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Guinea Pig Adenovirus
A.
1,2
Schucker ,
M.
2
Troutman ,
2
Bauer ,
1
Jiang ,
1
Armien ,
E. Drake
Y.
A.
3
1
D. Y. Kim and R. Porter
D.
1
Marthaler ,
J. L.
1
Shivers ,
1University
of Minnesota Veterinary Diagnostic Laboratory, St. Paul, MN
2American Preclinical Services, Minneapolis, MN
3Veterinary Medical Diagnostic Laboratory University of Missouri, Columbia, MO
Abstract
Necrosuppurative bronchopneumonia was diagnosed in one-month-old guinea pigs. Clinical signs
ranged from decreased body condition, respiratory distress to sudden death. Gross necropsy findings
included dark red and heavy cranial lung lobes and multifocally similarly affected caudal lung lobes.
Histopathologic findings included ectatic bronchi and bronchioles containing cellular and karyorrhectic
debris, neutrophils, fibrin and sloughed necrotic respiratory epithelial cells. These epithelial cells often
contained a single, large, 5 – 15 um diameter, basophilic, intranuclear inclusion body. The intranuclear
inclusion bodies were immunopositive for adenoviral antigen by immunohistochemistry. Lungs and
feces were positive for guinea pig adenovirus via PCR. DNA extracted and amplified from feces, fresh
and formalin fixed lung yielded 99.9% homology with the hexon gene sequence of guinea pig
adenovirus reference strain. Sloughed, necrotic bronchiolar epithelial cells contained non-enveloped,
round to icosahedral, 70 – 90 nm diameter, variably electron dense viral particles consistent with
adenovirus detected by electron microscopy. Adenovirus of guinea pigs, although infrequently
reported, remains a relevant cause of bronchopneumonia. Histopathology, immunohistochemistry,
PCR and electron microscopy are all useful modes of diagnosis.
Case Description
Intact male, one-month-old, white Hartley guinea pigs (Cavia porcellus) were obtained at different dates
from a commercial supplier and quarantined prior to use in a specific-pathogen-free facility. The guinea
pigs were free of ectoparasites, endoparasites, Salmonella spp., Bordetella bronchiseptica, betahemolytic Streptococcus, Streptococcus pneumoniae, Pasteurella spp., Sendai virus (SEN), Reovirus 3
(REO3), Pneumonia virus of mice (PVM), Lymphocytic choriomeningitis virus (LCM), Simian virus 5
(SV5), and Cytomegalovirus (CMV).
Four guinea pigs demonstrated increased respiratory rate, dyspnea, weight loss and/or sudden death,
either during quarantine or after being placed on study. The first guinea pig demonstrating clinical signs
died after showing respiratory symptoms. Subsequent guinea pigs were euthanized via CO2 inhalation
when clinical signs were initially observed.
Histopathologic findings included bronchi, bronchioles and alveolar lumina containing numerous
neutrophils, macrophages, lymphocytes, and fewer plasma cells and extravasated erythrocytes (Figure
2). The lumina of the bronchi and bronchioles were often mildly to moderately ectatic, distended with
abundant cellular and karyorrhectic debris, extravasated erythrocytes, fibrin and sloughed degenerate
to necrotic respiratory epithelial cells. These epithelial cells often contained a single, large, 5 – 15 um
diameter basophilic, intranuclear inclusion body (Figure 3). Multifocal bronchi and bronchioles were
lined by attenuated, degenerate to necrotic epithelial cells that frequently were multinucleated or
formed syncytia. Multifocal alveolar septa were expanded by lymphocytes, macrophages, type II
pneumocytes and congested blood vessels. The interstitium was multifocally expanded by infiltrates of
few neutrophils, lymphocytes and plasma cells and/or edema.
B
A
Figure 3. Lung; guinea pig. A: Sloughed degenerate and necrotic bronchiolar epithelial cells often
contained a single large basophilic intranuclear inclusion (arrows). (HE 60X) B: Immunohistochemistry.
