Fetal infections and antibody profiles in pigs naturally infected with porcine circovirus type 2 (PCV2).
ABSTRACT The aim of this study was to describe early infections with porcine circovirus type 2 (PCV2) in naturally infected piglets and the piglets' serologic profiles. A total of 20 sows (15 PCV2-vaccinated and 5 unvaccinated) and 100 newborn piglets were studied. Colostrum and serum of the sows and serum of the presuckling piglets were obtained on the day of parturition. Milk samples were collected on day 20 postpartum. Blood samples were taken and the piglets weighed on days 1, 20, 42, 63, and 84 postpartum. Colostrum and milk were evaluated for infectious PCV2 and for PCV2 total antibody (TA), neutralizing antibody (NA), and IgA. Serum samples were evaluated for PCV2 TA, NA, IgA, IgM, and DNA. The sows had high levels of TA and NA in serum and colostrum; however, 11 and 5, respectively, of the 20 colostrum and milk samples contained infectious PCV2. In the serum, PCV2 DNA and IgM were detected in 17 and 5, respectively, of the 20 sows. Nine piglets were born with PCV2 antibodies, which indicates in utero transmission of PCV2 after the period of immunocompetence (> 70 d of gestation). On day 1 postpartum, PCV2 DNA was detected in 29 of the 100 serum samples from the piglets. There was no difference between the weights of viremic and nonviremic piglets throughout the study. In conclusion, even on farms with sows that have high PCV2 antibody titers, vertical transmission of PCV2 may occur, resulting in piglet infection.
- SourceAvailable from: ncbi.nlm.nih.gov[show abstract] [hide abstract]
ABSTRACT: In order to examine an association between porcine circovirus type-2 (PCV2) infection and reproductive failure in pigs, sera (n = 171) from stillborn fetuses were collected from 3 different farms with prolonged histories of reproductive problems. These sera were tested for the presence of antibodies to PCV2 using an immunoperoxidase monolayer assay. Of the 171 sera tested, 28 had PCV2 antibody titers of > or = 1:16. When these 28 samples were tested by a polymerase chain reaction assay,13 were found to contain PCV2 viral DNA. Of these 13 samples containing both PCV2 antibodies and viral DNA, 9 yielded PCV2 on virus isolation. Amino acid sequences comprising open reading frame 2 of PCV2 from 2 of these isolates were compared to PCV2 isolates from cases of post-weaning multi-systemic wasting syndrome (PMWS). The amino acid sequences of the 2 isolates from stillborn pigs were shown to be nearly identical to each other, as well as to other PCV2 isolates associated with reproductive failure. When compared with PMWS isolates, the isolates from the stillborn fetuses showed differences of at least 2 amino acids. These results confirm previous findings that transplacental infection of PCV2 occurs in the field and that stillbirths in pigs may be associated with PCV2 infections. At present, the significance of minor differences in amino acid sequences is not known.Canadian journal of veterinary research = Revue canadienne de recherche vétérinaire 06/2003; 67(2):108-13. · 1.19 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Porcine circovirus type 2 (PCV2) is the essential infectious agent of postweaning multisystemic wasting syndrome (PMWS). Despite first sequencing studies did not find any association between PCV2 sequences and PMWS occurrence, recent works have suggested the opposite. In the present study, 87 open reading frame 2 (ORF2) sequences obtained from pigs with different clinical conditions and coming from farms with different PMWS status were analyzed. Results further confirmed the existence of two genogroups and the definition of two PCV2 genotypes (1 and 2) is proposed. All sequences included in genotype 1 came from pigs from PMWS affected farms, while all sequences obtained from non-PMWS affected farms corresponded to genotype 2. Moreover, infection of single pigs from PMWS affected farms harbouring both genotypes is described. Present results suggest that PCV2 genotype 1 may potentially be more pathogenic than PCV2 genotype 2.Veterinary Microbiology 05/2008; 128(1-2):23-35. · 3.13 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Swine share with most placental mammals the same five antibody isotypes and same two light chain types. Loci encoding lambda, kappa and Ig heavy chains appear to be organized as they are in other mammals. Swine differ from rodents and primates, but are similar to rabbits in using a single VH family (VH3) to encode their variable heavy chain domain, but not the family used by cattle, another artiodactyl. Distinct from other hoofed mammals and rodents, Ckappa:Clambda usage resembles the 1:1 ratio seen in primates. Since IgG subclasses diversified after speciation, same