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Schmallenberg virus – what we know so far

April 2, 2012

Watching the research that surrounds the emergence of a novel virus is fascinating. I’m always amazed at how quickly scientists basically dissect the disease and the organism to find out what is going on.

Today’s post is going to look at Schmallenberg virus – a novel virus affecting livestock that was first identified only in November 2011.

The story actually begins before November 2011.  It’s thought that the virus first started affecting livestock in Europe in summer 2011: cattle in Germany and the Netherlands started to show a few non-specific signs of disease (fever, diarrhoea, a drop in milk production).   The animals generally got better again after a few days and herds were generally only affected for a few weeks.  Samples were collected and tests were run to find out what was going on but the tests ruled out known viruses and it remained a mystery…

… until November.  It was then that the virus was isolated by scientists who named it after the town, Schmallenberg, that the first positive sample came from.  (I’m not sure how happy residents of Schmallenberg will be to have a virus named after their town!)

Since its first identification scientists have learnt a lot:  SBV is very closely related to a subgroup of viruses in the Orthobunyavirus group. Other viruses in this subgroup are commonly transmitted from mammal to mammal by insects like midges and mosquitoes so it has been suggested that SBV may also be transmitted this way. This would fit in with the fact that the initial cases were seen in August and September – prime insect months.

The reason we (at least in the UK) started to hear of new cases at the beginning of 2012 is probably not because animals are still getting infected (in winter there are usually no midges or mosquitos around).  We are seeing the long term consequences of animals infected by the virus when they were in their early pregnancy.  Farmers are seeing an increase in the numbers of miscarriages and stillbirths of deformed young, especially in sheep, although cattle and goats have also been affected by the virus.

Since scientists first isolated SBV it has been grown in the lab and a very small number of cattle have been experimentally infected with it, resulting in a similar picture of non-specific symptoms as was seen in cattle in the summer of 2011.  There is still a lot of work to be done in this area – we don’t yet know if animals can pass the virus directly to each other and we don’t know what is going to happen in 2012.  Exposed animals may prove to have some immunity but what about those animals who were unexposed but are close to exposed ones?

SBV is currently not thought to be zoonotic: the European Centre for Disease Prevention and control states that  it is “unlikely that this virus will cause disease in humans, but it cannot be excluded at this stage“.  It actually must be quite hard to prove that a virus doesn’t cause disease in humans.  You can do cell culture work and see if the virus affects particular cell lines, but barring injecting a large number of people with the virus, you basically have to say well x number of people have been exposed and no one has caught any disease (and you would have greater confidence the larger x is).  (Well that’s how I understand it anyway – please correct me below if I am wrong.)

Countries across Europe are trying to get a handle on the disease and plan for the months when midges and mosquitoes will be around in 2012.  In the UK, as of 30th March 2012 it had been detected 235 farms, mostly sheep farms.  However the number of cattle herds affected may increase as those cattle infected in their pregnancy in late summer are now starting to calve.   SBV is not currently a notifiable disease (although Defra does ask farmers to notify their vets if they suspect it) but I don’t know if this will change as the months go on.

I think it’s amazing how much scientists have learnt in the space of about 9 months since vets first saw the signs of infected cattle and I’ll be keeping a close eye out for the next set of results to be published.

Places to go for more info:

Latest UK SBV situation

Information from Defra on the virus

Scenarios for the future spread of Schmallenberg virus  (Veterinary Record, 2012 170 245-246 doi: 10.1136/vr.e1598 – BEHIND A PAYWALL)

Information from the ECDC

ECDC Preliminary Risk Assessment 

 

Image:

Lamb picture made available by Evelyn Simak under a Creative Commons Attribution-Share Alike 2.0 licence

Cow picture made available by CRV Arnhem under a CC-BY 3.0 licence

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Society for General Microbiology Conference ’12: #sgmdub

March 29, 2012
  1. This is the first time I’ve ever used Storify so fingers crossed…
  2. Share
    2 girls, 5 days, 1 piece of checked luggage weighing no more than 15kg… this could be a challenge! #sgmdub
  3. We got into Dublin Sunday night, registered and then went off wandering around the city 🙂

