Occurrence of Schistosoma mansoni in Puerto Ricans

Abstract

ATA FROM diagnostic surveys on the extent of Schistosoma mansoni infections in Puerto Rico have, been available since the disease was first detected in Mayagiiez in 1904 (1). These data, valuable in epidemiologic studies and control planning, are evaluated in this paper as a means of estimating the current sta,tus of the disease in Puerto Rico. Information available for this evaluation includes (a) stool examination data derived from the direct s'aline smear technique (used until about 1938) and data derived from a variety of egg concentrating methods (used during the past 25 years), (b) rectal biopsy da,ta,, (c) autopsy data,, and (d) serologic and intradermal test data. The advantages or disadvantages of these diagno,stic techniques are only briefly mentioned. A definitive summary has been published by Kagan and Pellegrino (2). There is a growing need for a diagnostic method that is readily adaptable t,o procedures for evaluating schistosomiasis control programs. Data from tests on fecal samples taken from 1904 to 1955 were summarized in May 1955. At this time a total of 127 such diagnostic investigations had been performed in Puerto Rico. Of 82,212 single fecal tests, 3,764 (5 percent) were positive for S. mansoni (3). Kagan and associates noted that approximately 50 to 60 percent of the true incidence is detected on examination of a single stool sample from each subject (4). Significantly, current infection can be proved only by demonstrated passage of viable fecal eggs or by detection of eggs in rectal biopsy material. Survey data were derived from both simple saline fecal smear and egg concentration techniques. Additional surveys conducted since 1955 brought the total to 139 in 1963 (personal data). At this time 9,047 (7 percent) of 126,244 fecal specimens were positive. A total of 120 fecal surveys have been made by the Puerto Rico Department of Health in 9 experimental control projects, which were started during the period of 1952-58 in nearby Vieques Island and 8 valleys in Puerto Rico. Selection of these areas was based on the kind of Australorbis glabratus habitat. Primary surveys in these control projects were made on single fecal samples from the majority of the first-grade school children (aged 6 to 10 years) in each watershed. The highest infection rates reported in each project development period are shown in table 1. In the Lajas Valley project an attempt is being made to prevent the spread of the disease in an irrigated basin. Data from principa,l studies which used a single fecal exa,mination are summarized for the years from 1904 to 1959 in table 2. Both simple and refined test methods were reported by the authors. Of 240,605 single fecal tests, 10 percent were positive for S. mansoni. Repeated fecal testing of persons suspected of being infected is known to raisie the index. For example, 74 percent of 430 such patients showed positive results when tested from 1 to 12 times at hospitals in San Juan (5). The overall percentage of persons with positive results (table 2) is relatively low in comparison with data obtained by other techniques cited below. The range of percent positive was 7 to 30. KopDr. Ferguson is chief of the Puerto Rico Field Station, Biology/Chemistry Section, Technology Branch, Communicable Disease Center, Public Health Service, San Juan, Puerto Rico.