Categorizing viral infections by the organ system most commonly affected (eg, lungs, gastrointestinal tract, skin, liver, central nervous system, mucous membranes) can be clinically useful, although certain viral disorders (eg, mumps) are hard to categorize. Many specific viruses and the disorders they cause are also discussed elsewhere in THE MANUAL.
(See also Overview of Viruses.)
Respiratory infections
Some Respiratory Viruses
Principal Syndromes |
Prevalence and Distribution |
Specific Therapy |
Specific Prevention* |
Epidemic influenza viruses A, B, and C and avian influenza viruses |
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AFRD |
A and B: Seasonal (winter) epidemics, occasionally pandemic C: Endemic Global |
A and B: Baloxavir, oseltamivir or zanamivir |
A and B: Vaccine, oseltamivir or zanamivir |
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Avian H5N1 and avian H7N9: Poultry-associated |
Oseltamivir, zanamivir, and possibly baloxavir |
Avoiding contact with birds |
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Parainfluenza viruses 1–4 |
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Acute febrile respiratory disease (children) |
1: Local epidemics 1, 2, and 3: Widespread in children |
None |
Vaccines under investigation |
Adenoviruses |
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Acute febrile respiratory disease (children) Acute pharyngoconjunctival fever Acute follicular conjunctivitis Diarrhea Hemorrhagic cystitis |
Global Mostly children |
None |
Vaccine containing types 4 and 7 for epidemics in military populations |
Coronaviruses |
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Local origin becomes widespread SARS: China; no cases after 2004 MERS: Arabian Peninsula COVID-19: Wuhan, China |
None |
COVID-19 vaccine under development MERS: Avoid contact with camels |
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Orthohantaviruses |
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Hantavirus pulmonary syndrome (eg, due to Sin Nombre hantavirus, Black Creek Canal virus, Bayou virus, or New York virus) Hemorrhagic fever with renal syndrome (eg, Hantaan, Seoul, and Dobrava viruses) |
North, Central, and South America |
None for hantavirus pulmonary syndrome IV ribavirin for hemorrhagic fever with renal syndrome |
None |
Respiratory syncytial virus and human metapneumovirus |
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Mild upper respiratory illness (adults) |
Widespread in children |
Ribavirin sometimes used in immunocompromised patients |
Palivizumab IM† monthly (only for certain infants at high risk of respiratory syncytial virus [RSV] infection) |
Rhinoviruses |
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Acute coryza with or without fever |
Universal, especially during cold months |
None |
None |
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* Nonspecific precautions (eg, avoidance of infected patients and insect and animal vectors, routine hygiene measures) are also recommended. |
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† Unlike RSV-IVIG (respiratory syncytial virus-IV immune globulin), palivizumab does not interfere with immunizations (eg, measles, mumps, and rubella [MMR], chickenpox). |
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The most common viral infections are probably upper respiratory infections. Respiratory infections are more likely to cause severe symptoms in infants, the elderly, and patients with a lung or heart disorder.
Respiratory viruses include the epidemic influenza viruses (A and B), H5N1 and H7N9 avian influenza A viruses, parainfluenza viruses 1 through 4, adenoviruses, respiratory syncytial virus A and B and human metapneumovirus, and rhinoviruses (see Table: Some Respiratory Viruses).
Several coronaviruses have been identified that cause a respiratory infection that can be severe. In 2002 and 2003, an outbreak of severe acute respiratory syndrome (SARS) caused a number of deaths mostly in China and Hong Kong. There have been no cases of SARS reported since 2004. In 2012, a novel coronavirus Middle East respiratory syndrome coronavirus (MERS-CoV) appeared in Saudi Arabia; it can cause severe acute respiratory illness and is sometimes fatal. In 2019, another coronavirus (SARS-CoV2) that can cause an acute, sometimes fatal respiratory illness (COVID-19) emerged in Wuhan, China and is currently spreading worldwide.
Respiratory viruses are typically spread from person to person by contact with infected respiratory droplets.
Gastrointestinal infections
Gastroenteritis is usually caused by viruses and transmitted from person-to person by the oral-fecal route.
Age group primarily affected depends on the virus:
Local epidemics may occur in children, particularly during colder months.
The main symptoms are vomiting and diarrhea.
No specific treatment is recommended, but supportive care, particularly rehydration, is important.
