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Case Study
Peer-reviewed
Effect of pig age and autogenous sow vaccination on nasal
mucosal colonization of pigs by Haemophilus parasuis
Roy N. Kirkwood, DVM, PhD; Shirley A. Rawluk; Artur C. Cegielski,
DVM; Arlene J. Otto
RNK: FAEMS, Royal Veterinary College, Hawkshead Lane, Herts
AL9 7TA, UK,
e-mail: rkirkwoo@rvc.ac.uk; SR,AC,AO: Alberta Agriculture,
Edmonton, Alberta,
Canada
Kirkwood RN, Rawluk SA, Cegielski AC, et al. Effect of pig
age and autogenous sow vaccination on nasal mucosal colonization
of pigs by Haemophilus parasuis. J Swine Health Prod.
2001;9(2):77-79. Also available in PDF
format (108k).
Summary
This report describes an attempt to evaluate the effect of
piglet age (with or without weaning), sow parity, and sow vaccination,
on the timing of nasal mucosal colonisation of piglets by Haemophilus
parasuis. We also determined the serotypes involved and compared
serotypes isolated from the nasal mucosa and the trachea. Compared
to tracheal swabs, nasal mucosal swabs were more easily performed
and also more consistently yielded H parasuis. Serotypes
obtained from each site were the same. A lower level of colonisation
was found within the litters of young sows and a low level of
colonization by H parasuis at weaning likely predisposes
piglets to clinical disease in the nursery, assuming the presence
of a virulent serotype. We found that more than one serotype of
H parasuis was present in the herd and that vaccination
of sows did not influence the timing of apparent colonization
or the serotypes prevalent within a litter.
Keywords: swine, Haemophilus
parasuis, vaccination
Received: May 16, 2000
Accepted: November 28, 2000
Bacteria that colonize
mucosal surfaces during the first two weeks of life have been
termed early colonizers.1 Assuming adequate transfer
of specific colostral immunoglobulins, immunity against early
colonizers (e.g., Haemophilus parasuis) is good in early
lactation but declines progressively. Between about 10 and 15
days of age, antibody levels no longer prevent colonization, but
do limit it such that clinical disease is prevented.1
With time, level of H parasuis colonization increases to
the point where the pigs develop their own active immunity (about
3 weeks of age). Therefore, there is a balance between infection
and resistance such that the piglets are subjected to a relatively
slow and controlled exposure to a potential pathogen that allows
them the time to developtheir immunological defences.
Short lactations, high health status, and the isolated swine
populations associated with modern swine production have increased
the incidence and severity of disease due to infection with H
parasuis (Glasser's disease).2,3 To be able
to implement strategies to control H parasuis requires
a knowledge of when pigs become colonized, the effect of piglet
age on the proportion of the litter that becomes colonized, and
the role of the immune status of the sow. An earlier study has
demonstrated that, when the sows are free of H parasuis
and hence fail to provide passive immunity to their litters, epizootic
Glasser's disease may occur.4 More recent studies have
shown that maternally derived passive immunity is essential for
protection against H parasuis challenge3 but
that sow immunity (and hence pig immunity via colostral immunoglobulins)
following vaccination may be serovar specific.2 While
vaccination of sows may improve the level of protection afforded
to the litter, it is possible that it may also prolong the period
of slow colonization. For early weaned pigs, the effect of this
could be a reduction in the proportion of a litter that is colonized
at weaning and consequently an increased risk of clinical disease
in the nursery. To further examine the relationship between sow
immune status and piglet age, studies were undertaken using a
herd positive for H parasuis.
Case description
All pigs used in these studies were from the University of
Alberta swine research unit and the experimental procedures were
approved by the University of Alberta Animal Care committee. Herd
composition consisted of a 100-sow commercial farrow-to-finish
herd housed in a single barn, and a second component for reproduction
research where sows were housed in separate breeding-gestation
and farrowing barns and were killed prior to production of a second
litter. Nursery rooms were operated all in-all out, by room. All
buildings were on the same site. Gilts for both herd components
were purchased from the same source and the lactation length was
25 to 28 days,
except where indicated otherwise for specific experiments. Piglets
from both components were co-mingled at weaning.
