TREMATODES

 

Trematodes are characterized by a sucker around the mouth and an additional ventral sucker that is used for locomotion and attachment to the host. Their life-cycle occurs in at least two different hosts and involves several generations (Mehlhorn, 2001). Molluscs are typically the first intermediate hosts whereas amphibians can be second intermediate- or definitive hosts. 

Halipegus spp. –

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Azygiida, Family Halipegidae, Genus Halipegus.

Description: Possesses a non-encysted metacercariae (Marquardt, Demaree, & Grieve, 2000). The vitellaria are divided into two compacted masses located at the posterior end of the body and are about 6 to 6.5 mm long (Olsen, 1986).

Lifecycle (by Thomas, 1939): Embryonated eggs passed in the feces of the frog hatch when eaten by a snail and develop cercariae which are swallowed by copepods. The infected cyclopoid copepods are swallowed by tadpoles. The worms remain in the mesentery until metamorphosis. Then the parasite migrates up to the esophagus into the Eustachian tubes. 

Pathology: Unknown

Location and Lifestage in Frog: Adult found in the eustachian tubes

Echinostoma spp. –

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Echinostomida, Family Echinostomidae, Genus Echinostoma or Echinoparyphium

Description: Medium-sized distome flukes with a collar of large spines surrounding the oral sucker (Olsen, 1986). The number, size, and position of spines are of taxonomic value (Marquardt, Demaree, & Grieve, 2000). Cysts are relatively small and highly spherical

Lifecycle: Snail first intermediate host; snail, tadpole, frog, and mollusk secondary intermediary host; definitive hosts are bird or mammal that ingests an intermediate host with metacercariae (Schmidt, 1992). Very adaptable to many species of hosts so these parasites are cosmopolitan (Schmidt & Roberts, 1989). The most common species found in the lab are Echinostoma trivolvis, and E. revolutum. They are 0.2mm,

Pathology: Heavy infections can decrease amphibian growth and cause whole-body edema, especially in early stage larvae (Johnson and McKenzie 2008). The number of metacercariae within amphibian kidneys can number in the thousands.

Location and Lifestage in Frog: Metacercariae found in the Gill Re-absorption Site, occationally the tail reabsorption site, but most commonly the kidneys (Olsen, 1986).

Megalodiscus temperatus

Taxonomy: Kingdom Animalia, Phylum Platyhelminths, Class Trematoda, Order Echinostomida, Family Paramphistomatidae, Genus Megalodiscus, Species temperatus

Description: It has a unique bell shape due to its large posterior sucker. Pharynx has two “saccular appendages” and the intestinal caeca extends near the posterior sucker (Prudhoe & Bray, 1982). About 6 mm long and 2 mm wide.

Lifecycle (by Schmidt, 1992): Miracidia infect young snails of Helisoma spp. Three generations of rediae with the final generation developing into cercariae which infect tadpoles via respiration and frogs through digesting their own stratum corneum.

Pathology: No documented effects to the host.

Location and Lifestage in Frog: Adults found in the rectum, occasionally the bladder (Prudhoe & Bray, 1982).

Ribeiroia ondatrae

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Echinostomida, Family Psilostomatidae, Genus Ribeiroia, Species ondatrae.

Description: Similar to echinostomes but they lack collar spines and have distinctive esophageal diverticula characteristic of the genus (Johnson & Sutherland, 2003). Another characteristic is the winding excretory vesicles and the cysts are elliptical and sometimes melanized in older hosts, giving cysts a golden hue.

Lifecycle (Johnson et al. 2004): Adults live and reproduce in the intestines of birds and mammals. Eggs are deposited in feces and rediae develop in snails, maturing into cercariae. This stage leaves the snail and then encysts in tadpoles or fish as metacercariae. When infected tadpoles or fishes are eaten by definitive hosts the metacercariae mature into adult worms.

Pathology: Ribeiroia infection can cause severe pathology and mortality in amphibian hosts, including mortality and limb malformations (extra limbs, missing limbs, skin webbings, bony triangles).  Malformations are expected to reduce infected host survival and may increase predation by definitive hosts (Johnson et al. 2004).

Location and Lifestage in Frog: Metacercariae found along the Tail Re-absorption Site, mandible, Gill Re-absorption Site, and Skin.

Auridistomum spp. –

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Plagiorchiida, Family Auridistomidae, Genus Auridistomum.

Description: According to Bogitsh (1959), the only known description of Auridistomum spp. was made by Stafford in 1900. The article questions the validity of Stafford’s designation and the genus of Auridistomum. From its order and suborder, the parasite lacks the caudal excretory vessels in all stages of development but has a Y-shaped excretory bladder and a horizontal stylet (Olsen, 1986).

Lifecycle: Known to infect snapping turtles as a definitive host (Bogitsh, 1959).

Pathology: Unknown

Location and Lifestage in Frog: Found in the Tail Re-absorption Site, Gill Re-absorption Site, and the mesentery.

