AFIP Wednesday Slide Conference - No. 13
December 9, 1998

Conference Moderator: Dr. F.M. Garner, Diplomate, ACVP
4416 Oak Hill Road
Rockville, MD 20853

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Case I - 92749 (AFIP 2642676)
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Signalment: Twelve-week-old, male, golden Syrian hamster (Mesocricetus auratus).
History: Numerous adult hamsters in a breeding colony of approximately 4,000 Syrian hamsters developed skin tumors, with most of the affected animals being males four to five months of age. Female animals developed tumors at 10 to 12 weeks of age (after the first litter). Affected animals were immediately removed from the population, and two of the hamsters were submitted for necropsy. No data concerning spontaneous recovery of affected animals in this population is available.
Gross Pathology: Multiple skin tumors measuring up to five millimeters in diameter were found on the chin, neck, thorax, and abdomen. Identical tumors measuring up to two millimeters in diameter were found at the mucocutaneous junctions of the mouth.
Laboratory Results: No clinical laboratory data are available. Attempts at virus isolation in tissue cultures using the hamster kidney cell line BHK 21 were unsuccessful.
Contributor's Diagnosis and Comments: Cutaneous trichogenous tumors, papova (polyoma)-virus induced.
The cutaneous tumors are of trichogenous origin. The incidence of the tumors within the affected population suggested a contagious process of viral etiology. This suspicion was confirmed by electron microscopy which revealed numerous, irregularly arranged, viral particles measuring approximately 40nm within the nuclei of degenerate epithelial cells; viral particles were also occasionally found in the cytoplasm. The size of virions suggests infection with a polyomavirus.
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Case 13-1. Skin. Numerous hair follicle-like structures expand the dermis.
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Case 13-1. Dermis. There are glassy basophilic intranuclear inclusions within more mature central cells of follicle.
AFIP Diagnosis: Haired skin: Benign hair follicle tumor, with few intranuclear inclusion bodies, golden Syrian hamster (Mesocricetus auratus), rodent.
Conference Note: An unencapsulated, well-circumscribed, multilobulated neoplasm expands the dermis and subcutis, and compresses subjacent skeletal muscle. The neoplasm is composed of lobules of epithelial cells arranged in nests, broad cords and hair follicle-like structures. A peripheral layer of basophilic polygonal cells aligns along the basement membrane, and neoplastic cells are more eosinophilic within inner layers of the abortive hair follicles. Small numbers of intranuclear inclusions are within the more mature, inner layers of neoplastic follicular epithelium.
The first spontaneous outbreak of polyomavirus-induced multicentric cutaneous masses in hamsters was reported during the late 1960's in the Buch golden Syrian hamster (HaB) colony in Berlin, Germany. Tumors appear spontaneously in young animals between three months and one year of age, and typically begin as miliary nodules on the face, head and neck that progressively thicken and enlarge to form coalescing masses in the skin and subcutis. The tumors result from proliferation of the follicular epithelium, and often contain central areas of keratin. Viral infection is thought to occur by horizontal transmission. Viral particles identified by electron microscopy are found in the nuclei of epithelial cells immediately subjacent to the central areas of keratin, but not within the more basal cells; the ultrastructural morphology of virions is consistent with a polyomavirus (hamster polyomavirus or HaPV). A closely related virus causing similar cutaneous neoplasms in Syrian hamsters in Alabama has been reported.
HaPV also induces lymphoma and leukemia in newborn animals when injected percutaneously in a unique, essentially tumor free colony of Syrian hamsters bred in Potsdam, Germany. While viral particles are found within neoplastic epithelial cells in the cutaneous form of the disease, neoplastic hematopoietic cells are virus free but contain large amounts of extrachromosomal viral DNA. Newborn mice may develop one of several types of hair follicle tumors when inoculated with the Py (PTA) strain of murine polyomavirus, but they do not develop hematopoietic neoplasia.
