Malaria and yellow fever are absent from Puerto Rico, but dengue fever and schistosomiasis are present in lowland areas. Neither is much of a problem in the area of El Verde. Rabies shot are recommended for those that have to handle mammals. No dangerous snakes occur in Puerto Rico. The sap of some plants (e.g. Comocladia glabra) can cause a severe reaction similar to poison ivy. Falls from slippery rocks or trees are dangerous and care should be taken in choosing footwear. Bees and wasps are sometimes found in the forest, researchers should bring their own medicines.