AFIP Wednesday Slide Conference - No. 2
15 September 1999

Conference Moderator:
COL Nancy Jaax, Diplomate, ACVP
Pathology Division
U.S. Army Medical Research Institute of Infectious Disease
Ft. Detrick, Frederick, MD 21702-5011
NOTE: Click on images for larger views. Use browser's "Back" button to return to this page.
Return to WSC Case Menu
Case I - 78536 (AFIP 2677920)
Signalment: 6-month-old, female, athymic, nude mouse, Mus musculus
History: Swollen, firm abdomen; no experimental manipulations had been performed.
Gross Pathology: Markedly enlarged liver and spleen; bilaterally, kidneys have large (2cm) yellow, nodular masses engulfing kidneys; masses are firm on cut section and core material is gritty.
Contributor's Diagnoses and Comments:
1. Kidney, nephritis, pyogranulomatous, multifocal and coalescing, severe with intralesional coccoid bacteria and Splendore-Hoeppli (botryomycosis), etiology consistent with Staphylococcus sp.
2. Kidney, nephritis, interstitial, chronic with tubular degeneration, regeneration, peritubular and periglomerular sclerosis

Although bacterial culture of the kidney was not done, the diagnosis is most likely renal botryomycosis cased by Staphylococcus. No obvious route of entry for the organism was noted at necropsy. Abscesses, furunculosis and similar histomorphologic lesions are reported and are not uncommon on the face and mandibular area in athymic nude mice. S. aureus is most commonly isolated. Although reactive lymphocytic hyperplasia may be seen in regional lymph nodes and spleen with these lesions, a literature search did not reveal any reports of similar systemic or renal lesions.
AFIP Diagnosis:
1. Kidney and mesenteric fibroadipose tissue: Abscesses, chronic, multifocal and coalescing, with large colonies of cocci surrounded by Splendore-Hoeppli material, athymic nude mouse ( Mus musculus), rodent.
2. Kidney: Nephritis, interstitial, chronic-active, multifocal, moderate.
Conference Note: The term botryomycosis originates from the characteristic histologic finding of granules in clusters and the early belief that the cause was fungal. It usually follows some form of trauma and typically involves the deep dermis, subcutis, and occasionally extends to muscle, adjacent bone, and rarely viscera. Splendore-Hoeppli material is not unique to botryomycosis and is seen in other microbial infections and foreign body reactions. It is thought to represent glycoprotein antigen-antibody complexes.
Bacteria that may cause botryomycosis include: Staphylococcus, Streptococcus, Pasteurella, Proteus, Pseudomonas, and Actinobacillus; eumycotic and actinomycotic mycetomas may have a similar appearance. The presence of cocci within the pyogranulomas shortens this list to Staphylococcus sp. and Streptococcus sp. Staphylococcus aureus is the most common cause of botryomycosis.
Homozygous nude mice (nu/nu) have been shown to be more resistant to experimental challenge with Staphylococcus aureus than heterozygous controls (nu/+). The increased resistance is attributed to the presence of naturally occurring activated macrophages in the reticuloendothelial organs. The enhanced activation of macrophages may be explained by the absence of T lymphocyte suppressor cells.
Tissue Gram stains demonstrated that the bacteria are Gram positive. Some sections do not have identifiable kidney.
Contributor: FDA/CBER/VSS, HFM-22, 8800 Rockville Pike, Bldg. 29A, rm. 1A17, Bethesda, MD 20892
1. Abe Y, Akiyama H, Arata J: Furuncle-like lesions in mouse experimental skin infections with Staphylococcus aureus. Journ Dermatology, 20:198-202, 1993
2. Biberstein EL, Jang SS, and Hirsch DC: Species distribution of coagulase-positive staphylococci in animals. J Clin Microbiol 19(5):610-615, 1984.
3. Bywater JEC: Furunculosis in a mouse. Vet Rec 101:385, 1977
4. McBride DF, Stark DM, Walberg JA: An outbreak of staphylococcal furunculosis in nude mice. Lab Anim Sci 31(3):270-72, 1981
5. Percy DH, Barthold SW: Staphylococcal Infections. In: Pathology of Laboratory Rodents and Rabbits, pp. 35-36. Iowa State University Press, Ames, IA, 1993
Case II - 99-275X (AFIP 2679285)
Signalment: One-year-old, male, ferret (Mustela putorius)
