History
As production models have changed from continuous flow confinement systems to all-in, all-out (AIAO) and more recently to single age group AIAO systems, respiratory diseases have likewise evolved. There was a time in the not so distant past when the swine veterinary community believed that multi-site production would end or greatly lessen serious respiratory disease in our growing pigs. This has not come to past, in fact many systems spend as much or more dollars on treatment and prevention per pig than many of the continuous flow systems of the past. Growth rates and feed conversion have generally improved but the costs to achieve these gains have brought about a reassessment of large scale AIAO production design. The latest attempt to conquer this has been the so-called "Nur-Fin" or "Nu-Fin" wean to finish barn. These buildings have the advantage of fewer pig movements, more flexible closeout management, eliminate the nursery cost center, and generally reduce the incidence of serious respiratory disease. The evidence that these buildings will live up to the reputation established in recent meetings is yet to be established but early results are promising.
For years Progressive Atrophic Rhinitis, Actinobacillus
pleuropneumoniae (Haemophilus Pneumonia), Mycoplasma,
and Salmonella choleraesuis were considered the major respiratory
agents involved in finishing deaths and disease related losses.
Pasteurella multocida and Streps were the major secondary
bacterial agents and Pseudorabies was considered the major primary
viral precursor in many outbreaks. More recently PRRS, Respiratory
Corona virus (PRCV), influenza virus, cytomegalo virus, and perhaps
Circo or other viruses have been incriminated in the Porcine Respiratory
Disease Complex (PRDC). This complex has received wide attention
in our industry. Many of us that witnessed the feeder pig industry
sill recognize this new syndrome as the enzootic pneumonia/shipping
fever complex of the past. There is little doubt that the high
mortality and morbidity coupled with very poor performance associated
with co-mingling multiple health sources of pigs out paced the
percent losses of today. However, the size and scale of modern,
state of the art pig production has kept respiratory disease alive
and well and a major source of losses.
PRDC Philosophy
As the incidence and severity of respiratory disease
have evolved, likewise diagnostic and preventative strategies
have been forced to change to meet this new challenge. It appears
both new and old agents are role players in the new PRDC syndrome.
Mycoplasma hyopneumoniae is the leading bacterial candidate
in the onset of this disease. It is an agent that can cause disease
without the help of other bacteria or viruses.
This classifies it as a Primary Respiratory Agent.
Primary pathogens can be either viral or bacterial. The viral
agents most often incriminated are PRRS, Pseudorabies virus (PRV),
or Swine Influenza. These may act alone or in tandem. Many times
an outbreak may look like a flu epidemic without the influenza
virus present. This is due to group susceptibility to any variety
of these and other agents. Bacterial primary pathogens like Haemophilus
parasuis, Streptococcus suis, Bordetella bronchiseptica, Actinobacillus
suis, or Actinobacillus pleuropneumoniae and any number of
secondary bacteria (typically Pasturella multocida) appear
to be involved. When PRRS is involved the bacterial isolates
will often vary considerably between individual pigs in a group.
This is due to immunosuppression. These situations require careful
and methodical diagnostic data collection, thoughtful interpretation
and specifically designed and managed interventions. The rule
of thumb is each system requires it's own strategic diagnostic,
intervention, and management plan. Some of the steps that are
required are listed below. In all cases you must be proactive
in your prevention and diagnostic management else partial or complete
failure will result.
Diagnostic Strategies
There are a host of new diagnostic tests that can
lead to an accurate determination of the agents involved in a
respiratory outbreak. They can also lead to a great deal of confusion
and misinterpretation if not used with a certain amount of wisdom
and skepticism. The only thing any serological test indicates
is the animal has been exposed to a disease agent (or it's mother
was exposed). These tests rarely if ever give accurate information
concerning infection status of the animal, whether it is shedding
the agent, nor can they accurately predict the exact time of exposure.
