Effects of wetland vs. landscape variables on parasite communities of Rana pipiens: links to anthropogenic factors

The emergence of several diseases affecting amphibian populations worldwide has prompted investigations into determinants of the occurrence and abundance of parasites in frogs. To understand the spatial scales and identify specific environmental factors that determine risks of parasitism in frogs, helminth communities in metamorphic frogs of the northern leopard frog (Rana pipiens) were examined in relation to wetland and landscape factors at local (1 km) and regional (10 km) spatial extents in an agricultural region of Minnesota (USA) using regression analyses, ordination, and variance partitioning techniques. Greater amounts of forested and woody wetland habitats, shorter distances between woody wetlands, and smaller-sized open water patches in surrounding landscapes were the most consistently positive correlates with the abundances, richness, and diversity of helminths found in the frogs. Wetland and local landscape variables were suggested as most important for larval trematode abundances, whereas local and regional landscape variables appeared most important for adult helminths. As previously reported, the sum concentration of atrazine and its metabolite desethylatrazine, was the strongest predictor of larval trematode communities. In this report, we highlight the additional influences of landscape factors. In particular, our data suggest that anthropogenic activities that have resulted in the loss of the availability and connectivity of suitable habitats in the surrounding landscapes of wetlands are associated with declines in helminth richness and abundance, but that alteration of wetland water quality through eutrophication or pesticide contamination may facilitate the transmission of certain parasite taxa when they are present at wetlands. Although additional research is needed to quantify the negative effects of parasitism on frog populations, efforts to reduce inputs of agrochemicals into wetlands to limit larval trematode infections may be warranted, given the current high rates of amphibian declines and extinction events.

Impacts of agriculture on the parasite communities of northern leopard frogs (Rana pipiens) in southern Quebec, Canada

Given that numerous amphibians are suffering population declines, it is becoming increasingly important to examine the relationship between disease and environmental disturbance. Indeed, while many studies relate anthropogenic activity to changes in the parasitism of snails and fishes, little is known of the impact on the parasites of amphibians, particularly from agriculture. For 2 years, the parasite communities of metamorphic northern leopard frogs from 7 agricultural wetlands were compared with those from 2 reference wetlands to study differences in parasite community diversity and abundance of various species under pristine conditions and 3 categories of disturbance: only agricultural landscape, only pesticides, and agricultural landscape with pesticides. Agricultural (and urban) area was negatively related to species richness, and associated with the near absence of adult parasites and species that infect birds or mammals. We suggest that agriculture and urbanization may hinder parasite transmission to frogs by limiting access of other vertebrate hosts of their parasites to wetlands. The only parasite found at all localities was an unidentified echinostome infecting the kidneys. This parasite dominated communities in localities surrounded by the most agricultural land, suggesting generalist parasites may persist in disrupted habitats. Community composition was associated with dissolved organic carbon and conductivity, but few links were found with pesticides. Pollution effects may be masked by a strong impact of land use on parasite transmission.

SMALL FROGS GET THEIR WORMS FIRST: THE ROLE OF NONODONATE ARTHROPODS IN THE RECRUITMENT OF HAEMATOLOECHUS COLORADENSIS AND HAEMATOLOECHUS COMPLEXUS IN NEWLY METAMORPHOSED NORTHERN LEOPARD FROGS, RANA PIPIENS, AND WOODHOUSE'S TOADS, BUFO WOODHOUSII

