Sunday, December 16, 2012

A new (old) headline.

This week, the authors of that previous outrageous mischievous vaccination headline, (74 per cent success rate for badger vaccination, in case anyone has forgotten) have revisited their work. The revamped paper was published in Plosone with a strap line claiming a 54 per cent drop in bTB in (pre screened) badgers vaccinated with BCG, by using a bank of modeled diagnostic tests. Progress of a sort, we suppose.

From the abstract:
Here we present new evidence from the same study identifying both a direct beneficial effect of vaccination in individual badgers and an indirect protective effect in unvaccinated cubs. We show that intramuscular injection of BCG reduced by 76% [] the risk of free-living vaccinated individuals testing positive to a diagnostic test combination to detect progressive infection. A more sensitive panel of tests for the detection of infection per se identified a reduction of 54% [] in the risk of a positive result following vaccination. In addition, we show the risk of unvaccinated badger cubs, but not adults, testing positive to an even more sensitive panel of diagnostic tests decreased significantly as the proportion of vaccinated individuals in their social group increased. [] When more than a third of their social group had been vaccinated, the risk to unvaccinated cubs was reduced by 79%
This sounds encouraging until we go back to the original study, which pre screened its 844 badgers with the three or four tests mentioned, and excluded any positives. This is not made particularly clear in this paper, but for clarification, we quote:
A total of 252 individuals qualified for the event history analysis, following the removal of those individuals caught only once and those that were likely to have been infected prior to vaccination.
From personal communications, the infection rate in these badgers was 43 per cent. Thus to launch, as has been done, the concept of blanket vaccination of a genuinely wild and similarly infected population is a completely different ball game which is likely to have substantially different results and possibly some unintended consequences.

We also would respectfully point out that the results of this research are described as by 'proxy'. That means a mathematical model of projected data achieved not by measured exposure and postmortem, but by random exposure and 2, 3 or 4 diagnostic tests.
The authors explain :
Vaccinating free-living wild badgers with BCG significantly reduced the risk of an individual developing a positive result to a range of diagnostic tests used as a proxy for M. bovis infection.
. They also explain this - but way beyond that attention grabbing headline:
The effect of vaccination on the triple testV outcome was to reduce the risk of a positive result by 54% in vaccinated individuals. Without post-mortem data it was not possible to ascertain what proportion of the triple testV-negative, vaccinated badgers were protected from infection and what proportion still acquired infection, but were not detected using the triple testV.
It is unsafe to assume that triple testV negativity equates to the absence of infection.
Quite.  'Unsafe' it may be, but nevertheless that headline will be used, particularly as publication of this paper, once again coincides with a Consultation on vaccination.  As ever,  FERA has shown impeccable timing and media manipulation, particularly in their use of the word 'iconic' as a description of badgers in the paper which is somewhat less than scientific.

To the Badger Trust that description would definitely apply. To the Wildlife trusts whose collecting tins bear its silhouette, probably. And as an 'asset'  to provide constant research to FERA and others, most definitely. But to most of the population, if they think about it at all, a badger is a part of the ecology. Not the part, a part. And it is neither 'iconic', 'endangered' nor about to be 'exterminated'. But we digress:

There are quite a few references to the presence of infectious adults within the social group, adding to the burden of infection within the group and negating any vaccination attempts. Common sense really and answered 6 years ago in our PQs : 
2 Feb 2004: Column 1560W
Mr. Paterson: To ask the Secretary of State for Environment, Food and Rural Affairs what assessment has been made of whether infection of M. bovis bacillus between infectious female badgers and their offspring leads to an increase over time in the incidence of infection within a social group. [153924]
Mr. Bradshaw: From research carried out by the Central Science Laboratory, it is believed that the transmission of infection from mothers to cubs may be important in the maintenance of TB infection in badger populations. There is a correlation between the presence of infectious females in a group and the proportion of TB positive cubs. No information is available as to whether this has influenced the incidence of infection within a social group over time.
This paper repeats that information thus:
"The argument that many badger cubs will become infected during this period (i.e. before they can be caught and vaccinated), has been identified as a key potential constraint on the effectiveness of badger vaccination as a management tool."

"The risk of an individual being culture-positive has been shown to be related to the presence of other culture-positive (i.e. infectious, actively excreting) animals in its social group."
Pretty obvious really. So here's a thought. Why not screen the badger populations using the same tools which we propose for targeted culling? Reactor mapping, overlaid with badger group identification and PCR for disease status confirmation? Then offer vaccination (at the Badger Trust's expense) to groups testing clean? Particularly as a cordon to act as a buffer after removal of infected groups in endemically infected areas. Simples.

But we are puzzled by an apparently contradictory observation in this paper which is explained thus:
Prevalence for the population as a whole based on the combined outcomes of the above three tests reduced from 53% in 2006 to 35% in 2009. Reductions in prevalence were observed in both vaccinate and control groups.
So at a cost of £2500 per sq/ km or around £156 per badger for an average head count, (Defra / WAG figures) did BCG work at all on these pre screened badgers - or not?  As it would seem from that paragraph, the unvaccinated control group also experienced a reduction in disease prevalence.

And we also note that the authors have used 51 points of reference in this paper and many of the named authors appeared several times. What did we say about the asset value of those 'iconic' tuberculous badgers?

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