Resolution
Three February sentinels from G21 and G27 and one mouse from
one cage in the G27 colony were shown to have antibodies to Mouse
Parvovirus (MPV) on 2/18/2000. This resulted in both rooms being
quarantined on the day the serology results were received from
the contract diagnostic laboratory, 2/25/2000. However, all four
of the seropositives were interpreted to be false positives and
quarantine of both rooms was discontinued based upon the following:
Cage mates of the three sentinels did not show evidence suggestive
of infection because they did not have serum antibodies against
parvovirus when tested on 2/25/2000 and parvovirus DNA could not
be demonstrated in their feces. Follow-up serology done on 3/16/2000
showed the three cage mates again to be free of MPV antibodies.
In the case of the positive colony mouse, serologic results were
inconsistent. For example, the index mouse, shown to be seropositive
on 2/28/2000, was seronegative at one lab on 3/6/2000 and had
equivocal results at another lab. Serology done on this same mouse
on 3/14/2000 did not demonstrate antibodies against MPV. A second
mouse in the cage was seropositive on March 6 and reverted to
seronegative on March 14. One other adult mouse in the breeding
cage was seronegative on both of the dates. Eight recent weanlings
did not show serologic evidence of passively acquired maternal
antibody. PCR analysis of feces for parvoviral DNA was negative.
A synopsis of the testing is given in Table 4 below.
Three of 67 Rollins sentinels in February (Table 2, rows 1-3)
and 1 of 131 mice subsequently tested were seropositive for MPV
(Table 3) for an overall 2% prevalence. A 5% rate of false positives
is within the realm of expectation for a serologic test.
ARCHIVAL INFORMATION
(3/07/99)
Situation
The February assessment of sentinels showed antibodies to Mouse
Parvovirus from two of the sentinel mice from G27 and one from
G21. All other sentinels in all other colonies have been free
of antibodies to MPV from September 1999 through February 2000.
The finding of seropositive sentinels is a situation that the
DAR takes very seriously and is pursuing vigorously. At this point
it is possible that these results may be reflective of true positives
or may be false positives. Should these findings be true positives
reflective of virus infection of certain mice, transmission from
cage-to-cage should be prevented by the filter top cages providing
they are opened only in a laminar flow hood and personnel are
properly attired and using the phenolic disinfectant (Expose II)
supplied by DAR. A false positive rate of 5%, however, is within
the realm of normal probability for a serologic assay.
Table 1: Quarantined Rooms
| Site |
Quarantine Imposition
|
Quarantine Revocation
|
| Rollins G21 |
2/25/2000
|
3/17/2000
|
| Rollins G27 |
2/24/2000
|
3/17/2000
|
Preventive Medicine Procedures
Until otherwise notified, both rooms have been placed under quarantine.
Under these conditions, as always, all mouse users must wear the
prescribed PPE for mice and keep hands moist with disinfectant
when handling mice. In addition, the following temporary procedures
have been enacted for G21 and G27 Rollins:
No new users will be permitted in these rooms until quarantine
is lifted.
No mice should be relocated from G21 or G27 to other rooms or
sites without authorization from the vet staff.
All room waste will be packaged for incineration.
Tissues or biological materials from mice in these rooms should
not be inoculated into other rodents.
Soiled empty cages should be stacked near the sink for packaging
by DAR staff for autoclaving.
Harvesting tissues or euthanizing mice should be done in the
hood in the room, if appropriate, or in the DAR necropsy. Animals
should not be taken to labs without notification of the veterinary
staff and specific, documented instruction in ABSL2 isolation
techniques. Schedule the necropsy through Nancy Stump (7-3248).
Veterinary Diagnostic Procedures
- Sentinel Cage Contacts
- Serology. All three CD-1 cage mates of the three seropositive
sentinels were anesthetized on 2/24/2000 and split serum samples
were collected and sent to two diagnostic labs. All three
mice were shown to be free of antibody to MPV by ELISA and
IFA.
- Fecal PCR. Fresh fecal pellets were collected daily from
the cage mate contacts of the seropositive mice and did not
show evidence of parvovirus DNA using PCR assessment.
- Other Sentinels
The remaining CD-1 sentinel mice in both rooms (n=29) were anesthetized
for blood collection for MPV serology on 2/25/00. All were free
of antibodies to MPV.
- Colony Mice
Ninety-nine colony mice (B6, 129, FVB, etc. background) from
the populations monitored by the seropositive sentinels were
anesthetized by 2/28/00 and all but two were seronegative for
MPV (see #4 below). These two seropositive mice were not consistently
seropositive between different labs or over time.
- MPV Seropositive Colony Mice
One mouse from a breeding trio in G27 had a titer against MPV
on 2/28/00. On 3/6/00 all three adult mice in the cage were
anesthetized, serum was split for serology by two diagnostic
labs, and feces were collected for MPV PCR. The mice, and a
recently weaned litter from the cage (n=8), were also assessed
by serology on 3/14/2000. While there were two positive results,
they were inconsistent over time and between laboratories (Table
4). PCR analysis of feces for parvoviral DNA was negative.
Table 2: February Sentinels - MPV Serologic Results
| Population |
Positive Results
|
Number Tested
|
| G21 Sentinels |
1
|
12
|
| G27 Sentinels |
2
|
20
|
| Other Rollins Sentinels |
0
|
35
|
| All Other Sentinels (February) |
0
|
96
|
|
TOTAL
|
3 (1.8%)
|
163
|
Table 3: Subsequent MPV Diagnostics
| Population |
Positive Results
|
Number Tested
|
| G21 Sentinel Cohorts |
0
|
10
|
| G21 Sentinel Fecal PCR |
0
|
1
|
| G21 Colony Mice |
0
|
22
|
| G27 Sentinel Cohorts |
0
|
19
|
| G27 Sentinel Fecal PCR |
0
|
2
|
| G27 Colony Mice |
1
|
77
|
|
TOTAL
|
1
|
131
|
Note: By probability a positive result would be a true positive
(predictive value) only half the time for an assay with a sensitivity
of 95% and where the pathogen has a 5% prevalence. The predictive
value of a positive result drops as pathogen prevalence decreases.
Table 4: Index Case Serology
|
Serology Dates:
|
2/28/2000
|
3/6/2000
|
3/6/2000
|
3/14/2000
|
|
Mouse
|
Lab A
|
Lab A
|
Lab B
|
Lab A
|
| 1 |
POSITIVE
|
Equivocal
|
negative
|
negative
|
| 2 |
|
Equivocal
|
negative
|
negative
|
| 3 |
|
POSITIVE
|
POSITIVE
|
negative
|
| 4 |
|
|
|
negative
|
| 5 |
|
|
|
negative
|
| 6 |
|
|
|
negative
|
| 7 |
|
|
|
negative
|
| 8 |
|
|
|
negative
|
| 9 |
|
|
|
negative
|
| 10 |
|
|
|
negative
|
| 11 |
|
|
|
negative
|
Additional Information on MPV
Details regarding the virus and our experiences with it last
summer and fall may be found at: MPV Outbreak.