Studies on the life cycles and epizootiology of North American frog lung flukes indicate that most species utilize odonates as second intermediate hosts; adult frogs become infected by ingesting odonate intermediate hosts. Newly metamorphosed frogs are rarely infected with these parasites, predominantly because they are gape-limited predators that cannot feed on large intermediate hosts such as dragonflies. We examined the role of the frog diet and potential intermediate hosts in the recruitment of the frog lung fluke, Haematoloechus coloradensis, to metamorphosed northern leopard frogs (Rana pipiens), Woodhouse's toads (Bufo woodhousii), and bullfrogs (Rana catesbeiana) from western Nebraska. Because of the uncertain validity of H. coloradensis as a distinct species from Haematoloechus complexus, morphological characters of both species were reevaluated and the life cycles of both species were completed in the laboratory. The morphological data on H. coloradensis and H. coimplexus indicate that they differ in their oral sucker to pharynx ratio, uterine loop distribution, and placement of vitelline follicles. However, in terms of their life cycles, both species are quite similar in their use of physid snails as first intermediate hosts, a wide range of nonodonate and odonate arthropods as second intermediate hosts, and leopard frogs and toads as definitive hosts. These results indicate that H. coloradensis and H. complexus are generalists at the second intermediate host level and might be able to infect newly metamorphosed leopard frogs and toads by using small nonodonate arthropods more commonly than other frog lung fluke species. Comparisons of population structure of adult flukes in newly metamorphosed leopard frogs indicate that the generalist nature of H. coloradensis metacercariae enables it to colonize young of the year leopard frogs more commonly than other Haematoloechus spp. that only use odonates as second intermediate hosts. In this respect, the generalist nature of H. coloradensis and H. complexus at the second intermediate host level is an avenue for the colonization of young of year frogs.

Rearing density and susceptibility of Rana pipiens metamorphs to cercariae of a digenetic trematode

Cercariae of many digenean trematodes target particular developmental stages of their hosts. For some digeneans that are parasites of amphibians, infection appears timed to host metamorphosis. The success and timing of metamorphosis is itself affected by a number of factors, including host density. We investigated the degree to which rearing density of Rana pipiens larvae influenced time to metamorphosis and snout-to-vent length and mass at metamorphosis, as well as establishment of cercariae of the trematode Manodistomum syntomentera Stafford, 1905. As expected, individuals metamorphosed later, were smaller, and weighed less at metamorphosis if they were reared under intermediate to high densities compared with low densities, in experimental outdoor mesocosms. Cercariae establishment was higher in smaller metamorphs that took longer to metamorphose within the low-density treatment. Additionally, cercariae establishment was lower in larvae from the low-density tanks compared with larvae from the intermediate- to high-density tanks. However, more tadpoles had failed to metamorphose in the intermediate to high rearing densities by the time cercariae were no longer available from natural collections of first intermediate hosts, Physa spp. Larval amphibians under crowded conditions should experience increased susceptibility to trematode establishment in nature, but only if they metamorphose within the time period when cercariae are still available.

In vitro excystment of the metacercariae of Ribeiroia ondatrae

In vitro excystation studies were done on the metacercarial cysts of Ribeiroia ondatrae obtained from naturally infected leopard frogs, Rana pipiens. Studies were done in Petri dish cultures in various media maintained at 41 degrees C. The media consisted of 0.5% trypsin-0.5% bile salts in Earle's balanced salt solution at pH 7.8 (TB), 1% acid pepsin (AP) in 0.85% saline adjusted to pH 2 with HCl; acid saline (AS) adjusted to pH 2 with HCl, and saline (S). The TB medium, used successfully to excyst the metacercariae of numerous species of digeneans, did not induce excystation of Ribeiroia ondatrae. Some excystation occurred in AS but not in S. Excystation was 100% in AP with most organisms excysting within 30 s after placement in the medium at 41 degrees C. Excystation in vitro in AP at 41 degrees C is compatible with the fact that this organism establishes itself in the acid-pepsin environment of the proventriculus of avian hosts.

Haematoloechus sp. infection in wild-caught northern leopard frogs (Rana pipiens)

Three male, wild-caught northern leopard frogs (Rana pipiens) died over a 1-week period with no previous history of clinical illness or disease. Noteworthy necropsy findings in one of the three frogs included depleted fat bodies in the coelomic cavity, indicating a poor nutritional condition, and a heavy parasite burden in the lungs. The location of infection and morphologic characteristics of the parasite were consistent with infection by the common lung fluke, Haematoloechus sp. In contrast to the heavy fluke load, only minor microscopic changes were observed in the lungs. Lesions included mild hypertrophy of the bronchiolar epithelium, with few submucosal inflammatory cells consisting predominantly of lymphocytes. Subsequent review of the literature revealed little about the pathologic effects of these parasites except that small numbers are thought to cause the host little harm. Our findings suggest that even with a large number of parasites, there is minimal pathologic impact in the lungs. We conclude that heavy lung-fluke infection should not be diagnosed as the sole or major etiology of death or illness in leopard frogs.