name subclass homologs do not exist among swine and other mammals unless very closely related. Swine possess six putative IgG subclasses that appear to have diversified by gene duplication and exon shuffle while retaining motifs that can bind to FcgammaRs, FcRn, C1q, protein A and protein G. The epithelial chorial placenta of swine and the precosial nature of their offspring have made piglets excellent models for studies on fetal antibody repertoire development and on the postnatal role of gut colonization, maternal colostrum and neonatal infection on the development of adaptive immunity during the "critical window" of immunological development. This chapter traces the study of the humoral immune system of this species through its various eras of discovery and compiles the results in tables and figures that should be a useful reference for educators and investigators.Developmental and comparative immunology 10/2008; 33(3):321-33. · 3.29 Impact Factor
38 The Canadian Journal of Veterinary Research 2012;76:38–44
Porcine circovirus type 2 (PCV2) is the etiologic agent of several
syndromes collectively known as porcine circovirus-associated
diseases (PCVAD), including postweaning multisystemic wasting
syndrome (PMWS), enteritis, respiratory disease, and reproductive
failure (1). Today, many PCV2 vaccines are available and can be
used in piglets and sows. Owing to the combination of vaccine use
and the ubiquitous nature of PCV2, most females in breeding herds
have been exposed to the virus, and their piglets have varied levels
of passively acquired PCV2 antibodies (1).
Reproductive failure associated with PCV2 is characterized
by late-term abortions, decreased numbers of viable piglets,
and increased numbers of stillborn and mummified fetuses (2).
Inoculation of sows with PCV2 3 wk before parturition can result
in lethargy, abortion, and delivery of stillborn piglets as early as 7 d
after inoculation (3). Although PCV2-associated reproductive failure
has been characterized in experimental studies (2), some reports
suggest that it is rare under natural conditions, whereas others have
found that 13% of aborted fetuses and stillborns are infected (4,5).
Reports of naturally occurring PCV2-associated reproductive failure
have mainly concerned newly established production facilities with
Fetal infections and antibody profiles in pigs naturally infected with
porcine circovirus type 2 (PCV2)
Priscilla F. Gerber, Flávia M. Garrocho, Ângela M.Q. Lana, Zélia I.P. Lobato
The aim of this study was to describe early infections with porcine circovirus type 2 (PCV2) in naturally infected piglets and the
piglets’ serologic profiles. A total of 20 sows (15 PCV2-vaccinated and 5 unvaccinated) and 100 newborn piglets were studied.
Colostrum and serum of the sows and serum of the presuckling piglets were obtained on the day of parturition. Milk samples
were collected on day 20 postpartum. Blood samples were taken and the piglets weighed on days 1, 20, 42, 63, and 84 postpartum.
Colostrum and milk were evaluated for infectious PCV2 and for PCV2 total antibody (TA), neutralizing antibody (NA), and
IgA. Serum samples were evaluated for PCV2 TA, NA, IgA, IgM, and DNA. The sows had high levels of TA and NA in serum
and colostrum; however, 11 and 5, respectively, of the 20 colostrum and milk samples contained infectious PCV2. In the serum,
PCV2 DNA and IgM were detected in 17 and 5, respectively, of the 20 sows. Nine piglets were born with PCV2 antibodies, which
indicates in utero transmission of PCV2 after the period of immunocompetence (. 70 d of gestation). On day 1 postpartum, PCV2
DNA was detected in 29 of the 100 serum samples from the piglets. There was no difference between the weights of viremic and
nonviremic piglets throughout the study. In conclusion, even on farms with sows that have high PCV2 antibody titers, vertical
transmission of PCV2 may occur, resulting in piglet infection.
La présente étude visait à décrire les débuts d’infection par le circovirus porcin de type 2 (PCV2) chez des porcelets infectés naturellement ainsi
que les profils sérologiques de ces porcelets. Au total, 20 truies (15 vaccinées avec PCV-2 et 5 non-vaccinées) et 100 porcelets nouveau-nés ont
été étudiés. Du colostrum et du sérum chez les truies, et du sérum chez les porcelets ont été prélevés le jour de la mise-bas. Des échantillons
de lait furent également prélevés au jour 20 post-partum. Des échantillons sanguins ont été prélevés et les porcelets pesés aux jours 1, 20,
42, 63 et 84 post-partum. Le colostrum et le lait ont été évalués pour la présence de PCV2 infectieux, ainsi que pour les anticorps anti-PCV2
totaux (TA), les anticorps neutralisants (NA), et les IgA. Les échantillons de sérum ont été évalués pour PCV2 TA, NA, IgA, IgM et l’ADN.