To confirm that H parasuis was present in the herd,
nasal swabs were obtained from 11 randomly selected pigs in the
nursery after wiping the nasal planum rostrale with alcohol. Swabs
were submitted to the Alberta Agriculture bacteriology laboratory
(Edmonton, Alberta) for culture. Nasal swabs were inoculated into
modified Amies clear transport medium and delivered to the laboratory
within 60 min of collection. Swabs were cultured to both enrichment
(modified Haemophilus Mueller Hinton medium, H, Difco, Detroit,
Michigan; [H]) and selective enrichment (as above with either
3 µg per mL vancomycin [HV] or 0.1 µg per mL crystal
violet and 4.5 µg per mL bacitracin [HCB]) primary plating
media in order to optimize recovery of
H parasuis.Organisms were presumptively identified as H
parasuis if they were V-factor dependent, positive for catalase,
mannose, and saccharose, and negative for indole, urease, lactose,
mannitol, raffinose, sorbitol, and CAMP; and if they grew luxuriously
on H, HV, and HCB plating media.
Haemophilus parasuis was isolated from 11 of 11 swabs
cultured. Some colonies cultured from four of 11 swabs were identified
as most likely to be H parasuis, since they showed the
appropriate biochemical characteristics except that acid production
in mannose and (or) saccharose was usually absent and, when present,
was observed as a delayed weak reaction. Also, these colonies
either failed to grow or grew sparsely on HCB medium.
Study One
The litters from eight sows were used. Four of the litters
were derived from multiparous sows housed in the commercial production
barn and were weaned at 28 days of age. The remaining four litters
were derived from primiparous sows housed in the reproduction
research farrowing barn and were weaned at 14 days of age. Within
each weaning group, the nasal passages of all piglets from each
of the four litters were swabbed at 14 and 28 days of age, and
the swabs were cultured for H parasuis. Serotyping of isolates
was not done.
All piglets were weaned into the same nursery, but each weaning
age occupied the nursery at a different time. Pig health was monitored
daily during the nursery period. At 14 days of age, 53% of piglets
from multiparous sows were sufficiently colonized by H parasuis
to yield a positive culture, while none of the piglets from primiparous
sows yielded a positive culture (Chi square, P<.001).
At 28 days of age, nearly all (97%) of the piglets that remained
with their dams yielded a positive culture, but only 50% of pigs
weaned at 14 days of age yielded a positive culture at 28 days
of age (Chi square, P<.01). These results indicate that
the level of apparent colonization was reduced either by low parity
or barn and, further, that from 14 days of age, the rate of apparent
colonization of pigs was slower if the pigs were weaned. Weaning
delayed apparent colonization in this study, likely as a consequence
of there being relatively few pigs in the nursery with a sufficient
H parasuis load to allow efficient pig-to-pig infection.
In contrast, unweaned pigs continued to have intimate contact
with their dams, the presumed source of H parasuis. Eighteen
days after weaning, a disease outbreak occurred in the pigs that
had been weaned at 14 days, and three died. Post mortems revealed
polyserositis, but a definitive etiology was not established.
Because the above data was confounded by parity and barn, we
performed another replicate using four litters from each barn,
weaned at 28 days of age, but all from primiparous sows. Piglets
(n=6 or 7 per litter) were nasal swabbed at 14 and 28 days of
age and the swabs were cultured for H parasuis.
Serotyping of the isolates was not done. At 14 days of age, 39%
of piglets in the commercial barn, and 25% of piglets in the reproduction
research barn, were culture-positive for H parasuis, and
this difference was not significant (Chi square, P=.27).
