Hey tejaswi,
Who can purse  phd in public health are mentioned below
1. One should have completed their PG degree in public health
2. Completion of a second class master's degree in a relevant subject from any recognized University with an aggregate of 55 percent
3. You must qualify the National eligibility test examination with good rank
4.  You should have 5 year relevant experience in Public health sector .
If you are satisfying above conditions then you are eligible otherwise not.
Good luck!