Tuberculosis is one of Earth’s deadliest infectious diseases, with as many as three human deaths every minute. Bovine tuberculosis (Mycobacterium tuberculosis var bovis) is closely related and can significantly limit the productivity of livestock.
It is estimated that around 10 percent of total human TB cases worldwide are caused by bovine TB. While it is well controlled in many high-income countries, the disease is still regularly found in low-income countries where socio-economics limits the ability to cull the animals to halt the spread of the disease.
"Test and slaughter" is a method of infection control that is exactly as it sounds. To curb the spread of tuberculosis, cattle are tested for TB and, if positive, killed. It is a highly successful means to an end but also one that is improbable for most developing countries with small cattle owners who live life on the edge, their income and nutrition gained from the animals they raise.
So why kill and not mend the cow? Antibiotic medicine is expensive, say the team, and it can remove the cow from service for up to years at a time. Unfortunately, it’s not a practical enough solution to be widely implemented. Instead, something better was needed.
Now, a team from Penn State University say they have that better idea. The team created a test that can distinguish between an infected animal and one that has been vaccinated with the BCG strain – a major issue with the centuries-old TB tuberculin skin test.
"While BCG rarely provides sterilizing immunity for either humans or cattle, it has been shown to be effective at preventing a substantial number of infections and protecting against the more severe forms of human TB," said study author Vivek Kapur, a professor of microbiology and infectious diseases, in a statement. "However, the inability to tell whether a cow has the disease or has simply been vaccinated has prevented governments from implementing cow vaccination programs, leaving both animals and humans vulnerable to infection."
The team’s new test ensures this doesn’t happen by targeting proteins in bovine tuberculosis that are not expressed in the vaccine.
"Our diagnostic reagent is a simple cocktail of synthetic peptides representing antigens that are present in the naturally occurring TB bacteria but not recognized by the immune system following BCG vaccination," said Sreenidhi Srinivasan, a graduate student at Penn State. "These antigens, when applied to the skin, cause an immune reaction in cows that have TB, whereas no reaction occurs in animals that have been vaccinated with BCG."
The new development improves upon an old standard and enables the implementation of vaccination programs to hasten the control of bovine tuberculosis. The test could also be used in countries like India, where the slaughter of cows is illegal due to the cultural significance of the creature.