The polyomaviruses and papillomaviruses are within the Papovaviridae family. Papovaviridae are small, nonenveloped, icosahedral, double-stranded, circular DNA viruses that measure between 45 - 55nm and replicate in the nucleus. Members of the Papovaviridae are widely recognized for their ability to cause proliferative or tumorigenic lesions in various animal species. With oncogenic DNA viruses, viral replication does not occur in transformed rapidly dividing cells, and viral particles are not usually found in the germinal epithelium. The cells of the upper or more differentiated layers permit viral replication, and viral particles can be found in these areas; on occasion, intranuclear inclusions can be seen by light microscopy. This viral property explains the finding of intranuclear inclusions within epithelial cells subjacent to the keratin elements in the trichogenous tumors of the hamster.
Contributor: Institute of Veterinary Pathology, University of Munich, Veterinarstr. 13, 80539 Munchen, Germany.
1. Breur W, et al.: Papovavirus-induced trichogenous tumors in Syrian hamsters (Mesocricetus auratus). J Vet Med 40:337-342, 1993.
2. Graffi A, et al.: Uber einen neuen virushaltingen Hauttumor beim Goldhamster. Arch Geschwulstforsch 30:277-283, 1967.
3. Graffi A, et al.: Virus-associated skin tumors of the Syrian hamster: Preliminary note. J Nat Cancer Inst 40:867-873, 1968.
4. Graffi I, et al.: Elektronenmikroskopische untersuchungen uber das papova (papillom)-virus des Goldhamsters [Electronmicroscopic investigations on papova virus of Syrian hamsters]. Arch Geschwulstforsch 40:191-236, 1972.
5. Scherneck S, et al.: The hamster polyomavirus - a brief review of recent knowledge. Arch Geschulstforsch 60:271-278, 1990.
6. Prokoph H, Jandrig D, Arnold W, Scherneck S: Generation of lymphoma-type variant hamster polyomavirus genomes in hamsters susceptible to lymphoma induction. Arch Virol 142:53-63, 1997.
7. Jones TC, Hunt RD, King NW: Diseases caused by viruses. In: Veterinary Pathology, 6th ed., pp. 251-257, Williams and Wilkins, Philadelphia, 1997.
Case II - RAT-1 (AFIP 2638256)
Signalment: Two-year-old, male, Long Evans rat.
History: The animal was humanely euthanized for necropsy at the end of a two year carcinogenicity study. The animal was in the control group.
Gross Pathology: One testis was greatly enlarged (8cm x 4cm x 4cm), oblong and soft. Sectioning revealed central necrosis with cavitation. The other testis was normal. There were no other gross findings.

Laboratory Results: Clinical pathology was within normal limits.
Contributor's Diagnosis and Comments: Seminoma, malignant.
Histologically, neoplastic tissue replaced most of the testis, with a few remaining atrophic and compressed tubules at the periphery of some sections. The neoplastic cells were organized into tightly packed sheets and large lobules divided by very fine fibrovascular trabeculae with variably sized, scattered foci of necrosis that often coalesced. Cells were large, and round to polygonal with a round, normochromatic to hyperchromatic nucleus positioned centrally or often eccentrically within a moderate amount of eosinophilic, slightly granular cytoplasm. There was moderate anisocytosis and anisokaryosis, and mitotic figures (which were frequently bizarre) varied from 1 to 5 per high power field. In many sections, clusters of neoplastic cells were seen within peripheral blood or lymphatic vessels. Periodic acid-Schiff (PAS) stains for glycogen revealed that most cells were negative with slight patchy staining around the periphery of the nucleus in some cells. Electron microscopy showed that the cells were very undifferentiated and were not consistent with Sertoli cells or Leydig cells, but contained some features of very early germ cell differentiation. Immunohistochemistry revealed that the cells were strongly positive for vimentin and S-100, but negative for cytokeratins, neuron-specific enolase, placental alkaline phosphatase and alpha fetoprotein.
Testicular germ cell tumors in humans are divided into three groups: seminomas, spermatocytic seminomas, and a mixed group that includes embryonal carcinoma, teratoma, choriocarcinoma and yolk sac carcinoma (Damjanov, 1990). The rat neoplasm was not morphologically consistent with embryonal carcinoma, teratoma, choriocarcinoma, or yolk sac carcinoma, and was negative for cytokeratins for which most of these would stain positively. However, there was also a lack of advanced spermatocytic differentiation that would allow a definitive diagnosis of spermatocytic seminoma, suggesting by exclusion the diagnosis of an undifferentiated seminoma.
