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Journal of Virology, January 2007, p. 411-415, Vol. 81, No. 1
0022-538X/07/$08.00+0 doi:10.1128/JVI.01825-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
Disseminated Simian Varicella Virus Infection in an Irradiated Rhesus Macaque (Macaca mulatta)
Krishnan Kolappaswamy,1,2,6
Ravi Mahalingam,3
Vicki Traina-Dorge,7
Steven T. Shipley,1,2
Donald H. Gilden,3,4*
Bette K. Kleinschmidt-Demasters,3,5
Charles G. McLeod Jr.,1
Laura L. Hungerford,6 and
Louis J. DeTolla1,2,6
Program of Comparative Medicine,1
Departments of Pathology,2
Epidemiology and Preventive Medicine, University of Maryland School of Medicine, Baltimore, Maryland, 21201; Departments of,6
Neurology,3
Microbiology,4
Pathology, University of Colorado Health Sciences Center, Denver, Colorado 80262,5
Division of Microbiology, Tulane National Primate Research Center, Covington, Louisiana 704337
Received 21 August 2006/
Accepted 27 September 2006

ABSTRACT
We describe correlative clinicopathological/virological findings
from a simian varicella virus (SVV)-seronegative monkey that
developed disseminated varicella 105 days after gamma-irradiation.
Twelve other monkeys in the colony were also irradiated, none
of which developed varicella. Before irradiation, sera from
the monkey that developed disseminated infection and one asymptomatic
monkey were available. Analysis indicated that subclinical reactivation
of latent SVV from an asymptomatic irradiated monkey likely
led to disseminated varicella in the seronegative irradiated
monkey. These findings parallel those from humans with disseminated
varicella infection and support the usefulness of SVV infection
as a model for human varicella-zoster virus infection, particularly
virus reactivation after gamma-irradiation.

