JPC SYSTEMIC PATHOLOGY
Signalment (JPC# 3121691): Adult female guppy (Poecilia reticulata) from a pet store
HISTORY: The fish was euthanized following a prolonged period of anorexia and weight loss.
HISTOPATHOLOGIC DESCRIPTION: Scaled skin with subjacent skeletal muscle: Extending through the multifocally eroded and ulcerated scaled skin, further extending through the dermis and multifocally into the variably affected subjacent skeletal muscle, and multifocally expanding the submesothelial space of the coelomic cavity by up to 300um, are numerous ciliate trophozoites. Ciliate trophozoites are 30 to 40 um diameter, ovoid, with a thin cell wall lined circumferentially by cilia of equal length and distribution, cytoplasm that contains variably sized eosinophilic globules, one irregularly oval to elongate deeply basophilic macronucleus, and occasionally a contractile vacuole. Trophozoites are frequently admixed with a small amount of eosinophilic cellular and karyorrhectic debris (necrosis), minimal fibrin, edema, and rare hemorrhage as well has low to moderate numbers of granulocytes and few lymphocytes (most significant in the areas of cutaneous ulceration/erosion). Individual rhabdomyocytes are surrounded, separated, and rarely replaced by ciliate trophozoites, and are often characterized by one of the following: shrunken with irregularly sized sarcoplasm (atrophy); pale, swollen, vacuolated sarcoplasm with loss of cross striations (degenerate); or hypereosinophilic, fragmented sarcoplasm with nuclear pyknosis, karyolysis, or karyorrhexis (necrotic).
Liver, hepatocytes: Hepatocellular cytoplasm is frequently expanded by single varisized vacuoles which often peripheralize the nucleus (lipid).
Intestine: Within the intestinal lumen is a cross section of a 350um diameter adult cestode with a 3um brightly eosinophilic tegument bounding a spongy parenchyma containing basophilic calcareous corpuscles and a uterus with many 10-20 um thin walled eggs.
- Scaled skin, skeletal muscle, and coelomic cavity: Ciliated trophozoites, numerous, with associated mild to moderate granulocytic inflammation, rhabdomyocyte degeneration and necrosis, and erosive to ulcerative dermatitis, etiology consistent with Tetrahymena corlissi, guppy, (Poecilia reticulata), Cyprinodontiform.
- Liver: Hepatic lipidosis, diffuse, marked.
- Intestine: Adult cestode.
ETIOLOGIC DIAGNOSIS: Tetrahymenal coelomitis, myositis, and dermatitis
CAUSE: Tetrahymena corlissi
SYNONYMS: Guppy disease; spectacle eye; tetrahymeniosis; “tet disease”
- Tetrahymenids are common, typically free-living, saprophytic, freshwater ciliate protozoans but can be highly lethal fish pathogens and may cause systemic disease
- Tetrahymeniosis causes severe economic losses in commercial guppy farms worldwide
- Called “guppy disease” because of its predilection for guppies (including mortality up to 100%), but can infect other livebearers, cichlids, tetras, golden perch, laboratory zebrafish, and even freshwater leeches
- Reported to infect amphibians
- Environmental contamination à direct skin invasionà reproduction by binary fission forming small reproductive cysts containing 2-8 tomites à may cause systemic infection
- Stress, such as poor water quality or concurrent disease, predisposes fish to disease
- Poor water quality: g. high ammonia content, high organic load, extreme water temperature
TYPICAL CLINICAL FINDINGS:
- Nonspecific, including anorexia, weight loss, abnormal swimming in water column, and death
- Acute death, with mortality between 87-100% in guppies; variable mortality in other species
TYPICAL GROSS FINDINGS:
- Muscular swelling may be evident
- White patches on skin due to high numbers of ciliates in copious mucus
- A mass of ciliates can form a rim around the orbit (“spectacle eye”)
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- 30-50um ciliate protozoan with a thin cell wall and circumferential surface cilia of equal length and distribution (“holotrich”)
- Can invade viscera (muscle, kidney, brain), epithelium, causing necrosis and degeneration; penetration into muscle and deep tissues is highly diagnostic
- Minimal/mild granulocytic inflammation
ADDITIONAL DIAGNOSTIC TESTS:
- Ciliate can be found on wet mount of skin, gills, internal organs; ciliate has circumferential, evenly distributed cilia with one long caudal cilium (present in only some species of Tetrahymena)
- Icthyophthirius multifiliis: similar gross appearance, different parasite morphology
- Paramecium sp. and other free-living, non-pathogenic ciliates: similar parasite morphology, lacks pathogenic lesions
- Few ciliated protozoae are pathogenic, and the organisms are usually incidental findings within the intestinal tract or occasionally as post mortem reflux into the respiratory tract
- Pathogenic ciliates include:
- Balantidium are common ciliates of pigs, rodents, and non-human primates; is rarely associated with mild to severe enteritis and dysentery
- Tetrahymena pyriformis: Pathogenic ciliate affecting internal organs and musculature of common carp, catfish, and rainbow trout
- Other Tetrahymena : Deep ulcerative dermatitis of Atlantic salmon in fresh water; can affect some crustaceans and turbellarians
- Icthyophthirius multifiliis (see I-P16) and Cryptocaryon irritans are respectively, the freshwater and marine ciliated protozoa which cause white punctuate lesions in the integument of fish; these are predominantly non-pathogenic, however can result in severe lesions and death in crowded environments causing stress and immunosuppression in aquaculture environments
- Uronema , primarily Uronema marinum is a typically free-living holotrich ciliate that has been recognized as a dangerous disease to marine fish in aquaria and in the wild; seem to be the marine counterpart to Tetrahymena spp.
- Other holotrichs: Philasterides dicentrarchi causes disease in leafy and weedy sea dragons and several species of sharks (Stidworthy 2014), Pseudocohnilembus persalinus causes disease in sea bass and turbot
- Trichophrya piscium is a suctorian ciliate commonly encountered on the gills of fresh-water fish; pathogenicity is questionable
- Gardiner CH, Fayer R, Dubey JP. An Atlas of Protozoan Parasites in Animal Tissues. 2nd ed. Washington, DC: Armed Forces Institute of Pathology; 1998:16-17.
- Leibowitz MP, Zilberg D. Tetrahymena infection in guppies, Poecilia reticulata Peters: parasite characterization and pathology of infected fish. J Fish Dis. 2009:32(10):845-855.
- Noga EJ. Fish Disease: Diagnosis and Treatment. 2nd Ames, IA: Wiley-Blackwell; 2010:140-141.
- Roberts RJ. The parasitology of teleosts. In: Roberts RJ ed. Fish Pathology. 3rd Philadelphia, PA: W.B. Saunders; 2003:272-273.
- Sharon G, Pimenta Leibowitz MP, Kumar Chettri J, Isakov N, Zilberg D. Comparative study of infection with Tetrahymena of different ornamental fish species. Jour Comp Pathol. 2014; 150:316-324.
- Stidworthy MF, Garner MM, Bradway DS, et. al. Systemic scuticociliatosis (Philasterides dicentrarchi) in sharks. Vet Pathol. 2014;51(3):628-632.