Ci a ion: López-Lo enzo, G.; P ie o,
A.; López-No o, C.; Díaz, P.; Remesa ,
S.; Mo ondo, P.; Fe nández, G.;
Díaz-Cao, J.M. P esence o Po cine
Ci co i us Type 2 in he En i onmen
o Fa m Facili ies wi hou Pigs in
Long Te m-Vaccina ed
Fa ow- o-Wean Fa ms. Animals 2022,
12, 3515. h ps://doi.o g/10.3390/
ani12243515
Academic Edi o s: Da id H. Baum,
Soph onia Wa d and Je ey
J. Zimme man
Recei ed: 26 Oc obe 2022
Accep ed: 9 Decembe 2022
Published: 13 Decembe 2022
Publishe ’s No e: MDPI s ays neu al
wi h ega d o ju isdic ional claims in
published maps and ins i u ional a il-
ia ions.
Copy igh : © 2022 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
animals
A icle
P esence o Po cine Ci co i us Type 2 in he En i onmen o
Fa m Facili ies wi hou Pigs in Long Te m-Vaccina ed
Fa ow- o-Wean Fa ms
Gonzalo López-Lo enzo , Albe o P ie o * , Cyn hia López-No o , Pablo Díaz , Susana Remesa ,
Pa ocinio Mo ondo , Gonzalo Fe nández and JoséManuel Díaz-Cao
Depa men o Animal Pa hology (INVESAGA G oup), Facul y o Ve e ina y Sciences, Uni e sidade de San iago
de Compos ela, 27002 Lugo, Spain
*Co espondence: [email p o ec ed]; Tel.: +34-982-822-127
Simple Summa y:
Po cine Ci co i us Type 2 (PCV2) accina ion is a widesp ead measu e ha
e ec i ely educes in ec ion p e alence in swine a ms. Howe e , his ool has ailed o e adica e he
in ec ion, p obably because o he pe sis ence o PCV2 in he en i onmen o he a ms. Thus, he
aim o he p esen s udy was o e alua e he p esence o PCV2 in di e en a eas o swine a ms o
iden i y c i ical poin s which may ac as possible i al ese oi s. Fou a ow- o-wean long- e m
accina ed a ms we e s udied, sampling di e en su aces om animal and non-animal a eas and
analyzing hem by qPCR o de ec and quan i y he PCV2 load. The esul s show he nea absence
o PCV2 in animal a eas; in con as , he i us is equen ly de ec ed in o ices, a m s a clo hing
and he a m pe ime e . As PCV2 accina ion does no p o ide s e ilizing immuni y, he de ec ed
i al load is p obably he esul o low shedding om subclinically in ec ed animals on he a m;
hus, PCV2 would end o accumula e in a eas no cleaned and disin ec ed egula ly. Ne e heless,
an ex e nal sou ce o PCV2 canno be o ally uled ou . This s udy shows he exis ence o po en ial
c i ical poin s o PCV2 pe sis ence in accina ed a ms, indica ing he need o conside ing hem o
u u e e adica ion plans.
Abs ac :
Vaccina ion agains Po cine Ci co i us Type 2 (PCV2) e en o e se e al yea s has p o en
as an insu icien measu e o e adica e he in ec ion om a ms, possibly due o no p oducing
s e ilizing immuni y. Vi al pe sis ence in he a m en i onmen has been p oposed as a possible
cause o ein ec ion, and o ha eason, he main objec i e o his s udy was o iden i y po en ial
c i ical poin s whe e PCV2 could pe sis in a ow- o-wean a ms which had been accina ing pigle s
o yea s. Su ace samples we e collec ed om di e en a m acili ies wi h and wi hou animals and
analyzed by qPCR o de ec and quan i y he i al load. Mos o he samples aken in animal housing
acili ies es ed nega i e (96.6%); howe e , PCV2 was mo e equen ly de ec ed in samples om
he o ices (37.5%), he a m s a (25%) and he pe ime e (21%). These esul s indica e ha PCV2
con amina ion is equen in acili ies despi e he long- e m use o accina ion p og ams. The e o e,
PCV2 con ol p og ams should include mo e exhaus i e cleaning and disin ec ion p o ocols in non-
animal acili ies, as well as he implemen a ion o speci ic biosecu i y measu es in hese a eas o
minimize he isk o PCV2 in oduc ion om ex e nal sou ces.
