Agriculture Reference
In-Depth Information
18.5.5
Respiratory or systemic
As is the case with enteric diseases, adult swine generally have been exposed and have
developed immunity to most of the endemic diseases present on the farm. Therefore,
clinical signs of respiratory diseases such as coughing and sneezing are usually not a
common feature of the breeding herd. However, the incoming replacement gilts may
arrive on the farm without protective immunity and respiratory disease in these naive
animals is not uncommon. For example, incoming gilts may become exposed to
Mycoplasma hyopneumoniae
for the first time as they enter the breeding herd, resulting
in gilts going off-feed and displaying a dry non-productive cough. Infected animals are
more prone to secondary bacterial infections such as pasteurellosis and may become
seriously ill. Vaccination of the incoming gilts with
M.
hyopneumoniae
bacterins can
greatly reduce these health problems.
There are important respiratory viral diseases that spread from farm to farm and cause
herd outbreaks of disease in the sow herd. Swine influenza is possibly one of the most
common and important of these diseases. When an influenza virus enters a susceptible
herd, all ages of pigs can be affected, but often the older animals exhibit the most severe
clinical signs, including high fever, coughing, difficult breathing, nasal discharge and
anorexia. Mortality is generally low but sows with influenza may not nurse piglets very
well and suckling pig mortality can be increased. In addition, pigs with influenza have
reduced immune function and secondary or concurrent infections may result in a
more serious case of disease. Treatment, if required, is directed at reducing secondary
bacterial infections.
As discussed previously, PRRS virus also moves readily from farm to farm and creates
outbreaks affecting all age groups. Commonly the first clinical signs in a herd are a wave
of anorexia and respiratory disease passing through the gestation barn, followed by signs
of abortion and suckling pig losses. The PRRS virus can mutate rapidly and there are
many different strains with widely varying abilities to cause disease. There are some
highly pathogenic strains of PRRS virus that result in a high incidence of sow deaths.
Vaccines have historically been modified live virus types that have spread among the
swine population in addition to field strains. Unfortunately, protection against mutated
viruses requires previous exposure to viruses that are very similar to the new challenge
strain, and therefore protection through vaccination with commercial products tends
to be of limited value. The swine industry generally relies on exposure to field strains to
create herd immunity.
There are a number of very important reportable diseases that cause systemic illness in
sows, including classic swine fever (hog cholera) and African swine fever. Discussion of
these diseases is beyond the scope of this chapter but such diseases need to be always
considered when a sudden outbreak of disease occurs in the sow herd, particularly if
mortality is significant.
Historically, parasites have been a source of respiratory disease in sows but confinement
rearing and modern anthelmintics make these diseases of little relevance today except in
