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PMWS Case History
Michael R Muirhead BVM&S, DPM, FRCVS

PMWS Case History - Final update 28th June 2002

The following sections have been updated and revised:
Light at the end of the Tunnel
Final Summary
Mortality Rates

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This case history describes the appearance of PMWS and PDNS, from April 2001 to April/May 2002, in a 240 sow breeding/finishing herd. I am grateful for the permission from the owner of this farm to use the data in the hope that it will not only benefit the farm itself, but also through the generation of comment, discussion and interest on it will provide a continuous learning curve to this very difficult disease and its control.

The farm is located in a pig dense area in the UK and it had been closed to the import of live pigs for approximately 3 years with only AI being used for genetic improvement. I would consider the biosecurity on the farm to be good with 24 hours down time for visitors and a strict entry routine with on farm-boots and overalls.

The pigs are weaned each week at a mean of 24 days of age to all-in/all-out self-contained groups of approximately 110 pigs. Each weaned batch is held in this contained group for a period of approximately 2-4 weeks. At the end of this they move in to 2nd stage grower accommodation in small groups of 25-30, again individual pens with their own air space.

This housing had been used continually for at least 2 years with high throughput and only being dry-cleaned and disinfected by aerosol between batches intermittently. Without any doubt the continual use of this accommodation was a contributing factor to the development and severity of disease.

Health History

The herd has been exposed to PRRS and influenza over many years and periodic minor episodes of both diseases are experienced. Effects however on production had been minimal prior to PMWS. Mycoplasma hypneumoniae and App type 3 have been diagnosed in the past but since vaccination against M.hyo (Fort Dodge, M-Hyo) the herd has shown few signs of respiratory disease apart from a few cases of Glässer's Disease (Haemophilus parasuis).

In January 2001 it was decided to use Fort Dodge's combined M.hyo parasuis vaccine in an effort to control this. Sows are routinely vaccinated against Erysipelas and gilts once against parvovirus. Piglets have been vaccinated at 7 and 24 days of age with M.hyo. This commenced approximately 6 years ago. The response to this has been quite remarkable.

No herd medication has been used apart from in feed for the first 14 days post weaning, when 3.1kg of zinc oxide and 500g of CTC have been included.


Health and performance have been excellent over the last 3 years with 2.3 litters per sow per year and 24 pigs weaned. In the growing/finishing herd weaner mortality (7 to 35kg) has averaged 2.3% with finishing mortality at 1.8% (this includes pigs shot on welfare grounds). Feed efficiency to 95kg has been 2.20. Detailed records of treatments and mortality have always been maintained and this has given the opportunity for the close scrutiny from the veterinary point of view of the disease and its progression.

The Appearance of Disease

In January/February/March of 2001 the owner reported some inappetence in a few sows at farrowing and poor milking but no increase in piglet mortality. A slight cough was noticed in sucking pigs and transient cyanosis (Blue Ears) were noted in a few sows. There was no increase in mortality in growing pigs and this episode was considered to be an upsurge of PRRS. In hindsight this could have been the first signs of PMWS/PDNS.

Post mortem examinations of pigs showed a severe pneumonia with pericarditis, epicarditis, pleurisy, severe consolidating pneumonia and oedema (fluid) on occasions and peritonitis. At this stage there was little evidence of enlarged lymph glands particularly in the inguinal regions. Samples were taken from lymph glands for histological and biochemical analysis. These confirmed the presence of inclusion bodies in lymphoid tissues in the cells, typical of PMWS. This was in April when it was determined the herd probably had become affected by PMWS.

At this point the manager was convinced that the disease had coincided with the introduction of the parasuis component of the M-Hyo vaccine. He therefore decided to return to just the M-Hyo only vaccination. As it turned out was a disastrous decision because 2 months later in the middle of June mortality rose to 24% with evidence of both severe Glässer's Disease and App type 3. Glâsser's disease vaccination using the combined vaccine recommenced immediately.

Commencing in early June it was decided to totally depopulate the second stage accommodation, steam clean the whole of the building, disinfect using Virkon S and rest it for 2 weeks. Repopulation of this building them commenced late in June. The first stage has always operated on an all-in, all-out basis.

Six to eight week old pigs would normally leave the weaner accommodation and move into the second stage and be reduced in size to groups of 30 pigs or less. During the period of depopulation however 3 weekly groups each of approximately 110 pigs (7 weeks old) from the first stage yards were moved out, each into separate large straw yards, to facilitate the depopulation. These pigs were the ones not vaccinated against H-parasuis with the subsequent disastrous effects on the respiratory disease in June and July.