Cellular debris and necrotic epithelial cells within bronchiolar lumen exhibited strong immunopositivity
to adenovirus. (IHC 60X)
Immunohistochemistry for general adenovirus using monoclonal anti-adenovirus antibody (clone
MAB805, Chemicon) revealed strong immunopositive reaction within nuclei and cytoplasm of sloughed
necrotic epithelial cells and free viral particles within the lumen admixed with cellular debris (Figure 3B).
A
Gross necropsy findings were similar for all guinea pigs (Figure 1). The thoracic cavities contained
small amounts of watery, red, clear fluid. The left and right cranial lung lobes were diffusely dark red,
heavy and wet. Sections of the left and right cranial lung lobes sank in 10% neutral buffered formalin.
The right middle and accessory lung lobes were diffusely dark red and firm. The left and right caudal
lung lobes contained multifocal to coalescing, dark red, firm, irregular, smooth, flat foci.
A
B
Figure 4. Lung; guinea pig – Within necrotic bronchiolar epithelial cells were numerous 70 – 90 nm
diameter, variably electron dense, round to icosahedral viral particles, loosely arranged and in
paracrystalline array. (TEM formalin fixed lung and negative stain of fresh homogenized lung). A: scale
bar 500 nm. B: scale bar 100 nm.
Transmission electron microscopy (TEM) of formalin fixed lung revealed bronchiolar lumina containing
necrotic cells with markedly enlarged nuclei exhibiting discontinuous nuclear membranes, clumping of
chromatin and lacking a clear distinction between the nucleus and the cytoplasm (Figure 4). The
necrotic cells contained numerous loosely arranged and in paracrystalline array, nonenveloped, round
to icosahedral, 70 – 90 nm diameter, variably electron dense, icosahedral viral particles consistent with
adenovirus.
B
Figure 2. Lung; guinea pig. A: Multifocal bronchi, bronchioles and alveoli contained inflammatory cell
infiltrates admixed with necrotic respiratory epithelial cells. Multifocal alveolar septa were expanded by
lymphocytes and macrophages. (H&E 2X) B: Multifocal bronchi and bronchioles were lined by
attenuated, degenerate to necrotic epithelium that frequently were multinucleated or formed syncytia
(arrow). (HE 60X)
Discussion
Adenoviruses are non-enveloped, linear double stranded DNA viruses with icosahedral symmetry that
infect a wide variety of animals with clinical signs ranging from subclinical to enteric or respiratory
manifestations. Guinea pig adenovirus (GpAV) is a distinct serotype within the genus Mastadenovirus
and has the highest level of homology with other animal Mastadenoviruses (mammalian adenoviruses)
and human subgroups A, C and F.1,2 Adenoviruses derived from birds (Aviadenovirus, Atadenovirus),
frogs (Siadenovirus), fish (Ichtadenovirus) and some reptiles (Atadenovirus) are serologically distinct
from Mastadenoviruses.3
Guinea pig adenovirus was first reported in 1981, as the cause of necrotizing bronchitis and
bronchiolitis with low morbidity and high mortality in guinea pigs from two commercial breeders and a
closed colony.4 The adenovirus observed in this outbreak was described as 58 – 72 nm diameter viral
particles in hexagonal crystalline array, forming large, basophilic, intranuclear inclusion bodies by light
microscopy. Additional outbreaks of GpAV in guinea pigs were characterized as necrotizing bronchitis
and bronchiolitis with similar prominent basophilic intranuclear inclusions in sloughed, necrotic epithelial
cells.5 Inclusions contained typical adenoviral particles of 68 – 72 nm diameter, arranged individually
or in crystalline arrays. GpAV infection was reproduced via intranasal inoculation of newborn guinea
pigs and was found to be nonpathogenic in hamsters and rats.6,7 Subclinical infection has been
reported in guinea pigs, but the asymptomatic animals were found to have microscopic lesions of
minimal bronchial epithelial necrosis with typical large basophilic intranuclear inclusions.8
B
Figure 1; A and B. Lung, guinea pig – Two different animals. The cranial lung lobes, right middle lung
lobes, and accessory lung lobes were diffusely dark red and firm. The caudal lung lobes contained
multifocal to coalescing, dark red, firm, irregular, smooth, flat foci.
