Download Infectious bovine rhinotracheitis in New Zealand

Surveillance Vol.17 No.2 1990
Infectious bovine rhinotracheitis in New Zealand
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Bovine herpesvirus 1 is a cause of
upper respiratory tract infections (IBR)
an3 genital infections (infectious pustular vulvo-vaginitis or IPV) in New Zealand cattle. The virus has never been
isolated from other disease syndromes.
Numerous attempts have been made to
isolate IBR virus from aborted foetal and
placental tissues over the last 15 years
without success. There has been one
experimental attempt to induce abortion
in cattle using a New Zealand isolate, but
this also was unsuccessful.' In 1982 there
was an outbreak of encephalitis affecting
48 calves which, it was considered at the
time, could possibly have been due to
IUR infection', but no fresh material was
received to confirm or refute this possibility.
Outbreaks of clinical disease
Most samples from suspected cases of
IBR infection are examined at Ruakura
Animal Health Laboratory. These
samples originate almost entirely from
North Island farms. The laboratory findings for the years 1975 to 1990 are sumniarised i n Table 1.
IBK virus isolations in any one year
varied from 0 to25, whilesignificant rises
i n antibody titre (four-fold rises) were
detected in between 3 and 31 herds in any
one year. Thesedata indicate that even in
the worst years, IBR infection is confirmed in fewer than 50 North Island
herds annually.
In many years the
number of diagnoses made is fewer than
ten. Even allowing for the fact that veterinary advice or laboratory confirmation would not be sought for all clinical
cases, especially where only one or two
animals were affected, it is apparent that
IBR infection is not a serious clinical disease in this countrv.
The clinical history of the five affected
herds diagnosed in 1990 is summarised
in Table 2. These can be regarded as
typical of the pattern of clinical disease
caused by IBR virus under New Zealand
conditions of extensive pastural farming.
Antibody prevalence studies
Several studies" have been carried
out to determine the prevalence of IBR
antibodies in New Zealand cattle, including one nationwide survey of 1,070 dairy
and beef herds. About 10% of dairy
herds are vaccinated using an attenuated
N e w Zealand strain of IBR virus'.
Th12results, shown in Table 3, indicate
IBR is widespread throughout the country, with infection being less common in
dairy cattle in the eastern North Island
and the South Island.
Molecular studies
The DNA fingerprints of New Zealand strains of IBR virus have been studied.5 Eight respiratory and six genital
Table 1: IBR diagnoses :Diagnostic data from Ruakura Animal Health Laboratory, 1975-90
Virus isolations
Year
No.
samples*
No.
isolates
Rises in titre
Serology
No.
samples
No.
positive
Animals
Herds
1975
33
8
1976
52
8
275
172
NR
NR
I977
61
3
28 1
NR
23
NR
1978
52
9
193
145
8
NR
1979
156
2s
369
218
41
NR
19843
53
4
256
176
9
NR
1981
135
19
688
399
18
NR
1982
I87
3
550
344
17
NR
1983
182
9
430
248
NR
9
1984
I87
11
69 1
364
NR
11
198.5
194
10
466
305
NR
31
1986
174
6
917
468
NR
14
198'7
90
1
310
123
NR
6
1988
60
0
36 1
157
NR
3
I980
I47
1
627
295
16
NR
7
5
47
32
0
I770
122
6 180+
3446
1990
(to 1 April)
(6.8%)
No.
infected
herds
15
5
(56%)
NR = Not recorded
* Samples examined include abortion samples and semen samples
in addition to nasal and vaginal swabs
+ 1977 figure exclude
Table 2: Clinical history of five herds with IBR infection, 1990
Herd
No.
affected
Breed
1
20140
L
Age
Sex
Clinical Signs
Fr
15 m
F
Rhinitis,
conjunctivitis
21149
Fr/J
3Y
F
Upper respiratory
tract infection
3
?
FrX
Mixed
F
Vaginitis
4
301100
Mixed
2Y
MC
Rhinitis,
conjunctivitis
5
24168
Fr-FrX
2-3 y
F
Rhinitis,
'
production drop
Fr 2: Friesian
J = Jersey
F = female
MC = male castrate
Surveillance 17(2) 25
Surveillance Vol.17 No.2 1990
Table 3: IBR antibody prevalence rates
Animals
No.
Tested
Herds
No.
Tested
%
Positive
%
Positive
NI
NI
SI
2028
64
31
338
42000
58
40
1070
6180
56
Reference
SI
:3 .5
References
~
Table 1
NI = NorthIsland
SI = South Island
isolates were examined and their DNA
patterns were identical with each other
and with similar Australian isolates.
Australian strains of virus isolated from
cases of encephalitis were, however, totally different.
Conclusions
From the above data we can make the
following observations:
Outbreaks of clinical disease are rare.
This is possibly due to the high preva-
26 Surveillance 17(2)
lates.
New Zealand strains of virus are relatively avirulent as judged by the absence of IBR abortion and encephalitis.
lence of antibody in the population
following repeated subclinical infections and/or vaccination.
Clinical disease fluctuates from year
to year. More outbreaks occur some
years (1979, 1981, 1984) than others
(1980, 1987-89). This may be related
to climatic factors or to the fluctuating
immune status of the population.
Younger cattle (1-3 years) are more
commonly affected.
Most clinical disease occurs in the
summer months.
About 30% of isolates are genital iso-
Durham, PJK, Forbes-Faulkner, JC, Poole,
WSH, 1975: Infectious bovine rhinotracheitis
virus: experimental attempts at inducing bovine abortion with a New Zealand isolate. New
Zealund Vcvcvinarj Journal23: 93-94.
Horner, GW, 1982: Suspected infectious bovine rhinotracheitis encephalitis in calves.
Sur~~eillunce
9 ( 2 ) :21.
Durham, PJK, Sillars, HM, 1986: Evaluation
of an enzyme-linked immunosorbent assay
(ELISA) for serodiagnosis of infectious bovine
rhinotracheitis infection, with results of a preliminary survey. N ~ M
Zealand
'
Veterinary
Journal 34: 21-30.
Neilson, FJA, Grace, PJ, 1988: Infectious
bovine rhinotracheitis widespread in New
Zealand. Sur\~eillunce15 (21: 29.
Brake, F, Studdert, MJ, 1985: Molecular
epidemiology and pathogenesis of ruminant
herpesviruses including bovine, buffalo and
caprine herpesviruses 1 and bovine encephalitis herpesvirus. Australian Veterinury Journal
62: 331-334.
G W Horner
Chief Veterinary Virologist
Central Animal Health Laboratory