The most common travel-related diseases, such as dysentery and hepatitis, are acquired by consumption of contaminated food and water, so limit your risk by following safe food and water habits.
Zika outbreaks have been reported in the Dominican Republic in the past. The Center for Disease Control (CDC) warns that because of the risk of birth defects in babies born to women infected with Zika while pregnant, pregnant women should consult with their healthcare provider before traveling to the DR.
It’s also worth noting there’s a small risk of malaria (in the western provinces and in La Altagracia, including Punta Cana) and dengue fever (in Santiago, inland and north coast). In these areas, long pants and long sleeves, mosquito repellent and bed nets are recommended (dengue bites happen during the daytime).