The capability of a virus to infect particular tissues is called tissue tropism and to infect particular cell types is called cellular tropism; the capability to infect a particular host species is called host tropism. Categorizing viral infections by the organ system or type of tissue or cell most commonly affected (eg, upper or lower respiratory tract, gastrointestinal tract, skin, liver, central nervous system, mucous membranes) can be clinically useful, although certain viral infections (eg, mumps) are usually disseminated to more than one organ system and are hard to categorize.
(See also Overview of Viruses.)
Viral respiratory infections
Some Respiratory Viruses
Principal Clinical Syndromes | Distribution | Specific Therapy | Specific Prevention* |
|---|---|---|---|
Epidemic influenza viruses A, B, and C and avian influenza viruses | |||
Acute febrile respiratory disease | Global A and B: Seasonal (winter) epidemics, occasionally pandemic C: Endemic | A and B:Baloxavir, oseltamivir, or zanamivir | A and B:Influenza vaccine, baloxavir, oseltamivir, or zanamivir |
Avian H5N1 and avian H7N9: Poultry-associated | Oseltamivir, zanamivir, and possibly baloxavir | Avoiding contact with saliva, mucous, or feces of infected birds | |
Parainfluenza viruses 1–4 | |||
Acute febrile respiratory disease (children) | 1: Local epidemics 1, 2, and 3: Widespread in children | None | Vaccines under investigation |
Adenoviruses | |||
Acute febrile respiratory disease (children) Acute respiratory disease (adults and 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 | |||
Severe acute respiratory syndrome (SARS) | Local origin becomes widespread SARS: China; no cases after 2004 MERS: Arabian Peninsula COVID-19: Global pandemic 2020 | SARS: Remdesivir, corticosteroids, anticoagulants MERS: None COVID-19: Nirmatrelvir/ritonavir, remdesivir, molnupiravir, monoclonal antibodies | MERS: Avoid contact with camels COVID-19:Vaccines |
Orthohantaviruses | |||
Hantavirus pulmonary syndrome (HPS) (eg, due to Sin Nombre hantavirus, Black Creek Canal virus, Bayou virus, or New York virus) Hemorrhagic fever with renal syndrome (HFRS) (eg, Hantaan, Seoul, and Dobrava viruses) | HPS: North, Central, and South America HFRS: Global | None for hantavirus pulmonary syndrome IV ribavirin for hemorrhagic fever with renal syndrome | Rodent control |
Respiratory syncytial virus and human metapneumovirus | |||
Lower respiratory illness (infants and some adults) Mild upper respiratory illness (most adults) | Widespread in children | Ribavirin sometimes used in immunocompromised patients | Vaccines (for older adults, pregnant persons), nirsevimab (all infants in first RSV season [if mother not given vaccine during pregnancy]) Palivizumab IM monthly (only for certain infants at high risk of severe disease when nirsevimab is not available) |
Rhinoviruses | |||
Acute coryza with or without fever | Global, especially during cold months | None | None |
* Nonspecific precautions (eg, avoidance of infected patients and insect and animal vectors, routine hygiene measures, and use of appropriate personal protective equipment) are also recommended. † Common cold can also be caused by other types of viruses, including coronaviruses, adenoviruses, parainfluenza viruses, enteroviruses (including EV-D68), and human metapneumovirus. | |||
Upper respiratory infections are likely the most common viral infections. Respiratory infections are more likely to cause severe symptoms in infants, older adults, and patients with a lung or heart disorder. Respiratory viruses are typically spread from person to person by contact with infected respiratory droplets.
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, rhinoviruses, hantaviruses, and coronaviruses.
Several coronaviruses cause a respiratory infection that can cause severe morbidity and mortality. In 2002 and 2003, an outbreak of severe acute respiratory syndrome (SARS caused by infection with the virus SARS-CoV) resulted in approximately 770 deaths (case fatality rate is approximately 3%) (1), mostly in China and Hong Kong (1, 2). There have been no cases of SARS reported since 2004. In 2012, a novel coronavirus Middle East respiratory syndrome coronavirus (MERS caused by the virus MERS-CoV) appeared in Saudi Arabia; it can cause severe acute respiratory illness and is often fatal (case fatality rate of 35%) (3). In 2019, another coronavirus (SARS-CoV2) that can cause a severe, sometimes fatal respiratory illness (COVID-19) emerged in Wuhan, China and spread in a global pandemic that has killed millions of people (4).