Visual and postmortem examinations have a much greater sensitivity
than serology in this regard. Another limitation of all tests
is they have some inherent level of false positives and false
negatives. These are a result of a number of causes that include
sample mix-ups, cross contamination, procedure errors, test limitations,
cross-reactions, antigenic diversity of the agent, and the genetic
diversity of the individual pigs. Other tests that allow us to
see the agent while doing microscopic examinations on tissue samples
only indicate the agent's presence and not necessarily the importance
of this finding. Culturing the agent from lesions also has its
limitations but generally gives us an accurate identification
of the bacteria involved. This does not rule out other agents
that may not grow as easily or that die quickly after the death
of the host animal. Even the newer tests that are highly specific
for an agent's genetic code (PCR) have limitations in both interpretation
and accuracy.
Serological Profiling
This has become a popular method to measure the pig/agent
exposure level. There are two main approaches that are in use.
The first is the age "snap shot". The advantage of
this procedure is it can be quickly done to determine the pigs'
age when heavy exposure to the disease agent is occurring. Representative
numbers of representative age groups are sampled and the exposure
level calculated and interpreted. Whole batteries of tests are
often done and the results will give the veterinarian an idea
of the chronology of disease exposure. The limitation of this
procedure is it only tells you when exposure is occurring in the
specific groups of pigs sampled the day of sampling. It will
not uncover the dynamic and always changing balance between herd
immunity and agent activity. Maternal antibodies, vaccinations,
weather conditions, facility stresses, and a host of other factors
can change the appearance of the profile at any given time. A
good analogy of this procedure is the photograph (snap shot) of
a rapidly moving vehicle. You can determine, for example that
it is an automobile and not a truck but it is difficult to determine
the speed and direction the car came from or is going to. You
know it was there at the moment of the snap shot but little more.
The second serological profiling technique is to
follow the same group of pigs through a system, taking sequential
samples after a set period of time until the pigs leave for market.
This is usually done on an every other week or monthly basis.
This will shed light on the disease dynamics in this group of
pigs if properly done but only this specific group. The influence
of time of year, changing breeding herd immunity status, and numerous
difficult to measure factors will alter the profile in future
groups. Profiling will not always accurately predict the disease
interactions in the very next group through the system and only
rarely for groups of the distant future.
Although both of these disease management tools can
yield useful information the limitations must be considered.
Respiratory disease is a moving target and diagnostic profiling
must be done on a continuous seasonal basis to be proactive in
disease prevention methods. Vaccines, drugs, ventilation, temperatures,
controlled exposure techniques, and other management interventions
should be strategically implemented prior to expected problems.
To do this properly, gathering of diagnostic data must be on
a routine and regular basis if proactive interventions are to
be effective. The best source of information is the postmortem
examination if routinely done throughout the year. Like profiling
this requires a statistical representative number of pigs before
the data can be meaningful.
We generally find ourselves fighting a defensive
battle that is behind the explosive exposure curve that will always
develop in large populations of pigs that have no prior immunity
to the disease agent(s) involved. This is especially dramatic
(costly) in pigs that are immunologically compromised by PRRS
virus. There is increasing scientific data that link PRRS with
increased pathology (mortality and morbidity) when concurrent
with mycoplasma, salmonella, streptococcus suis and other
viral or bacterial diseases.
Vaccine and Antibiotics
In recent years vaccines and antibiotics have increasingly
been used in a strategic manner. This is an attempt to use them
in a "best cost" systematic approach. In the past,
once a vaccine or drug program was implemented it would remain
a part of the standard operating procedure (SOP) until the farm
went out of business or management/ownership changed. This is
a warranted approach with some diseases such as Parvovirus and
Erysipelas. When dealing with respiratory disease, flexible designer
programs are frequently needed. Very few vaccines available in
the United States have duration of immunity statistics. Further,
trials are conducted without concurrent disease challenge and
are often based on serological results. This does not allow veterinarians
to make accurate predictions of efficacy nor the cost effectiveness
of the procedure. To ensure "best cost" use of vaccines
and antibiotics they must be implemented and removed on a predictable
but flexible basis. This must be approached as an evolving process
that by necessity will be altered periodically if we are to keep
ahead of the dynamic interaction between the "bugs"
and pigs. This requires continuous data gathering and interpretation
if logical and cost effective decisions are to be accomplished.
We are just beginning to learn how to use health-based data in
statistical control charts for the purpose of strategic interventions.
