What Is a Viral Fever?

Viral infections can cause moderate fevers.
The human body can raise its temperature to fight off viruses.
Body temperature elevation due to a virus is known as a viral fever.
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  • Written By: Geisha A. Legazpi
  • Edited By: Allegra J. Lingo
  • Last Modified Date: 22 September 2014
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In medical terminology, basal body temperature elevation due to a viral infection is called a viral fever. The actual virus that causes the fever may or may not be identifiable. A viral fever may be accompanied by other signs and symptoms, such as runny nose, red eyes, malaise, irritability, joint and muscle pains, enlarged lymph nodes, and skin rash. Most of the time, a viral fever resolves after three to seven days and is considered benign and self-limiting. It can, however, cause complications, particularly among the very young, the very old, and the immunocompromised.

The transmission of a particular virus usually occurs when a person inhales aerosolized particles, eats or drinks contaminated food or water, or is in direct contact with another infected person. Some viruses are spread through direct inoculation or sexual contact. Viruses may affect a certain organ, and medical symptoms may localize to that organ. For instance, adenovirus and rhinovirus affect the upper respiratory tract, causing upper respiratory tract infection, while rotavirus and norovirus affect the gastrointestinal tract, causing gastroenteritis or diarrhea. After the virus has spread locally, it is transported into the blood or lymph and is eventually fought off by the immune system.


A viral fever occurs because substances like prostaglandins, interleukin-1 (IL-1), and tumor necrosis factor (TNF) are released by activated lymphocytes and macrophages. Fever occurs when these substances stimulate the hypothalamus to reset the body’s temperature set point at a higher level. Paracetamol, aspirin, and nonsteroidal anti-inflammatory drugs are able to reduce fever because they prevent prostaglandin synthesis.

Additionally, a viral fever plays an important role in helping limit the viral infection. It is hypothesized that with the elevation of body temperature, special proteins called heat shock proteins (HSPs) are activated to boost the response of lymphocytes to the infecting virus. Fever between 38 to 39 degrees Celsius (100.4 to 102.2 degrees Fahrenheit) is classified as a low-grade fever, and between 39 to 40 degrees Celsius (102.2 and 104 degrees Fahrenheit) is classified as a moderate-grade fever. A high-grade fever occurs when the body temperature goes beyond 40 degrees Celsius (104 degrees Fahrenheit). Hyperpyrexia occurs when the body temperature reaches 42 degrees Celsius (107.6 degrees Fahrenheit) and above.

A viral fever can be beneficial, but a fever classified as moderate grade or high grade is a cause for concern. Temperature-lowering measures, such as taking antipyretic medicines and having cold baths, should be given to the patient. In particular, hyperpyrexia is considered a medical emergency because it reaches the limit of what is compatible with life.


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