    The next morning the first session I attended was the biocontrol of diseases…
  4. First up was: 
    Novel engineering of attenuated Salmonella enterica serovar Typhi strains for use as live vectors
    Jim Galen (University of Maryland)
  5. Share
    Using salmonella as live vector for vaccination #sgmdub
  6. Share
    Use non-antibiotic selection method to avoid antibiotic resistance genes in vaccine vector strains. #sgmdub
  7. Share
    Live vectors can be used to export antigens. More attenuation means less immune response #sgmdub
  8. Share
    Likely tht delivery of mutiple ags using single plasmid-bearing live vector vaccine will require chromosomal expression of =/>1 ag #sgmdub
  9. Share
    “Attenuated s typhi live vectors represent flexible platform for expression of foreign ags” #sgmdub
  10. Share
    V interesting talk by J Galen #sgmdub
  11. Share
    Genome Atlas – allows you to see secondary structure of your chromosome. #sgmdub
  12. Next up… 
    Vaccination against Clostridium difficile infection
    Simon Cutting (Royal Holloway, University of London)
  13. Share
    Use of bacterial spores as vaccine. Many advantages… #sgmdub
  14. Share
    Cheap, long-lasting, survive well, possibility for oral delivery, heat stable #sgmdub
  15. Share
    Spores also serve as adjuvant and can (?)Adsorb antigens eg viruses. #sgmdub
  16. Share
    C diff infection – 30% of patients develop relapse #sgmdub
  17. Share
    using c diff spores to protect against c diff infection. V interesting talk. #sgmdub
  18. Share
    Oral dosing is better. ?mucosal immunity most important? #sgmdub
  19. The SGM Prize Medal Lecture this year was given by Julian Davies (University of British Columbia)  
    “Molecules, microbes and me” 

    It was a brilliant talk from clearly a brilliant man!

  20. Share
    “Molecules microbes and me” by Julian Davies about to start #sgmdub
  21. Share
    Most expensive hyrolytic reaction in history: betalactamase action. #sgmdub prize lecture
  22. *hydrolytic! 
  23. Share
    #sgmdub cool. In nature, antibiotics may not actually be ANTIbiotics.
  24. Share
    Environmental role of antibs poorly understood V interesting – I’d assumed we knew… #sgmdub
  25. I thought that we knew antibiotics were soil microbes way of protecting themselves from other bugs – apparently we don’t actually know that…
  26. After lunch I ran between the Food Borne Pathogens session and the New Media session.  Sadly I couldn’t be in both places at the same time so I’m sure I missed some great talks but here is what I went to…
  27. Interaction of Salmonella enterica and E. coli pathotypes with edible fruit and vegetables
    Gad Frankel (Imperial College London)
  28. Share
    #sgmdub shift of salmonella transmission: used to be mostly poultry, now vegetables playing larger role
  29. Social media for researchers – maximizing your personal impact
    Alan Cann (University of Leicester)
  30. Share
    “Having online profile no longer an issue of vanity”alan cann #sgmdub
  31. Share
    Build up network of trusted individuals says A Cann in New Media session #sgmdub
  32. Share
    Don’t have time for social media? If you care bout your career you don’t have time not to do it says A cann in New Media session #sgmdub
  33. Share
    Definitely identify with “ploughing lonely furrow” in social media with my dept! #sgmdub
  34. Share
    Back to importance of choosing who is in your network. New Media session at #sgmdub
  35. Share
    “Process of curation never stops”. A Cann. #sgmdub
  36. Scientists and social media
    Alice Bell (Imperial College London)
  37. Share
    Audioboo – like twitter but with sounds according to @alicebell. Anyone know if blackberries can get it as well as iphone? #sgmdub
  38. Share
    Blogging allows parents w/children who can’t go 2conference 2potentially have sane networking opportunity #sgmdub #womeninscience
  39. Share
    Obviously my last tweet shd have read “same networking” rather than “sane”! #womeninscience #sgmdub. May still b applicable!
  40. To be honest I had never really thought of that point before but obviously being a parent will to some extent limit your conference attendance.  I’m hoping that my tweeting from the conference might be interesting to some of those that couldn’t make it this year.
  41. Share
    .@alicebell talk reminding me why I blog – I learn lots and it’s fun. Also great when authors of papers I talk about get in touch #sgmdub
  42. Share
    Excellent talk by @alicebell on scientists and social media #sgmdub
  43. Food from the fire: how the host response feeds Salmonella
    Andreas Baumler (University of California, Davis)
  44. Share
    Hydrogen sulhpide makes food “smell interesting”! Lovely understatement! #sgmdub
  45. Every defeat is a small victory: the what, when, where and how of setting up a microbiology blog
    Benjamin Thompson (Wellcome Trust, London)
  46. Share
    The who what how and why of setting up a micro blog – what shd I have done? Now at #sgmdub
  47. Share
    Make sure ur blog name will come up early on google! #sgmdub
  48. Share
    Scaleabiity is important. Need to balance the rest of ur life and ur blog. #sgmdub
  49. Share
    “Flickr search creative commons = your friend” #sgmdub
  50. Share
    Editing important. Remember short paragraphs for internet posts. #sgmdub
  51. Share
    Get someone to read ur work before u post it. #sgmdub
  52. All of the New Media talks I went to were fantastic.  Sadly I couldn’t make the Twitter Journal Club talk so I don’t know what came out of it – maybe some microbiologist will be setting up a micro twitter journal club soon…
  53. The Peter Wildy Prize for Microbiology Education went to 
    Vincent Racaniello who gave an excellent talk titled
    “Educating the world about microbes”

