Strains of HIV are becoming resistant to an antiretroviral drug commonly used to prevent and fight the virus, research has suggested. HIV was resistant to the drug Tenofovir in 60% of cases in several African countries, according to the study, covering the period from 1998 to 2015. The research, led by University College London, looked at around 2,000 HIV patients worldwide. The work compared patients with HIV in Africa with those in Europe and found that 60% of patients in Africa were resistant to Tenofovir, whereas in Europe the figure was only 20%. The paper said poor administration of the drug, in terms of regularly taking the right levels of Tenofovir could be explanation for the discrepancy. “If the right levels of the drug are not taken, as in they are too low or not regularly maintained, the virus can overcome the drug and become resistant,” Dr Ravi Gupta, lead author, said. The paper also suggested that Tenofovir-resistant strains of HIV could be passed on from person to person. HIV is the world’s most deadly infectious disease, according to the World Health Organisation.