Trichomonads are anaerobic flagellated protozoa within the family Trichomonadidae (subphylum Mastigophora) found in many different species of mammals and birds.4 These protozoa are most often commensal, non-pathogenic organisms; however, there are several species associated with clinical disease. Tritrichomonas foetus causes disease in both cattle and young cats. In cows, this sexually transmitted protozoa is associated with vaginitis, endometritis, placentitis, fetal infection, early abortion and pyometra.4,6 In young cats, T. foetus is associated with colitis and chronic large bowel diarrhea.9 Trichomonas gallinae causes severe necrotizing and ulcerative lesions within the upper gastrointestinal tract in several different avian species.8 Tritrichomonas mobilensis has been identified within the colon and cecum of several non-human primates.2,3,7 Pathological changes associated with this protozoan include penetration of the mucosal epithelium and desquamation of the crypt epithelium in the absence of an inflammatory response.2,7 The pathogenicity of trichomonads can also be influenced by the immune status of the host. Rhesus macaques (Macaca mulatta), for instance, infected with simian immunodeficiency virus can develop a necrotizing and suppurative gastritis associated with gastric trichomonads.5
To the author's knowledge, gastric trichomonads have not been previously described in marine mammals. This retrospective study describes the light microscopic features associated with gastric trichomonads in stranded California Sea Lions (Zalophus californianus).
A total of twenty cases of gastric trichomonads were identified via histopathological examination of California sea lions by the Pathology Service, University of California at Davis, CA between 1993 and 2007. All animals stranded along the central California coast and were housed at the Marine Mammal Center, Sausalito, CA. The majority of animals included in this study either died or were euthanized within one week of standing and the time in rehabilitation ranged from less than one day to three and a half months. Affected animals were identified within all age classes, including adults (11/20), juveniles (7/20), and yearlings (2/20). The majority of the cases stranded between July and December, corresponding to the seasonality of sea lion strandings in central California. Gender distribution slightly favored females, with 12/20 females and 8/20 males. Causes of clinical disease and death were generally unrelated to gastrointestinal disease and included domoic acid toxicity (7/20), disseminated urogenital carcinoma (4/20), leptospirosis (3/20), protozoal meningoencephalitis (2/20), pneumonia (2/20), shark bite trauma (1/20), and severe emaciation (1/20).
Trichomonads were identified within the pylorus, fundus, and, rarely, the proximal duodenum. In mild cases, the trichomonads were present along the epithelial brush border, within the gastric lumen, and within mildly dilated crypts and glands. In more severely affected cases, there was individual epithelial cell necrosis, moderate gland or crypt ectasia, and multifocal cryptitis and crypt abscessation. Occasionally, the trichomonads were clustered within areas of mucosal erosion or ulceration. In all cases, the trichomonads were restricted to the mucosa and never penetrated the basement membrane. On routine hematoxylin and eosin stains, the organisms were pale basophilic, teardrop shaped, and measured approximately 5 to 7 µm by 8 to 10 µm. Faint hyperchromatic, apically oriented, approximately 1 µm diameter nuclei were occasionally apparent. Occasionally, luminal and glandular debris and mucous made identification of the protozoa difficult. Other gastric lesions inconsistently identified included multifocal mucosal erosion and ulceration, anisakid nematode-associated ulcers, and multifocal lymphoplasmacytic gastritis with multiple lymphofollicular aggregates.
Further characterization and definitive diagnosis was obtained with immunohistochemistry and transmission electron microscopy. Immunohistochemical stains using a polyclonal antibody against Trichomonas foetus, performed at the California Animal Health and Food Safety Laboratory, revealed numerous trichomonads within the gastric mucosa and lumen. Ultrastructural examination of the organisms identified morphological features consistent with those described for trichomonads.1 The organisms had a recurrent flagellum with an undulating membrane, axostyle, numerous hydrogenosomes, and a prominent costa.
In conclusion, this study characterizes the histological and ultrastructural features associated with gastric trichomonads in stranded California sea lions. The absence of an inflammatory response directly associated with the trichomonads was attributed to their restriction to the mucosa and lack of basement membrane penetration. This is similar to the findings in colonic trichomonads discussed previously in some species of non-human primates.2,7 Mild lymphoplasmacytic gastritis is a common finding within stranded California sea lions and was not likely directly associated with the presence of trichomonads. However, trichomonads were clustered around eroded and ulcerated areas, reflecting possible opportunistic overgrowth secondary to gastric damage from other causes. Molecular analysis is currently being completed to further characterize the trichomonads and their possible relatedness to other known Trichomonad spp.
The authors wish to thank the staff and volunteers of The Marine Mammal Center, the UC Davis veterinary pathology residents for initial review of some of the cases, and Bob Nordhausen for electron microscopy.
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