Journal of Swine Health and Production — Volume 12, Number 3 123

SO, CP, RM: Department of Clinical and Population Sciences, College of Veterinary Medicine,University of Minnesota, St Paul, Minnesota.

Corresponding author: Dr Carlos Pijoan, University of Minnesota, College of Veterinary Medicine,Department of Clinical and Population Sciences, 1988 Fitch Ave #385, St Paul, MN 55108;Tel: 612-625-2245; Fax: 612-625-1210; E-mail: pijoa001@tc.umn.edu.

This article is available online at http://www.aasv.org/shap.html.

Oliveira S, Pijoan C, Morrison R. Evaluation of Haemophilus parasuis control in the nursery usingvaccination and controlled exposure. J Swine Health Prod. 2004;12(3):123-128.

Original researchPeer reviewed

Evaluation of Haemophilus parasuis control in the nurseryusing vaccination and controlled exposureSimone Oliveira, DVM, MS, PhD; Carlos Pijoan, DVM, MS, PhD; Robert Morrison, DVM, PhD, MBA

SummaryObjective: To evaluate the effectiveness ofthree control measures in reducing nurserymortality caused by Haemophilus parasuis,namely, a commercial vaccine, an autog-enous vaccine, and controlled exposureusing a low dose of live, virulentorganisms.

Methods: The experiments were performedin a multi-farm system experiencing highnursery mortality (> 4.8%) due to Hparasuis infection. In Experiment 1, pigswere vaccinated at weaning using a com-mercially available, one-dose H parasuisvaccine. In Experiment 2, pigs were vacci-nated at processing and at weaning with anautogenous vaccine. In Experiment 3, pigs

were orally inoculated at processing using abacterial suspension containing a total of105-6 colony forming units per mL of threeH parasuis strains prevalent in the studiedherd. Experiments 1 and 2 were repeatedfive times (5 consecutive weeks of produc-tion), and Experiment 3 was repeated ninetimes.

Results: Mortality in pigs exposed to Hparasuis was lower (P < .001) than that ingroups vaccinated with either commercialor autogenous vaccines.

Discussion: The lack of effect of parenteralvaccination may be due to lack of cross-protection between heterologous strains,timing of vaccination, and potential inter-ference of maternally-derived immunity.

The efficacy of controlled exposure likelyreflects the induction of homologous mu-cosal immunity preventing pathogen sys-temic invasion.

Implications: The use of controlled expo-sure of young pigs to the prevalent Hparasuis strains involved in nursery mortal-ity provides a valuable alternative for con-trol of H parasuis, compared to traditionalvaccination using commercial or autog-enous products.

Keywords: swine, Haemophilus parasuis,control, vaccination, controlled exposure

Received: July 10, 2003Accepted: November 15, 2003

H aemophilus parasuis is normallyisolated from the nasal cavity,tonsils, and trachea of healthy

pigs.1,2 This organism can potentially invadethe host and cause severe systemic infectioncharacterized by fibrinous polyserositis,arthritis, and meningitis. The factors in-volved in systemic invasion by H parasuishave not been clearly defined.3 The potentialinteraction between H parasuis and someviral agents, such as porcine reproductiveand respiratory syndrome virus (PRRSV),4

pseudorabies,5 and porcine circovirus type2 (PCV2),6 has been investigated. However,no direct association between any of theseagents and H parasuis has been conclusivelyestablished. The relationships between Hparasuis virulence and serovar,7 genotype,8

and whole-cell protein profiles9 have also

been evaluated. Although virulent strainsshare similar genotype and protein profiles,no specific virulence factors have been de-scribed for H parasuis.

