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Establishment of a PPR Global Research and Expertise Network (PPR-GREN)

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michael baron <[log in to unmask]>
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michael baron <[log in to unmask]>
Date:
Fri, 7 Feb 2014 16:47:53 +0000
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Dear colleagues,

With respect to the degree of seroconversion, surely what matters is whether the immune response is sufficient for protection, not how high the VNT titre is?

We have a tendency to focus on the measurable antibody titre, but I want to point out again that it has never been shown that it is serum antibody that is protective. It could be the (much more difficult to measure) T cell immunity. The OIE manual only says that a PPRV vaccine has to give a VNT titre of 1:10 because we know from experience that an effective PPRV vaccine will give such a titre, not that such a titre is protective.

For those not familiar with the old RPV literature, it was shown that recombinant poxviruses that gave no detectable anti-RPV antibody were still protective. Yilma et al made recombinant RPV glycoproteins, injected them into cattle, and got nice antibody responses - but no protection.

The difference between sheep and goats may be in the balance of immune responses; as Dr Singh has just posted, PPRV may replicate a bit better in goats, and so elicit a higher immune antibody response. The only thing that counts, in the end, is whether the animal is protected.

best wishes
Michael




Michael D Baron PhD
Group Leader, Paramyxo&Bunyaviruses
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From: Establishment of a PPR Global Research and Expertise Network (PPR-GREN) [mailto:[log in to unmask]] On Behalf Of Paul Rossiter
Sent: 07 February 2014 15:59
To: [log in to unmask]
Subject: From Dr Srinivasan on the possible need for species specific vaccines

Dear Colleagues,

When we first developed PPR Sungri/96 vaccine, during the initial field
evaluation of vaccine we observed goats were better sero-converters than
Sheep. In a study involving more than 500 post-vaccinate sera samples in
each of the species, we observed 98% sero-conversion in goats and 83% in
sheep. Even the VN titer was lesser in sheep than goats (eg., most of the
goats had 1:64 to 1:128 and sheep it was 1:32 to 1:64).

PPR Sungri/96 virus which was used to develop attenuated vaccine was
originally rescued from post-mortem samples from a goat died in the PPR
outbreak.

Does this suggests that we should have separate vaccine candidates for
sheep and goat? I must confess I am not keeping abreast of PPR literature
as I have moved away from PPR research almost 11 years back.

Regards
Srinivas
I hope that several of you will give us your views on this radical idea - moderator
________________________________
Dr.B.P.Srinivas
Principal Scientist
Indian Veterinary Research Institute (IVRI)
Hebbal, Bangalore-560024
India

Tel:  91-80-23410729 (Work)
Fax: 91-80-23412509

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