Keywo ds:
biosecu i y; en i onmen al sampling; po cine ci co i us ype 2 (PCV2); eal- ime PCR;
swine
1. In oduc ion
Po cine Ci co i us Type 2 (PCV2) is conside ed one o he mos impo an pa hogens
o swine p oduc ion due o he p oduc i e and economic epe cussions ha i s in ec ion
en ails [
1
,
2
]. I can in ec pigs om he weaning age o adul ones, showing a conside able
a ie y o synd omes [
3
]. One o he main cha ac e is ics o his i us is i s s uc u e: i s
Animals 2022,12, 3515. h ps://doi.o g/10.3390/ani12243515 h ps://www.mdpi.com/jou nal/animals
Animals 2022,12, 3515 2 o 9
small size and he absence o an ex e nal en elope p o ide a high esis ance o ad e se
condi ions [
4
–
6
]. Thus, he possibili y ha PCV2 may emain in he a m en i onmen o
ex ended pe iods should be conside ed in he con ol and p e en i e measu es.
Vaccina ion agains PCV2 is a highly ecommended p e en i e measu e in swine
p oduc ion due o wo main easons. Fi s , his i us is conside ed o be p esen in all
swine a ms [
1
]. Second, accina ion has shown g ea e icacy in p e en ing PCV2 Sys emic
Disease and in a oiding he losses associa ed wi h i , ep oduc i e losses and he dec ease
in p oduc i e pe o mance associa ed wi h subclinical in ec ion. The e o e, since he
in oduc ion o PCV2 accines in he 2000s, hei use has been e y widesp ead and
nowadays pigs ha each slaugh e a e accina ed in mos coun ies [
7
]. As a consequence
o he high PCV2 accina ion le el on pigle s, gil s/sows, o e en bo h du ing hese pas
yea s, in some a ms, a conside able p opo ion o pigs al eady each slaugh e wi hou
ha ing been in ec ed [8–10].
PCV2 accines do no p oduce s e ilizing immuni y, bu he p o ec ion ha hey con e
a oids he in ec ion o accina ed pigle s du ing he weaning phase so ha , a leas in
a ow- o-wean a ms, an e en ual e adica ion would be possible [
11
]. Ne e heless, his
has no been achie ed ye despi e i s widesp ead use. In an a emp o a ain he sough -
a e e adica ion, Feng e al. (2014) launched a p o ocol o mass accina ion agains PCV2
(sows, boa s and gil s: h ee doses/animal/yea ; pigle s: accina ed a 3 and 7 weeks o age)
o one yea . The esul s showed ha nei he PCV2 i emia no any se ological esponse o
his i us we e de ec ed; howe e , when accina ion ceased, he in ec ion became e iden
again. Thus, hese au ho s sugges ed ha he i us had ne e been comple ely wiped ou
om he a m [
12
]. Ano he possibili y o he ein ec ion o a ms could be an ex e nal
sou ce o PCV2. In his sense, isi o s such as comme cial agen s, e e ina y p ac i ione s,
e c., who usually isi di e en a ms on he same day may in oduce he i us o an
unin ec ed a m, so he a eas whe e hese isi o s a e ecei ed (main en ance o he a m,
o ice) could be c i ical poin s o he en y o he in ec ion. Al hough a m isi o s ypically
wea con en ional disposable co e alls and boo co e s, se e al p e ious in es iga ions
ha e e ealed ha hei clo hes o oo wea could become con amina ed in PCV2-in ec ed
he ds, and he e o e hey may ac as a “T ojan ho se” o o he a ms [
13
–
15
]. Ne e heless,
Pa e son e al. (2011) managed o main ain a b eeding he d ee o in ec ion o a leas
20 mon hs a e using PCV2-naï e pigs o epopula ing and pe o ming an exhaus i e
cleaning and disin ec ion p ocedu e oge he wi h a s ic biosecu i y plan [16].
