JPC SYSTEMIC PATHOLOGY

URINARY SYSTEM

January 2024

U-V01

 

Signalment (JPC# 320229): Leopard frog (Rana pipiens).

 

HISTORY: Large abdominal mass found at necropsy.

 

HISTOPATHOLOGIC DESCRIPTION: Kidney: Effacing 90% of renal architecture and extending to submitted borders is a multilobular, unencapsulated neoplasm composed of polygonal cells arranged in variably sized (up to 500 µm in diameter), irregularly shaped tubules and papillary projections, supported by a fine fibrovascular stroma. Neoplastic cells are closely packed, cuboidal to columnar with variably distinct cell borders, and contain a moderate amount of eosinophilic, granular cytoplasm. The neoplastic cells frequently pile up to 10 cell layers thick. Nuclei are round to oval, centrally to basally positioned, with coarsely stippled chromatin and up to two variably indistinct nucleoli. Mitotic figures are less than 1 per 10 high powered fields. There are frequent round, up to 15 µm in diameter, eosinophilic, intranuclear viral inclusion bodies that expand the nucleus and peripheralize the chromatin. Within the cystic lumens formed by neoplastic cells, there are variable amounts of flocculent eosinophilic debris, eosinophilic fluid, occasional sloughed epithelial cells and inflammatory cells. Multifocally, remaining tubules are ectatic and lined by attenuated epithelium and contain sloughed epithelial cells and debris. Within remaining parenchyma, there is a mild, multifocal lymphocytic inflammation and minimal hemorrhage.   

 

MORPHOLOGIC DIAGNOSIS: Kidney: Renal adenocarcinoma with intranuclear viral inclusions, Northern Leopard Frog (Rana pipiens), amphibian.

 

ETIOLOGIC DIAGNOSIS: Ranid herpesvirus renal adenocarcinoma

 

CAUSE: Ranid herpesvirus 1 (RaHV-type1)

 

CONDITION: Lucké's tumor of leopard frogs, Lucké’s renal adenocarcinoma

 

GENERAL DISCUSSION:  

·    Ranid herpesvirus 1 is a herpesvirus that affects free range and captive northern leopard frogs, causing renal adenocarcinoma

• Family Alloherpesviridae 
  • Family includes herpesviruses of fish and amphibians, with four genera: Ictalurivirus, Salmonivirus, Cyprinivirus, and Batrachovirus

• RaHV-1 has tropism for renal convoluted tubules
• Tumor invasion and metastasis is temperature dependent

• Warm = Metastasis, increased growth, no viral inclusions/light microscopy  
• Cool = Rare metastasis, replication in renal tubules, visible inclusion bodies 

 

PATHOGENESIS:  

·    The virus infects frog eggs and tadpoles as they develop in the water during the spring 

·    Virus has a tropism for developing renal cells and appears to be latent until animals are over two years old; carcinomas develop in the third or fourth summer of the frog's life

·    Tumor grows rapidly during the summer and may expand sufficiently to kill the frog; tumor growth halts with hibernation in the autumn

• Digestion of types I & IV collagen is dependent on higher ambient temperatures (due to increased collagenase activity at higher temps), resulting in dormancy of tumor growth in the winter
• During the summer (calid phase), high environmental temperatures are invasion permissive; no evidence of viral inclusions or particles are found during the summer

·    During the winter (algid phase), invasion is arrested because of low environmental temperatures (7-21 degrees Celsius); virus replicates in the convoluted tubules of the kidney, causing host cell lysis and excretion of the virus into the urine

·    By lowering the environmental temperature of the host frog, tumor cells may be converted from the virus-free summer form to the less permissive winter state 

·    Virus is excreted into the urine and is expelled into the pond at the end of hibernation where it infects eggs and tadpoles in the spring; age at exposure and population density of the group may also affect the tendency of tumors develop                   

·    Metastasis (most commonly liver) is more likely at higher temperatures

 

TYPICAL CLINICAL FINDINGS:  

• Tumors do not have an obvious effect on the health of the frogs until the tumor destroys essentially all useful kidney tissue or metastasizes to critical tissues (lungs, liver)
• Lethargy, ascites, emaciation, and death 

 

TYPICAL GROSS FINDINGS:  

·    Single to multicentric, smooth to multilobular, white to yellow masses in the kidney that in advanced stages fill the coelomic cavity and displace viscera 

·    Masses may replace up to 95% of the renal tissue, displace adjacent organs and occasionally fill the abdominal cavity 

         

TYPICAL LIGHT MICROSCOPIC FINDINGS:  

• Unencapsulated but well demarcated from unaffected kidney
• Variably-sized tubules and papillary projections of neoplastic epithelial cells forming structures resembling renal tubules with occasional solidly cellular regions
• Cells lining tubules are larger, cuboidal to columnar and often pseudostratified
• Eosinophilic inclusions (Cowdry type A) are seen in frogs collected in the winter (algid phase) or maintained at a low temperature
• Mitotic figures frequently observed in tumors in the summer

 

ADDITIONAL DIAGNOSTIC TESTS:

