Host Susceptibility Is Altered by Light Intensity After Exposure to Parasites

Translating research advances to natural systems using experimental laboratory studies is often difficult because of the variability between the natural environment and experimental conditions. Because environmental conditions have a large effect on an organism's physiology, responses to stressors like nutrient limitation, temperature, oxygen deprivation, predation, and parasite/pathogen infection are likely to be context dependent. Therefore, it is essential to examine the impact the study environment has on the experimental outcome. Here, we explored the effect of light exposure on susceptibility to parasite infection. The Biomphalaria glabratalSchistosoma mansoni study system is a well-established model for studying schistosomiasis. It has been general practice to maintain the vector, B. glabrata, in dark conditions after exposure to miracidia of the human pathogen S. mansoni. We evaluated susceptibility of B. glabrata to S. mansoni under 3 different light conditions during the prepatent period, light (125 lx) on a 12-12 cycle, dim light (3 lx) on a 12-12 cycle, and no light (24 hr at 0 lx). We hypothesized that stress due to photoperiod disruption (24 hr of darkness) would result in compromised immune function and lead to higher susceptibility to infection. Prevalence of infected snails differed significantly between the light conditions, and higher susceptibility was observed in the full light and complete dark conditions compared with the low light conditions. The dim conditions are representative of current methods for evaluating susceptibility in this system. Our results indicate that light exposure during the prepatent period can affect infection outcomes, and environmental conditions must therefore be considered when assessing fitness and immune response clue to interactions between host genotype and environment.Keywords: Biomphalaria Glabrata, Hemocytes, Stress, Marine, Crassostrea Gigas, Responses, Invertebrates, Immunit

Apophallus microsoma N. SP. from Chicks Infected with Metacercariae from Coho Salmon (Oncorhynchus kisutch ) and Review of the Taxonomy and Pathology of the Genus Apophallus (Heterophyidae)

Metacercariae of an unidentified species of Apophallus Luhe, 1909 are associated with overwinter mortality in coho salmon, Oncorhynchus kisutch (Walbaum, 1792), in the West Fork Smith River, Oregon. We infected chicks with these metacercariae in order to identify the species. The average size of adult worms was 197 x 57 μm, which was 2 to 11 times smaller than other described Apophallus species. Eggs were also smaller, but larger in proportion to body size, than in other species of Apophallus. Based on these morphological differences, we describe Apophallus microsoma n. sp. In addition, sequences from the cytochrome c oxidase 1 gene from Apophallus sp. cercariae collected in the study area, which are likely conspecific with experimentally cultivated A. microsoma, differ by >12% from those we obtained from Apophallus donicus (Skrjabin and Lindtrop, 1919) and from Apophallus brevis Ransom, 1920. The taxonomy and pathology of Apophallus species is reviewed.Keywords: Mortality, St. Lawrence River, Life cycle, Parasite, Perch Perca flavescens, Trematoda, Yellow perch, Brevis, Oregon, Nanophyetus salmincol

Non-Invasive Sampling of Schistosomes from Humans Requires Correcting for Family Structure

For ethical and logistical reasons, population-genetic studies of parasites often rely on the non-invasive sampling of offspring shed from their definitive hosts. However, if the sampled offspring are naturally derived from a small number of parents, then the strong family structure can result in biased population-level estimates of genetic parameters, particularly if reproductive output is skewed. Here, we document and correct for the strong family structure present within schistosome offspring (miracidia) that were collected non-invasively from humans in western Kenya. By genotyping 2,424 miracidia from 12 patients at 12 microsatellite loci and using a sibship clustering program, we found that the samples contained large numbers of siblings. Furthermore, reproductive success of the breeding schistosomes was skewed, creating differential representation of each family in the offspring pool. After removing the family structure with an iterative jacknifing procedure, we demonstrated that the presence of relatives led to inflated estimates of genetic differentiation and linkage disequilibrium, and downwardly-biased estimates of inbreeding coefficients (F[subscript IS]). For example, correcting for family structure yielded estimates of F[[subscript ST] among patients that were 27 times lower than estimates from the uncorrected samples. These biased estimates would cause one to draw false conclusions regarding these parameters in the adult population. We also found from our analyses that estimates of the number of full sibling families and other genetic parameters of samples of miracidia were highly intercorrelated but are not correlated with estimates of worm burden obtained via egg counting (Kato-Katz). Whether genetic methods or the traditional Kato-Katz estimator provide a better estimate of actual number of adult worms remains to be seen. This study illustrates that family structure must be explicitly accounted for when using offspring samples to estimate the genetic parameters of adult parasite populations

Interactions between Natural Populations of Human and Rodent Schistosomes in the Lake Victoria Region of Kenya: A Molecular Epidemiological Approach

