The correct answer is to properly normalize your database. You shouldn't use comma separated values (as suggested in comments). I am sure you can find many articles teaching normalization, so I won't go into details here.
You need to separate the symptoms from the diseases.
Diseases table
id | d_name
---------------------
1 | Dengu
2 | Typhoid
3 | Cervical
Symtoms table
id | s_name
---------------------
1 | Fever
2 | Pain
3 | Vomit
4 | Abc
5 | Xyz
Diseases-Symptom table (this is an intersection)
id | d_id | s_id
---------------------------
1 | 1 | 1
2 | 1 | 2
3 | 1 | 3
2 | 2 | 3
3 | 2 | 2
1 | 2 | 4
2 | 3 | 2
3 | 1 | 5
This way you don't create duplicate symptoms and makes your data easier to use and present, for example
SELECT id, s_name FROM symptoms
will give you a list of all symptoms available.
SELECT diseases.id, diseases.d_name, symptoms.s_name
FROM diseases
JOIN diseases_symptoms ON d_id = diseases.id
JOIN symptoms ON symptoms.id = diseases_symptoms.s_id
WHERE diseases.id = 1;
will give you a result similar to:
id | d_name | s_name
---------------------------
1 | Dengu | Fever
2 | Dengu | Pain
3 | Dengu | Vomit