A rotavirus vaccine that is effective against most pathogenic strains is part of the recommended infant vaccination schedule. Hand washing and good sanitation measures can help prevent spread.
Exanthematous infections
Some Exanthematous Viruses
Principal Syndromes |
Prevalence and Distribution |
Specific Therapy |
Specific Prevention* |
Rubeola virus |
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Encephalomyelitis Central nervous system involvement (rare) |
Global Prevalence increasing due to decrease in vaccination |
None |
Vaccines |
Rubella virus |
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Birth defects due to infection during pregnancy |
Universal |
None |
Vaccines |
Human parvovirus B19 |
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Erythema infectiosum (fifth disease) Rash (red rash on cheeks more common in children), malaise, arthritis (polyarthropathy more common in adults) Hydrops fetalis (infection during pregnancy) Anemia (transient aplastic crisis in immunocompromised hosts or patients with hemoglobinopathies) |
Sporadic outbreaks |
IV immune globulin (for severe anemia) |
None |
Human herpesvirus type 6 |
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Roseola infantum (exanthem subitum) |
Widespread Affects young children |
None |
None |
Varicella-zoster virus |
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Before vaccine, almost universal in children, occasionally in adults |
Acyclovir, famciclovir, valacyclovir |
Immune globulins, vaccine |
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Common in adults, resulting from reactivation of latent virus |
Acyclovir, famciclovir, valacyclovir |
Vaccine |
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Variola |
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Natural disease eradicated |
Cidofovir† Smallpox vaccine up to 4 days after exposure |
Vaccine Cidofovir† |
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Alphaviruses (some) |
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Chikungunya disease (acute febrile illness followed by more chronic polyarthritis) |
Transmitted by Aedes mosquitoes Africa, Southeast Asia, India, Europe, the Americas |
None |
None |
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Mayaro disease (a dengue-like disease) |
Mosquito-borne South America, Trinidad, Haiti |
None |
None |
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Ross River virus disease (epidemic polyarthritis) |
Aedes mosquitoes Australia, Papua New Guinea, South Pacific |
None |
None |
Molluscum contagiosum virus |
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Molluscum contagiosum papules |
Genital (adults) Exposed skin (children) More severe (AIDS patients) |
Cryotherapy, curettage |
None |
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* Nonspecific precautions (eg, avoidance of infected patients and insect and animal vectors, routine hygiene measures) are also recommended. |
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† Based on animal studies. |
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Some viruses cause only skin lesions (as in molluscum contagiosum and warts); others also cause systemic manifestations or lesions elsewhere in the body.
Transmission is typically from person to person; alphaviruses have a mosquito vector.
Hepatic infections
Viral Hepatitis
Principal Syndromes |
Prevalence and Distribution |
Specific Therapy |
Specific Prevention* |
|
Hepatitis A (acute) |
Widespread, often epidemic |
None |
Immune globulin, vaccine |
|
Hepatitis B (acute and chronic) |
Widespread |
Interferon, other antivirals, including nucleoside analogs (eg, entecavir) and nucleotide analogs (eg, tenofovir disoproxil fumarate) |
Screening for hepatitis B surface antigen Vaccine, hepatitis B immune globulin (HBIG) |
|
Hepatitis C (acute and chronic) |
Widespread |
Interferon, ribavirin, direct-acting antivirals (eg, protease inhibitors, nucleotide analog inhibitors, nonstructural protein 5A [NS5A] inhibitors) |
Screening for hepatitis C |
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Hepatitis D (delta) |
Endemic pockets in several countries Parenteral drug users at relatively high risk Can infect only in the presence of hepatitis B |
Interferon |
None |
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Outbreaks Genotypes 1 and 2: Developing countries Genotype 3: Europe; transmitted by eating undercooked pork products Severe during pregnancy |
None |
Vaccine (not available in US) |
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* Nonspecific precautions (eg, avoidance of body fluids of infected patients, aseptic precautions, routine hygiene measures) are also recommended. |
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At least 5 specific viruses (hepatitis A, B, C, D, and E viruses) can cause hepatitis; each causes a specific type of hepatitis. Hepatitis D virus can infect only when hepatitis B is present. Transmission is from person to person by contact with infected blood or body secretions or by the fecal-oral route for hepatitis A and E (genotypes 1 and 2).
Other viruses can affect the liver as part of their disease process. Common examples are cytomegalovirus, Epstein-Barr virus, and yellow fever virus. Less common examples are echovirus, coxsackievirus, and herpes simplex, rubeola, rubella, and varicella viruses.
