A Quantitative Approach to the Experimental Transmission Success of Echinostoma Friedi (Trematoda: Echinostomatidae) in Rats

Abstract

Using a range of parameters, the ability of rats (Rattus norvegicus) to successfully transmit Echinostoma friedi to the next host was examined under experimental conditions. The concept of Experimental Transmission Success (T M ), defined as the number of hosts that become successfully infected after exposure to a number of infective stages produced by a previous host per unit of inoculation at which this latter host was exposed, was introduced. Using data for the egg output and miracidium hatching and infectivity, the T M permits us to estimate the ability of a particular defintive host species to successfully transmit a parasite species. This concept may be also useful to compare the transmission fitness of a parasite in different definitive host species. Moreover, variations of the Experimental Transmission Success over the course of the infection were calculated by the use of the Weekly Experimental Transmission Success (T MW ). Overall, considering the complete duration of the experiment, the T M of E. friedi using rats as definitive hosts was 0.68 infected snails/metacercaria. However, positive values of the T MW were only obtained from 2 to 4 wk post-infection, with a maximum during the third wk post-infection. When comparing the T M values of E. friedi in rats with those calculated in hamsters on the basis of previously published data, E. friedi appears to be more appropriate to move through this portion of its life cycle when using hamsters (Mesocricetus auratus) as the final host than rats.

Assessment of Akodon cursor (Rodentia, Sigmodontinae) as permissive host to Schistosoma mansoni infection: morphology of adult worms

“…Our previous studies (Machado e Silva et al 1991, Maldonado Jr. et al 1994) and others (Ribeiro et al 1998) have demonstrated that available knowledge can be learnt from wild rodents experimentally infected under laboratory conditions. In addition, the success of S. mansoni development in a wild rodent may provides a measure to assay its susceptibility or ability to maintain this parasite (Toledo et al 2006). A. cursor possesses many qualities which would be highly desirable in a laboratory animal: it is capable of breeding successfully under simple conditions of management and displays good adaptation to laboratory facilities (D'Andrea et al 1996).…”

“…Much of the interest in describing and modeling the population dynamics of helminths has concerned parasite fecundity in the definitive host (Toledo et al 2006). However, morphological characteristics of adult worms demonstrate that phenotypic plasticity is an important means through which helminths respond to changes in environmental conditions.…”

Immunology and pathology of echinostome infections in the definitive host.

“…The elimination of E. trivolvis from mice occurs within 2-3 wpi (Weinstein and Fried 1991) , while in hamsters worms survived for up to 123 days postinfection (dpi) (Mabus et al 1988) . Similarly, E. friedi was able to survive for at least 12 wpi in hamsters, whereas the infection was expelled at 3-4 wpi in rats (Toledo et al 2003a(Toledo et al , 2006aMuñoz-Antoli et al 2004) . Differences in the pattern of worm expulsion between strains of mice also have been observed.…”

“…There is evidence suggesting a role of the host immune response in the regulation of the fecundity of echinostomes. Differences in egg counts in relation to the host species have been reported for E. caproni (Toledo et al 2004a) , E. trivolvis (Franco et al 1986) , and E. friedi (Muñoz-Antoli et al 2004 ;Toledo et al 2006a) . In some cases, the differences observed in the egg output could be attributed to the different number of worms established in each host species in relation to the host-parasite compatibility.…”

“…Chronic infections in mice and hamsters have been associated with high levels of systemic IgG responses and strong local infiltration of inflammatory mononuclear cells. In contrast, infections in rats are characterized by a rapid parasite expulsion together with low levels of IgG in serum and weaker infiltration of inflammatory cells (Toledo et al 2003b(Toledo et al , 2004b(Toledo et al , 2006aMuñoz-Antoli et al 2007 ;Sotillo et al 2007) . Further studies on these topics may be useful for the understanding of the factors responsible for the differences in the host responses and their consequences in the parasite and the course of the infection.…”