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 | |||
AFRD | Global A and B: Seasonal (winter) epidemics, occasionally pandemic C: Endemic | A and B: | A and B:Influenza vaccine |
Avian H5N1 and avian H7N9: Poultry-associated | 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: MERS: None COVID-19: | COVID-19:Vaccines MERS: Avoid contact with camels |
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 | Rodent control |
Respiratory syncytial virus and human metapneumovirus | |||
Lower respiratory illness (infants) Mild upper respiratory illness (adults) | Widespread in children | ||
Rhinoviruses | |||
Acute coryza with or without fever | Universal, especially during cold months | None | None |
* Nonspecific precautions (eg, avoidance of infected patients and insect and animal vectors, routine hygiene measures) are also recommended. | |||
Upper respiratory infections are likely the most common viral infections. Respiratory infections are more likely to cause severe symptoms in infants, the elderly, 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, and coronaviruses.
Several coronaviruses 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 often fatal (case fatality rate of 34%). In 2019, another coronavirus (SARS-CoV2) that can cause an acute, sometimes fatal respiratory illness (COVID-19) emerged in Wuhan, China and spread in a worldwide pandemic that has killed millions of people (1).
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:
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.
Centers for Disease Control and Prevention Child and Adolescent Immunization Schedule by Age. Hand washing and good sanitation measures can help prevent spread.
Exanthematous infections
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 | Vaccines |
Rubella virus | |||
Birth defects due to infection during pregnancy | Universal | 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) | Sporadic outbreaks | IV immune globulin (for severe anemia) | None |
Human herpesvirus type 6 | |||
Roseola infantum (exanthem subitum) | Widespread Affects young children | None | None |
Varicella-zoster virus | |||
Before vaccine, almost universal in children, occasionally in adults | Immune globulins, vaccine | ||
Common in adults, resulting from reactivation of latent virus | Vaccine | ||
Pox viruses | |||
Smallpox (variola virus) | Natural disease eradicated | Vaccine | |
Global outbreak in 2022 Person-to-person transmission occurs through prolonged close contact | Vaccines Avoiding direct physical contact with infected individuals | ||
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, Trinidad, Haiti | 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 (AIDS patients) | Cryotherapy, curettage | None |
* Nonspecific precautions (eg, avoidance of infected patients and insect and animal vectors, routine hygiene measures) 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.
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 | Screening for hepatitis B surface antigen | |
Hepatitis C (acute and chronic) | Widespread | Screening for hepatitis C | |
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 |
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 US) | |
* Nonspecific precautions (eg, avoidance of body fluids of infected patients, aseptic precautions, routine hygiene measures) 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.
Neurologic infections
Some Neurologic Viruses
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) | 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, US, 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 US | 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 and eastern US Symptomatic infection primarily in children | None | None |
Mammarenaviruses (some) | |||
Lymphocytic choriomeningitis | US, Europe, possibly elsewhere Chief reservoir: House mouse Primarily in adults during autumn and winter | None | None |
Rabies virus | |||
Worldwide | None | Vaccine Vaccinate pets | |
* Nonspecific precautions (eg, avoidance of contaminated food and water and arthropod and animal vectors, routine hygiene measures) 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 | for travelers to endemic areas and for populations experiencing an outbreak | |
Tropics and subtropics, worldwide | None | Dengue vaccine for certain people ages 9 to 45 with previous dengue infection | |
Orthohantaviruses (some) | |||
Hemorrhagic fever with renal syndrome due to Hantaan, Puumala, Dobrava (Belgrade), or Seoul virus | Global | 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 US, used in the DRC (Democratic Republic of Congo) outbreaks Ad26.ZEBOV/MVA-BN-Filo vaccine in use in the DRC |
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) | 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 | 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) 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 | 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 | Universal Common, often recurrent | 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, 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 AIDS): Retinitis, gastrointestinal disorders, central nervous system disorders, pneumonia | Widespread Congenital Common among immunocompromised patients | ||
* Nonspecific precautions (eg, adequate sanitation, hand washing) 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 US, 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 US | 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 US | None | None |
* Treatment is usually supportive. | |||
† Nonspecific precautions (eg, avoidance of the means of transmission, routine hygiene measures, 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 mosquitos (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).
Reference
1. Mahase E: Coronavirus covid-19 has killed more people than SARS and MERS combined, despite lower case fatality rate. BMJ 368:m641, 2020. doi: 10.1136/bmj.m641
