Fever


 * Associate Editor(s)-In-Chief: ;

Overview
Fever (also known as pyrexia, or a febrile response from the Latin word febris, meaning fever, and archaically known as ague) is a frequent medical symptom that describes an increase in internal body temperature to levels that are above normal (the common oral measurement of normal human body temperature is 36.8±0.7 °C or 98.2±1.3 °F). Fever is most accurately characterized as a temporary elevation in the body's thermoregulatory set-point, usually by about 1–2°C. Fever differs from hyperthermia, which is an increase in body temperature over the body's thermoregulatory set-point (due to excessive heat production or insufficient thermoregulation, or both). Carl Wunderlich discovered that fever is not a disease but a symptom of disease.

The elevation in thermoregulatory set-point means that the previous "normal body temperature" is considered hypothermic, and effector mechanisms kick in. The person who is developing the fever has a cold sensation, and an increase in heart rate, muscle tone and shivering attempt to counteract the perceived hypothermia, thereby reaching the new thermoregulatory set-point.

When a patient has or is suspected of having a fever, that person's body temperature is measured using thermometer. At a first glance, fever is present if:
 * temperature in the anus (rectum/rectal) or in the ear (otic) is at or over 38.0°C (100.4°F)
 * temperature in the mouth (oral) is at or over 37.5°C (99.5°F)
 * temperature under the arm (axillary) is at or over 37.2°C (99.0°F)

However, there are many variations in normal body temperature, and this needs to be considered when measuring fever. The values given are for an otherwise healthy, non-fasting adult, dressed comfortably, indoors, in a room that is kept at a normal room temperature, during the morning, but not shortly after arising from sleep. Furthermore, for oral temperatures, the subject must not have eaten, drunk, or smoked anything in at least the previous fifteen minutes.

Body temperature normally fluctuates over the day, with the lowest levels at 4 a.m. and the highest at 6 p.m. Therefore, an oral temperature of 37.5°C (99.5°F) would strictly be a fever in the morning, but not in the afternoon. Normal body temperature may differ as much as 0.4°C (0.7°F) between individuals or from day to day. In women, temperature differs at various points in the menstrual cycle, and this can be used for family planning (although it is only one of the variables of temperature). Temperature is increased after meals, and psychological factors (like the first day in the hospital) also influence body temperature.

There are different locations where temperature can be measured, and these differ in temperature variability. Tympanic membrane thermometers measure radiant heat energy from the tympanic membrane (infrared). These may be very convenient, but may also show more variability.

Children develop higher temperatures with activities like playing, but this is not fever because their set-point is normal. Elderly patients may have a decreased ability to generate body heat during a fever, so even a low-grade fever can have serious underlying causes in geriatrics.

Mechanism
Temperature is regulated in the hypothalamus, in response to PGE2. PGE2 release, in turn, comes from a trigger, a pyrogen. The hypothalamus generates a response back to the rest of the body, making it increase the temperature set-point.



Pyrogens
A pyrogen is a substance that induces fever. These can be either internal (endogenous) or external (exogenous). The bacterial substance lipopolysaccharide (LPS) is an example of an exogenous pyrogen.

Endogenous
The cytokines (such as interleukin 1) are a part of the innate immune system, produced by phagocytic cells, and cause the increase in the thermoregulatory set-point in the hypothalamus. Other examples of endogenous pyrogens are interleukin 6 (IL-6), and the tumor necrosis factor-alpha.

These cytokine factors are released into general circulation where they migrate to the circumventricular organs of the brain, where the blood-brain barrier is reduced. The cytokine factors bind with endothelial receptors on vessel walls, or interact with local microglial cells. When these cytokine factors bind, they activate the arachidonic acid pathway.

Exogenous
One model for the mechanism of fever caused by exogenous pyrogens includes LPS, which is a cell wall component of gram-negative bacteria. An immunological protein called lipopolysaccharide-binding protein (LBP) binds to LPS. The LBP–LPS complex then binds to the CD14 receptor of a nearby macrophage. This binding results in the synthesis and release of various endogenous cytokine factors, such as interleukin 1 (IL-1), interleukin 6 (IL-6), and the tumor necrosis factor-alpha. In other words, exogenous factors cause release of endogenous factors, which, in turn, activate the arachidonic acid pathway.

