(warmwell's bTB page - click here has been running since 2004.)Email received July 6th 2011 from Dr Ruth Watkins on the subject of
bTB badger vaccinesIt should be remembered that Ruth Watkins is an expert virologist. She is a very strong advocate of vaccines for foot and mouth and other diseases for which vaccination is known to be very effective and in 2001 worked harder than anyone I know to try to get the culling policy changed to one of emergency vaccination. She is a farmer and also a dedicated conservationist. Her knowledge of wildlife and botany is extraordinary, and she cares deeply for all animals.
In this contentious issue of bovine TB , her voice is one of the most valuable we have.
The false expectations being peddled about the BCG vaccine come from wishful thinking. I heard one person say (who is against culling badgers as a means to reduce bovine TB) that vaccination of badgers would eliminate the infection in 4 generations. It stems from the Badger Trust lobby. They also believe it would be very effective used to vaccinate cattle; I doubt this very much.
You were kind enough to refer to my email of a year or more ago yesterday on your site so I read it again. I try to explain that the immune response to bacteria is different from that to viruses. I think the language is difficult to follow. Basically the reason why BTV8 vaccine, FMD vaccine or rinderpest vaccine work so well is that they PREVENT infection because they induce neutralising antibody (billions of molecules) which is circulating in the bloodstream and secreted in saliva etc. This special subset of antibodies, even when only a few molecules attach to the virus, render it defunct- it cannot replicate even if it gets into a cell. There is no equivalent in the immune response to bacteria.
In the case of bacteria antibodies attaching to the surface aid the swallowing of bacteria by macrophages- that may prevent disease in the case of pnemococci or Neisseria meningitidis, but in the case of mycobacteria this provides the environment they can survive in and multiply. The immune response that is effective in preventing mycobacteria from multiplying and eventually causing disease and spreading to distant sites in the body from its site of entry, is the stimulation of macrophages by gamma interferon. This stimulation makes the macrophage kill the engulfed mycobacteria. The T-cell response to mycobacteria leads to the release or this molecule, gamma interferon. However a large amount of mycobacterial antigen can switch off the T-cell response eventually (the infection over time can be thought of as the accumulation of antigen) so antibody is made rather than gamma interferon. This is useless. However antibody is a marker of advanced uncontrolled infection and is detected in the Brock TB STAT-PACK test for badgers.
Thus a fall in badgers testing positive by the STAT-PACK test in the field does not necessarily signify a fall in infection rates but rather a fall in the number of badgers with advanced disease- this was the finding of the BCG field vaccination trial of badgers.
The common feature that BCG and FMD vaccines share is that to be effective they must be given before infection.
I suspect that bacterial vaccines do not prevent carriage or limited infection of the host. They prevent DISEASE. This is the well documented role of BCG vaccine, it prevents dissemination in the bloodstream that results in meningitis, generalised infection, infection of distant organs such as the kidney. This is why the lives of so many human neonates and young people have been saved by BCG. This protective action of BCG is nullified by environmental mycobacterial infection or exposure, so in certain parts of the world this vaccine does not provide protection against disease.
It has been difficult to show that BCG vaccine prevents infection in the first place in humans (it has been given to over a billion). The studies done on badgers also show that it does NOT prevent infection in the first place (see Proceedings of the Royal Society B published on line, 'BCG vaccine reduces the severity and progression of tuberculosis in badgers' by Mark A Chambers et al 2010). BCG vaccine was shown in badgers to prevent spread within the body from the site of initial infection, generalised disease and a heavy load of mycobacteria, and shedding from organs like the kidney in the urine.
This is VERY useful to prevent contamination of the environment by badgers shedding M bovis in urine for example, that leads to the infection of others (badgers, cattle, cats, alpacas etc). The fact that transmission from the environment is not fully understood has been a bone the Badger Trust has never ceased to pick at and throw back at everybody. Perhaps it is aerosolisation by fallen raindrops. I don't know. But lack of understanding never stopped an infectious disease from spreading. M bovis remains infectious for many months on our pastures, cool moist and protected from ultra-violet light. The dose for infection by aerosol is very small in contrast to oral ingestion, swallowing, where large doses are necessary for infection.
The effect vaccinating badgers in the field has on the infection rate of cattle herds remains to be seen. Culling badgers has a relatively small but significant effect on reducing cattle herd breakdown with TB infection. Would the effect of vaccination of badgers be the same, greater or smaller? I guess it depends on the numbers vaccinated or killed as a fraction of the population- killing the infected badgers and vaccinating the uninfected badgers!
BCG does not prevent lung infection, a primary site of infection and the most common primary site in humans, badgers and cattle. Thus if disease in the lungs progresses to cavities in the lungs so that shedding occurs from the lungs on the breath, the infection of others by inhalation is not prevented, whether they are vaccinated or not. Hence BCG vaccine has never eliminated TB in the human population. The excitement of the new TB vaccine in development with proteins expressed in the new vaccine that are not in BCG vaccine is that it could evoke a more effective immune response to active disease; it could prevent the disease of the lungs for instance that is the source of infectious shedding. So far this is only in laboratory mice. This new vaccine might really make a difference to the incidence of TB where diagnosis and treatment is not on offer- impoverished human communities and to animals such as badgers, cattle and so on.
best wishes Ruth
NB- booster doses of BCG are not normally given or thought necessary for humans, it is a live vaccine. Booster doses are given of dead or killed virus vaccines and vaccine to toxins ie tetanus. Booster doses are not always given with bacterial non-living vaccines such as the Pneumococcal vaccine I had, though I see on the children's vaccine schedule they have several doses of haemophilus, meningitis and pneumococcal vaccines but these may be differently formulated. I do not know what effect booster doses of BCG vaccine would have on badgers, but obviously if they are given oral vaccine they will have booster doses ad lib.
Yet another complicating factor is the strain of BCG used as the vaccine which is the same for badgers and humans. The consideration in humans was lack of side effects but that was set against a lowered potency. I suppose it is convenience or rules for trials that has led to the use of the current human strain of BCG being used for badgers, bur another strain might be more potent in raising an immune response or more suitable for oral use in badgers. The initial strain from the 1920s that was first used is lost in the mists of time as they had no means of keeping seed lots indefinitely in long term storage. BCG does not remain latent or persist in the vaccinated host beyond the infection period after vaccination lasting a few months.