ISRAEL JOURNAL OF
VETERINARY MEDICINE
Case report:
Vol. 58 (1) 2003
AN APPARENT ASSOCIATION BETWEEN
NEWCASTLE DISEASE
AND MAREK'S DISEASE IN COMMERCIAL
FLOCKS
I. Davidson1 and M. Kedem2
1. Division of Avian Diseases, Kimron Veterinary Institute, Bet Dagan
2. Akko Regional Poultry Laboratory
Abstract
Based on the clinical signs of paralysis appearing in certain flocks of domestic
fowl, the involvement of Marek's disease virus in these cases was suspected.
Recently, novel MDV isolates were described in the United States, that are
associated with clinical symptoms other than neoplasia. Thus brain tissues from
birds with clinical Newcastle disease-like symptoms were examined using specific
MDV PCR primers, in parallel to isolation of NDV. Both viruses were diagnosed
in 18 out of 32 chicken, turkey and geese flocks. No association of MDV with
other pathogens was observed in flocks affected with other diseases, such as
infectious bronchitis, infectious bursal disease or turkey rhinotracheitis. Most of
the NDV/MDV positive flocks were broilers (9/13) or layers (6/16). The
similarities between the presentations of the infections with NDV and MDV
indicate the need for differential laboratory diagnosis.
Introduction
Marek' sdisease (MD) (1) and Newcastle disease (ND) (2) are well known avian
diseases with distinct presenting signs. The first is a herpesvirus, which is associated
with immunosuppression, T cell transformation and tumor formation. However, in
addition to these properties MDV also causes neurological signs, although being
studied much lesser.
The paralytic syndrome of MDV involving brain lesions was described by Zander
(3). More recently a paralytic syndrome in broilers was the subject of a study aimed to
apply the differential diagnosis by molecular means (4). Neurological signs associated
with MDV infection are mostly prevalent in young chickens and two possible
explanations might be anticipated; a) the paralytic signs appeared shortly after
infection and not there was not enough time for the tumor to be formed; b) The signs
reflect biological characteristics of the new MDV isolates, as described lately by
Witter (5). In a very elegant study Gimeno et al. (6) detailed the kinetics of the
various neurological syndromes caused by virulent MDV strains in experimentally
infected birds.
NDV is a paramyxovirus associated with a severe respiratory disease and can vary
in pathogenicity. NDV also causes paralytic syndromes such as muscular tremors,
torticollis and paralysis of the limbs. During the Newcastle disease outbreaks that
occurred during the last two years in Western Galillee, the presenting clinical signs
indicated the occurrence of ND, but also the apparent involvement of MD was
suspected due to typical signs of paralysis. The association between MDV in the NDV
cases was investigated for two reasons; the clinical picture, on one hand, and the
possibility that various non-neoplastic MDV isolates, lately described in the US, were
involved in causing new and different clinical displays and not only tumors.
As demonstrated, the target organ for MDV identification in cases of transient
paralysis was the brain (4), thus brains were analyzed in the present study. Flocks
with or without clinical Newcastle disease were examined for MDV by PCR
amplification, in parallel to the NDV isolation performed by standard procedures (2).
MDV was detected by amplification of the 132 bp tandem repeat fragment (BamH1H/D genomic fragments) using primers M1 and M2 (7). The primers used in the
present study were:
M1 (direct)
M2 (reverse)
5‫ ם‬TAC TTC CTA TAT AGA TTG AGA CG T
5‫ ם‬GAG ATC CTC GTA AGG TGT AAT ATA
The PCR conditions for the amplification were: a 25 ?l PCR reaction mixture
contained: 10 mM Tris HCl (pH 8.5), 50 mM KCl, 1.5 mM MgCl2, dATP, dCTP,
dGTP and dTTP, each at 200 mM, primers (1.2 mM, each) and 0.5 units Taq
polymerase (Advanced Biotechnologies LTD, U.K.). PCR cycling parameters were:
one cycle of 940C for 1 min, 31 cycles of 940C for 1 min, 550C for 1 min and 720C
for 1 min, followed by a final elongation at 720C for 10 min (8,9).
During the last two years some overlapping of clinical signs of MD and ND
occurred in various commercial flocks with ‫ל‬MD/ND-like signs‫מ‬. These are shown in
Table 1.
Table 1: Commercial flocks with "ND/MDV-like” clinical signs
Flock type
Viral identification
Total
NDV +/
MDV +
NDV +/
MDV -
NDV -/
MDV +
NDV -/
MDV -
Broiler
9
4
0
0
13
Broiler
1
0
0
0
1
breeder
Layer
6
6
1
3
16
Turkey
1
0
0
0
1
Geese
1
0
0
0
1
Total
18
10
1
3
32
Most cases were recorded in broiler and laying flocks, and one case each was
observed in broiler breeders, turkeys, and geese, an exceptional host for both viruses.
Out of a total of 32 flocks with these symptoms, ND was diagnosed in 28 flocks, and
19 flocks were diagnosed with MD. One flock was positive only for MD, while 10
flocks were positive only for ND. However, in 18 flocks both viruses were
recognized, indicating that clinical signs can be indicative of ND and MD in the same
flock. The laboratory diagnosis of MDV is therefore justified in such cases.
Table 2 shows commercial flocks with various clinical diseases to evaluate whether
MDV infection has a preferential affinity to NDV or has an affinity for other other
pathogens as well. Similarly aged flocks, from the same region were examined for the
causal agent, and for MDV, in parallel. These flocks included broilers with respiratory
signs, suspected for infection with infectious bronchitis or infectious bursal disease
virus or suffering from transient paralysis. The turkey flocks were suspected as being
infected with turkey rhinotraceitis virus or Mycoplasma gallisepticum, but were
negative for NDV. Table 2 indicated that only 2/19 flocks were infected with MDV.
Flock type
Viral identification
Total
NDV +/
NDV +/
NDV -/
NDV -/
MDV +
MDV -
MDV +
MDV -
Broiler
0
0
2
11
13
Turkey
0
0
0
6
6
Total
0
0
2
17
19
In summary, an apparent association between MDV and NDV in commercial flocks
was observed. The two viruses are unrelated, but both infect birds by inhalation, and a
common route of infection or transport might be present; Moreover, immune
deficiency might play an important role in the clinical picture, by adding a synergistic
aspect. In addition, sub-clinical infection with MDV might lead to enhanced
susceptibility to NDV. Such interactions were suspected during the recent ND
outbreak in Australia (10).
It might be speculated that infection with ND renders the flocks more receptive to a
further infection with MDV, or vice versa. That hypothesis might be further
investigated, since the real impact on commercial flocks is probably the result of more
than one virus.
LINKS TO OTHER ARTICLES IN THIS ISSUE
References
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