PGE2 release
PGE2 release comes from the arachidonic acid pathway. This pathway (as it relates to fever), is mediated by the enzymes phospholipase A2 (PLA2), cyclooxygenase-2 (COX-2), and prostaglandin E2 synthase. These enzymes ultimately mediate the synthesis and release of PGE2.

PGE2 is the ultimate mediator of the febrile response. The set-point temperature of the body will remain elevated until PGE2 is no longer present. PGE2 acts on neurons in the preoptic area (POA) through the EP3 subtype of PGE receptors and the EP3-expressing neurons in the POA innervate the dorsomedial hypothalamus (DMH), the rostral raphe pallidus nucleus in the medulla oblongata (rRPa) and the paraventricular nucleus of the hypothalamus (PVN). Fever signals sent to the DMH and rRPa lead to stimulation of the sympathetic output system, which evokes non-shivering thermogenesis to produce body heat and skin vasoconstriction to decrease heat loss from the body surface. It is presumed that the innervation from the POA to the PVN mediates the neuroendocrine effects of fever through the pathway involving pituitary gland and various endocrine organs.

Hypothalamus response
The brain ultimately orchestrates heat effector mechanisms. These may be The autonomic nervous system may also activate brown adipose tissue to produce heat (non-exercise-associated thermogenesis, also known as non-shivering thermogenesis), but this seems mostly important for babies. Increased heart rate and vasoconstriction contribute to increased blood pressure in fever.
 * increased heat production by increased muscle tone, shivering and hormones like epinephrine.
 * prevention of heat loss, such as vasoconstriction.

Types
Pyrexia (fever) can be classed as:
 * low grade: 38–39°C (100.4–102.2°F)
 * moderate: 39–40°C (102.2–104.0°F)
 * high-grade: 40–42°C (104.0–107.6°F)
 * hyperpyrexia: over 42°C (107.6°F)

The last is clearly a medical emergency because it approaches the upper limit compatible with human life.

Most of the time, fever types can not be used to find the underlying cause. However, there are specific fever patterns that may occasionally hint the diagnosis:
 * Pel-Ebstein fever: a specific kind of fever associated with Hodgkin's lymphoma, being high for one week and low for the next week and so on. However, there is some debate as to whether this pattern truly exists.
 * Continuous fever: temperature remains above normal throughout the day and does not fluctuate more than 1°C in 24 hours, e.g. lobar pneumonia, typhoid, urinary tract infection, brucellosis, or typhus. Typhoid fever may show a specific fever pattern, with a slow stepwise increase and a high plateau.
 * Intermittent fever: temperature is present only for some hours of the day and becomes normal for remaining hours, e.g. malaria, kala-azar, pyaemia, or septicemia. In malaria, there may be a fever with a periodicity of 24 hours (quotidian), 48 hours (tertian fever), or 72 hours (quartan fever, indicating Plasmodium vivax). These patterns may be less clear in travelers.
 * Remittent fever: temperature remains above normal throughout the day and fluctuates more than 1°C in 24 hours, e.g. infective endocarditis.

Febricula is a mild fever of short duration, of indefinite origin, and without any distinctive pathology.

Common Causes
Fever is a common symptom of many medical conditions:
 * Infectious disease, e.g. influenza, common cold, HIV, malaria, infectious mononucleosis, or gastroenteritis.
 * Various skin inflammations, e.g. boils, pimples, acne, or abscess.
 * Immunological diseases, e.g. lupus erythematosus, sarcoidosis, inflammatory bowel diseases.
 * Tissue destruction, which can occur in hemolysis, surgery, infarction, crush syndrome, rhabdomyolysis, cerebral hemorrhage, etc.
 * Drug fever
 * directly caused by the drug, e.g. lamictal, progesterone, or chemotherapeutics causing tumor necrosis.
 * as an adverse reaction to drugs, e.g. antibiotics or sulfa drugs.
 * after drug discontinuation, e.g. heroin withdrawal.
 * Cancers, e.g. Hodgkin disease.
 * Metabolic disorders, e.g. gout or porphyria.
 * Thrombo-embolic processes, e.g. pulmonary embolism or deep venous thrombosis.

Persistent fever which cannot be explained after repeated routine clinical inquiries, is called fever of unknown origin.

