AFIP Wednesday Slide Conference - No. 10

10 November 1999
Conference Moderator:
LTC David G. Young
Diplomate, ACVP
US Army Center for Health Promotion and Preventive Medicine
Directorate of Toxicology
Aberdeen Proving Ground, MD 21010-5422
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Case I - ND1 (AFIP 2676132)
Signalment: Four adult mink (Mustela vison) carcasses were submitted to North Dakota State University Veterinary Diagnostic Laboratory.
History: Clinical signs included: anorexia, dyspnea, tremors, seizures, and ataxia. Ten percent of affected animals died, primarily dark and mahogany color varieties. Death occurred in some animals as long as three weeks after the onset of symptoms. Mink on the ranch were vaccinated for canine distemper virus, mink enteritis virus and botulism.
Gross Pathology: Diffuse congestion of lungs and livers in all animals.
Laboratory Results: Bacterial culture of brain tissue from all animals yielded low numbers of mixed contaminants. Fluorescent antibody and virus isolation tests performed on brain tissue were negative for pseudorabies virus, canine distemper virus and rabies virus. Immunohistochemical stains for Newcastle's disease virus, Listeria monocytogenes, Toxoplasma gondii and Neospora caninum were negative.
Aleutian disease parvovirus (ADV) was identified through PCR examination of mesenteric lymph node, spleen, brain, and liver. DNA sequencing of the isolate showed the capsid sequence of the virus had several amino acid differences from other characterized pathogenic ADV isolates suggesting a tropism for the central nervous system.

Contributor's Diagnosis and Comments: Meningoencephalitis, nonsuppurative, diffuse, subacute, severe with gliosis, astrocytosis and satellitosis due to Aleutian Disease parvovirus.

