This forum strand looks at the general issues involved in the bovine TB debate.
4 Jun 2010, 3:36 PM
Rowena is concerned regarding the potential spread of bTB bacteria (and other potential diseases) from slurry. She sent us a link to http://news.bbc.co.uk/1/hi/wales/south_west/8655083.stm which relates to a news item about a slurry spill in the River Teifi. It is believed that 600 young salmon and trout were found dead in a stream feeding the River Teifi. The Environment Agency Wales believe the dish were killed by a slurry spill. The spill affected a 3km (1.8 miles) stretch of the river. The source of the slurry was traced and stopped.
She says 'surely a more integrated approach to bTB control would look at factors directly attributable to the industry, before proceeding with such a drastic and destructive act as eliminating all the badgers from the area. What part has breeding to maximise milk production played in the decreased disease-resistance of dairy herds? We understand that studies have shown that high yielding is genetically associated with susceptibility to bTB. The Dairy Development Council's figures show that lameness, mastitis and mortality have all increased dramatically over the last 50 years, indicating systemic ill-health, which no amount of badger culling will alleviate. Only recently, a slurry spill into the Afon Cych, which forms one boundary of the IAPA, killed 600 salmon and trout. As bTB can survive in slurry for months, incidents like this are clearly a serious breach of biosecurity.'
How many other incidences go unreported? Does anyone know just how much risk slurry poses. It is routinely spread on the ground and waste milk (a known carrying substance for bTB) is currently allowed to be mixed with slurry as a means of disposal.
16 May 2010, 7:27 PM
In same issue of Gwlad, Glossop WAG's chief vet, in an article on the importance of vaccinating stock for bluetongue, says 'During 2009 over 11,000 susceptible animals were brought into Great Britain fro continental Europe, mainly from Germany and the Netherlands, some of which come to wales. It is certainly worth asking whether this movement is really necessary.' Whilst this is specifically referring to bluetongue disease and not TB it does reveal the extent of cattle movement. in the UK and is a worry regarding the control of any disease.
In the May 2010 (issue 95) issue of Gwlad, biosecurity is again stressed and, in particular, in relation to bringing animals on to the farm. This time the emphasis is on the passive transfer of infected materials. We are told that 'objects which carry pathogens, without themselves being affected, are technically known as fomites'. The key is to have elaborate procedures in place to minimise risk if fomite spread. Suggestions include wheel washes, foot baths, wearing dedicated clothing and showering. Without appropriate security we are tyold there is a real risk of introducing diseases such as 'Salmonella, E coli, or even TB and the highly infectious notifiable diseases.' Let's hope vets and ministry staff take heed.
16 May 2010, 7:22 PM
Just been reading latest issue Gwlad issue 94 which has an article about 'leading the fight against tb' and it talks about bought-in stock. As this is the publication done specifically for farmers one would assume the information is accurate. It says 'there is always a risk associated with bringing in stock from other locations'. It goes on to say 'Purchased stock may introduce infection to your resident animals. This potentially can be very damaging to the health, welfare and profitability of your stock'. It says, 'With regards to TB, a farm frequently buying in replacement breeding stock, or fattening purchased store animals will always be at risk of buying an infected animal. Pre-movement testing for TB will reduce the risk, but it is still possible that animals could have become infected after (or just before) the test took place.' And presumably also to bear in mind is the accuracy issues relating to the skin test. It goes on to say TB is not the only disease to consider and it is possible 'that the animals you acquire have little or no resistane to disease agents (pathogens), which may be present on your farm.' It gives a common example being the purchase of young calves, 'bought from market, often tired and stressed after the experience, which are mixed with resident animals, only to succumb to pneumonia or diarrhoea because their own dams did not produce colostrum with the relevant protective antibodies. Any purchased stock represent a risk'.
This is also another indication that cattle movement is the main cause of the spread of disease!
21 Apr 2010, 4:21 PM
Could M bovis be carried on a wheel and so be spread to new pasture and new cattle herds and badgers? I doubt this largely on general reasoning. M bovis and M tuberculosis are not so infectious as FMD or rotavirus or norovirus, for example. I would think that large numbers of bacilli would need to be transferred either by an infected host who is shedding or by harvested silage or manure upon/ into which many organisms have been shed - the moisture and acidity preserving the viablility of the organisms. I don't know of instances where silage or manure have spread bovine TB but I believe this has been taken account of in the rules for the area where the attempt is to be made to eradicate bovine TB in North Pembrokeshire.