Antibiotic treatments, or vaccination witheither commercial or autogenous products,may be used to control H parasuis. Theeffectiveness of autogenous vaccines againsthomologous challenge has been demon-strated.10,11 A lack of cross-protection be-tween different H parasuis serovars andstrains has also been reported.12-14 Com-mercial vaccines provide satisfactory ho-mologous protection against H parasuisstrains from the same serovar group.15,16

However, vaccination failures using com-mercially available products have also beendemonstrated, especially when the Hparasuis strains prevalent in the herd differ

from those included in the vaccine. In thiscase, autogenous vaccines may be used toreduce nursery mortality.17

Controlled exposure of 5-day-old pigs to alow dose of live, virulent H parasuis hasbeen recently proposed as an alternativemethod to control nursery mortality.18

This method is based on the hypothesisthat early colonization of piglets with theprevalent strains of H parasuis in the presenceof maternal immunity reduces the risk ofsystemic infection after weaning. This con-trol measure has been reported to reducemorbidity19 due to Streptococcus suis andmortality18 due to S suis and H parasuissystemic infection in affected nurseries. Inthe present study, control of H parasuis in aherd experiencing high nursery mortalitywas attempted using a commercial vaccine,an autogenous vaccine, or controlled expo-sure to live H parasuis in different cohorts.

Materials and methodsMulti-farm systemA multi-farm system (30,000 sows) experi-encing high nursery mortality due to Hparasuis infections 1 to 4 weeks after weaningwas selected to evaluate vaccination and

!Oliveira 3/31/04, 4:16 PM123

124 Journal of Swine Health and Production — May and June, 2004

controlled exposure as control measures.Tissue samples collected from nursery pigsin this system were positive by polymerasechain reaction (PCR) for PRRSV, PCV2,and swine influenza virus (SIV), and werenegative by PCR for Mycoplasmahyopneumoniae.

Pigs were weaned at an average of 21 daysof age and transferred to off-site nurseries.Each nursery contained eight rooms, whichwere filled with approximately 1000 pigseach. Pigs remained in the nursery for 7weeks.

Experimental designThe mortality data (3.25%, SD 1.1%) ob-tained from the last nonvaccinated groupof pigs housed in the nurseries used in thisstudy were used to calculate the sample sizeneeded to detect a 1% decrease in mortality,with α = .05 and a power of 80%. Threeexperiments were performed. In Experi-ment 1, pigs were vaccinated with a com-mercial H parasuis vaccine. In Experiment2, pigs were vaccinated with an autogenousvaccine containing two different strains. InExperiment 3, pigs were exposed to a lowdose of live, virulent H parasuis (three dif-ferent strains). Experiments were not con-current, and were performed using differentcohorts of pigs.

The experimental design used in each ex-periment is summarized in Table 1. In eachexperiment, a randomized complete blockdesign was used, with barn as the blockingfactor and room as the experimental unit.At the start of the trial, each barn was emp-tied, cleaned, and disinfected. One barnwas filled each week for 5 consecutiveweeks (Experiments 1 and 2) or 9 consecu-tive weeks (Experiment 3). Treatment wasallocated to rooms within barns by randomlyselecting the first room of the first barn tobe used for a control or vaccinated group,and consecutive rooms were systematicallyallocated thereafter.

Mortality data, farm visits, andsample collecting and processingFarm personnel were instructed to reportmortality data at each nursery closeout.Mortality data used for comparison betweencontrols and treated groups included pigsthat died and pigs that were euthanized.Farm visits, for the purpose of determiningthe prevalent strains of H parasuis in thenursery, were completed before the beginningof Experiments 2 and 3, and during the

fourth week after the first exposed pigs fromExperiment 3 had entered the nursery(Table 1). Samples collected for detectionof PRRSV, SIV, PCV2, and M hyopneumoniaewere tested by PCR at the Veterinary Diag-nostic Laboratory (University of Minnesota,St Paul, Minnesota). Samples collected forH parasuis isolation and detection by PCRwere processed at the laboratory of Dr Pijoan(College of Veterinary Medicine, Universityof Minnesota, St Paul, Minnesota).Haemophilus parasuis fingerprinting andgenetic analysis were also performed at DrPijoan’s laboratory.