Neurologic infections
Some Neurologic Viruses
Principal Syndromes |
Prevalence and Distribution |
Specific Therapy |
Specific Prevention* |
Polioviruses |
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Poliomyelitis (acute flaccid paralysis) Aseptic meningitis |
Global Incidence now low because of vaccine |
None |
Vaccines: Live (oral), killed (injected) |
Alphaviruses (some), mosquito-borne |
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Western equine encephalitis |
North and South America |
None |
None |
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Eastern equine encephalitis |
North America, South America (Madariaga) |
None |
Vaccine available to protect equines Investigational vaccine used in laboratory workers at risk |
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Venezuelan equine encephalitis |
Gulf states to South America |
None |
Vaccine available for equines Investigational vaccine used in laboratory workers at risk |
Flaviviruses (some), mosquito-borne |
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Japanese encephalitis |
Southeast Asia, Japan, Korea, China, India, Philippines, eastern former Soviet Union |
None |
Vaccine |
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Murray Valley encephalitis |
Australia, New Guinea |
None |
None |
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St. Louis encephalitis |
North and South America |
None |
None |
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Africa, Middle East, southern France, former Soviet Union, India, Indonesia, US, Canada, South America (Argentina, Brazil) |
None |
Screening blood and blood products for the virus Vaccine available for equines |
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Flaviviruses (some), tick-borne |
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Powassan encephalitis |
Canada, eastern and upper midwestern US |
None |
None |
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Tick-borne encephalitis |
Eastern and Central Europe, Balkans, former Soviet Union Outbreaks that coincide with periods of tick activity
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None |
Vaccine available in Europe and Russia |
Orthobunyaviruses (some), mosquito-borne |
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California encephalitis and related types (eg, La Crosse encephalitis) |
Probably worldwide Common in midwestern and eastern US Symptomatic infection primarily in children |
None |
None |
Mammarenaviruses (some) |
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Lymphocytic choriomeningitis |
US, Europe, possibly elsewhere Chief reservoir: House mouse Primarily in adults during autumn and winter |
None |
None |
Rabies virus |
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Worldwide |
None |
Vaccine Postexposure rabies immune globulin Vaccinate pets |
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* Nonspecific precautions (eg, avoidance of contaminated food and water and arthropod and animal vectors, routine hygiene measures) are also recommended. |
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Most cases of encephalitis are caused by viruses (see Table: Some Neurologic Viruses). Many of these viruses are transmitted to humans by blood-eating arthropods, mainly mosquitoes and ticks; these viruses are called arboviruses (arthropod-borne viruses). For such infections, prevention includes avoiding mosquito and tick bites.
Hemorrhagic fevers
Some Viruses That Cause Hemorrhagic Fever
Principal Syndromes |
Distribution |
Specific Therapy |
Specific Prevention* |
Flaviviruses (some) |
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Former Soviet Union (Siberia) |
None |
None |
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India, China (Nanjianyin virus) |
None |
None |
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Africa, Central and South America |
None |
Vaccine for travelers to endemic areas and for populations experiencing an outbreak |
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Tropics and subtropics, worldwide |
None |
Vaccine in phase 3 trials |
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Orthohantaviruses (some) |
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Hemorrhagic fever with renal syndrome due to Hantaan, Puumala, Dobrava (Belgrade), or Seoul virus |
Northern Asia, Europe Seoul virus: In pet rats and wild rat populations worldwide |
Ribavirin |
None |
Filoviruses |
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Lake Victoria Marburg virus disease |
Africa |
None |
None |
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Sudan Ebola virus disease |
Africa, Sumatra |
None |
None |
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Bundibugyo Ebola virus disease |
Uganda |
None |
None |
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Zaire Ebola virus disease |
Africa |
Monoclonal antibody cocktails (compassionate use/expanded access) |
rVSV-ZEBOV vaccine approved in US, used in current outbreak Ad26.ZEBOV/MVA-BN-Filo vaccine in use in the Democratic Republic of the Congo (DRC) |
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Reston ebolavirus disease |
Philippines |
None |
None |
Mammarenaviruses (some) |
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Bolivian hemorrhagic fever (due to Machupo virus) Argentinian hemorrhagic fever (due to Junin virus) Venezuelan hemorrhagic fever (due to Guanarito virus) Brazilian hemorrhagic fever (due to Sabia virus) |
South America, Africa (only Lassa fever) |
Ribavirin Convalescent plasma for all except Lassa fever |
Vaccine for Argentinian hemorrhagic fever |
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Lujo virus disease |
Zambia |
None |
None |
Orthonairovirus |
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Crimean-Congo hemorrhagic fever |
Tick-borne; former Soviet Union, western Pakistan, Africa, Asia, Middle East, Eastern Europe |
Ribavirin |
Vaccine (efficacy unknown) |
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* Nonspecific precautions (eg, avoidance of the means of transmission, routine hygiene measures) are also recommended. |
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Certain viruses cause fever and a bleeding tendency. (See also Arbovirus, Arenavirus, and Filovirus Infections.)