TEXT
Simian varicella virus (SVV) causes chicken pox (varicella)
in primates. Outbreaks have been recorded to occur in multiple
animal facilities (
5). Serious, often fatal SVV infection was
described previously for
Chlorocebus aethiops (
4). In 1967 to
1968, 48 cases occurred in
Erythrocebus patas (
11). Milder outbreaks
were reported to occur in
Macaca nemestrina (
3),
M. fascicularis (
3,
13), and
M. fuscata (
3) at the Washington National Primate
Research Center, Seattle, Washington. Closely related viruses
isolated from different outbreaks, such as deltaherpesvirus
(
1), Medical Lake macaque virus (
16), and Liverpool vervet virus
(
4), were classified by geographical location and/or monkey
species.
Clinical and pathological features of SVV and human varicella-zoster virus (VZV) infection are similar. Also, SVV and VZV are related antigenically, share DNA homology, and become latent in ganglionic neurons (6, 7). VZV reactivates in irradiated (2, 14) and immunocompromised humans, and dissemination has previously been described to occur in a bone marrow transplant recipient 265 days after total-body irradiation (14) and in 12/27 children who received total-body irradiation after stem cell transplantation (8).
Our report herein is necessarily restricted to a single monkey, but the descriptive information provided by these first correlative clinicopathological and virological parameters from a macaque that developed disseminated SVV infection after whole-body irradiation is relevant to our understanding of the pathogenesis of varicella infection.
Case report.
Thirteen male macaques (12 M. mulatta macaques and one M. fascicularis macaque) (Table 1), aged 5 to 7 years, were housed in individual cages in one room. All monkeys were seronegative for Chlorocebus herpesvirus 1, simian immunodeficiency virus, simian T-lymphotrophic virus, and type D simian retrovirus. Except for monkey no. 2, which was born in Vietnam and had a history of antibody to measles virus, the monkeys were born and bred domestically. There is no history of spontaneous SVV infection in any monkeys housed in the University of Maryland School of Medicine (UMSOM) animal facility. All animals were part of a study of stem cell reconstitution after exposure to gamma-irradiation, performed in accordance with U.S. Department of Agriculture Animal Welfare Act regulations and the Guide for Care and Use of Laboratory Animals and with approval of the Institutional Animal Care and Use Committee at the UMSOM.
Monkey no. 1 developed a generalized maculopapulovesicular rash
(Fig.
1A and B) 105 days after receiving 600 cGy of total-body
irradiation. This monkey and its cage were immediately removed
from the room. A plaque reduction assay, performed (
12) on plasma
obtained before irradiation from the affected monkey, did not
reveal any anti-SVV antibody (Table
1). After irradiation, platelets,
total white blood cells (WBCs), and blood mononuclear cells
(MNCs) were reduced from preirradiation levels of 300,000, 10,000,
and 6,000 to 4,000, 7,000, and 3,000 per µl, respectively.
Furthermore, serum creatine phosphokinase (2,182 U/liter) and
aspartate aminotransferase (131 U/liter) were elevated, while
total protein (4.8 g/dl) and albumin (2.9 g/dl) were mildly
decreased after irradiation.
Preirradiation plasma from one other monkey (no. 2) was available
and revealed antibody to SVV at a dilution of 1:160. Of 13 total
monkeys that were irradiated, 3 (no. 1, no. 2, and no. 3) were
positive, after irradiation, for anti-SVV immunoglobulin G (IgG)
and IgM antibodies by indirect immunofluorescence (Table
1).
Seropositivity of these three samples was confirmed by SVV plaque
reduction assay, which detected anti-SVV antibodies at dilutions
of 1:160, >1:800, and 1:100, respectively. The plaque assay
revealed that the antibody titer increased from <1:25 before
irradiation to 1:160 after irradiation in monkey no. 1 with
disseminated disease. In monkey no. 2, the antibody titer increased
from 1:160 before irradiation to >1:800 after irradiation,
supporting the possibility that subclinical reactivation was
the likely source of SVV that infected irradiated monkey no.
1.
After irradiation, in monkey no. 2, WBCs and MNCs increased from 10,000 and 4,000 per µl to 11,000 and 5,000 per µl, respectively, and platelets decreased from 340,000 to 300,000 per µl. The increase in WBCs and MNCs in monkey 2 months after irradiation most likely reflected immunological recovery. In monkey no. 3, platelets and red blood cells increased from 1,000 to 3,000 per µl and 2,000 to 4,000 per µl, respectively, after irradiation.
Because of concern for an infectious (or zoonotic) disease outbreak, monkey no. 1 was euthanized 6 h later and necropsied under biosafety conditions to prevent contamination of personnel or environment. Organs were examined histologically and virologically. Paraformaldehyde-fixed, paraffin-embedded sections were analyzed immunohistochemically by use of a 1:500 dilution of rabbit polyclonal anti-SVV antibody as described previously (10).
Gross pathology.