VaccinesPigs in Experiment 1 were vaccinated intra-muscularly at weaning (21 days of age) usinga single dose of a commercially available Hparasuis bacterin (Ingelvac HP-1; BoehringerIngelheim Vetmedica, Inc, St Joseph, Mis-souri). This vaccine is reported to protectagainst heterologous challenge.20

In order to select the H parasuis strains forinclusion in the autogenous vaccine (Ex-periment 2), 32 nursery pigs were necropsied,including 15 clinically affected pigs and 17pigs found dead, and swabs for H parasuisisolation were collected from pleura, peri-

cardium, peritoneum, joints, and meninges,plus lung tissue. Swabs were cultured ontoblood agar with a nurse Staphylococcusaureus streak, and plates were incubated at37˚C for 24 hours. Collected swabs werealso tested by PCR21 to assess the preva-lence of H parasuis systemic infection inthe nursery. Haemophilus parasuis isolateswere genotyped by enterobacterial repetitiveintergenic consensus-based PCR (ERIC-PCR) as described previously.8 Genomicfingerprints were analyzed using theBioNumerics software (Applied Maths,Kortrijk, Belgium), and one representativeisolate from each prevalent group of Hparasuis strains was included in the autog-enous vaccine. Haemophilus parasuis isolates(one strain from genotype group A and onestrain from genotype group B; Figure 1)were forwarded to Boehringer IngelheimVetmedica, Inc (St Joseph, Missouri),where the autogenous vaccine was producedwith an adjuvant similar to that used in thecommercial vaccine. Haemophilus parasuiswas inactivated using 0.3% formalin. Thevaccine was formulated to contain a mini-mum of 108 of H parasuis organisms permL. Pigs were vaccinated intramuscularly at

tnemirepxE lortnoCerusaem

gnimiT smoorfo.oN 1 fo.oNsetacilper

# etadtratS lortnoC detaerT1 1002ceD laicremmoC

eniccav 2tA

gninaew2 6 5

2 2002luJ suonegotuAeniccav 3

gnissecorptAtadnagninaew

4 4 5

3 3002naJ dellortnoCerusopxe 4

tAgnissecorp

2 2 9

Table 1: Experimental design used to assess the effectiveness of vaccinationand controlled exposure for control of nursery mortality due to Haemophilusparasuis infection

1 Each nursery barn contained eight rooms each with a capacity for 1000 pigs. Onebarn housing experimental groups was filled each week for 5 consecutive weeks(Experiments 1 and 2) or 9 consecutive weeks (Experiment 3).

2 Ingelvac HP-1; Boehringer Ingelheim Vetmedica, Inc, St Joseph, Missouri. Pigs werevaccinated once intramuscularly at weaning (21 days of age).

3 The autogenous vaccine (killed bacterin with the same adjuvant used in thecommercial vaccine) included one representative H parasuis isolate from each groupof prevalent strains (A and B) recovered from nursery pigs in Experiment 1. Pigs werevaccinated intramuscularly with a dose of 2 mL at processing (5 days of age) and atweaning (21 days of age).

4 The inoculum included one representative H parasuis isolate from each group ofprevalent strains (A, B, and C) recovered from nursery pigs in Experiment 2. Pigs wereinoculated orally at processing (5 days of age) using a spray pump that delivered a 1-mL dose of bacterial suspension containing approximately 105-6 colony formingunits per mL.

!Oliveira 3/31/04, 4:16 PM124

Journal of Swine Health and Production — Volume 12, Number 3 125

Figure 1: Cluster analysis by means of enterobacterial repetitive intergenic consensus-based PCR (ERIC-PCR) fingerprintingof 30 Haemophilus parasuis isolates recovered from affected nursery pigs in a production system experiencing highmortality due to H parasuis 1 to 4 weeks after weaning at 21 days of age. The scale indicates the percentage of geneticsimilarity. Columns (left to right) indicate isolate identification, site of isolation, and date of isolation. Three major clusters ofprevalent strains are identified (A, B, and C).

processing (5 days of age) and at weaning(21 days of age) using a 2-mL dose. Nega-tive control pigs were not vaccinated.