HELMINTH COMMUNITY STRUCTURE OF SYMPATRIC EASTERN AMERICAN TOAD, BUFO AMERICANUS AMERICANUS, NORTHERN LEOPARD FROG, RANA PIPIENS, AND BLUE-SPOTTED SALAMANDER, AMBYSTOMA LATERALE, FROM SOUTHEASTERN WISCONSIN

One-hundred twelve amphibians, including 51 blue-spotted salamanders, Ambystoma laterale, 30 eastern American toads, Bufo americanus americanus, and 31 northern leopard frogs, Rana pipiens, were collected during April-October 1996 from Waukesha County, Wisconsin and examined for helminth parasites. The helminth compound community of this amphibian assemblage consisted of at least 10 species: 9 in American toads, 8 in leopard frogs, and 3 in blue-spotted salamanders. American toads shared 7 species with leopard frogs, and 2 species occurred in all 3 host species. Although there was a high degree of helminth species overlap among these sympatric amphibians, statistically significant differences were found among host species and percent of indirect or direct-life cycle parasites of amphibian species individual component communities (chi2 = 1,015, P < 0.001). American toads had a higher relative abundance of nematodes, 59%, than larval cestodes, 31%, and larval and adult trematodes, 10%, whereas leopard frogs had a higher relative abundance of larval cestodes, 71.3%, and larval and adult trematodes, 25.3%, than nematodes 3.4%. This is related to ecological differences in habitat and dietary preferences between these 2 anuran species. Helminth communities of blue-spotted salamanders were depauperate and were dominated by larval trematodes, 94%, and few nematodes, 6%. Low helminth species richness in this host species is related to this salamander's relatively small host body size, smaller gape size, lower vagility, and more fossorial habitat preference than the other 2 anuran species. Adult leopard frogs and toads had significantly higher mean helminth species richness than metamorphs, but there was no significant difference in mean helminth species richness among adult and metamorph blue-spotted salamanders. Considering adult helminths, the low species richness and low vagility of caudatans as compared with anurans suggest that local factors may be more important in structuring caudatan helminth communities of salamanders than of anuran hosts. Helminth species infecting salamanders may be more clumped in their geographic distribution as compared with anurans, and the role of other hosts and their parasites at the compound community level may be important in structuring helminth communities of salamanders.

Relationship of tadpole stage to location of echinostome cercariae encystment and the consequences for tadpole survival

The effect of echinostome infections on the survival of Rana pipiens tadpoles was examined in relation to developmental stage of tadpoles. Individual tadpoles of Gosner stages 25, 27, 32-33, and 37-39 were exposed to 1 of 4 levels of cercariae (0, 20, 50, or 100). Only tadpoles at stage 25, the earliest stage infected, died within a 5-day experimental period. This stage-specific mortality rate could be explained, in part, by the stage-specific location of encystment of cercariae, which was documented in a separate experiment. In accordance with kidney development, cercariae predominately encysted in the pronephroi during early stages of tadpole development (stages 25 through 31-32) and only in the mesonephroi and associated ducts at later stages (stages 37 through 46). As the mesonephros develops, renal capacity presumably increases. Thus, tadpoles died only when metacercariae concentrated in the functional portion of the kidney with the most limited renal capacity. As tadpoles aged, they also became less susceptible to infections. On average, 69.5% of cercariae that were exposed to stage 25-26 tadpoles successfully encysted. compared with only 8.4% of cercariae exposed to stage 37-38 tadpoles. Exposures of metamorphic frogs (poststage 46) to cercariae revealed that these individuals can become infected with echinostomes. Collectively, our data highlight the host stage-dependent dynamics of tadpole-echinostome interactions.

Exposure of leopard frogs to a pesticide mixture affects life history characteristics of the lungworm Rhabdias ranae