These expe iences sugges ha he i us may emain on he a m no in he pigs bu in
he en i onmen , and his en i onmen al con amina ion migh be one o he easons ha
p e en he e adica ion o PCV2 in a ms. In ac , mo e han a decade ago, Ho len e al.
(2008) sugges ed ha he educ ion o he en i onmen al i al load may be a key ac o o
conside when planning PCV2 con ol s a egies [
17
]. In his ega d, ecen s udies ha e
ied o de e mine he epidemiological ole o he en i onmen al p esence o PCV2, showing
ha he i us is widely dis ibu ed in he a m en i onmen ega dless o he p oduc ion
s age and ha he i al loads a e highe in PCV2 sys emic disease si ua ions [18–22].
In a p e ious s udy, we de ec ed PCV2 DNA in he en i onmen o di e en a m a eas
as well as in omi es and a m s a om non- accina ed a ow- o-wean a ms, e ealing
ha weaning a eas we e he mos con amina ed acili ies and highligh ing a high PCV2 load
in he en i onmen o wa ehouses. These esul s sugges ha hese loca ions may ac as
poin s o main aining and sp eading he i us wi hin a ms [
20
]. Howe e , as has al eady
been men ioned, nowadays mos a ms pe o m a PCV2 accina ion p og amme, and no
in o ma ion abou he PCV2 dis ibu ion and i al load in he en i onmen o accina ed
a ms is a ailable. Thus, he iden i ica ion o speci ic a eas o omi es ha can ac as i al
ese oi s in hese a ms is impo an o imp o e he cu en PCV2 con ol p og ams.
The e o e, his s udy was pe o med o iden i y c i ical poin s o PCV2 con amina ion in
he en i onmen o a ow- o-wean a ms which had been accina ing pigle s o yea s.
Animals 2022,12, 3515 3 o 9
2. Ma e ials and Me hods
2.1. Included Fa ms, PCV2 Su eillance and En i onmen al Sampling
Fou in ensi e a ow- o-wean a ms om he egion o Galicia (NW Spain) we e
included in he s udy. B ie ly, all o hem we e o small size (less han 120 li es ock uni s
acco ding o Spanish Real Dec e o 306/2020 [
23
]), and hey we e selec ed because all o
hem had been ca ying ou a pigle accina ion scheme agains PCV2 o a leas se en
yea s, wi hou e idence o suspicion o PCV2 in ec ion du ing ha ime. A mo e de ailed
desc ip ion o he a ms is supplied in Table 1.
Table 1. Cha ac e is ics o he a ms.
Fa m A B C D
Numbe o sows 360 200 300 300
Numbe o buildings 3 1 1 1
Numbe o a owing ooms 7 6 6 6
Numbe o weaning ooms 6 4 6 7
Numbe o ges a ion ooms 1 1 1 1
PCV2 accina ion s a egy Only pigle s a
4 weeks o age
Only pigle s a
3 weeks o age
Only pigle s a
3 weeks o age
Only pigle s a
3 weeks o age
Yea s o accina ing agains PCV2 7 7 8 8
PRRS in ec ion Nega i e Nega i e Nega i e Posi i e
The ou a ms used he same comme cial PCV2 accine (ORF2 exp essed in bac-
ulo i us sys em) and we e managed in 3-week ba ches, sending pigle s o a ening a ms
upon inishing he weaning phase (a app oxima ely 9–10 weeks o age). In addi ion, o all
a ms, he o igin o eplacemen gil s and semen was he same. Al hough he numbe o
buildings was di e en , all o hem p esen ed a simila dis ibu ion, including an o ice o
adminis a i e wo k and mee ing a m isi o s and a wa ehouse. Rega ding ex e nal biose-
cu i y, all a ms ga he ed he equi emen s es ablished by egula ions, such as a pe ime e
ence, egis e book, dis ance o o he a ms, e c. As he main cha ac e is ics o in e nal
biosecu i y, all a ms p ac iced an all-in/all-ou sys em, applying a cleaning and disin-
ec ion p o ocol wi h a 1-week acancy pe iod be ween consecu i e ba ches in a owing
and weaning ooms. No p o ocol o cleaning and disin ec ion o o he acili ies such as
o ices o wa ehouses was es ablished, no ha e alua ed he e icacy o ha measu es. The
change o clo hes and oo wea be o e en e ing he a m and he use o exclusi e wo kwea
and wo k boo s we e compulso y in all o hem. Howe e , all a ms p ac iced he change
o clo hes and boo s among he di e en a m acili ies, and none p esen ed an es ablished
p o ocol o moni o he compliance o biosecu i y measu es.