History: This ferret was inoculated intranasally with a type A avian influenza virus. The ferret became lethargic, developed a serous nasal discharge, and began sneezing. In addition, it became febrile. Three days after inoculation, the ferret was euthanized.
Gross Pathology: The right and left caudal dorsal lung lobes and the caudal dorsal region of the right cranial lung lobe were red. The abdomen contained serosanguinous fluid. The stomach was filled with mucus and lacked food. The liver was tan and had an enhanced lobular pattern.
Laboratory Results: Influenza virus was isolated from the nasal turbinates, lung, spleen, and nasal washes taken at one and three days post-inoculation
Contributor's Diagnoses and Comments: Interstitial bronchopneumonia, subacute, diffuse, severe, with edema and bronchiolar epithelial hyperplasia.
Clinical signs of influenza infection in ferrets include fever, sneezing, mucoid or mucopurulent nasal discharge, lethargy, inappetance, ocular discharge, photophobia, and conjunctivitis. It has a 7-14 day course, and is generally self-limiting. Neonates may develop more serious disease than adults, and death may ensue. Lower respiratory tract infection is less common, but when it occurs it is usually confined to the bronchial epithelium. Limited enteritis may occur and experimentally infected ferrets have been reported with signs referable to hepatic and renal disease.
Histologic findings included interstitial bronchopneumonia with a mixed inflammatory reaction composed predominately of lymphocytes. Pulmonary edema was multifocal and moderate. In addition, the bronchiolar epithelium was hyperplastic.
Differential diagnosis of pneumonia in ferrets includes viral diseases caused by influenza virus, canine distemper virus and respiratory syncytial virus. Streptococcus zooepidemicus, S. pneumoniae, groups C and G streptococci, Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Bordetella bronchiseptica, and Listeria monocytogenes are the most common bacteria isolated from ferrets with pneumonia. In addition Pneumocystis carinii can also infect ferrets, resulting in pneumonia.
The ferret is a common model for the study of influenza. Infection generally results in clinical signs and lesions similar to those seen in humans. As a result, ferrets are often used for studies of potential vaccine candidates prior to clinical trials in humans.
AFIP Diagnosis: Lung: Pneumonia, bronchointerstitial, serofibrinous, subacute, diffuse, severe, with bronchiolar epithelial hyperplasia, ferret ( Mustela putorius furo), mustelid.
Conference Note: Several influenza viruses are readily transmitted to ferrets from humans and vice versa. The differential diagnosis discussed at the conference included: influenza, canine distemper (morbillivirus), and Aleutian mink disease (mink parvovirus). The significant neutrophilic component suggests secondary bacterial infection; however, tissue gram stains did not demonstrate bacteria.
The bronchiolar pattern is strongly suggestive of nasal aerosol exposure. Inhalation chamber exposure to the same pathogen would generally produce a diffuse alveolar pattern. This variation is associated with particle size. Particles of less than 5mm diameter are required to produce an alveolar infection.

Contributor: Emory University, Div. Animal Resources, G70 Rollins Bldg, 1510 Clifton Road, Atlanta, GA 30322
1. Collie MH, Rushton DI, Sweet C, Smith H: Studies of influenza infection in newborn ferrets. J Med Microbiol 13:561-571, 1980
2. Hinshaw VS, Webster RG, Easterday BC, and Bean WJ: Replication of avian influenza A viruses in mammals. Inf and Immun 34:354-361, 1981
3. Renegar BR: Influenza virus infection and immunity: A review of human and animal models. Lab Ani Sci 42(3):222-232, 1992
4. Reuman PD, Keely S, and Schiff GM: Assessment of signs of influenza illness in the ferret model. J of Viro Meth 24:27-34, 1989
5. Rosenthal KL. Respiratory Diseases. In: Clinical medicine and surgery. eds. Hillyer EV, and Quesenberry KE, pp. 79-81. WB Saunders Co., Philadelphia, 1997
6. Smith, H, and Sweet, C: Lessons for human influenza from pathogenicity studies with ferrets. Review of Infectious Diseases 10(1):56-75, 1988
Case III - MT299 (AFIP 2675680)
Signalment: The brains are from double knockout mice, Mus musculus. The strain is 129 SvEv X C57Bl/6 Fn

