Types of Viral Disorders: Viruses: Merck Manual Professional

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Infectious Diseases
	Viruses
		Types of Viral Disorders
			Respiratory infections
			GI infections
			Exanthematous infections
			Hepatic infections
			Neurologic infections
			Hemorrhagic fevers
			Cutaneous or mucosal infections
			Multisystem diseases
			Nonspecific febrile illness

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Types of Viral Disorders

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Categorizing viral infections by the organ system most commonly affected (eg, lungs, GI tract, skin, liver, CNS, 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.

Respiratory infections: The most common viral infections are probably URIs. Respiratory infections are more likely to cause severe symptoms in infants, the elderly, and patients with a lung or heart disorder.

Respiratory viruses include influenza viruses (A, B, C), parainfluenza viruses 1 through 4, adenoviruses, respiratory syncytial virus, and rhinoviruses (see Table 1: Viruses: Some Respiratory Viruses and see Respiratory Viruses). They are typically spread from person to person by contact with infected respiratory droplets.

Table 1

Some Respiratory Viruses
Principal Syndromes	Prevalence and Distribution	Specific Therapy	Specific Prevention*
Influenza viruses A, B, and C
Influenza AFRD Acute bronchitis and pneumonia Croup	A and B: Epidemic, occasionally pandemic C: Endemic	A: AmantadineSome Trade Names SYMMETREL Click for Drug Monograph or rimantadineSome Trade Names FLUMADINE Click for Drug Monograph A and B: OseltamivirSome Trade Names TAMIFLU Click for Drug Monograph or zanamivir	A and B: Vaccine, oseltamivirSome Trade Names TAMIFLU Click for Drug Monograph or zanamivir A: AmantadineSome Trade Names SYMMETREL Click for Drug Monograph and rimantadineSome Trade Names FLUMADINE Click for Drug Monograph
Parainfluenza viruses 1–4
AFRD (children) Acute bronchitis and pneumonia Croup	1: Local epidemics 1, 2, and 3: Widespread in children	None	Vaccines under investigation
Adenoviruses
AFRD (children) Acute respiratory disease (adults) Acute pharyngoconjunctival fever Epidemic keratoconjunctivitis Viral pneumonia Acute follicular conjunctivitis Diarrhea Hemorrhagic cystitis	Global Mostly children	None	Vaccine containing types 4 and 7 for epidemics in military populations
Respiratory syncytial virus
Lower respiratory illness (infants) Mild upper respiratory illness (adults)	Widespread in children	RibavirinSome Trade Names VIRAZOLE Click for Drug Monograph sometimes used in immunocompromised patients	PalivizumabSome Trade Names SYNAGIS Click for Drug Monograph IM^† monthly
Rhinoviruses
Common cold 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, palivizumabSome Trade Names SYNAGIS Click for Drug Monograph does not interfere with immunizations (eg, MMR, chickenpox).
AFRD = acute febrile respiratory disease; MMR = measles, mumps, and rubella; RSV = respiratory syncytial virus; IVIG = IV immune globulin.

GI infections: Gastroenteritis is usually caused by viruses (see Gastroenteritis) and transmitted from person-to person by the oral-fecal route. Age group primarily affected depends on the virus:

Rotavirus: Children
Norovirus: Older 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 (see Table 12: Approach to the Care of Normal Infants and Children: Recommended Immunization Schedule for Ages 0–6 yr). Hand washing and good sanitation measures can help prevent spread.

Exanthematous infections: Some viruses cause only skin lesions (as in molluscum contagiosum and warts—See Viral Skin Diseases); others also cause systemic manifestations or lesions elsewhere in the body (see Table 2: Viruses: Some Exanthematous Viruses). Transmission is typically from person to person; alphaviruses have a mosquito vector.

Table 2

Some Exanthematous Viruses
Principal Syndromes	Prevalence and Distribution	Specific Therapy	Specific Prevention*
Rubeola virus
Measles Encephalomyelitis CNS involvement (rare)	Global Incidence decreasing because of vaccine	None	Vaccines
Rubella virus
German measles Birth defects due to infection during pregnancy	Universal	None	Vaccines
Human parvovirus B19
Erythema infectiosum (fifth disease) Rash, malaise, arthritis Hydrops fetalis (infection during pregnancy) Anemia (in immunocompromised hosts or patients with hemoglobinopathies)	Sporadic outbreaks	IVIG (for severe anemia)	None
Human herpesvirus type 6
Roseola infantum (exanthem subitum)	Widespread Affects young children	None	None
Varicella-zoster virus
Chickenpox	Before vaccine, almost universal in children, occasionally in adults	AcyclovirSome Trade Names ZOVIRAX Click for Drug Monograph , famciclovirSome Trade Names FAMVIR Click for Drug Monograph , valacyclovirSome Trade Names VALTREX Click for Drug Monograph	Immune globulins, vaccine
Zoster	Common in adults, resulting from reactivation of latent virus	AcyclovirSome Trade Names ZOVIRAX Click for Drug Monograph , famciclovirSome Trade Names FAMVIR Click for Drug Monograph , valacyclovirSome Trade Names VALTREX Click for Drug Monograph	Vaccine
Variola
Smallpox	Natural disease eradicated	CidofovirSome Trade Names VISTIDE Click for Drug Monograph ^† Smallpox vaccine up to 4 days after exposure	Vaccine CidofovirSome Trade Names VISTIDE Click for Drug Monograph ^†
Alphaviruses (some)
Chikungunya disease (acute febrile illness followed by more chronic polyarthritis)	Transmitted by Aedes mosquitoes Africa, Southeast Asia, India, Europe	None	None
Mayaro disease (a dengue-like disease)	Mosquito-borne South America, Trinidad	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.

