Signalment:  

10-year-old, male white faced ibis (Plegadis chihi)Animal presented to the Department of Animal Health for digital abnormalities. During amputation of P2 and P3 of right D2, bird arrested under anesthesia. Resuscitative efforts (IM and IV epinephrine, atropine, dopram, and fluids; cardiac massage; positive pressure ventilation with 100% oxygen) were unsuccessful.

Gross Description:  

The white-faced ibis is in excellent postmortem condition. There is sufficient musculature overlying the keel and moderate stores of coelomic and subcutaneous adipose tissue. The small intestine contains minimal amounts of tan, mucoid digesta, and the colon contains small amounts of urates. There is marked curvature of the spine between T4 and T7. There is a healed fracture at P2 of digit 3 on the left. Digit 2 on the right is absent distal to P1.

Histopathologic Description:

SMALL INTESTINE: There are a few heterophils scattered throughout the lamina propria. Multifocally throughout the sections there are many, 5 x 10 micron, crescent-shaped to oval trophozoites overlying the mucosa (Giardia) (Fig. 1-1).

Morphologic Diagnosis:  

Intestine, small: Giardiasis, moderate, with mild, heterophilic enteritis

Lab Results:  

Hypophosphatemia (phosphorus 0.7 mg/dl) was observed in a blood sample collected near the time of death.

Condition:  

Giardia sp.

Contributor Comment:  

Giardia sp. are flagellated protozoa that can be found in the upper intestine of many species of mammals, birds, reptiles, and amphibians. Though the taxonomy is poorly understood and subject to debate, it is generally accepted that Giardia duodenalis (a.k.a. Giardia lamblia) is classified into approximately eight separate assemblages.(5) Giardia appear to be host specific (5) with assemblages A and B being most common in humans; dogs are associated with assemblage C; and organisms from assemblage E have been isolated from livestock. G. psittaci has been isolated from budgerigars (6), G. ardeae from herons, and a genetically similar strain from straw-necked ibis.(2) Many animals harbor the organism in their intestinal tracts without evidence of clinical illness, indicating that there is a natural carrier state.(1)

Giardia colonize the upper small intestine, usually the duodenum, in the trophozoite form.(1) The trophozoites are piriform, with four paired flagella, paired nuclei and a ventral disk on the concave surface which attaches to the host enterocyte. Reproduction by binary fission occurs in the gut lumen. This form may be passed in the feces, but more commonly, oval cysts are seen in direct smears. Transmission of the environmentally-stable cyst is by the fecal-oral route.(1) Diagnosis is best made by seeing the organism in a direct fecal preparation from a clinically ill animal, but ELISA and PCR tests have been developed.

Though giardiaisis is generally an asymptomatic condition, the presence of the organism has been associated with vitamin E/selenium deficiencies in cockatiels.(6) The proposed mechanism involves malabsorption of these nutrients due to the presence of the organisms on the intestinal mucosal surface. Though speculative, hypophosphatemia in this white-faced ibis may also have resulted from a focally extensive and heavy parasite load. Phosphorus is absorbed from the diet in the proximal small intestine where the heaviest load of parasitism was found in this bird. The bird of this report had adequate fat and muscling, but antemortem bloodwork revealed a PO4 of 0.7mg/dl (ref. 3.1-6.6mg/dl). Additionally, marked thoracolumbar scoliosis was present in addition to the fractured and dislocated digits. Thus, while the protist in this particular animal did not appear to cause a direct effect on intestinal health, it may have acted indirectly on bone health by blocking absorption of some nutrients needed for maintenance of healthy, structural bone.

JPC Diagnosis:  

Small intestine: Enteritis, heterophilic, diffuse, mild with numerous surface-associated trophozoites, etiology consistent with Giardia sp.

Conference Comment:  

Dr. Viner, the conference moderater, submitted this case and did an excellent job elucidating the importance of this organism in domestic species. The preservation of morphologic detail of the organism in the sections was excellent. This particular slide did not have extensive associated tissue reaction, thus driving home the point that Giardia species often cause minimal gross and histologic lesions and also often cause subclinical infections. 

Giardia is an ubiquitous organism with worldwide distribution and is the most common flagellate of mammals and birds(3). Giardiasis is also a zoonotic disease. The life cycle of Giardia species is direct. Trophozoites and cysts are present in feces and passed from infected hosts into the environment. Once outside the host the trophozoites die, but the cysts are resistant. They are protected from the environment by a membranous layer with an inner and outer cyst membrane and filamentous layer forming a dense mat of interlacing branches.(2) Cysts are ingested via fecal-oral transmission. Enzymes within the stomach and small intestine cause excystation releasing two trophozoites. The organisms attach and feed in the upper small intestine and multiply by binary fission. Once the organisms reach the colon, they encyst in preparation for the external environment. 

References:

1. Brown CC, DC Baker, IK Barker: Alimentary system. In: Pathology of Domestic Animals, ed. MG Maxie, 5th ed., pp. 277-279. Elsevier, Philadelphia, PA, 2007
2. Cheville NF: Ultrastructural Pathology, pp. 722-723. Iowa State University Press, Ames, Iowa, 1994
3. Gardiner CH, Poynton SL: An Atlas of Metazoan Parasites in Animal Tissues, 2nd ed., pp. 6-7. Armed Forces Institute of Pathology, Washington, DC 1984
4. McRoberts KM, BP Meloni, UM Morgan, R Marano, N Binz, SL Erlandsen, SA Halse, RCA Thompson: Morphological and molecular characterization of Giardia isolated from the straw-necked ibis. J. Parasitol. 82(5):711-718, 1996
5. Monis PT, RCA Thompson: Cryptosporidium and Giardia-zoonoses: fact or fiction? Infection, Genetics and Evolution 3:233-244, 2003
6. Ritchie B, GJ Harrison, LR Harrison: Avian Medicine: Principles and Application. pp. 732, 1014-5. Wingers Publishing, Lake Worth, FL, 1994

Click the slide to view.

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1-1. Small intestine, ibis.

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