By the time of weaning at 28 days of age, 96 to 100% of all piglets
were culture-positive. The reason that the level of apparent colonization
in the reproduction research barn was higher in this replicate
than in the first was not resolved.
Study Two
This study was undertaken to determine the prevalent serotypes
of H parasuis present within the herd and to examine the
possibility that the serotypes identified would be different depending
on whether the nasal cavity or trachea was swabbed. At 25 days
(preweaning) and 50 days of age, 31 pigs were anesthetized with
xylazine (2 mg per kg, IM) and ketamine (10 mg per kg, IM), and
nasal cavity and tracheal swabs were collected. The tracheal swabs
were guarded. If colonies were identified as either H parasuis
or H parasuis-like, a representative colony of each bacterial
type from each pig was submitted for serotyping (Bayer, Worthington,
Minnesota). Additionally, colonies that appeared atypical on growth
media and (or) biochemical reactions were also sent for serotyping.
Of the 31 nasal swabs obtained at 25 days of age, serotype
9 was isolated from 19 swabs, a non-typable serotype (NT) from
one swab, and serotype 9 plus NT from 11 swabs. Serotype 9 was
isolated from 14 tracheal swabs and NT from one tracheal swab.
Sixteen swabs were negative for Hparasuis. Only 29 pigs
were swabbed at 50 days of age. Of the 29 nasal swabs obtained
at 50 days of age, serotype 9 was isolated from 12 swabs, NT serotype
from seven swabs, and both serotypes 9 and NT from eight swabs.
Two swabs were negative for H parasuis. Tracheal swabs
obtained at 50 days of age yielded seven serotype 9, one NT, and
two serotype 9 plus NT. Nineteen swabs were negative for Hparasuis.
When the organisms identified as most likely H parasuis
were serotyped, all were
H parasuis serotype 9. With the exception of two pigs at
50 days of age, tracheal swab isolates were always represented
by the same serotype as that isolated from nasal swabs (e.g.,
if the nasal swab yielded either serotype 9 or NT or both, either
serotype 9 and NT or both were isolated from the tracheal swab).
However, the success of isolation from tracheal swabs was considerably
less than that from nasal swabs. A comparison of H parasuis
serotypes recovered from pigs swabbed at the two different ages
revealed that six pigs carrying only serotype 9 at 25 days yielded
only NT at 50 days. A further eight pigs that carried only serotype
9 at 25 days yielded both serotypes 9 and NT at 50 days. In contrast,
ten pigs that carried both serotypes 9 and NT at 25 days yielded
only serotype 9 at 50 days.
Study Three
The objective of this study was to determine the effect of
maternal vaccination against H parasuis on the timing and
cumulative incidence of apparent colonization of pig nasal mucosa
by H parasuis. Of 17 sows housed in the commercial barn,
nine received an autogenous anti-Hparasuis vaccine at 5
and 2 weeks pre-farrowing, and eight served as unvaccinated controls.
The vaccine was prepared commercially (Bayer Laboratories, Worthington,
Minnesota) using one serotype 9 and one NT organism isolated during
Study Two. The reason for using only one NT organism was that
five NTs were determined to have the same outer membrane protein
profiles, and so it was reasonable to conclude that they represented
a single serotype (VJ Rapp-Gabrielson, personal communication).
All pigs in each litter were nasally swabbed at 14, 21, and 28
days of age and the swabs were cultured for H parasuis.
Representative colonies from two pigs from each litter were submitted
for serotyping.
To confirm a greater intake of colostral anti-H parasuis
antibodies by pigs nursing vaccinated sows, each piglet was bled
at 7 days of age and serum titers against Hparasuis were
determined by ELISA (Biovet, St. Anthony, Minnesota). Since the
sow was the experimental unit, the mean titer for each litter
was calculated and the treatment titer is the mean of the litter
titers. Vaccination of the sow against Hparasuis was associated
with elevated anti-H parasuis titers in pigs 7 days of
age (Table 1). There appeared to be no association between pig
serum titers within a litter and the proportion of the litter
that was apparently colonized at 14 days. Overall, there was no
apparent effect of sow vaccination on the number of pigs within
a litter that were apparently colonized by Hparasuis at
any of the ages examined. Similarly, there was no effect of sow
vaccination on the serotypes of H parasuis recovered from
the litters (Table 1).
