Fever or pyrexia, is the rise in body temperature as a reaction to an infection or result of an inflammation. The commonest causes of fever include inflammatory conditions, illnesses caused due to an infection, injuries, etc. It is necessary to know the normal and abnormal body temperatures and understand causes of fever in detail.

Normal and Abnormal Temperature

Normal body temperature fluctuates between 97.70 F (36.50 C) and 99.50 F (37.50 C). The temperature of 98.6 0 F or 37 0 C is considered as an average normal body temperature. Temperature above 99.50 F (37.5 0 C) is considered as fever or pyrexia.

Body temperature during fever may increase up to 1040 F (400 C), which is commonly known as high fever. Some conditions show mild rise of temperature, which may show slight increase but remains below 1000 F (380 C).

Common Causes of Fever

Common Causes of Fever

Most common causes of fever or pyrexia are viral or bacterial infections. Some of the conditions that usually cause fever include the following,

  • Otitis media is an infection causing inflammation of the middle ear, mostly caused by virus and bacteria. It often causes fever and is more common in children.
  • Pharyngitis- One of the commonest causes of fever; pharyngitis is the infection of throat and mouth mostly caused by viruses and bacteria.
  • Laryngitis- Infection of voice box or larynx mostly due to viruses and bacteria, which causes fever. Also presents with hoarseness of voice.
  • Bronchitis- Infection of bronchi mostly caused by viruses and bacteria is also one of the common causes of fever.
  • Tracheitis- Infection of trachea mostly caused by viruses and bacteria.
  • Pneumonia- Infection of alveoli (lungs) mostly caused by viruses and bacteria. Less often fever is associated with fungal infection of lungs. This is another commonest cause of fever, accompanied with cough, chest pain
  • Gastritis- Infection of stomach mucosal membrane mostly caused by viruses and bacteria. This too is one of the most common causes of fever and is associated with gastric disturbances, nausea and vomiting.
  • Enterocolitis- Enterocolitis is the infection of small and large intestine mostly caused by viruses and bacteria, less often parasites and protozoa
  • Cholecystitis- Infection of gall bladder mostly caused by bacteria and less often by viruses, is also an important cause of fever.
  • Appendicitis- Infection of appendix mostly caused by bacteria and less often by viruses is another common cause of fever.
  • Meningitis is a severe infection of the meninges, the lining of the brain. Infection is caused by either bacteria or viruses, which causes fever and can be life threatening.
  • Urinary tract infection (UTI) is a bacterial infection of the bladder, urethra, kidneys, or ureters caused by viruses or bacteria. It is one of the common causes of fever and is usually accompanied with urinary complaints, vomiting and sometimes back pain.

Systemic Illnesses That Cause Fever

  1. Infections

    Infection is the most common cause of fever. Infection causes mild to severe fever. Mild fever is observed in infection caused by parasites as well as fungi. Viral or bacterial infections are usually the causes of high fever.

    1. Viral Infection

      Fever due to viral infection is caused by viruses. Viruses are divided in RNA and DNA virus. In most cases of viral infection, viruses enter into endothelial cells of gastrointestinal and respiratory system resulting in symptoms like, running nose, cough, nausea, vomiting and diarrhea along with fever. Few cases of viral infection results in systemic disease such as pneumonia (lung infection), hepatitis (liver infection), meningitis (meningeal infection), encephalitis (brain infection) and kidney infection.

      The viral infection is caused by major group of viruses. The group viruses causing respiratory and gastrointestinal infection are Adenovirus, Coxsackievirus, Heptovirus, Orthomyxovirus, Parovavirus, Poliovirus, Reovirus, Retrovirus and Rhinovirus. These are the commonest causes of fever.

    2. Bacterial Infection-

      Most bacterial infections are caused by staphylococcus, streptococcus, E. Coli, salmonella and pseudomonas bacteria. The less common systemic bacterial infections, which often results in fever are caused by Shigella, Brucella, Campylobacter, Chlamydophilia, Listeria, Ligionella, Mycobacterium tuberculosis and Mycobacterium Avium, Syphilis, Rickettsia, Tetanus and Yersinia bacteria.

      Skin infections like cellulitis, folliculitis and boils are caused by staphylococcus and staphylococcus bacteria, which are other common causes of fever. Bacterial infections due to E. Coli, Salmonella, Shigella and Pseudomonas too are some of the commonest causes of fever, associated with nausea, vomiting and diarrhea.

      Rarely fever is associated with diarrhea and severe abdominal cramps caused by Campylobactrer Jejuni and Listeria Monocytogenes. Abdominal cramps and fever may be predominant symptoms with diarrhea in E. Coli and Salmonella bacterial infection. Listeria Monocytogenes bacterial infection often causes severe muscle ache and high fever.