Choledocystus spp. –

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Plagiorchiida, Family Plagiorchiidae, Genus Choledocystus.

Description (by Prudhoe & Bray 1992): Rounded, oval body with the ventral sucker a little anterior to middle of body. Oral sucker is subterminal and larger than the ventral sucker. Testes are rounded and arranged symmetrically in middle region of body. The excretory vesicle is more or less Y-shaped (Gibson, Jones, and Bray, 2008). Receptaculum seminis lacking.

Lifecycle (by Schmidt & Roberts, 1989): Family Plagiorchiidae use aquatic snails as first intermediate hosts and insects are the second intermediate hosts however this family is adaptable to different situations so the exact lifecycle of Choledocystus is not known. They parasitize vertebrates from fishes through birds and mammals.

Pathology: Unknown

Location and Lifestage in Frog: Metacercariae in the intestines.

Glypthelmins quieta

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Plagiorchiida, Family Plagiorchiidae, Genus Glypthelmins, Species quieta.

Description (Miller, 1930): Round oral sucker near the anterior end with a very small prepharynx. Presence of pharyngeal glands. Small ventral sucker and the testes are not always in the same place among individuals. The oral sucker is larger than the ventral sucker and the intestinal caeca almost reaching the posterior end of the body (Prudhoe & Bray, 1982). Size not specified

Lifecycle: Cercariae encyst in the skin of frogs. The metacercariae are shed with stratum corneum which the frogs eat, becoming infected with their own flukes. (Olsen, 1986).

Pathology: Unknown

Location and Lifestage in Frog: Adult found in the small intestines (Odlaug, 1954).

Gorgoderidae –

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Plagiorchiida, Family Gorgoderidae.

Description: It has a very large ventral sucker that protrudes off the body much larger than the oral sucker (Olsen, 1986). Vitellaria consits of two compact or lobed glands located behind the ventral sucker and between the caeca (Olsen, 1986). About 3 to 5 mm long.

Lifecycle (by Coil, 1954): Gorgoderina attenuata uses a clam Sphaerium occidentalis as an intermediate host with a tadpole and later frog as its definitive host.

Pathology: Unknown

Location and Lifestage in Frog: Adult found in the urinary bladder (Olsen, 1986).

Haematoloechus spp. –

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Plagiorchiida, Family Haematoloechidae, Genus Haematoloechus.

Description: Elongate worms with very small ventral sucker anterior to ovary anterior to testes (Schmidt, 1992). Presence of an extensive vitellaria (Schmidt & Roberts, 1989). Has a well defined and colorful gonads and digestive tract. However, there are a wide range of species with variable attributes. Approximately 7 mm long.

Lifecycle: Eggs layed in lungs of frog or toad then carried up respiratory tract by ciliary action to digestive tract and out of the body (Schmidt & Roberts, 1989). Snails function as an intermediate host and produce xiphidiocercariae which are drawn to a dragonfly naiad (Schmidt, 1992). Adult dragonflies are then eaten by a frog definitive host where the parasites climb back up the esophagus into the lungs. (Olsen, 1986).

Pathology: Creates poor nutrition and a heavy burden on the lungs with minor lesions. Unlikely to cause death even with heavy infection (Hsu, Carter, Williams, & Besch-Williford, 2004).

Location and Lifestage in Frog: Adult in lungs.

Manodistomum syntomentera (synonym of Paralechriorchis syntomentera)

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Plagiorchiida, Family Ochetosomatidae, Genus Paralechriorchis, Species syntomentera

Description: This parasite has distinguishing Y-shaped excretory vesicles at posterior end and the intestinal ceca do not extend past the anterior end of the excretory vesicles (Prudhoe & Bray, 1982). The anterior and ventral sucker are about the same size.

Lifecycle: Miracidia infect snails, xiphidiocercariea encyst in snails or insect larva or frog, metacercariae occur in frogs, and adult worms in snakes (Prudhoe & Bray, 1982).

Pathology: Unknown

Location and Lifestage in Frog: Metacercariae found in the Tail Re-absorption Site, mandible, Gill Re-absorption Site, and mesentery.

Euryhelmis spp. –

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Opisthorchiida, Family Heterophyidae, Genus Euryhelmis

Description (by Ameel, 1938): Small, leaf-like body with an excretory visicle either Y- or T-shaped. Cirrus-pouch absent. Seminal vesicle present or absent. Relatively shrt uterus of three loops mainly on the left side of the body between the ventral and excretory sucker. Vitelline follicles numerous and lateral. About 0.4 mm long

Lifecycle (by Ameel, 1938): Mammal definitive host, snail first intermediate host, and frog second intermediate host where they penetrate and encyst in the skin.

Pathology: Unknown

Location and Lifestage in Frog: Metacercariae under the skin of frog hosts (Bowman, Hendrix, Lindsay, & Barr, 2002)

Clinostomum attenuatum

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Strigeatida, Family Clinostomatidae, Genus Clinostomum, Species attenuatum.

