Paul,
I have been following your e-conference with great
interest. I would like to enter the
following comments but use your judgment as to where they best fit. Perhaps this response could fit in with your
13 Feb comment on seromonitoring along with those of Adyl Bachir and John
Andersen.
David Ward
Dushanbe/Almaty
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Colleagues,
I am David Ward, a not so retired former FAO/AGAH staff
member. I wish to comment on two issues
connected with PPR eradication strategy and recent comments. First, is the value of serosurveillance and
the second is to suggest that 'PPR eradication' might not be the best immediate
strategy to promote. But suggest instead
a dual control strategy against PPR and brucellosis diseases in small
ruminants.
Taking the latter suggestion first, for many reasons a
strategy linking of PPR and brucellosis control in small ruminants could be a
‘bankable’ strategy. These are two high
profile diseases of small ruminants; brucellosis is a zoonosis with ever increasing
visibility among national veterinary and public health services, donors, FAO
and, often the public, and there is a large body of research
particularly on brucellosis. Straight
economic benefit:cost analysis of each disease separately may not reach a
figure high enough to interest donors or economists but taken together could be higher and most
interesting. Most importantly, a
practical strategy (targeted, twice yearly vaccination) and an effective vaccine
(Rev1) are proven to control brucellosis in small ruminants to low and stable
prevalences. Numerous countries (Kyrgyzstan,
Azerbaijan, B&H, Tajikistan, Oman, Greece and others have followed this general strategy
and successfully reduced brucellosis prevalences in a matter of a few years. The veterinary service in France using nearly
this strategy combined with test and slaughter has officially eradicated
brucellosis in small ruminants.
I suggest that targeted, twice yearly vaccination with a
quality assured PPR vaccine should be equally successful in building herd
immunity in a matter of several years and sufficiently control PPR
disease to low levels. Campaign logistics that target unvaccinated
adults and young replacements twice yearly is one technically sound way to
protect young stock in the face of interference with maternal PPR immunity
using current vaccines.
Combining vaccinations against both diseases should be more
cost effective and technically sound than vaccinating against one or the other disease.
As for the value of post-vaccination serosurveillance,
for brucellosis control in many countries this has proved an essential quality
monitoring tool. District-based, post-vaccination
random sampling within 30 days of vaccination and RBT testing allows estimating
vaccination coverage and spotting problem districts with low coverage or vaccine
failure. The same useful information
could be obtained for PPR using the same sera.
Additional random serosurveys at inter-vaccination
intervals every several years will gage progress toward control of each
disease. For PPR we want to see a
rising percentage of herd immunity in villages and districts. For brucellosis, we want a decreasing
sero-prevalence over time. The beauty is
that testing randomly selected sera, collected at optimum times post-vaccination,
will monitor progress for controlling both diseases. Mass serosampling is not suggested here but a random, targeted serosampling of a few thousand animals per district is sufficient for brucellosis when the prevalence is in the single digits. This sample size will be more than sufficient for PPR when the prevalence of post-vaccination or natural disease antibody rises into the double digits.
Hope these suggestions have useful technical and
diplomatic appeal. I hope too that a dual PPR – brucellosis disease control strategy becomes
part of the continuing debate in this e-conference. I also
believe that we have sufficient knowledge and adequate vaccines and tests for each
disease to begin a dual control strategy in countries or zones. In a few years, seromonitoring will
give us sound data allowing better informed discussions with donors and
decision makers about the feasibility of eradication, potential costs, critical constraints and time frames.
Regards,
David Ward
Veterinary Consultant