Abstract

Direct fecal exams and intestinal wet mounts from cichlid fishes presented for necropsy at the John G. Shedd Aquarium often reveal one or more species of flagellates in variable numbers. These flagellates are typically diplomonad and/or trichomonad types. The presence of these protozoa can be associated with anything from clinically normal fish to specimens exhibiting multiple problems. Moreover, histologic changes in the intestine associated with these protozoa are only occasionally encountered. This suggests that these flagellates may be endocommensals that are able to exploit a debilitated host.

In Europe, however, a parasitic bodonid flagellate, Cryptobia iubilans has been described in four species of neotropical cichlids and was associated with pathology of the digestive tract and various other internal organs.^1,2 In North America, a necrotic and granulomatous gastritis was described in Lake Tanganyika cichlids (Tropheus duboisii).³ Both Clostridium hastiforme and flagellated protozoa were associated the tissue changes in these Tanganyikan cichlids but the significance of either was unknown.

In July and August of 1995, high mortality rates (>50% of the population) were observed in three different species of East African cichlids: Cyphotilapia frontosa, Dimidiochromis compressiceps, and Aulonocara stuartgranti. C. frontosa is from Lake Tanganyika. D. compressiceps and A. stuartgranti are both from Lake Malawi. The C. frontosa and D. compressiceps were long-term captives that originated from broodstock held at the Shedd Aquarium. The A. stuartgranti were also captive-born but were recent acquisitions from a midwestern wholesaler. All three species of fish were in different tanks but shared a common water source and a centralized filter. The C. frontosa and D. compressiceps were held in single-species tanks. The A. stuartgranti shared a quarantine tank with Herichthys meeki and Herichthys nicaraguensis. Commercial flake, gelatinized and pelleted feeds make up 75% of the diet; the balance includes minced whole smelt, minced krill, and occasionally live adult artemia.

The initial clinical signs included inappetance, decreased activity, and a tendency for affected fish to isolate themselves from their tankmates. These fish stayed near the surface and became increasingly tachypneic. The fish typically died within 48 hours of exhibiting tachypnea. Closer examination of tachypneic fish under anesthesia (MS-222 at 100 ppm) revealed extreme pallor of the gill lamellae. Blood samples taken from five of the fish revealed marked anemias (HCT< 5%).

Gross postmortem findings consistently included visible gastric granulomata. In some of the specimens, the granulomata were so large as to obliterate the gastric lumen. Impression smears of gastric mucosa and wet mount squash preparations of kidney, liver, and spleen often revealed both extracellular flagellates and intracellular flagellates within macrophages. The flagellates were fusiform in shape and measured 5-12 um long by 3-5 um wide. Two flagella were observed, a free anterior flagellum and a posterior flagellum that was attached along the entire body length. Giemsa stains revealed the presence of a triangular kinetoplast.

Histologic findings always included moderate to severe-transmural and obliterative, multifocal, histiocytic, lymphocytic gastritis with or without intralesional flagellates. Approximately 80% of the fish that succumbed exhibited disseminated granulomatous lesions with intralesional flagellates. In these cases, the granulomata could be found in cranial kidney, caudal kidney, spleen, liver, mesentery, mesenteric fat, mesenteric pancreas, swim bladder, eye, heart, and/or gonads. Fite and Ziehl-Neelson stains were utilized to rule out mycobacteriosis. Based upon the identity of the hosts (only cichlids), the microscopic appearance of the parasites, and the gross and histologic postmortem findings, a presumptive etiologic diagnosis of cryptobiosis due to Cryptobia iubilans was made. The identity of the flagellate was subsequently confirmed with transmission electron microscopy, which allowed evaluation of ultrastructural details.¹

Sixty cichlids sharing the same water system representing twelve non-endangered species were then randomly selected and euthanized for histopathology. Because gastric lesions are considered to be relatively uncommon in teleosts³ and fifty-nine out of sixty cichlids (98%) were found to have a granulomatous gastritis, it appeared that exposure to the parasite was already widespread. In addition, fifteen of the sixty cichlids (25%) were found to have active infections with protozoa present on histology. The majority of the gastric lesions, however, appeared to be resolving granulomata. This suggests that many of the exposed fish were able to survive the infection.

Treatment was not attempted for several reasons. The life cycle apparently can have a prominent intracellular component^.1,2 No therapeutants have ever been found to be effective against any of the Cryptobia sp.⁴ At the time of discovery, the disease was already widespread. And finally, other specimens at risk included seven species of critically endangered SSP fishes (Lake Victoria cichlids). Control of the epizootic was achieved through isolation of cichlid groups, identification of affected groups by sampling of randomly selected individuals for histology, and finally, aggressive culling of affected species.

This epizootic represents the first confirmed report of Cryptobia iubilans in North America. Five new host species can be confirmed based on the presence of intralesional flagellates: Dimidiochromis compressiceps, Cyphotilapia frontosa, Oreochromis esculentus, Herichthys synspilus, and Aulonocara stuartgranti. Six additional species probably represent new hosts, but only granulomatous gastritis +/- disseminated granulomatous disease without protozoa could be found. These six species include the following: Haplochromis macula, Herichthys nicaraguensis, Labeotropheus fuelleborni, Herichthys aureus, Pseudotropheus elongatus, and Pseudotropheus zebra. Herichthys meeki represents the twelfth species found to have this granulomatous disease at the Shedd Aquarium, but H. meeki has already been reported as a host for C. iubilan.¹

There is currently no known treatment for C. iubilans that has been demonstrated to be effective in controlled clinical trials. Efficacy claims have been made for 2-amino-5-nitrothiazol administered as a prolonged immersion bath, but the authors did not employ untreated control fish nor did they perform any post-treatment diagnostics to confirm the presence or absence of the flagellates.⁵ Current protocols for containment of this parasite at the Shedd Aquarium include a minimum sixty day quarantine for all cichlids, screening for parasites by either randomly selecting specimen(s) for euthanasia and histology, or performing gastric washes for cytology in rare, expensive, or endangered species, and finally, aggressive culling of affected groups.

There is a dearth of information in the scientific literature concerning Cryptobia iubilans outside of a few descriptive studies of its morphology and its associated histopathology.^1,2 Potentially effective therapeutants need to be investigated in a controlled manner. Moreover, the exact mode of transmission of C. iubilans has never been elucidated although the trophozoites are believed to be directly infective via the oral route. Whether or not a reservoir host exists is also unknown. Because of its broad host range and presumed mode of transmission, this parasite represents a potentially significant threat to cichlid fishes whether in the ornamental fish trade, zoological institutions, or in nature.

References

1.  Nohynkova E. 1984. A New Pathogenic Cryptobia from Freshwater Fishes: A Light and Microscopic Study. Protistologica, T. XX, fasc. 2, p. 181-195.

2.  Dykova I, J Lom. 1985. Histopathological Changes due to Infections with Cryptobia iubilans Nohynkova 1984, in Two Cichlid Fishes. Z. Angew. Ichthyol., 1:34-38.

3.  Ferguson HW, Rosendal S, S Groom. 1985. Gastritis in Lake Tanganyika Cichlids (Tropheus duboisii). Veterinary Record, 116. 687-689.

4.  Woo PTK. 1996. Personal Communication.

5.  Steinhagen D, Jendrysek S, Ernst S, Hemmer N, W Korting. 1994. Diagnose und Therapie von Cryptobia iubilans, Einem Pathogenen Flagellaten aus dem Darm von Buntbarschen. Kleinterpraxis, 39. Jahrg., S. 749-754.