Post-weaning multisystemic wasting syndrome (PMWS) Introduction ...

Post-weaning multisystemic
wasting syndrome (PMWS)
Introduction
• Globally emergent disease of swine.
• First described in Canada in 1991, it has been reported
in all major pig producing countries in Europe and Asia.
• PMWS is one of the most common forms of porcine
circovirus associated disease (PCVD) on a global scale.
The role of porcine circovirus type 2 (PCV2) is clear in
terms of its association with the pathology, but less
clear in terms of the mechanisms of disease induction
and pathogenesis.
Meritxell Donadeu
PIC Europe
October 2005
PMWS Impact &
Implications
• Reduced Slaughter pig numbers GB by 4% costing
£30M/year, similar effects EU € 562-900 M/year
(Armstrong, IPVS 2004).
• PCV2- associated diseases, especially PMWS, cost
European producers € 600 M/year (Charreyre, 2005).
• Implications: increased mortality, fewer pigs at slaughter,
poor feed conversion rates, increased costs for management
and medication of sick pigs, and costs of secondary diseases.
• PMWS has also potential effects on food safety
immunosuppression may result in an increased prevalence on
farm and shedding of food borne pathogens.
• Trade barrier?
Clinical Signs of PMWS
INDIVIDUAL LEVEL
– Pigs 6-14 weeks of age.
– Wasting, depression, paleness, intermittent diarrhoea,
dyspnoea, enlarged inguinal lymph nodes and occasional
jaundice.
– Deteriorate rapidly over a period of 1-2 weeks.
– Signs of secondary or super-imposing viral or bacterial
diseases: PRRSV, Salmonellosis, H. parasuis, Ileitis.
– Refractory to treatment with antimicrobials.
Clinical Signs of PMWS
HERD LEVEL
HERD LEVEL
• Increase in mortality associated with pathogens already
endemic in the herd, for example, Glasser’s Disease;
followed some weeks later by the appearance of typical
clinical signs of PMWS in individual pigs.
• Morbidity is variable (3-50%) depending underlying health
status.
• Mortality of affected animals is high (70-80%).
– UK: Average 18%, for a minimum 3-5 months.

Mortality over time
Herd A: poor general health status
Mortality over time
Herd B: high general health status
% Mortality 7-30kg
70
60
50
40
30
20
10
0
21/09/2000
05/10/2000
Waddilove 2001
19/10/2000
02/11/2000
16/11/2000
30/11/2000
14/12/2000
28/12/2000
11/01/2001
25/01/2001
08/02/2001
22/02/2001
08/03/2001
22/03/2001
05/04/2001
19/04/2001
mortality
20%
18%
16%
14%
12%
10%
8%
6%
4%
2%
0%
Donadeu 2002
Jan
Feb
March
April
May
June
July
August
Sept
Oct
Nov
Dec
Diagnosis of PMWS
Diagnosis of PMWS
Individual level: (Evolved from Sorden et al, 2000)
• 3 components: all must be present in the
following order and in the same pig:
1- Clinical signs, including wasting.
2- Gross pathological findings, including emaciation, and
usually lymphadenopathy.
3- Demonstration of the presence of PCV2 in pathological
lesions by IHC or ISH (moderate to high amounts of
PCV2).
• At field level, not always going to step 3.
• The definition per-se, involves PCV2.
• Difference between PCV2 presence and PCV2 disease.
Herd level:
• Various criteria. Proposed from Segales et al, 2004:
1- Clinical process, characterised mainly by wasting, in
excess of the expected level. Evaluation of historical
data. Increased mortality of 5%?
2- Confirmation of PMWS in individual cases. Presence
and prevalence of other pathogens that could result in
differential diagnoses should also be assessed.
• No response to treatment.
• Increased mortality over a period of time.
Control and Prevention
1- Management Strategies
Why is PMWS so difficult to control?
1- Dealing with the unknown: how does the casual
agent behave, how it spreads, how interacts with
the immune system…. “Best guess available”
2- Diagnosis: over and under diagnosis
3- Big problem, so different strategies at used at the same
time.
4- Information available: majority circumstantial evidence,
difficult to separate facts, beliefs and opinions.
5- Clinical trials difficult to perform under field conditions.
Objective: CONTROL
a- 20 Madec points. Good Management practices:
• Basics of pig management: strict AI/AO, limit stress, reduce
stocking densities and strict hygiene. Minimum 16 points for
significant response.
PRACTICAL RECOMMENDATIONS AT FARM LEVEL:
1- Minimize stress: Environmental, nutritional, emotional and
immunological stress.
2- Start best quality piglets: Ensure colostrum intake, delay
weaning.
3- Minimize secondary problems: Improve hygiene, Control other
diseases present in the herd. Review current medication practices.

1- Management Strategies
4- Therapeutic strategies & other diseases
b- Batch farrowing:
c- Partial depopulation
d- Total Depopulation/repopulation:
2- Nutritional Strategies
e- Bioflavonoids, Vit E, Se, antioxidants: Nutraceutical products. Not
very successful.
3- Genetics
f- Breed susceptibility/resistance:
Changing the boar led to an improvement. Pietrain and Hampshire
based lines are the most preferred options. Change in boar might
mean change in source.
g- Vaccination for PCV2:
• “Circovac”: Merial is marketing a new PCV2 vaccine since last Autumn.
• Provisional registration in France (Nov 04) and some regions of
Germany (August to Dec 04). Intended for gilts and sows to provide
passive immunity to piglets.
• Iowa state: Chimeric PCV 2 and PCV1. Finisher pigs.
• Autogenous vaccines
h - Serotherapy:
Originally in flat decks but later also in the farrowing house.
First used to decrease incidence, but also to treat pigs already showing
disease.
i- Closed herd
j- take replacements from PMWS positive farms.
And many other measures have been tried…
PMWS has a major impact for the European industry and a
better understanding of the disease is needed in order to
reduce it.
• Standard biosecurity approaches do not appear to have
prevented the entry of PMWS. How can we protect the
units?
• How can we make a more accurate and faster diagnosis?
• How can we control PMWS in a consistent way?
• Interactions of PMWS with other diseases?
• How can we know when the farm is stable for the
disease? How can we obtain negative animals from positive
farms?
• …