We tested the hypothesis that exposure of leopard frogs ( Rana pipiens) to agricultural pesticides can affect the infection dynamics of a common parasite of ranid frogs, the lungworm Rhabdias ranae. After a 21-day exposure to sublethal concentrations of a pesticide mixture composed of atrazine, metribuzin, aldicarb, endosulfan, lindane and dieldrin, or to control solutions (water, dimethyl sulfoxide), parasite-free juvenile frogs were challenged with 30 infective larvae of R. ranae. Approximately 75% of the larvae penetrated the skin and survived in both exposed and control animals, suggesting that pesticides did not influence host recognition or penetration components of the transmission process. Rather, we found that the migration of R. ranae was significantly accelerated in hosts exposed to the highest concentrations of pesticides, leading to the establishment of twice as many adult worms in the lungs of frogs 21 days post-infection. Pesticide treatment did not influence the growth of lungworms but our results indicate that they matured and reproduced earlier in pesticide-exposed frogs compared to control animals. Such alterations in life history characteristics that enhance parasite transmission may lead to an increase in virulence. Supporting evidence shows that certain components of the frog immune response were significantly suppressed after exposure to the pesticide mixture. This suggests that the immune system of anurans exerts a control over lungworm migration and maturation and that agricultural contaminants can interfere with these control mechanisms. Our results also contribute to the ongoing debate regarding the role that anthropogenic factors could play in the perplexing disease-related die-offs of amphibians observed in several parts of the world.

Effects of agricultural pesticides on the immune system of Rana pipiens and on its resistance to parasitic infection

In the past 30 years, many amphibian species have suffered population declines throughout the world. Mass mortality have been frequently reported, and in several instances, infectious diseases appear to be the cause of death. The role that contaminants could play in these die-offs through immunotoxic effects has been poorly investigated. In this study, juvenile leopard frogs (Rana pipiens) were exposed for 21 d to a mixture of six pesticides (atrazine, metribuzin, aldicarb, endosulfane, lindane, and dieldrin) and subsequently challenged with a parasitic nematode, Rhabdias ranae. Exposure to the mixture at environmentally realistic concentrations significantly reduced lymphocyte proliferation. Three weeks after the end of the exposure, lymphocyte proliferation had recovered and was stimulated in frogs challenged with parasites with the exception of those previously exposed to the highest concentration. No pesticide effects on phagocytosis and splenocyte numbers were detectable at the end of the exposure period, but these two parameters were diminished 21 d after the infection challenge in frogs previously exposed to the highest levels of pesticides. In these animals, the prevalence of lung infection by R. ranae also tended to be higher. These results suggest that agricultural pesticides can alter the immune response of frogs and affect their ability to deal with parasitic infection.

Whirling disease: host specificity and interaction between the actinosporean stage of Myxobolus cerebralis and rainbow trout Oncorhynchus mykiss

Scanning electron microscopic studies were conducted on rainbow trout Oncorhynchus mykiss in the first 60 min after their exposure to the triactinomyxon spores of Myxobolus cerebralis. The results demonstrated that as early as 1 min post exposure the whole process, from the attachment of the triactinomyxon spores to the complete penetration of their sporoplasm germs, had occurred. The triactinomyxon spores sought out the secretory openings of mucous cells of the epidermis, the respiratory epithelium and the buccal cavity of trout and used them as portals of entry. Exposure experiments of the triactinomyxon spores of M. cerebralis to non-salmonid fish, such as goldfish Carassius auratus, carp Cyprinus carpio, nose Chondrostoma nasus, medaka Oryzias latipes, guppy Poecilia reticulata and also the amphibian tadpole Rana pipiens as well as to rainbow trout fry indicated a specificity for salmonids. Attempts to activate the triactinomyxon spores by exposure to mucus prepared from cyprinid and salmonid fish showed no significant differences from those conducted in tap water. The results suggest that the simultaneous presence of both mechano- and chemotactic stimuli was required for finding the salmonid fish host.

The life history and host specificity of Hepatozoon clamatae (Apicomplexa: Adeleorina) and ITS-1 nucleotide sequence variation of Hepatozoon species of frogs and mosquitoes from Ontario

The life cycle of an intraerythrocytic hemogregarine, Hepatozoon clamatae, was studied in green frogs (Rana clamitans melanota), bullfrogs (Rana catesbeiana), northern leopard frogs (Rana pipiens), and in the mosquito, Culex territans. Gametogenesis, fertilization, and sporogony occurred within cells of the Malpighian tubules of laboratory-reared Cx. territans that had fed on naturally infected frogs. Mature oocysts containing hundreds of sporocysts were observed in mosquitoes 30 days postfeeding. Each sporocyst enclosed 4 sporozoites. Merozoites appeared in the peripheral circulation of laboratory-reared bullfrogs, green frogs and leopard frogs that had been fed sporocysts 35-70 days previously. Attempts to infect American toads (Bufo americanus) and blue-spotted salamanders (Ambystoma laterale) were not successful. Gamonts of this parasite induced nuclear fragmentation or segmentation in host erythrocytes. The life cycle, morphological, and morphometric features of H. clamatae are compared with H. catesbianae, a similar species that also infects ranids. Nucleotide sequence analysis of the internal transcribed spacer region (ITS-1) of these sympatric species revealed that only 6 nucleotide sites of the 129 base pairs of this region were variable among 4 isolates of H. clamatae and 2 isolates of H. catesbianae. A redescription of H. clamatae is presented based on data from this study and from the original description by Stebbins in 1905.

