The objective of this article is to assess whether serum canine parvovirus (CPV) and canine distemper virus (CDV) antibody titers can be used to determine revaccination protocols in healthy dogs.

1. In response to the debate in veterinary medicine con-
cerning issues related to vaccine efficacy and safety
as well as the duration of immunity induced by the
currently available vaccines,1-36
there is a compelling
need for more objective and scientific data.26,29-31,36,37
Determination of serum antibody titers is 1 method
commonly used to assess host humoral immune
responses to a number of disease-causing organisms. In
dogs, canine parvovirus (CPV) and canine distemper
virus (CDV) antibody titers have been measured in
serum samples in the past to help determine duration
of immunity induced by vaccines against these 2 virus-
es. The rationale for selecting CPV and CDV for serum
antibody testing is based on the clinically important
diseases they cause, combined with the usefulness of
the host’s humoral immune response to these viruses
for determining the need for revaccination.30,37
Although measuring serum antibody titers in cats
was not a goal of the study reported here, a similar
approach applies to feline diseases.8,9,17,18,20-27,29,30,32,36-39
As
with determination of serum antibody titers in dogs,
which focuses on the clinically important infectious
diseases, feline panleukopenia virus (FPV) antibody
titers yield comparable information in cats.17,18,37
In 1
study,17
it was indicated that antibody titers remained
adequate for at least 6 years for FPV and 4 years for
feline calicivirus in cats vaccinated at 8 and 12 weeks
of age with polyvalent killed vaccine. Results of subse-
quent challenge studies with these cats support the
earlier predictions of protection made on the basis of
antibody titers.18,37
In a similar fashion, the purpose of
the study reported here was to assess whether CPV and
CDV serum antibody titers can be used to determine
revaccination protocols in healthy dogs.
Materials and Methods
Animals and samples—Serum samples for determina-
tion of CPV and CDV antibody titers were obtained from
1,441 healthy dogs brought to veterinary clinics for routine
health care visits or revaccination in 17 states and 6 Canadian
provinces between March 1996 and June 1999. Most of the
dogs (1,169; 81.1%) were purebreds and represented 114
breeds, with breed frequencies generally representative of
their respective popularity as companion animals.40
Two hun-
dred fifty-two dogs were mixed-breeds; breed was not report-
ed for 20 (1.4%) dogs. Dogs ranged from 6 weeks to 17 years
old. Only 3 (0.2%) dogs were < 4 months old. There were
400 sexually intact males, 222 castrated males, 451 sexually
intact females, 351 spayed females, and 17 dogs for which
sex was not reported. Vaccination histories for 468 of 1,441
(32.5%) dogs were reported by the submitting veterinarians;
all but 4 of these dogs had been vaccinated previously.
Vaccination against CPV was reported for all of these dogs,
whereas vaccination against CDV was reported for 457
(97.6%). For 75 dogs, serum antibody titers had been mea-
sured annually for the previous 2 (n = 59), 3 (13), 4 (2), and
5 (1) years, and all titers remained adequate. For these dogs,
only the most recent titer was included in this study. Thirty-
three serum samples for which CPV and CDV titers were >
1:5 were randomly selected and serially diluted to determine
titer endpoints.
Indirect fluorescent antibody test—Antibody respons-
es to CPV and CDV vaccination or natural viral exposure
were measured in serum samples at a commercial veterinary
diagnostic laboratory,a
using indirect immunofluorescent
antibody (IFA) tests.28,b
Serum samples were sent by mail or
courier at ambient temperature or with cold packs and
arrived at the laboratory within 1 to 5 days. On the basis of
JAVMA, Vol 217, No. 7, October 1, 2000 Scientific Reports: Original Study 1021
SMALLANIMALS
Clinical use of serum parvovirus and distemper
virus antibody titers for determining
revaccination strategies in healthy dogs
Lisa Twark, DVM, and W. Jean Dodds, DVM
Objective—To assess whether serum canine par-
vovirus (CPV) and canine distemper virus (CDV) anti-
body titers can be used to determine revaccination
protocols in healthy dogs.
Design—Case series.
Animals—1,441 dogs between 6 weeks and 17 years
old.
