Cryptobia iubilans in Cichlids1
Ruth Francis Floyd and Roy Yanong2
What is Cryptobia?
Cryptobia is a flagellated protozoan, closely related to Hexamita
and Spironucleus, but not nearly as well understood. Like Hexamita
and Spironucleus, Cryptobia is a very tiny (single-celled)
organism and, consequently, can be difficult to identify and study. There have
been 52 species of Cryptobia identified in fish; however, because of
its small size and difficult taxonomy, these may not all be separate species.
Of the 52 species that have been identified, five are classified as
ectoparasites that infect the gills and skin; seven are classified as enteric
parasites that infect the gastrointestinal system; and 40 are classified as
hemoflagellates which are found in the bloodstream. It has recently been
proposed that the hemoflagellates be assigned to a subgenus called
Trypanoplasma. The hemoflagellates have an indirect life cycle and are
transmitted by leeches, whereas the gastrointestinal and ectoparasitic forms
have direct life cycles.
Cryptobia iubilans and Cichlids
Cryptobia iubilans was first recognized in cichlids some 20 years
ago. The organism is typically associated with granulomas (a tissue reaction)
in the stomach, but systemic infections that involve the organism in blood and
organ systems (including liver, gall bladder, kidney, ovary, brain, and eye)
have been reported. It is not known how the organism is able to spread from
the intestinal tract to other organs, or what causes the internal spread.
Mortalities associated with the systemic form may exceed 50% of the infected
population.
The gastrointestinal form of Cryptobia has been reported in East
African and Central American cichlids, including: Herichththys
cyanoguttatus, Cichlasoma meeki, Cichlasoma nigrofasciatum,
and Cichlasoma octofasciatum. Our laboratories have found it in some
additional species, but most of the work has been done with Pseudotropheus
zebra (Department of Fisheries and Aquatic Sciences, Gainesville, FL) and
Symphysodon spp. (Tropical Aquaculture Laboratory, Ruskin, FL).
In the summer of 1995, there was an outbreak of the systemic form of
Cryptobia iubilans in cichlids at the Chicago Shedd Aquarium. The outbreak
resulted in loss of 50% of the collection of East African cichlids including
Cyphotilapia frontosa, Dimidiochromis compressiceps, and
Aulonocara stuartgranti. The outbreak seemed to originate with the
Aulonocara that had been purchased from a midwest wholesaler. While the
fish were in quarantine, the infection spread to Cichlasoma meeki and
C. nicaraguense housed in the same tank. From there it spread to the
C. frontosa and D. compressiceps that were housed in separate tanks
but shared the same water due to a common filtration system. The sick fish
went off feed for one to two days, becoming progressively more listless and
withdrawing from contact with other fish. Just prior to death, they would move
to the surface of the water and their respiration rate would increase
dramatically, suggesting that they were hypoxic (suffering from low dissolved
oxygen). Closer examination of fish at this stage of the disease revealed
severe anemia, with packed cell volumes around 5% (normal should be greater
than 30%). Death usually occurred within 24 hours of the development of severe
anemia.
Veterinarians at Shedd aquarium wanted to see how many species in their
collection carried the parasite so they sacrificed 60 apparently healthy fish,
and found evidence of Cryptobia iubilans in all but one (98%
prevalence). These fish had granulomatous gastritis (the tissue reaction in
the stomach) but no evidence of the systemic disease. The affected species
included Haplochromis macula, Cichlasoma nicaraguense,
Labeotropheus fuelleborni, Cichlasoma aureus, Pseudotropheus
zebra and P. elongatus. Since the 1995 epizootic (disease
outbreak), Shedd Aquarium has instituted a new quarantine protocol for all
cichlids. All incoming cichlids are subjected to a minimum 60-day mandatory
quarantine. A number of animals are screened for the presence of Cryptobia;
any infected cichlid is culled.
Comparing Cryptobia and Spironucleus infections
Clinical Disease:
Both Cryptobia and Spironucleus can result in similar disease
scenarios on cichlid farms. Both parasites become more serious under
conditions of crowding, poor sanitation, high organic load, and handling
stress. Diet also may play a role in the development of the disease. It has
been demonstrated in laboratory mice that changes in the intestinal bacterial
flora, caused by changes in diet, can affect the presence of intestinal
flagellates, suggesting greater potential for clinical disease.
