Showing papers by "Andrew P. Dobson published in 1978"

Experimental studies of infection dynamics: infection of the definitive host by the cercariae of Transversotrema patialense

Abstract: The number of cercariae of Transversotrema patialense which attach to the fish host Brachydanio rerio, during a fixed exposure period, is shown to be directly proportional to cercarial density within an experimental infection arena. The distribution of successful infections/host is shown to change from a random pattern to an over-dispersed form as cercarial exposure density or duration of host exposure to infection increases. A stochastic simulation model is used to demonstrate that small differences in host susceptibility to infection, within a population of hosts, can generate patterns of dispersion in parasite numbers/host similar to those observed in the experimental studies. Differences in host behaviour, during the period of exposure to infection, are thought to generate variability in host susceptibility to cercarial infection.

Concomitant predation and infection processes: an experimental study

Abstract: SUMMARY (1) The functional response of the fish predator Brachydanio rerio HamiltonBuchanan to changes in the density of two prey species, Daphnia magna L. and the cercarial stage of the ectoparasitic digenean Transversotrema patialense (Soparkar), is shown to be of the type II form where the instantaneous predation rate is unaffected by changes in prey density. (2) A model is developed to describe this functional response, based on the concept of predator satiation. The number of prey items required to create satiation is shown to be dependent on the experimental procedures used to elicit the functional response. (3) The fish predator, Brachydanio rerio, acts in the dual role of predator/host for the cercarial stage of Transversotrema patialense. The concomitant predation and infection processes created by this ecological association are shown to be characterised by constant instantaneous predation and infection rates which appear to be unaffected by changes in prey/parasite density. (4) The infection process is unaffected by density dependent constraints over a wide range of exposure densities and the number of parasites attached per host is shown to be directly proportional to cercarial numbers. (5) Stochastic elements are shown to be important determinants in the dynamics of the infection process and overdispersion in the frequency distribution of the number of parasites attached per host is thought to be generated by heterogeneity between fish and heterogeneity in time created by changes in infective stage density. (6) The relevance of concomitant predation and infection processes to the dynamics of digenean life cycles is discussed.