The Emergence of Schistosoma japonicum Cercariae from Oncomelania quadrasi

Abstract

The release of Schistosoma japonicum cercariae from Leytean Oncomelania quadrasi snails was observed under laboratory conditions. Two patterns of emergence were noted. The initial, nonperiodic emergence occurred immediately after submerging the snails in water and was followed by a periodic, diurnal emergence which peaked in the afternoon. The daily cercarial output of the periodic emergence appeared to be affected by exogenous light intensity. Furthermore, there was a cessation or reduction in cercarial output every 3rd or 4th day.

Using variable importance measures from causal inference to rank risk factors of schistosomiasis infection in a rural setting in China

“…While diurnal variations in the infectivity of cercaria have been recognized for decades, little is known about the variability in infection risk throughout the transmission season [8]. Li et al observed two annual peaks in S. japonicum infection prevalence in the lower Yantzee basin [9].…”

The cercarial emergence of Schistosoma japonicum from Oncomelania quadrasi under outdoor conditions in the Philippines

“…Although there were no records of changes of light intensity and water temperature, both experiments may have been carried out in a room without temperature control or air-conditioning. In contrast to these studies, NOJIMA et al (1980) recently reported on the emergence of S. japonicum cercariae from O. quadrasi in the laboratory and two patterns were noted: one a non-periodic emergence occurred immediately after submerging the snail in water and the other, a diurnal periodic emergence which peaked in the afternoon (14:00 to 18:00). Moreover, they pointed out that the nocturnal release of cercariae which was reported by BAUMAN et al (1948) may actually have been the non-periodic emergence that followed immediately upon submersion.…”

“…In the Philippines, the emergence of S. japonicum from O. quadrasi has been studied by BAUMAN et al (1948) and PESIGAN et al (1958) who suggested that it is nocturnal. Recently NOJIMA et al (1980) reported that, under constant laboratory conditions, there are two patterns of emergence: one is the initial, non-periodic emergence which occurs immediately after submersion of the snails and the other is a periodic diurnal emergence which peaks in the afternoon.…”

Rythme d émission des cercaires deSchistosoma japonicumde Chine continentale par desOncomelania hupensis

“…L'analyse chronobiologique par intervalles d'une heure pendant la photophase montre que lorsque les mollusques sont maintenus en immersion, l'émission des cercaires se fait suivant un rythme circadien dont le maximum se situe en moyenne 6 heures après le début de l'éclairement. D'après la bibliographie relative à l'émission des cercaires de S. japonicum, il apparaît que pour cette espèce la sortie des cercaires peut avoir lieu à des heures différentes du nycthémère : soit pendant le jour (Mao et al, 1949 ;Chou, 1965 ;Nojima et al, 1980), soit pendant la nuit (Isobe, 1923 ;Bauman et al, 1948 ;Pesigan et al, 1958 ;Kawashima et al, 1985), soit encore le jour et la nuit (Komiya et Ishii, 1954). Certains auteurs (Kawashima et al, 1985) ont attribué ces variations de la période d'émission des cercaires de S. japonicum aux conditions expérimentales parfois très différentes utilisées pour les études chronobiologiques.…”

“…Ces recherches qui ont surtout porté sur l'aspect quantitatif de la production cercarienne ont également fourni des informations sur les périodes du nycthémère les plus favorables à l'émission. Ce n'est que plus récemment que l'aspect chronobiologique des rythmes journaliers d'émer gence a été abordé (Nojima et al, 1980 ;Kawashima et al, 1985). Il ressort de ces études que des variations importantes du rythme d'émergence peuvent exister sui vant les auteurs ou l'origine géographique du parasite.…”