Ultrastructural features of cystic and merogonic stages of Hepatozoon sipedon (Apicomplexa: Adeleorina) in northern leopard frogs (Rana pipiens) and northern water snakes (Nerodia sipedon) from Ontario, Canada

The cystic and merogonic stages of the haemogregarine Hepatozoon sipedon, infecting Northern water snakes (Nerodia sipedon sipedon) and Northern leopard frogs (Rana pipiens), respectively, in Ontario, Canada, were investigated by transmission electron microscopy. Cysts, which were observed in the liver of Northern leopard frogs (Rana pipiens) after these anurans ingested mosquitoes (Culex pipiens) containing oocysts of the parasite, harboured two cystozoites, each of which contained a large crystalloid inclusion anterior to the nucleus. Two types of meronts were observed in snakes that were fed the liver of infected frogs. Macromeronts, which matured in endothelial cells of the liver approximately 16 d after snakes ingested infected frogs, contained about 50 large macromerozoites. Macromerozoites emerged from macromeronts, entered the bloodstream of the snake, and reinfected endothelial cells. Micromeronts, which matured about 34 d post-inoculation, contained about 150 micromerozoites that infected erythrocytes and transformed into gamonts. The ultrastructural features of micromeronts and macromeronts differed only slightly: immature macromeronts and macromerozoites contained numerous amylopectin and lipid inclusions, whereas immature micromeronts and micromerozoites did not contain amylopectin inclusions and featured fewer, smaller lipid inclusions. A comparison of cystic stages among Hepatozoon species in different groups of vertebrates is presented with respect to their structure and evolutionary significance.

Experimental infection of Rana pipiens tadpoles with Echinostoma trivolvis cercariae

Studies were done on laboratory-raised Rana pipiens tadpoles experimentally infected with Echinostoma trivolvis cercariae. Tadpoles exposed individually to 250 cercariae died within 24 h. They were edematous at death and their kidneys were heavily infected with metacercarial cysts. Of 20 tadpoles exposed to 100 cercariae each, 9 survived the infection, and their growth was compared for 4 weeks postinfection (p.i.) with that of 20 control tadpoles that had not been exposed to cercariae. There was a significant weekly decline in the total length and body weight of the infected versus control tadpoles. Surviving tadpoles retained their metacercarial infections in the kidneys following metamorphosis to frogs. Following exposure of tadpoles to cercariae, cercarial bodies were first seen in the kidneys by 0.5 h p.i. Metacercariae that were molding their inner and outer cyst walls were first seen at 2.3 h, and by 8.5 h the inner and outer cyst walls were clearly defined. Domestic chicks exposed to cysts aged 2.5 and 4.0 h did not become infected, whereas ovigerous adults of E. trivolvis were recovered from chicks fed 12-h-old cysts. Cercariae aged 6 to 8 h were more infective to tadpoles than were either 1- or 20-h-old cercariae. The E. trivolvis-R pipiens tadpole model is suitable for the study of host-parasite relationships of echinostome larvae in a cold-blooded vertebrate host.

