Necessary is a synonym of Necessity. Necessity is a synonym of Fate. Fate is related to Death. 
Epidemic is related to Disease. Disease is related to Condition. Condition is related to Diagnose. Diagnose is a type of Analyze. 
Necessary <--Synonym--> Necessity <--Synonym--> Fate <--RelatedTo--> Death 
Epidemic <--RelatedTo--> Disease <--RelatedTo--> Condition <--RelatedTo--> Diagnose --IsA--> Analyze 