Causes of non-suppurative meningoencephalitis in mink include Encephalitozoon spp., Toxoplasma gondii, a Sarcocystis neurona-like protozoan, Newcastle disease virus (NDV), pseudorabies virus (PRV), canine distemper virus (CDV), and although not reported but still a consideration, rabies virus (RV). Aleutian mink disease parvovirus (ADV) infection in adult animals is associated with glomerulonephritis, interstitial nephritis, disseminated plasmacytosis and polyarteritis, plasma cell hepatitis with bile duct proliferation, uveitis, and hyperplastic intrapulmonary lymphoid tissue. Infection of newborn mink kits results in acute interstitial pneumonia. Nonsuppurative encephalomyelitis is reported in ferrets seropositive for ADV. Idiopathic nonsuppurative meningoencephalitis in ranch mink, and lymphoplasmacytic meningitis, arteritis and periarteritis have been described in mink seropositive for ADV; however, severe meningoencephalitis associated with tissues from which ADV DNA has been identified has not been reported.
Variability in lesion location and intensity associated with ADV infections appears to be at least in part dependent upon factors such as age, color variety, immune status of the host, and strain of the virus. The aforementioned interstitial pneumonia in kits may show wide variability in mortality and lesion development dependent upon the strain of ADV encountered. Nervous system disease associated with ADV also may be the result of similar or as yet undefined host factors.
Pathogenicity of ADV has been suggested to be determined by the capsid proteins. The capsid sequence of the virus identified in this outbreak, showed several amino acid differences from other characterized pathogenic ADV isolates. Perhaps, these few differences endow the isolate with the ability to produce more severe disease in the central nervous system.
AFIP Diagnosis: Brain: Meningoencephalitis, nonsuppurative, multifocal, moderate, with necrosis, mink (Mustela vison), mustelid.
Conference Note: Aleutian mink disease (AMD) is caused by Aleutian Disease Virus (ADV) (Genus Parvovirus, Family Parvoviridae), a small (28nm), enveloped, single-stranded DNA virus. ADV was originally characterized as affecting only mink with the Aleutian phenotype, but it is now known to affect all colors of mink to varying degrees, as well as ferrets. Forty-two percent of adult female mink were positive for ADV antibody in one study, and skunks, raccoons, and foxes have been reported to have titers to ADV. Transmission can be horizontal or vertical, and the incubation period is generally 5-6 months. The two classic features of AMD are multisystemic plasmacytic inflammation and hypergammaglobulinemia. ADM is used as an animal model for immune-mediated glomerulonephritis.
Contributor: North Dakota State University, Fargo, ND 58105
1. Aasted B, Alexandersen S, Christensen J: Vaccination with Aleutian mink disease parvovirus (AMDV) capsid proteins enhances disease, while vaccination with the major non-structural AMDV protein causes partial protection from disease. Vaccine 16:1158-1165, 1998
2. Alexandersen S: Acute interstitial pneumonia in mink kits: experimental reproduction of the disease. Vet Pathol 23:579-588, 1986
3. Alexandersen S, Larsen S, Aasted B, Uttenthal A, Bloom ME, Hansen M: Acute interstitial pneumonia in mink kits inoculated with defined isolates of Aleutian mink disease parvovirus. Vet Pathol 31:216-228, 1994
4. Bjerkas I: Brain and spinal cord lesions in encephalitozoonosis in mink. Acta Vet Scand 31:423-432, 1990
5. Bloom ME, Fox JM, Berry BD, Wolfinbarger JB: Construction of pathogenic molecular clones of Aleutian mink disease parvovirus that replicate both in vivo and in vitro. Virol 251:288-296, 1998
6. Dietz HH, Henriksen P, Lebach M, Henricksen SA: Experimental infection with Toxoplasma gondii in farmed mink (Mustela vison S.). Vet Parasitol 47:1-7, 1993
7. Drommer W, Trautwein G: Pathogenesis of Aleutian mink disease. VII. Chronic hepatitis with bile duct proliferation. Vet Pathol 12:77-93, 1975
8. Dubey JP, Hedstrom OR: Meningoencephalitis in mink associated with a Sarcocystis neurona-like organism. J Vet Diagn Invest 5:467-471, 1993
9. Haagsma J, Rondhuis PR, Lensing HH: Meningo-encephalitis in mink caused by NCD virus. Tijdschr Diergeneeskd 100:633-640, 1975
10. Hadlow WJ: Ocular lesions in mink affected with Aleutian disease: Vet Pathol 19:5-15, 1982
11. Hadlow WJ, Race RE, Kennedy RC: Comparative pathogenicity of four strains of Aleutian disease virus for pastel and sapphire mink. Infect Immun 41:1016-23, 1983
12. Jericho KW: Intrapulmonary lymphoid tissue in mink infected with Aleutian disease virus. Res Vet Sci 32:206-212, 1982
13. Kanno H, Wolfinbarger JB, Bloom ME: Identification of Aleutian mink disease parvovirus transcripts in macrophages of infected adult mink: J Virol 66:5305-5312, 1992
14. Kimman TG, van Oirschot JT: Pathology of Aujeszky's disease in mink. Vet Pathol 23:303-309, 1986
15. Mori S, Nose M, Miyazawa M, Kyogoku M, Wolfinbarger JB, Bloom ME: Interstitial nephritis in Aleutian mink disease. Possible role of cell-mediated immunity against virus-infected tubular epithelial cells. Am J Pathol 144:1326-1333, 1994
16. Nieto JM, Alvarez C, Flores JM, Romano J: Glomerular lesions in Aleutian disease of mink (Mustela vison): a morphological and differential morphometrical study. Histol Histopathol 6:141-148, 1991
17. Oie KL, Durrant G, Wolfinbarger JB. Martin D, Costello F, Perryman S, Hogan D, Hadlow WJ, Bloom ME: The relationship between capsid protein (VP2) sequence and pathogenicity of Aleutian mink disease parvovirus (ADV): a possible role for raccoons in the transmission of ADV infections. J Virol 70:852-61, 1996
18. Schmitz JA, Wustenberg W, Gorham JR: Nonsuppurative meningoencephalitis of unknown etiology in mink. Vet Pathol 22:112-116 1985
19. Sutherland-Smith MR, Rideout BA, Mikolon AB, et al: Vaccine-induced canine distemper in Europeon mink, Mustela lutreola. J Zoo Wildl Med 28:312-318, 1997
20. Welchman D de B, Oxenham M, Done SH: Aleutian disease in domestic ferrets: diagnostic findings and survey results. Vet Rec 132:479-84,1993
Case II - C99094102 (AFIP 2689020)
Signalment: A 4-week-old, female, dachshund puppy
History: This puppy had been sick for one day. A littermate had died the previous day and two others were weak. The puppy presented for necropsy had an increased respiratory rate and labored breathing for 6 hours prior to death. The owner had vaccinated against DHLP/CPV/CCV and dewormed with Strongid two days prior to death.
Gross Pathology: The lungs were mildly congested. Epicardial blood vessels were injected and pronounced. No other significant gross findings were noted.
Contributor's Diagnosis and Comments: Heart, myocardium: Myocarditis, interstitial, nonsuppurative, mild to moderate, subacute, with intranuclear inclusion bodies, dachshund, canine.

