Biomedical Engineering Reference
In-Depth Information
consistently seronegative for herpes B virus infection
(
Morton et al., 2008
), universal precautions should be fol-
lowed even in these colonies. The risk of zoonotic infection
is certainly lowered in these situations (
Hilliard and Ward,
1999
), but serology should never be used to definitively
state that an individual animal or group of animals are
uninfected. All macaques should be treated as if they are
potentially infected with B virus.
B virus screening is generally accomplished with
serological assays. ELISA is highly (98%) sensitive. Most
of these assays forgo the use of B virus antigen in favor of
antigen from the related viruses Simian agent 8 (SA8),
Herpes simplex virus, or Herpesvirus papio. This reduces
the risk to personnel preparing and running the assays but
also reduces the sensitivity of the test and these tests are
unable to distinguish between these closely related alpha-
herpesviruses. Regardless, in most situations these tests are
adequate for colony screening and positive tests from
macaques are assumed to be due to B virus (
Elmore and
Eberle, 2008
). If necessary, the National B Virus Resource
Center has more specialized serological assays to distin-
guish between specific viruses (
Katz et al., 1986
).
PCR methods for diagnosing B virus have been devel-
oped (
Perelygina et al., 2003
) but are generally not used in
screening large numbers of animals. These tests are highly
specific, can distinguish between a variety of herpesviruses,
but lack sensitivity as latently infected animals will not be
identified. These tests are useful to determine if individual
animals are shedding virus (i.e. post-personnel exposure)
but not for colony screening.
More recently, a microplex multibead immunoassay
(MMIA) was developed that can simultaneously detect
antibodies to herpes B virus, simian retrovirus type D,
simian immunodeficiency virus, simian foamy virus,
simian cytomegalovirus, and simian t-lymphotropic virus.
This assay has a high throughput, is relatively easy to
perform, may have a higher sensitivity than ELISA, and
because it screens for six diseases at once can save
personnel time and energy (
Khan et al., 2006
). Specialized
equipment is necessary, but the initial outlay of costs can be
earned back relatively rapidly in certain situations.
Finally, viral culture can be used, like PCR, to test
individual animals for viral shedding. Care should be taken
to follow appropriate biosafety protocols to limit the risk to
lab personnel. Sampling of the oral cavity, eyes, and
genitalia can be used to determine viral shedding in animals
with suspect lesions.
(SFV), simian sarcoma virus, and Gibbon-Ape leukemia
virus (
Lerche and Osborn, 2003
). Historically, these viruses
have caused significant morbidity and mortality in NHP
colonies, especially macaques. Disease syndromes and
natural history of these diseases is covered extensively
elsewhere in this topic.
There are at least five distinct serotypes of SRV-D that
infect primarily Asian macaques. Differences may exist in
susceptibility of different species to different serotypes.
Disease due to SRV-D ranges from subclinical carriers to
severe and rapidly fatal immunosuppressive disease
resembling Acquired Immunodeficiency Syndrome
(simian AIDS). The severity of the disease in macaques
led to SRV-D being one of the initial targets for eradication
from specific pathogen free colonies (
Lerche et al., 1994
).
SRV-D is somewhat unique in that there are a large
number of antibody-negative viremic animals, and vice
versa. As such, a good screening program for the
establishment or maintenance of an SPF colony must
include methodologies to detect both antibody-positive
and antibody-negative but viremic animals (
Kwang et al.,
1987; Wilkinson et al., 2003
).
Serology using enzyme immunoassay, Western Blot, or
fluorescent antibody assays is the mainstay of screening
for antibody-positive animals (
Liska et al., 1997
). ELISA
is most commonly used, however this technique suffers
from drawbacks including relatively low specificity and
inability to identify antibody-negative viremic animals
(
Pedersen et al., 1986
). Western blot can be used to
confirm positive ELISA results. Multiplex microbead
immunoassay can also be used and has benefits as previ-
ously described (
Khan et al., 2006
). Viral isolation and
PCR are commonly used to identify viremic animals. A
variety of PCR assays have been developed and are
commercially available (
Lerche et al., 1997; Liska et al.,
1997; Wilkinson et al., 2003; Hara et al., 2005
). It is
important for the PCR assay to use primers specific
enough to not identify endogenous retroviral sequences
which are ubiquitous in many species of primates but are
nonpathogenic (
Morton et al., 2008
). In one report, SRV
was eradicated from a large group following antibody
screening using an enzyme immunoassay, confirmation of
positive results with Western blot and detection of viremic
animals with viral isolation and/or PCR assay. Animals
that tested positive either for antibody or virus were
removed from the group (
Schroder et al., 2000
).
Unlike SRV-D, SIV is not a natural infection of Asian
macaques. SIV naturally infects African species (i.e. ver-
vets) and chimpanzees and in these animals causes
subclinical disease. Virus can be transmitted to macaques
via contact with infected African species or artificially in
a laboratory setting and, once infected, Asian macaques
can transmit virus to other macaques. Similar to SRV-D,
disease in Asian macaques is quite serious and leads to an
Retroviruses
Retroviruses are single-stranded RNA viruses. NHPs are
natural hosts for six known retroviruses: simian retrovirus
type D (SRV-D), simian immunodeficiency virus (SIV),
simian T-lymphotropic virus (STLV), simian foamy virus
