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Echinostoma trivolvis

By Jessica Sosnicki

Geographic Range

Geographic range and population size of a trematode is usually dependent on host availability and movement in nature (Detwiler & Minchella, 2009). On the continental scale, Echinostoma trivolvis are found only in North America (Kanev, 1995; Klockars et al. 2007). Their first intermediate host, Planorbella trivolvis, has a widespread distribution across the continent, only absent from the northern Canadian provinces, the Pacific northwest, the desert southwest, and perhaps several Great Plains states (Burch 1989). Their primary definitive hosts, muskrats (Ondatra zibethicus), are distributed across the entirety of North America, excepting the northernmost parts of Canada, the desert southwest and parts of California (Patterson et al., 2003). From these first-intermediate and definitive host distributions, coupled with low specificity for second intermediate hosts, it is tenable to suggest a very wide distribution of Echinostoma trivolvis across North America.

At the local scale, Klockars and her associates (2007) studied sites in New Jersey with Planorbella trivolvis, the first intermediate host, to determine the prevalence of parasites found in the organism. Nine of ten sites studied were found to have P. trivolvis infected with E. trivolvis. (Detwiler and Minchella, 2009; Kanev, et al., 1995; Klockars, et al., 2007; Patterson, et al., 2003)

Habitat

For organisms with complex life cycles, including several free-swimming stages and several hosts, defining the organism’s habitat is difficult. The habitat of the parasitic stages is primarily dictated by parasite location inside hosts (Bush et al., 2001). For example, as an adult, E. trivolvis inhabit the digestive system of vertebrates – but even within the intestines of a muskrat there is a wide range of conditions along the length of the intestine (i.e. changes in pH). Most often scientists’ understanding of the physical requirements of a parasite, in terms of within-host habitats, is poorly known. Habitat also changes ontogenetically, that is, as the parasite go through various stages in its lifecycle. In the first host, snails are infected in the ovotestis and hepatopancreas, an organ that functions like the liver and pancreas in mammals, by miracidia (Fried et al., 1987). Echinostoma trivolvis metacercariae encyst in the kidneys of snails and amphibians (Schmidt & Fried, 1996), while most adults live in the digestive tract of the definitive host, which can be a muskrat or bird (Fried & Graczyk, 1997). (Bush, et al., 2001; Fried and Graczyk, 1997; Fried, et al., 1987; Schmidt and Fried, 1996)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

Like most other trematodes, E. trivolvis is unsegmented, and as an adult, has a pair of suckers, an incomplete digestive system, a primitive brain, and is hermaphroditic (individuals have both female and male sex organs) (Bush et al., 2001).

The anatomy of Echinostoma trivolvis changes dramatically through its life cycle. As an adult, E. trivolvis is a 37-collar-spined trematode (Fried et al., 1997). The 37-collar-spines refer to the spines found around the mouth of the trematode, attached to the distal cytoplasm (Roberts & Janovy Jr., 2000). The distal cytoplasm is another name for a trematode’s tegument, a secreted cuticle used for protection and defense against water loss. Like other species of the phylum Platyhelminthes, Echinostoma trivolvis lacks circulatory, respiratory, and skeletal systems (Bush et al. 2001). They have protonephridium (also known as flame cells) that aid in the excretory system, similar to the function of human kidneys.

Eggs and miracidia are roughly 100 micrometers long, while adults vary in size, but typically range from 1 to 5 mm (Fried & Graczyk, 1997). Miracidia have cilia that allow for movement to find a host, while cercariae have a flagellum (Bush et al., 2001). Echinostoma trivolvis metacercarial cysts are spherical with walls partially created from pieces of the host’s kidneys (Fried & Bennett, 1979). Trematodes, like E. trivolvis, have both male and female reproductive organs. The male part typically has two testes, while the female region has one ovary (Fried & Graczyk, 1997). (Bush, et al., 2001; Fried and Bennett, 1979; Fried and Graczyk, 1997; Fried, et al., 1997; Roberts and Janovy Jr., 2000)

Development

The lifecycle of Echinostoma trivolvis consists of seven basic stages, which include two transmission or infective stages, miracidia and cercariae (Davis, 2005).