      Bacterial infection caused by Clostridium Botulinum (C. Botulinum) results in fever and neurotoxicity. Neurotoxicity is caused by neurotoxin that is release by the bacteria. The effect of neurotoxin causes severe muscle weakness and nerve damage. Some of the bacterial infection causes sexual transmitted disease (STD). STD infection like gonorrhea is cause by bacteria known as Neisseria Gonorrhea. Syphilis is another STD that is cause by bacteria Treponema Pallidum. Pelvic inflammatory disease resulting from STD is caused by bacteria Chlamydia Trachomatis.

    3. Parasite Infection

      The parasite infections cause mild fever and other systemic symptoms like cough, diarrhea and abdominal pain. Parasite infections are caused by protozoa, helminths and ectoparasites.

      1. Protozoal Infection. The four groups of protozoa cause infection in humans, which can cause fever. Fever may or may not present during later phase of the disease.

        • Sarcodina (Amoeba) causes amebiasis,
        • Mastigophora (Flagellates) causes giardiasis and leishmaniasis.
        • Ciliophora (Ciliates) - causes balantidium infection.
        • Sporozoa- Causes plasmodium and cryptosporidium infection.
      2. Helminths Infections. Helminths are worms and live in human body as a parasite and are the common causes of fever. Helminths causing human infection are broadly classified in three groups.

        • Flukes (trematodes) causes infection of lungs, liver, blood and intestine.
        • Roundworms (Nematodes) - The infection caused by roundworm may not result in fever. Occasional mild fever may be observed in few cases. The subspecies of species nematodes cause infections like filariasis, pinworm (threadworm), whipworm, hookworm and roundworm infection.
        • Tapeworms (Cestodes) causes infection known as tapeworm infection. The symptoms are mild fever, abdominal pain and occasional diarrhea. The worms are also known as Taenia saginata, Taenia solium, Diphyllobothrium latum, Hymenolepis nana and Echinococcus species.
    4. Fungal Infection

      Fungal infection rarely causes fever. Fungal infection occurs slowly. Fungi are classified as yeasts (single round cells) or molds (multiple cells that forms thin long threads). Fungal infection causes skin diseases like cutaneous candidiasis, Athlete's Foot (Tinea Pedis), ringworm (Tinea Corporis), Tinea Capitis and Tinea Versicolor.

  2. Cancer - Primary Or Secondary May Cause Fever

    Certain primary and secondary cancers cause mild to moderate fever. Cancer of lung, kidney, bone, liver and pancreas are the common causes of fever.

  3. Autoimmune Diseases That Can Cause Fever

    Autoimmune disease increases the activities of white blood cells. White blood cells attack and cause destruction of their own normal cells. The metabolites trigger the temperature center and sets the temperature setting to higher temperature. The autoimmune disease like systemic lupus erythematosus, rheumatoid arthritis and collagen disorders cause a rise in body temperature, which are common causes of fever.

  4. Vascular Diseases That Can Cause Fever

    Vascular diseases like peripheral vascular disease may not always cause fever. Fever is observed when vascular diseases obstruct or restrict blood flow to normal tissue. The lack of blood flow causes increased secretion of ischemic metabolites. Such metabolites cause increase body temperature, which causes fever. Acute myocardial infarction, pulmonary embolism, tissue hemorrhage and thrombosis are the common causes of fever in vascular diseases.

  5. Fever Caused Due to Trauma

    Fever is a predominant symptom when severe tissue trauma results in massive injury. The toxic substances released from tissue following an injury are the causes of fever.

  6. Endocrine Disorders

    Endocrine diseases like Thyrotoxicosis and Addison's disease changes tissue metabolism resulting in catabolic activities. Increased tissue activities increases production of heat, which causes mild to moderate fever or pyrexia.

  7. Metabolic Diseases That Cause Fever

    Diseases that increase body metabolism often cause increase in body temperature. The disease like gout, porphyria and acute hemolytic crisis triggers increase in body metabolism, which causes fever. Gout is presented with swelling of joints in foot and difficulties to move the joint.

    Fever is often the only symptom observed in metabolic and endocrinal diseases. History of trauma and vascular diseases often rules out the other causes of fever when presented without any other symptoms.

Written, Edited or Reviewed By:

, MD, FFARCSI

Last Modified On: July 6, 2017

Pain Assist Inc.

Pramod Kerkar
  Note: Information provided is not a substitute for physician, hospital or any form of medical care. Examination and Investigation is necessary for correct diagnosis.

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