Bovine tuberculosis, the BCG vaccine reduces infections by 89%

Bovine tuberculosis, the BCG vaccine reduces infections by 89%

Bovine tuberculosis is one of the main infectious diseases of these animals and, in addition to being linked to important economic losses for the agricultural sector, it is responsible for approximately 10% of tuberculosis cases in humans. It is mainly caused by Mycobacterium bovis and, to a lesser extent, from M. capraetwo bacteria that are part of the complex Mycobacterium tuberculosis. Now, one study just posted on Science reveals, for the first time, the effectiveness of livestock vaccination in reducing not only the severity of the disease, but also the risk of spreading the disease within farms.

Bovine tuberculosis

Breeding cattle constitute the main reservoir of Mycobacterium bovis, which can however also affect other domestic and wild species. The bacterium has in fact been isolated from African and Asian buffaloes, bison, sheep, goats, camels, from some species of pigs, but also from dogs, cats and primates, just to name a few examples. As anticipated, M. bovis It can also infect humans, in which it more frequently causes gastrointestinal infections linked to the consumption of contaminated milk. However, the disease can in some cases spread to the airways, causing a chronic infection of the lungs which is often difficult to treat due to the resistance of this strain to the antibiotics commonly used against tuberculosis.

In cattle the disease manifests itself with signs of fatigue, loss of appetite and body weight, episodes of fever, cough, recurrent pneumonia, diarrhea and swollen lymph nodes. Transmission between animals occurs mainly through the air. Additionally, calves can become infected through ingestion of contaminated milk.

The study conducted in Ethiopia

“Bovine tuberculosis is an uncontrolled infection in low- and middle-income countries, including Ethiopia,” he explains Abebe Fromsa, one of the main authors of the study and professor of agriculture and veterinary medicine at the University of Addis Ababa. The study was conducted in Ethiopia, the country with the largest cattle breeding in Africa and a growing spread of the disease also due to the absence of specific control programs. But the disease and the resulting economic and health burden also affect high-income countries, such as the United Kingdom, Ireland and New Zealand, experts explain. The research is in fact the result of extensive collaboration, which saw the involvement of various European, Asian and US universities and research institutes, including the University of Cambridge (United Kingdom) and Penn State University (United States).

The scientists first examined the ability of the BCG (Bacillus Calmette-Guérin) vaccine – the same one used to prevent tuberculosis in humans – to both directly protect livestock from severe disease and prevent transmission of the bacterium. To do this, animals – vaccinated or not – were put in close contact with cattle that had contracted the infection naturally. This phase of the study lasted a total of two years.

“Our study found that BCG vaccination reduces TB transmission in cattle by almost 90%,” he explains. Andrew Conlan, professor of epidemiology at the University of Cambridge’s department of veterinary medicine and one of the study’s lead authors – Vaccinated cows also developed significantly fewer visible signs of TB than unvaccinated cows. This suggests that vaccination not only reduces disease progression, but that if vaccinated animals become infected, they are substantially less contagious to others.”

Vaccination reduces the R0 of the disease

Subsequently, using census and livestock movement data in Ethiopia, the research team developed a transmission model to analyze the potential impact of routine vaccination in bovine tuberculosis control: “The model results suggest that Vaccinating calves within Ethiopia’s dairy sector could reduce the bacteria’s reproduction number – R0 – below 1, halting the predicted increase in disease impact and putting herds on the line. route towards the elimination of TB,” continues Conlan.

In the past, he explains Vivek Kapur, who co-led the study and is a professor of microbiology and infectious diseases at Penn State University, the programs for the eradication of bovine tuberculosis have been based above all on intensive screening and culling of infected animals: “This approach – concludes the expert – is not implementable in many parts of the world for economic and social reasons, and involves considerable suffering for animals and economic losses linked to reduced productivity, as well as a greater risk of spreading the infection to humans. By vaccinating cattle we hope to be able to protect both livestock and humans from the consequences of this devastating disease.”

Source link