A
Figure 5. Mastadenovirus partial amino acid hexon phylogenetic tree. The Minnesota/2012
sequence had 99.9% homology to GenBank accession No.X95630.
Lung and feces from two guinea pigs tested positive for guinea pig adenovirus by quantitative real-time
polymerase chain reaction (qPCR) at a commercial testing facility. DNA was extracted and amplified
from feces, fresh and formalin fixed lung samples and was sequenced (Figure 5). The nucleic acid
sequence of an approximately 250 base pair segment of the hexon gene had approximately 99.9%
homology with guinea pig adenovirus reference strain GenBank No. X95630. Aerobic culture of the left
cranial lung lobe of one animal yielded rare colonies of Escherichia coli.
Bronchopneumonia due to GpAV is typically of low morbidity with up to 100% mortality. Clinically
affected animals are often young, but infections have also been reported in adult guinea pigs in
breeding colonies.2,9,10 Infected guinea pigs often show no or only brief clinical signs prior to death.
On gross necropsy the cranial lung lobes are usually consolidated or diffusely red, while the caudal
lung lobes show multifocal consolidation. Histopathologic findings are characterized by a necrotizing
bronchitis and bronchiolitis with sloughing of necrotic epithelial cells into the airways, often resulting in
occlusion of the affected airways with necrotic cells admixed with cell debris, leukocytes and fibrin. The
necrotic epithelial cells often exhibit karyomegaly with extremely large basophilic, round to oval, 7 – 15
um diameter, intranuclear inclusion bodies.4-6
Other differentials for pneumonia in guinea pigs include Parainfluenza virus, Cytomegalovirus and
bacteria such as Bordetella bronchiseptica, Streptococcus species, Staphylococcus species and
Pseudomonas aeruginosa.9 Diagnosis of GpAV infection can be performed via immunohistochemistry,
electron microscopy, serology or polymerase chain reaction.
References
1.
Pring-Akerblom P, Blazek K, Schramlova J, et al. Polymerase chain reaction for detection of guinea pig adenovirus. J Vet Diagn Invest. 1997;9:232-236.
2.
Feldman SH, Sikes R, Eckhoff G. Comparison of the deduced amino acid sequence of guinea pig adenovirus hexon protein with that of other Mastadenoviruses. Comp Med. 2001;51(2):120-126.
3.
King, AMQ, Adams MJ, Carstens EB, et al. Virus Taxonomy. London, UK: International Committee on Taxonomy of Viruses, Elsevier Inc; 2012.
4.
Naumann S, Kunstyr I, Langer I, et al. Lethal pneumonia in guinea pigs associated with a virus. Lab Animals. 1981;15:235-242.
5.
Brennecke LH, Dreier TM, Stokes WS. Naturally occurring virus-associated respiratory disease in two guinea pigs. 1983;20:488-491.
6.
Kaup, FJ, Naumann S, I Kunstyr, et al. Experimental viral pneumonia in guinea pigs: An ultrastructural study. 1984;21:521-527.
7.
Kunstyr I, Maess J, Naumann S, et al. Adenovirus pneumonia in guinea pigs: an experimental reproduction of the disease. 1984;18:55-60.
8.
Crippa L, Giusti AM, Sironi G, et al. Asymptomatic adenoviral respiratory tract infection in guinea pigs. 1997:47(2):197-199.
9.
Percy DH, Barthold SW. Pathology of Laboratory Rodents and Rabbits, Third Edition. Ames, Iowa: Blackwell Publishing Professional; 2007.
10.
Harris IE, Portas BH, Goydich W. Adenoviral bronchopneumonia of guinea pigs. Aust Vet Journal. 1985;62(9):317-318.