Intervention Examples
NurseryMycoplasma hyopneumoniae
It is a rare occurrence in modern nurseries when
Mycoplasma pneumonia is a clinically important problem requiring
intervention. When the sow herd is positive, the pigs will have
maternal antibodies for protection lasting up to 60 days in some
pigs. This does not mean that all pigs will have adequate protection
through the nursery period. The antibodies that are measured
by most serological tests are not necessarily the ones that are
known to be protective, rather the ones that are easiest to measure
after exposure to the agent of interest. Another pitfall is these
antibodies may have a blocking effect preventing substantial immunity
after vaccination while providing little disease protection.
The presence or absence of these antibodies may shorten the duration
of vaccine immunity in a specific herd or modify the age when
the disease becomes apparent in unvaccinated pigs. This situation
sounds complicated and unfortunately it is. PRRS or some other
immunosuppressive agent will usually be involved when Mycoplasma
occurs in a nursery. Bordetella bronchiseptica (Bb), Streptococcus
suis (Ss), and Haemophilus parasuis (Hps) will frequently
be found in the diagnostic summary of the lab report. In cases
where Mycoplasma is diagnosed from Immunohistochemical staining
(IHC) or strongly positive fluorescent antibody (FA) results from
multiple nursery age pigs, a breeding herd vaccination program
may be the "best cost" method of control. This should
be administered much like an E.coli vaccination program.
Gilt litters will be the most susceptible in most cases. If
pigs have no detectable antibodies at two weeks of age then this
program should be considered. It should be monitored for effectiveness
both clinically and serologically. Three to six months are usually
required to accurately evaluate any vaccine program. The choice
of mycoplasma vaccine is often of little significance but may
be farm specific. Whenever M. hyo. is an active part of a nursery
respiratory problem, PRRS, influenza, and other viruses should
be considered in the diagnosis. Sow herd stability for these
viruses is important but the method of achieving stability for
each virus is very different and specific.
A treatment strategy for mycoplasma in nurseries
is much like the game of roulette. An effective program will
be dependent upon the other disease agents involved in the complex
and may require some experimentation before an acceptable antibiotic
schedule can be derived. Bordetella, Strep, and Haemophilus are
frequently co-conspirators and often don't respond to those antibiotics
that are most effective against mycoplasma. Tetracyclines and
lincomycin are generally thought to be the most effective for
mycoplasma but tylosin is also often used. Combinations of injectables,
feed antibiotics and water medications should be considered when
the problem is severe. In the past ASP-250 or CSP-250 in the
feed has offered reasonable overall preventative control for nursery
diseases. Other medications that are frequently are used include
tetracycline/tiamulin (Denagard) and Pulmotil. Denegard is effective
when Streptococcus is a major player in the nursery respiratory
disease complex. Amoxicillin, ampicillin, or penicillin may be
used for prevention and treatment of Streptococcus suis and haemophilus
but will not control mycoplasma. Water medications are often
effective as treatments but palatability issues are important
with this age pig. Flavor enhancers and citric acid improve the
process and avoid some of the clogging water nipple problems.
Grower/Finisher Mycoplasma hyopneumoniae
It has been my experience that the "19 week"
wall can occur anytime from 16 weeks to 24 weeks after birth.
Although variable, the timing when pigs begin to demonstrate
clinical signs of M. hyo. in specific systems is usually relatively
repeatable. When the age of onset changes it is an indication
that one or more of the dynamic forces that dictate the disease
course have also changed. This may be a variety of circumstances
but the level of stress or other immune suppressing disease such
as PRRS may be involved. Vaccination can also influence when
the disease will occur, often only pushing it out to a later age
rather than preventing the illness. Since the duration of immunity
is variable and not predictable and most of our vaccines only
provide partial protection, adjustments in vaccination protocol
may improve the results. The principle here is to get the maximum
amount of protection into the pig approximately two weeks before
it is needed. There are two ways to determine this. The first
is routine serological profiling by the chronological group method.
It is not necessary to identify the individuals but collect samples
from an age group every two weeks until the sero-conversion rate
accelerates. It normally takes three to five weeks for animals
to develop antibodies against M. hyo. after the bacteria begins
to build up in the respiratory tract of the pig. Back up six
weeks from this approximate time and give the first vaccination
followed in two to three weeks by a booster. This will usually
divide the vaccination between the nursery and the finisher personnel.