Eggs are produced as a result of sexual reproduction by hermaphroditic adult worms within the definitive host. They are released with the host’s digesettive tract, and released during defecation. Eggs take approximately 2-3 weeks to develop into miracidia in an aquatic environment (Baker & Muller, 1996).

The miracidia find and infect a first intermediate host, the gastropod Planorbella trivolvis, by penetrating the head-foot area of the snail (Toledo et al., 2007). We don't know how long this takes for this species, but in penetration takes roughly 30 minutes for most trematodes (Roberts & Janovy Jr., 2000).

Inside the first host, each miracidium transform into a sac, called a sporocyst. Within this structure, embryos form and develop into rediae, which themselves duplicate and produce daughter rediae via asexual reproduction. Each redia, in turn, can produce many cercariae through asexual reproduction.

The cercariae exit their parent redia through a birth pore (Detwiler & Minchella, 2009). After 4-6 weeks in the gastropod, the cercariae leave the first host (Baker and Muller, 1996). They can then infect a number of different second intermediate hosts, including both gastropods and amphibians. In this second intermediate host, the trematode develops into a metacercaria that will encyst, typically in the kidneys, for several weeks, and may remain, dormant, for months or years, waiting for the second intermediate host to be consumed by a suitable definitive host (Detwiler & Minchella, 2009).

A few metacercariae eventually enter a definitive host via consumption of the second intermediate host. The body of the definitive host, either a bird or muskrat, will become the habitat for the adult Echinostoma trivolvis. The adult parasites most likely remain in the digestive tract, eventually laying eggs that will finally enter an aquatic habitat, starting the lifecycle over again (Bush et al., 2001).

Studies conducted by N. E. Davis investigating the eggs of Echinostoma revolutum, a closely related species, have shown that the duration of hatching time in trematodes depend the temperature of the environment. Eggs can remain dormant until warm water temperature to avoid the chance of freezing as miracidia. The ideal water temperatures for these parasites vary depending on the habitat. In addition, temperature also affects the activity of miracidia and cercariae stages. As temperature is increased, activity increases, which causes the parasite to use more resources from the host (Davis, 2005). (Baker and Muller, 1996; Bush, et al., 2001; Davis, 2005; Detwiler and Minchella, 2009; Roberts and Janovy Jr., 2000; Toledo, et al., 2007)

Reproduction

Adults of Echinostoma trivolvis are hermaphroditic, and capable of both cross- and self-insemination. (Nollen, 1997)

Adults of Echinostoma trivolvis release large numbers of eggs into the digestive tract of their hosts. These eggs pass out of the host during defecation. Refer to the Development section for more information on the lifecycle of this species. (Roberts and Janovy Jr., 2000)

Except for the provisioning of eggs, there is no parental investment in this species.

  • Parental Investment
  • pre-hatching/birth
    • provisioning
      • female

Lifespan/Longevity

Refer to the Development section for the longevity of each stage in Echinostoma trivolvis.

Behavior

These worms are capable of motion in nearly all life-stages, as they locate host organisms and sites within their hosts. Once there though, they are very sedentary. (Roberts and Janovy Jr., 2000)

Communication and Perception

We have little information concerning perception by E. trivolvis in particular, but there are studies of host-perception and host-finding behavior in other trematodes (Thiemann & Wassersug, 2000). Trematodes have several mechanisms of finding a host, which include the use of chemo-orientation, and sensitivity to shadow stimuli, touch, and water turbulence. The cues that allow trematodes to distinguish between host and non-host in chemo-orientation are driven by the recognition of molecules given off by the host (Fried & Graczyk, 1997). Free swimming stages, miracidia and cercariae, cannot survive long outside a host, and are vulnerable to predation, so must find a host quickly. This suggests that trematodes engage is some sort of host-finding behavior (Fried & Graczyk, 1997). Miracidia will follow snail host excretory-secretory (ES) chemicals to find them. The chemicals are macromolecules which can stimulate trematode activity into finding their host. E. trivolvis has also been seen to respond to products such as acetic acid, sulfuric acid, and hydrochloric acid, by gathering near the source. Although more research is being conducted on miracidial host-finding behavior, scientists are still unsure as to what actually causes miracidia to attach to gastropod hosts (Haas et al., 1995). Cercariae also exhibit chemo-orientation host-finding behavior. However, they respond to smaller molecules, like amino acids, instead. Although sharing the same genes, miracidia and cercariae utilize different chemicals to achieve the same objective, finding and penetrating the host (Haberl et al., 2000).

