Bovine TB is transmitted to cows through aerosol from coughing animals, but also directly from pastures and water sources, by ingestion.

Certain wild animals are a reservoir - the germ can survive in their population because they are sensitive and get ill, it is hosted by ill or carrier individuals - they spread the germ in the environment, and from there the cows can take it.

Campaigns against wild animals have been successful (New Zealand - the possum) and they are based on the statistical assumption that reducing the population (presumably eliminating the weakest individuals), the germ has less hosts and therefore more difficulty surviving and doing harm. (A similar judgment is used in vaccination - you do not necessarily have to vaccinate 100% of population - if 2% remain non vaccinated they will still be surrounded by so many immunized individuals that the germ cannot spread from them even if they are ill, so it becomes no more a social threat, perhaps even dissapears). In what concerns the wild animals (to my understanding), the idea is to reduce the population by a certain percentage every year so the threat be acceptably low.

A microorganism has usually afinity for a certain specie or group of individuals, this is why not any transmission is possible. And also why the other species' types of tuberculosis may not be of our concern - they cannot harm us or the animals of our economical interest. Human TB is specific only to humans, but bovine TB affects more species, humans included.

It is controversial, indeed, or anyway raises questions. For example, the alternative of vaccines (which reminds us of why the BCG cannot be 100% protective for humans).

Bravo Jane! We have many between sc Systemic disease, Sarcoidosis, Hodgkins lymphoma and disseminated malignant syndroma, uro genital TB, bone TB, ect. By children is described the TB avium, too.

Unfortunately it is no more BCG vacine in EU states....!?

Bravo Jane! We have many between sc Systemic disease, Sarcoidosis, Hodgkins lymphoma and disseminated malignant syndroma, uro genital TB, bone TB, ect. By children is described the TB avium, too.

Unfortunately it is no more BCG vacine in EU states....!?

Thank you, dr. Ilankovic. Could you please be more specific with your comment, I am not sure I understand it well.

....many not investigated TB (bacteriologicaly, PCR)) as etiology between so called....

An extract from an article by Nicola Weber in today's Conversation:

"This revealed that direct contact between badgers and cattle on pasture in Woodchester Park, Gloucestershire (an area with a fairly high density badger population that has been intensively studied) was relatively rare despite ample opportunity. However, indirect visits by both species to badger latrines (a single point outside the burrow where badgers, tidy animals, keep their droppings) were significantly more common. This suggests that it is these and perhaps other indirect contact away from pasture, for example in farm buildings, that is the common route of TB transmission."

As I had suspected, there is little direct contact. Why should indirect contact be more effective? It is still not making any sense.

Tuberculosis caused by M.bovis represents a major zoonosis and as a cause of economic losses, the infection is more in dairy cattle, not only because their useful economic life is longer than beef cattle, but because dairy cattle are in closer contact with one another during milking Tuberculosis is transmitted between cattle mainly via aerosols.The digestive route is important before weaning take place. Pulmonary as well as extra pulmonary forms of human tuberculosis of animal origin continue to be a problem in areas where the prevalence of infection in cattle is high, because not all milk consumed is boiled, many products are prepared from unpasteurized milk. and in addition cases of infection are contracted via aerosols.

"Tuberculosis is transmitted between cattle mainly via aerosols"

This makes sense epidemiologically for spread between cows, and from cows to people. But I still don't see how TB transmits between cows and badgers, and vice versa.

It happens because m. tuberculosis is very resistant, it can survive for months in the environment. Many disinfectants cannot destroy it. Also, unfortunately, a very limited number of germs is sufficient for an efficient infection (this is why, when the microbiological diagnosys is made on a bioptic sample, if in, say, 50 microscopic fields studied even one bacterium is found, the disease is confirmed)

"It happens because m. tuberculosis is very resistant, it can survive for months in the environment."

So you are saying that animals are basically catching it from germs lurking on the ground, rather than from direct contact with other animals.

Yes.

Thanks for the USDA APHIS factsheet link above.  The quote below from it, however, does not really answer my question:

"Q. What is the risk of TB transmission from local wildlife?

A. In areas where free-ranging deer are known to be infected with TB, deer that have direct contact with cattle could pose a risk of transmitting the disease. While the risk of transmitting TB is greatest in enclosed areas, such as barns, livestock can become infected if they share common watering or feeding places contaminated with saliva and other bodily discharges from infected wildlife."

This abstract from Ecology Letters rules out direct badger/cow contact.   I never thought this likely.  My gundog would go after anything, including herds of deer, but always beat a hasty retreat when confronted by cows.  The transmission route is still up in the air, perhaps literally.

"Badgers prefer cattle pasture but avoid cattle: implications for bovine tuberculosis control....Rosie Woodroffe,...

First published: 4 August 2016Full publication history

DOI: 10.1111/ele.12654View/save citation

Abstract

Effective management of infectious disease relies upon understanding mechanisms of pathogen transmission. In particular, while models of disease dynamics usually assume transmission through direct contact, transmission through environmental contamination can cause different dynamics. We used Global Positioning System (GPS) collars and proximity-sensing contact-collars to explore opportunities for transmission of Mycobacterium bovis [causal agent of bovine tuberculosis] between cattle and badgers (Meles meles). Cattle pasture was badgers’ most preferred habitat. Nevertheless, although collared cattle spent 2914 collar-nights in the home ranges of contact-collared badgers, and 5380 collar-nights in the home ranges of GPS-collared badgers, we detected no direct contacts between the two species. Simultaneous GPS-tracking revealed that badgers preferred land > 50 m from cattle. Very infrequent direct contact indicates that badger-to-cattle and cattle-to-badger M. bovis transmission may typically occur through contamination of the two species’ shared environment. This information should help to inform tuberculosis control by guiding both modelling and farm management."

Thank you sir,

Actually, there are many instances through which cows get infectefd with TB particularly due to M.bovis and M. tb as members of the MTBC. Badgers and other wildlife have shown to play a vital role in the transmission circle to cattle, as they are the potential reservoirs and can shed as many as millions mycobacterium in their bodily secretions especially inside the feeds and water opun which cattle do consume. Likewise, deer is some parts of Europe, can also transmit to TB to cattle.

Human-to-Animal transmission route has also been advocated to be possible among cattle owners, butchers, milkers and other PAR who happened to be infected with either Mtuberculosis or M. bovis. Mostly through contact, coughing and feeds contamination.