Inoculum preparation andadministrationForty-three animals were necropsied, in-cluding 41 clinically affected pigs and twopigs found dead. Pools of lung tissue ob-tained from these pigs were tested forPRRSV, PCV2, SIV, and M hyopneumoniaeby PCR. Samples were collected and the

obtained H parasuis isolates were character-ized as described. One representative Hparasuis isolate from each group of prevalentstrains (A, B, and C) was included in theinoculum used for controlled exposure(Figure 1). Haemophilus parasuis isolateswere cultured onto chocolate agar and in-cubated in a candle jar at 37˚C for 24hours. A seed culture containing the preva-lent H parasuis strains isolated from affectedanimals was prepared by harvesting thebacterial growth from chocolate agar plates

and suspending it in 10% sterile skimmilk. The bacterial suspension was distrib-uted in 1-mL aliquots and stored at -20˚Cuntil use. The final inoculum was preparedby diluting a 1-mL aliquot in 1 liter of ster-ile phosphate buffered saline (PBS).22 Theinoculum was then transferred to plasticspray pumps and maintained at 4˚C untiluse. A survivability test was performed inorder to assess the viability of the inoculumafter dilution in PBS. The diluted inoculumwas maintained at 4˚C and bacterial counts

!Oliveira 3/31/04, 4:16 PM125

126 Journal of Swine Health and Production — May and June, 2004

were performed at 0, 4, 8, 24, 48, 72, 96,120, 144, 168, and 192 hours after dilu-tion (Figure 2).

Pigs were inoculated with 105-6 colony-forming units (CFU) per mL by the oralroute. At processing, each piglet in thetreatment group received an oral spray(1-mL dose) of the inoculum containing105-6 CFU per mL. Pigs in the controlgroup were not exposed to H parasuis. Thedelivered amount of inoculum was validatedby collecting the volume delivered by onespray in a microcentrifuge tube. All spraypumps were permanently regulated to delivera 1-mL dose by using a pen marker. Thesame spray pumps were used throughoutthe whole experiment. Four weeks after thefirst group of inoculated pigs had beenweaned, two or three pigs from eachtreated and control room were selected foreuthanasia, on the basis of clinical signscharacteristic of H parasuis systemic infec-tion. Isolates from these pigs were culturedonto blood agar with a nurse streak of Saureus, and plates were incubated at 37˚Cfor 24 hours. Swabs were tested by PCRfor H parasuis. Haemophilus parasuis iso-lates were genotyped by ERIC-PCR andcompared using the BioNumerics software.

Statistical analysisThe room (air space) was used as the ex-perimental unit. A main effect ANOVAwas performed in Statistica (StatSoft, Inc,Tulsa, Oklahoma), with percent mortality

at closeout as the dependent variable androom and treatment as the independentvariables. The average mortality in controland treated rooms was compared.

ResultsIsolation, PCR, and genotyping ofH parasuisHaemophilus parasuis isolation and PCRresults are summarized in Table 2. Based onPCR results, prevalence of H parasuis sys-temic infection in the nursery was 50.0%at the first visit, 53.5% at the second visit,

and 35.3% at the third visit. Two prevalentgenotypes (A and B) were identified amongthe isolates recovered from seven pigs inthe first farm visit, and a third group ofprevalent strains (genotype C) wasidentified among the isolates recoveredfrom 20 pigs necropsied at the second farmvisit. Isolates A and B were found to be stillprevalent 1 year after the first isolation(Figure 1). At the third visit, when the firstgroup of inoculated pigs had been in thenursery for 4 weeks, only strains A and Bwere recovered from clinically affected ani-mals. Haemophilus parasuis was mainly iso-lated from nontreated control pigs (four offive isolates, compared to one isolate recov-ered from the joint of an inoculated pig).

In addition to H parasuis, S suis was iso-lated, during the first farm visit, from thelungs of six pigs found dead and fromjoints of two euthanized pigs. Pasteurellamultocida (20 of 43 pigs) and S suis (six of43 pigs) were also isolated from lungsamples collected during the second farmvisit. Pools of lung tissue collected duringthe second farm visit from pigs 2 weekspostweaning were PCR-negative forPRRSV, PCV2, SIV, and M hyopneumoniae.Pools from pigs 3 and 4 weeks postweaningwere PCR-positive for PRRSV and PCV2.Pools from pigs 5 weeks postweaning werePCR-positive for PRRSV, PCV2, and SIV.

