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A fever is a body temperature that is higher than normal. It is not an illness. It is part of your body's defense against infection. Most bacteria and viruses that cause infections do well at the body's normal temperature (98.6 F). A slight fever can make it harder for them to survive. Fever also activates your body's immune system.

Infections cause most fevers. There can be many other causes, including

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Results 1 - 10 of 5,004 for pyrexia
  1. Fever (National Library of Medicine)  
    A fever is a body temperature that is higher than normal. It is not an illness. It is part ... body's normal temperature (98.6 F). A slight fever can make it harder for them to survive. ...
  2. Hemorrhagic Fevers (National Library of Medicine)  
    Viral hemorrhagic fevers (VHFs) are a group of illnesses caused by four families of viruses. These include the Ebola and Marburg, Lassa fever, and yellow fever viruses. VHFs have common features: ...
  3. Dengue (National Library of Medicine)  
    ... in the United States. Symptoms include a high fever, headaches, joint and muscle pain, vomiting, and a ... In some cases, dengue turns into dengue hemorrhagic fever, which causes bleeding from your nose, gums, or ...
  4. Streptococcal Infections (National Library of Medicine)  
    ... sometimes with white spots on the tonsils Scarlet fever - an illness that follows strep throat. It causes ...
  5. Tick Bites (National Library of Medicine)  
    ... bite are Lyme disease, ehrlichiosis, Rocky Mountain spotted fever and tularemia. Some ticks are so small that ...
  6. Ebola (National Library of Medicine)  
    Ebola hemorrhagic fever is caused by a virus. It is a severe and often fatal disease. It can affect humans and ... after exposure to the virus. Symptoms usually include Fever Headache Joint and muscle aches Weakness Diarrhea Vomiting ...
  7. Hay Fever (National Library of Medicine)  
    ... can trigger a type of allergy called hay fever. Symptoms can include Sneezing, often with a runny ... eyes Your health care provider may diagnose hay fever based on a physical exam and your symptoms. ...
  8. Valley Fever (National Library of Medicine)  
    Valley Fever is a disease caused by a fungus (or mold) called Coccidioides. The fungi live in the soil ... from person to person. Anyone can get Valley Fever. But it's most common among older adults, especially ...
  9. Salmonella Infections (National Library of Medicine)  
    ... reptiles like snakes, turtles, and lizards. Symptoms include Fever Diarrhea Abdominal cramps Headache Possible nausea, vomiting, and ... be serious. The usual treatment is antibiotics. Typhoid fever, a more serious disease caused by Salmonella, is ...
  10. Bacterial Infections (National Library of Medicine)  
    Bacteria are living things that have only one cell. Under a microscope, they look like balls, rods, or spirals. They are so small that a line of 1,000 could fit ...
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