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The role of Porcilis® AR-T in an Atrophic Rhinitis eradication programme

by 5m Editor
14 November 2005, at 12:00am

By Marc Martens, Intervet - Before 1960, it was assumed that pig farms once infected with Atrophic Rhinitis (AR) would always remain that way. Depopulation followed by complete repopulation with new AR-free animals was the only means to become free of AR. The problem of AR was addressed in this way by state-run programmes in many European countries (East and West).

Intervet Pigs

The aetiology of AR was first clarified after 1975 when publications appeared showing that it was not Bordetella bronchiseptica, but the Dermo-Necrotic Toxin (DNT)- forming strains of Pasteurella multocida, that caused AR.

These DNT-forming P.multocida strains (Pm+) were isolated on only a few pig farms, by contrast with B.bronchiseptica. Furthermore it was possible to reproduce the disease, and the subsequent economic damage, by infection with these Pasteurella species alone.

In the Netherlands at that time, the initial eradication programme based on depoprepop was brought to a halt and a certification programme, organised by the regional Animal Health Institutes, took its place. It was then found that farms that had been vaccinating for years with Nobivac AR had become free of the Pm+bacteria. The Dutch experience has been the basis for a new eradication programme in Austria, which involves vaccination over several years and removing only the Pm+ individuals.

The certification programme of the Animal Health Institute in the Netherlands

Farms infected with AR were eligible for a sustainment programme. Advice was given on epidemiology, housing, climate control and management. The DNT-pasteurella was isolated in the laboratory, its resistance pattern determined, and medication regimes proposed. In 1985, Intervet was the first company to introduce an ARtoxin vaccine (Nobivac AR-T) onto the market. As soon as it was available, it was used on these farms.

Figure 1. Percentage certified PM+ free-farms in the Netherlands


Figure 2. Sales of AR-vaccine (million doses) by year (75-85% Porcilis ART)

Pm+-free certification programme was begun. Initially it was only for breeding and rearing farms, but now piglet producers can participate as well. Early on, vaccination was allowed on some farms belonging to breeding companies that were so concerned about the disease that they were unwilling to stop vaccinating, but later, vaccination was completely forbidden under the rules of the programme.

The conditions for the Pm+-free certificate are:

  1. Swabs must be taken from nose and tonsils three times a year, for two years. All samples must be examined in the laboratory and must all be free of toxin-producing P.multocida.
  2. No AR vaccination is allowed.
  3. Only Pm+-free animals and/or animals from certified Pm+-free farms may be introduced.

In fact, over 90% of breeding farms are now certified, and over 95% of replacement gilts are sold with a Pm+-free certificate. Recently, also piglet producers have joined the programme in order to be able to offer Pm+-free finishers.

At first an ELISA test was used for routine diagnosis, but this has been replaced by PCR techniques with a far greater sensitivity. The advantage of the PCR is that, even on farms which vaccinate, the chances of missing Pm+ bacteria are very small.

Eradication

Dr M de Jong from Animal Health Institure Deventer / Holland found that AR-infected farms that had been vaccinating for a number of years with Porcilis AR-T had become Pm+-free. Neither the ELISA nor with the PCR tests were able to demonstrate any DNT-Pasteurella on these farms (ref.3).

Investigation of these particular farms revealed that:

  1. Herds had been vaccinated for at least 3 years with Intervet's Porcilis AR-T
  2. Replacement gilts (7 months of age) had come from certified Pm+-free farms, were housed for 6 weeks in quarantine and vaccinated twice with Porcilis AR-T before introduction to the herd. They were then vaccinated for the third time, 4 weeks before farrowing.
  3. A strict "all in-all out" procedure had been followed in the farrowing and growing units.

Factors with a negative influence on Pm+ eradication were:

  1. Purchasing boars or gilts from infected farms.
  2. Introduction of piglets from around 12 weeks of age that could not be vaccinated beforehand.
  3. Immediate introduction into the infected herd without a quarantine period, so vaccination was started too late.
  4. Replacement gilts taken from own breeding stock.

These findings led to the conclusion that it was possible to clear AR-infected and vaccinating farms of Pm+ by identifying and eliminating carrier sows only, avoiding the cost of complete depopulation.

Figures 1 and 2 show that with the increase of certified Pm+-free farms in the Netherlands, the overall use of AR-vaccine has decreased.

AR eradication in Austria

At the moment, 300 farms in Nieder Thann Oberösterreich are involved in an eradication programme based on the system already described (intensive vaccination and screening using PCR). The samples are taken by local practitioners. Dr Martin de Jong from AHI Deventer is the AR expert for this programme.

Discussion and conclusions

Porcilis AR-T not only protects pigs against the clinical symptoms of Atrophic Rhinitis but also reduces the transmission of the toxin-producing Pasteurella multocida within the herd. This property of Porcilis AR-T has not yet been elucidated.

Intensive vaccination with a potent vaccine and a test and remove protocol are ideal tools for an eradication programme, and bear similarities with Aujeszkys Disease eradication. In the Netherlands, as the percentage of certified Pm+-free farms has increased, sales of Porcilis AR-T have gone down.

Porcilis AR-T DF

The above results have been achieved with Porcilis AR-T, which will soon be replaced by an improved version of the vaccine named Porcilis AR-T DF. Porcilis AR-T DF is already officially registered by the centralised EU procedure and will soon be launched in several countries. The adjuvant in Porcilis AR-T DF is Diluvac forte which is more tissue-friendly than an oil adjuvant. In addition, the PMT toxin is now produced in a very pure form, in E coli bacteria producing a non-toxic recombinant derivative of PMT. The new vaccine also contains inactivated cells of B. Bronchiseptica.

The improved vaccine will be able to produce the same results as reported above.

Further information

Click the links below for additional information:

References

1. Meyer K. and Schöss P. Eradication of Progressive Atrophic Rhinitis by bacteriological and serological examination. Proc. IPVS Bologna 1996 p246

2. De Jong M.F. Kamp E. and Bokken G. Selecting sows harboring AR toxigenic Pasteurella multocida by a PCR test to eliminate PAR in a breeding herd. Proc. IPVS Bangkok 1994 p167

3. De Jong M.F. Kamp E. van der Schoot A. and von Banniseth T. Elimination of AR toxinogenic Pasteurella from infected sow herds by a combination of AR-T vaccination and testing sows with a PCR and ELISA test. Proc. IPVS Bologna 1996 p245

4. De Jong M.F. Fortschritte in der Rhinitis Atrophicans Bekaempfung. BgVV symposium 2000 Jena Germany

Source: Intervet UK Ltd - November 2005