A common diagnostic test for bovine tuberculosis (BTB) may not work properly if animals are also infected with a widespread livestock parasite, reports a paper published in Nature Communications this week. The finding suggests that not all cattle infected with BTB might be identified as such and may in part explain why the current BTB eradication campaign in the UK is failing.

BTB has been eradicated in much of the European Union, Australia and North America, but is still endemic in the UK, Ireland and New Zealand. In an effort to curb the disease in the UK, live animals are tested for tuberculosis and immediately slaughtered if found positive. Diana Williams and her team demonstrated that infection of cattle with the common livestock parasite Fasciola hepatica interferes with the diagnosis of BTB with a commonly used immunological test. Using epidemiological and geographical data, they found that diagnoses of BTB were less frequent in areas in the UK were Fasciola hepatica is widespread. The researchers calculated that up to one third more BTB cases could be diagnosed in these areas in the hypothetical absence of the parasite.

These findings could have implications for ongoing BTB eradication programmes.