 

ULTRASTRUCTURAL FINDINGS:

• Calid (warm phase): Herpesvirus particles are rare or undetectable à viral genome incorporated into the host nucleus
• Algid (cool phase): Many typical icosahedral herpesvirus particles present in nuclei and cytoplasm of neoplastic cells

 

DIFFERENTIAL DIAGNOSIS:

• RaHV-1 associated neoplasms have only been described in the Northern Leopard Frog
• Histologically similar renal adenocarcinomas are sporadically observed in other amphibians 

 

COMPARATIVE PATHOLOGY: 

• Other known members of Alloherpesviridae:
  1. Ranid herpesvirus 2 is associated with massive edema
  2. Ranid herpesvirus 3 has been associated with a proliferative dermatitis
  3. Ictalurid herpesvirus 1 (channel catfish virus)
  4. Cyprinid herpesvirus 1 (carp pox herpesvirus)
  5. Cyprinid herpesvirus 2 (hematopoietic necrosis herpesvirus of goldfish)
  6. Cyprinid herpesvirus 3 (koi herpesvirus)

 

Adapted from MacLachlan, Dubovi (2017)

Viruses that can induce tumors in Domestic or Laboratory Animals or Humans

Family/Genus                         Virus                                                    Type of Tumor

DNA Viruses

Poxviridae/Leporipoxvirus      Rabbit and squirrel fibroma virus Fibromas and myxomas

 

Poxvirinae/Yatapox                Yaba monkey tumor virus           Histiocytoma in monkeys

 

Herpesviridae:

Alphaherpesvirinae                 Marek’s disease virus                  T cell lymphoma in fowl

 

Gammaherpesvirinae             Epstein-Barr virus                        B cell lymphoma, etc

                                                Baboon herpesvirus                    Lymphoma in baboons

                                                Cottontail rabbit herpesvirus        Lymphoma in rabbits

                                                

Alloherpesviridae                    Lucke frog herpesvirus                Renal adenocarcinoma in frogs 

                                                                                                                        

Papillomaviridae                     Bovine papillomavirus 4               Papillomas, carcinoma of 

                                                                                                                 intestine/bladder                                                                                      

                                                Bovine papillomavirus 7               Papillomas, carcinoma of eye

                                                Cottontail rabbit papillomavirus   Papillomas, skin cancer

                                                Equine papillomavirus                 Squamous cell carcinoma

 

Polyomaviridae/Polyomavirus Murine polyomavirus                   Tumors in newborn rodents

                                                Raccoons                                    Central nervous system

                                                 

Reverse Transcribing Viruses

Hepadnaviridae/                      Woodchuck hepatitis virus           Hepatocellular carcinoma

Orthohepadnavirus

 

Hepadnaviridae/

Avihepadnavirus                     Duck hepatitis virus                     Hepatocellular carcinoma

Retroviridae/Alpharetrovirus      Avian Leukosis virus                 Lymphoma, leukemia,    osteopetrosis, nephroblastoma in fowl 

                                                Rous sarcoma virus                    Sarcoma in fowl

                                                Avian myeloblastosis virus          Myeloblastosis in fowl

 

Betaretrovirus                         Mouse mammary tumor virus      Mammary carcinoma 

                                                Ovine pulmonary                         Pulmonary adenocarcinoma 

                                                Adenocarcinoma virus

                                                (jaagsiekte virus)

 

Gammaretrovirus                    Feline Leukemia virus                 Leukemia

                                                Feline sarcoma virus                   Sarcoma in cats

                                                Murine leukemia/sarcoma virus  Leukemia, lymphoma, sarcoma

 

Deltaretrovirus                        Avian reticuloendotheliosis virus Reticuloendotheliosis in fowl

                                                Bovine Leukemia virus                B cell lymphoma, leukemia

                                                

References:  

1. Green DE, Harshbarger JC. Spontaneous neoplasia in amphibia. In: Wright KM, Whitaker BR, eds. Amphibian Medicine and Captive Husbandry. Malabar, FL: Krieger Publishing; 2001:365-368. 

2. Licheri M, Origgi FC. Consensus PCR protocols for the detection of amphibian herpesviruses (Batrachovirus). J Vet Diagn Invest. 2020;32(6):864-872.

3.  MacLachlan JN, Dubovi  EJ, eds. Fenner’s Veterinary Virology. 5th ed.  London, UK: Academic Press; 2017:77, 191, 213, 215.

4. Origgi FC, Otten P, Lohmann P, Sattler U, Wahli T, Lavazza A, Gaschen V, Stoffel MH. Herpesvirus-Associated Proliferative Skin Disease in Frogs and Toads: Proposed Pathogenesis. Vet Pathol. 2021;58(4):713-729.

5. O’Rourke DP, Schultz TW. In: Anderson LC, Fox JG, Loew FM, Quimby FW, eds. Laboratory Animal Medicine. 2nd ed. London, England; Academic Press; 2002:817-818.

6. Pessier AP. Amphibia. In: Terio KA et al. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 925-928.

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