Experiment 1 (commercial vaccine)Statistical analysis showed that percentmortality was normally distributed acrossall rooms, with an average of 5.1% (SD

Figure 2: Graph showing viable counts of the Haemophilus parasuis inoculumused in the controlled exposure of 5-day-old pigs. Counts were made at 0, 4, 8,24, 48, 72, 96, 120, 144, 168, and 192 hours after dilution in phosphate bufferedsaline. The bacterial suspension was maintained at 4˚C during and afterdilution.

etaDfo

mraftisiv

sgipforebmuNdeisporcen

niemiTeht

yresrun)skeew(

sgipfo.oN)%(evitisop 2

tnelaverPsepytoneg

dezinahtuE deiD latoT RCP noitalosIvoN1002

51 71 23 6–2 61)0.05(

7)88.12(

B,A

tcO2002

14 2 34 5–2 32)84.35(

02)15.64(

C,B,A

raM3002

71 0 71 4–3 6)92.53(

5)14.92(

B,A

Table 2: Haemophilus parasuis isolation and polymerase chain reaction (PCR)results for swabs collected from nursery pigs euthanized or found dead1

1 Each off-site nursery barn, containing eight rooms each with a capacity for 1000 pigs,was filled weekly with a cohort of pigs weaned at an average of 21 days of age. Highnursery mortality due to H parasuis infections was occurring in this productionsystem 1 to 4 weeks after weaning.

2 Swabs collected from pleura, pericardium, peritoneum, joints, and meninges, pluslung tissue, were cultured for H parasuis isolation and tested by PCR. Pigs positive byisolation were also positive by PCR. Isolates were genotyped by enterobacterialrepetitive intergenic consensus-based PCR.

0

1

2

3

4

5

6

7

100 150 200

Hours

Co

lon

y fo

rmin

g u

nit

s /m

L (lo

g)

0 50

!Oliveira 3/31/04, 4:16 PM126

Journal of Swine Health and Production — Volume 12, Number 3 127

1.74%). Average mortality was 4.8% (SD1.17%) in nonvaccinated groups (n = 10)and 5.2% (SD 1.22%) in vaccinated groups(n = 30). Room was significantly associatedwith mortality (data not shown), whiletreatment was not.

Experiment 2 (autogenous vaccine)As in Experiment 1, percent mortality ap-peared to be normally distributed across allrooms, with an average of 7.4% (SD 3.28%).Average mortality was 7.7 % (SD 2.02%)in nonvaccinated groups (n = 20) and 7.1%(SD 2.47%) in vaccinated groups (n = 20).Neither room nor treatment wassignificantly associated with mortality.

Experiment 3 (controlled exposure)Across all rooms, percent mortality appearedto be normally distributed, with an averageof 10.4% (SD 5.99%). Average mortalitywas 14.3% (SD 4.98%) in control groups(n = 18) and 6.4% (SD 1.79%) in treatedgroups (n = 18). Treatment was significantlyassociated with mortality (P < .001), whileroom was not.

DiscussionResults of this study showed that nurserymortality was not affected by vaccinationusing either commercial or autogenous vac-cines, while mortality was lower in pigsexposed at 5 days of age to a low dose oflive, virulent H parasuis. Although thesethree control measures were tested in thesame herd, they were used in differentpopulations of pigs at different time points.Considering these factors, care should betaken that each study be assessed individually.

The lack of cross-protection between thecommercial vaccine strain and the preva-lent H parasuis strains in the herd is a po-tential factor that might have influencedthe lack of effectiveness of the selected vac-cine. Other factors to be considered includeincorrect timing of vaccination, interferenceby maternally-derived immunity, the doseused, and possibly a need for a booster vac-cination, although the manufacturer’s labeldirections were to use only one dose.