Viral gastroenteritis
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:
Rotavirus: Children
Norovirus: Children and adults
Astrovirus: Usually infants and young children
Adenovirus 40 and 41: Infants
COVID-19: All ages
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 theCenters for Disease Control and Prevention Child and Adolescent Immunization Schedule by Age. Hand washing and good sanitation measures can help prevent spread.
Viral exanthems
Some Exanthematous Viruses
Major Clinical Syndromes | Prevalence and Distribution | Specific Therapy | Specific Prevention* |
|---|---|---|---|
Rubeola virus | |||
Encephalomyelitis Central nervous system involvement (rare) | Global Prevalence increasing due to decrease in vaccination | None; if < 72 hrs post-exposure, vaccine; if < 6 days, immune globulins | Vaccines |
Rubella virus | |||
Birth defects due to infection during pregnancy | Global prior to vaccine | None | Vaccines |
Human parvovirus B19 | |||
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) | Global; sporadic outbreaks | IV immune globulin (for severe anemia) | None |
Human herpesvirus type 6 | |||
Roseola infantum (exanthem subitum) | Global Affects young children | None | None |
Varicella-zoster virus | |||
Before vaccine, almost global in children, occasionally in adults | Acyclovir, famciclovir, valacyclovir; varicella vaccine within 3 days post-exposure; or varicella-zoster immunoglobulin | Immune globulins, vaccine | |
Common in adults, resulting from reactivation of latent virus | Acyclovir, famciclovir, valacyclovir; see chickenpox for post-exposure treatment | Vaccine | |
Pox viruses | |||
Smallpox (variola virus) | Natural disease eradicated | Cidofovir† Smallpox vaccine up to 4 days after exposure | Vaccine Cidofovir† |
Global outbreak in 2022 | Cidofovir, tecovirimat, vaccinia immune globulin | Vaccines | |
Alphaviruses (some) | |||
Chikungunya disease (acute febrile illness followed by more chronic polyarthritis) | Transmitted by Aedes mosquitoes Africa, Southeast Asia, India, Europe, the Americas | None | None |
Mayaro disease (a dengue-like disease) | Mosquito-borne South America, Central America, Caribbean | None | None |
Ross River virus disease (epidemic polyarthritis) | Aedes mosquitoes Australia, Papua New Guinea, South Pacific | None | None |
Molluscum contagiosum virus | |||
Molluscum contagiosum papules | Genital (adults) Exposed skin (children) More severe (patients with late-stage HIV) | Cryotherapy, curettage | None |
* Nonspecific precautions (eg, avoidance of infected patients and insect and animal vectors, routine hygiene measures, and use of appropriate personal protective equipment) are also recommended. | |||
† Based on animal studies. | |||
Some viruses cause only skin lesions (as in molluscum contagiosum); others also cause systemic manifestations or lesions elsewhere in the body.
Transmission is typically from person to person; alphaviruses have a mosquito vector.
Viral hepatitis
Viral Hepatitis
Principal Syndromes | Prevalence and Distribution | Specific Therapy | Specific Prevention* |
|---|---|---|---|
Hepatitis A (acute) | Global, often epidemic | None | Immune globulin, vaccine |
Hepatitis B (acute and chronic) | Global | 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) | Global | Interferon, ribavirin, direct-acting antivirals (eg, protease inhibitors, nucleotide analog inhibitors, nonstructural protein 5A [NS5A] inhibitors) | Screening for hepatitis C |
Hepatitis D (delta) | Endemic pockets in several countries People who inject illicit drugs at relatively high risk Can infect only in the presence of hepatitis B | Interferon | None |
Outbreaks Genotypes 1 and 2: Developing countries Genotypes 3 and 4: Europe; transmitted by eating undercooked pork products Severe during pregnancy | None | Vaccine (not available in United States) | |
* Nonspecific precautions (eg, avoidance of body fluids of infected patients, aseptic precautions, routine hygiene measures, and use of appropriate personal protective equipment) are also recommended. | |||
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.