  54. Share
    V excited about “educating the world about microbes” with Vincent Racaniello #sgmdub
  55. Share
    Blogs give ppl access to scientists – Vincent Racaniello’s talk #sgmdub
  56. Share
    Before my phone battery dies… Fascinating talk by Vincent Racaniello and great day at #sgmdub looking forward to tomorrow!
  57. Share
    Possible to do both research and outreach/education effectively #sgmdub
  58. Food Borne Pathogens again today – not all lectures are covered as some went a little over my head! (There are times when not having done a Microbiology based undergrad degree is a bit of a hindrance!)
  59. The Marjory Stephenson Prize Lecture was given by 
    Yuan Chang & Patrick Moore (University of Pittsburgh Cancer Institute) 
    “Old themes and new variations in human tumor virology”
  60. Share
    Settling down for Marjory Stephenson Prize Lecture being given by Yuan Chang & Patrick Moore #sgmdub
  61. Share
    #sgmdub infections responsible for ~20% of human cancer
  62. Share
    #sgmdub why do some viruses cause cancer when their near relatives don’t? We don’t fully know yet…
  63. Share
    Viral tumours are biological accidents #sgmdub
  64. Share
    #sgmdub kshv innate immune evasion genes = also oncogenic
  65. Share
    #sgmdub “tumour suppression and innate immunity: 2 sides of same coin?”
  66. Share
    #sgmdub mcv almost ubiquitous so why does it only sometimes cause cancers?
  67. Share
    Mcv is replication deficient in mcc #sgmdub
  68. Viral oncology is really not my area but the talk was aimed at a low enough level that even I could keep up – was fascinating 
  69. Intensive broiler chicken production systems and the infection biology of Campylobacter
    Tom Humphrey (University of Liverpool)
  70. Share
    #sgmdub campylobacter is defined as ‘commensal’ in chickens but can cause dz in the birds…
  71. Share
    #sgmdub campylobacter a poorly controlled chicken commensal? Chicken mounts marked response to campy but little to lactobacillus commensal
  72. Share
    #sgmdub antibody response confines bug to chicken gut
  73. Share
    #sgmdub problem with surface contamination- cross contamination. Bigger problem is internal contamination – liver pate outbreaks etc
  74. Share
    #sgmdub can get transient campylobacter bacteraemia in chickens
  75. Effects of co-culture on Campylobacter
    Friederike Hilbert (University of Vienna)
  76. Share
    Campylobacter almost never alone in its natural life cycle #sgmdub
  77. Share
    Campy survives longer in oxygen if cocultured with pseudomonas #sgmdub
  78. Try not to breathe: the role of oxygen in the Campylobacter lifestyle
    Arnoud van Vliet (Institute of Food Research, Norwich)
  79. Share
    Bact. response2stress: parasitism, symbiosis, commensal, sporulation/biofilm, death Gd analogy2managment conflict resolution scheme #sgmdub
  80. Offered paper Campylobacter enteritis; emerging dynamics of human infection
    Susan Bullman (Cork Institute of Technology)
  81. Share
    Campylobacter ureolyticus – an emerging gi pathogen? #sgmdub
  82. Offered paper Bacterial rejuvenation: lag phase is a distinct growth phase that prepares bacteria for exponential growth and involves transient metal accumulation
    Matthew Rolfe (University of Sheffield & Institute of Food Research, Norwich)
  83. Share
    #sgmdub v interesting talk by Matthew Rolfe on bacterial lag phase of growth.
  84. There was a  Hot Topic Lecture given by 
    Richard Elliott 
    “Schmallenberg virus: fact from fiction”

