Roach droppings can trigger asthma attacks, as well as spread Salmonella and bacterial illnesses that cause diarrhea. Rodents have been linked to the transmission of over 35 diseases, including food-borne infections, Hantavirus, and plague. Fire ants can cause fatal allergic responses in some people. Mosquitoes spread a variety of serious disease-causing viruses, including Zika, West Nile, malaria, as well as several kinds of encephalitis.