Description: The Superfamily Clinostomatoidae has pigmented eyespots (Schmidt & Roberts, 1989) and the Family Clinostomatidae an oral sucker surrounded by a “collar-like fold” (Olsen, 1986).  The ventral sucker is very close to the oral sucker with intestinal caeca running the length of the body.  About 1.5–2 mm in diameter.

Lifecycle (by Olsen, 1986): Adults reside in the mouth cavity of bitterns. The eggs are deposited through feces, hatch, and infect a snail intermediate host where they mature and eventually release cercariae. Cercariae infect frogs or fishes as second intermediate hosts, which are then eaten by a bittern, and the developed metacercariae migrate from the stomach to the mouth of the bird and reach sexual maturity.

Pathology: No effect to host when encysted except an increased amount of malanomacrophages around the cyst (McAllister, Bursey, Niemiller, Miller, 2007). Metabolic costs on frog hosts unknown.

Location and Lifestage in Frog: Unusually large metacercariae found underneath the skin and in the mesenteries (Olsen, 1986).  They have a thin cyst wall and are highly mobile when the cyst wall is broken.

Alaria spp. –

    Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Strigeatida, Family Diplostomidae, Genus Alaria.

    Description: The mesocercariae are about 2.5 to 4 mm long, covered in body spines, and have a smaller forebody than hindbody with a centralized ventral sucker (Schmidt & Roberts, 1989).

    Lifecycle (Olsen 1986): The eggs leave with the feces of a mammal definitive host, hatch in two weeks and penetrate a snail. They then shed their ciliated coverings and produce daughter sporocysts. Cercariae are fully developed in 2 to 3 weeks after maturation of daughter sporocysts. When tadpoles swim by, the cercariae attach and enter; mature into mesocercariae while the tadpole metamorphoses. The tadpole or frog is then eaten by the definitive host where eggs are produced in the intestines within 34 to 37 days after ingestion. Another method of ingestion involves a paratenic host (a snake for example). This method transports mesocercariae into terrestrial environments where the definitive host then consumes the paratenic host.

    Pathology: Alaria infections can be pathogenic in vertebrate hosts when high in number or when the vertebrate is not a typical host (e.g., a human).  Mesocercaria can kill an intermediate host with a severe infection (Schmidt & Roberts, 1989) but often pathology is minimal (Johnson et al. 1999).

    Location and Lifestage in Frog:  The mesocercariae are found in the Tail Re-absorption Site and around the sternum. They lack a cyst wall and are highly mobile.

Strigeidae –

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Strigeatida, Family Strigeidae

Description: The forebody is cup-shaped with the acetablum and tribocytic organ located inside. The hindbody is short, stout, and is curved dorsally (Schmidt & Roberts, 1989).

Lifecycle: The metacercariae stage is referred to as a “tetracotyle” and possesses the ability to enter a host already infected by another species of trematode and infect the parasite – a “hyperparasite” (Schmidt & Roberts, 1989). Life histories of Strigeidae have considerable variation (Olsen, 1986)

Pathology: Unknown

Location and Lifestage in Frog: Metacercariae under the skin or in mesentery of frogs (Olsen, 1986).

Fibricola spp.  –

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Strigeatida, Family Diplostomatidae, Genus Fibricola.

Description (by Chandler, 1942): Spoon shaped with numerous calcareous granules enclosed in terminal vesicles in the diplostomulum stage. The esophagus forks about midway between the pharynx and the ventral sucker and the ceca extends almost to the hind end of the forebody. The cyst is delicate and will easily excyst.

Lifecycle (Seo, Lee, Chai, Hong, & Hong, 1988): Eggs hatch into miracidia which infect snails, cercariae infect tadpoles of frogs and develop into metacercariae. When consumed by a mammal definitive host, the parasite sexually matures.

Pathology: Unknown in amphibians, but some records of pathology in humans as accidental hosts.

Location and Lifestage in Frog: Metacercariae found mainly in leg muscles, but can also be present in the Tail Re-absorption Site, urinary bladder, and mesentery (Seo, Lee, Chai, Hong, & Hong, 1988).

Apharyngostrigea pipientis

Taxonomy: Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda, Order Strigeatida, Family Strigeidae, Genus Apharyngostrigea, Species pipientis.

Description: Information on this genus and species is largely lacking. The Family Strigeidae has fork-tailed cercariae with two suckers, oral and ventral, a two-lobed tribocytic organ, and a hindbody that is cylindrical (Schmidt, 1992). About 0.35 to 0.45 mm in length.

Life cycle: The definitive host are birds (Goldberg, Bursey, McKinnell, & Tan, 2001). The exact life cycle of Apharyngostrigea pipientis is unknown.

Pathology: Unknown

Location and Lifestage in Frog: The metacercariae are encysted in masses around the urinary bladder, heart, and on the muscles of the throat (Odlaug, 1954) but can also encyst underneath the skin.

(Sullivan and Byrd, 1970)

(Ameel, 1938)