Severe lesions were seen on the gingiva, hard palate, and tongue of monkey no. 1 (Fig. 1C). The liver was friable and contained petechial hemorrhages and multifocal white plaques (Fig. 1D). The lungs were pale and appeared consolidated (Fig. 1E), with numerous discrete, 1- to 4-mm, firm, elevated plaques.
Histology.
Skin revealed melanosis and epidermal hyperplasia with increased keratin and some cells with poorly defined basophilic intranuclear inclusions and necrosis (Fig. 2A). Petechial hemorrhages were present on the mucosa of the stomach, jejunum, and ileum with Cowdry A inclusions, a hallmark of herpesvirus infection (Fig. 2B). Areas of mucosal sloughing in the large intestine were seen (Fig. 2C). The liver had several small areas of necrosis-containing neutrophils (Fig. 2D). In the lung, hemorrhage and fibrin were seen in some alveoli along with scattered small areas of inflammation, primarily neutrophilic (Fig. 2E and F). The spleen had a cloudy appearance with generalized petechial hemorrhage. Mesenteric lymph nodes were reactive with eosinophils and macrophages (data not shown). The adrenal glands were hemorrhagic (Fig. 2G). Cowdry A inclusion bodies were found in multiple organs (Fig. 2A, B, D, F, and G).
Virology.
PCR (Zoologix, Inc., Chatsworth, Calif.) revealed SVV gene 21-specific
sequences in DNA extracted from blood of monkey no. 1 on the
day of rash (Fig.
2H). Because the abundance of viral DNA would
be high during acute infection, PCR for SVV DNA was not nested.
PCR for other viruses (VZV, rhesus cytomegalovirus, and monkeypox
virus) and reverse transcription-PCR for measles virus were
negative in all monkeys (data not shown).
Immunology.
SVV-specific antigen was found in necrotic skin of monkey no. 1 (Fig. 3A).
Most disseminated SVV outbreaks have been reported to occur
in monkeys in captivity (
4,
11,
15,
17). Spontaneous SVV outbreaks
have been reported for both species (
M. mulatta and
M. fascicularis)
that were used in this study (
5). To our knowledge, only one
previous occurrence has been attributed to spontaneous SVV reactivation
(
15). Our report is the first to document pathological/virological
findings from an SVV-seronegative rhesus macaque that developed
disseminated varicella after irradiation. Serological analysis
before irradiation was available only for monkey no. 1 and no.
2. The detection of anti-SVV antibody in monkey no. 2 before
irradiation and the presence of anti-SVV IgG and IgM antibodies
along with an increased antibody titer after irradiation is
consistent with subclinical varicella reactivation, as described
for immunocompromised humans (
9). Because serum from monkey
no. 3 was not available before irradiation, the significance
of detecting anti-SVV IgG and IgM antibody in this monkey after
irradiation is unknown. The absence of SVV IgG antibody in monkeys
no. 4 to 13 after irradiation indicates that these monkeys were
probably seronegative before irradiation and thus not a source
of SVV for monkey no. 1; the reason these monkeys did not develop
varicella is unknown. Most likely, irradiation of monkey no.
2 and possibly monkey no. 3 led to subclinical reactivation
of latent SVV, which in turn led to primary SVV infection in
monkey no. 1. Although irradiation seems to be the most likely
reason for virus reactivation, we cannot rule out the stress
of captivity or related factors which have been predicted earlier
to result in virus reactivation (
5). Correlative clinicopathological
and virological information provided by this first study of
even a single monkey is relevant to understanding the pathogenesis
of varicella infection. Further, our results suggest the usefulness
of irradiation of primates latently infected with SVV as a model
for VZV reactivation in humans. Future studies will analyze
SVV reactivation in latently infected immunosuppressed monkeys.

ACKNOWLEDGMENTS
We thank Marco Goicochea, Mary Wellish, Mattew Gessner, Kathryn
Bonistalli, and Sharon Asselin for technical assistance in necropsy,
histopathology, and immunohistochemistry; Lisa Litzenberger
for excellent photography; BioReliance Corporation, Rockville,
Md., Antech Diagnostics, Baltimore, Md., and Zoologix, Inc.,
Chatsworth, Calif., for analysis of sera and DNA samples; Marina
Hoffman for editorial assistance; and Cathy Allen for manuscript
preparation.
This work was supported in part by Public Health Service grants NS32623 (D.H.G. and R.M.) and AG06127 (D.H.G.) from the National Institutes of Health.

FOOTNOTES
* Corresponding author. Mailing address: Department of Neurology, University of Colorado Health Sciences Center, 4200 East 9th Avenue, Mail Stop B182, Denver, CO 80262. Phone: (303) 315-8281. Fax: (303) 315-8720. E-mail:
don.gilden{at}uchsc.edu.

Published ahead of print on 1 November 2006. 

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Journal of Virology, January 2007, p. 411-415, Vol. 81, No. 1
0022-538X/07/$08.00+0 doi:10.1128/JVI.01825-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
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