Obtaining three-dimensional geometrical data of vascular systems is of major importance to a number of research areas in medicine and biology. Examples are the characterization of tumor vasculature, modeling blood flow, or genetic effects on vascular development. The performance of the General Electric Medical Systems MS8 microCT scanner is examined in the context of these applications. The system is designed to acquire high-resolution images of specimens up to 5 cm in diameter. A maximum resolution of 38 lp/mm at the 10% modulation transfer function level or 22 microm full width at half maximum of the plane spread function can be achieved with 8.5 microm voxels and a 17 mm field of view. Three different contrast agents are discussed and applied for imaging of small animal vasculature: corrosion casting material Batson's No. 17 with an added lead pigment, silicon rubber MICROFIL MV122, and a suspension of barium sulfate (Baritop) in gelatin. Contrast for all of these agents was highly variable in different vessels as well as within the same vessel. Imaging of PMMA tubing filled with MICROFIL shows that even vessels below 20 microm in diameter are detectable and that diameter estimation of vessels based on thresholding is possible with a precision of 2-3 pixels.

Approaches based on organismal DNA found in the environment (eDNA) have become increasingly utilized for ecological studies and biodiversity inventories as an alternative to traditional field survey methods. Such DNA-based techniques have been largely used to establish the presence of free-living organisms, but have much potential for detecting and quantifying infectious agents in the environment, which are necessary to evaluate disease risk. We developed an eDNA method to examine the distribution and abundance of the trematode Ribeiroia ondatrae, a pathogenic parasite known to cause malformations in North American amphibians. In addition to comparing this eDNA approach to classical host necropsy, we examined the detectability of R. ondatrae in water samples subject to different degradation conditions (time and temperature). Our test exhibited high specificity and sensitivity to R. ondatrae, capable of detecting as little as 14 fg of this parasite’s DNA (1/2500th of a single infectious stage) from field water samples. Compared to our results from amphibian host necropsy, quantitative PCR was ∼ 90% concordant with respect to R. ondatrae detection from 15 field sites and was also a significant predictor of host infection abundance. DNA was still detectable in lab samples after 21 days at 25 °C, indicating that our method is robust to field conditions. By comparing the advantages and disadvantages of eDNA versus traditional survey methods for determining pathogen presence and abundance in the field, we found that the lower costs and effort associated with eDNA approaches provide many advantages. The development of alternative tools is critical for disease ecology as wildlife management and conservation efforts require reliable establishment and monitoring of pathogens.

Understanding linkages between environmental changes and disease emergence in human and wildlife populations represents one of the greatest challenges to ecologists and parasitologists. While there is considerable interest in drivers of amphibian microparasite infections and the resulting consequences, comparatively little research has addressed such questions for amphibian macroparasites. What work has been done in this area has largely focused on nematodes of the genus Rhabdias and on two genera of trematodes (Ribeiroia and Echinostoma). Here, we provide a synopsis of amphibian macroparasites, explore how macroparasites may affect amphibian hosts and populations, and evaluate the significance of these parasites in larger community and ecosystem contexts. In addition, we consider environmental influences on amphibian-macroparasite interactions by exploring contemporary ecological factors known or hypothesized to affect patterns of infection. While some macroparasites of amphibians have direct negative effects on individual hosts, no studies have explicitly examined whether such infections can affect amphibian populations. Moreover, due to their complex life cycles and varying degrees of host specificity, amphibian macroparasites have rich potential as bioindicators of environmental modifications, especially providing insights into changes in food webs. Because of their documented pathologies and value as bioindicators, we emphasize the need for broader investigation of this understudied group, noting that ecological drivers affecting these parasites may also influence disease patterns in other aquatic fauna.

Many animals respond behaviourally to the infective stages of parasites, but the efficacy of such responses in reducing risk of parasitism often is not established. It was found that tadpoles of Rana clamitans Latr., 1801 (green frogs) and R. sylvatica LeConte, 1825 (wood frogs) increased their activity when exposed to live infective stages (cercariae) of the trematode Echinostoma trivolvis Rudolphi, 1809. The susceptibility to parasitism for green frog tadpoles subjected to three different treatments was compared. Tadpoles were housed at 20 °C and allowed to respond to cercariae, held at 6–8 °C and showing reduced behavioural responses, or anesthetized and showing no responses. Low levels of parasitism were found for tadpoles that responded behaviourally to cercariae; such responses are expected to occur under normal field conditions in the absence of factors suppressing activity of tadpoles. We also demonstrate that infectivity of E. trivolvis cercariae to non-responding (anesthetized) wood frog tadpoles was higher at warm than at cool temperatures. Thus, lowered parasitism at warm temperatures in the first experiment likely resulted from host behavioural responses and not from low infectivity of cercariae. These results have implications for observing effects of environmental factors on susceptibility to parasitism where susceptibility is thought or known to be mediated by host behaviour.

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Susceptibility of free-living infective stages of parasites to contaminants is relatively understudied compared with independent effects on measures of host health or immunity, but may be important in affecting prevalence and intensity of parasite infections. We investigated whether atrazine, an herbicide commonly used in North America, affected the cercariae of 4 different species of digenetic trematodes, and found that effects of atrazine concentration on mortality and activity of cercariae varied among species. Mortality of Echinostoma trivolvis increased in a 200 microg/L atrazine solution, and a species of Alaria showed both decreased activity and increased mortality. We also examined whether the ability of E. trivolvis to infect the second intermediate host, larval amphibians, was compromised by atrazine exposure. Longevity and prevalence of E. trivolvis cercariae was affected at 200 microg/L atrazine, whereas intensity of infection in Rana clamitans tadpoles was reduced at both 20 microg/L and 200 microg/L atrazine. Our results indicate that the viability of cercariae of some species is compromised by exposure to atrazine, emphasizing the importance of considering the influence of contaminants on free-living stages of parasites in addressing how environmental degradation may relate to host parasitism.

Environmental changes are simultaneously affecting parasitic diseases and animal migrations, making it important to understand the disease dynamics of migratory species, including their range of infections and investment into defences. There is an urgent need for such knowledge because migratory animals, especially birds, are important for pathogen transmission and also particularly sensitive to environmental changes. Here we compare the nematode species richness and relative immune investment (via relative spleen size) of almost 200 migratory and non‐migratory species within three diverse groups of birds (Anseriformes, Accipitriformes and Turdidae) with worldwide distributions and varied ecology. Our results provide the first large‐scale demonstration that migratory birds face greater challenge from macroparasites as they have significantly dissimilar nematode fauna and higher nematode species richness compared to non‐migratory species. Even though birds with relatively large spleens had more nematode species, there was no difference in relative spleen size between migratory and non‐migratory bird species. The physiological stress of migration can be exacerbated by the potential range of pathologies induced by their richer nematode communities, particularly in combination with environmental perturbations. Altered migration stemming from global changes can also have important consequences for nematode transmission.

The emergence or increased prevalence of various parasites may be linked to alterations in host-parasite interactions caused by environmental changes. We investigated prevalence of trematode infections in grey tree frog (Hyla versicolor) tadpoles from ponds in nonagricultural settings versus ponds adjacent to cornfields in southern Ontario. We found that agricultural activity was a significant factor in determining the percentage of tadpoles infected by 1 or more trematodes from 1 or more species (combined trematode infection). However, we found no associations between combined trematode infection and forest cover; pond size; road density; and measures of water quality, such as nitrate level and the presence of the herbicide atrazine. Although combined trematode prevalence was associated only with agricultural activity, prevalence of Alaria species showed a positive association with forest cover. This latter result probably reflects the importance of habitat suitability for the canid definitive hosts of this trematode species.