Seminomas are extremely rare neoplasms in rats, in contrast to humans and dogs. Indeed, one institution determined the incidence within an historical data base to be 1 case in 31,868 animals (0.003%) (Curtis, Bullock and Dunning, 1931). This is reflected in a notable lack of literature about rat seminomas (Boorman, 1987). A recent search indicated that there were only two articles in the literature describing the ultrastructural and/or immunohistochemical features of rat germ cell tumors, and these were of spermatocytic seminomas; one in a Fischer-344 rat (Nyska et. Al., 1993) and one in a Wistar rat (Kim, Fitzgerald and De La Iglesia, 1985).
Because of the lack of data, the biological behavior of these neoplasms in rats is unclear. The large size, necrosis, anaplasia and vascular invasion associated with this case suggest malignancy, although no distant metastases were found.
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Case 13-2. Testis. Neoplastic polygonal cells with brightly eosinophilic globular cytoplasm form pockets & nests.
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Case 13-2. Testis. Packeted polygonal tumor cells rarely contain globular PAS positive cytoplasmic material.
AFIP Diagnosis: Testis: Interstitial (Leydig) cell tumor, malignant, Long Evans rat, rodent.
Conference Note: Conference participants had great difficulty with this case. While the majority agreed with the contributor's diagnosis of malignant seminoma, several favored malignant interstitial (Leydig) cell tumor. An unencapsulated, lobulated, densely cellular neoplasm with multifocal to coalescing areas of necrosis replaces most of the testicular parenchyma. The neoplasm is composed of polygonal to elongate cells arranged in nests, packets, and variably broad cords supported by a fine to moderate fibrovascular stroma. A key histological feature present in some sections is packets and lobules of large polygonal cells that have abundant, brightly eosinophilic, granular to globular cytoplasm and round, centrally placed nuclei with prominent nucleoli; these cells are interpreted as neoplastic Leydig cells. Cells with features intermediate between the Leydig-like cells and the poorly differentiated cells are also present.
This case was reviewed by the Department of Genitourinary Pathology. They interpreted the neoplasm as of Leydig cell origin, based primarily on the characteristic cells described above. In humans, seminomas and interstitial (Leydig) cell tumors are distinguished primarily based on histomorphology. Additionally, human seminomas often contain glycogen and are frequently immunopositive for placental alkaline phosphatase. In immunohistochemical studies conducted at the AFIP, this tumor was negative for placental alkaline phosphatase, and most cells were PAS-negative.
An electron micrograph of this neoplasm published in a report of this case shows ultrastructural features of steroid producing cells, such as interstitial (Leydig) cells, including abundant smooth endoplasmic reticulum, presence of a Golgi complex, lamellar and tubular mitochondrial cristae, and intracytoplasmic lipid. No feature diagnostic of seminoma is evident.
This case demonstrates the difficulty in diagnosis of poorly differentiated neoplasms. The malignant neoplasm in the rat testis, like malignant Leydig cell tumors in humans, contains areas of clonal differentiation. Only in scattered areas of the neoplasm are there clearly identifiable features of Leydig cell differentiation. Examination of multiple sections of poorly differentiated neoplasms may be necessary for diagnosis. The presence of clonal differentiation, high mitotic rate with bizarre mitoses, and intravascular neoplastic cells warrants the interpretation of malignancy.
Contributor: Pfizer Central Research, Department of Drug Safety Evaluation, Bldg. 274, Eastern Point Road, Groton, CT 06333.
1. Boorman GA, et al.: Seminoma, testis, rat. In: Monographs on Pathology of Laboratory Animals, Genital System, Jones TC, Mohr U, Hunt RD, eds., pp.192-198, Springer-Verlag, New York, 1987.
2. Curtis MR, Bullock FD, Dunning WF: A statistical study of the occurrence of spontaneous tumors in a large colony of rats. Amer J Cancer 15:67-121, 1931.
3. Damjanov I: Male reproductive system. In: Anderson's Pathology, 10th ed., Damjanov I, Linder J, eds., pp. 2166-2230, Mosby, St. Louis, MO, 1990.