Adults of this species can perceive adjacent individuals in their host's digestive tract, and may move together to mate. (Fried and Graczyk, 1997; Haas, et al., 1995; Haberl, et al., 2000; Thiemann and Wassersug, 2000)

Food Habits

The adults of this species feed on digested food absorbed from their surroundings in the gut of their host. The feeding immature stages feed on nutrients taken from host tissues and fluids. Host-seeking miracidia and cercariae do not feed. Trematodes like E. trivolvis, are facultative anaerobes (Roberts & Janovy Jr., 2000). Their metabolism relies on the breakdown of carbohydrates (primarily glucose and glycogen). Unlike other organisms that utilize most of the energy potential of a carbohydrate, trematodes incompletely catabolize their energy rich resources. Scientists have no definite explanation as to why they do this, but hypothesize it might be due to the relatively inexhaustible supply of nutrients the host provides to the parasite. (Roberts and Janovy Jr., 2000)

  • Animal Foods
  • amphibians
  • body fluids
  • mollusks

Predation

No specific predators are known. Host-seeking miracidia and cercariae are probably consumed by animals that feed on zooplankton, such as filter-feeding molluscs, small fish, and micro-crustaceans.

Ecosystem Roles

While largely unexplored empirically, parasites like E. trivolvis may play important roles in regulating the abundance and distribution of particular host species. In particular, parasitism may interact with other stressors like predation or pollution (Thiemann & Wassersug, 2000). Tadpoles can differentiate between infected and uninfected snails and move away from infected snails. This helps them avoid being penetrated by cercariae that seek them out as a host. However, with the addition of a predator, tadpoles decreased their movement, and exhibited an increase in trematode infection. This has important implications when assessing increased fish (predators) introductions into ponds and lakes where snails and trematodes are present. These introductions may result in an elevation of trematode infections and thus a decrease of native amphibian populations. Pollution can also play a role in parasite-host interactions (Budischak et al. 2008). Exposure to pesticides damages the immune system, leading to an increase in susceptibility to trematode infections. Eutrophication caused by pollution stimulates snail growth and parasite prevalence within the snail. However, these snails may lack healthy immune responses to prevent parasite infection and thus become a host. This field of parasitology is important when considering global climate change, which may cause an increase in parasite numbers (stimulated by longer reproductive seasons, ideal warmer conditions, and larger habitat ranges) because of a warmer climate (Budischak et al. 2008). (Budischak, et al., 2008; Thiemann and Wassersug, 2000)

Parasites can affect the behavior of their hosts. Levri (1998) showed that snails infected with Microphallus, a genus of trematode, expose themselves to predation risk more often than those that were uninfected. This exposure would allow the internal parasite to pass from one host to another, by increasing the probability that its host would be consumed. (Levri, 1998)

These flukes use freshwater snails, including Planorbella trivolvis, as first intermediate hosts, and tadpoles of ranid frogs as second intermediate hosts. Their primary definitive host is the common muskrat Ondatra zibethicus, but they may also mature and reproduce in mallard ducks (Anas platyrhynchos) and other birds or mammals. (Budischak, et al., 2008; Schmidt and Fried, 1996)

Species Used as Host

Economic Importance for Humans: Positive

No known positive economic importance.

Economic Importance for Humans: Negative

There are no known adverse effects of Echinostoma trivolvis on humans.

