Reprinted in the IVIS website with the permission of
the meeting organizers
Abstract No: O.25-02
THE LIKELIHOOD RATIO PROBABILITY OF PMWS IN A DANISH CASE-CONTROL STUDY
EO Nielsen1, K Barfod1, B Svensmark1, G Holm1, V Bille-Hansen2, SE Jorsal2
1
The National Committee for Pig Prod., COPENHAGEN, Denmark
The Danish Inst. for Food and Veterinary, COPENHAGEN, Denmark
2
Materials and Methods
The Danish PMWS case-control study was conducted in
2003-2004. A herd was considered PMWS positive when:
1) giant cells/inclusion bodies and porcine circo virus
type 2 (PCV2) was found in lymphoid tissues from
autopsied pigs; 2) clinical signs indicative of PMWS and
an elevated mortality in weaners (>5%) was observed.
Seventy-four herds fulfilling the criteria for PMWS were
selected as cases. Each of the cases was matched on
veterinary surgeon’s practice with a control with no
clinical signs compatible with PMWS, adding up to a total
of 148 herds. The matched design was used to take account
of differences in diagnostic capabilities and treatment
routines, and geographical location. Veterinarians selected
three pigs in each herd on clinical signs of unthriftiness,
often with respiratory signs or diarrhoea. The pigs were
euthanized, and autopsied at the Laboratory of Swine
Diseases, Kjellerup, DK. The macroscopic examination
followed a scheme covering externals, lungs, heart, liver,
spleen, stomach, intestine, bladder, kidneys and lymph
nodes. The PMWS diagnosis of each pig was reached by
histological and virological examination (1) of the
superficial inguinal lymph nodes, mesenteric lymph nodes
and spleen at the Danish Institute for Food and Veterinary
Research. The criteria for categorizing a pig as PMWS
positive were: Presence of depletion together with
histiocytic infiltration and/or inclusion bodies and/or giant
cells as well as detection of PCV2 in moderate to massive
quantity within the lesions in lymphoid tissues. The
macroscopic findings in each pig were analysed with
respect to positive or negative PMWS diagnosis in a
stepwise logistic regression (SAS ver 9.1). The predictive
values of macroscopic findings were estimated by
Likelihood ratio diagnostics (2). The analysis was
performed on case herds and control herds separately.
Results
The analysis included 416 of the sampled weaner pigs (1014 weeks-of-age), because in 28 pigs the record on
macroscopic findings was missing. The prevalence of
PMWS positive pigs from case herds was 35% (74/213).
The prevalence of PMWS positive pigs for herds with no
indication of PMWS was 12% (24/203). Four macroscopic
signs (Table 1) were significant in a logistic regression
model (P<0.05) for having positive PMWS diagnosis. Pigs
158
exhibiting: heavy lungs, dilated atonic intestine, enlarged
bronchial lymph nodes, or enlarged inguinal lymph nodes
had higher probability of being PMWS positive.
Coincidence of these four findings gave a probability of
being PMWS positive of 0.72 for an unthrifty pig in a herd
with PMWS. The same four findings in an unthrifty pig
from a herd with no herd diagnosis of PMWS increased the
probability of finding histological lesions of PMWS and
PCV2 virus in lymph nodes too. In a control herd the
predictive value of PMWS was 0.73 in an unthrifty pig
with all four findings (Figure 1).
Table 1 Prevalence of significant macroscopic findings
Percentage of pigs
Case herds
Control herds
with or without
Pos.
Neg.
Pos.
Neg.
PMWS diagnosis
pigs,% pigs,% pigs,% pigs,%
Heavy lungs
38
21
17
5
Dilated,atonic
28
16
54
25
intestines
Enlarged lnn. ing.
61
47
46
32
Enlarged lnn. bron.
68
58
46
25
Predictive value
Introduction
Postweaning Multisystemic Wasting Syndrome (PMWS)
has affected many herds in Denmark during the last five
years. PMWS causes a variety of clinical findings, mainly
respiratory symptoms, diarrhoea and unthrifty weaner and
grower pigs. The aim of this study was to investigate the
correlation between macroscopic pathologic lesions and
the histopathologic verification of PMWS.
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Prevalence Heavy lungs
Dilated,
atonic
intestines
Control herds
Enlarged
lnn. ing.
Enlarged
lnn.bron.
PMWS case herds
Figure 1 The probability that an unthrifty pig had
histological and virological findings consistent with
PMWS given macroscopic findings in the same pig
Discussion and Conclusion
The probability of an unthrifty pig fulfilling the criteria for
PMWS in relation to the macroscopic lesions of the same
pig was identical in herds with PMWS and in control
herds. Macroscopic lesions of pneumonia and enlarged
lymph nodes have been reported as indicative of PMWS
(3,4). In this study dilated atonic intestines was also
suggestive of PMWS. The likelihood ratio estimation of
the predictive value of macroscopic findings gives a tool
for choosing the best material for histology and virology,
when clinical symptoms of PMWS in a herd are to be
verified at the laboratory.
References
1. Sorden, S.D. (2000). Swine Health Prod. 8, 133-136
2. Sackett, D. et al. (1991). Clinical epidemiology, 69-152
3. Madec, F. et al. (2000). The Pig Journal 45, 69-75
4. Segalés, J. et al. (2004). Vet. Micro. 98, 137-149
Proceedings of the 19th IPVS Congress, Copenhagen, Denmark, 2006 · Volume 1