Procedure—CPV and CDV antibody titers in serum
samples submitted to a commercial diagnostic labo-
ratory were measured by use of indirect fluorescent
antibody (IFA) tests. On the basis of parallel measure-
ments of CPV and CDV serum antibody titers in 61
paired serum samples determined by use of hemag-
glutination inhibition and serum neutralization meth-
ods, respectively, we considered titers ≥ 1:5 (IFA test)
indicative of an adequate antibody response.
Results—Age, breed, and sex were not significantly
associated with adequate CPV- or CDV-specific anti-
body responses. Of 1,441 dogs, 1,370 (95.1%) had
adequate and 71 (4.9%) had inadequate antibody
responses to CPV, whereas 1,346 of 1,379 (97.6%)
dogs had adequate and 33 (2.4%) had inadequate
responses to CDV. Vaccination histories were avail-
able for 468 dogs (468 for CPV, 457 for CDV). Interval
between last vaccination and antibody measurement
was 1 to 2 years for the majority (281/468; 60.0%) of
dogs and 2 to 7 years for 142 of 468 (30.3%) dogs.
Interval was < 1 year in only 45 of 468 (9.6%) dogs.
Conclusions and Clinical Relevance—The high
prevalence of adequate antibody responses (CPV,
95.1%; CDV, 97.6%) in this large population of dogs
suggests that annual revaccination against CPV and
CDV may not be necessary. (J Am Vet Med Assoc
2000;217:1021–1024)
From Hemopet and Antech Diagnostics, 17672A Cowan Ave, Irvine,
CA 92614. Dr. Twark’s present address is 5423 Hwy 66N,
Rogersville, TN 37857.
Address correspondence to Dr. Dodds.
1021_1024.QXD 8/22/2005 3:21 PM Page 1021

2. replicate testing of 10 samples stored for 1 to 7 days at room
temperature (approx 21 to 24 C [70 to 75 F]), transit time to
the laboratory did not appear to influence results.
The IFA substrate slides consisted of cells infected with
CPV or CDV fixed in wells.b
A 1:5 dilution of control and
patient serum was prepared. Control serum comprised an in-
house serum pool and serum purchased from a commercial
supplier.b
Virus-infected cells were incubated with diluted
serum in a humidified chamber for 45 minutes at 37 C. Slides
were thoroughly washed and air-dried before incubating with
fluorescein-conjugated affinity-purified rabbit anti-dog IgG
in a humidified chamber for 45 minutes at 37 C. Slides were
washed again, and coverslips of each slide were prepared and
mounted, using glycerol-phosphate-buffered saline mount-
ing solution. Technicians experienced with reading IFA slides
evaluated the degree of cellular fluorescence, using a fluores-
cent microscope.
To evaluate the titer determined by use of IFA testing at
which humoral immune responses were considered ade-
quate, 61 of the 1,441 (4.2%) serum samples were submitted
to a university-based veterinary diagnostic laboratoryc
for
measurement of CPV and CDV antibody titers by use of
hemagglutination inhibition (HAI) and serum neutraliza-
tion (SN) tests, respectively. This laboratory recommends
that revaccination be considered when CPV titers are < 1:80
and CDV titers are < 1:32. In 55 of 61 (90.2%) serum sam-
ples, CPV antibody titers were ≥ 1:5 and ≥ 1:80, as deter-
mined by use of the IFA and HAI tests, respectively. Titers to
CDV in those same samples were ≥ 1:5 and ≥ 1:32, as deter-
mined by use of the IFA and SN tests, respectively. Of the
remaining 6 samples, 5 had proportionately lower CPV titers
(1:10 to 1:40) on the HAI test than titers (1:5) determined by
use of IFA tests, and 3 had proportionately lower CDV titers
(negative to 1:24) on SN tests than titers (1:5) determined by
use of IFA tests. One sample had a CPV titer < 1:5 on the IFA
test and < 1:10 on the HAI test. Using these results, in rela-
tion to antibody titers previously determined as indicative of
an adequate degree of humoral immunity, 4,13,30
we considered
serum CPV and CDV antibody titers ≥ 1:5, as determined by
use of IFA tests, indicative of an adequate antibody response.