A single isi was ealized o each a m in 2019. Du ing ha isi he ollowing
ac i i ies we e pe o med:
Fi s , a o al o 36 en i onmen al samples om di e en su aces and elemen s (co e-
sponding o a owing, weaning and ges a ion a eas, wa ehouses, o ice, a m pe ime e
and a m s a ) we e aken using a p e iously epo ed swabbing me hod using s e ile-
co on swabs o 11 mm in diame e [
24
]. B ie ly, he p o ocol o swabbing consis ed
o mois ening each swab wi h PBS-T (phospha e bu e saline wi h 0.05% o Tween 20,
pH = 7.4
) and swabbing he en i e a ea o sampling; he speci ic swabbing p o ocol used
o each ype o sample is desc ibed in Table 2. Subsequen ly, swab heads we e in oduced
in s e ile sc ew-cap ubes by b eaking he wooden s ick o he swab and placed in a sample
ack, which was main ained a oom empe a u e in a oam box un il p ocessing in he
labo a o y in he ollowing 24 h.
Second, he p esence o PCV2 in ec ion was assessed in pigle s o app oxima ely
8–9 weeks old in he weaning a ea: animals we e isually e alua ed in o de o de ec
clinical signs compa ible wi h PCV2 in ec ions such as was ing, dyspnoea and/o skin
pallo [
1
]; a o al o 20 blood samples o hese pigle s ( andomly aken o diagnos ic
pu poses di e en om his s udy and p o ided by he e e ina y p ac i ione s o he a m)
Animals 2022,12, 3515 4 o 9
we e also employed o PCV2 PCR analysis. The analysis o hese 20 blood samples ensu es
he de ec ion o a leas one in ec ed animal i he in ec ion p e alence is a leas 15% [25].
Table 2. En i onmen al samples and hei swabbing p o ocol.
En i onmen al Sample Swabbing P o ocol (One Swab Pe Sample)
Sow eede
1
, pigle es ing a ea
1
, pigle hoppe
2
, weaning pen
wall 2, ges a ion sow hoppe .
In eigh di e en elemen s o each ype, a 25 ×25 cen ime e
a ea pe elemen [26].
Sow c a e 1.
The su ace o la e al and ea wa d lowe ba s o eigh di e en
c a es.
Fa owing co ido 1, weaning pen loo 2, weaning co ido 2,
ges a ion pen loo , ges a ion co ido , wa ehouse loo , o ice
loo , pa king a ea, a m main en ance, pig loading a ea.
100 s eps we e aken on each su ace wea ing polye hylene boo
co e s, and hen bo h boo co e s we e swabbed as indica ed
p e iously [13]: in zigzag om he oe egion o he heel.
Fa owing ai an 1, weaning ai an 2.The su ace o he an blades o he p o ec i e g a ing
Deli e y managemen oolbox 1.The whole en al ex e nal su ace, 50% o he in e nal su ace
and all he sy inges included in i .
Weaning pen ailing 2.1 m in leng h in zigzag.
Wo king u ensils. The handle o a leas i e di e en u ensils (b ushes, paddles
. . . ) o 10 s each.
Feed wagons, p essu e washe , so ing panel, o ice
ables/chai s. 50% o he su ace.
Doo handles. The su ace o he ex e io and he in e io o ice doo handles.
Pens/Compu e keyboa d. The su ace o a compu e keyboa d o i e di e en pens.
Ca cass con aine The whole su ace o he winch.
Feed silo ungs.
The e ical and ho izon al su aces o i e di e en ungs in a
leas wo di e en silos.
Fa me hands and hai /ha . Hands: he do sal and en al su ace o he hands, including
each inge and he en al su ace o each inge nail.