Les truies avaient des niveaux élevés de TA et NA dans le sérum et le colostrum; toutefois, respectivement 11 et 5 des 20 échantillons de
colostrum et de lait contenaient du PCV2 infectieux. Dans le sérum, l’ADN de PCV2 et des IgM ont été détectés chez, respectivement, 17 et
5 des 20 truies. Neuf porcelets sont nés avec des anticorps contre PCV2, ce qui indique une transmission in utero de PCV2 après la période
d’immunocompétence (. 70 j de gestation). Au jour 1 post-partum, l’ADN de PCV2 a été détecté dans 29 des 100 échantillons de sérum
provenant des porcelets. Tout au long de l’étude aucune différence n’a été notée dans les poids des porcelets virémiques et non-virémiques.
En conclusion, la transmission verticale de PCV2 peut survenir même dans des élevages où les truies ont des titres élevés d’anticorps contre
PCV2, entraînant des infections chez les porcelets.
(Traduit par les auteurs)
Laboratório de Pesquisa em Virologia Animal, Departamento de Medicina Veterinária Preventiva, Universidade Federal de Minas Gerais, Minas
Gerais, Brazil (Gerber, Garrocho, Lobato); Departamento de Zootecnia, Universidade Federal de Minas Gerais, Minas Gerais, Brazil (Lana).
Address all correspondence to Dr. Zélia I.P. Lobato; telephone: +55 31 34092101; fax: +55 31 34092080; e-mail: email@example.com
Received September 22, 2010. Accepted January 6, 2011.
2000;64:0–00 The Canadian Journal of Veterinary Research 39
gilts that do not have PCV2 antibodies (6). Under field conditions,
sow vaccination reduces PCV2-associated reproductive failure and
improves sow performance (7). However, data from a recent experi-
mental study indicate that vertical transmission of PCV2 can occur
even in vaccinated gilts (8).
Field studies have shown great variability in the frequency of
sow PCV2 viremia at parturition, from 8/105 (7.6%) to 1/130 (0.8%)
(9,10). Sow PCV2 viremia was significantly related to pig mortal-
ity (10). At the moment, little is known about sow PCV2 viremia
at parturition, its relation to PCV2 vertical transmission, and the
onset in the postnatal period of PMWS in piglets infected naturally.
The objective of this study was to describe the frequency of PCV2
infection in peripartum sows and the serologic profile of antibodies
in naturally infected pigs.
Materials and methods
Animals and sample collection
The experimental protocol (089/04) was approved by the Ethics
Committee in Animal Experimentation of the Universidade Federal
de Minas Gerais, Minas Gerais, Brazil. Twenty sows with a parity
range of 1 to 10 [mean 6 standard deviation (s) 4.21 6 3.39] from 4
farrow-to-finish herds (H1 to H4; 5 sows per herd) were studied. The
sows in H1 were not vaccinated against PCV2. Those in H2, H3, and
H4 were vaccinated twice with 2 mL of commercial PCV2 vaccine
licensed for breeding animals (Circovac; Merial, Lyon, France), at
30 d and 15 d before parturition. On the day of parturition, samples
of the sows’ blood and colostrum were collected. A total of 100 new-
born piglets (5 piglets per sow) were ear-tagged, and presuckling
blood samples were collected from the umbilical cord. Milk samples
were collected on the 20th day postpartum. Further blood samples
from the piglets were taken by venipuncture and the piglets weighed
on days 1, 20, 42, 63, and 84 postpartum. Fat-free colostrum and milk
were prepared by centrifugation at 900 3 g at 58C for 10 min; the
skim colostrum or milk was pipetted carefully from underneath the
fat layer and stored at 220°C until used.
