Juan Javier Rios |
Madrid (EFE).- Is it safe to eat beef? Are cows killed for tuberculosis that later were not infected? Is the tuberculin diagnostic test reliable? These are just some of the questions raised these days on account of the controversy generated in Castilla y León by the regulations to contain bovine tuberculosis.
On the one hand are the farmers most affected, supported by some agricultural organizations and the Junta de Castilla y León, who are asking to relax the regulations because they understand that, after years of controls, no more progress will be achieved and, on the other, the veterinarians , the central government and the European Union that see it as a danger to animal health and even to public health.
The data collected by EFE and the consultation made to the researcher and tuberculosis expert at the Institute for Research in Hunting Resources (IREC-Csic) of the University of Castilla-la Mancha, Christian Gortázar, explain some of these questions that have arisen.
Can I get tuberculosis by eating beef or drinking milk?
QUESTION: Can I get tuberculosis by eating beef or drinking milk?
ANSWER: Food safety mechanisms make infection from eating food very difficult.
In 2021 (latest data available), Spain analyzed 92.7 million food samples for the tuberculosis bacterium Mycobacterium spp and only detected it in 0.01% of the samples.
For this reason, in Spain the incidence in humans is very low: about 30 cases per year and mainly affects farmers in direct contact with an infected cow (contamination mainly by air) or a slaughterer (contamination if an open wound comes into contact with any infected carcass lesion).
However, the risk from food is not zero and the most likely source is consuming unpasteurized milk and dairy products, that is, raw.
Q: At the livestock level, what is its incidence?
A: 1.48% of Spanish herds test positive for bovine tuberculosis (2022 data), a percentage with slight increases and decreases for years but far from the 10% that was around the end of the 80s of the last century before beginning the eradication programs, according to Cortázar.
The Basque Country, the Canary Islands, Galicia, Asturias, Murcia and Catalonia are officially free of this disease and, on the other hand, the main incidence is found in all of Extremadura and in the regions of Seville, Córdoba, Málaga, Cádiz, Jaén, Huelva, Salamanca, Ávila , Segovia, Madrid, Ciudad Real, Toledo and Guadalajara.
Q: What would happen if the rules were relaxed?
A: The problem lies in the danger of the disease spreading to areas with low or no incidence and, therefore, the possibility of affecting some of the 98% of farms without positives.
Why has the problem focused on Castilla y León?
Q: Why has the problem focused on Castilla y León?
A: Although there are other areas with a similar incidence in the country, in that area there are two conditions that make control more difficult, such as the presence of extensive livestock (greater interaction with other livestock and wildlife that may be infected) and fragmented farms, that is, producers who usually have several farms distributed throughout the territory or in communal pastures, facilitating the interaction between animals.
Q: The farmers who protested this week in Salamanca complain about the high false positives in the tests done on cattle, how reliable is the tuberculin test?
A: There are no data to confirm these supposed false positives, because when a cow is sent to the slaughterhouse for testing positive, it is not confirmed on the farm with any other analysis, beyond the visual inspection of the carcass by the slaughterhouse veterinarian. .
The problem is that there are positive cattle that arrive at the slaughterhouse without having yet developed visible lesions from the disease and this leads the farmer to think that this head of cattle was not infected, according to the expert.
Q: Is that test rudimentary? No other options?
A: This expert acknowledges that although the test may be “outdated”, it has proven its validity in eradicating the disease in areas such as Australia, the United States or “many” European countries.
It is somewhat rudimentary (an intradermal injection of antigen from the bacteria to analyze the skin reaction) but this bacterium “is very special” because it generates few antibodies in its initial phases, making it difficult to detect with a standard blood test.
It detects 70% of infected cattle (three out of 10, therefore they are not detected), but for this reason, in the areas with the highest incidence, all cattle are tested once every six months to detect these false negatives.
The option of the well-known PCR (direct search for the presence of the genetic material of the bacterium) is still complex to apply because it would require taking a sample of lymphoid or lung tissue for biopsy.
Are there vaccines available for cattle?
Q: Are there vaccines available for cattle?
A: Yes, there are vaccines available but in the European Union they are discouraged because, apart from the fact that they are not fully effective (“they are not a silver bullet”, according to Cortázar), the problem stems from the fact that in a sanitation of cows both the infected as well as vaccinated, without the possibility, for the moment, of distinguishing between one and the other, although there is scientific research in the United Kingdom that is trying to achieve it.
Q: What other preventive measures are of interest?
A: The farmer can reduce the chances of contagion in his cattle with preventive measures such as meshes to prevent the entry of wild fauna into his farm and all those biosecurity actions so that contacts between wild and domestic animals are not frequent.