There was mild to moderate interstitial inflammation in the myocardium composed of macrophages and occasional lymphocytes. There was degeneration of occasional myocardial fibers characterized by cytoplasmic eosinophilia and loss of striations. Some myocardial fibers had enlarged nuclei with amphophilic to basophilic intranuclear inclusion bodies. Microscopic lesions in other tissues included severe chronic pulmonary edema, hepatic centrilobular congestion and multifocal lymphoid necrosis in the spleen. The lesions and myocardial intranuclear inclusions were considered compatible with canine parvovirus infection. Direct fluorescent antibody staining of fixed and frozen sections of myocardium were positive for canine parvovirus-2.
During the original epizootic in the 1970's, canine parvovirus produced 2 main forms of the disease: vomiting and diarrhea in dogs of approximately 8-12 weeks of age with histologic findings of necrotizing enteritis, and sudden death in puppies 3-8 weeks of age with histologic findings of nonsuppurative myocarditis with intranuclear inclusions. The myocardial form was presumed to be due to infection while replication of myocardial cells was occurring. In recent years, the myocardial form of the disease has become very uncommon, and disease associated with CPV-2 is attributed primarily to the enteric form. In recent weeks, we have seen several cases of the myocardial form, and at this time the significance is unknown.
AFIP Diagnosis: Heart: Myocarditis, lymphohistiocytic, necrotizing, diffuse, moderate, with intranuclear inclusion bodies, dachshund, canine.
Conference Note: Canine parvovirus type 2 (CPV2) is a small (28nm), enveloped, single-stranded DNA virus. Another parvovirus, feline panleukopenia virus, is thought to have mutated to form the original CPV2. CPV2 can naturally infect most wild canids including coyotes, bush dogs, wolves, crab eating foxes, and has experimentally infected raccoons, cats, ferrets, and minks.
The myocardial form of CPV2 results from infection of neonatal (<2 weeks) puppies that are deprived of colostrum or are born to bitches that have no previous exposure to CPV2 antigen. CPV2 infection occurs oronasally; the virus enters epithelial and lymphoid cells and is disseminated throughout the body. The virus is dependent on DNA polymerase, and therefore, replicates in rapidly dividing cells. Cardiomyocytes actively divide for approximately two weeks after birth, thus explaining the limited window of cardiac infection (<2 weeks cardiomyocyte susceptibility + 1-2 weeks incubation = first 1-4 weeks of life).

Clinically, animals can have a spectrum of cardiac lesions depending on the severity of infection and the duration of infection. The cases that are generally attributed to CPV2 present with dyspnea or sudden death, but animals that survive the initial infection may develop heart failure as adults as a result of myocardial fibrosis.

Other causes of nonsupurative myocarditis in dogs include: canine distemper virus, canine parvovirus type 1 (minute virus of canines), infectious canine hepatitis, vitamin E/selenium toxicity, and Pseudomonas sp.
Contributor: Texas Veterinary Medical Diagnostic Lab, Texas A&M University System, P.O. Box 3040, College Station, Texas 77843
1. Agungpriyono DR, Uchida K, Tabaru H, Yamaguchi R, Tateyama S: Subacute massive necrotizing myocarditis by canine parvovirus type 2 infection with diffuse leukoencephalomalacia in a puppy. Vet Pathol 36:77-80, 1999
2. Hoskins JD: Canine Viral Enteritis. In: Greene's Infectious Diseases of the Dog and Cat, ed. Greene CE, 2nd ed, pp. 40-48. W.B. Saunders, Philadelphia PA, 1998
3. Robinson WF, Humtable CR, Pass DA: Canine parvoviral myocarditis: A morphologic description of the natural disease. Vet Pathol. 17:282-293, 1980
4. Lenghaus C, Studdert MJ: Acute and chronic viral myocarditis. Acute diffuse nonsuppurative myocarditis and residual myocardial scarring following infection with canine parvovirus. Amer Journ of Pathol 115(2):316-319, 1984
Case III - MK96-944 (AFIP 2674593 )
Signalment: 18-month-old male common marmoset, Callithrix jacchus.
History: This young adult marmoset was found dead in his cage; clinical signs were limited to a 6 gram weight loss over a 2 week period.
Gross Pathology: Left lung lobes were consolidated and diffusely reddened. 1 to 2ml of thick blood tinged fluid was present in the left pleural cavity. Left parietal pleura was thickened and rough.
Laboratory Results: Bacterial cultures from thoracic cavity and lung yielded Klebsiella pneumoniae. Enterococcus faecalis and alpha hemolytic Streptococcus was also isolated from the lung, but in fewer numbers.