History: These mice are the product of a mating to produce double-knockout mice in which the genes coding for the VLDL and ApoE2 lipoprotein receptors have been deleted. By day 10 after birth (P10), failure to thrive became apparent in the double knockout mice. By P13 to P15 neurological signs developed, characterized by progressive ataxia, wide gait and tremor. The animals frequently flipped onto their backs and had difficulty righting themselves. By P20 the mice were distinctly smaller than their unaffected littermates. Progressive hind-limb paralysis developed between P16 and P20 and the animals died shortly thereafter.
Gross Pathology: The brains were smaller than those of the wild-type animals of the same age. This difference was most dramatic for the cerebellum that in the double knockout was rudimentary.
Contributor's Diagnoses and Comments: Neocortical, hippocampal and cerebellar dysgenesis, diffuse, marked, brain, Mus musculus.
The lesions in the brains of these mice are a consequence of the deletion of two lipoprotein receptors, ApoER2 and VLDLR.
The pyramidal cells in the CA 1 region of the hippocampus are split, forming two layers rather than one, and the neurons of the dentate gyrus are scattered, distorting the normal C-shaped pattern characteristic of the dentate. The rudimentary cerebellum completely lacks foliation and the Purkinje cells are aggregated in the cerebellar peduncle. The granular cell layer is thin. In the neocortex, the cortical laminations are indistinct. As well, there are an increased number of neurons in the marginal layer, which is normally free of cell bodies.
The lesions are an exact phenocopy of those seen in two previously described spontaneous mutant mice named Reeler and Scrambler in which the genes for the extracellular protein "reelin" and the intracellular protein "disabled" are mutated respectively.
Reelin is involved in a molecular pathway that regulates the migration of neurons along the radial glial fiber network during development of the brain. In the cortex, this protein is either associated with the extracellular matrix or with the surface of Cajal-Retzius neurons that produce it in the outermost layer just beneath the pial surface. The Cajal-Retzius neurons are formed during the early stages of neural development. When the gene encoding reelin is defective, migratory neurons apparently do not receive a critical cue that informs them of their position during their migration away from the ventricular zone, leading to an inversion of the cortical layers. The cortical laminae normally form from the inside out, with later-born neurons migrating past old ones to form progressively more superficial, and thus younger, layers of the neocortex. When reelin is defective, the cortical laminae are inverted, i.e. the cortex is inside out. In the cerebellum, reelin is required for the Purkinje cells to migrate outward, where they form a well-defined cortical plate through which postmitotic granule cells migrate inward to form the internal granule layer. Both of these laminate structures do not form normally in the reeler mouse.
In 1991 at the Jackson Laboratory an exact phenocopy of Reeler occurred and was found to be caused by a spontaneous mutation in mDab1, the mouse homologue of the Drosophila disabled gene. This mouse was named Scrambler. Mouse Dab1 is an intracytoplasmic adapter protein, which is thought to interact with tyrosine kinases of the Src and Abl families. Unlike reelin, mDab1 is expressed in the neurons that manifest the Reeler phenotype suggesting that it is a key element of the response to a reelin signal.
The fact that the deletion of the ApoER2 and VLDLR results in a phenocopy of Reeler and Scrambler mice suggests that VLDLR and ApoER2 participate in transmitting the extracellular reelin signal to an intracellular signaling cascade initiated by mDab1.
AFIP Diagnosis: Brain: Dysgenesis, with marked cerebellar hypoplasia, 129 SvEv X C57Bl/6 Fn mouse (Mus musculus), rodent.

