The infection prospers in crowds, spreading to people in close reach. Containing an outbreak requires contact tracing, as well as isolation and treatment. Tuberculosis, the biggest infectious-disease killer worldwide, claim[s] 1.5 million lives each year. Until this year, TB and its deadly allies, H.I.V. and malaria, were on the run. The toll from each disease over the previous decade was at its nadir in 2018, the last year for which data are available. Yet now, as the coronavirus pandemic spreads around the world, consuming global health resources, these perennially neglected adversaries are making a comeback. "Covid-19 risks derailing all our efforts and taking us back to where we were 20 years ago," said Dr. Pedro L. Alonso, the director of the World Health Organization's global malaria program. It's not just that the coronavirus has diverted scientific attention from TB, H.I.V. and malaria. The lockdowns, particularly across parts of Africa, Asia and Latin America, have raised insurmountable barriers to patients who must travel to obtain diagnoses or drugs, according to interviews with more than two dozen public health officials, doctors and patients worldwide. About 80 percent of tuberculosis, H.I.V. and malaria programs worldwide have reported disruptions in services, and one in four people living with H.I.V. have reported problems with gaining access to medications, according to U.N. AIDS. Interruptions or delays in treatment may lead to drug resistance.