Analysis of isolates within species of anuran trypanosomes using random amplified polymorphic DNA

A total of 20 decamer primers were used to generate random applied polymorphic DNA (RAPD) markers from 5 isolates of Trypanosoma fallisi, 3 isolates of T. ranarum, 2 isolates of T. rotatorium, and 2 isolates of T. rotatorium-like trypanosomes in addition to 2 species from the American Type Culture Collection, T. chattoni (ATCC 50294) and Trypanosoma sp. (ATCC 50295). A slight polymorphism was observed among the four isolates of T. fallisi obtained form American toads, Bufo americanus, collected in Algonquin Park, Ontario, Canada, and an isolate obtained from the same species of host collected in Marquette, Michigan, United States, and produced similarity coefficients ranging from 80.7% to 96.9%. Pronounced polymorphism was recorded among the three isolates of T. ranarum from bullfrogs, Rana catesbeiana, collected in Ontario, Canada, and in Maryland, United States, and from a Northern leopard frog, R. pipiens, collected in Minnesota (USA). The similarity coefficients ranged from 54.7% to 59.5%, suggesting that alleles of these isolates were conserved over a wide geographic range. The high degree of polymorphism observed in two isolates of T. rotatorium from a bullfrog collected in Ontario and two isolates of a T. rotatorium-like parasite from the green frog R. clamitans, collected in Louisiana (USA) suggests that they are different species. These results reflect the high similarity among isolates from the same geographic location and the pronounced polymorphism apparent among isolates from distant geographic locations.

Second intermediate host-specificity of Haematoloechus complexus and Haematoloechus medioplexus (Digenea: Haematoloechidae)

Second intermediate host-specificity was examined for 2 species of the frog lung fluke genus Haematolechus. Nine species of freshwater arthropods were exposed to cercariae of H. complexus and H. medioplexus. Metacercariae of H. complexus developed in all arthropod species used. Metacercariae of H. medioplexus developed only in anisopteran odonate naiads. This difference in host utilization may have epizootiological implications. The potential development of H. complexus in a greater number of arthropods than H. medioplexus may increase the chances of ingestion of H. complexus by an anuran host. The range of arthropods parasitized by H. complexus indicates that host-specificity of the metacercarial stage of this fluke is not restricted by the phylogeny of aquatic arthropods.

The development of Hepatozoon sipedon sp. nov. (Apicomplexa: Adeleina: Hepatozoidae) in its natural host, the Northern water snake (Nerodia sipedon sipedon), in the culicine vectors Culex pipiens and C. territans, and in an intermediate host, the Northern leopard frog (Rana pipiens)

The life cycle of Hepatozoon sipedon sp. nov. was studied in two snake species, the Northern water snake and the Eastern garter snake, in its mosquito hosts Culex pipiens and C. territans, and in the Northern leopard frog. Gametogenesis, fertilization and sporogony occurred within fat body cells in the haemocoel of mosquitoes that had fed on infected water snakes. Mature oocysts averaging 263 microns in diameter and containing more than 500 sporocysts were observed in mosquitoes 28 days post-feeding. Each sporocyst enclosed eight sporozoites. Dizoic cysts were found in the liver of frogs that had been fed infected mosquitoes seven days previously. Two rounds of merogony in various internal organs and intraerythrocytic gamonts were observed in snakes that had been fed frogs which had been orally inoculated with infected mosquitoes. Developmental stages were not seen in snakes that were fed infected mosquitoes directly. A comparison of this life cycle with those described for other Hepatozoon species infecting snakes is presented with reference to the different modes of transmission featured by these parasites.

Efficacy of ivermectin as an anthelmintic in leopard frogs

Ivermectin administered cutaneously at dosages of 2 mg/kg of body weight eliminated nematode infections in leopard frogs. Three clinical trials were conducted. In the first trial, 5 groups of 11 frogs were given ivermectin IM at dosages of 0, 0.2, 0.4, 2, or 20 mg/kg. All frogs given ivermectin IM at dosages of 2.0 mg/kg or greater died. In trial 2, 44 frogs, allotted to 5 groups, were given ivermectin cutaneously at 0, 0.2, 2, or 20 mg/kg. Cutaneously administered ivermectin was not toxic at dosages up to 20 mg/kg. In trial 3, nematode infections were eliminated in all 10 frogs treated cutaneously with ivermectin at 2.0 mg/kg.

Occurrence of tetrathyridia of Mesocestoides sp. (Cestoidea: Cyclophyllidea) in North American anurans (Amphibia)

A new host and geographic locality record is reported for tetrathyridia of Mesocestoides sp. in two species of ranid frogs (Rana berlandieri and R. pipiens) from Texas and New York, respectively. Tetrathyridia were found encapsulated in liver and mesenteries of the hosts. Morphological examination and experimental inoculation of these tetrathyridia into mice demonstrated the absence of capacity for asexual proliferation. Overall prevalence of infection was low in anurans from Arkansas, Texas and New York, but intensities can be generally high. In addition, a summary of frogs and toads from North America reported as hosts of tetrathyridia of Mesocestoides sp. is presented.