Conservation Status

E. trivolvis is not of conservation concern, though trematodes that infect humans have been studied extensively (e.g., schistosomes). Relatively little is known about trematode effects on amphibians (Fried et al. 1997) or other wildlife hosts. Recently, trematode infections have been linked to declines in some amphibian populations. When some trematodes, like Ribeiroia ondatrae, encyst inside an amphibian, they can cause kidney damage and limb deformities (Johnson et al., 1999). Studies conducted by Holland et al. (2006) have shown that frog tadpoles have an elevated risk of mortality, as well as increased edema rates, if exposed to cercariae of echinostomes. Tadpoles exposed early in their development were more likely to have higher percentages of mortality, than those further along in development (Holland et al., 2006). In addition, pesticides may lower immunity and raise susceptibility to trematode infections (Rohr et al., 2008). Amphibians, then, may be facing numerous interactive threats (Rohr et al., 2008). (Fried, et al., 1997; Holland, et al., 2006; Johnson, et al., 1999; Rohr, et al., 2008)

Other Comments

Echinostoma trivolvis is one of roughly 100 species in its genus.

Many parasites species are difficult to identify or distinguish, since they often exhibit simplified morphology, parasitize similar hosts, and exhibit wildly different morphologies throughout their life cycle. The difficulty of culturing a parasite through several host organisms also makes taxonomy problematic. Echinostoma trivolvis was initially confused with Echinostoma revolutum, and many past scientific articles studied the former, but identified it incorrectly as as the latter. For example, there were over 60 studies conducted by B. Fried and his colleagues on “*E. revolutum*” between 1968 and 1988, in addition to articles written by Paul C. Beaver in 1936 and Clyde M. Senger in 1954 (Baker & Muller, 1996). Fried and colleagues also were the ones to correct the identification (Kanev 1995). E. trivolvis differs from most other trematodes because of its 37-collar-spine and definitive hosts, which can be a bird or muskrat (Mucha et al., 1990). Unlike E. revolutum, the adult stage of E. trivolvis can infect both birds and mammals, while E. revolutum adults are only known from birds. E. trivolvis is also distinguished by cercariae that only infect planorbid snails; E. revolutum infect lymnaeid snails. Echinostoma trivolvis occurs across North America, while Echinostoma revolutum is found in Europe and Asia (Kanev, 1995). (Baker and Muller, 1996; Bush, et al., 2001; Cribb, et al., 2002; Kanev, et al., 1995; Mucha, et al., 1990; Poulin and Morand, 2004)

Contributors

Jessica Sosnicki (author), Radford University, Jeremy Wojdak (editor), Radford University, Karen Powers (editor), Radford University, George Hammond (editor), Animal Diversity Web Staff.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

asexual

reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

visual

uses sight to communicate

References

Baker, J., R. Muller. 1996. Advances in Parasitology. San Diego, CA: Academic Press Inc.

Budischak, S., L. Belden, W. Hopkins. 2008. Effects of malathion on embryonic development and latent susceptibility to trematode parasites in ranid tadpoles. Environmental Toxicology and Chemistry, 27: 2496-2500.

Burch, J. 1989. North American Freshwater Snails. Hamburg, Michigan: Malacological Publications.

Bush, A., J. Fernandez, G. Esch, J. Seed. 2001. Parasitism: The diversity and ecology of animal parasites. Cambridge, UK: Cambridge University Press.

Cribb, T., L. Chisholm, R. Bray. 2002. Diversity in the Monogenea and Digenea: Does lifestyle matter?. Australian Society for Parasitology, 32: 321-328.

Davis, N. 2005. Storage and incubation of Echinostoma revolutum eggs recovered from wild Branta canadensis, and their infectivity to Lymnaea tomentosa snails. Journal of Helminthology, 79: 321-326.

Detwiler, J., D. Minchella. 2009. Intermediate host availability masks the strength of experimentally-derived colonisation patterns in echinostome trematodes. International Journal for Parasitology, 39: 585-590.

Fried, B., M. Bennett. 1979. Studies on encystment of Echinostoma revolutum cercariae. Journal of Parasitology, 65: 38-40.

