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18 THE RURAL VOICE
DIAGNOSTICS
"MYSTERY DISEASE" IN SWINE HERDS
by Dr. S. E. Sanford — Veterinary Laboratory Services, Huron Park
In the winter and spring of 1989
on hog farms in midwest U.S. states,
there were outbreaks of abortions and
stillbirths in sow herds and high pre -
weaning mortality in suckling pigs.
This condition has become known
as the "Mystery Disease." Its major
features are:
• Sows develop moderate to high
fevers, go off feed, and may exhibit
signs of heavy breathing or some
respiratory distress.
• A sow may die, but this is rare.
• Usually, several sows abort or
have stillborn pigs or pigs born a few
days early (a SMEDI-like syndrome).
• These early -born pigs are usually
small and weak. Those that are unable
to nurse eventually die.
• Grower and finishing hogs may
also go off feed and exhibit respiratory
signs. But they seldom die.
Although the news came out of
Indiana most forcefully in the spring
of 1989, it is now obvious that this
syndrome was much more widespread.
It is clear that similar outbreaks had
been occurring in Iowa, Minnesota,
Nebraska, other midwest states, and
North Carolina. Also, outbreaks in
those other states (and maybe Indiana
too) had occurred back in the winter of
1987-88, though not with nearly the
severity of the 1989 outbreaks.
Here in Ontario, we experienced
an apparently identical outbreak in the
fall and winter of 1987-88. Sows on
several farms in southwestern Ontario
went off feed suddenly, aborted, and
in some cases developed respiratory
problems. Similar outbreaks have
been reported from Quebec for 1988-
89 and to a lesser extent for 1987-88.
Intensive investigations were
launched in Ontario in 1987-88 to find
out what was causing these problems.
But despite several valuable leads, a
conclusive diagnosis to explain these
outbreaks was never reached.
In the U.S. an exhaustive hunt for
the cause is still in progress. Once
again, several valuable clues have
been picked up, but a definite diag-
nosis has proven elusive.
Because of the pattern of the out-
breaks, most investigators believe they
are caused by a virus. At this time,
Encephalomyocarditis (EMC) virus
has got the most attention. But though
EMC virus activity has been identified
in some of the problem herds, it has
not been identified often enough to
explain these outbreaks reasonably.
Similarly, although many other
viruses and other agents have all been
considered and investigated, they have
all been ruled out or have not been
adequate to explain the outbreaks.
Without knowing the specific
cause of these outbreaks, one can only
recommend general disease -preven-
tion steps. Those suggested by Purdue
University, Indiana, include:
• Maintain a closed herd, if possi-
ble. If new additions must be made,
be sure to isolate them for 30 days.
• Keep stray animals — dogs, cats,
and humans — out of the barn.
• Keep vehicles out of the swine
operation. Clean and disinfect the
trucks used to haul hogs to market.
• Change clothes and boots after
working in another hog unit or after
marketing hogs.
• If signs similar to those described
are seen, call a veterinarian as soon as
possible to rule out diseases that may
produce a similar pattern.
• Bum or bury all dead pigs.
To end on a more positive note,
I can say that after our Ontario out-
breaks of 1987-88, we expected a
repeat in the fall or winter of 1988-89.
This did not happen. There were a
few suspicious cases, but no outbreak
pattern.
To date, although there is a much
higher awareness among veterinarians
and some producers of the "Mystery
Disease" problem, and although there
have been several queries and some
suspicious cases, there is very little
evidence of new outbreaks. We may
be out of the woods on this one.0