Everything inside small dark vial showing disease (7)
I believe the answer is:
malaria
'disease' is the definition.
(malaria is a kind of health problem)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for malaria that I've seen before include "Fever disease transmitted by mosquitoes" , "Tropical disease" , "Fever-inducing disease" , "Am a liar (anag) - fever" , "Tropical fever" .)