Dengue fever is caused by viruses that are carried by mosquitoes. Symptoms appear three to six days after the person is bit by a mosquito. Dengue fever is mostly found in the tropics. The heartworm may cause serious illness or even death. Adult heartworms live in a dog's heart, but young forms of the worm are found in their blood.
Mosquitoes transmit the infection when they feed on the blood of an infected dog.