Wo kwea and s ee wea .
The ho ax a ea, he on and he back o each leg om he knee
o he ankle, and he on and he back o each a m om he
elbow o he w is .
Wo k boo s and s ee boo s. In zigzag om he oe egion o he heel.
Fa m s a ehicle.
A swab was ubbed on he doo handle, he s ee ing wheel, he
gea shi le e , he handb ake, he pedals, he passenge sea
and he dashboa d
1
In he a owing ooms wi h pigle s olde han 10 days.
2
In he weaning ooms wi h pigle s olde han 8 weeks.
2.2. Labo a o y Analysis
Blood samples om each a m we e pooled ( ou pools/ a m); en i onmen al samples
we e p ocessed by adding 5 mL o PBS-T di ec ly o each ube con aining he swab head.
The ubes we e subsequen ly o exed o 1 min and le o s and e ically o 15 min;
1 mL o supe na an om each ube was ans e ed o a s e ile Eppendo ube and
kep a
−
20
◦
C un il he DNA ex ac ion was pe o med [
27
]. B ie ly, bo h blood and
en i onmen al samples we e p ocessed using a comme cial DNA ex ac ion ki (High Pu e
PCR Templa e P epa a ion Ki , Roche Diagnos ics GmbH, Mannheim, Ge many) ollowed
by eal- ime PCR (qPCR) analysis. Fo hose en i onmen al samples which es ed nega i e,
a second DNA ex ac ion p o ocol was ca ied ou using he comme cial ki Nucleospin
®
Soil (Mache ey-Nagel GmbH & Co KG, Dü en, Ge many) ollowing he manu ac u e ’s
ins uc ion. In all ex ac ions, he s a ing olume was 200
µ
L o he swab elua e and he
ob ained DNA was collec ed in 100
µ
L o elu ion bu e . An exogenous in e nal con ol
(EXOone EXIC, EXOPOL S.L., Za agoza, Spain) was added o each en i onmen al sample
du ing he ex ac ion in bo h p o ocols o iden i y possible qPCR inhibi ion and o e alua e
he quali y o DNA isola ion. The collec ed DNA was kep a −20 ◦C un il qPCR analysis.
The DNA samples we e analysed using a comme cial PCV2 qPCR ki (EXOone PCV2
oneMIX, EXOPOL S.L., Za agoza, Spain), ollowing he manu ac u e ’s ins uc ions. A
syn he ic DNA posi i e con ol supplied wi h he ki was employed as he posi i e con ol
and molecula -g ade wa e was used as he nega i e con ol. A sample was conside ed
posi i e when C
≤
40 o he PCV2 de ec ion channel acco ding o he manu ac u e ’s
Animals 2022,12, 3515 5 o 9
ins uc ions. Quan i ica ion (copies/swabs) was pe o med by he s anda d cu e me hod,
using se ial en- old dilu ions o he posi i e con ol (10
5
–10
1
copies/
µ
L) (Supplemen-
a y Ma e ials). All qPCR eac ions we e un on an Applied Biosys ems ABI P ism 7500
he mocycle (The moFishe Scien i ic, Wal ham, MA, USA).
3. Resul s
None o he e alua ed pigle s a he end o he weaning s age showed clinical signs
compa ible wi h PCV2 in ec ion o PCV2 i emia a he end o he weaning s age (0/16
posi i e pool samples).
Rega ding he en i onmen al samples, he esul s o each sample om each a m a e
shown in Table 3. B ie ly, a o al o 22 ou o 141 (15.60%) samples es ed posi i e o PCV2
DNA. Only Fa m C es ed nega i e o PCV2 DNA. In he posi i e a ms, he pe cen age o
PCV2-con amina ed samples pe a m anged om 19.44% o 22.22% (Table 3).
Table 3. Numbe o PCV2 copies/swabs in each en i onmen al sample in each a m.