Single radial immunodiffusion (SRD)
Total IgG antibodies in sow colostrum and piglet serum on the
day of parturition and day 1 postpartum were detected by SRD
performed according to a previously described protocol (11). In
brief, IgG antibodies against porcine antigen were prepared in
rabbits, purified, titrated, and mixed with an equal volume of 3%
noble agar. The mixture was poured between glass slides 5 3 5 cm
separated by a plastic frame, to a gel thickness of 1 mm. Wells 2 mm
in diameter were punched, and 2-mL aliquots of the purified IgG or
samples were added to each well. The development of zones was
analyzed after 72 h of incubation of the plates in a moist chamber.
Total IgG was quantified by a regression equation obtained with
different dilutions of purified pig IgG as described previously (12).
The sensitivity of the assay was 5 mg/mL. The concentration of total
IgG was expressed in milligrams per milliliter.
Immunoperoxidase monolayer assay (IPMA)
A previously described IPMA protocol (13) was used, with modi-
fications, to detect PCV2-specific IgG in serum and colostrum. Serial
4-fold dilutions from 1:20 to 1:5120 were pipetted into 96-well plates
containing fixed PCV2-infected PK15 cells free of porcine circovirus
(PCV). The plates were incubated for 1 h at 378C and then washed
with phosphate-buffered saline and Tween 20 (PBS-T). Then 50 mL
of protein G conjugated with peroxidase (Molecular Probes, Eugene,
Oregon, USA) at 0.25 mg/mL in PBS-T was added to the wells, which
were incubated for another hour at 378C. Finally, the plates were
washed, and a substrate solution of 3-amino-9-diethylcarbazole
in 0.1 M acetate buffer with 0.05% hydrogen peroxide was added
to reveal the reaction. The TA concentration was expressed as the
average log2 titer, with dilutions corresponding as follows: 20 = 4.32;
80 = 6.32; 320 = 8.32; 1280 = 10.32; and 5120 = 12.32. The TA titers
were classified as follows: , 4.32 log2 = negative; 4.32 to 6.32 log2
= low; 8.32 to 10.32 log2 = moderate; and . 12.32 log2 = high. An
age-group seroconversion was indicated when at least 50% of the
sampled animals presented a 4-fold or greater rise in TA concentra-
tion between successive samplings.
The PCV2-specific IgM antibodies in piglet serum and IgA anti-
bodies in milk, colostrum, and piglet serum on day 1 postpartum
were measured by isotype-specific IPMA. First, 96-well plates
containing PCV2-infected PK15 cells that were free of PCV1 were
blocked with 2% casein for 1 h at 378C. The plates were then washed
with PBS-T, and serial 4-fold dilutions (1:20 to 1:5120) of samples in
PBS-T that contained 0.2% casein were pipetted into the wells. The
plates were incubated for 1 h at 378C and then washed. Next, goat
Table I. Number of animals positive for IgG antibodies to porcine circovirus type 2 (PCV2) and concentrations of
total IgG in colostrum and piglet serum at parturition and on day 1 postpartum in the 4 herds
s — standard deviation.
a,b Different superscripts within the column indicate significant differences (P , 0.05) between the groups.
Number of positive animals/total number of animals; total IgG concentration (mean 6 s), mg/mL
5/5 (107.84 6 37.26)
5/5 (80.48 6 45.07)
5/5 (97.48 6 48.50)
5/5 (89.91 6 38.68)
20/20 (93.82 6 20.03)
Day of parturition
6/25 (0.04 6 0.06)
5/25 (0.02 6 0.04)
2/25 (0.00 6 0.02)
5/25 (0.01 6 0.03)
18/100 (0.02 6 0.04)
Day 1 postpartuma
25/25 (46.59 6 14.01)a
25/25 (40.87 6 13.32)a,b
25/25 (45.78 6 16.69)a
25/25 (35.6 6 7.95)b
100/100 (42.23 6 13.89)
40 The Canadian Journal of Veterinary Research 2000;64:0–00
antibodies against porcine IgM or IgA (Immunology Consultants,
Newberg, Oregon, USA) were added to the wells, and the plates
were again incubated for 1 h. The plates were washed, and IgG
against goat antigen conjugated with peroxidase was added (Sigma
Chemical Company, St. Louis, Missouri, USA), and the plates were
incubated for another hour. The cells were stained for PCV2 with the
use of protein G visualization as previously described (13).
