Schistosomiasis mansoni in areas of low transmission: epidemiological characterization of Venezuelan foci

Abstract

Severe schistosomiasis is a rare event in Venezuela nowadays, after a successful national campaign by the Schistosomiasis Control Program. Unfortunately, this program has practically disappeared, and snail surveillance in field is not a priority, anymore. Thus, schistosomiasis has become a neglected disease in this country. However, surveys in different populations from the endemic area have shown particular epidemiological features described herein. In five communities we evaluated 2,175 persons and searched for the presence of Biomphalaria glabrata snails. Some markers were used for classifying schistosomiasis foci: mean age of the persons with Schistosoma mansoni eggs in the stools, serological tests, presence of B. glabrata snails, and intensity of infection. Places without B. glabrata snails and with few schistosomiasis cases were defined as "past transmission sites"; a site with abundant snails but few cases was defined as "potential risk"; "new transmission" foci were characterized by the presence of infected snails and young people passing eggs in the stools. A "re-emergent" focus has shared these last features, showing in addition a place where schistosomiasis had been reported before. Recent evidences of active transmission with the increasing dispersion of B. glabrata snails, point out the necessity for the re-establishment of the Schistosomiasis Control Program in Venezuela

Comparison of Schistosoma mansoni Soluble Cercarial Antigens and Soluble Egg Antigens for Serodiagnosing Schistosome Infections

“…Insensitivity is another serious defect of egg detection methods of diagnosis, especially of the intestinal schistosome infections [3], [4] and many light infections are missed because of the absence of eggs in the small volumes of excreta that can be routinely examined microscopically [5]–[9] These limitations impose significant constraints on current control initiatives [10], [11] Considerable effort has been expended in the effort to develop immunodiagnostic tests that are an improvement on microscopical parasitology. It has been argued that methods to detect circulating or excreted schistosome antigens are desirable because they are likely to reflect active infection most accurately.…”

Venezuela and its rising vector-borne neglected diseases

“…In Venezuela, most of the cases are found in the northern coastal part of the country [34, 35]. Mass drug administration with praziquantel has had an impact on reducing the prevalence in many endemic communities [36], but it is believed that, in some areas, there has been an increase in schistosomiasis transmission due to depletion of surveillance and control activities [35], while urban foci of schistosomiasis may also remain [37]. …”