  85. Share
    Looking forward to “Schmallenberg virus: fact from fiction” with Richard Elliott #sgmdub
  86. Share
    #sgmdub orthobunyavirus genus – >170 named viruses – now includes schmallenberg
  87. Share
    “It is unlikely that this virus can cause dz in humans but it cannot be completely excluded at this stage” #sgmdub
  88. Share
    #schmallenberg #sgmdub been detected in france, germany, uk, italy, spain, jersey
  89. Share
    #schmallenberg #sgmdub adult animals show little to no dz but congenital abnormalities in offspring. Healthy newborns not viraemic
  90. Share
    #sgmdub #schmallenberg by december ’11 getting congenital defects in lambs and calves positive for sbv
  91. Share
    #sgmdub #schmallenberg is not a notifiable dz. Are we missing cases?
  92. Share
    #sgmdub likely that sbv was in midges blown across channel
  93. Share
    #sgmdub I can’t help but think is pretty impressive that from 1st known cases2virus isolation2now ppl have managed2learn so much bout virus
  94. Share
    #sgmdub need to look in midge head to find evidence cd transmit to animal.virus cd b in gut purely because fed on infected animal recently
  95. Share
    #sgmdub with akabane (related virus) get waves of immunity in livestock
  96. It was an absolutely fantastic lecture bringing us all up to date on the latest on the virus
  97. Campylobacter jejuniexploits host cell processes 
    Michael Konkel (Washington State University)
  98. Share
    #sgmdub seeing increase in c jejuni isolates resistant to antib’s
  99. Share
    #sgmdub c jejuni binds to fibronectin – 37kDa OMP exhibits fn-binding activity
  100. Share
    #sgmdub anti-flaA chick maternal antibodies can inhibit motility. Can we use maternal antibodies to show poss vaccine targets?
  101. Share
    V interesting talk by M Konkel – looks like promising approach to vaccine development #sgmdub
  102. At this point I nipped across to the phylogeography session…