4. Kim SN, Fitzgerald JE, De La Iglesia FA: Spermatocytic seminoma in the rat. Toxicol Pathol 13:215-221, 1985.
5. Nyska A, Harmelin A, Sandbank J, Scolnik M, Warner T: Intratubular spermatocytic seminoma in a Fischer-344 rat. Toxicol Pathol 21:397-401, 1993.
6. Kerlin RL, et al.: A poorly differentiated germ cell tumor (seminoma) in a Long Evans rat. Toxicol Pathol 26:691-694, 1998.
7. McConnell RF, et al.: Proliferative lesions of the testes in rats with selected examples from mice. In: Guides for Toxicological Pathology, pp. 1-23, Society for Toxicological Pathology, American Registry of Pathology, and the Armed Forces Institute of Pathology, Washington DC, 1992.
8. Boorman GA, et al.: Interstitial cell tumor, testis, rat. In: Monographs on Pathology of Laboratory Animals, Genital System, Jones TC, Mohr U, Hunt RD, eds., pp.185-192, Springer-Verlag, New York, 1987.
Case III - C98-1029 (AFIP 2641899)
Signalment: 1½ to 2-week-old male and female Sprague Dawley rats.
History: Three litters of Sprague Dawley rats ranging in age from 1½ to 2 weeks developed diarrhea characterized by yellow pasty to liquid feces. The perianal region of several rats was stained with feces. Both sexes were equally affected.
Gross Pathology: Gross examination of the infant rats revealed distension of the small intestine and large intestine with yellow fluid.
Laboratory Results: Group D streptococcus was isolated from the small intestine of affected rats.
Contributor's Diagnosis and Comments: Small intestine: Streptococcus enteropathy.
Etiology: Streptococcus Group D.
The bacteria lining the villi stained gram-positive and were morphologically compatible with cocci. The diagnosis of streptococcal enteropathy was based on:
1. Gram-positive cocci attached to the intestinal epithelium.
2. Streptococcus isolated as a predominate organism from the small intestine.
3. Lack of inflammation or necrosis associated with the bacteria.
The disease has been observed at our facility only twice during the past sixteen years.
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Case 13-3. Small intestine. Abundant basophilic cocci line the mucosal epithelium of some crypts.
AFIP Diagnosis: Small intestine: Numerous luminal epithelium adherent cocci, Sprague Dawley rat, rodent.
Conference Note: Since 1985, there have been several reports of an enteropathy in suckling neonatal rats caused by enteric streptococci. Infected neonatal rats are often abnormally small, have distended abdomens, poor haircoats, and fecal soiling around the perineum. The disease is not associated with mortality. Histologically, numerous epithelium adherent enterococci are found along the intestinal villi with no other microscopic changes or inflammation.
Enterococci are normally considered commensal bacteria in the intestine and are not thought of as etiologic agents of diarrhea. There are several reports, however, of enterococcal diarrhea in neonates of various domestic animal species including foals, gnotobiotic piglets, chickens, and a puppy. In the horse, rat, and pig, the most consistent histologic finding is the presence of numerous Gram positive enteric cocci lining the epithelial cells of small intestinal villi. Other microscopic changes noted in the small intestine of the horse and pig include mild villus atrophy and fusion, in contrast to the lesion in rats. The ability of some species of enterococci to adhere to intestinal epithelium is probably a key factor in the pathogenesis. The findings in these reports seem to suggest that enterococci should be considered potential etiologic agents of diarrhea in neonatal animals.
Diarrhea and enteric disease of viral or bacterial etiology occur uncommonly in the rat. Infectious diarrhea of infant rats (IDIR), caused by a rotavirus, is characterized by diarrhea, runting, and malabsorption in suckling rats less than twelve days of age; the mortality rate is low. Potential bacterial causes of gastrointestinal disease in rats include Clostridium piliforme, the etiologic agent of Tyzzer's disease, and Salmonella sp.
Contributor: Saint Jude Children's Research Hospital, Comparative Medicine Division/ARC, 332 N. Lauderdale, Memphis, TN 38105.
1. Hoover D, et al.: Streptococcal enteropathy in infant rats. Lab Anim Sci 35:635-641, 1985.
2. Etheridge ME, Yolken RH, Vonderfecht SL: Enterococcus hirae implicated as a cause of diarrhea in suckling rats. J Clin Microbiol 26:1741-1744, 1988.
