Paul,

Hope this is not too late.

Ciao
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Colleagues,
 
I take this opportunity to bring up what I believe are a few underestimated and spurious issues relating directly to this past week’s session on tackling multiple diseases in small ruminants.  Nick Honhold started us off very well with his proposal for a 3-in-1 strategy.  But it seems that the momentum was lost.
 
First I believe the vaccines at hand are pretty good against PPR, brucellosis (in small ruminants) sheep/goat pox and clostridial diseases.  The notion that ‘multi-component vaccines’, i.e. several immunizing antigens ‘in the same bottle’ is a diversion for researchers.  Conjunctival Rev1 vaccine is as good as any vaccine against brucellosis.  There is no compelling need to replace it or to spend money on the research required to make it into a multi-component vaccine.  And conjunctival administration has the distinct advantage of avoiding residual post-vaccination antibody titres which is a huge advantage for control programmes.   PPR vaccine too is a satisfactory immunogen, with long-term protection when injected; residual antibody is desirable in order to measure hopefully rising herd immunity over time.  Gijs van’t Klooster provided a practical reason to be able to selectively use one or another vaccine as and when at the end of a campaign, one vaccine may be banned.  Also to reduce cost only one vaccine may be needed in targeted areas where one disease is persisting and others are under control.
 
The possibility of immunosuppression was raised when multiple antigens are co-administered to animals at the same time.  There is literature from South American countries from the 1980s – 1990s on concurrent brucellosis plus FMD vaccination in cattle.  Antibody titres of brucellosis or FMD were usually equal when vaccination was co-administered compared to vaccination with these antigens when given separately to different animals.  There is one report that FMD antibody levels were lower following co-administration.  In the few papers where vaccinated animals were challenged with virulent Brucella abortus or FMD virus, protection was equal.  In one report from the Soviet Union, in sheep co-administered Rev1 and FMD vaccines the antibody titres were equal with animals given the vaccines separately.   During the last week, Dr. Saya Parida related his experiment with co-administration of FMD and PPR vaccines in goats and found equally good protection following challenge.  Measuring antibody levels post-vaccination is a poor index for protection.  I believe, but do not have the papers at hand, that similar co-administration of vaccine studies were carried out in the late 1990s in East Africa using FMD, anthrax or brucellosis vaccinations.  No untoward effects were noted and antibody titres were acceptable.
 
The political appeal to donors and decision-makers of the efficiency of a 3-in-1 strategy for disease control was, I believe, sorely underestimated in discussions last week.  The efficiency factor of controlling two or three diseases, in generally neglected sheep and goats no less, cannot help but be a strong selling point.
 
Lastly, the inclusion of brucellosis (conjunctival Rev1 vaccination) in the package is critical for its appeal as a zoonotic disease.  Brucellosis rates in humans and animals are very high and even rising in some Middle Eastern and Central Asian countries and even recognized this year in a conference in China.  This disease might command higher priority from African countries if the vets and physicians had done the serosurveillance work to measure the rates.  Brucellosis is an underdiagnosed and untreated cause of ‘fevers of unknown origin’ in Africa along with malaria (see Andrew J. Bouley, John A. Crump & others. Brucellosis among Hospitalized Febrile Patients in Northern Tanzania. Am. J. Trop. Med. Hyg., 87(6), 2012, pp. 1105–1111).
 
So in summary, it seems to me that the diagnostic tools and vaccines at hand today are robust enough to start PPR, brucellosis and sheep/goat pox control programmes.  Talk of eradication of any of these diseases is premature and may do us a disservice by scaring off donors.  But a strong technical and socio-economic case can be made for progressive control of these diseases.  Anchoring a control strategy around PPR and brucellosis brings the experience of recent eradication of rinderpest, a similar viral disease to PPR, and the appeal of controlling a zoonosis.  There are technical issues needing better understanding, e.g. how to handle maternal immunity to PPR vaccination where out-of-season breeding in small ruminants is common and will twice-annual vaccination schedules be sufficient to overcome potential antibody interference in young stock.  Immunosuppression is not likely to be one.
 
This electronic conference is surly serving a useful purpose for shaping future global animal disease control.  But I hope the start is not too far in the future.  Thanks for the opportunity to make these contributions.
 
David Ward
Veterinary Consultant


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