Protozoans

 

Protozoans are the “animal-like” members of Protista, a paraphyletic grouping of mostly single-celled eukaryotic organism that feed heterotrophically and exhibit diverse mechanisms of mobility. They can contain more than one nucleus and developed organelles (Schmidt & Roberts, 1989).

Nyctotherus spp.

Taxonomy: Kingdom Protozoa, Phylum Ciliophora, Class Ciliatea, Order Heterotrichida, Family Spirostomidae, Genus Nyctotherus

Description (by Olsen, 1986): Somewhat flattened, oval body with the dorsal surface arched and the ventral concave. The peristome begins at the anterior end and about midway turns to the cytostome. The cytopharynx is a curved funnel-shaped tube that enters the cytoplasm from the cytostome with a row of membranelles along the right margin. Rows of cilia cover the body and they are about 60 to 200 µm long (Schmidt, 1992).

Lifecycle (by Olsen, 1986): The cysts are excreted in feces from definitive host (frog) where tadpoles eat them. Transverse binary fusion, conjugation, and finally cyst formation continue during tadpole metamorphosis.

Pathology: unknown

Location and Lifestage in Frog: Found in the intestines (Schmidt & Roberts, 1989).

Trichodina spp. –

Taxonomy: Kingdom Protozoa, Phylum Ciliophora, Class Oligohymenophorea, Family Trichodinidae, Genus Trichodina.

Description (by Schmidt & Roberts, 1986): Lacks stalks, mobile, and the oral-aboral axis is shortened with a prominent basal disc (usually at the aboral pole). A protoplasmic fringe/velum lies on the border of the basal disc and a circle of cilia lies underneath. Additionally a second circle of cilia can always be found above the disc. It is about 30 to 50 µm in diameter.

Lifecycle: Direct lifecycle (one host) by binary fission (Diller, 2005).

    Pathology: unknown. Innocuous in shellfish (Bower, McGladdery, & Price, 1994)

Location and Lifestage in Frog: In the skin and Gill Re-absorption Site (Diller, 2005).

Tritrichomonas spp. –

Taxonomy: Kingdom Protozoa, Phylum Metamonada, Class Flagellata, Order Trichomonidad, Family Trichomonadidae, Genus Tritrichomonas

Description: Pear-shaped with four to six flagella near the single large nucleus where one is extending to the posterior end and is about 10 µm long (Olsen, 1986). A tubular axostyle extends from the anterior end of the body and is sausage shaped (Marquardt, Demaree, & Grieve, 2000).

Lifecycle: Reproduction by binary fission and transmission during sexual intercourse in the intestinal or reproductive tracts of their hosts (Schmidt and Roberts, 1989).

Pathology: Unknown

Location and Lifestage in Frog: The intestines or reproductive tract (Schmidt & Roberts, 1989).

Entamoeba spp. –

Taxonomy: Kingdom Protozoa, Phylum Sarcomastigophora, Class Lobosa, Order Amoebida, Family Entamoebidae, Genus Entamoeba

Description: Uninucleate form with no flagellate stage (Schmidt, 1992). Cysts are roundish and mature cysts have four nuclei and are about 10-15 µm (Olsen, 1986).

Lifecycle (by Olsen, 1986): Cysts passed through feces are eaten by definitive hosts and ruptures producing four amoebae who enter the crypts of the large intestines and feed on the mucosa. They multiply by binary fission and irritate the mucousa producing ulcers. Destruction of the tissue on a massive scale results in dysentery where cysts are expelled in feces.

Pathology: unknown in frogs but has caused diphtheroid colitis, endoparasitism, focal pneumonia and inclusion bodies typical for inclusion body disease (IBD) in a boa constrictor (Richter, Kübber-Heiss, & Weissenböck, 2008).

Location and Lifestage in Frog: Found in the colon (Schmidt, 1992).

Opalina spp.–

Taxonomy: Kingdom Protozoa, Phylum Sarcomastigophora, Class Opalinea, Order Opalinida, Family Opalinidae, Genus Opalina

Description: Multinucleate with pseudopodia and flagella; very mobile because of parallel oblique rows of cilia (Olsen, 1986). With the naked eye under the microscope, they swim in circles and reflect the light in a colorful display. They are about 10 to 20 µm long.

Lifecycle (by Smyth and Smyth, 1980): Direct; adults encyst and expelled by feces, eaten by tadpoles where the protozoa conjugate and mature into adults. Asexual binary fission follows until encysted and expelled once again.

Pathology: No effect

Location and Lifestage in Frog: Adult trophozoite in rectum, bladder, and small intestines (Schmidt, 1992).

(Brace et al.,1953)

(Mueller, 1937)

(Brooke and Melvin, 1969)

(Wood, 2009)