Conference Note: The normal formation of the central nervous system involves a precisely orchestrated series of waves of migration of post-mitotic neurons from ventricular zones to their final anatomic locations. In humans, neuronal migratory defects have been associated with lissencephaly syndrome, Fukuyama type cerebromuscular dystrophy, Norman-Roberts syndrome, Neu-Laxova syndrome, Joubert syndrome, pediatric epilepsy, schizophrenia and others. Mice models help elucidate the neuronal migration abnormalities.

Contributor: University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd. Dallas, TX. 75235
1. Curran T, D'Arcangelo G: Role of reelin in the control of brain development. Brain Res. Brain Res Rev. 26: 285-294, 1998
2. D'Arcangelo G, Miao GG, Chen SC, Soares HD, Morgan JI, and Curran T: A protein related to extracellular matrix proteins deleted in the mouse mutant reeler. Nature 374: 719-723, 1995
3. Falconer DS: Two new mutants "trembler" and "reeler" with neurological actions in the house mouse. J Genet. 50: 192-201, 1951
4. Gallagher E, Howell BW, Soriano P, Cooper JA, Hawkes R: Cerebellar abnormalities in the disabled (mdab1-1) mouse. J Comp Neurol. 402: 238-251 1998
5. Howell BW, Hawkes R, Soriano P, Cooper JA: Neuronal position in the developing brain is regulated by mouse disabled-1. Nature 389: 733-737, 1997
6. Sweet HO, Bronson RT, Johnson KR, Cook SA, Davison MT: Scrambler, a new neurological mutation of the mouse with abnormalities of neuronal migration. Mamm. Genome 7: 798-802, 1996
7. Trommsdorff M, Gotthardt M, Hiesberger T, Shelton J, Stockinger W, Nimpf J, Hammer RE, Richardson JA, Herz J: Reeler/disabled-like disruption of neuronal migration in knockout mice lacking the VLDL receptor and ApoE receptor-2. Cell 97: 689-701, 1999
Case IV- 96458/148-16, 16A, 16B, 16C (AFIP 2681373)
Signalment: 10-month-old, CD-1, male mouse (Mus musculus).
History: This animal was a control mouse (no experimental manipulation) on a long-term study and was housed under conventional conditions.

Gross Pathology: At necropsy, the lungs appeared enlarged due to failure to completely deflate. The lungs were diffusely discolored red and white with a nodular surface. There were multiple, firm, white, pleural nodules associated with the mediastinum.
Laboratory Results: None
Contributor's Diagnoses and Comments: Lung: Pulmonary ossification with mineralization, diffuse, severe.
Pulmonary osseous metaplasia is an uncommon incidental finding in aged mice. The lesion is usually confined to a small focus. This case was submitted because of its unusual severity.
AFIP Diagnosis: Lung: Osseous metaplasia, diffuse, CD-1 mouse (Mus musculus), rodent.
Conference Note: Subpleural and centriacinar foci of ossification are occasionally observed in laboratory mice. These foci may contain osteoid with or without mineralization. They must be differentiated from osteosarcoma. In this case, the regular organization of the bony spicules, the lack of cellular atypia, and a low mitotic rate support the diagnosis of osseous metaplasia.
Pulmonary osseous metaplasia in mice and rats was originally thought to result from inhalation of feed dust containing fishmeal. However, the current theory is that osseous metaplasia arises within the alveolar walls. The intra-alveolar appearance is an artifact that results from herniation into the alveolar spaces during sectioning.

Contributor: Schering-Plough Research Institute 144 Route 94, P.O. Box 32, Lafayette, NJ 07871
1. Dixon D, Herbert RA, Sills RC, Boorman GA: Lungs, pleura and mediastinum, miscellaneous lesions. In: Pathology of the Mouse, reference and atlas, ed. Maronpot RR, pp. 320. Cashe River Press, Vienna, IL, 1999
2. Dungworth DL, Ernst T, Mohr U: The respiratory system, Nonneoplastic lesions in the lungs. In: Pathobiology of the aging rat, Vol. 1, ed. Mohr U, Dungworth DL, Capen CC, pp. 157-158. International Life Sciences Institute,. Washington, DC, 1992.
J Scot Estep, DVM
Captain, VC, USA
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.
Return to WSC Case Menu