Actions and Conclusions (where applicable)

The farm has generally followed the rules and points explained in the article "CONTROLLING PMWS". In doing so, approximately sixteen of the twenty "Madec principles" were adopted. Generally, it has to be said that the application of (16/20) Madec Principles had limited effect on this farm.

Evidence across numerous farms suggests that the application of these principles can make a considerable difference, but as typical with PMWS, this not the case for all farms, including this one.

The table below summarises the specific actions taken to try to control the outbreak of PDNS/PMWS on this farm. The specifics of each of these actions are explained in more detail in the text below the table.

The table is broken down into two columns. On the left are a list of procedures that were applied and do not appear to give a response to the incidence of PMWS. On the right are the list of procedures that did appear to have an effect in some form or another. Specifically, the combination of two of the procedures had a significant benefit.

Remember, the one consistency with PMWS is it's inconsistency. Just because a procedure appears to have had limited effect on this farm does not mean to say it will not work elsewhere. Beating PMWS is a trial and error process but as can be seen from these results, it would appear it can be beaten on this farm.

Procedures and their effect on the incidence of PMWS
No discernible response
Appears to have helped
All in all out - No reduction in PMWS incidence. All all out - Improved general health but not PMWS incidence.
Reduction in group sizes at weaning from 100 to 50. Improved diet using natural supplement with increased levels of dietary antioxidants
Altered timing of piglet vaccinations Serum injections - This was tried at 5 days of age and at weaning (5ml doses).
Immune stimulation of the sow and gilt. Serum treatment of sick pigs.
Depopulation, cleaning, disinfection and repopulation of the stage 2 housing Good hospital pens.
Improved hygiene, teeth clippers etc. Prompt removal to hospital pens.
Any form of treatment, individual or group (except serum treatment of diseased pigs). Aerial disinfection with Virkon S - Reduced secondary pneumonias
Improved environments and management Glässers Disease vaccination
Vaccinations at weaning against parvovirus.     

Further information

Treatment of individual pigs:
Generally, conventional treatment methods in individual pigs was unsuccessful. The manager reported that around 20% of pigs survive irrespective of treatments and become normal. Severely affected pigs were destroyed on welfare grounds.
This farm has tried the following conventional treatments with no dramatic effects:
  • Antibiotics by injection
  • Water medication
  • In feed medication with CTC or penicillin to prevent secondary infections.
Response to corticosteroid and amoxicillin did not materialise and was abandoned.

HOWEVER, the use of serum as a treatment (introduced in January 2002) appears to have been successful in helping some of the affected pigs to recover (see Mortality below).

Parvovirus vaccination of weaners:
It has been suggested by various authors that the disease is associated with pigs that have no maternal antibody to parvovirus. When they meet PCV2 and parvovirus (=PCV2x) this initiates the lymphoid depletion and results in PMWS (this has now been demonstrated experimentally as reported at the St Malo conference. The same also occurs with PRRS virus).
     To test this out a group of weaned pigs were vaccinated against parvovirus at 24 days of age and compared to a non-vaccinated group.
     The objective was to try and stimulate immunity of the weaned pigs prior to exposure to PCV2 to see if this had an effect.
Final Conclusions: A total of 393 pigs were vaccinated with an 18.6% affected level. This compares to the total non vaccinated population of 2711 with a level of 19%.
From this is would appear that in this herd vaccination of the weaner against PPV was ineffective, probably because (PMWS) infection and initial damage has occurred prior to this vaccination.

Vaccination of sows:
At the St Malo conference experimental work indicated that piglets from sows sero-negative to PPV (and no colostral antibodies) could become infected as early as 3 days of age. Since at least 15-20% of sows in any herd at any one time could be sero-negative to PPV this suggests that sows should be boosted against PPV at least 2 weeks before farrowing to increase maternal antibody.
     Looking along similar lines, this also suggests that the use of the newly launched killed PRRS vaccine (PROGRESSIS) for use in sows could be used prior to farrowing to raise maternal antibodies against PRRS. Piglets with high levels of antibody to PPV and/or PRRS do not appear to succumb to the disease even though they may be infected with PCV2 virus.
     Based on this information sows were vaccinated before farrowing with both the PPV and Merial's new killed PRRS vaccine, PROGRESSIS.
Conclusions: Unfortunately, due to the small numbers of sows vaccinated no conclusions can be drawn. However, if there are problems in a herd with PRRS, vaccination with PROGRESSIS is certainly worth considering.

