The cause of the disease is difficult to pin down precisely.

病因目前还难以解释清楚。

《牛津词典》

None of the doctors knew the cause of the disease.

没有一个医生知道这种病的病因。

youdao

Zhong spent much time in finding the cause of the disease.

钟南山花了很多时间来寻找病因。

youdao

The cause of the disease is not known.

VOA: special.2009.01.06

Malaria causes a million deaths per year, and schistosomiasis, which is a parasitic disease, is unfortunately a common cause of death in the world.

疟疾每年造成一百万死亡,而血吸虫病,这是一种寄生虫病,不幸的是,它是世界上很常见的死因

耶鲁公开课 - 生物医学工程探索课程节选

But most important is finding the cause of the disease so it can be prevented or cured.

VOA: standard.2010.08.09

Neurologists fiercely debate whether the amyloid clumps are the cause of the disease--or merely a consequence.

FORBES: Alzheimer's Drug Showdown

Even after decades of research, the case that amyloid buildup is the main cause of the disease is hardly airtight.

FORBES: Magazine Article

"The cause of the disease may not be new, but the scale at which it is occurring has not been observed in recent years, " the WHO said in an email.

WSJ: Unexplained Disease Kills Over 60 Children in Cambodia