Transmission may involve mosquitoes, ticks, or contact with infected animals (eg, rodents, monkeys, bats) and people. Prevention involves avoiding the means of transmission.
Cutaneous or mucosal infections
Some Viruses That Cause Recurrent or Chronic Skin or Mucosal Lesions
Principal Syndromes |
Prevalence |
Specific Therapy |
Specific Prevention* |
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Herpes labialis Herpetic gingivostomatitis Dermatitis Keratoconjunctivitis Encephalitis Vulvovaginitis Neonatal disseminated disease |
Labial: Recurrent; HSV-1 infection in an estimated two thirds of the global population < 50 years Gingivostomatitis: Frequent in infants and children |
Acyclovir, famciclovir, valacyclovir, penciclovir |
Neonatal infection: Treatment of maternal infection; suppressive therapy beginning at 36 weeks of gestation if patients have a history of recurrent HSV; cesarean delivery if lesions or prodromal symptoms are present at time of delivery |
Human papillomavirus |
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Warts (verrucae) |
Universal Common, often recurrent |
Cryotherapy, interferon (possibly for genital), podophyllin (genital), imiquimod |
Vaccines for up to 9 subtypes of human papillomavirus (HPV) most commonly associated with cancers and genital warts Condoms |
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* Nonspecific precautions (eg, routine hygiene measures, safe-sex practices) are also recommended. |
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Some viruses cause skin or mucosal lesions that recur and may become chronic. Mucocutaneous infections are the most common type of herpes simplex virus infection. Human papillomavirus causes warts; some subtypes cause cervical cancer, other anogenital cancers, and oropharyngeal cancer.
Transmission is by person-to-person contact.
Multisystem diseases
Some Viruses That Cause Multisystem Disease
Principal Syndromes |
Distribution and Prevalence |
Specific Therapy |
Specific Prevention* |
Coxsackieviruses |
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Acute febrile respiratory disease (children) Paralysis Fever and exanthem |
Varies with types Most people infected Increased during warm months in temperate climates and year round in the tropics and in children Person-to-person spread usually via the fecal-oral route |
None |
None |
Echoviruses† and high-numbered enteroviruses |
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Fever and exanthem Paralysis |
As for coxsackieviruses |
None |
None |
Cytomegalovirus |
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Congenital defects (cytomegalic inclusion disease) Hepatitis (cytomegalovirus mononucleosis) In immunocompromised patients (including those with AIDS): Retinitis, gastrointestinal disorders, central nervous system disorders, pneumonia |
Widespread Congenital Common among immunocompromised patients |
Ganciclovir, foscarnet, cidofovir, sometimes immune globulin (eg, in organ transplant recipients with pneumonia) |
Ganciclovir, foscarnet |
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* Nonspecific precautions (eg, adequate sanitation, hand washing) are also recommended. |
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† Echovirus types 10, 21, 22, and 28 have been reclassified; these numbers are no longer used. More recently described enteroviruses have been designated as types 68 to 72. |
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Enteroviruses, which include coxsackieviruses and echoviruses, can cause various multisystem syndromes, as can cytomegaloviruses (see Table: Some Viruses That Cause Multisystem Disease).
Transmission is by the fecal-oral route.
Nonspecific febrile illness
Some Viruses That Cause Nonspecific Acute Febrile Illness
Some viruses cause nonspecific symptoms, including fever, malaise, headaches, and myalgia. Transmission is usually by an insect or arthropod vector. (See also Arbovirus, Arenavirus, and Filovirus Infections.)
Rift Valley fever rarely progresses to ocular disorders, meningoencephalitis, or a hemorrhagic form (which has a 50% mortality rate).
