Biomedical Engineering Reference
In-Depth Information
macaques results in the induction of an immunodeficient
state that frequently progresses to AIDS (
Baskin et al.,
1988; Lackner et al., 1988
). Although since 1980, SIV has
not been documented in domestic nonhuman primate
centers other than in those animals experimentally infected
or those accidentally housed with infected animals, SIV has
been included as a target virus for elimination from SPF
programs. Because SIV is a group of closely related lenti-
viruses, serological testing routinely involves whole-virus
preparations that contain conserved regions of the genome,
i.e. the core p27 region (
Morton et al., 2008
). A test-and-
remove strategy has proved effective in eliminating this
virus from colonies; provided that stringent separation is
maintained between experimentally infected and nonin-
fected animals, inadvertent transmission of SIV should not
occur.
status, genetic background, and potential health and
behavioral concerns. Once identified, founder animals are
placed into small social groups (3
e
4 individuals) and blood
samples collected for virological testing. The size of the
peer groups should be such that it encourages normal
behavior but limits the risk of virus transmission should an
animal seroconvert. Candidate SPF founders should
undergo quarterly viral screening for at least 2 years before
being placed into breeding groups (
Mansfield, 2005
).
Owing to the potential of delayed seroconversion, testing
for BV should continue on a quarterly basis throughout the
animal's life. The initial breeding groups formed are often
referred to as Level 1 SPF animals. Progeny from the SPF
Level 1 cohorts are frequently referred to as Level 2 SPF.
Should seroconversion occur in a Level 1 group, the
affected animal should be removed. The remainder of the
cohort should be isolated from the SPF colony and undergo
rigorous serological testing to confirm continued seroneg-
ative status.
Housing strategies play a major role in the development
and success of SPF colonies. Depending on their
geographical location and size, facilities may house their
breeding groups in harems of 8
e
10 animals or in large
outdoor corrals containing up to 150 individuals. In the
formation of SPF colonies, harem breeding may be more
advantageous, particularly in the initial period. In this
configuration, seroconversion of one animal poses a threat
of virus transmission to a maximum of 10 contact indi-
viduals. In contrast, seroconversion within corral housing
can result in potential exposure of 100
Viral Screening Tests
Various diagnostic tests, including ELISA, immunofluo-
rescent assays, polymerase chain reaction (PCR), Western
blot, and viral isolation, are used in screening animals for
these four target viruses. Samples may either be tested in
house or sent to a commercial testing laboratory. On-site
screening is inexpensive and may decrease time between
seroconversion and removal of an animal from the colony.
Details for the production of ELISA plates using purified
whole-virus preparations for on-site screening can be found
in the literature (
Daniel et al., 1988; Blewett et al., 1999;
Takano et al., 2001
). Regardless of which test is used, when
analyzing results it is important that the sensitivity and
specificity of the test is understood (
Gardner et al., 2000
).
The test specificity reflects the percentage of animals that
are negative for the disease that the test accurately reports
as negative, whereas the sensitivity reflects the ability of the
test to identify truly positive animals. Regardless of the test
used, false-positive and false-negative results will occur on
occasion. Increased numbers of false-negative results may
be seen during the early periods after formation of an SPF
colony, whereas more false positives may be reported after
the colony is established (
Mansfield, 2005
). Confirmational
testing should always be performed at a reference labora-
tory when positive or questionable results are reported. To
increase throughput, many commercial laboratories are
now employing multiplex microbead immunoassay tech-
nology (Luminex Corp. Austin TX), which facilitates the
concurrent detection of numerous pathogens in one sample
(
Khan et al., 2006
).
animals. Addi-
tionally, the testing and removal strategy for viral screening
may be more efficiently accomplished in smaller group
settings. Normally breeding harems are housed in indoor
pens or outdoors in “corn cribs.” Indoor housing may be
beneficial if there are requirements for eradication of
additional pathogens such as bacteria, parasites, and
protozoa. At some facilities, breeding strategies such as
timed-mating or assisted reproductive technologies are
employed as an adjunct to harem or coral breeding. Both of
these are useful in pathogen elimination and in the
production of timed pregnancies for research protocols.
However, these approaches are expensive to implement and
frequently result in a reduction in colony reproductive
performance.
Table 8.5
lists advantages and disadvantages
of various
þ
reproductive strategies used in breeding
macaques.
The success of SPF colonies depends not only on
continued screening for the target viruses but also on
a rigorous surveillance program for other potentially
detrimental pathogens. Ideally, preventative health exami-
nations should be performed on a quarterly basis. Proce-
dures normally performed at this time include clinical
examination, collection of blood samples for virological
testing, DNA banking and MHC typing,
Formation of Specific Pathogen-free Colonies
The methods employed in the formation of SPF colonies
will vary depending on the infrastructure of the parent
facility. Ideally, candidate animals 8
e
12 months of age
should be selected. Selection criteria include virological
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