vieques c 11/163 1/73 0/153 Untreated: Caguas 31/274 (11.3%) 21/663 17/1 425(3.2 %) (1.2 %) a Number positive/total tested. b Data from Palmer et al. (1969). c Data from Ferguson, Palmer & Jobin (1968). Puerto Rico Department of Health. Subsequently, the schistosomiasis control programme was expanded to other parts of the island, and finally on 1 July 1968 an island-wide programme was initiated. Lest this report be a source of over-optimism, it is worth noting that the disease was first described in Puerto Rico in 1904, that it was 50 years before even a pilot control programme was started, that the pilot programme lasted 15 years, and that it will probably be another 10 years before the problem can be said to have been eliminated. This 75-year episode can hardly be called a triumph in an age when a programme to put a man on the moon took 9 years from conception to completion. At the present costs, control of schistosomiasis is practical only in small and relatively wealthy areas such as Puerto Rico. A great deal of work is necessary on cheaper control methods, on safe drugs and on better epidemiological techniques before this disease can be controlled in the rest of the tropics. ACKNOWLEDGEMENTS Credit for the effort represented by the 14 years of disease control must be given to Mr Guillermo Col6n Atilano, the inspector in charge of the Guayama-Arroyo project, and to his labourers who accomplished a job that few considered possible. The project was a joint venture of the Public Health Service of the US Depart- ment of Health, Education, and Welfare and the Puerto Rico Department of Health. l55 156 W. R. JOBIN, F. F. FERGUSON & J. R. PALMER RESUMt LUTTE CONTRE LA SCHISTOSOMIASE A GUAYAMA ET ARROYO, PORTO RICO A Porto Rico, un programme de lutte contre la schis- tosomiase a Schistosoma mansoni a ete lanc6 en 1953 dans deux municipalites du sud du pays, Guayama et Arroyo. 11 s'agissait d'ameliorer directement 1'etat de sante de la population en reduisant a zero le taux de prevalence de la maladie chez les enfants de 6 ans. On a avant tout cherche 'a detruire les mollusques en utilisant soit le pentachlorophenate de sodium, soit l'action du mollusque predateur Marisa cornuarietis, mais le recours a la chimiothdrapie et les progres accomplis en matiere d'hygiene du milieu et d'education sanitaire ont certai- nement contribue au succes du programme. En 1966, le but etait de toute evidence atteint et le cout des opera- tions restait dans des limites raisonnables. Le programme visait un autre objectif qui etait d'eva- luer scientifiquement les avantages et le couit de l'emploi du pentachlorophenate de sodium pour detruire le mol- lusque Biomphalaria glabrata et reduire la prevalence de la schistosomiase. Ce but n'a ete que partiellement atteint, car il est difficile de suivre et impossible d'empecher les nombreux changements socio-6conomiques et epidemio- logiques qui n'ont pas manque de se produire au sein des municipalites considerees pendant les 14 annees oiu se sont deroulees les operations. Le chiffre de S7,80 par 1oo m3, qui represente le cofit annuel du traitement chi- mique des habitats des mollusques, n'est qu'approxima- tif. En outre, si la situation economique generale ne s'etait pas amelioree, il aurait fallu plus longtemps pour mener le programme a bien. REFERENCES Bogart, D. B., Arnow, T. & Crooks, J. W. (1964) Water resources of Puerto Rico: a progress report, Wash- ington, D.C., US Government Printing Office, p. 68 Ferguson, F. F., Palmer, J., and Jobin, W. R. (1968) Amer. J. trop. Med. Hyg., 17, 859-863 Palmer, J., Colon, A., Ferguson, F. F. & Jobin, W. R. (1969) Publ. Hlth Rep. (Wash.), 84, 1003-1007 Ritchie, L. S., Lin, S., Moon, A. P., Frick, L. P., Wil- liams, J. E., Asakura, S. & Hishinuma, Y. (1960) Amer. J. trop. Med. Hyg., 9, 444-449 Ritchie, L. S., Radke, M. G. & Ferguson, F. F. (1962) Bull. Wld Hlth Org., 27, 171-181 Ruiz-Tiben, E., Palmer, J. R. & Ferguson, F. F. (1969) Bull. Wld Hith Org., 41, 329-333