The pathogenicity, localization, and cyst structure of echinostomatid metacercariae (Trematoda) infecting the kidneys of the frogs Rana clamitans and Rana pipiens

Light and scanning electron microscopy were used to examine the localization and pathogenicity of echinostomatid metacercariae infecting the kidneys of leopard frogs, Rana pipiens, and green frogs, Rana clamitans. Cysts occurred predominantly in the ventrolateral renal cortex, and at least some were confined to the lumen of the Bowman's capsules. Each vermiform metacercarial body was enclosed by a spherical cyst wall that had a uniform thickness. The wall was composed of a homogeneous material containing basic and keratinlike proteins, with sulfated acid mucopolysaccharides on the outer surface. Most cysts were enclosed by a fibrous capsule of host origin, or were surrounded by an inflammatory focus. Fibrosis was always focal, but its degree varied between individual hosts and between different cysts within the same host. Some heavily encapsulated cysts were darkened and contained disintegrating worms. In heavily infected kidneys, confluence of fibrotic or inflammatory foci resulted in the displacement of functional renal tissue. These data suggest that infection by echinostomatids may impair renal function and that the host's response affects parasite viability.

A light and electron microscopic study of Trypanosoma fallisi N. Sp. in toads (Bufo americanus) from Algonquin Park, Ontario

Trypanosoma fallisi n. sp. is described from Bufo americanus in Ontario. The parasite was observed in 65 of 94 toads examined. The trypanosomes were pleomorphic with respect to the age of infections, being longer and broader in early infections (during spring and summer) and shorter and more slender during late summer and autumn. They ranged in size from 38-76 microns in body length and 3-8 microns in width, with a free flagellum 6-30 microns long. Epizootiological and experimental evidence suggests that this trypanosome is transmitted to the toads by the leech, Batracobdella picta. Trypanosoma fallisi is morphologically similar to T. bufophlebotomi described in Bufo boreas from California, but geographic isolation, host and vector differences as well as slight morphological differences indicate that speciation has occurred. Similar trypanosomes from Bufo americanus (which were identified as T. bufophlebotomi) in Michigan, are probably T. fallisi. This species shares many ultrastructural features with trypanosomes of other lower vertebrates and also of mammals.

Haematoloechus medioplexus: light and electron microscope localization of dipeptidyl aminopeptidases I and II in the gastrodermis

The exopeptidases, dipeptidyl aminopeptidases I and II (EC 3.4.14.1 and EC 3.4.14.2, respectively) were demonstrated cytochemically at light and electron microscope levels in the gastrodermis of adult Haematoloechus medioplexus recovered from the lungs of naturally infected Rana pipiens. Lys-Ala-4-methoxy-beta-naphthylamide and Pro-Arg-4-methoxy-beta-naphthylamide were used as specific substrates. Reaction products from both enzymes were observed in the gastrodermis in what are believed to be vesicles analogous to secondary lysosomes. The localization of the enzymes in these vesicles coincides with previous reports of the distribution of acid phosphatase and esterase activities. The hydrolases are believed to function both intracellularly by autophagy and extracellularly by digestion of host globin in the cecal lumen. Cathepsin B activity was not observed following the cytochemical protocol used in this investigation.

Sensitivity of diagnostic techniques in determining the prevalence of anuran trypanosomes

Two hundred thirty-three leopard frogs (Rana pipiens) from Oshkosh, Wisconsin, USA, were divided into two groups and their blood examined for trypanosomes. In Group I (n = 157), where the blood was examined by the hematocrit centrifuge technique (HCT), 36 (23%) were infected with trypanosomes. Eighteen were infected with Trypanosoma pipientis, 13 with Trypanosoma ranarum, three with Trypanosoma rotatorium and two with mixed infections of T. pipientis and T. ranarum. In Group II (n = 76) the blood was cultured and also examined by HCT and wet mounts. Trypanosomes (T. pipientis and T. ranarum) were detected in 24 frogs (33%) using all three techniques. Eleven T. pipientis were detected by HCT, however none by culture and two by wet mounts. Twelve T. ranarum were detected by culture while only 10 were found by HCT and five by wet mounts. One T. ranarum infection detected by HCT was missed by culture because of bacterial contamination. The HCT was consistently better than wet mount examinations. It is suggested that the HCT be used whenever possible in future trypanosome surveys.