Detection of PCV2 NA
A previously described protocol (13), with modifications, was
used to detect PCV2 NA in colostrum and serum. First, 50 mL of
each sample was serially diluted 2-fold (1:16 to 1:2048) in complete
Dulbecco’s Modified Eagle’s Medium (DMEM). The samples were
added to 96-well plates, and 200 median tissue culture infective dose
[(TCID50) of PCV2] was added to each well. After 1 h of incubation,
freshly trypsinized PK15 cells free of PCV 50 000/cm2, were added
to the samples, and the plates were incubated for 72 h at 378C in 5%
CO2. The plates were then fixed and incubated for 1 h at 378C with
an anti-PCV2 polyclonal serum (VMRD, Pullman, Washington, USA).
Next, the plates were incubated for 1 h with protein G conjugated with
peroxidase and stained for PCV2 as previously described (13). The NA
titer was established as the reciprocal of the last dilution in which a
given sample was able to reduce by 50% the number of PCV2-infected
cells. The equivalent dilutions were as follows: 16 = 4; 32 = 5; 64 = 6;
128 = 7; 256 = 8; 512 = 9; 1024 = 10; and 2048 = 11. The titers were
classified as follows: , 4 log2 = negative; 4 to 6 log2 = low; 7 to 8 log2
= moderate; and . 9 log2 = high. An age-group seroconversion was
indicated when at least 50% of the sampled animals presented a 4-fold
or greater rise in NA concentration between successive samplings.
DNA extraction and amplification
The presence of PCV2 DNA was tested in serum from the sows
and piglets obtained on day 1 postpartum. The DNA extraction was
performed with a Wizard Genomic DNA Purification kit (Promega,
Madison, Wisconsin, USA). Quantitative real-time polymerase chain
reaction (qPCR) was performed as previously described (14), with
modifications. The results were recorded as the number of PCV2
copies log10 transformed per milliliter of serum.
Colostrum and milk samples were tested for the presence of PCV2
by virus isolation based on a previously described protocol (15),
with modifications. Serial 10-fold dilutions (1:10 to 1:10 000) of the
samples were added to 96-well plates containing 1-d-old PK15 cell
monolayers free of PCV. After adsorption for 1 h, complete DMEM
supplemented with 5% fetal bovine serum was added. After incuba-
tion for 72 h at 378C in 5% CO2 the cells were fixed and stained for
PCV2 as described for PCV2 NA. The PCV2 titers were expressed
as TCID50 per 50 mL.
The data are reported as mean 6 s unless otherwise indicated.
The Shapiro-Wilk test was used to evaluate the normality of the
data distribution of the examined variables. The nonparametric
Kruskal-Wallis test was used to analyze the PCV2 TA, NA, IgM, and
IgA levels and the difference in PCV2 titer between herds. Fisher’s
exact test was applied to compare the proportions of positive and
negative results of PCV2 antibody testing and viral titers between
the herds. Spearman’s correlation was used to correlate the levels
of the different immunoglobulins and to correlate immunoglobulin
level with PCV2 titer. A linear regression model was built to correlate
the TA and NA levels in piglet serum. The results were considered
significant at P , 0.05.
Total IgG in colostrum and piglet serum
Total IgG levels were measured in samples of sow colostrum
and piglet serum on the day of parturition and day 1 postpartum
to assess the transfer of passive immunity. The colostrum samples
had high total IgG levels (93.82 6 20.03 mg/mL), similar to those
reported from other studies (95.60 ± 32.50 mg/mL) (16); there was
no significant difference between the herds (Table I).
On the day of parturition 18 of the 100 piglets had serum levels of
total IgG from 0.08 to 0.26 mg/mL, higher than previously described
for natural fetal antibody (0.03 mg/mL) (17), which suggests antigen
stimulation in utero after the period of immunocompetence (. 70 d
of gestation). There was no significant difference in total serum IgG
level between the herds (Table I). Of the 18 piglets demonstrating
some total IgG on the day of parturition, 5 were positive for PCV2
DNA on day 1 postpartum (data not shown).