Fa m Facili y Sample Fa m
N◦o En i onmen al Samples (% o PCV2 Posi i e Samples)
A
33 (21.21%)
B
36 (22.22%)
C
36 (0%)
D
36 (19.44%)
Fa owing a ea
(pigle s olde han
10 days)
Sow eede - - - -
Sow c a e - - - -
Pigle es ing a ea - - - -
Co ido - - - -
Ai an - - - -
Deli e y managemen oolbox No sampled * - - -
Weaning a ea
(pigle s olde han
8 weeks)
Pigle hoppe - - - -
Pen wall - - - -
Pen loo - - - -
Co ido - - - -
Pen ailing - - - -
Ai an - - - -
Ges a ion a ea
Sow hoppe - - - -
Pen loo 2.63 ×103- - -
Co ido 1.74 ×105- - -
Wa ehouses
Floo 9.55 ×103- - 5.01 ×104
Wo king u ensils - - - -
Feed wagons 1.02 ×103- - -
P essu e washe No sampled * - - -
So ing panels - - - -
O ice
Floo - 7.94 ×102-1.20 ×107
Doo handles 1.45 ×1039.77 ×102- -
Pens/Compu e keyboa d - 7.08 ×102- -
Tables/Chai s - 9.12 ×103- -
Fa m pe ime e
Pa king a ea - - - -
Fa m main en ance - - - 8.13 ×102
Pig loading a ea No sampled * - - 1.51 ×103
Ca cass con aine - 1.10 ×103- -
Feed silo ungs - 6.46 ×102- -
Fa m s a
Hands - 1.02 ×103- -
Hai /ha - - - -
Wo kwea - 9.33 ×103- -
Wo k boo s 1.66 ×104- - 1.95 ×107
S ee wea - - - 5.89 ×102
S ee boo s 7.76 ×102- - 1.95 ×105
Fa m s a ehicle - - - -
- Indica es a nega i e esul . * Indica es ha his elemen was no a ailable on he a m.
Animals 2022,12, 3515 6 o 9
The samples om he su aces in di ec con ac wi h animals ( a owing, weaning
and ges a ion a eas) we e nega i e (96.61%) excep in he case o Fa m A, which p esen ed
PCV2 con amina ion in he ges a ion a ea (Table 3).
In con as , PCV2 DNA was de ec ed in non-animal acili ies; in pa icula , he o ices
and he a m pe ime e es ed posi i e in h ee and wo a ms, which ep esen ed 37.50%
and 21.05% o all he posi i e samples om all he s udied a ms, espec i ely. Simila ly, he
samples om he a m s a we e posi i e in all he posi i e a ms (Table 3), ep esen ing
25.00% o all posi i e samples, and a wide a ia ion was obse ed ega ding he i al
load de ec ed in hem (5.89
×
10
2
–1.95
×
10
7
copies/swab). Mo eo e , he samples om
s ee wea , s ee boo s and/o ehicle accoun ed o 42.86% o he posi i e a m s a
samples.
4. Discussion
The p esen s udy e eals ha PCV2 DNA can be de ec ed in he en i onmen o
long- e m clinically heal hy a ow- o-wean a ms despi e yea s o accina ion. Ou mos
ema kable esul is he de ec ion o PCV2 DNA in di e en a m acili ies wi hou di ec
con ac wi h he pigs, which con as s wi h he sca ce numbe o posi i e samples in he
acili ies housing animals. Al hough posi i e samples om hese non-animal acili ies
(o ices and a m pe ime e , as well as a m s a ’s s ee wea and boo s) we e no he same
ype o sample in all he a ms, he p esence o i al con amina ion indica es a possible isk
ha hese a eas and omi es can be ac ing as i al ese oi s. Mo eo e , his obse a ion,
oge he wi h he absence o PCV2 con amina ion in animal housing a eas and he nega i e
PCR esul s om blood samples, migh sugges an ex e nal o igin o he de ec ed PCV2
con amina ion.