Viral neurologic infections
Some Viruses That Cause Neurologic Disease
Principal Syndromes | Prevalence and Distribution | Specific Therapy | Specific Prevention* |
|---|---|---|---|
Polioviruses | |||
Poliomyelitis (acute flaccid paralysis) Aseptic meningitis | Global Incidence now low because of vaccine | None | Vaccines: Live (oral), killed (injected) |
Alphaviruses (some), mosquito-borne | |||
Western equine encephalitis | North and South America | None | Vaccine available to protect equines Investigational vaccine used in at-risk laboratory workers |
Eastern equine encephalitis | North America, South America (Madariaga virus) | None | Vaccine available to protect equines Investigational vaccine used in laboratory workers at risk |
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 | |||
Japanese encephalitis | Southeast Asia, Japan, Korea, China, India, Philippines, eastern former Soviet Union | None | Vaccine |
Murray Valley encephalitis | Australia, New Guinea | None | None |
St. Louis encephalitis | North and South America | None | None |
Africa, Middle East, southern France, former Soviet Union, India, Indonesia, United States, Mexico, Canada, South America (Argentina, Brazil) | None | Screening blood and blood products for the virus Vaccine available for equines | |
Flaviviruses (some), tick-borne | |||
Powassan encephalitis | Canada, northeastern and upper midwestern United States | None | None |
Tick-borne encephalitis | Eastern and Central Europe, Balkans, former Soviet Union Outbreaks that coincide with periods of tick activity | None | Vaccine |
Orthobunyaviruses (some), mosquito-borne | |||
California encephalitis and related types (eg, La Crosse encephalitis) | Probably worldwide Common in midwestern, western and eastern United States Symptomatic infection primarily in children | None | None |
Mammarenaviruses (some) | |||
Lymphocytic choriomeningitis | United States, Europe, possibly elsewhere Chief reservoir: House mouse Primarily in adults during autumn and winter | None | None |
Rabies virus | |||
Global | None | Vaccine Postexposure rabies immune globulin Vaccinate pets | |
* Nonspecific precautions (eg, avoidance of contaminated food and water and arthropod and animal vectors, routine hygiene measures, and use of appropriate personal protective equipment) are also recommended. | |||
Most cases of encephalitis are caused by viruses. Many of these viruses are transmitted to humans by blood-sucking 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) | |||
Former Soviet Union (Siberia) | None | None | |
India, China (Nanjianyin virus) | None | None | |
Africa, Central and South America | None | Yellow fever vaccine for travelers to endemic areas and for populations experiencing an outbreak | |
Tropics and subtropics, global | None | Dengue vaccine for certain people with previous dengue infection | |
Orthohantaviruses (some) | |||
Hemorrhagic fever with renal syndrome due to Hantaan, Puumala, Dobrava (Belgrade), or Seoul virus | Global | Ribavirin | None |
Filoviruses | |||
Lake Victoria Marburg virus disease | Africa | None | None |
Sudan Ebola virus disease | Africa, Sumatra | None | No vaccines approved to date; existing Zaire Ebola vaccines are not effective against the Sudan strain |
Bundibugyo Ebola virus disease | Uganda | None | None |
Zaire Ebola virus disease | Africa | Monoclonal antibody cocktails (FDA approved; compassionate use/expanded access) | rVSV-ZEBOV vaccine approved in United States, used in the Democratic Republic of Congo outbreaks Ad26.ZEBOV/MVA-BN-Filo vaccine in use in the Democratic Republic of Congo |
Reston ebolavirus disease | Philippines | None | None |
Mammarenaviruses (some) | |||
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 |
Lujo virus disease | Zambia | None | None |
Orthonairovirus | |||
Crimean-Congo hemorrhagic fever | Tick-borne; former Soviet Union, western Pakistan, Africa, Asia, Middle East, Eastern Europe | Ribavirin | Vaccine (efficacy unknown) |
Phleboviruses (some) | |||
Severe fever with thrombocytopenia syndrome | Tick-borne; China, Korea, Japan | None | None |
* Nonspecific precautions (eg, avoidance of the means of transmission, routine hygiene measures and use of appropriate personal protective equipment) are also recommended. | |||
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* |
|---|---|---|---|
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 | |||
Warts (verrucae) Cervical cancer, vulvar cancer, vaginal cancer, anal cancer, and oropharyngeal cancer | Global Common, often recurrent | Cryotherapy, laser, surgical excision, interferon (possibly for genital), podophyllin (genital), imiquimod | HPV vaccines for up to 9 subtypes of human papillomavirus (HPV) most commonly associated with cancers and genital warts Condoms provide partial protection |
* Nonspecific precautions (eg, routine hygiene measures, use of appropriate personal protective equipment, and safe-sex practices) are also recommended. | |||
Transmission of herpes simplex virus infection and human papillomavirus is by person-to-person contact.