The weakness of this program relies on the assumption that each
group will follow the same course of the disease over time. Observing
clinical signs may work just as well, backing up six weeks from
the time when pigs normally begin to cough for the initial vaccination,
administering the booster three weeks later. Single vaccination
schemes may rely on already developing immunity in which case
the single dose of vaccine acts as a booster. It is very difficult
to determine the optimum timing of vaccination and in my hands
the single dose has been an unreliable method of mycoplasma control.
New single dose vaccines are on the way and await our evaluation
in the field.
I have observed Mycoplasma as a seasonal disease
in some systems. If this can be predicted with any reasonable
reliability then the use of vaccination may only be necessary
during a certain period of the year. Some managers don't like
this approach even though it reduces costs. This is because it
requires changing protocols that confuse farm personnel and makes
management more difficult.
Treatments for mycoplasma outbreaks should also take
into account the other agents involved in the PRDC farm problem.
Atinobacilus pleuropneumoniae can be especially difficult.
Some farms have difficulty with Hps and Pasteurella multocida
along with other bacterial and viral agents. Tetracycline (oxy-
or chlor) at the 10 mg/pound treatment level or lincomycin at
the 200 g/ton level have been the two most effective feed additives
for treatment in my experience. Water delivery of these drugs
may be necessary in severe outbreaks. Injections are also frequently
needed but require excessive labor inputs that are often not available.
Generally it is more effective to prevent the disease than treat.
Pre-emptive use of antibiotics is difficult since the timing
required is in a much narrower window than vaccination.
Nursery/Finisher Strep.suis & Haemophilus
parasuis
These two diseases are very similar in appearance
and outcome in nursery age pigs. Both can cause meningitis, septicemia,
and pneumonia. Either may result in sudden deaths or chronic
"poor doers". Intervention can be very difficult for
a variety of reasons. Clinical observations and postmortem exams
are more reliable than serological profiling. Finding either
of these bacteria in the brain, lung, or lesions in other parts
of the pig are always significant. Strategic vaccine usage may
or may not be effective. Both disease agents become extremely
difficult in the presence of PRRS. My experience has been that
this is an area where an autogenous vaccine may be beneficial
depending on the age of the pig when affected. Strategic antibiotic
use (both timing and the specific drug) is required. The group
of antibiotics that are generally effective for treatment and
prevention are the so-called Beta-lactam class. In veterinary
medicine these are the penicillins (penicillin G, amoxicillin,
ampicillin etc.) and cephalosporins (Naxcel). Bacterial resistance
may develop to any or all of these but timing is the major factor
in treatment and prevention failures. Tiamulin water medication
or at the 200g/ton level in the feed often provide effective treatment
but relapses often occur after removal of the drug. It has been
my experience that most strep meningitis cases start to appear
around the end of the second week in the nursery or around the
time when finisher pigs sero-convert to PRRS positive status.
It is difficult to time vaccinations in a strategic
fashion which will successfully prevent either disease in the
early nursery phase. Maternal antibody blocking, the lack of
cross-protection between different genetic strains of the bacteria,
true all-in and all-out, ratio of naïve to carrier pigs,
and numerous other factors contributes to the disease process.
Ventilation, fly control, sanitation, and stocking density also
have a big influence on the severity of the disease in my opinion.
Correctly managing these must also be a part of any effective
plan for intervention. Haemophilus outbreaks that occur in the
finishing barn are often the result of mixing pigs from different
barns or sources, crowding stress, and poor ventilation. Outbreaks
in this age pig require injectable antibiotics if losses are to
be minimized. Wean to finish barns appear to lessen the severity
and number of pigs affected. Stabilizing the breeding herd is
essential for effective control. This is especially important
for PRRS virus. Eradication of the virus from the herd is the
best alternative in many cases. Intervention always requires
incorporating multiple control strategies, which may include vaccine
and antibiotics. However, these are not the essential elements
of control.
Actinobacillus pleuropneumoniae
This bacterium can be one of the most serious of
all pneumonia causing agents. Although there may be considerable
variation in the severity of disease with this organism, it is
generally one disease agent that cannot be tolerated due to the
overall effect it has on production. It has been my experience
that App can frequently reduce productivity by 25% or more in
continuous flow systems and by more than 15% in three site and
multi-site systems. This variation is largely due to the pathogenicity
of the different serotypes but management and facility factors
also have a great bearing on the losses. Acceptable control strategies
can be difficult to attain while draining the enthusiasm and endurance
of the farm or system personnel. This is the one disease that
may be more costly than PRRS in some systems.