    Global spread of multidrug resistant Salmonella Typhi
    Kathryn Holt (University of Melbourne) 
  103. Share
    #sgmdub v interesting to see how different drug regimes may have affected resistance profile of S typhi
  104. Clonal evolution and spread of a transmissible cancer lineage in Tasmanian devils 
    Elizabeth Murchison (Wellcome Trust Sanger Institute, Cambridge)
  105. Share
    #sgmdub shd we consider transmissible cancers to be microbes?
  106. Share
    #sgmdub horizontal transmission of living cancer cells – wow
  107. This was one of my favourite talks of the whole conference – very clearly explained and an interesting topic.
  108. Fleming Prize Lecture
    Plagues and populations – patterns of pathogen evolution 
    Bill Hanage (Harvard School of Public Health, Boston, Massachusetts)
  109. Share
    #sgmdub Plagues and Populations: patterns of pathogen evolution with Bill Hanage
  110. Share
    #sgmdub 3 E coli isolates (therefore supposedly same species) – only 39% genes present in all 3 strains (Weich et al 2002)
  111. Share
    #sgmdub Are bacteria bags of genes brought together for transient benefit? Interesting question
  112. The lecture was brilliant (and I think someone compared Bill Hanage to House!)
  113. Offered paper Out of the environment and into the host; mapping the path to pathogenicity across the genus Yersinia
    Thomas Connor (Wellcome Trust Sanger Institute, Cambridge)
  114. Share
    #sgmdub if we only consider pathogenic Yersinia we are missing most of diversity in the genus
  115. Offered paper Assessing Bartonella henselae diversity using whole-genome sequencing and single-nucleotide polymorphism analysis
    Gemma Chaloner (University of Liverpool)
  116. Share
    Bartonella henselae – a few uncommon STs responsible for most human infections (vets beware!) #sgmdub #zoonosis
  117. Offered paper Assessing the diversity of antimicrobial resistance in animal and human Salmonella Typhimurium DT104 using phenotypic and genotypic data
    Alison Mather (Wellcome Trust Sanger Institute, Cambridge)
  118. Share
    V interesting talk on antimicrobial resistance by Alison Mather #sgmdub #zoonosis
  119. Offered paper The transcriptional architecture of Salmonella Typhimurium SL1344
    Jay Hinton (Trinity College Dublin)
  120. Share
    V clear description of RNAseq results from Jay Hinton. #sgmdub
  121. Share
  122. Offered paper Non-O157 verocytotoxigenic Escherichia coli (VTEC) on bovine farms
    Declan Bolton (Teagasc Food Research Centre, Ashtown)
  123. Share
    Non-O157 STEC/VTEC – shdnt forget this grp of E coli #sgmdub #zoonosis
  124. Share
    Only 1 more #sgmdub event left for me 😦 But it is “Stopping the Spread of Superbugs” which I’m really looking forward to 🙂
  125. Share
    Fab description of how and why infection with MRSA in diff places causes diff symptoms #sgmdub
  126. Share
    Dogs, cats, pigs all been found with MRSA – another gd reason to wash ur hands after playing with ur pet. #sgmdub #zoonosis
  127. I loved this session – I thought it was a great way to approach public engagement.  It didn’t feel like microbiologists were just telling stuff to the audience – (IMO anyway) it felt like the audience’s opinions were valued.
  128. Overall the conference was a brilliant experience (and I really need to get a thesaurus – sorry!) I met many friendly people and learnt a lot.  Thanks to the poster presenters, the speakers, the exhibitors, the CCD staff and everyone at the SGM who organised the event – you did a stunning job 🙂
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Conference report to come

March 27, 2012

Anyone following my twitter feed over the last few days can’t have missed the fact that I’m currently at the Society for General Microbiology’s spring conference in Dublin (#sgmdub)! In fact they may well be fed up with my constant tweeting (sorry!) But there is a reason behind it…

Last year I wrote a report on the conference as a standard blog post. This year I thought I would try something different – I’m going to (attempt to) storify it.

Now I have never actually used Storify before so this could go horribly wrong but hopefully in the end I will have something on here that brings together tweets on the talks I went to with the relevant press releases and any other bits and pieces that are related. We’ll see…

In the meantime if any of you do/have used storify and have any tips/advice please comment below 🙂

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MicrobeWorld need your help

March 18, 2012

For anyone unfamiliar with MicrobeWorld it’s a fantastic resource focusing on the microbiological world.  It’s run by the American Society for Microbiology and is host to the excellent podcasts “This Week in Microbiology“, “This Week in Virology” and “This Week in Parasitism“.  It also has articles on basic microbiology, cool experiments you can try at home, as well as links to news articles, videos and images all on microbiology.  Something for everyone in fact, from small children to professional microbiologists.  (Go on, open it in a new tab!  You know you’re curious!)

So that’s why I think it’s fab but why am I plugging it today?  Well MicrobeWorld have a grant application in the Knight Foundation News Challenge and whilst there’s not a voting system as such by which the grants will be decided (the trustees make the final decision) the Knight Foundation says:

“In evaluating your ability to conduct your project, we will also look at your ability to encourage support for, and critiques of, your idea on the News Challenge Tumblr and elsewhere online.”
 