3. Etheridge ME, Vonderfecht SL: Diarrhea caused by a slow-growing Enterococcus-like agent in neonatal rats. Lab Anim Sci 42:548-550, 1992.
4. Tzipori S, Hayes J, Sims L, Withers M: Streptococcus durans: An unexpected enteropathogen of foals. J Infect Dis 150:589-593, 1984.
5. Harkness JE, Wagner JE: Specific diseases and conditions. In: The Biology and Medicine of Rabbits and Rodents, 3rd ed., pp. 180-181, Lea & Febiger, Philadelphia, PA, 1989.
Case IV - N97-136 (AFIP 2642346)
Signalment: Young adult, mixed breed, male, canine.
History: This animal appeared normal until the second week of July when hair loss and foul-smelling skin were noted. Skin scrapings did not reveal any agent, but mange was suspected. There was no improvement after ivermectin treatment, and the animal was euthanized.

Gross Pathology: The hair coat was thin over large portions of the carcass, especially the flank, ventrum, axilla, groin, and around the ears. Both ears had moderate crusting along free borders.
Contributor's Diagnosis and Comments: Moderate to severe, chronic, locally-extensive dermatitis with intralesional mites. Etiology: Sarcoptes scabiei var. canis.
Multiple sections of skin from various body sites, including the ears (section submitted), have changes ranging from acanthosis with increased layers of surface keratin (orthokeratotic hyperkeratosis) to focal zones of parakeratosis and cellular crusts. Moderate numbers of bacterial colonies admixed within keratin can be seen over the skin surface, as well as within a few of the keratin-plugged hair follicles. The stratum corneum of the auricular skin has various stages and sizes of mites (200-400um) consistent with Sarcoptes sp. Inflammation within the subjacent dermis is mild to moderate and consists of eosinophils and mast cells, with fewer plasma cells and occasional macrophages. There is moderate dermal fibrosis. The previously described inflammatory cells occasionally surround other adnexal structures (apocrine glands and sebaceous glands).
Canine sarcoptic acariasis is an intensely pruritic, potentially zoonotic, ectoparasitic infestation, the diagnosis of which relies upon identification of the mite in skin scrapings and/or histologic section. Varieties of Sarcoptes scabiei from different hosts are highly host-specific, but morphologically indistinguishable.
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Case 13-4. Skin. A serocellular crust overlies the cross section of the mite. There is marked thickening of the stratum spongiosum and corneum (acanthosis), intracellular edema of corneal keratinocytes (hydropic degeneration), and a brisk inflammatory infiltrate in the papillary dermis.
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Case 13-4. Note the subcorneal microabscess filled with viable and degenerate eosinophils and neutrophils. The surrounding keratinocytes are undergoing hydropic degeneration.
AFIP Diagnosis: Haired skin, pinna: Dermatitis, eosinophilic, mastocytic, lymphocytic, and plasmacytic, chronic, diffuse, moderate, with hyperkeratotic crust, intracorneal microabscesses, epidermal and follicular hyperplasia, parakeratotic and orthokeratotic hyperkeratosis, and intracorneal mites, mixed breed dog, canine, etiology consistent with Sarcoptes scabiei var. canis.
Conference Note: Canine scabies is a highly contagious, pruritic, skin disease caused by the epidermal mite Sarcoptes scabiei var. canis. The mite is relatively host specific, though the parasite may uncommonly cause transient pruritic skin disease in other species, including humans and cats. Feline scabies is caused by Notoedres cati, while Sarcoptes scabiei var. hominis is the scabies mite of humans. Sarcoptes is a common and economically important ectoparasite in swine, causing depressed growth rates and decreased rates of food conversion. The disease also occurs in cattle and goats, but is probably less important than psoroptic mange.