Control methods have varied over the years but without
a highly effective vaccine, producers have been forced to rely
on heavy antibiotic usage or eradication techniques. This is
one disease that has been successfully eliminated through medicated
early weaning (MEW) or IsoweanÔ techniques. Sero-type 5
and 2 has been the most difficult to control while 7 and others
are rarely complicated in mature systems. Start up herds may
be initially spared even when App positive but eventually nursery
and finisher involvement will erupt. Injectable antibiotics that
have been effective include the penicillin's, and cyclosporins.
Lincocin-spectinomycin combination has also been used over the
years but this is extra label. Test and removal and rollover
techniques have been attempted in recent years but most of these
attempts have been in relatively small herds. Effective vaccines
have been produced but these have been in oil adjuvants that result
in a high level of injection abscesses. This is one disease that
has frequently led to cash flow problems.
Actinobacillus suis
In recent years this bacteria has more frequently
been involved in respiratory outbreaks. It has been associated
with skin lesions resembling the diamond skin disease of Erysipelas.
The bacteria usually responds to penicillin injections or other
beta lactams. This agent appears to remain an opportunist but
outbreaks resembling pleuropneumonia do occur. Control is not
necessary but a rapid diagnosis is needed when the bacteria is
active in finisher age pigs. The postmortem and culture of the
bacteria from affected lungs is the only way to accurately diagnose
and evaluate the impact of this disease agent.
Salmonella choleraesuis
Although Salmonella choleraesuis is not spread
by aerosol in can be pneumonic. This salmonella is what we call
host adapted. It only rarely infects other species and seems
to be a disease that has little impact in age group reared pigs
on total slats. In recent years several Animal Health companies
have marketed modified live or low virulence live vaccines. These
have provided effective control and the labor saving convenience
of water delivery. Diagnosis of this agent is usually a simple
matter of isolating the bacteria from lung and other tissues at
postmortem. This disease is appears to be on the way out much
like swine dysentery.
Other Disease Agents
There are a number of other bacterial and viral agents
that can be involved in modern production systems. Most of these
are self-limiting. They appear and disappear, occasionally returning
but just as often never to be seen again. Porcine cytomegalovirus
is a good example of an agent that often appears in growing pigs
from start up herds. Clinical signs include excessive sneezing
and snout deviation. The virus tends to disappear within a year
of full production but can persist in some herds. It may be associated
with rhinitis and strep.suis meningitis. It will likely increase
the turbinate damage associated with Bordetella bronchiseptica
infections. Methods of intervention have been strict all-in,
all-out by age, feed back and so called "seeder pig"
exposure in the breeding and gestation barns.
Bordetella is usually a mild disease that is controlled
by sow vaccination, feed antibiotics, and all-in, all-out farrowing
house management. It is not known to be potentiated with PRRS
but sometimes the virus can cause turbinate damage on it's own
that may increase Bordetella induced snout scores at slaughter
check. I have isolated pure cultures out of Bordetella bacteria
from the lungs of finishing and nursery pigs with severe pneumonia.
It has been my experience that outbreaks of Bordetella pneumonia
are extremely uncommon in the industry today even in herds with
chronic PRRS problems.
Circo virus has received a lot of attention recently
and may be involved in lung and other organ system pathology.
It is associated with wasting and eventual death. The virus may
be genetic variant of the Circo virus that naturally resides in
the US swine population. Most of the field cases that I know
about also have concurrent PRRS infection. Like Cytomegalovirus,
this virus produces large intra-nuclear inclusion bodies that
can easily be observed by the pathologist. Without them we would
likely recognize these pigs as PRRS infected pigs. At this time
there is no easy method to distinguish the virulent strain from
the naturally occurring avirulent virus since the serology results
are the same for both. It is likely that this virus is completely
self-limiting in most normal PRRS negative populations. There
have been reports out of Canada that indicate the Circo virus
II may be a primary viral agent capable of immune suppression
and severe disease. This awaits further characterization and
research.
Take-Home Message
