Parasitol Res (2006) 98: 545–549 DOI 10.1007/s00436-005-0047-1 ORIGINAL PAPER Nelmar García . Gina Isturiz . Silvia Aular . Renzo Nino Incani The efficacy of human schistosomicide treatment may depend on the rate of transmission Received: 6 August 2005 / Accepted: 27 September 2005 / Published online: 18 January 2006 # Springer-Verlag 2006 Abstract The efficacy of different treatment protocols in humans infected with Schistosoma mansoni at sites with different transmission conditions was evaluated by the disappearance of anti-worm intestine IgM antibodies in an indirect fluorescence antibody test (IgM-IFT) and anti-egg antibodies in the circumoval precipitin test (COPT). Patient sera coming from sites of active low transmission (ALT), active high transmission (AHT) and low interrupted transmission (LIT) from Venezuela were studied. Chemo- therapy protocols were (1) ALT, 60 mg/kg praziquantel (Pzq60); (2) AHT, one dose of 40 mg/kg Pzq followed by one dose of 20 mg/kg oxamniquine for one group and one dose of 40 mg/kg Pzq alone for the other group; (3) LIT, one dose of 40 mg/kg Pzq repeated every 3 months up to three doses. Cure rates occurred mostly between 3 and 12 months with the exception of Pzq60-ALT where it was evident before 3 months. Higher cure rates were evident in both places of low transmission (ALT and LIT) and the lowest in the AHT regardless of the treatment protocol. Cure was more evident with COPT compared to IgM-IFT. The rate of serological cure appears then to depend on the previous state of transmission. The differential cure rate evaluated by both techniques is probably due to the persistence of antibodies against antigens in different stages of the parasite. Introduction Schistosomiasis remains as one of the most prevalent parasitic infections having significant public health con- sequences. While the distribution of schistosomiasis has changed over the last 50 years, and there have been successful control projects, the number of people infected or at risk of infection has not been reduced (Savioli et al. 1997). It is estimated that 200 million people are infected, of whom 120 million are asymptomatic and 20 million have severe disease (Chitsulo et al. 2000). In Venezuela, the epidemiological characteristics of schistosomiasis man- soni have changed from high to low prevalence. As a consequence, near 80% of infected individuals harbour low worm loads (<100 eggs/g of faeces), the majority being asymptomatic. Under these conditions, the coprologic detection of eggs (Kato–Katz) becomes inefficient (Incani 1987; Alarcón de Noya et al. 2002). Serological tests like enzyme-linked immunosorbent assay (ELISA) with crude extract of adult worms or eggs have good sensitivity, but there is cross-reaction with sera of patients infected with other intestinal nematodes, a limitation that was improved by oxidation of carbohydrates responsible for the cross- reactivity (Alarcón de Noya et al. 2000). Nevertheless, the persistence of antibodies after an effective treatment con- stitutes a limiting factor. The alkaline phosphatase immu- noassay (Pujol and Cesari 1990) is highly specific (100%) and sensitive (89%) (Alarcón de Noya et al. 1997), but, as other immunoenzimatic tests based in antibodies detection, it remains positive after cure. In spite of the labour and cost, the circumoval precipitin test (COPT) has remained a confirmatory test due to the high sensitivity and specificity, with additional advantage of antibody reduction several months after treatment (Mott and Dixon 1982). The immunofluorescence test for the detection of IgM anti- bodies against Schistosoma mansoni gut associated poly- saccharide antigens (IgM-IFT) on adult worm paraffin sections showed high sensitivity (97.7%) for diagnosis of both acute and chronic schistosomiasis (Silva et al. 1992) and good specificity (98.2%) (Kanamura et al. 1998), and there is also reduction in antibody titres after treatment Financial support was from WB-UNDP-VEN/92/002, CONICIT- Venezuela S1-2650, CDCH, Universidad de Carabobo, Venezuela- 2002-007. N. García . G. Isturiz . S. Aular . R. N. Incani (*) Departamento de Parasitología, Facultad de Ciencias de la Salud, Universidad de Carabobo, Valencia, Venezuela e-mail: rincani@uc.edu.ve Tel.: +58-241-8675017 Fax: +58-241-8431938