I mus be no ed ha ou aim he e was o iden i y possible c i ical poin s o he
accumula ion o PCV2 in he en i onmen , so his is he eason why we ook di e en
en i onmen al samples om each acili y. This allowed us o obse e ha PCV2 was no
sys ema ically p esen in he same samples ac oss a ms, bu he i al DNA was de ec ed
in di e en samples om he same acili y. Vi al loads we e gene ally low, so he ole o
his en i onmen al con amina ion as a possible sou ce o animal in ec ion is unce ain;
howe e , some samples showed high i al loads, such as he o ice loo in Fa m D. Gi en
ha his is a c oss-sec ional s udy we canno iden i y he ime o con amina ion, so i al
load and isk o in ec ion may a y by ime. In any case, ou esul s indica e ha high PCV2
con amina ions can be de ec ed in a m a eas wi hou any con ac wi h he animals. I is
wo h men ioning ha al hough he de ec ion o PCV2 DNA does no imply iabili y, i s
me e p esence should be in e p e ed as a po en ial isk o a ms, due o he high esis ance
o his i us o ad e se condi ions [5,28].
As i has p e iously men ioned, isi o s such as e e ina ians, loading ucks, comme -
cial agen s, e c., can ac as an ex e nal sou ce o in ec ion, since hey can come con amina ed
om o he a ms o p emises [
13
–
15
]. The p esence o PCV2 DNA in he loading a ea
om one a m may suppo his hypo hesis. Al hough he esul om his sample migh
espond o he exis ence o in ec ed pigle s ha shed PCV2, i seems unlikely acco ding o
he ob ained esul s, since hese animals had been housed o almos wo mon hs in he
weaning a eas, whe e no PCV2 was de ec ed. Thus, con amina ion om he uck canno
be disca ded as he possible o igin o he de ec ed PCV2 DNA [
29
]. I should be no ed ha
he same ehicle can be used i s o anspo adul pigs o he slaugh e house, pa o
which can become in ec ed and shed PCV2. La e , he ehicle can be used o ca y pigle s
om a ow- o-wean a ms, such as he ones included in he p esen s udy, o a ening
ones. As a consequence, anspo a ion ehicles play a well-known ole in he ansmission
o he i us be ween a ms [
9
,
10
,
30
–
32
]. Thus, his cons an con ac wi h ex e nal and
uncon ollable a m e en s makes hese a eas he mos c i ical poin s o elimina e he PCV2
om he a m en i onmen .
Rega ding pig a eas, PCV2 DNA was ne e de ec ed in he en i onmen o a owing
and weaning a eas and was only ound in he ges a ion a ea o a single a m, which
Animals 2022,12, 3515 7 o 9
indica es a possible in ec ion in he b eeding popula ion. Al hough we did no analyse
animals om he b eeding popula ion, acco ding o p e ious in o ma ion, adul sows a e
unlikely o be in ec ed in a ms ha accina e pigle s, bu eplacemen gil s may a i e
in ec ed om hei o igin a m [
33
–
35
]. Thus, i seems likely ha in he a m wi h posi i e
esul s in he ges a ion a ea, some animals ( eplacemen gil s/sows) may ha e been in ec ed
and shedding PCV2, he e o e con ibu ing o con amina ing he en i onmen o hese
acili ies.
The exis ence o PCV2 con amina ion in a m acili ies migh en ail a sou ce o in ec-
ion o suscep ible animals, con ibu ing o e-in ec ions and limi ing he possibili y o
achie ing an e en ual e adica ion o PCV2. Rega ding his, he con amina ion obse ed
in samples aken om he a m s a suppo s hei p obable ole as i al dissemina o s
among he di e en a m acili ies, ega dless o he o igin o he sou ce o con amina ion.
Fo example, i acili ies such as o ices o wa ehouses become con amina ed wi h PCV2
om an ex e nal sou ce, he a m s a can acili a e he sp ead o he i us o animal
dependencies [
13
,
36
]. Al hough biosecu i y measu es, such as he manda o y change o
boo s and clo hes be o e en e ing he a m a e e y equen , ou esul s sugges ha hey
may no o e he expec ed e icacy; mo eo e , he lack o s ic p o ocols which moni o
he compliance and he e ec i eness o hese measu es ag ees wi h wha has been s a ed
by o he au ho s [
37
]. The e o e, he implemen a ion o a speci ic biosecu i y p o ocol o
wo king in pens o dependencies used o house sick pigs would be ad isable.
