BCG vaccine could help prevent TB in cattle, study finds

A BCG vaccine against tuberculosis could become a useful tool in the battle to rid herds of the disease, a new study has concluded.

The world’s first veterinary field trials of a Bacille Calmette-Guérin (BCG) vaccine and the associated skin test for differentiating infected and vaccinated animals (Diva) are currently under way in England and Wales.

Defra says the trials are “progressing well” and it remains on course to roll out the vaccine in cattle herds in 2025.

See also: Farmer attitudes to bovine TB vaccination mixed, study finds

A global study (PDF), led by Mexican researcher Feliciano Milián-Suazo and published this week, has assessed the potential use of the BCG vaccine against bovine TB in infected herds.

In several countries, including the UK and Mexico, there is a growing interest, both from farmers and authorities, in integrating the vaccine into the current control programmes, especially in dairy cattle, where the prevalence of the disease is high.

Currently, no country in the world uses vaccination to control bovine TB, even though the BCG vaccine has been in use since 1921 to prevent the disease in children.

Diva test ‘vital’

One reason for not using the vaccine is that it interferes with the tuberculin test, which is used to eliminate sick animals in herds. In the EU, there is also concern about restrictions that could be imposed on the movement of vaccinated cattle.

Vaccinated animals would be positive to the tuberculin test and therefore suspected of having the disease.

That is why an effective Diva test will prove vital alongside the use of the BCG vaccine in cattle in developed countries, the researchers note.

There have been many studies experimenting with the efficacy of different BCG strains and vaccines formulas. But little work has been carried out under natural conditions in the field.

However, field studies have shown levels of vaccine efficacy from 22% to 86%, depending on the parameter used to determine efficacy, the researchers say.

In any vaccination strategy, the researchers say it is important to establish short-, medium- and long-term goals.

For example, if the goal is to reduce prevalence rates to levels where a “test-and-slaughter” strategy is economically feasible, the vaccination period could be eight to 10 years.

Two studies at very small scale, conducted in Germany, concluded that bovine TB could be eliminated from the herd in about seven years; however, these studies were dropped at that time due to the benefits observed with the test-and-slaughter practice.

A 2011 study found that British farmers would be willing to pay for a vaccine if the cost were around £17 an animal a year. However, the real cost of a vaccine on the open market remains undetermined.

Study conclusion

The Mexican research team concludes that vaccination of cattle with the BCG strain “has the potential to reduce the impact of the disease in vaccinated animals, reducing the rate of infection, the magnitude and number of visible lesions”.

They add: “Therefore, the incorporation of the vaccine in current control programmes would undoubtedly help reduce the impact of this costly disease both in domestic animals and in free-living animals.”

However, they say more field trials under natural conditions are needed to “confirm or contradict this assertion”.