Statistical analyses—Serologic test results and potential
associations with age, breed, and sex were assessed by use of
a Student t-test and a statistical software program.d
Differences were considered significant at P < 0.05.
Results
Serum antibody titers for CPV were evaluated in
1,441 dogs, and serum antibody titers for CDV were
evaluated in 1,379 dogs. Of the 1,441 dogs, 1,370
(95.1%) had adequate antibody responses to CPV (ie,
titers ≥ 1:5, as determined by use of the IFA test), and
71 (4.9 %) had inadequate responses. For CDV, 1,346
(97.6 %) dogs had adequate antibody responses, and
33 (2.4%) had inadequate responses (Table 1). The
youngest dog was 6 weeks old and had a CPV titer <
1:5. This dog had been vaccinated when it was 4 weeks
old. The oldest dog was 17 years old and had been vac-
cinated against CPV and CDV 2 years earlier; antibody
titers for both viruses were ≥ 1:5. Age, breed, and sex
were not significantly associated with adequate CPV or
CDV serum antibody titers.
Of the 33 serum samples that were serially diluted
to determine endpoint titers, endpoint titers for CPV
ranged from 1:10 to 1:320; the median endpoint was
1:128. For CDV, endpoint titers ranged from 1:10 to
1:1,280, with a median endpoint of 1:256. The end-
point titers for CPV and CDV in dogs for which titers
were > 1:5, as determined by use of IFA tests, are,
therefore, likely to be higher.
Vaccination histories were available for 468 of
1,441 (32.5%) dogs. Of these 468 dogs, history regard-
ing vaccination against CPV and CDV was available for
457 dogs and against CPV only for 11 dogs. Of the
dogs for which vaccination history was known, 401 of
423 (94.8%) had an adequate response to CPV for
more than 1 year after vaccination, and 390 of 412
(94.7%) had an adequate response to CDV for more
than 1 year after vaccination. Moreover, 133 of 142
(93.7%) dogs and 127 of 136 (93.4%) dogs had ade-
quate responses to CPV and CDV, respectively, more
than 2 years after vaccination.
Of the 1,370 dogs with an adequate CPV antibody
response, vaccination history was recorded for 444
(32.4%). Interval from last vaccination was < 1 year for
43 (9.7%) dogs, 1 to 2 years for 268 (60.4%) dogs, and
2 to 7 years for 133 (30.0%) dogs. Of the 1,346 dogs
with an adequate CDV serum antibody titer, vaccina-
tion history was recorded for 433 (32.2%; Table 2).
Of the 71 dogs with inadequate CPV antibody
responses, vaccination histories were available for 19
(26.7%). Interval from last vaccination was < 1 year for
2 of 19 dogs, 1 to 2 years for 13 of 19 dogs, and 2 to 7
years for 4 of 19 dogs. Fifty-three of the 71 dogs
(74.6%) with inadequate CPV responses had adequate
CDV responses.
1022 Scientific Reports: Original Study JAVMA, Vol 217, No. 7, October 1, 2000
SMALLANIMALS
CPV antibody response CDV antibody response
Age (y) Inadequate* Adequate† Inadequate* Adequate†
Not known 1 42 1 40
Ͻ 1 5 33 3 21
1 5 84 5 82
2 7 87 1 88
3 4 123 2 121
4 9 132 2 134
5 7 113 1 112
6 7 111 1 113
7 2 119 2 117
8 11 134 2 136
9 0 86 1 81
10 4 90 5 85
Ն 11 9 216 7 216
Total (%) 71 (4.9) 1,370 (95.1) 33 (2.4) 1,346 (97.6)
*Titer Ͻ 1:5. †Titer Ն 1:5.
Table 1—Serum antibody responses against canine parvovirus
(CPV; n ϭ 1,441) and canine distemper virus (CDV; 1,370) deter-
mined by use of indirect fluorescent antibody (IFA) tests in
healthy dogs of various ages
Time since last
vaccination (y) CPV CDV
Ն 5 5 5
Ն 3 but Ͻ 5 44 41
Ն 2 but Ͻ 3 84 81
Ն 1 but Ͻ 2 268 263
Ͻ 1† 43 43
Total‡ 444 433
*Determined by use of IFA tests; titers Ն 1:5 were considered adequate.