So any and all support you can offer them would be fantastic.  You can heart (is this the correct term? *whispers*I confess to having never used Tumblr), reblog or comment on the post.

Please support this great website if you can.

Image

By Gaspirtz licenced under CC-BY-SA-3.0

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Sadly pet ownership comes with risks

March 13, 2012

Maryn McKenna over at SUPERBUG has got a post up discussing a recent paper (see below) that looked at 3 cases of (human) infection with Pasteurella multocida.  In all 3 cases it is thought that the patients involved caught the bacteria from nursing their sick pets.

Pasteurella multocida is a nasty species of bacteria and infection with it can very easily be fatal in humans.  Human cases are mostly associated with scratches and bites from cats and dogs (P. multocida can and does live happily in their mouths without causing any problems to them). However, in the cases published in the paper the transmission from animal to human seems to be effectively from mouth to mouth, rather than via injection through the skin as would happen with a bite.

It’s a very sad reminder that whilst pet ownership has many many benefits, we shouldn’t ignore the risks.

 

Paper Cited:

Myers EM, Ward SL, Myers JP. Life-threatening respiratory pasteurellosis associated with palliative pet care. Clin Infect Dis. 2012 Mar;54(6):e55-7. Epub 2012 Jan 11. DOI: 10.1093/cid/cir975 (May be behind paywall)

Images:

Photo by Adriano and released under a Creative Commons Attribution- Share Alike 3.0 Unported Licence

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“Pig” MRSA – are the pigs really to blame?

February 23, 2012

Photo by Keith Weller

There is a strain of MRSA (methicillin-resistant Staphylococcus aureus) that has been tracked passing from pigs to humans.  It was always thought that the MRSA initially came from the pigs, but new research published in mBio (open access) suggests that pigs might not be the original source. 

Instead it looks like the strain may have originated in humans but been methicillin-susceptible.  It then at some point passed into pigs where it picked up some antibiotic resistance genes from other bacteria before then going back into humans (especially farm workers and others who have close contact with pigs) as a more dangerous strain.

Unfortunately antibiotic resistance is one of the problems we face when bugs (in the sense of pathogens, rather than insects!) can so easily share and swap their genetic material.

One of the co-authors on the paper, Tara Smith has written an interesting post about it over at her blog, Aetiology which is well worth a read.  (If you’re interested in antibiotic resistance, public health and epidemiology her blog is definitely one to add to your RSS feed.)

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Bovine TB and badgers – why it all matters

January 17, 2012

I’ve been meaning to write about bovine TB for some time.  The news in December that there will be a badger cull trial in England has finally spurred me into actually doing so. 

Before I start I should mention that this post will not be about the political aspects of the cull decision.  Nor will it be about the scientific data that is being used to support and oppose the government’s plans.  I am not an expert in these areas and so do not feel competent enough to blog about the issues.  However, please feel free to discuss these things in the comments (please keep it polite and attack the argument rather than the person you disagree with).

What I want to write about today is why it is actually important to reduce the levels of bovine TB in our cattle and wildlife.  There is a good review article here (unfortunately behind a paywall) and it is from this that much of what will follow is taken.

Bovine tuberculosis (bTB) is caused by Mycobacterium bovis – a species closely related to Mycobacterium tuberculosis which is the most common cause of human TB. M. bovis can infect and potentially cause disease in most mammals, and is zoonotic (so can infect humans too).

Humans and Mycobacterium bovis

People can be infected by three main routes:

  1. Infected milk – this was the most common route before pasteurisation and is still a potential hazard in places where milk is not routinely pasteurised
  2. Inhalation of aerosolised infectious droplets – ie. when an infected cow with tuberculous lung disease breathes out there may well be droplets that carry the Mycobacterium.  Again, this was a reasonably common route historically.  The main group of people at risk from this route are farm workers.  (I was actually wondering whether this could potentially be a problem from places like children’s farms where more of the population could be exposed to infected animals.  I’ve not seen any information on it.  It’s probably not a problem at the moment but if the TB levels in the cattle herd keep increasing perhaps it could be in the future?)
  3. Infected meat – this is a very rare route of infection as gross signs of disease are easily spotted at meat inspection.