E coli 0157 and shigella are examples where a few bacteria can infect and cause disease, but for salmonella 1000+ organisms are required. I used to have contractors to spread my muck. They arrived one year with a muck spreader dripping with fresh cow dung from another farm. 5 months later I had an outbreak of Salmonella typhimurium Group B in the sheep and lambs put out into that one particular field where my muck was spread. No other animals anywhere else on the farm had salmonella nor did my muck when tested. The bacterium had been spread I believe from the filthy muckspreader. The contractor denied it and that he would ever be prepared to wash it before coming so I bought my own second hand muck spreader. The pathologists at the VLA investigated the outbreak. Salmonella infection can be symptomatic or carried by cattle, but in sheep it is not carried though it can make some ill and is shed for a few months. Apart from sick and dead lambs the only adult sheep in that field to get ill had been treated with tetracycline for foot infections within the few previous months. This story illustrates the potential for spread through muck of infections shed in the faeces, and the protective effect of normal bowel flora.
It may be that cattle and badgers can acquire it from each other by inhaling aerosols from organisms deposited on the ground in the pasture. M bovis can survive for 6 months on pasture and rain may aerosolise it. Once in an aerosol it may not be viable for long, from work done at Porton Down, and its half life as viable bacteria as an aerosol may be about 30 minutes. On the ground the viablility is prolonged. I don't think it has to be associated with cow pats as also assumed by some, as Prof Wellington showed it was present on pasture. There is another disease which can be spread from soil to humans in some places by aerosolisation by rain and that is meliodosis another bacterial infection. This is a route which is difficult to study and prove but there is circumstantial evidence for it.
Oral ingestion as a route of infection has occurred in some cattle as evidenced from pathology of gut infection but in the main the pathology is of lung infection and the lymph nodes associated with the respiratory tract. Many more bacteria are required for the oral infection route than by inhalation. So of course the biosecurity will do some good but again will not be the whole answer. If your cattle were indeed infected, and I know the jury is out on this as the perfunctory PM showed no sign of infection but would not actually have ruled it out, how do you think biosecurity would have helped you?
21 Apr 2010, 4:15 PM
I wonder if the bacteria that causes bTB can be spread to farms on vehicle types and feet? There is much debate regarding the spread of bTB as a result of the much increased cattle movements but more contractors are used these days too.
16 Apr 2010, 1:58 PM
The temperate and damp conditions in the UK do, I believe, increase the longevity of mycobacteria in the environment. We rarely have a summer where the ground is baked dry by the sun and all the vegetation is dead so UV bathes the soil surface (thus killing off bacteria). I don't know if the last few wet years have been any more conducive than the previous 10 years. We were taught the conditions in Ireland were particularly conducive to the survival of mycobacteria in the sphagnum moss and without UV one would would wade about in bacteria.
One could also notice that the badger population is most dense in areas where bovine TB is a particular problem. Badgers are infrequent in the South East.
There are such a variety of soils in the UK I am not sure if soil type, pH and mineral composition plays any role in M bovis longevity in the environment.
16 Apr 2010, 1:57 PM
The microbacteria that causes bTB is endemic in the environment and it is known to last for many months if conditions are right for its survival. bTB in the UK tends to be concentrated in the wettest areas, Could climate therefore be an inmportant contributing factor?
25 Mar 2010, 6:56 PM
BVD and IBR are virus infections, bovine viral diarrhoea and infectious bovine rhinotracheitis. Either the farmer did not already have these infections in his cattle and they were introduced by the cattle he bought at least one of which must have been infected, or he replaced immune culled cattle with susceptible cattle who had never been infected and were exposed to infected individuals in the herd. Stress does not really have much to do with infection it is a question of exposure of a susceptible individual to an infectious individual. Both viruses can produce immunosuppression, IBR lung infection is associated with pasteurella lung infection in calves and BVD infection routinely produces a period of low white blood cell count for several months after acute infection (just as some virus infections do in humans too). I have wondered if BVD infection might temporarily suppress the skin test in a TB infected cow. IBR is an alpha herpes virus with three distinct subtypes causing respiratory, genital or encephalitic clinical syndromes. BVD is a pestivirus and as well as causing acute virus infection in postnatal animals, and it can cause abortion in pregnant cows, it can also infect the foetus in utero and cause a persisitent infectious state in the resultant live calf where they are a souce of infection to any other susceptible cattle in the herd and themselves may develop a fatal mucositis at 6 to 24 months of age. Both diseases can be vaccinated against. Unfortunately farmers don't think of these diseases (leptospirosis is another) when they purchase new animals for the herd. In herds where animals are bought in these diseases are likely to flourish and roll around the herd causing problems as there are new susceptibles born avery year, until the whole herd is vaccinated and the vaccination policy sustained.
