Lymnaea cousinni (Gastropoda: Lymnaeidae) as transmitter of fascioliasis

Abstract

Dear Editor,In the article entitled “First report of Lymnaea cou-sini Jousseaume, 1887 naturally infected with Fasciolahepatica (Linnaeus, 1758) (Trematoda: Digenea) inMachachi, Ecuador” recently published by AngelVillavicencio A and Mauricio Carvalho de Vasconcellosin Memorias do Instituto Oswaldo Cruz (vol. 100, is-sue 7, pages 735-737, November 2005), it is stated thattheir finding in Ecuador represents the first report ofspecimens of this lymnaeid species naturally infectedby the liver fluke. However, it is well known from longago that this species acts as intermediate host of fascio-liasis in Andean countries. In the first half of the lastcentury, Brumpt et al. (1939-1940) already demonstratedthat L. bogotensis Pilsbry, 1935, a synonym of L. cousiniproposed and established by Hubendick (1951) and al-ways accepted (see Pointier et al. 2004), even also rec-ognized by Villavicencio and Carvalho de Vasconcellos(2005) in their paper here in question, is the intermedi-ate host of Fasciola hepatica in the surroundings of SantaFe de Bogota, Colombia.Materials studied by Villavicencio and Carvalho deVasconcellos (2005) were from Machachi, in the Andeanregion of Ecuador. These authors further note that fas-cioliasis prevalence in humans in the Andean region ofEcuador ranges from 24 to 53% and add the referenceof the Servicio Ecuatoriano de Sanidad Animal (SESA2003) concerning this information. However, these veryhigh human prevalences do not fit with results obtainedin surveys carried out up to the present in Andean com-munities of Ecuador, in which human prevalences alwaysappear to be low or very low: 6% by serology (Trueba etal. 2000); 0.5% by coprology (Gozalbo et al. 2004).Authors additionaly note that, according to WHO (1995),almost 200,000 people in Ecuador are infected, but itshall be clarified that these WHO data were only esti-mations available at the beginning of the 90s decade.Villavicencio and Carvalho de Vasconcellos (2005)emphasize the high prevalence of infection of 31.43%by F. hepatica they detected in L. cousini snails as thehighest value ever reported for lymnaeid snails naturallyinfected with this parasite. However, although this preva-lence is evidently high when compared to currentprevalences by fasciolids in lymnaeid snails, which areusually less than 5%, F. hepatica prevalences in snailssimilar and even higher than that reported by Villavicencioand Carvalho de Vasconcellos (2005) have been foundelsewhere. In fascioliasis human endemic areas of An-dean countries, for instance, a confirmed 31.6% preva-lence by F. hepatica in Galba truncatula was detectedin the center of the Northern Bolivian Altiplano villageof Tambillo (Bargues et al. 1995), that is, even in a hu-man settlemen instead of in a field place inhabited bylivestock.The fasciolid prevalence reported by Villavicencioand Carvalho de Vasconcellos (2005) was found in 70 L.cousini snail specimens collected in a 4.5-m