Immune stimulation::
Of the maiden gilt::
On the basis that nearly all pathogenic organisms stimulate the immune systems, management procedures commenced in week 24 to challenge gilts to PCV2x. This is carried out by exposure and co-mingling them with pigs affected with PMWS for 2 weeks, 3 weeks prior to anticipated mating.
Of the sow:
At the St Malo conference it was reported that experimental inoculation of foetuses in-utero less than 75 days of age may produce severe disease with stillbirths and mummification. Piglets inoculated after 75 days (piglets at this time have an active immune system) developed an immunity and no adverse effects. This suggests that sows should not purposely be exposed to PCV2 until after 80 days pregnant.
     Sows on this farm were exposed to PCV2, 3 times weekly for 2 weeks when they were between 80 - 95 days pregnant. All these sows have now farrowed normally with no apparent effects on piglets. Twenty-seven sows and gilts underwent these processes, producing a total of 275 pigs. The final results of these pigs has shown no positive benefit.
Conclusions: There appears to have been no adverse effects in either sows or litters following this procedure. However, a word of caution - fertility problems have being reported in the US associated with PCV2. Interestingly, results from tests of serum samples taken from a few sows have shown high levels of antibody to PCV2. This serum has subsequently been used for treatment.

Colostrum/Cross fostering:
The basis that some litters do not develop PMWS suggests protective mechanisms in the colostrum of such sows. For 3 weeks all litters where feasible were suckled from two different sows within 24 hours of birth, for 6 hours or so on each.
Conclusions: This proved to be an onerous task for the farm staff to manage, and as a result efforts to implement this procedure have been stopped. No conclusions could be drawn on the effectiveness of the procedure on those litters that were cross fostered.
NOTE: A variation on this theme is to try 'litter swapping'. Here litters are changed over after birth once the piglets have had a first suckle (ideally this occurs within 4-6 hours of birth), but definitely within 12 hours of birth. The piglets are then left on their new 'mothers'. This cuts down on the time needed to implement the procedure and doubles the chance the piglets having a more widespread maternal antibody.

Improved Hygiene:
Equipment Disinfection: Ten needles are now held in a container with 2% Virkon S (Antec) and rotated between litters. Needles are also changed every 5 pigs at vaccination time. When needles are changed they are shaken out prior to use. Three pairs of teeth clippers are used and changed every piglet. They are also held in the 2% Virkon S solution.
Conclusions: In spite of heroic attempts by the staff, complete all in - all out, improved hygiene and a reduction in group size at weaning, the herd reported no improvements prior to the feed and serum procedures being introduced.

In the middle of June 2001, the second stage housing was totally depopulated cleaned, disinfected, dried and repopulated. Prior to this event 1771 pigs (all-in, all-out) passed through this accommodation with a 19% mortality to 14 weeks. Since clean down 895 pigs have passed through on an all-in, all-out basis with a final mortality rate of 18% although the incidence of acute pneumonias reduced considerably. This can only be considered a poor response and is not as good as some herds have reported.
Conclusions: Mortality in October, November and December did not improved in spite of rigorous hygiene improvements commencing in June.

Aerial Disinfection:
Pens of weaned pigs have been fogged with 1% Virkon S twice daily from 6 to 12 weeks of age. This involves using a hand held electric fogging machine. The nozzle is held in each pen for 3-4 seconds morning and night
Conclusions: This continues to appear to help in reducing the secondary pneumonias which are no longer very evident. The manager felt this was a worthwhile technique. However, over the first 4 months there were no apparent improvement in the PMWS disease levels, thus is can not be said to be have had an effect on the disease itself, probably as I suspect that the course of the disease is already determined prior to weaning.