The World Health Organisation has this to say about bovine TB:

TB due to M. bovis often occupies sites other than the lungs (it is extra-pulmonary), but in many cases is clinically indistinguishable from M. tuberculosis infection. However, patients with M. bovis often do not respond to the drugs commonly used to treat TB, sometimes resulting in a fatal outcome.

In general there is a period of latency after exposure to the organism – in this period there are no clinical signs of disease.  Some (but not the majority) of latent infections will then go on to develop active disease which if not treated can be fatal.  This progression is more common if the person is immunosuppressed.

Cattle and Mycobacterium bovis

The picture in cattle is reasonably similar to that in humans.  Animals most commonly get infected via aerosolised droplets but there is the potential for calves to be infected via milk.  Some animals may never show signs of disease, in some the signs of disease may start off being quite vague (loss of appetite, weight loss) but cases can then develop into tuberculous lung disease.

Badgers and Mycobacterium bovis

Badgers, like cattle, are considered a “maintenance host” for bovine TB – the organism multiplies and infects the population from generation to generation and even if badgers never came into contact with any other possible Mycobacterium host the organism would still survive in the population. 

Again, some badgers may never show any signs of clinical disease but some may suffer from “florid disease” (as the paper by Gallagher and Clifton-Hadley – see below – beautifully describes it) including tuberculous lung disease and tuberculous lesions in other body sites.  That same paper proposes that it is those badgers with the most advanced disease that are the main reservoir of infection for other animals species such as cattle.

Other animals and Mycobacterium bovis

Some other species have also been proposed to act as maintenance hosts including deer and possibly goats.  Some species are thought to act as “spill-over” hosts (in these species the infection is self-limiting and they can be considered a “dead-end” host unless they happen to infect a maintenance host).  Currently considered as spill-over hosts are pigs, cats and dogs.  These animals may also show signs of disease (although again it can take a long time for disease to develop).

Importance in the UK

Because of milk pasteurisation and the control methods currently implemented in cattle the human cases of M. bovis are extremely rare.  This disease is much more of a problem in the developing world where these control mechanisms may not be in place. 

However, this does not mean the the disease should be forgotten about.

The incidence of the infection in cattle seems to be increasing (see the HPA link below) so there’s more chance of people coming into contact with it, if not directly from cattle, then from some of the spill-over hosts like cats and dogs. 

Another extremely important reason not to forget this disease is because the number of immunosuppressed people in the population is increasing (this includes people suffering from diseases like AIDs and also includes people on immunosuppressive drugs like chemotherapy) and as I mentioned before, this leads to greater chance of an infection becoming active and clinical symptoms developing. 

It may be (this is my speculation here) that in the future the most common picture for human infection (although it will still be extremely rare) will be an immunosuppressed person getting infected via a spill-over host like a pet cat or dog.

So…

As I’ve discussed, this disease is not only bad for us but it is also bad for cattle, for badgers, and for many other animals should they become infected.  In the end, it is in all (and I’m including animals in this ‘all’) of our best interests to eradicate this disease from our country.

And this is generally accepted.  However, what still remains to argue about is “How?”

Images

Badger picture: Made available by BadgerHero under a CC-BY 3.0 licence

Cow picture: Made available by CRV Arnhem under a CC-BY 3.0 licence

Further Information

World Organisation for Animal Health (OIE)‘s handout (NB: It is a PDF) on bovine TB

Defra’s policy statement on bovine TB control from December 2011  (also PDF)

Health Protection Agency information on bovine TB

Animal Health information on bovine TB

GALLAGHER, J. (2000). Tuberculosis in badgers; a review of the disease and its significance for other animals Research in Veterinary Science, 69 (3), 203-217 DOI: 10.1053/rvsc.2000.0422

de la Rua-Domenech, R. (2006). Human Mycobacterium bovis infection in the United Kingdom: Incidence, risks, control measures and review of the zoonotic aspects of bovine tuberculosis Tuberculosis, 86 (2), 77-109 DOI: 10.1016/j.tube.2005.05.002