Merck Manual

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Types of Viral Disorders

By

Laura D Kramer

, PhD, Wadsworth Center, NYSDOH

Last full review/revision Mar 2020| Content last modified Mar 2020
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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

Table
icon

Some Respiratory Viruses

Principal Syndromes

Prevalence and Distribution

Specific Therapy

Specific Prevention*

Epidemic influenza viruses A, B, and C and avian influenza viruses

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

Avian H5N1 and avian H7N9: Poultry-associated

Oseltamivir, zanamivir, and possibly baloxavir

Avoiding contact with 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 pharyngoconjunctival fever

Acute follicular conjunctivitis

Diarrhea

Hemorrhagic cystitis

Global

Mostly children

None

Vaccine containing types 4 and 7 for epidemics in military populations

Coronaviruses

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

Orthohantaviruses

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

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

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.

† Unlike RSV-IVIG (respiratory syncytial virus-IV immune globulin), palivizumab does not interfere with immunizations (eg, measles, mumps, and rubella [MMR], chickenpox).

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.

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:

  • Rotavirus: Children

  • Norovirus: Children and adults

  • Astrovirus: Usually infants and young children

  • Adenovirus 40 and 41: Infants

  • Coronavirus-like agents: Infants

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

Table
icon

Some Exanthematous Viruses

Principal 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

Acyclovir, famciclovir, valacyclovir

Immune globulins, vaccine

Common in adults, resulting from reactivation of latent virus

Acyclovir, famciclovir, valacyclovir

Vaccine

Variola

Natural disease eradicated

Cidofovir

Smallpox vaccine up to 4 days after exposure

Vaccine

Cidofovir

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

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 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

Table
icon

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

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

Genotype 3: 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

Table
icon

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

None

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, eastern 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 available in Europe and Russia

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

Postexposure rabies immune globulin

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 (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

Table
icon

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

Vaccine for travelers to endemic areas and for populations experiencing an outbreak

Tropics and subtropics, worldwide

None

Vaccine in phase 3 trials

Orthohantaviruses (some)

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

Lake Victoria Marburg virus disease

Africa

None

None

Sudan Ebola virus disease

Africa, Sumatra

None

None

Bundibugyo Ebola virus disease

Uganda

None

None

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)

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)

* 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

Table
icon

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)

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

* Nonspecific precautions (eg, routine hygiene measures, safe-sex practices) are also recommended.

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

Table
icon

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

Ganciclovir, foscarnet, cidofovir, sometimes immune globulin (eg, in organ transplant recipients with pneumonia)

Ganciclovir, foscarnet

* 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 (see Table: Some Viruses That Cause Multisystem Disease).

Transmission is by the fecal-oral route.

Nonspecific febrile illness

Table
icon

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)

Congenital infection in babies infected in utero causing microcephaly; Guillain-Barré syndrome

Africa, Asia, Americas, the Pacific Islands

None

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

Severe fever with thrombocytopenia syndrome

Tick-borne; China, Korea, Japan

None

None

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 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).

Drugs Mentioned In This Article

Drug Name Select Trade
Gammagard S/D
VALTREX
FAMVIR
CYTOVENE
DENAVIR
TAMIFLU
SYNAGIS
VISTIDE
FOSCAVIR
VIREAD
VIRAZOLE
BARACLUDE
ZOVIRAX
RELENZA
ALDARA
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