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Long-term records of parasite infection are rare for individuals in wild host populations. This study, on an introduced population of Xenopus laevis in Wales, demonstrates powerful control by acquired immunity of the monogenean, Protopolystoma xenopodis. Field evidence was based on a 10 year dataset for 619 individually-marked hosts screened at each capture for patent (egg-producing) infection. The adult parasite population occurred predominantly in juvenile hosts. Invasion began rapidly 'post-birth' (in early tadpoles). Longitudinal records for animals aged ≥15 years showed that, after loss of this primary infection, most hosts had strong resistance to re-infection. For ca. 80% of the population, no infections were recorded during adult life; for ca. 15%, there were isolated brief episodes of patent infection; for ca. 5%, parasites persisted as repeated short-term or chronic long-term infections. Acquired immunity was confirmed by laboratory challenge infection of wild-caught X. laevis: in 30/32 exposures, no parasites survived to maturity; in the two infected, development was retarded. Parasite persistence depends principally on host recruitment generating naïve young (as in human measles). In some hosts, retarded parasite development delays reproduction for several years: these infections show 'Typhoid Mary' characteristics, persisting in 'latent' form with potential to initiate epidemics in naïve cohorts., (Copyright © 2012 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.)

Macroparasites of vertebrates usually occur in multi-species communities, producing infections whose outcome in individual hosts or host populations may depend on the dynamics of interactions amongst the different component species. Within a single co-infection, competition can occur between conspecific and heterospecific parasite individuals, either directly or via the host's physiological and immune responses. We studied a natural single-host, multi-parasite model infection system (polystomes in the anuran Xenopus laevis victorianus) in which the parasite species show total interspecific competitive exclusion as adults in host individuals. Multi-species infection experiments indicated that competitive outcomes were dependent on infection species composition and strongly influenced by the intraspecific genetic identity of the interacting organisms. Our results also demonstrate the special importance of temporal heterogeneity (the sequence of infection by different species) in competition and co-existence between parasite species and predict that developmental plasticity in inferior competitors, and the induction of species-specific host resistance, will partition the within-host-individual habitat over time. We emphasise that such local (within-host) context-dependent processes are likely to be a fundamental determinant of population dynamics in multi-species parasite assemblages.

Protopolystoma xenopodis and Protopolystoma orientalis are polystomatid monogeneans respectively specific to the parapatric anurans Xenopus laevis and Xenopus muelleri. Parasite larval stages may invade the kidneys of foreign Xenopus spp. but die before migration to the definitive urinary bladder site. Laboratory experiments to assess the effect of a primary incompatible kidney infection on a secondary compatible infection found: (1) a small, significant decrease in the survivorship of P. xenopodis kidney stages (23-37 days p.i. at 25 degrees C) in X. laevis laevis previously challenged with P. orientalis; (2) a significant effect of prior P. orientalis challenge on P. xenopodis development and establishment in the urinary bladder of X. laevis 100 days p.i. (at 21 degrees C); (3) no effect of prior P. xenopodis challenge on adult P. orientalis establishment in X. muelleri (at 21 degrees C), but a significant negative influence on reproductive output (days 0-50 post-patency). Partial cross-resistance to heterospecifics may therefore be induced by Protopolystoma spp. infections in the kidneys of an incompatible host, demonstrating that at least some elements of the host response are non-species specific. The effects observed were weak compared to the strong host resistance known to be generated by an established compatible primary infection with respect to conspecifics. This difference suggests that strong acquired resistance to Protopolystoma species is species-specific and/or induced only by older stages surviving in compatible hosts.