One of the world's most prevalent neglected diseases is schistosomiasis, which infects approximately 200 million people worldwide. Schistosoma mansoni is transmitted to humans by skin penetration by free-living larvae that develop in freshwater snails. The origin of this species is East Africa, where it coexists with its sister species, S. rodhaini. Interactions between these species potentially influence their epidemiology, ecology, and evolutionary biology, because they infect the same species of hosts and can hybridize. Over two years, we examined their distribution in Kenya to determine their degree of overlap geographically, within snail hosts, and in the water column as infective stages. Both species were spatially and temporally patchy, although S. mansoni was eight times more common than S. rodhaini. Both species overlap in the time of day they were present in the water column, which increases the potential for the species to coinfect the same host and interbreed. Peak infective time for S. mansoni was midday and dawn and dusk for S. rodhaini. Three snails were coinfected, which was more common than expected by chance. These findings indicate a lack of obvious isolating mechanisms to prevent hybridization, raising the intriguing question of how the two species retain separate identities

Molecular and morphological systematics of the Leptorhynchoides thecatus (Acanthocephala: Rhadinorhynchidae) complex of species

Recognition of species boundaries is fundamental to many biological disciplines, yet remains problematic. One difficulty is the existence of morphologically cryptic sibling species. Sibling species commonly may form in organisms, such as autogenic parasites, that are characterized by high speciation rates and conserved body plans. Leptorhynchoides thecatus is an acanthocephalan parasite of freshwater fishes that occurs throughout eastern North America. This species is autogenic and exhibits subtle variation in morphology, host use, habitat use, and developmental patterns, which led to the suspicion that L. thecatus comprised multiple species. Identification and characterization of possible species within the L. thecatus complex was undertaken using phylogenetic and morphometric analyses with specimens collected throughout its distribution range in the eastern U.S.A. and Canada. Phylogenetic analyses utilized sequences of the cytochrome oxidase I (cox1) gene and the internal transcribed spacer region (ITS). Morphometric analyses included multivariate and univariate statistical techniques using discrete and continuous characters. Additionally, three methods were developed for the classification of new specimens: classification functions based on a canonical discriminant analysis, a decision tree, and a dichotomous key. These methods were employed on new specimens to assess their utility. Results of the phylogenetic analyses indicated that L. thecatus comprises six species. Deep phylogenetic divergence among each of the proposed species and their exclusiveness indicate that each is an independent lineage with its own evolutionary tendencies and historical fate. A canonical discriminant analysis detected morphological divergence among the proposed species and correctly discriminated 92% of males and 90% of females. Two pairs of species are morphologically cryptic and one species is polytypic. The most powerful discriminating morphological characters were the length of the trunk, the number of longitudinal rows of hooks, and the length of the longest hook. The six proposed species also differ in their patterns of host use, habitat use, and development. The existence of multiple species explains some of the variation detected previously in the L. thecatus complex and gives a credible explanation for apparent discrepancies reported in the literature

Multi-strain compatibility polymorphism between a parasite and its snail host, a neglected vector of schistosomiasis in Africa

Interactions between Schistosoma mansoni and its snail host are understood primarily through experimental work with one South American vector species, Biomphalaria glabrata. However, 90% of schistosomiasis transmission occurs in Africa, where a diversity of Biomphalaria species may serve as vectors. With the long-term goal of determining the genetic and ecological determinants of infection in African snail hosts, we developed genetic models of Biomphalaria sudanica, a principal vector in the African Great Lakes. We determined laboratory infection dynamics of two S. mansoni lines in four B. sudanica lines. We measured the effects of the following variables on infection success and the number of cercariae produced (infection intensity): (i) the combination of parasite and snail line; (ii) the dose of parasites; and (iii) the size of snail at time of exposure. We found one snail line to be almost completely incompatible with both parasite lines, while other snail lines showed a polymorphism in compatibility: compatible with one parasite line while incompatible with another. Interestingly, these patterns were opposite in some of the snail lines. The parasite-snail combination had no significant effect on the number of cercariae produced in a successful infection. Miracidia dose had a strong effect on infection status, in that higher doses led to a greater proportion of infected snails, but had no effect on infection intensity. In one of the snail-schistosome combinations, snail size at the time of exposure affected both infection status and cercarial production in that the smallest size class of snails (1.5–2.9 mm) had the highest infection rates, and produced the greatest number of cercariae, suggesting that immunity increases with age and development. The strongest predictor of the infection intensity was the size of snail at the time of shedding: 1 ​mm of snail growth equated to a 19% increase in cercarial production. These results strongly suggest that infection status is determined in part by the interaction between snail and schistosome genetic lines, consistent with a gene-for-gene or matching allele model. This foundational work provides rationale for determining the genetic interactions between African snails and schistosomes, which may be applied to control strategies

Schistosome CAA titers

This file contains CAA titers, schistosome status, season, age and capture information for buffalo involved in this publication. Additional information is published under Dryad submission http://dx.doi.org/10.5061/dryad.q2m38