Despi e PCV2 accina ion p og ammes ha ing been e ec i e in dec easing he p e a-
lence o he disease and i s associa ed losses, achie ing e adica ion seems o be mo e
complex since in ec ions usually end o e-eme ge when he accina ion p og ammes
cease. Ou esul s e idence he p esence o PCV2 in long- e m accina ed swine a ms and
poin ou he use ulness o examining su ace samples o de ec he i us, hus con ibu ing
o he knowledge o he in ec ion dynamics. Howe e , p o ided ha he numbe o a ms
included in his s udy is low, he ex apola ion o he esul s o a la ge popula ion may no
be comple ely eliable, since exposu e isks a y be ween a ms due o he di e ences in
managemen p ac ices and, u he mo e, in ec ion le els can change o e ime. Howe e ,
he de ec ion o i al con amina ion in some acili ies wi hou animals is no ewo hy, he e-
o e, hese a eas mus be conside ed in con ol p og ammes since hey could ac as i al
ese oi s.
E en so, he iabili y o he de ec ed pa icles o PCV2 DNA, as well as he assessmen
o he con amina ion lows, and he po en ial mechanisms o i al pe sis ence a e some
aspec s ha should be conside ed in u he s udies o achie e a be e cha ac e iza ion o
he PCV2 in ec ion dynamics and o iden i y he c i ical poin s o a u u e e adica ion.
5. Conclusions
Al hough PCV2 accina ion has been pe o med o yea s in he s udied a ms, he
p esence o PCV2 DNA in en i onmen al samples could indica e ha he i us is s ill
p esen in ce ain speci ic poin s o he a ms. PCV2 con amina ion was almos inexis en
in he animal housing acili ies bu was mo e equen in hose wi hou animals, such as
he o ices, he a m pe ime e o he a m s a ’s s ee elemen s, indica ing hei po en ial
ole as i al. As he p esence o PCV2 in hese c i ical poin s could imply a isk o he
e-eme gence o he disease i accina ion ceases, ou esul s poin ou he need o egula
and e ec i e cleaning and disin ec ion p ocedu es in hese acili ies and elemen s in o de
o minimize he isk o ein ec ion om en i onmen al sou ces.
Supplemen a y Ma e ials:
The ollowing suppo ing in o ma ion can be downloaded a : h ps:
//www.mdpi.com/a icle/10.3390/ani12243515/s1, qPCR s anda d cu e pa ame e s and cycle
h eshold alues o i s calcula ion.
Animals 2022,12, 3515 8 o 9
Au ho Con ibu ions:
Concep ualiza ion, G.L.-L., G.F., A.P. and J.M.D.-C.; me hodology, G.L.-L.,
A.P. and C.L.-N.; w i ing—o iginal d a p epa a ion, G.L-L., G.F., C.L.-N. and S.R.; w i ing— e iew
and edi ing, J.M.D.-C., P.D., S.R. and P.M.; unding acquisi ion, P.M. and G.L.-L.; supe ision, P.D.
and J.M.D.-C. All au ho s ha e ead and ag eed o he published e sion o he manusc ip .
Funding:
This esea ch has been unded by he Eu opean PCV2-Awa d sponso ed by Boeh inge
Ingelheim Animal Heal h, Ge many.
Ins i u ional Re iew Boa d S a emen :
Pig blood sampling was no pe o med o he analysis
desc ibed in he p esen pape . I was pe o med by e e ina y p ac i ione s o hei ou ine analyses
and an aliquo was gi en o he au ho s o analyse PCV2 i emia. The e o e, he animal/human
e hical commi ee app o al was no necessa y.
In o med Consen S a emen :
The samples om he a m s a we e included o assess hei possible
ole in pa hogen dissemina ion. In o med consen was ob ained o all he indi idual pa icipan s
included in he s udy ( his included a m s a ’s samples as well as hose om hei pigle s).
Da a A ailabili y S a emen :
The da a o his s udy a e a ailable om he co esponding au ho
upon easonable eques .
Acknowledgmen s:
We would like o hank COREN and he a me s o hei disposi ion o de elop
he p esen s udy and Ma ín Rod íguez Villa o his collabo a ion in he samplings and his echnical
assis ance.
Con lic s o In e es : The au ho s decla e no con lic o in e es .
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