In the second trial, the failure of vaccinationusing the autogenous product was unexpect-ed, since homologous protection has beenreported to be effective.10,17 Previous resultsobtained in field trials suggest that use ofautogenous vaccines may be a viable alter-native to control H parasuis when commer-cial products are not effective.17 However,in the present study, it was demonstrated

that this may not be true for all swineherds. Again, several factors might haveinfluenced the effectiveness of the autog-enous vaccine, especially timing of vaccina-tion and interference of maternal immunity.In the present study, pigs were vaccinatedwith the autogenous product at processingand at weaning due to the early onset of Hparasuis systemic infection in the nursery(1 to 4 weeks after weaning). When pigsare initially vaccinated at such an early age,there is always a concern regarding interfer-ence of maternal immunity in the develop-ment of the active immune response inducedby the vaccine. However, some studies havedemonstrated that maternal immunity maynot always interfere with the immune re-sponse. Solano-Aguilar et al15 tested a com-mercial vaccine containing H parasuisserovars 4 and 5, using two doses, andshowed that vaccinated pigs born to vacci-nated gilts were protected against challengewith a virulent H parasuis strain, whereassome vaccinated pigs born to nonvaccinatedgilts developed central nervous system signsand lameness. Baumann and Bilkei16 alsodemonstrated that vaccination of sows andtheir piglets resulted in protection againsthomologous challenge. Further studies arenecessary to better characterize the potentialinterference of maternal antibodies in pigvaccination. Another factor that mighthave influenced the outcome observed inExperiment 2 was the nonrandomized dis-tribution of experimental groups in roomswithin barns. This difference may have im-paired the observation of a greater effec-tiveness of the autogenous vaccine in thetreatment group.

Another potential factor to be considered isthat the autogenous vaccine was missingone of the prevalent genotypes later identifiedin the nursery (type C). Genotyping resultsshowed that strains A and B, which wereisolated in the previous year, were stillprevalent in the herd. A third prevalentstrain (C) was identified after the secondsampling. This strain was not included inthe autogenous vaccine. Strain C was laterincluded in the inoculum used for controlledexposure. A general increase in mortalitywas observed in the second experimentcompared with the first experiment. Thisincrease in mortality coincided with aPRRS outbreak in the system. Mortalitywas even higher in the control group afterthe third experiment compared with con-trols in the first and second experiments.

This time, SIV was identified as the mainagent co-infecting nursery pigs. However,the association between PRRS or SIV andH parasuis co-infection in the nursery hasnot been established.

Regarding controlled exposure, Pijoan etal23 hypothesized that early mucosal colo-nization of piglets with the herd’s prevalentstrains of H parasuis while they are stillprotected by maternal immunity mightreduce the risk of systemic infection afterweaning. Following this hypothesis, itwould be desirable that a large number ofpigs be exposed to these potentially virulentstrains before they become susceptible (ie,with waning of maternal antibody levels).Some practices currently used in modernswine production, such as early weaningand three-site production systems, mayreduce exposure to these virulent strains, orspread of infection among pigs. Kirkwoodet al24 demonstrated that levels of coloniza-tion by H parasuis appear to be influencedby weaning age. Their study showed thatlevels of colonization were lower in pigsweaned at 14 days than in pigs weaned at28 days.

The mechanisms involved in developmentof protective immunity after controlledexposure to H parasuis have not beenclearly defined. Nielsen25 demonstratedthat exposure of specific-pathogen-free pigsto an aerosol containing live, apathogenicH parasuis strains resulted in developmentof circulating antibodies, and protectedpigs against heterologous challenge with avirulent strain. However, further studies arenecessary to better characterize the mecha-nisms involved in development of protectiveimmunity by pigs exposed to live, virulentH parasuis.

