Dementia has unseated AIDS as one of the world’s top killers, new figures from the World Health Organization show, as drugmakers struggle to either curb or cure it.

Alzheimer’s disease and other forms of dementia killed 1.54 million people in 2015, more than twice the number of deaths from the disease in 2000, according to documents posted on the WHO website. It replaced HIV/AIDS as No. 7 on the global health watchdog’s list of the 10 biggest causes of death worldwide. New therapies helped push fatalities from HIV/AIDS from 1.5 million down to 1.1 million over the same 15-year period.

Drugmakers have struggled to understand Alzheimer’s, with Merck & Co. abandoning a high-profile study this week, less than three months after a similar defeat for Eli Lilly & Co. More than 100 experimental treatments have failed to slow the condition, which dismantles memories and leaves patients incapacitated.

Dementia afflicts some 47 million worldwide, and the number will probably rise to 75 million by 2030, said Shekhar Saxena, director of the WHO’s department of mental health.

“We are making slow progress,” Saxena said, calling for more public money to be directed toward developing treatments. “I am less optimistic than I would like to be.”

Dementia’s climb up the WHO ranking is partly due to the aging of society, and partly to doctors diagnosing it more frequently because they are more familiar with the disease, he said. In high-income economies, Alzheimer’s and other dementia rank as the No. 3 cause of death, trailing only heart disease and stroke. By contrast, HIV/AIDS remains on the top 10 list in the poorest countries, alongside problems such as malaria and diarrhea.

The most recent drug to help treat symptoms of Alzheimer’s is more than a decade old, and there is no cure.

The Centers for Disease Control and Prevention reported more evidence of progress against HIV in the U.S. this week, citing an 18 percent decline in the number of U.S. infections between 2008 and 2014. Heterosexuals saw a 36 percent decline, and intravenous-drug users experienced a 56 percent drop.

The estimated number of infections fell from 45,700 in 2008 to 37,600 in 2014.