†Three dogs were Ͻ 4 months old. ‡Only CPV-specific antibody titers were
determined for 11 of 444 dogs.
Table 2—Number of dogs with adequate serum antibody
responses* to CPV and CDV at various times after vaccination
1021_1024.QXD 8/22/2005 3:21 PM Page 1022

3. Vaccination histories were reported for 9 of the 33
(27.3%) dogs with inadequate CDV serum antibody
responses; 6 of the 9 dogs also had inadequate CPV
responses. One of these 6 dogs (age, 1 year) had
received 2 polyvalent vaccines 2 months apart when it
was a puppy; the last vaccine was administered 9
months prior to obtaining serum for the IFA test.
Another of these 6 dogs (age, 3 years) had been vacci-
nated approximately 2 years before titer measurement,
and a third dog in this group (age, 13 years) had been
vaccinated 7 years prior to IFA testing. The 3 remain-
ing dogs had been vaccinated 1 year prior to testing. Of
the 33 dogs with inadequate CDV titers, 15 (45.5%)
had adequate CPV titers.
Discussion
The goal of measuring serum antibody titers in
companion animals is to provide a rational way of estab-
lishing whether an animal has had an adequate antibody
response to a specific disease agent and to use this infor-
mation as a practical indicator of the need for revaccina-
tion.30
The rationale for selecting CPV and CDV for our
study was based on the fact that these viruses cause clin-
ically important diseases associated with high morbidity
and mortality rates, but it was also based on the useful-
ness of CPV and CDV serum antibody titers in predict-
ing the need for revaccination.30,37
In the study reported
here, antibody titers ≥ 1:5 for CPV or CDV, as deter-
mined by use of IFA tests, were considered equivalent to
antibody titers previously determined to indicate an ade-
quate degree of humoral immunity.4,13,30
Data collected in this study were obtained from a
large population of healthy dogs located across the
United States and Canada. Results indicated that near-
ly all dogs from this population had adequate antibody
responses to CPV (95.1%) and CDV (97.6%) at the
time of testing. Because challenge studies were not per-
formed, we do not know whether these antibody titers
correlate with prevention of viral infection. However,
antibody titers in these dogs were likely a result of
prior immunization combined with any natural expo-
sure and suggest that these dogs had adequate
immunologic memory, the mechanism that provides
animals with protection from clinical disease during
natural viral challenge.
Our findings, based on determining serum anti-
body titers of 1,441 dogs for CPV and 1,379 dogs for
CDV, confirmed our preliminary results from 365 and
307 dogs, respectively. 28,34
Results of a similar investi-
gation31
indicated that 89 of 122 (73%) dogs had pro-
tective CPV antibody titers, and 92 of 117 (79%) dogs
had protective CDV antibody titers. Antibody titers to
CPV and CDV in that study were determined by use of
HAI and SN tests, respectively, at the same university-
based veterinary diagnostic laboratory that we used for
testing paired serum samples. However, authors of that
study defined protective titers to CDV as ≥ 1:96,
whereas we defined an adequate antibody response as
a titer ≥ 1:32, as determined by SN testing. In both
studies, an adequate antibody response for CPV was
considered ≥ 1:80, as determined by HAI tests. Because
dogs in the previous study were all revaccinated at 1
veterinary teaching hospital, results may not extrapo-
late to the general population. It also is possible that a
single vaccine supplier may have been used by the
teaching hospital, whereas in our study, a number of
suppliers would likely be represented.
Results of both studies indicate that adequate anti-
body titers to CPV were found slightly less consistently
than for CDV. In our study, the number of dogs with an
inadequate CPV titer but an adequate CDV titer (53/71;
75%) was significantly (P = 0.003) higher than the
number of dogs with an inadequate CDV titer but an
adequate CPV titer (15/33; 45%). Several factors may
explain these findings. It is established that vaccination
against CPV in puppies provides a window of vulnera-
bility to infection.7,19,26
This is when maternally derived
antibodies are at a concentration that interferes with
vaccination but are not sufficiently high to provide pro-
tection.19,26
Some of the dogs with inadequate CPV titers
may have been inadequately immunized as puppies.
