Ace-specific decrease in seroprevalence of schistosomiasis in Puerto Rico

In our previous work, we reported the first systematic, island-wide, serolo gic survey for schistosomiasis in Puerto Rico in 40 years. In that study, a pproximately 3,000 serum samples from the 76 municipalities comprising the island of Puerto Rico were tested for the detection of antibodies to S. man soni microsomal antigens by the Falcon assay screening test-enzyme-linked i mmunosorbent assay (FAST-ELISA(TM)) and those positive were confirmed by an enzyme-linked immunoelectrotransfer blot (EITB). The highest EITB positivi ty was found in 17 municipalities, which comprised 48% of all seropositive samples. An additional finding was that 10% of the 215 EITB-positive sample s were from individuals 25 years or younger and were for the most part of r esidents from the high seroprevalence areas. Thus, for this study we focuse d on 766 individuals 25 years of age or younger (45.5% males and 54.4% fema les), two-thirds of which were from 10 municipalities with the highest EITB seropositivity, and one-third from the 10 municipalities with the lowest E ITB seropositivity found in our previous study. Of all samples, the results showed an overall FAST-ELISA positivity of 11.6%, with males similar to fe males (12.6 versus 10.7%, respectively). Confirmation by EITB was only 1.8% , with a males three-fold higher than females (3% versus 0.7%). When seropo sitivity was measured by age in five-year increments, a clear age-specific decrease in seropositivity was observed. Thus, by FAST-ELISA, 16.7% of the 21-25-year-old age group was positive, decreasing to 14.6%, 9.9% 7.9%, and 9.3% in the 16-20-, 11-15-, 6-10-, and 1-5-year-old age groups, respectivel y. Confirmatory EITB showed even more impressive results: 4.7%, 2.6%, 1.2%, 0.7%, and 0% in the same age brackets. With regard to the high prevalence municipalities, only four of 10 (11 of 228 = 4.8%) had confirmatory EITB-po sitive samples and most were from municipalities of the Rio Grande de Loiza River basin and tributaries. The male to female positivity ratio was 4:1. Of the low prevalence municipalities, only single positive cases (by EITB) were found in three disperse municipalities. These results support the conc ept that there has been little transmission of S. mansoni in Puerto Rico du ring the first half of the 1990s and confirms anecdotal comments of local p hysicians who have seen virtually no new infections during the past three y ears. This makes the documentation of eradication of schistosomiasis from P uerto Rico feasible, a goal that should be set as being before the 100th an niversary of its discovery on the island by Isaac Gonzalez-Martinez in 1904 .