Sarcoptes completes its life cycle in tunnels burrowed into the stratum corneum of the epidermis. The female mates with a male in a molting pocket close to the skin surface and then burrows through the stratum corneum to feed on cells of the stratum granulosum and stratum spinosum over several weeks. The mite is equipped with cutting mouthparts and cutting hooks on the legs. Epidermal cell damage incites proliferative changes in adjacent keratinocytes, and the tunnel openings at the skin surface become sealed with a thick parakeratotic crust. The female lays her eggs in these burrows, then vacates the tunnels to allow the eggs to hatch. The eggs hatch and develop through larval and nymph stages to reach maturity in 10-15 days, depending upon species. The lesions of sarcoptic mange result from direct mechanical damage to keratinocytes, irritant effects of parasite secretions and excreta, and the hypersensitivity reaction that develops against the mite.
The distribution of gross lesions in the dog result from the preference of the mites to infect sparsely haired skin. The ventral abdomen, margins of the pinnae, chest, and lateral elbows are common sites for sarcoptic lesions. Erythematous maculopapular eruptions with crusting alopecia accompanied by self-traumatic excoriations develop in these areas. Occasionally, the disease may become generalized in immunosuppressed dogs, and affected animals have severe, thick, adherent crusts with marked alopecia.
Microscopically, the epidermis is characterized by moderate to severe acanthosis and variable spongiosis, with both orthokeratotic and parakeratotic hyperkeratosis. Serocellular crusts may occur. Rarely, cross-sections of mites (200-400mm) or their eggs (100-150mm) are found within the superficial layers of the epidermis. Inflammatory cells are often present in the dermis, with scattered eosinophils and mast cells intermingled with perivascular infiltrates of lymphocytes and macrophages, characteristic of a hypersensitivity response. Neutrophils and plasma cells may be present in specimens from sites of erosions, excoriations, and crusting due to trauma. In dogs suffering from generalized scabies, numerous mites may be found embedded in thick crusts.
The differential diagnosis includes other causes of parasitic allergic skin diseases, especially flea allergy dermatitis. Clinically, the distribution of the lesions previously described may suggest the diagnosis of sarcoptic mange. Also, the degree of epidermal hyperplasia is generally greater in chronic sarcoptic mange than in chronic flea allergy. Histologic lesions of sarcoptic acariasis in which there is extensive parakerakeratosis and no mites may resemble zinc responsive dermatosis.
Contributor: Department of Pathobiology, School of Veterinary Medicine, Tuskegee, AL 36088.
1. Morris DO, Dunstan RW: A histomorphological study of sarcoptic acariasis in the dog: 19 cases. J Amer Anim Hosp Assoc 32:119-124, 1996.
2. Arlian LG, Morgan MS, Arends JJ: Immunologic cross-reactivity among various strains of Sarcoptes scabiei. J Parasitol 82:66-72, 1996.
3. Arlian LG, Morgan MS, Rapp CM, Vyszenski-Moher DL: Some effects of sarcoptic mange on dogs. J Parasitol 81:698-702, 1995.
4. Arlian LG, Runyan RA, Estes SA: Cross infestivity of Sarcoptes scabiei. J Amer Acad Dermatol 10:979-986, 1984.
5. Yager JA, Wilcock BP: Perivascular dermatitis. In: Color Atlas and Text of Surgical Pathology in the Dog and Cat, volume 1, pp. 60-61, Mosby-Year Book, London, England, 1994.
6. Gross TL, Ihrke PJ, Walder EJ: Perivascular diseases of the dermis. In: Veterinary Dermatopathology, Reinhardt RW, ed., pp. 123-125, Mosby-Year Book, St. Louis, MO, 1992.
7. Yager JA, Scott DW: The skin and appendages. In: Pathology of Domestic Animals, Jubb KVF, Kennedy PC, Palmer N, eds., 4th ed., volume 1, pp. 681-682, Academic Press, San Diego, CA, 1993.

International Veterinary Pathology Slide Bank:
Laser disc frame# 04357, 04572, 04571, 04818, 09941, 18667, 18668.
Ed Stevens, DVM
Captain, United States Army
Registry of Veterinary Pathology*
Department of Veterinary Pathology
Armed Forces Institute of Pathology
(202)782-2615; DSN: 662-2615
* The American Veterinary Medical Association and the American College of Veterinary Pathologists are co-sponsors of the Registry of Veterinary Pathology. The C.L. Davis Foundation also provides substantial support for the Registry.

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