Discussion
The present results serve to remind us that pigs nursing young
sows will likely have a reduced exposure to early-colonizing normal
mucosal flora. The potential clinical significance of this is
illustrated by the example of a new herd that was farrowing too
many primiparous sows for the available facilities. This necessitated
a temporary shift in weaning age from 16 to 18 days to 11 to 14
days and, although a causal relationship was not proven, the nursery
soon suffered an outbreak of Glasser's disease. Further, it is
interesting to note that during the first replicate of Study One,
an outbreak of disease occurred 18 days into the nursery phase,
involving pigs weaned at 14 days of age. Three pigs died and post
mortems were suggestive of Glasser's disease (polyserositis),
although a Streptococcus suis etiology could not be ruled
out. The occurrence of disease specifically in that group of pigs
is consistent with the theory proposed by Pijoan,1
that a low level of colonization by H parasuis (or S
suis) at weaning predisposes piglets to clinical disease in
the nursery.
The conclusions to be drawn from Study Two are that nasal swabbing
provides an effective means of establishing the presence of H
parasuis and the prevalent serotypes. Also, as previously
shown by others,5,6 a herd may be infected concurrently
with different serotypes of H parasuis, which may occur
singly or in combination within a pig. Further, within the limits
of the serotypes within a herd, the prevalent serotype within
a pig may change over time.
Finally, the results of Study Three indicate that vaccination
of the sow alone did not change the timing of apparent colonization
by H parasuis, or the prevelant serotype. This implies
that full protection at an early age requires vaccination of both
the sow and litter as demonstrated by Solano-Aguilar et al.3
Implications
- Compared to tracheal swabs, nasal mucosal swabs were more
easily performed and more consistently yielded H parasuis.
Serotypes obtained from each site were the same.
- A lower level of colonization can be expected within the
litters of young sows, and a low level of colonization by H
parasuis at weaning likely predisposes piglets to clinical
disease in the nursery, assuming the presence of a virulent serotype.
- More than one serotype of H parasuis can be present
in the herd.
- Vaccination of sows did not influence the timing of apparent
colonization by H parasuis or the serotypes prevalent
within a litter.
Acknowledgements
We gratefully acknowledge the excellent technical support provided
by Annette Visser, Suzanne Gibson, and Evelyn Bowlby. Financial
assistance was generously provided by Intervet Canada.
References -- refereed
2. Rapp-Gabrielson VJ, Kocur GJ, Clark JT, Muir SK. Haemophilus
parasuis: Immunity in swine after vaccination. Vet Med.
1997;92:83-90.
3. Solano-Aguilar GI, Pijoan C, Rapp-Gabrielson VJ, Collins
J, Carvalho LF, Winkelman N. Protective role of maternal antibodies
against Haemophilus parasuis infection. Am J Vet Res.
1999;60:81-87.
4. Nielsen R, Danielsen V. An outbreak of Glasser's disease.
Studies on etiology, serology and the effect of vaccination. Nord
Vet Med. 1975;27:20-25.
5. Rapp-Gabrielson VJ, Gabrielson DA. Prevalence of Haemophilus
parasuis serovars among isolates from swine. Am J Vet Res.
1992;53:659-664.
6. Smart NL, Miniats OP, Rosendal S, Friendship R. Glasser's
disease and prevalence of subclinical infection with Haemophilus
parasuis in swine in southern Ontario. Can Vet J. 1989;30:339-343.
References -- non refereed
1. Pijoan C. Diseases of high health pigs: some ideas on pathogenesis.
Proc AD Leman Swine Conf. 1995; 22:16-17.
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