On day 1 postpartum the total IgG levels in the piglet serum
ranged from 18.32 to 77.52 mg/mL, similar to the levels reported
from other studies (18.7 6 39.0 mg/mL) (18). The average concen-
tration of total IgG was higher in H1 and H3 than in H4 (P , 0.05)
Serologic profile and viremia in the sows
On the day of parturition all the sows had high titers of PCV2
TA and NA in the serum (11.63 6 1.32 log2 and 9.51 6 1.01 log2,
respectively). There was no significant difference in mean PCV2
TA, NA, or IgM level between the herds (Figure 1). A single sow in
H2, 3 sows in H3, and 1 sow in H4 (5/20, 25%) had moderate PCV2
Figure 1. Mean titer of porcine circovirus type 2 (PCV2) total antibodies
(TA), neutralizing antibodies (NA), and IgM, and PCV2 load in sow serum
from herds H1 to H4 at parturition. Standard deviation is indicated by
2000;64:0–00 The Canadian Journal of Veterinary Research 41
IgM titers (6.32 to 8.32 log2). No correlation was found between the
levels of PCV2 IgM, which is indicative of recent infection, and PCV2
shedding in colostrum and milk.
On the day of parturition 17 (85%) of the sows were qPCR-
positive, with 3.20 to 3.69 log10 PCV2 copies/mL of serum. The
mean viral load of the herds was 2.94 6 1.28 log10 PCV2 copies/mL
(Figure 1). There was no difference in the number of viremic sows
between the herds (data not shown).
Antibodies and virus titers in colostrum and milk
On the day of parturition all the colostrum samples were posi-
tive for the highest PCV2 TA, NA, and IgA dilutions tested (TA and
IgA, 12.32 log2; NA, 11.00 log2). In the milk samples the PCV2 IgA
titers were variable but averaged 8.54 6 3.05 log2 (Table II). There
was no significant difference between the herds in the IgA titer in
colostrum or milk. Regardless of the high titers of PCV2 antibodies,
PCV2 was isolated from 11 (55%) of the colostrum samples (mean
titer 101.00 6 1.03 TCID50/50 mL) and 5 (25%) of the milk samples
(mean titer 100.30 6 0.57 TCID50/50 mL). For colostrum the number of
PCV2-positive samples and the virus titers were higher in H1 than
in H3 and H4 (P , 0.05), although no difference was found for milk
(Table II). There was no correlation found between infectious PCV2
shedding in colostrum and milk, between the infectious PCV2 titer
and the TA and NA titers in colostrum and milk, or between the
infectious PCV2 titer and the IgA titers in colostrum and milk.
Serologic profile and viremia in the piglets
On the day of parturition 7 piglets had low levels of PCV2 TA
(Table III), ranging from 4.32 to 8.32 log2, 1 piglet had an NA titer of
5.0 log2, and 2 other piglets had low PCV2 IgM titers in the serum (4.36
log2) in the absence of PCV2 TA. There was no significant difference
between the herds in the number of seropositive piglets at parturition.
On day 1 postpartum, PCV2 DNA was detected in the serum
of 29 of the 100 piglets (3.34 to 5.05 log10 PCV2 copies/mL); there
were 1 to 3 positive piglets per litter. Of these animals, 1 had
PCV2 TA and another had PCV2 IgM on the day of parturi-
tion. There was no difference in the number of viremic pig-
lets between the herds (Table III). There was no correlation
between sow viremia or PCV2 infectious shedding in the
colostrum and piglet viremia on day 1 postpartum. There was
no difference between the weights of viremic and nonviremic
piglets at any of the 5 times of weighing from day 1 to day 84
postpartum (data not shown).
The evolution of the piglet serologic profile from the day of par-
turition to day 84 postpartum is shown in Figure 2. The herds had
similar PCV2 TA profiles up to day 63, with a gradual decline in the
titers of maternally derived antibodies. The TA and NA titers were
lowest on days 42 and 63 in herds H1, H2, and H4. The PCV2 IgM
levels increased from day 42 in H1 and H4, peaking on day 63. In H1
and H4, PCV2 TA and NA seroconversion occurred on day 84, 6 wk
Table II. Number of animals positive for IgA to PCV2 or for infectious PCV2 and the corresponding titers in colostrum and milk
from the 4 herds
s — standard deviation.
a Log2 transformed titer (mean 6 s).
b Log10 transformed titer (mean 6 s). TCID50 — median tissue culture infective dose. Different superscripts within the column indicate signifi-
cant differences (P , 0.05) between the groups.