Complete Differential Diagnosis of the causes of Fever
In alphabetical order.


 * 2,4-Dinitrophenol
 * Abacavir
 * Abatacept
 * Abrin
 * Acetazolamide
 * Acetohexamide
 * Acute Chest Syndrome
 * Acute Disseminated Encephalomyelitis
 * Acute lymphoblastic leukemia
 * Acute myeloid leukemia
 * Acute posterior multifocal placoid pigment epitheliopathy
 * Acyclovir
 * Adalimumab
 * Adenoviridae
 * Adiposis dolorosa
 * Adjustable gastric band
 * Adrenal hemorrhage
 * African Hemmorhagic Fever
 * African horse sickness
 * African swine fever virus
 * African Trypanosomiasis
 * Albuterol
 * Aldesleukin
 * Alefacept
 * Alemtuzumab
 * Alendronate
 * Alfuzosin
 * Alglucerase
 * Alkhurma virus
 * Allergic bronchopulmonary aspergillosis
 * Allopurinol
 * Alphavirus
 * Altretamine
 * Alveolitis
 * Aminopterin
 * Amitriptyline
 * Amobarbital
 * Amphotericin B
 * Anagrelide
 * Anakinra
 * Anal abscess
 * Anastrozole
 * Ancrod
 * Anisindione
 * Anthrax
 * Aphthovirus
 * Appendicitis
 * Arbovirus
 * Arenavirus
 * Aripiprazole
 * Arterivirus
 * Asparaginase
 * Aspergillosis
 * Astroviridae
 * Atazanavir
 * Atelectasis
 * Atorvastatin
 * Atovaquone
 * Atropine Ophthalmic
 * Auranofin
 * Babanki virus
 * Babesiosis
 * Bacillary angiomatosis
 * Bacillus Calmette-Guerin (BCG) Vaccine
 * Bacterial pneumonia
 * Bartonellosis
 * Benazepril
 * Benztropine Mesylate
 * Bepridil
 * Bevacizumab
 * Bezold's abscess
 * Bisphosphonate
 * BK virus
 * Blackwater fever
 * Blastomycosis
 * Bleomycin
 * Blood transfusion
 * Blue diaper syndrome
 * Bordetella pertussis
 * Bornholm disease
 * Borrelia
 * Bortezomib
 * Boutonneuse fever
 * Brain Abscess
 * Brinzolamide Ophthalmic
 * Bronchitis
 * Brucellosis
 * Bubonic plague
 * Bumetanide
 * Burkitt lymphoma
 * Buruli ulcer
 * Busulfan
 * Butabarbital
 * Butoconazole Vaginal Cream
 * Bwamba Fever
 * Cabin fever
 * Cadmium poisoning
 * Caecitis
 * Calcitriol
 * Campylobacter jejuni
 * Candesartan
 * Capecitabine
 * Captopril
 * Carboplatin
 * Carbuncle
 * Carisoprodol
 * Carmustine
 * Caroli's Disease
 * Carteolol
 * Caspofungin
 * Cat scratch fever
 * Cefaclor
 * Cellulitis
 * Cephalosporin
 * Cetuximab
 * Chagas disease