Stress Reduction:
At the St Malo conference experiments were reported showing that disease results from a combination of immuno-suppression and immuno-stimulation. When a PCV2 infected pig undergoes immuno-stimulation (e.g PPV/PRRS infection etc.) this appears to be the trigger factor that allows the PCV2 virus to enter the lymphoid system. The PCV2 virus then damages the lymphoid system resulting in PMWS. This suggests that different herd have their own trigger factors in this respect.
     The wrong timing of vaccination may have a part to play in this. However in quite a number of herds severe disease has occurred where no vaccines have been used in the pig. An assessment of the timing of vaccination programs may be necessary. It is vital however to continue a program of M-hyo and/or parasuis vaccination in these susceptible herds. Veterinary discussions should be held on each individual herd.
     In this herd the timing of the vaccination program was altered to commence from 6 weeks of age onwards. i.e. pigs are not vaccinated under 6 weeks of age (other than serum).
Conclusions: There were no apparent changes as a result of this technique prior to the feed and serum procedures being introduced.

Light at the end of the Tunnel?

As mentioned earlier, two specific procedures seem to have had a significant effect in reducing the devastating effects of PMWS. Light at the end of the tunnel for this farm?

These procedures were the introduction of a natural feed supplement high in antioxidants and the use of serum to both treat affected pigs and "immunise" piglets and/or weaners at weaning time.

Improved Nutrition
A number of nutritional supplements are available on the market which are reported to improve health and growth rates.

At the St Malo conference SOGEVAL Laboritories from France also reported the results of feeding acetaminophen in a very large controlled field trial. This showed a statistically significant reduction in the mortality of wasting piglets

A number of feed manufactures are testing products in this arena. However, one product specifically, seemed to be receiving generally positive field reports (ViraMatrix). Consequently, this supplement, which uses a mixture of natural nutritional ingredients containing high levels of antioxidants, was introduced for assessment. All pigs on the farm from weaning to 14 weeks of age have had their diet fortified with ViraMatrix.

Use of Serum
Serotherapy was tried in two ways. Firstly it was used to inoculate pigs at 5 days of age and subsequently to inoculate pigs at weaning. In both cases the aim was to attempt to raise immunity levels.

Three Groups - improving success

Over a period of time three groups of pigs went through the above regimes, each with improving success.

Group 1
    In mid November 2001 all pigs from weaning to 14 weeks of age had their feed rations fortified with ViraMatrix, a nutritional supplement providing high levels of antioxidants. This was added to first and second stage creeps and the weaner rations.

    Six weekly batches, a total of 655 pigs, were in this first group. These pigs had an affected level of 13%. This was a significant improvement from the 23% in December 2001 and the average level of 21% seen from June to December 2001.
Group 2
    Four weekly batches of 398 pigs make up the second group of pigs. In addition to the improved diet, this group were treated with serum (5ccs) at 5 days of age, as they were given their iron injections. These pigs had an affected level of 4%.
Group 3
    The third group was made up of seven weekly batches totalling 591 pigs. In addition to the improved diet, this group was treated with serum (5ccs) at weaning (approx. 24 days of age). These pigs had an affected level of 8.5%
Results from the use of ViraMatrix and serum.
Pre Feed and Serum Changes: 3082 pigs 21% affected (Apr-Dec 01).
1. Feed changes only 655 pigs 13% affected (8% reduction)
2. Feed + Serum (5 days) 398 pigs 4% affected (a further 9% reduction
3. Feed + Serum (weaning) 591 pigs 8.5% affected (a further 4.5% reduction)
TOTAL Feed + Serum 989 pigs 6.5% affected (14.5% overall reduction)
TOTAL Feed (with/without Serum) 1644 pigs 9% affected (12% overall reduction)

The most remarkable clinical observations were the changes in health, general demeanour, activity, feed intake and growth rate of the pigs, seen in the first group following the introduction of ViraMatrix.

In the second and third groups (ViraMatrix and serum) this response had been even more striking. The manager said that these were the best pigs he had seen on the farm for many years. I have to say they certainly looked extremely well and growth rates were to be excellent.

  • This was the first time since PMWS became evident in April 2001, that there was a dramatic response. I would add a note of caution however. Remember experiences tell us that what appears to work on one farm may not give a response on another, but this regime (summary below) certainly seems worth a try and these procedures are worth discussing with your veterinary surgeon if you have an intractable problem.
  • Is ViraMatrix and serum inoculation the key on this farm and is it repeatable? I don't know because this can only be determined on a farm by farm basis and serum alone has not been tried here.
  • The dose of serum has been quite small and probably insufficient to suggest a response alone due to low levels of antibody but perhaps as yet unknown immune complexes.
  • Serum inoculation (alone) on other farms generally appears to reduce mortality by up to 50% or more. As is typical of PMWS, some farms respond better that others.
  • It is interesting to note that there was a response time of 4 - 8 weeks before the benefits of the improved nutrition was seen. This has been similarly reported on other farm observations which also show that the benefits tend to continue improving with time. Continuing improvements are being seen on this farm, however due to the introduction of serum it is not possible to conclude the extent to which each procedure (improved nutrition or serum) is contributing, other than to say together the ongoing results speak for themselves.
Final Summary

With the herd now well on its way to completing its depopulation I will now summarise the results and thoughts on the disease.