Contributor's Diagnoses and Comments:
1. Lung, left: Bronchopneumonia, fibrinosuppurative, diffuse, severe; etiology: Klebsiella pneumoniae.
2. Liver: Bacteremia (liver sections are not present on all slides)
Klebsiella pneumoniae is a gram-negative, aerobic, encapsulated bacillus that may be cultured from soil, air, water, and fresh vegetables; it may also occur as normal flora in the gastrointestinal and respiratory tracts in some animals. K. pneumoniae is an important pathogen in New World monkeys, where it can cause lymph node abscessation, meningitis, air sacculitis, pneumonia and peritonitis. The organism is generally considered an opportunistic pathogen, causing disease in debilitated or immunocompromised individuals. It can invade the body through inhalation, aspiration, ingestion or through an open wound. It disseminates hematogenously and can infect multiple organs. Clinical signs include listlessness, anorexia, nasal discharge, swelling or abscessation of lymph nodes, and/or depression. Klebsiella pneumoniae is generally susceptible to a variety of antibiotics, but may develop multi-drug resistance through plasmid-transfer. Some strains may resist phagocytosis and complement-mediated killing.
This marmoset was part of a colony maintained in an AAALAC accredited biomedical research facility, which were used in minimally invasive behavioral studies. Over a 28-month period, between December 1995 and February 1998, 49 clinical cases (out of approximately 70 marmosets) occurred, with a case fatality rate of 84%. In this outbreak, the animals were generally young adults, with no evidence of debilitation or pre-existing disease (which is in marked contrast to the usual view of K. pneumoniae as an opportunistic invader). Weight loss over one to several weeks period, was the most consistent clinical sign. Affected animals were generally depressed, with variable pyrexia and lymphadenopathy. Common necropsy findings included peritonitis, pneumonia, pleuritis, lymph node abscessation and tonsillitis. Survivors generally manifest cervical swelling and abscessation which generally responded to antibiotic therapy and lancing.
A small colony of squirrel monkeys housed in different rooms in the same building were less severely affected, with the majority of affected animals recovering with appropriate therapy.
Klebsiella pneumoniae was cultured from the feces of rhesus and capuchin monkeys, which were also housed in the building, although none of these species manifested clinical disease. It appears likely that the infection was introduced to the marmoset and squirrel monkey colonies by fecal contamination of a cart that was used throughout the building. Subclinically infected carriers, which shed pathogenic bacteria in their feces, apparently perpetuated the infection within the colony.
Frequent occurrence of mesenteric lymph node abscessation and peritonitis suggest that the organism invaded through the intestinal wall. Nodal parenchyma was frequently totally necrotic and effaced by myriad neutrophils and bacteria. As occurred in this case, most animals also had a terminal bacteremia, with bacilli easily visible on H&E stained sections within large and small vessels throughout the body. K. pneumoniae's capsule gives the bacilli a very characteristic appearance both in sections, smears and touch preparations. Preparation of Wright-Giemsa stained smears or touch impressions from affected organs at necropsy allows for a presumptive same-day diagnosis.
The reason for the increased virulence of K. pneumoniae in this outbreak is not apparent. Endotoxins released from the cell wall may vary in potency from strain to strain, and a few strains have been shown to produce enterotoxins of questionable potency.
Changes in husbandry practices that help to eliminate the infection from the colony included: elimination of the use of any equipment between species; repeat fecal, nasal, and oral cultures on all colony animals to identify carriers; separation of carriers and their cagemates from uninfected animals; treatment of the entire colony with neomycin and repeated treatment and culture of identified carriers; washing of all fruit with 10% bleach solution.
AFIP Diagnoses:
1. Lung: Pneumonia, fibrinosuppurative and hemorrhagic, acute, diffuse, severe, with myriad bacilli, common marmoset (Callithrix jacchus), non-human primate.
2. Liver: Bacteremia.
Conference Note: Among laboratory animals, infection with K. pneumoniae (Friedlander's bacillus) is most common in non-human primates, especially those subjected to some "stress", such as splenectomy or infection with malaria or yellow fever. It is an important cause of pneumonia, middle ear infections, meningitis, peritonitis, cystitis and septic abortion. The most common bacterial isolate from non-human primates with pneumonia is Klebsiella pneumoniae, followed by Escherichia coli, Streptococcus pneumonia, Bordetella bronchiseptica, Corynebacterium pseudotuberculosis, and Mycobacterium tuberculosis. Other bacteria that may be responsible for pneumonia in non-human primates include Diplococcus pneumoniae, Pasteurella multocida, Haemophilus influenza and ß-hemolytic Streptococci.
Contributor: Veterinary Resources Program, National Institutes of Health, Bethesda, MD 20892.
1. Berendt RF, Knutsen GL, Powanda MC: Nonhuman primate model for the study of respiratory Klebsiella pneumoniae infection. Inf and Immun 22:276-281, 1978
2. Hunt DE, Pittillo RF, Deneau GA: Control of an acute Klebsiella pneumoniae infection in a rhesus monkey colony. Lab Ani Care 18:182-185, 1968
3. Giles RC, Hildebrandt PK, Tate C: Klebsiella air sacculitis in the owl monkey (Aotus trivirgatus). Lab Ani Sci 24:610-616, 1974
4. Good RC, May BD: Respiratory pathogens in monkeys. Inf and Immun 3:87-93, 1971
5. Obaldia N: Detection of Klebsiella pneumoniae antibodies in Aotus l. lemurinus (Panamanian owl monkey) using an enzyme linked immunosorbent assay (ELISA) test. Lab Anim 25:133-141, 1991
6. Synder SB, Lund JE, Bone J: A study of Klebsiella infections in owl monkeys (Aotus trivirgatus). JAVMA 157:1935-1939, 1970
Case IV - 99-1215 (AFIP 2685269)
Signalment: Eight-week-old, male domestic feline kitten.
History: 4 day history of lethargy and pulmonary congestion. The kitten was euthanized.
Gross Pathology: The left lung lobes and right cranial and middle lung lobes were pink/brown with indistinct, white miliary foci intermingled. Foamy red fluid was present in the trachea and bronchi.
Laboratory Results: Chlamydia and bacterial cultures were negative. Feline calicivirus was isolated from lung tissue. Fluorescent antibody stain for feline herpesvirus was negative.

