posted by awsin .
why a disease that was once on the decline might re-emerge?
People could lose their immunity or new strains of the disease may develop.
due to the storage of hypnozoits and sporozoits stages of parasites(dorment stage)
It could be new strains that mutate so that they are not recognizable by the antibodies we developed to the previous strain (the flu does this year after year). Another reason is some people, though there isn't ANY evidence supporting this, believe that vaccinations give autism. Therefore there is a high percentage of babies not vaccinated for diseases we once thought were eradicated in the US. This sets the stage for communicability between these unvaccinated children in deadly diseases such as smallpox (a crime I personally believe should be gross negligence on part of the parents).