Fried, B., T. Graczyk. 1997. Advances in Trematode Biology. Salem, MA: CRC-Press.

Fried, B., P. Pane, A. Reddy. 1997. Experimental infection of Rana pipiens tadpoles with Echinostoma trivolvis cercariae. Parasitology Research, 83: 666-669.

Fried, B., S. Scheuermann, J. Moore. 1987. Infectivity of Echinostoma revolutum miracidia for laboratory-raised pulmonate snails. Journal of Parasitology, 73: 1047-1048.

Haas, W., B. Haberl, M. Kalbe, M. Kömer. 1995. Snail-host-finding by miracidia and cercariae: chemical host cues. Parasitology Today, 11: 468-472.

Haberl, B., M. Körner, Y. Spengler, M. Kalbe, W. Haas. 2000. Host-finding in Echinostoma caproni: miracidia and cercariae use different signals to identify the same snail species. Parasitology, 120: 479-486.

Holland, M., D. Skelly, M. Kashgarian, S. Bolden, L. Harrison, M. Cappello. 2006. Echinstome infection in green frogs (Rana clamitans) is stage and age dependent. Journal of Zoology, 271: 455-462.

Johnson, P., K. Lunde, E. Ritchie, A. Launer. 1999. The effect of trematode infection on amphibian limb development and survivorship. Science, 30: 802 - 804.

Kanev, I., B. Fried, V. Dimitrov, V. Radev. 1995. Redescription of Echinostoma trivolvis (Cort, 1914) (Trematoda: Echinostomatidae) with a discussion on its identity. Systematic Parasitology, 32: 61-70.

Klockars, J., J. Huffman, B. Fried. 2007. Survey of seasonal infections in Helisoma trivolvis (Gastropoda) from lenthic ecosystems in New Jersey, U.S.A. Comparative Parasitology, 74: 75-80.

Levri, E. 1998. Perceived predation risk, parasitism, and the foraging behavior of a freshwater snail (Potampyrgus antipodarum). Canadian Journal of Zoology, 76: 1878-1884.

Mucha, K., J. Huffman, B. Fried. 1990. Mallard ducklings (Anas platyrhynchos) experimentally infected with Echinostoma trivolvis (Digenea). The Journal of Parasitology, 76: 590-592.

Nollen, P. 1997. Mating behaviour of Echinostoma caproni and E. trivolvis in concurrent infections in hamsters. International Journal for Parasitology, 27/1: 71-75.

Patterson, B., G. Ceballos, W. Sechrest, M. Tognelli, T. Brooks, L. Luna, I. Ortega, B. Young. 2003. "Digital Distribution Maps of the Mammals of the Western Hemisphere, version 1.0" (On-line). Accessed April 01, 2009 at http://www.natureserve.org/getData/birdMaps.jsp.

Poulin, R., R. Morand. 2004. Parasite Biodiversity. Washington, DC: Smithsonian Institution Press.

Roberts, L., J. Janovy Jr.. 2000. Foundations of Parasitology. Boston, MA: McGraw Hill.

Rohr, J., A. Schotthoefer, T. Raffel, H. Carrick, N. Halstead, J. Hovermann, C. Johnson, L. Johnson, C. Lieske, M. Piwoni, P. Schoff, V. Beasley. 2008. Agrochemicals increase trematode infections in a declining amphibian species. Nature, 455: 1235-1239.

Schmidt, K., B. Fried. 1996. Experimental infection of Helisoma trivolvis (Colorado strain) with cercariae of Echinostoma trivolvis. International Journal for Parasitology, 26: 287-289.

Thiemann, G., R. Wassersug. 2000. Patterns and consequences of behavioural responses to predators and parasites in Rana tadpoles. Biological Journal of the Linnean Society, 71: 513-528.

Toledo, R., C. Muñoz-Antoli, B. Fried. 2007. The use of echinostomes to study host– parasite relationships between larval trematodes and invertebrate and cold-blooded vertebrate hosts. Parasitology Research, 100: 1177-1185.

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