Contributor's Diagnosis and Comments:
Bronchointerstitial pneumonia, necrotizing, subacute, moderate to severe lung. (Etiology: calcivirus).

Feline calicivirus causes infections, which generally fall into one of several types: 1.) upper respiratory track and oral epithelium. 2.) pneumonia. 3.) ulcerative stomatitis. 4.) enteritis. 5.) acute arthritis. 6.) chronic stomatitis.
The type of lesions seen tends to depend on the virulence and tropism of the strain. More than one type of lesion may occur in a given outbreak. Some strains have a strong tropism for alveolar type I cells resulting in severe pneumonia and up to 30% mortality. The lesions are an acute to subacute interstitial pneumonia with necrosis of pneumocytes and alveolar influx of neutrophils and serum protein. Hyalin membranes may form. As the disease progresses, type II pneumocytes proliferate along alveolar walls. Concurrent infection with other respiratory pathogens such as feline herpesvirus-1 may be present and complicate the picture.
AFIP Diagnosis: Lung: Bronchopneumonia, fibrinous, necrotizing, subacute, diffuse, moderate, domestic cat, feline.
Conference Note: Feline calicivirus (FCV) is a member of the family Picornaviridae. It is a non-enveloped single stranded RNA virus that replicates within the cytoplasm. Ultrastructurally, the 35-40nm virions have a dense 20nm core and often align into laminated arrangements. FCV is closely related genetically to swine vesicular exanthema virus and San Miguel sea lion virus.
FCV is a common upper respiratory infection of young cats, but rarely produces significant clinical disease, unless animals are immuno-compromised. As noted by the contributor, different strains produce different lesions; pneumonic infection is generally produced by strains that have a strong trophism for type I pneumocytes. Damage to type I pneumocytes leads to attraction of alveolar macrophages and replacement of type I pneumocytes with type II pneumocytes. In the absence of significant secondary infections, most animals recover with eventual maturation of type II pneumocytes to type I pneumocytes, resulting in normal pulmonary architecture.
Contributor: Arizona Veterinary Diagnostic Lab, 2831 N. Freeway, Tucson, AZ 85705-5021
1. Barr ME, Olsen CW, Scott FW: Feline Viral Diseases. In: Textbook of Veterinary Internal Medicine. eds. Ettinger BJ and Feldmen EC, 4th ed. Vol 1, pp409-439. W.B. Saunders, Philadelphia, PA, 1995
2. Dungworth DL: The Respiratory System. In: Pathology of the Domestic Animals, Vol 2, eds. Jubb KVF, Kennedy PC, and Palmer N, 4th ed., pp. 539-699. Academic Press Inc. San Diego, CA,1993
3. Hoover EZ, Kohn DE: Experimentally Induced feline calicivirus infection: Clinical signs and lesions. JAVMA, 166:436-468, 1975
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.
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