Enteric disease from either parasite may result in low level chronic
mortality, "wasting" or poor growth. The effect of Spironucleus is more
serious in fry and very young fish. It is not known if this is also true for
Cryptobia, but there is some evidence that supports this belief. The
impact of either disease on reproduction is not well understood; however, we
believe that breeders heavily infected with Spironucleus produce poor
quality eggs and weak fry.
Diagnosis:
Spironucleus can be tentatively identified by observing the motile
trophozoites in smears of intestinal contents or feces. Identifying the
parasite to genus requires both transmission and scanning electron microscopy
and therefore cannot be done on a routine basis. Cryptobia is most
easily detected by identification of granulomas in thin wet mounts of stomach
tissue (Figure 1). Because these granulomas are indistinguishable from the
granulomas observed with Mycobacterium, an acid-fast stain (eg. Ziehl-Nielson)
should be used to rule out that important disease (see IFAS Extension Fact
Sheet No. VM-96). In most instances, motile forms of Cryptobia will not
be seen on wet mounts that are examined with a light microscope. Electron
microscopy is also required to confirm the identity of this organism.
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Figure 1. Typical granuloma seen in a wet mount of stomach tissue from
an African cichlid with Cryptobia iubilans infection. The section
is unstained and is examined with a light microscope (100x)
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Transmission:
Both Spironucleus and Cryptobia have direct life cycles.
Infective forms are shed with feces, and ingestion of these forms is thought
to result in infection. Both organisms can live in the water column for at
least a few hours. Always remove carcasses as quickly as possible when they
are found, since both parasites may be spread by ingestion of infected tissue.
Treatment:
Spironucleus usually responds well to metronidazole administered in
feed or as a bath. The recommended dose in feed is 1% (4.5 grams active drug
per pound of feed) fed daily for five consecutive days (see IFAS Extension
Fact Sheet No. VM-67). The bath treatment is 6 mg/L (250 mg added to 10
gallons of water), followed by a water change four to eight hours after
treatment, repeated daily for five days (see IFAS Extension Fact Sheet No.
VM-67). These regimes have been very effective for control of Spironucleus
in cichlids for the past ten years.
Currently, there is no effective treatment for Cryptobia. Part of
the difficulty may be that the parasite seems to have an intracellular stage.
Parasites are occasionally seen in phagocytic cells, called macrophages, which
are part of the immune system and are supposed to destroy foreign protein by
engulfing it. Cryptobia seems to be able to live within these cells
rather than being destroyed by them. This can make it difficult to treat
Cryptobia because most drugs are not able to penetrate the cell wall of a
macrophage. Some Florida farms have used a sulfa drug (sulfadimethoxine) that
seems to help control mortalities in some cases, but has not eliminated the
parasite. Experiments are in progress at the Tropical Aquaculture Laboratory
(Ruskin, FL) to find an effective therapeutic agent.
Summary
Cryptobia iubilans is not a new parasite of cichlids but has
received significant attention in the past few years. It seems to be
widespread in East African cichlids and has been found in Pseudotropheus
zebra immediately following importation from Lake Malawi, suggesting that
it occurs naturally in wild fish. It has also been found in some South
American cichlids, most notably, discus. The parasite usually causes a
granulomatous gastritis and may be associated with chronic low-level
mortality. A systemic form of the disease has been reported in captive East
African and Central American cichlids. This form was associated with acute
mortalities and loss of 50% of affected animals. Currently there is no
effective treatment for Cryptobia. Water quality, stocking density and
diet may all effect the severity of infection. Work is in progress at the
University of Florida to learn more about this common, but important, cichlid
parasite.
Footnotes
1. This document is VM104, one
of a series of the Veterinary Medicine-Pathobiology Department, Florida
Cooperative Extension Service, Institute of Food and Agricultural Sciences,
University of Florida. Original publication date January 1, 1999. Revised
April 12, 2002. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.
2. Ruth Francis Floyd,
DVM, MS, Extension Veterinarian for Fisheries and Aquatic Sciences and
Professor, Department of Large Animal Clinical Sciences and Roy Yanong, VMD,
Assistant Professor for Department of Fisheries and Aquatic Sciences, Tropical
Aquaculture Laboratory, 1408 24th St. S E, Ruskin, FL 33570
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