The Rural Voice, 1993-11, Page 18Diagnostics
PRRS (Mystery Swine Disease) update
by Dr. S. Ernest Sanford
Veterinary Laboratory Services
Branch, Ontario Ministry of
Agriculture and Food
Huron Park
This will probably be my last
update on PRRS. One tiny bit of
good news to report is that we have
not come up with any more "new"
names for PRRS over the
last year. We are still
seeing sporadic outbreaks
in individual herds.
In a typical outbreak,
several sows in late
gestation suddenly go off
feed, spike slight fever,
and then abort to give
birth to premature
weakbom piglets. Some
mummified piglets may
also be seen. Weakbom
piglets may have a thumping
respiration. Even more common are
herds that may never have had any
abortions or farrowing room
problems but have ongoing nursery
pig infections such as Glasser's
Disease (caused by 1laemophilus
parasuis), Strep suis infections,
pneumonias, etc. as secondaries to
PRRS. Most herds infected with
the PRRS virus by far, however,
show absolutely no clinical signs
whatsoever, and that might be the
best news of all.
NEW INFORMATION ON PRRS
1. The PRRS virus circulates best
among weaned pigs in the nursery
in endemically infected herds.
2. Nursery pigs shed the virus via
nasal secretions and feces for up to
35 days after initial infection. The
PRRS virus seems to be shed in
feces even more actively than via
nasal or other body secretions.
3. This fecal shedding has raised
the possibility of a fecal -oral
method of transmission of the
PRRS virus in the nursery rather
than by the previously believed
respiratory route of transmission.
4. Several laboratories are now
capable of isolating the PRRS virus.
Serum (blood) is the best sample for
virus isolation. Virus isolation is
not yet available via the Ontario
Veterinary Laboratory Services
(VLS) but access to other
laboratories that can isolate the
virus is arranged through the VLS
labs.
5. There are several strains of the
PRRS virus. Only one strain seems
to be present in Europe. Many
strains are present in North
America. The European
strain seems to be
different from the North
American strains and do
not readily cross-react
with any of them. The
North American strains
have differences among
themselves. Different
strains might be active in a
single geographical area.
Different strains may also
be present in a single herd.
6. It does seem that infection
with one strain does not necessarily
provide cross -protection from
infection with another strain of the
New
rmation
info
au
now
ailable
14 THE RURAL VOICE
virus.
WHAT ABOUT A VACCINE?
Several pharmaceutical
companies in Europe and North
America are in the process of
developing a vaccine for PRRS.
There is no official word from any
of them about when a vaccine
would be released. It seems likely,
however, that one or more of these
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