Hemorrhagic fevers are caused by a variety of infections from viral agents that originate in animals and insects, including rodents and mosquitoes, according to the Mayo Clinic. The type of virus determines how the infection spreads, such as tick bites or contact with contaminated rat feces.
Examples of viral hemorrhagic fevers include dengue, yellow fever and ebola, the CDC Special Pathogens Branch states. VHFs are caused by four families of viruses that all rely on specific animal or insect hosts, known as natural reservoirs and vectors, and they only occur in the geographic regions of their host species. While VHFs never originate in humans, some variants can spread from person to person once contracted.
Contact with infected bodily fluids and secretions typically causes transmission of VHFs, according to the CDC Special Pathogens Branch. Occasionally, VHFs spread to geographic regions where they don’t occur naturally after an imported host or infected traveler carries the virus. A direct bite usually causes insect-related infections, but humans can also contract viruses from handling livestock infected by insect bites.
Symptoms of VHFs depend on the disease, but they commonly include high fever, muscle and joint aches, dizziness, shock and fatigue, the Mayo Clinic states. In more severe cases, these viruses cause bleeding from the eyes, mouth or ears and internal hemorrhaging under the skin and inside organs.