In the present study, nursery mortality wassignificantly lower in treated groups aftercontrolled exposure than in untreated con-trol groups. We have previously reportedthat after colonization of piglets with a lowdose of live, virulent H parasuis, nurserymortality was 36.6% lower in the exposedgroup than in the control group.18 Fourfactors may have improved the results ofthe colonization trial in the present studycompared with our previous report. Thesample size and number of replicates (8000pigs per group, five to nine replicates) usedin the present study were considerablylarger than those in the previous report (50pigs per group, two replicates). The herd

!Oliveira 3/31/04, 4:16 PM127

128 Journal of Swine Health and Production — May and June, 2004

used in the present study had a greaterprevalence of systemic infection and mortal-ity due to H parasuis. The dose of inoculumused in 5-day old pigs was higher in thepresent study (1 × 105-6 CFU per mL) thanin the previous study (7 × 103 CFU permL). The allocation of treated and controlgroups in the nursery, as well as the experi-mental unit used for statistical analysis,differed between studies. In the presentstudy, treated and control groups were allo-cated to different rooms in a single barn,and room, or air space, was considered theexperimental unit. In our previous study,all groups were allocated to different pensin the same nursery barn (ie, the same airspace), and the pig was considered the ex-perimental unit.

Results obtained in the present study dem-onstrated that nursery mortality may besignificantly reduced after early exposure ofpigs to live, virulent H parasuis, comparedwith the results of using autogenous andcommercial vaccines. Controlled exposurehas several advantages compared with tra-ditional vaccination, including lower costand reduction of workload. Furthermore,timing does not seem to be an issue withcontrolled exposure, whereas maternal im-munity may interfere with pig vaccination.There are some concerns regarding thesafety of this method. The interaction be-tween PRRS virus and H parasuis has notbeen scientifically demonstrated. However,field experiences suggest that these organismsmay co-infect nursery pigs, resulting inincreased mortality compared with eitherpathogen alone. It would appear to becounterindicated to inoculate pigs withlive, virulent H parasuis if PRRS virus in-fection is active in the sow farm. The vacci-nation results obtained in this study suggestthat the use of commercial and autogenousvaccines to control H parasuis infectionsmust be critically evaluated.

Implications• Controlled exposure may be an

alternative to other methods forcontrol of H parasuis systemicinfection in the nursery.

• Under the conditions of this study,controlled exposure was more effectivethan use of autogenous or commercialvaccines in reducing nursery mortalitydue to H parasuis systemic infection.

• Although the interaction of PRRSVand H parasuis has not beenscientifically proven, as a safety

measure, nursery pigs should not beexposed to live, virulent H parasuiswhen there is active PRRSV infectionin the sow herd.

AcknowledgementsThe authors would like to thank the Na-tional Pork Board for funding this project.We also would like to thank Dr ButchBaker, Ken Cantrell, and Dr John Kolb forcollaborating in this project.

References1. Møller K, Kilian M. V factor-dependent mem-bers of the family Pasteurellaceae in the porcine up-per respiratory tract. J Clin Microbiol.1990;28:2711-2716.

2. Vahle JL, Haynes JS, Andrews JJ. Experimentalreproduction of Haemophilus parasuis infection inswine: clinical, bacteriologic, and morphologicfindings. J Vet Diag Invest. 1997;7:476-480.

3. Nicolet J. Overview of the virulence attributes ofHAP-group bacteria. Can J Vet Res. 1990;54:S12-S15.

4. Solano GI, Segales J, Collins JE, Molitor TW,Pijoan C. Porcine reproductive and respiratory syn-drome virus (PRRSv) interaction with Haemophilusparasuis. Vet Microbiol. 1997;55:247-257.

5. Narita M, Kawashima K, Matsuura S, UchimuraA, Miura Y. Pneumonia in pigs infected with pseu-dorabies virus and Haemophilus parasuis serovar 4. JComp Path. 1994;110:329-339.

6. Kim J, Chung H, Jung T, Cho W, Choi C, ChaeC. Postweaning multisystemic wasting syndrome ofpigs in Korea: prevalence, microscopic lesions andcoexisting microorganisms. J Vet Med Sci.2002;64:57-62.

7. Kielstein P, Rapp-Gabrielson VJ. Designation of15 serovars of Haemophilus parasuis on the basis ofimmunodiffusion using heat-stable antigen extracts.J Clin Microbiol. 1992;30:826-865.