 * Chickenpox
 * Childbirth
 * Chlamydia
 * Chlamydophila pneumoniae
 * Chlorambucil
 * Chlordiazepoxide
 * Chlorothiazide
 * Chlorthalidone
 * Cholangitis
 * Cholecystitis
 * Cholesterol Emboli Syndrome
 * Chronic myelogenous leukemia
 * Churg-Strauss Syndrome
 * Ciclosporin
 * Cidofovir
 * Cladribine
 * Clofarabine
 * Clonazepam
 * Clorazepate
 * Clostridium Difficile
 * Clotrimazole
 * CMV
 * Cocaine
 * Coccidioidomycosis
 * Cogan syndrome
 * Colchicine
 * Coley's Toxins
 * Colistimethate
 * Colitis
 * Colorado tick fever virus
 * Community-acquired pneumonia
 * Congenital syphilis
 * Co-trimoxazole
 * Cotton fever
 * Coxiella burnetii infection
 * Coxsackie A virus
 * Craniopharyngioma
 * Crimean Congo Hemorrhagic Fever
 * Crohn's disease
 * Croup
 * Cryptosporidiosis
 * Cyanocobalamin
 * Cyclobenzaprine
 * Cyclosporiasis
 * Cystic Fibrosis
 * Cystitis, infective
 * Cytarabine
 * Cytokine release syndrome
 * Dacarbazine
 * Dacryocystitis
 * Dactinomycin
 * Dalteparin Sodium
 * Dapsone
 * Daptomycin
 * Darbepoetin alfa
 * Darunavir
 * Daunorubicin
 * De Quervain's thyroiditis
 * Deferasirox
 * Delavirdine
 * Dengue Fever
 * Desipramine
 * Dextroamphetamine and Amphetamine
 * Dextromethorphan
 * Diabetes insipidus
 * Diazepam
 * Diclofenac
 * Didanosine
 * Dientamoebiasis
 * Diethylpropion
 * Diflunisal
 * Diltiazem
 * Dimercaprol
 * Dinoprostone
 * Diphtheria
 * Disopyramide
 * Disseminated Intravascular Coagulation
 * Diverticulitis
 * Dobutamine
 * Dolasetron
 * Donepezil
 * Doxorubicin
 * Dressler's syndrome
 * Ebola haemorrhagic fever
 * Echovirus
 * Efalizumab
 * Efavirenz
 * Empyema
 * Emtricitabine
 * Enalapril
 * Enfuvirtide
 * Enoxaparin
 * Entacapone
 * Enterotoxigenic Escherichia coli
 * Epiglottitis
 * Epinastine Ophthalmic
 * Epoetin Alfa
 * Epstein-Barr virus
 * Erlotinib
 * Estazolam
 * Estradiol Topical
 * Etanercept
 * Ethchlorvynol
 * Ethosuximide
 * Etidronate
 * Etodolac
 * Etoposide
 * Exopthalmos
 * Ezetimibe
 * Fabry's Disease
 * Famciclovir
 * Familial Mediterranian Fever
 * Fasciolopsiasis
 * Fasciolosis


 * Fat Embolism Syndrome
 * Fenoprofen
 * Fetal alcohol syndrome
 * Filgrastim
 * Filoviridae
 * Fipexide
 * Flavivirus
 * Flavoxate
 * Floxuridine
 * Flucytosine
 * Fludarabine Phosphate
 * Fluorouracil
 * Fluphenazine
 * Fluticasone and Salmeterol Inhalation
 * Fluvastatin
 * Fluvoxamine
 * Fosamprenavir
 * Foscarnet Sodium
 * Fosinopril
 * Free-living amebic infection
 * Furosemide
 * Furunculosis
 * Fusarium
 * Gabapentin
 * Gallbladder empyema
 * Ganciclovir
 * Gastritis
 * Gastroenteritis
 * Gastrointestinal perforation
 * Gatifloxacin
 * Gefitinib
 * Gemcitabine Hydrochloride
 * Giardiasis
 * Glatiramer acetate
 * Glipizide
 * Glyburide
 * Gonorrhea
 * Goserelin
 * Gout
 * Gradenigo's syndrome
 * Granisetron
 * Grifulvin V
 * Group A streptococcal infection
 * Guanethidine
 * Haemophilus influenzae serotype B infection
 * Haloperidol
 * Hamman-Rich Syndrome
 * Hand-foot-mouth syndrome
 * Hantavirus Pulmonary Syndrome
 * Haverhill fever
 * Hay fever
 * Hemophagocytic lymphohistiocytosis
 * Heparin
 * Hepatitis A
 * Hepatitis B
 * Hepatitis E
 * Hepato-biliary diseases
 * Heroin withdrawl
 * Herpangina
 * Herpes zoster
 * Herpesviridae
 * Herxheimer reaction
 * Hidradenitis suppurativa
 * Histrelin
 * HIV/AIDS
 * Hodgkin's lymphoma
 * Hookworm
 * Human monocytotropic ehrlichiosis
 * Hydralazine
 * Hydrochlorothiazide
 * Hyperimmunoglobulinemia D with recurrent fever
 * Ibandronate
 * Idarubicin
 * Idiopathic pulmonary haemosiderosis
 * Ifosfamide
 * Ileitis
 * Imatinib
 * Imiglucerase
 * Imiquimod
 * Immune Globulin Intravenous
 * Immune reconstitution inflammatory syndrome
 * Impetigo herpetiformis
 * Indomethacin
 * Infectious mononucleosis
 * Infective Endocarditis
 * Influenza virus
 * Interstitial nephritis
 * Intra-abdominal abscess
 * Ipratropium and Albuterol Inhalation
 * Ischemic colitis
 * Isocarboxazid
 * Itraconazole
 * Juvenile Myelomonocytic Leukemia (JMML)
 * Kaposi's sarcoma
 * Kawasaki disease
 * Kikuchi disease
 * Krabbe disease
 * La Crosse encephalitis
 * Lamivudine
 * Langerhans cell histiocytosis
 * Laryngitis
 * Lassa Fever
 * Legionellosis
 * Leishmaniasis
 * Lemierre's Syndrome
 * Leptospirosis