The reproductive kinetics of Protopolystoma xenopodis primary and secondary infections in Xenopus laevis were monitored in a 3-year study. Thirty-five naïve, lab-raised, full-sib X. laevis from 1 spawning were each exposed to 30 P. xenopodis eggs. The course of infections at 20 degrees C was monitored by screening isolated hosts for parasite egg production. Ninety-four percent of toads supported the development of gravid parasites. Infections became patent 9-19 weeks p.i., lasted 3-30 months and produced estimated totals of 1-7152 eggs/host. Variation in primary infection characters was discontinuous: a subgrouping of hosts (16%) was characterized by extended infection duration and low reproductive rate. In order to test the effect of long-term infection history on a subsequent challenge, each host was re-exposed to P. xenopodis infective stages (30 eggs/host) 6 months after the loss of its original infection. Establishment of patent infection was significantly lower (15%), and pre-patent period (12-28 weeks) longer, than in primary infections of the same hosts, and than in concurrently exposed naïve controls (contemporary full-sibs of the primary/secondary infection group, maintained in parallel; n = 28). There was no relationship between primary infection characteristics and secondary infection outcome. Overall reproductive output per initial infective stage for the primary exposure exceeded that for the secondary exposure by a ratio of 15:1. Results suggest that primary infection with P. xenopodis can elicit strong, long-term protective immunity against re-infection in X. laevis.

Protopolystoma xenopodis is an oviparous monogenean occurring as an adult in the urinary bladder of the clawed toad Xenopus laevis. Oncomiracidia invade the host's kidneys where juveniles develop, subsequently migrating to the definitive site. In central Africa, the tetraploid X. laevis occurs in sympatry with octoploid congeners, including Xenopus wittei, believed to be the hybrid derivatives of X. laevis- and Xenopus fraseri-like parental lineages. Twenty laboratory-raised, naive specimens of an X. wittei-like species from southern Rwanda were each exposed to 30 embryonated P. xenopodis eggs (at 20 degrees C) and screened for parasite egg production until 9 months post-exposure. These toads failed to support the development of gravid parasites (comparable experimental procedures produce at least 35% prevalence of patent infection in the natural host X. laevis). Further X. wittei aff. (n = 26) and X. laevis (n = 17) were exposed to P. xenopodis oncomiracidia and dissected at variable times post-exposure: larvae were able to invade the kidneys of X. wittei aff. and began feeding and morphological development. Severe mortality of juveniles occurred in both natural and unnatural hosts between invasion and 39 days post-exposure. However, while small numbers of parasites persisted in X. laevis, no stages were found in X. wittei aff. beyond 39 days. Present data demonstrate the incompatibility of P. xenopodis with X. wittei aff. and are consistent with a hypothesis that specificity in Protopolystoma-Xenopus systems is determined primarily by the ability of juveniles to complete development in the host's kidneys.

The strigeoid metacercaria Diplostomulum xenopi is commonly found in the pericardial cavity of Xenopus laevis laevis. This paper provides the first description of the adult obtained from the intestine of an experimental host, the darter, Anhinga melanogaster. Natural cercarial infections were found in specimens of the freshwater snail Bulinus tropicus collected from dams in the Free State. South Africa. The life cycle was experimentally completed and all stages were described by light and scanning electron microscopy.

Gyrdicotylus gallieni is a viviparous gyrodactylid monogenean that infects the buccal cavity and pharynx of Xenopus laevis laevis. Offspring directly recolonize the same host as their parent and transmission is carried out exclusively by adult worms which are capable of leech-like stepping locomotion. The infrapopulation dynamics (at 20 degrees C) of this species were studied by experimental exposure to single worms of previously uninfected hosts (which were dissected at various time-intervals post-infection). Infrapopulations increased exponentially until 50 days post-infection (p.i.), during which time the intrinsic rate of increase was estimated by regression as 0.065/parasite/day. After this, infrapopulation sizes showed greater variability, with established infections becoming extinct 2-5 months p.i.: elimination was probably due to some form of host reaction, as parasite lineages were maintained for up to 10 months by transfers to successive uninfected hosts. The development of infrapopulations is similar to that reported for other viviparous gyrodactylids parasitic on the body surface of teleosts. However, the intrinsic rate of increase was comparatively slow in G. gallieni and the duration of infection in isolated hosts prolonged. Slow-growing infrapopulations may elicit a host response more slowly and extend the period during which dispersal to a new host or host population can occur. This might be important in G. gallieni for which the internal site of infection could limit the transmission rate, as worm migration from the oral cavity or accidental detachment and expulsion is necessary for host-host transfer to occur.(ABSTRACT TRUNCATED AT 250 WORDS)