8. Oliveira S, Blackall PJ, Pijoan C. Characterizationof the diversity of Haemophilus parasuis field isolatesby serotyping and genotyping. Am J Vet Res.2003;64:435-442.

9. Nicolet J, Paroz PH, Krawinkler M. Polyacryla-mide gel electrophoresis of whole-cell proteins ofporcine strains of Haemophilus. Int J Syst Bacteriol.1980;30:69-76.

10. Smart NL, Miniats OP. Preliminary assessmentof a Haemophilus parasuis bacterin for use in specificpathogen free swine. Can J Vet Res. 1989;53:390-393.

11. Miniats OP, Smart NL, Ewert E. Vaccination ofgnotobiotic primary specific pathogen-free pigsagainst Haemophilus parasuis. Can J Vet Res.1991;55:33-36.

12. Miniats OP, Smart NL, Rosendal S. Cross-pro-tection among Haemophilus parasuis strains in im-munized gnotobiotic pigs. Can J Vet Res. 1991;55:37-41.

13. Rapp-Gabrielson V, Kocus GJ, Clark JT,Stephen KM. Haemophilus parasuis: immunity inswine after vaccination. Vet Med. 1997;92:83-90.

14. Takahashi K, Nagai S, Yagihashi T, Ikehata T,Nakano Y, Senna K, Maruyama T, Murofushi J. Across-protection experiment in pigs vaccinated withHaemophilus parasuis serovars 2 and 5 bacterin, andevaluation of a bivalent vaccine under laboratoryand field conditions. J Vet Med Sci. 2001;63:487-491.

15. Solano-Aguilar GI, Pijoan C, Rapp-GabrielsonV, Collins J, Carvalho LF, Winkelman N. Protectiverole of maternal antibodies against Haemophilusparasuis infection. Am J Vet Res. 1999;60:81-87.

16. Baumann G, Bilkei G. Effect of vaccinatingsows and their piglets on the development ofGlässer’s disease induced by a virulent strain ofHaemophilus parasuis. Vet Rec. 2002;151:18-21.

17. Smart NL, Hurnik D, MacInnes JI. An investi-gation of enzootic Glasser’s disease in a specific-pathogen-free grower-finisher facility using restric-tion endonuclease analysis. Can Vet J. 1993;34:487-490.

18. Oliveira S, Batista L, Torremorell M, Pijoan C.Experimental colonization of piglets and gilts withsystemic strains of Haemophilus parasuis and Strepto-coccus suis to prevent disease. Can J Vet Res.2001;65:161-167.

19. Torremorell M, Pijoan C, Dee S. Experimentalexposure of young pigs using a pathogenic strain ofStreptococcus suis serotype 2 and evaluation of thismethod for disease prevention. Can J Vet Res.1999;63:269-275.

20. Ingelvac HP-1 [package insert]. St Joseph, Mis-souri: Boehringer Ingelheim.

21. Oliveira S, Galina L, Pijoan C. Development ofa PCR test to diagnose Haemophilus parasuis infec-tions. J Vet Diag Invest. 2001;13:495-501.

22. Morozumi T, Hiramune T. Effect of tempera-ture on the survival of Haemophilus parasuis inphysiological saline. Natl Inst Anim Health Q. (Jpn).1982;22:90-91.

*23. Pijoan C, Torremorell M, Solano G. Coloniza-tion patterns by the bacterial flora of young pigs.Proc AASP. 1997:463-464.

24. Kirkwood RN, Rawluk SA, Cegielski AC, OttoAJ. Effect of pig age and autogenous sow vaccina-tion on nasal mucosal colonization of pigs byHaemophilus parasuis. J Swine Health Prod.2001;9:77-79.

25. Nielsen R. Pathogenicity and immunity studiesof Haemophilus parasuis serovars. Acta Vet Scand.1993;34:193-198.

* Non-refereed reference.

!Oliveira 3/31/04, 4:16 PM128