Everyone always thinks of stress but infection can occur whether an animal or human is stressed or not, and the symptoms or disease if any are determined by a number of factors many unknown, for example genetic factors, infecting dose, route of infection, age, immunocompromise ( not frequent in animals but produced by modern medicine in humans Tx for cancer etc), malnutrition (effect on immune system). I would say that Alpacas have a genetic factor (s) that make them vulnerable to rapidly progressive and uncontrolled M bovis infection. Newborn lambs are suscepitble to severe cryptosporidiosis and may die from it unlike adult sheep- infecting dose may also come into it. etc. People with AIDS are particularly susceptible to becoming infected with TB and if infected the infection rapidly progresses and they are likely to be highly infectious.
With regards to the issue of re-stocking after an outbreak of bTB, it is important that infection could take place from bacteria on the ground, whether the source of these bacteria were cattle or badgers would be irrelevant.
Of course on restocking, the remaining living cattle on the farm are thought to be uninfected from the testing (of course that may not always be true), so the susceptible cattle are those who tested negative of the original herd as well as uninfected cattle brought in as new stock.
23 Mar 2010, 7:56 PM
There are so many factors that are not taken into account with the existing bTB policy. What about the costs and risks associated with re-stocking after a herd breakdown? In the Welsh Assembly Government's regular magazine 'Gwlad' (March 2010 issue) there was an article about the problems farmers face when re-stocking after bTB. It would seem that animals bought in are far more susceptible to disease and this can lower fertility and production - causing yet more problems for farmers. The case they referred to was a dairy farm which had firstly re-stocked quickly with local animals that some time later tested positive (despite being clear at the pre-movement tests) and had to be destroyed so they went to 'clean' areas and then had problems with BVD and IBR, which they had never had before. They had to vaccinate - which was expensive and fertility dropped off drastically.
16 Mar 2010, 7:01 PM
The book 'Mycobacterium Bovis Infection in Animals and Humans', 2006, 2nd edition is a very useful reference book for anyone interested in this subject. It was interesting to read that around 85% of cattle and 82% of the human population are in areas where bovine TB is either partially controlled or not controlled at all! It was also interesting to read that not all infected animals will be capable of spreading bTB. The number of pathogenic mycobacteria in the infecting dose, the route of entry and the ability of the infected animal to deal with the organisms at the site of entry often determine the outcome of infection, and ultimately, whether there will be any shedding of M bovis. Other aspects that are relevant include species, age, genetic factors, immune competence, nutritional status, physiological factors and population densities. Some breeds of cattle have a relatively high resistance to bTB. Apparently the intensification of livestock production systems increases the risk of bTB transmission. We have seen and are continuing to see a move towards larger herds to achieve economies of scale. How will this affect bTB in the UK in the future?
It is very disappointing to see that back in 2006 (when the above book was published) protection of cattle against infection with M bovis through vaccination was considered to be an important control strategy in some countries in which persistence of mycobacteria in wildlife results in re-infection of cattle (as in the UK). It says that control porgrammes should be carefully balanced to reflect the ecological importance of many wildlifespecies. It also suggests that vaccination of wildlife reservoirs of M bovis is ecologically and politically attractive option than depopulation of such maintenance hosts in countries in which eradication of tuberculosis in cattle using the test and slaughter programme has not been successful (as in the UK). So I wonder why Wales has opted for the politically and publicly unpopular depopulation of badgers? We are now several years on, increasing numbers of cattle still being slaughtered and more public money being spent, why is there still no vaccination approved for use here in the UK?
It was interesting to read that the intensification of livestock production systems increases the risk of bTB transmission. We have seen and are continuing to see a move towards larger herds to achieve economies of scale. How will this affect bTB in the UK in the future?
I am aware that the human form of TB is on the increase and London is one city where cases have increased significantly, mainly, I understand, as a result of immigrants coming in from abroad where the disease is endemic. Despite this, it is obviously not considered to be as serious a risk to human health as bTB as the government (in a cost cutting exercise) stopped its vaccination (BCG) programme for teenagers a few years ago and there are no plans to resume this!
Toby - a scientist (Guest)
2 Oct 2009, 6:42 PM
Not sure it has been Patty since Pasteurisation of milk was introduced. Though it is not my field, as a scientist myself, I really don't see what all the fuss is about.