Hepatic infections: At least 5 specific viruses (hepatitis A, B, C, D, and E viruses) can cause hepatitis; each causes a specific type of hepatitis (see Table 3: Viruses: Viral Hepatitis and see 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.

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.

Table 3

Viral Hepatitis
Principal Syndromes	Prevalence and Distribution	Specific Therapy	Specific Prevention*
Hepatitis A (acute)	Widespread, often epidemic	None	γ-Globulin, vaccine
Hepatitis B (acute and chronic)	Widespread	Interferon, other antivirals	Screening for hepatitis B surface antigen Vaccine, γ- or hyperimmune globulin
Hepatitis C (acute and chronic)	Widespread	Interferon, ribavirinSome Trade Names VIRAZOLE Click for Drug Monograph	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 infection	Interferon	None
Hepatitis E	Outbreaks Developing world Severe during pregnancy	None	Vaccine in development
*Nonspecific precautions (eg, avoidance of body fluids of infected patients, aseptic precautions, routine hygiene measures) are also recommended.

Neurologic infections: Most cases of encephalitis are caused by viruses (see Table 4: Viruses: Some Neurologic Viruses and Brain Infections). Many of these viruses are transmitted to humans by blood-eating arthropods, mainly mosquitoes and ticks (see Arboviridae, Arenaviridae, and Filoviridae); these viruses are called arboviruses (arthropod-borne viruses). For such infections, prevention includes avoiding mosquito and tick bites.

Table 4

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 and South America	None	Vaccine available to protect equines only
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
West Nile virus encephalitis	Africa, Middle East, southern France, former Soviet Union, India, Indonesia, US	None	Screening blood and blood products for the virus
Flaviviruses (some), tick-borne
Powassan encephalitis	Canada, northeastern 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
Bunyaviruses (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
Arenaviruses (some)
Lymphocytic choriomeningitis	US, Europe, possibly elsewhere Chief reservoir: House mouse Primarily in adults during autumn and winter	None	None
Rabies virus
Rabies	Worldwide	None	Vaccine Postexposure rabies immune globulin
*Nonspecific precautions (eg, avoidance of contaminated food and water and insect and animal vectors, routine hygiene measures) are also recommended.

Hemorrhagic fevers: Certain viruses cause fever and a bleeding tendency (see Table 5: Viruses: Some Viruses That Cause Hemorrhagic Fever and Arboviridae, Arenaviridae, and Filoviridae). Transmission may involve mosquitoes, ticks, or contact with infected animals (eg, rodents, monkeys, bats) and people. Prevention involves avoiding the means of transmission.

Table 5

Some Viruses That Cause Hemorrhagic Fever
Principal Syndromes	Distribution	Specific Therapy	Specific Prevention*
Flaviviruses (some)
Omsk hemorrhagic fever	Former Soviet Union (Siberia)	None	None
Kyasanur Forest disease	India	None	None
Yellow fever	Africa, Central and South America	None	Vaccine for travelers to endemic areas
Dengue fever	Tropics and subtropics, worldwide	None	None
Bunyaviruses (some)
Hemorrhagic fever with renal syndrome due to Hantaan, Puumala, Dobrava (Belgrade), or Seoul virus	Northern Asia, Europe, southwestern US	RibavirinSome Trade Names VIRAZOLE Click for Drug Monograph	None
Filoviruses (some)
Marburg virus infection	Africa	None	None
Ebola virus infection	Africa, Philippines	None	None
Arenaviruses (some)
Lassa fever 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)	RibavirinSome Trade Names VIRAZOLE Click for Drug Monograph Convalescent plasma for all except Lassa fever	Vaccine for Argentinian hemorrhagic fever under investigation
Nairovirus
Crimean-Congo hemorrhagic fever	Former Soviet Union, western Pakistan, Africa, Asia, Middle East, Eastern Europe	RibavirinSome Trade Names VIRAZOLE Click for Drug Monograph Possibly convalescent plasma	Vaccine available in Eastern Europe
*Nonspecific precautions (eg, avoidance of the means of transmission, routine hygiene measures) are also recommended.

