Issue |
Vet. Res.
Volume 31, Number 1, January-February 2000
|
|
---|---|---|
Page(s) | 148 - 149 | |
DOI | https://doi.org/10.1051/vetres:2000068 | |
How to cite this article | Vet. Res. (2000) 148-149 |
Aujeszky's disease virus (ADV) in mammalian wildlife on swine farms in Illinois (USA): Potential for transmission to non-infected herds
R.M. Weigel, E.C. Hahn, B. Paszkiet and G. ScherbaDepartment of Veterinary Pathobiology, College of Veterinary Medicine, University of Illinois, 2001 South Lincoln Avenue, Urbana, Illinois 61802, USA
Abstract -
After eradication of ADV from swine herds, non-porcine reservoirs can be
potential sources for reintroduction of ADV. Vaccination of swine with modified live, gene-deleted
vaccines, particularly intranasally (which promotes aerosol transmission), has the potential to immunize
wildlife populations. Immunized wildlife can survive exposure to virulent wild-type ADV. Mammalian
wildlife traveling between swine herds can also serve as vectors for between herd spread. The objective
of
this study was to determine the prevalence of infection of mammalian wildlife with wild-type and
vaccine
ADV on swine farms quarantined for ADV where vaccine was used, and to determine the potential for
between
herd spread of ADV by wildlife. Six swine farms in Illinois (USA) quarantined for infection with ADV
were
studied. All were in close proximity (maximum 30 km distance). Five farms studied in both 1996 and 1997
used modified live ADV vaccines with deletions for glycoprotein E (gE
-), one dose administered
intranasally at 3-4 weeks of age, and the other intramuscularly at 9-10 weeks. The sixth farm, studied
only in 1997, vaccinated pigs intramuscularly at 9 weeks of age with a gE
-gG
- vaccine. Each farm was
visited 6 times per year, between April and September. Overnight live trapping of wildlife (rodents and
medium sized mammals) was conducted. Blood samples were obtained from all captured animals. Detection of
anti-ADV antibodies was accomplished by using a serum neutralization (SN) test for sera from medium
sized
mammals and rats and a latex agglutination test (LAT) for sera from small rodents. All rodents were
euthanized and their brains were harvested. Upon first capture, each medium sized mammal trapped was
tattooed for identification and released. Upon recapture, if a medium sized mammal had been identified
as
seropositive for ADV on a previous trip, it was euthanized and its brain, trigeminal ganglia, and
tonsils
were removed. For all ADV seropositive animals, a polymerase chain reaction (PCR) for viral
detection was
performed on tissue samples (brains for rodents; brains, tonsils, and trigeminal ganglia for cats),
using
primers for glycoproteins C (gC) and E (gE). For each seropositive rodent, 4 matched (by trapping
trip on
the same farm) seronegative rodents were also tested using PCR. As another control, 6 rodents were
selected from each of 2 trips on the only seronegative farm and tested using PCR. There were
seropositive
cats
on 2 farms, house mice [Mus]
on 3 farms, and field mice
[Peromyscus]
, rats
, and rabbits
on 1 farm each; 5
of the 6
farms had seropositive wild mammals. There were no seropositive samples for raccoons
,
opossums
,
or skunks
.
There were 3 seropositive cats that were recaptured and
euthanized.
Two were PCR
+ for gC and gE, indicating infection with wild-type ADV. One was PCR
+ only for gC,
suggesting infection with gE
- vaccine. Among the 64 individual cats, 8 (13%) were trapped on 2
farms, of
which 2 were seropositive. The only seropositive rat was gC
+ and gE
- by PCR, indicating infection
with gE
- ADV vaccine. Among the 11 seropositive mice, 9 (82%) were gC
+gE
+ (indicating infection with
wild-type ADV) and 2 were gC
+gE
- (indicating infection with gE
-
ADV vaccine). However, for the 40
matched seronegative mice on farms seropositive for wildlife, 38 (95%) were gC
PCR
+, with 29 (73%)
gE
+
(indicating wild-type ADV) and 8 (20%) gE
- (indicating infection with gE
- ADV vaccine). For the one
farm that was entirely seronegative for wildlife, the 12 rodents tested were PCR
-. All PCR
+
results were
confirmed by Southern blot. It was not possible to isolate ADV from any of the animals that were
tested by PCR. Cats and rodents living on swine farms may be infected with ADV, either with wild-type or
vaccine genotypes. Thus, these species may serve as a reservoir for possible reintroduction of ADV
to swine. Seropositive cats can travel between farms, indicating that cats may serve as a vector for the
transmission of ADV between swine farms. A comparison of LAT and PCR results for rodents indicates
that the prevalence of ADV infection in rodents may be much higher than estimated by serological testing.
ADV eradication programs must consider the role of rodents as a reservoir for reintroduction of
ADV into swine herds, and cats as a possible vector for transmission of ADV between herds.
Corresponding author: R.M. Weigel Tel.: (1) 217 244 1365; fax: (1) 217 244 7421;
e-mail: weigel@uiuc.edu
© INRA, EDP Sciences 2000