Dear Paul, colleagues,

much as I hate to disappoint our moderator in his attempt to "stir things up a bit", I have to say that I agree with him on both of these points. I think we will have to maintain awareness of the possibility of morbillivirus infection in cattle, especially given the findings of new morbilliviruses and more in bat populations, but cattle can largely be set aside for the immediate focus, PPR control.

Wild life is much harder to get a handle on, and I agree with Richard Kock that it is an area where we need to improve our knowledge.

There is a great increase of small ruminant movement over the last 20 years, and defining the patterns of such movement will be an important part of our efforts at control.

With regard to the point of "should we", I think it would be a very costly programme if that is all we did. If we control, and eventually eradicate, PPRV as part of a general programme of uplift of veterinary services and small animal health, that would seem a more efficient use of resources.

One thing the RPV control programmes did was, in many countries, improve coordination of veterinary/laboratory services and education/awareness in livestock keepers. That has faded a bit, and will need to be built up again. These are tough tasks, no denying it, but not intrinsically unsolvable..

Michael


Michael D. Baron Ph.D. ([log in to unmask])
Group Leader, Paramyxo&Bunyavirus
The Pirbright Institute,
Ash Road, Pirbright,
Surrey GU24 0NF U.K.
Tel 01483 231024 (office)
Tel 01483 231145 (lab)


From: Establishment of a PPR Global Research and Expertise Network (PPR-GREN) [[log in to unmask]] on behalf of Paul Rossiter [[log in to unmask]]
Sent: 09 February 2014 18:14
To: [log in to unmask]
Subject: (1)Did PPR benefit from rinderpest eradication? (2). PPRV in cattle. Moderator's input

Dear Colleagues,
 
(1) Thanks to those of you who sent in answers to Dr Ithondeka’s question.  I am not sure that we have fully answered it and, since one of my jobs as moderator is to stimulate discussion or stir things up a bit, I  am going to put my head on the block with a few thoughts on the subject. 
The original question relates to the apparent upsurge in the distribution of PPR in many parts of the Old World at or just after the eradication of rinderpest from the same territories.  What I think is the underlying concern is whether or not the upsurge of PPR, especially in East Africa, was just a coincidence or was in some way aided or even caused by the eradication of rinderpest (see other comments  on this from Drs Richard Kock, Ashley Banyard and Tim Obi).  If the eradication of rinderpest did play a role then we should understand how this came about in order to avoid repeating it.  To me, it would mean that the presence of rinderpest must have been suppressing the transmission of PPRV in sheep and goats. Could this have been due to the virus itself immunizing nearby small ruminants or to rinderpest control measures especially vaccination?
Considering the possible immunizing potential of virulent RPV, we know from historical records and more recent serology that outbreaks of rinderpest in cattle did transmit infection to sheep and goats and other species.  But the published data on antibody prevalences in sheep and goats never remotely approached what might be considered sufficiently high levels of herd immunity capable of protecting whole populations against infection with PPRV. Furthermore, even if this was a workable mechanism, the amount of clinical rinderpest actually circulating in cattle in Africa and most of Asia since the mid to late 1980s was far too low to trigger much immunization of sheep and goats and certainly not of populations.  In fact the sheep and goats into which PPR spread were nearly all born long after any rinderpest circulated in their vicinity.  So I don’t think that virulent RPV immunization caused the “upsurge”.  
Similarly, I doubt that the vaccination of cattle with live RPV vaccine could have immunised nearby sheep and goats against PPR.   All the original laboratory work showed that vaccinated cattle did not shed tissue culture rinderpest virus. (It might have been better if they did because we would have had a much easier task of achieving high herd immunity rates thereby eradicating rinderpest earlier. Perhaps this is another challenge for the laboratories – please can we have a safe vaccine against PPR that transmits itself a little bit?).  If the vaccine couldn’t immunise other cattle by contact I cannot see how it would immunise sheep and goats to protective levels of herd immunity against PPRV. 
Another possibility is that RPV vaccine, especially when being withdrawn from use in cattle, was more widely used to protect sheep and goats against PPR than was accounted for.  Although this may have occurred in a few places I believe that most veterinary departments withdrew RPV vaccine from the field when cattle vaccination ceased and I think this is also unlikely to account for the epidemic surge of PPR through East Africa and other places.
So, in answer to Dr Ithondeka’s question I don’t think that the upsurge in PPR was due to the eradication of rinderpest and I suspect that the real reason lies in a combination of factors such as those described by Dr Libeau and other contributors.  But…..
(2) Considering the reverse scenario of PPRV infecting cattle, buffaloes and other species, a subject raised in several  contributions to the conference including one from Dr Balamurugan, we know that nature is supposed to hate a vacuum.   It is easy to imagine PPRV trying to grasp the opportunity of occupying the vacant niche or “natural vacuum” (cattle) left by the eradication of RPV.  Fortunately, the evidence from published studies and contributions to this conference is that although PPRV continues to have plenty of chances to fill this niche it has not yet succeeded in becoming “bovine PPRV” a virus (probably accompanied by a disease to facilitate transmission)  that is maintained independently of sheep and goats.  Occasional jumps by RPV from cattle into sheep and goats did not lead to self-sustaining small ruminant rinderpest and did not affect the eradication of RPV.  I don’t think occasional, self-limiting (no or very little clinical disease, no transmission of virus) transmissions to cattle will affect our plans to eradicate PPRV, at least not at present.  Whether or not this might become a problem in the future is another story and may depend on what we achieve in sheep and goats - and  some surveillance of cattle and other species.


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