 * Levalbuterol Inhalation
 * Levetiracetam
 * Levomepromazine
 * Linezolid
 * Liothyronine
 * Lisinopril
 * Listeriosis
 * Lithraea molleoides
 * Lorazepam
 * Lovastatin
 * Loxapine
 * Ludwig's angina
 * Lung abscess
 * Lung cancer
 * Lupoid hepatitis
 * Lyme disease
 * Lymphocytopenia
 * Lymphogranuloma venereum
 * Macrophage activation syndrome
 * Malakoplakia
 * Malaria
 * Malignant hyperthermia
 * Marburg hemorrhagic fever
 * Mastitis
 * Mastocytosis
 * Mastoiditis
 * Measles
 * Mechlorethamine
 * Meclofenamate
 * Mediastinitis
 * Mefenamic acid
 * Melarsoprol
 * Melioidosis
 * Melphalan
 * Meningitis
 * Meprobamate
 * Mercaptopurine
 * Mesothelioma
 * Metal fume fever
 * Methadone withdrawl
 * Methimazole
 * Methocarbamol
 * Methotrexate
 * Methsuximide
 * Methyclothiazide
 * Methyldopa and Hydrochlorothiazide
 * Methylphenidate
 * Metolazone
 * Metoprolol
 * Metronidazole
 * Micafungin
 * Miconazole
 * Mifepristone
 * Miliary tuberculosis
 * Minocycline
 * Mitomycin
 * Modafinil
 * Moexipril
 * Moricizine
 * Moxifloxacin ophthalmic
 * Muckle-Wells syndrome
 * Mumps
 * Murray Valley encephalitis virus
 * Mycobacterium avium complex
 * Mycophenolate
 * Mycoplasma pneumoniae
 * Myxoma
 * Nabumetone
 * Naegleria infection
 * Nafcillin Sodium
 * Nalmefene
 * Natalizumab
 * Necrotizing fasciitis
 * Nefazodone
 * Nephroblastoma
 * Neuroleptic malignant syndrome
 * Neutropenia
 * Nevirapine
 * Nilutamide
 * Nitrofurantoin
 * Nocardiosis
 * Noma (disease)
 * Norovirus infection
 * Nortriptyline
 * Occult abscess
 * Olanzapine
 * Omphalitis
 * Omsk hemorrhagic fever
 * Ondansetron
 * O'nyong'nyong virus
 * Opisthorchis infection
 * Oprelvekin
 * Orbital cellulitis
 * Oropouche virus
 * Oseltamivir
 * Otitis media
 * Oxacillin Sodium
 * Oxaliplatin
 * Oxamniquine
 * Oxazepam
 * Oxcarbazepine
 * Oxybutynin
 * Oxycodone and aspirin
 * Paclitaxel
 * Palifermin
 * Paliperidone
 * Pamidronate
 * Pancreatitis
 * Paracoccidioidomycosis
 * Paragonimus Infection
 * Paratyphoid fever
 * Pegaspargase
 * Peginterferon alfa-2a
 * Pel-Ebstein fever
 * Pelvic inflammatory disease
 * Pemetrexed
 * Penicilliosis
 * Penicillamine
 * Pentetic acid