From the mortality figures highlighted above it can be seen that since the introduction of the high levels of antioxidants in the feed, followed by the continual use of serotherapy, the mortality due to PMWS has reduced significantly and in the last month was down to around 4%. Note: Non PMWS deaths were elevated in April due to a number of pigs being destroyed on both welfare grounds and other reasons.

The Results table above shows a summary of the combination of ViraMatrix and serotherapy that would seem to have had an effect on this farm.

Using the ViraMatrix alone reduced the number of affected pigs from approximately 21% down to 13%. Anecdotal evidence from the field using this product shows on a number of farms a response greater than this to PMWS but also on a few farms with no reported effects.

Perhaps the most interesting results are the responses to serotherapy either given at 24 days of age or 5 days of age. There is a significant response in the pigs given the serotherapy at 5 days of age with only 4% of pigs affected.

Furthermore, on a twice weekly basis, as affected pigs were recognised they were moved out into hospital pens and given 10ml of serum as treatment. This has reduced the mortality from approximately 90% of affected pigs down to 50%. The results of this can be seen in the table below.

% due toPMWS
Mortality %
Prior to Treatment
3082 pigs
21% 17% 4% 21%
ViraMatrix alone
655 pigs
13% *7% 3% 10%
ViraMatrix + serum
591, 24 day old pigs
8.5% *4.5% 3.5% 8%
ViraMatrix + serum
398, 5 day old piglets
4% *2% 5% 7%
* Hospital mortality reduced by 50% with 10ml serum

It is important to emphasise at this point that procedures that appear to work on one farm sometimes do not appear to have an effect on another. Perhaps this due to the varying colostral antibody levels to PCV2 in the colostrum of the sows (See Pathogenesis Discussion Article).


To summarise, if you have an intractable problem with PMWS try the following regime:
  1. Fortify the feed fed to pigs from weaning to 14 weeks of age by adding ViraMatrix at the rates recommended by the manufacturer.
  2. Treat all pigs at 5 days (or weaning) with 5ml of serum (See Discussion Forum for Protocol).
  3. Promptly move any pigs that show signs of developing PMWS to a suitable hospital pen. Feed rations fortified with ViraMatrix and treat the pigs with 10ml of serum.
I can not say with any certainty this will work on other farms due to the vagaries of PMWS, all I can say is that significant benefits accrued from this protocol on this farm.

NOTE: Discuss the implementation of this procedure and specifically the use of serum with your Vet prior to taking any action.

Mortality Rates (Graphical)

Effects on Production (Easicare Data)

Statistic 12 Months
Prior to Disease
6 Months after
May to Oct
Farrowing Rate 83% 80%
Litters / Sow / Year 2.25 2.25
No.s Born Alive 11.4 11.17
No.s Born Dead 1.4 1.65
Pre Wean Mortality 10% 10.5%
No.s Weaned / Litter 10 10.01
Pigs sold 21.6 17.4
Weaner Mortality (to 14 weeks) 2% 17%
Grow Finish Mortality to 95kg 2.3% 4%
Total Wean-Finish Mortality 4.3% 21%
Feed Cost / Pig Produced* £34 - 35 £39.04
Daily Liveweight Gain 592g 526g
Cost kg Liveweight Gain 36p 41p
Feed Efficiency 2.22 2.4
* Feed prices constant

Comment on the Effects on Production:
The production data will yet to have reached its peak losses. Note however an increase in £5.00 per pig feed cost, 5p cost/kg lwt gain, feed efficiency worse by 0.18 and daily gain worse by 66g.

On lost sales costs of feed and mortality this equates to around £11.40 per pig, assuming 22 pigs sow per year had been sold.

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Note of thanks:
I would like to thank the Farm Manager for all his assistance and efforts during this study, Chris Clark at Clark Feeds for their efforts in handling all the feed requirements, and Park Tonks for supplying the ViraMatrix feed supplement.

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