Number of positive animals/total number of animals
5/5 (11.00 6 0.00)
5/5 (11.00 6 0.00)
5/5 (11.00 6 0.00)
5/5 (11.00 6 0.00)
20/20 (11.00 6 0.00)
PCV2 (TCID50/50 mL)b
5/5 (2.00 6 0.70)a
4/5 (1.40 6 0.89)a,b
1/5 (0.40 6 0.89)b
1/5 (0.20 6 0.44)b
11/20 (1.00 6 1.03)
5/5 (9.95 6 2.16)
4/5 (6.26 6 4.48)
5/5 (9.84 6 0.98)
5/5 (9.15 6 3.00)
19/20 (8.54 6 3.05)
PCV2 (TCID50/50 mL)b
1/5 (0.40 6 0.89)
1/5 (0.20 6 0.45)
3/5 (0.60 6 0.54)
0/5 (0.00 6 0.00)
5/20 (0.30 6 0.57)
Table III. Number of piglets born PCV2-seropositive, as well as PCV2 IgA titers and PCV2 load in serum on day 1 postpartum
s — standard deviation.
a Log2 transformed titer (mean 6 s). TA — total antibodies.
b Different superscripts within the column indicate significant differences (P , 0.05) between the groups.
c Log10 transformed titer (mean 6 s).
Number of positive animals/total number of animals
2/25 (0.35 6 1.21)
2/100 (0.09 6 0.62)
1/25 (0.17 6 0.87)
4/25 (0.93 6 2.29)
1/25 (0.17 6 0.89)
1/25 (0.17 6 0.87)
7/100 (0.36 6 1.39)
25/25 (11.00 6 0.00)a
25/25 (10.00 6 2.21)b
25/25 (10.16 6 1.51)a,b
25/25 (9.52 6 2.08)a
100/25 (10.41 6 1.93)
7/25 (1.14 6 1.90)
5/25 (0.64 6 1.32)
9/25 (1.27 6 1.75)
8/25 (1.32 6 2.00)
29/100 (1.09 6 1.75)
42 The Canadian Journal of Veterinary Research 2000;64:0–00
after the IgM level started to rise. In H2, PCV2 IgM was detected
3 wk later than in the other herds, on day 63, and a trend of increas-
ing TA and NA was noted 3 wk later. Although the IgM level started
to increase on day 42 in H3, there was no seroconversion to other
immunoglobulin types until the end of the study.
The correlation between TA and NA levels in piglet serum was
moderate to high (P , 0.000): on day 21, r = 0.61; on day 42, r = 0.75;
on day 63, r = 0.53; and on day 84, r = 0.81.
In the piglets in this study, the PCV2 seropositivity at birth and
the high frequency of viremia on day 1 postpartum suggest that
early infection can occur because of vertical transmission of PCV2
even from naturally infected sows with high PCV2 antibody titers.
In addition to transplacental infection, piglets could be infected with
PCV2 soon after birth via infected colostrum or environmental con-
tamination. Although the occurrence of natural antibodies reacting
with pathogens cannot be discarded (17), it seems that IgM and not
IgG has a leading role in those specific reactions (19). Furthermore,
the detection of NA in 1 newborn piglet reinforces the idea of in
utero infection after the period of fetal immunocompetence.
Experimental and field studies have associated in utero transmis-
sion of PCV2 with reproductive failure resulting in stillborn, mum-
mified, and nonviable piglets at birth (3). In utero transmission of
PCV2 has typically been reported in newly established herds with
a high proportion of gilts (6,20). However, in a recent study (8),
reproductive failure was not observed in gilts infected experimen-
tally at 56 d of gestation; regardless, PCV2 DNA was recovered in
the serum of 4 of 80 neonates. Together with our findings, these data
indicate that transplacental transmission of PCV2 may occur, even
in the absence of reproductive failure and in sows with high levels
of PCV2 antibodies, at a greater frequency than previously reported.