Some viruses cause skin or mucosal lesions that recur and may become chronic.
Multisystem diseases
Some Viruses That Cause Multisystem Disease
Principal Syndromes | Distribution and Prevalence | Specific Therapy | Specific Prevention* |
|---|---|---|---|
Coxsackieviruses | |||
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 | |||
Fever and exanthem Paralysis | As for coxsackieviruses | None | None |
Cytomegalovirus | |||
Congenital defects (cytomegalic inclusion disease) Hepatitis (cytomegalovirus mononucleosis) In immunocompromised patients (including those with late-stage HIV): Retinitis, gastrointestinal disorders, central nervous system disorders, pneumonia | Global Congenital Common among immunocompromised patients | Ganciclovir, valganciclovir, foscarnet, cidofovir, sometimes immune globulin (eg, in organ transplant recipients with pneumonia) | Ganciclovir, valganciclovir, foscarnet, letermovir |
* Nonspecific precautions (eg, adequate sanitation, hand washing, and use of appropriate personal protective equipment) are also recommended. | |||
† 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. | |||
Enteroviruses, which include coxsackieviruses and echoviruses, can cause various multisystem syndromes, as can cytomegaloviruses.
Transmission of enteroviruses is usually by direct contact with respiratory secretions or stool.
Nonspecific febrile illness
Some Viruses That Cause Nonspecific Acute Febrile Illness
Principal Syndromes | Distribution | Specific Therapy* | Specific Prevention† |
|---|---|---|---|
Colorado tick fever virus (coltivirus) | |||
Colorado tick fever, with leukopenia and thrombocytopenia | Western United States, Canada | None | None |
Flaviviruses (some) | |||
Mosquito-borne; congenital infection in babies infected in utero causing microcephaly; Guillain-Barré syndrome Africa, Asia, Americas, the Pacific Islands | None | Precautions to prevent mosquito bites Precautions to reduce sexual transmission: abstain from sex or use of condoms during times of risk and for duration of pregnancies Screening blood and blood products for the virus | |
Phleboviruses (some) | |||
Heartland virus (HRTV) | Tick-borne; midwestern and eastern Unites States | None | None |
Phlebotomus (sandfly) fever | Mediterranean basin, Balkans, Middle East, Pakistan, India, China, eastern Africa, Panama, Brazil | None | None |
Africa, Egypt, Saudi Arabia, Yemen | None | Vaccine for livestock Human vaccine under investigation | |
Orthomyxoviruses | |||
Bourbon virus | Tick-borne; midwestern and southern United States | None | None |
Orthobunyaviruses | |||
Oropouche | Mosquito and midge-borne; South America; Central America, The Caribbean | None | Precautions to prevent mosquito and midge bites |
* Treatment is usually supportive. | |||
† Nonspecific precautions (eg, avoidance of the means of transmission, routine hygiene measures, use of appropriate personal protective equipment, screening of bone marrow used for transplantation) are also recommended. | |||
Some viruses cause nonspecific symptoms, including fever, malaise, headaches, and myalgia. Transmission is usually by an arthropod vector. (See also Arbovirus, Arenavirus, and Filovirus Infections.)
Rift Valley fever is usually transmitted through contact with blood, body fluids, or tissues of infected animals, mainly livestock such as cattle, sheep, goats, buffalo, and camels. Transmission can also be through bites from infected mosquitoes (see Centers for Disease Control and Prevention: Rift Valley Fever Transmission). Rift Valley fever rarely progresses to ocular disorders, meningoencephalitis, or a hemorrhagic form (which has a 50% mortality rate).
References
1. World Health Organization (WHO). Severe Acute Respiratory Syndrome (SARS). Accessed December 11, 2024.
2. U.S. Centers for Disease Control and Prevention (CDC). SARS Basics Fact Sheet. Accessed December 11, 2024.
3. World Health Organization (WHO). Middle East respiratory syndrome coronavirus (MERS-CoV). Accessed December 11, 2024.
4. World Health Organization (WHO). Coronavirus disease (COVID-19). Accessed December 11, 2024.