 * Pentostatin
 * Peplomycin
 * Perianal abscess
 * Pericoronitis
 * Perindopril
 * Peritonitis
 * Peritonsillar abscess
 * Puerperal pyrexia
 * Pharyngitis
 * Pharyngoconjunctival fever
 * Phenazopyridine
 * Phenelzine
 * Phenobarbital
 * Phentermine
 * Phenytoin
 * Pimecrolimus topical
 * Pimozide
 * Pindolol
 * Piroxicam
 * Pityriasis rosea
 * Pleurisy
 * Plicamycin
 * Pneumocystis jirovecii pneumonia
 * POEMS syndrome
 * Poliomyelitis
 * Polyarteritis nodosa
 * Polytetrafluoroethylene
 * Pontiac fever
 * Posaconazole
 * Pravastatin
 * Prazepam
 * Praziquantel
 * Prazosin and polythiazide
 * Pregabalin
 * Primaquine
 * Primidone
 * Procainamide
 * Procarbazine
 * Prochlorperazine
 * Procyclidine
 * Propafenone
 * Propiomazine
 * Propylthiouracil
 * Prostatitis
 * Protriptyline
 * Pseudomembranous colitis/C.difficile
 * Psittacosis
 * Pulmonary alveolar proteinosis
 * Pyelonephritis
 * Pyrazinamide
 * Pyrexia of unknown origin
 * Q fever
 * Quetiapine
 * Quinapril
 * Rabies vaccine
 * Ramipril
 * Ranitidine bismuth citrate
 * Rasagiline
 * Rat-bite fever
 * Reactive Polyarticular Arthritis
 * Renal Cell Carcinoma
 * Retinoic acid syndrome
 * Rheumatic fever
 * Rheumatoid arthritis
 * Rhinovirus
 * Ribavirin
 * Rickettsial infections
 * Rifampicin
 * Rift Valley fever virus
 * Riluzole
 * Risedronate
 * Risperidone
 * Rituximab
 * Rocky Mountain Spotted Fever
 * Roseola
 * Ross River Fever
 * Rosuvastatin
 * Rotavirus
 * Rubella
 * Salmonella enteritidis
 * Salmonella typhi infection/ Typhoid fever
 * Salsalate
 * Saquinavir
 * Sarcoidosis
 * Sargramostim
 * Scarlet fever
 * Schistosomiasis
 * Scopolamine
 * Scrofula
 * Secobarbital
 * Selegiline
 * Sennetsu fever
 * Sepsis
 * Septic arthritis
 * Serotonin syndrome
 * Serum sickness
 * Severe acute respiratory syndrome
 * Shigellosis
 * Sibutramine
 * Sickle-cell disease
 * Silicosis
 * Silver sulfadiazine
 * Simvastatin
 * Sindbis virus
 * Sinusitis
 * Sirolimus
 * Sleeping sickness
 * Smallpox
 * Sodium oxybate
 * Solanine
 * Solifenacin
 * Spironolactone
 * Spotted Fever
 * Staphylococcal toxic shock syndrome
 * Staphylococcal enteritis
 * Still's disease
 * Stool softeners