Although in utero transmission of PCV2 and its association with
reproductive failure has been repeatedly described, little is known
about its asymptomatic occurrence and its implication in PCVAD. A
study found that sow PCV2 viremia in the peripartum period was
significantly related to piglet mortality (9). In another study, prena-
tal PCV2 infection did not induce PMWS, but prenatally infected
animals had a significantly lower body weight compared with con-
trol pigs (21). These findings differ from our finding in this study
that animals that were PCV2-seropositive at birth and viremic on
day 1 postpartum were similar in weight to the other animals at the
5 times of weighing from day 1 to day 84 postpartum. We could not
find an association between mortality, weight, and the occurrence
of PMWS among piglets that were viremic on day 1 postpartum
compared with nonviremic piglets. This may be related to the time
of infection or to the quantity and virulence of PCV2. In addition, our
study found that only 7 of the 18 piglets with some level of total IgG
at birth were positive for PCV2, which suggests that these animals
could have been infected in utero by other pathogens that affect the
postnatal antibody profile.
The high number of sows positive for PCV2 by qPCR at parturi-
tion suggests that the vaccination protocol may not be sufficient to
protect sows against PCV2 viremia. These results differ from the
finding in a previous study that vaccinated sows were protected
from viremia after experimental infection (8). This difference may
be explained by the low sample size (n = 3) of that study, which
investigated specific pathogen-free, PCV2-seronegative gilts, or by
differences in vaccination protocol, time of infection, or virulence of
Figure 2. Mean titer of PCV2 TA, NA, and IgM in the serum of piglets from H1 to H4 on days 0,
20, 42, 63, and 84 postpartum. Standard error is indicated by error bars.
2000;64:0–00 The Canadian Journal of Veterinary Research 43
the PCV2 isolate. In addition, persistence of PCV2 viremia has been
demonstrated (22,23), and studies have suggested that an animal
can be infected with different PCV2 isolates (24). This would help
to explain why some sows had PCV2 IgM simultaneously with high
levels of PCV2 TA at parturition, indicating recent reinfection. In
this study, the occurrence of low PCV2 antibody titers in pigs that
did not exhibit gross lesions at birth indicates that in utero infection
occurred close to parturition (25).
A recent study suggested that the local IgA immune response
is more important for controlling PCV2 replication during early
infection than the local IgG and IgM responses or the IgG systemic
response (26). Although no correlation between the PCV2 IgA titer
in milk and piglet weight at weaning was found in this study, the
presence of PCV2 IgA may protect against early mucosal infection
in suckling piglets. Thus, PCV2 IgA may have a role in reducing
piglet mortality that is similar to the protection provided by maternal
PCV2 TA (9,26).
Studies have indicated that although maternal antibodies provide
some protection against PCV2 infection through their neutralizing
activity, these antibodies are unable to completely prevent infection
(9,27). However, as suggested by the serologic profiles found in this
study, high titers of maternal antibodies seem to control infection in
a way that prevents an antigenic stimulus sufficient to elicit an active
immune response in piglets. Interestingly, regardless of early piglet
viremia, the PCV2 IgM titer increased only at day 42 postpartum,
which suggests that PCV2 stimulates antibody production only after
the titer of passive antibodies declines to a subprotective level. In
fact, this study showed that the level of PCV2 IgM increased earlier
in herds in which piglets had lower titers of NA. The PCV2 TA and
NA increases coincided with declining levels of IgM. The response
delay of NA compared with TA has been described previously
(13). In this study no such delay occurred, possibly owing to the
3-wk interval between sample collections and to the difficulty of dis-
tinguishing the decline in passive immunity from the onset of active
immunity. Previous studies found that some PMWS-affected pigs
lacked or had low levels of NA to PCV2 even in the presence of high
TA titers (13,28). However, there was a moderate to high correlation
between TA and NA in pig serum in this and other studies (13).
In conclusion, high PCV2 antibody levels in sows at parturition
did not prevent early PCV2 infection and viremia in piglets from
the first day of life or peripartum maternal viremia and virus shed-
ding into the lacteal secretions. Vertical transmission of PCV2 could
generate PCV2 seropositivity in viable piglets even on farms with
no symptoms of reproductive failure.
This work was funded by Fundação de Amparo à Pesquisa do
Estado de Minas Gerais, Minas Gerais, Brazil, and Conselho Nacional
de Desenvolvimento Científico e Tecnológico (CNPq), Brasilia, Brazil.
We thank veterinarians Flávia F. Pinto, Túlia M. Oliveira, and José
E. Cavalcanti for their assistance with the herds. We also thank
Grazielle Galinari for her excellent technical assistance. Dr. Lobato
has a research fellowship from CNPq.
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