This could explain their poor immunologic response to
revaccination as adults. In addition, certain breeds of
dogs (eg, Rottweiler, Doberman Pinscher, Labrador
Retriever, Alaskan sled dog, Pomeranian, and American
Staffordshire Terrier) have difficulty mounting an
appropriate immune response to CPV.6,7,11
Serologic test-
ing could be performed for these susceptible breeds
after puppies are vaccinated to determine whether an
adequate immune response has been established.11
Some dogs never appear to mount an adequate
antibody response to vaccination, but they still remain
healthy, presumably because of persistence of immune
memory cells and development of cell-mediated and
mucosal immune responses30
or, alternatively, lack of
exposure to infectious virus. It may be appropriate to
cease vaccination of these dogs, especially if they had
adverse reactions to vaccination in the past. Common-
sense management of such cases involves maintaining
the health and well-being of these dogs through good
nutrition, exercise, and annual health checkups as well
as reducing the risk of infectious disease by avoiding
areas of high viral exposure.
Because most current vaccines are likely to provide
immunity for greater than 1 year,2,7,9,10,13,14,17,18,26-31,34,36,37
we
believe that annual revaccination is not always neces-
sary or desirable. An alternative would be to imple-
ment serologic screening of companion animals to
identify those with an adequate humoral immune
response. This type of screening is currently practiced
in the poultry and swine industries.30
Screening also
may be appropriate for dogs that are genetically or
physiologically predisposed to developing adverse
reactions following vaccination.15,34,35
Reliable, afford-
able, and standardized serum antibody testing is need-
ed,30
and several private and university-based veteri-
nary diagnostic laboratories currently offer and pro-
mote this approacha-c
If serum antibody titers are found
to be inadequate in certain dogs, revaccination should
be considered for clinically important diseases, such as
those caused by CPV and CDV infection, in which vac-
cination has been shown to be beneficial.30
Because
clients have already incurred the expense of serum
antibody testing, some practices have elected to offer
the appropriate vaccinations at no additional charge.25
At this time, although serum antibody titers are
JAVMA, Vol 217, No. 7, October 1, 2000 Scientific Reports: Original Study 1023
SMALLANIMALS
1021_1024.QXD 8/22/2005 3:21 PM Page 1023

4. measured at several university-based and private veteri-
nary diagnostic laboratories, various techniques are
used, including HAI, SN, IFA, ELISA, and virus neu-
tralization tests.30,37
Because each laboratory should
have established its own standard for determination of
an adequate or protective antibody response,28,30,a-c
clini-
cians are advised to consult with laboratory profession-
als regarding interpretation of results of serologic tests.30
Generally, the higher the serum antibody titer, the
greater the protection afforded, although animals with
low serum antibody titers are not necessarily at risk for
disease because of the likely persistence of immune
memory cells and cell-mediated and mucosal immuni-
ty.30,37
However, when the titer is less than the value
determined to be adequate by the testing laboratory,
revaccination should be considered. When the serum
antibody titer is adequate, then the animal will likely be
able to mount an anamnestic immune response if chal-
lenged by the disease agent in question, indicating that
vaccination at that time may not be necessary.30
Analysis of results of the study reported here sug-
gests that a large percentage of healthy dogs have ade-
quate serum antibody titers to CPV and CDV, regard-
less of duration of the interval since last vaccination.
Moreover, of the dogs with a known CPV and CDV
vaccination history, 133 of 142 (93.7%) and 127 of 136
(93.4%) dogs, respectively, had adequate serum anti-
body responses even though they had last received a
vaccine more than 2 years ago. These results support
our contention that annual vaccination for these viral
diseases is unnecessary in most situations.
a
Antech Diagnostics, Irvine, Calif.
b
Hansen Immunologics, Dixon, Calif.
c
Diagnostic Laboratory, College of Veterinary Medicine, Cornell
University, Ithaca, NY.
d
Microsoft Excel 97, Microsoft Corp, Redmond, Wash.
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