 * Strep throat
 * Streptococcus pyogenes
 * Streptokinase
 * Streptozocin
 * Strontium-89 chloride
 * Stuve-Wiedemann syndrome
 * Subacute thyroiditis
 * Subdural hygroma
 * Succimer
 * Sulfadiazine
 * Sulfasalazine
 * Sulfinpyrazone
 * Sulfisoxazole
 * Sulindac
 * Sulprostone
 * Sunitinib
 * Swine flu
 * Synovial sarcoma
 * Syphillis
 * Systemic lupus erythematosus
 * Takayasu's Arteritis
 * Tamoxifen
 * Tamsulosin
 * Tanapox
 * Temazepam
 * Temozolomide
 * Temporal arteritis
 * Teniposide
 * Terbinafine
 * Teriparatide (rDNA origin)
 * Testosterone Transdermal
 * Thiabendazole
 * Thioamide
 * Thioguanine
 * Thiotepa
 * Thrombophlebitis
 * Thyroid Medication
 * Ticarcillin Disodium
 * Ticlopidine
 * Tiludronate
 * Tiotropium Inhalation
 * Tipranavir
 * Tirofiban
 * Tocainide
 * Tolazamide
 * Tolbutamide
 * Tolosa-Hunt syndrome
 * Topotecan Hydrochloride
 * TORCH infections
 * Toxic epidermal necrolysis
 * Toxic megacolon
 * Toxic Shock Syndrome
 * Toxocara infection
 * Tracheitis
 * Trandolapril
 * Transfusion reaction
 * Transfusion-associated graft versus host disease
 * Tranylcypromine
 * Trastuzumab
 * Traveler's diarrhea
 * Trazodone
 * Trench Fever
 * Triamterene
 * Triazolam
 * Trichinosis
 * Trichothecene
 * Trihexyphenidyl
 * Trimethadione
 * Trimetrexate Glucuronate
 * Trimipramine
 * Troleandomycin
 * Tropical pulmonary eosinophilia
 * Tuberculosis
 * Tularemia
 * Ulcerative colitis
 * Urate crystal arthropathy
 * Urinary tract infection
 * Valacyclovir
 * Valganciclovir
 * Valproate semisodium
 * Valproic Acid
 * Varicella (Chickenpox) Vaccine
 * Varicella-zoster virus
 * Vasculitis
 * Verapamil
 * Vibrio parahaemolyticus
 * Vibrio vulnificus
 * Vinblastine
 * Vinorelbine Tartrate
 * Viral Hepatitis A
 * Viral Hepatitis C
 * Viral infections
 * Visceral leishmaniasis
 * Vitamin A
 * Voriconazole
 * Vorinostat
 * Weber-Christian disease
 * Wegener Granulomatosis
 * West Nile Virus
 * Whipple's disease
 * Yellow Fever Vaccine
 * Yellow Fever Virus
 * Yersinia enterocolitica Infection (Yersiniosis)
 * Yersinia Pestis Infection
 * Yersinia pseudotuberculosis
 * Zalcitabine
 * Zika fever
 * Zinc oxide
 * Ziprasidone
 * Zoledronate
 * Zonisamide

Complete Differential Diagnosis of the Causes of Fever
(By organ system)

Usefulness of fever
There are arguments for and against the usefulness of fever, and the issue is controversial. There are studies using warm-blooded vertebrates and humans in vivo, with some suggesting that they recover more rapidly from infections or critical illness due to fever.

Theoretically, fever has been conserved during evolution because of its advantage for host defense. There are certainly some important immunological reactions that are sped up by temperature, and some pathogens with strict temperature preferences could be hindered. The overall conclusion seems to be that both aggressive treatment of fever and too little fever control can be detrimental. This depends on the clinical situation, so careful assessment is needed.

Fevers may be useful to some extent since they allow the body to reach high temperatures. This causes an unbearable environment for some pathogens. White blood cells also rapidly proliferate due to the suitable environment and can also help fight off the harmful pathogens and microbes that invaded the body.

Treatment
Fever should not necessarily be treated. Fever is an important signal that there's something wrong in the body, and it can be used for follow-up. Moreover, not all fevers are of infectious origin.

Even when treatment is not indicated, however, febrile patients are generally advised to keep themselves adequately hydrated, as the dehydration produced by a mild fever can be more dangerous than the fever itself. Water is generally used for this purpose, but there is always a small risk of hyponatremia if the patient drinks too much water. For this reason, some patients drink sports drinks or products designed specifically for this purpose.

Most people take medication against fever because the symptoms cause discomfort. Fever increases heart rate and metabolism, thus potentially putting an additional strain on elderly patients, patients with heart disease, etc. This may even cause delirium. Therefore, potential benefits must be weighed against risks in these patients. In any case, fever must be brought under control in instances when fever escalates to hyperpyrexia and tissue damage is imminent.

Treatment of fever should be based primarily on lowering the set-point, but facilitating heat loss may also contribute. The former is accomplished with antipyretics. Wet cloth or pads are also used for treatment, and applied to the forehead. Heat loss may be an effect of (possibly a combination of) heat conduction, convection, radiation, or evaporation (sweating, perspiration). This may be particularly important in babies, where drugs should be avoided. However, if water that is too cold is used, it induces vasoconstriction and prevents adequate heat loss.

Books

 * Rhoades, R. and Pflanzer, R. Human physiology, third edition, chapter 27 Regulation of body temperature, p. 820 Clinical focus: pathogenesis of fever. ISBN 0-03-005159-2
 * Kasper, D.L.; Braunwald, E.; Fauci, A.S.; Hauser, S.L.; Longo, D.L.; Jameson, J.L. Harrison's Principles of Internal Medicine. New York: McGraw-Hill, 2005. ISBN 0-07-139140-1.