Observations on spermatogenesis and inseminative behavior of Megalodiscus temperatus adults in frogs

Upon in vitro exposure to 3H-adenosine, spermatogonial cells in adult Megalodiscus temperatus were readily labeled on autoradiograms. At least 20 days were required for these cells to produce labeled sperm, the longest time reported so far for digenetic trematodes. Labelled worms transplanted to hosts for 24--31 days showed both self- and cross-insemination in multiple infections. When alone, half of the transplanted adults self-inseminated.

Observations on the seasonal prevalence, pathology and transmission of Dracunculus insignis (Nematoda: Dracunculoidea) in the raccoon (Procyon lotor (L.) in Ontario

Lesions due to Dracunculus insignis in the legs of raccoons (Procyon lotor) in southern Ontario occur seasonally as most larvigerous females emerge in the spring and early summer (April-June). The pathology of dracunculiasis in the raccoon is described and the transmission of the parasite in the wild is discussed with respect to seasonality and local agricultural practices. Crayfish, fishes and frogs (including tadpoles) were given infective third-stage larvae of D. insignis to test their suitability as paratenic hosts. Most of the larvae fed to adult Rana pipiens and R. clamitans were recovered from the somatic musculature. Larvae had increased in size and were highly infective to raccoons.

A survey of blood and other tissue parasites of leopard frogs Rana pipiens in the United States

In a survey of blood and other tissue parasites from 137 leopard frogs, Rana pipiens complex, purchased from 13 commercial vendors in 8 states in the United States, Trypanosoma pipientis was found in 2 R. p. berlandieri, Toxoplasma ranae in 1 R. pipiens, Isospora lieberkuehni in 1 leopard frog, Haemogregarina magna in 44, Lankesterella minima in 3, Leptotheca ohlmacheri in 3 and microfilariae of Foleyella sp. in 6. The report of I. lieberkuehni is presumably a new host record. Haemogregarina temporariae (Nöller,, 1920) nov. comb. is established as a new combination for Nematopsis temporariae.

Development of Physaloptera maxillaris (Nematoda: Physalopteroidea) in skunk (Mephitis mephitis) and the role of paratenic and other hosts in its life cycle

The development of Physaloptera maxillaris in skunk (Mephitis mephitis) was examined. The third moult was first observed at 5 days after infection and the fourth at 10 days. The prepatent period was determined as 41–45 days in skunk maintained under summer conditions. Various stages occurring in skunk are briefly described. Development of worms from the third stage to adulthood was consistently asynchronous in skunk.The striped skunk appears to be the only suitable definitive host of P. maxillaris. Experimentally it was not possible to produce patent infection in dogs (Canisfamiliaris), cats (Felis catus), mink (Mustela vison), ferrets (Mustela furo), rats (Rattus norvegicus), or raccoons (Procyon lotor) fed on the same diet as skunk. P. maxillaris is redescribed briefly.Leopard frogs (Rana pipiens) and garter snakes (Thamnophis sirtalis) may be potential paratenic hosts of P. maxillaris. Third-stage larvae did not penetrate tissues but remained in the gut for several days after infection and retained their infectivity. However, frogs and snakes are apparently not important components of the diet of skunk in the Guelph area.

The life cycle of Haematoloechus coloradensis Cort 1915 (Digenea: Plagiorchiidae), with emphasis on host susceptibility to infection

Mother and daughter sporocysts and xiphidiocercariae of Haematoloechus coloradensis develop in the snail, Physa virgata. Cercariae penerate and encyst in dragonfly nymphs, Tramea sp., Libellula sp., Anax sp., and in damselfly nymphs, Enallagma spp. Upon ingestion by the vertebrate host, metacercariae excyst and migrate into the lungs where they mature. Haematoloechus coloradensis is specific for its definitive host, R. pipiens, but shows some development in Ambystoma tigrinum. Although H. coloradensis is specific for its snail host, all odonate species tested served equally well as the second intermediate host.