Ph.D. links in the field of Medical Microbiology

A PhD requires a broad topic with several subgroups. Your idea about herbal research and hepatitis is interesting but limited and as a result may be difficult to pursue as a PhD. Perhaps focus on virology and then subdivide this into different studies that fall into that broad category 

Please notify me if a Ph.D. Position in epidemiology becomes available.

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Your Interest in Pursuing a PhD in infectious diseases especially herbal research for hepatitis viruses is a nice idea but it is a very narrow subject area that leads to limited opportunities. If you want to do PhD in abroad, You have to target a broad subject area in virology. There are several Universities/Institutions advertised on their websites, which can be found easily on google search. 
A few sample links are provided below.
https://www.findaphd.com/phds/virology/?30M782a1
https://virologyphd.hms.harvard.edu/apply

wishing you all the best in your future endeavors.