Cutaneous or mucosal infections: Some viruses cause skin or mucosal lesions that recur and may become chronic (see Table 6: Viruses: Some Viruses That Cause Recurrent or Chronic Skin or Mucosal Lesions). Mucocutaneous infections are the most common type of herpes simplex virus infection (see Herpesviruses: Herpes Simplex Virus (HSV) Infections). Human papillomavirus causes warts (see Viral Skin Diseases: Warts and see Sexually Transmitted Diseases (STD): Genital Warts); some subtypes cause cervical cancer (see Gynecologic Tumors: Cervical Cancer). Transmission is by person-to-person contact.

Table 6

Some Viruses That Cause Recurrent or Chronic Skin or Mucosal Lesions
Principal Syndromes	Prevalence	Specific Therapy	Specific Prevention*
Herpes simplex virus
Herpes labialis Herpetic gingivostomatitis Dermatitis Keratoconjunctivitis Encephalitis Vulvovaginitis Neonatal disseminated disease	Labial: Recurrent, almost universal Gingivostomatitis: Frequent in infants and children	AcyclovirSome Trade Names ZOVIRAX Click for Drug Monograph , famciclovirSome Trade Names FAMVIR Click for Drug Monograph , valacyclovirSome Trade Names VALTREX Click for Drug Monograph , penciclovirSome Trade Names DENAVIR Click for Drug Monograph	Neonatal infection: Treatment of maternal infection; suppressive therapy beginning at 36 wk 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) Genital warts Cervical cancer	Universal Common, often recurrent	Cryotherapy, interferon (possibly for genital), podophyllin (genital), imiquimodSome Trade Names ALDARA Click for Drug Monograph	Vaccine for the 4 subtypes of HPV most commonly associated with cervical cancers and genital warts Condoms
*Nonspecific precautions (eg, routine hygiene measures, safe-sex practices) are also recommended.

Multisystem diseases: Enteroviruses, which include coxsackieviruses and echoviruses (see Enteroviruses), can cause various multisystem syndromes, as can cytomegaloviruses (see Table 7: Viruses: Some Viruses That Cause Multisystem Disease and Herpesviruses: Cytomegalovirus (CMV) Infection). Transmission is by the fecal-oral route.

Table 7

Some Viruses That Cause Multisystem Disease
Principal Syndromes	Distribution and Prevalence	Specific Therapy	Specific Prevention*
Coxsackieviruses
Herpangina Epidemic pleurodynia Aseptic meningitis Meningoencephalitis Neonatal sepsis Myocarditis Pericarditis AFRD (children) Paralysis Fever and exanthem	Varies with types Most people infected Increased during warm months in temperate climates and year round in tropics and in children Person-to-person spread usually via the fecal-oral route	None	None
Echoviruses^† and high-numbered enteroviruses
Aseptic meningitis Fever and exanthem Meningoencephalitis Neonatal sepsis Paralysis Myocarditis Pericarditis	As for coxsackieviruses	None	None
Cytomegalovirus
Congenital defects (cytomegalic inclusion disease) Hepatitis (cytomegalovirus mononucleosis) In immunocompromised patients (including those with AIDS): Retinitis, GI disorders, CNS disorders, pneumonia	Widespread Congenital Common among immunocompromised patients	GanciclovirSome Trade Names CYTOVENE Click for Drug Monograph , foscarnetSome Trade Names FOSCAVIR Click for Drug Monograph , cidofovirSome Trade Names VISTIDE Click for Drug Monograph , sometimes immune globulin (eg, in organ transplant recipients with pneumonia)	GanciclovirSome Trade Names CYTOVENE Click for Drug Monograph , foscarnetSome Trade Names FOSCAVIR Click for Drug Monograph
*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.
AFRD = acute febrile respiratory disease.

Nonspecific febrile illness: Some viruses cause nonspecific symptoms, including fever, malaise, headaches, and myalgia (see Table 8: Viruses: Some Viruses That Cause Nonspecific Acute Febrile Illness and Table 1: Arboviridae, Arenaviridae, and Filoviridae: Arbovirus, Arenavirus, and Filovirus Diseases). Transmission is usually by an insect or arthropod vector.

Rift Valley fever rarely progresses to ocular disorders, meningoencephalitis, or a hemorrhagic form (which has a 50% mortality rate).

Table 8

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
Phleboviruses (some)
Phlebotomus (sandfly) fever	Mediterranean basin, Balkans, Middle East, Pakistan, India, China, eastern Africa, Panama, Brazil	None	None
Rift Valley fever	Eastern Africa, Egypt	None	Vaccine for livestock Human vaccine under investigation
*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.

Last full review/revision December 2009 by Kenneth M. Kaye, MD

Content last modified December 2009

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