Common Viral Respiratory Infections, OtherThan COVID-19¶
Part 5 | Infectious Diseases: Viral (incl. HIV) · Part 5 – Infectious Diseases: Viral (incl. HIV) · Chapter 204
Key Clinical Points¶
- Influenza A and B are the most common causes of severe lower respiratory tract disease in healthy subjects; Type A is more virulent.
- Human Respiratory Syncytial Virus (hRSV) is the most common viral cause of severe lower respiratory tract illness in infants and elderly.
- Rhinoviruses are the most common cause of the common cold and are associated with asthma exacerbations.
- Measles virus is the most contagious respiratory virus; vaccination rates must exceed 90-95% to prevent inevitable cases.
- Adenovirus types 4 and 7 cause Acute Respiratory Disease (ARD) in military recruits; live vaccine is available for military personnel.
- SARS-CoV-2, SARS-CoV, and MERS-CoV are coronaviruses with pandemic or zoonotic potential; MERS-CoV has ~35% mortality.
- Immunocompromised patients are susceptible to reactivation of latent viruses (HSV, CMV) and severe disease from common viruses (RSV, Adenovirus).
- Koplik's spots are pathognomonic for measles infection in the setting of rash and fever.
1. DEFINITION & OVERVIEW¶
• Classification Systems: Categorized by: ◦ Anatomic involvement (Upper vs. Lower respiratory tract) ◦ Disease syndrome (e.g., Common cold, Pneumonia, Croup) ◦ Etiologic agent (e.g., Orthomyxoviridae, Paramyxoviridae, Coronaviridae)
• Transmission Dynamics: ◦ Contact, droplets, fomites, and aerosols
• Pathogen Characteristics: ◦ Some viruses (e.g., rhinovirus) infect only the respiratory tract ◦ Others (e.g., measles) spread systemically ◦ Reinfection is common due to incomplete immunity ◦ Hundreds of viruses cause respiratory infections with significant antigenic diversity over time ◦ Specific antiviral treatments are limited
• Human Papillomavirus (HPV) Overview: Note: Included in source text regarding specific infections.
Definition (Harrison's 22e): Human Papillomavirus (HPV) infection is a sexually transmitted infection. ◦ Prevention: Only way to avoid is abstaining from sexual activity; safe sex may reduce transmission ◦ Clearance: Most infections cleared by immune system ◦ Management: Genital warts treated for cosmetic reasons and to prevent spread; precancerous cervical lesions must be treated to prevent cancer
• Table 203-1 Reference: Recommended Treatments for Genital Warts Caused by Human Papillomavirus Key Treatment Data: ◦ Imiquimod: Good effectiveness, frequent mild-to-moderate side effects, expensive ◦ Cryotherapy: Good effectiveness, good tolerability, inexpensive ◦ Interferon: Good effectiveness, frequently severe side effects, very expensive ◦ Surgical Removal: Excellent effectiveness, well tolerated, moderately expensive ◦ Laser: Excellent effectiveness, well tolerated, very expensive
2. EPIDEMIOLOGY¶
• Epidemic Patterns: ◦ Occur yearly in temperate regions (October–March)
• Demographics: ◦ Children have more frequent infections than adults
• Diagnostic Evolution: ◦ Early studies identified principal causes of acute viral respiratory infections ◦ RT-PCR improved understanding of viral etiologies ◦ Multiplex panels detect multiple viruses in clinical samples
• Impact of COVID-19 Measures (2020–2021): ◦ Public health measures reduced conventional virus incidence ◦ Altered seasonality observed ◦ Influenza B Yamagata lineage viruses disappeared post-pandemic
• Specific Seasonal Patterns: ◦ Influenza: October–March in temperate regions ◦ Rhinovirus: Year-round ◦ Enterovirus: Summer months in temperate areas ◦ Parechovirus: Unique seasonal patterns
• Transmission Dynamics: ◦ Contact, Droplets, Fomites ◦ Pre-symptomatic transmission ◦ Small-particle aerosols (e.g., measles virus)
3. ETIOLOGY & PATHOPHYSIOLOGY¶
• Anatomic Site Impact: Disease type depends on cell types and tissue organization ◦ Upper Respiratory Tract: Sinuses, Eustachian tubes, pharynx, larynx, and lymphoid tissue ◦ Lower Respiratory Tract: Trachea, bronchi, alveoli, and pneumocytes
• Viral Tropism & Clinical Syndromes: ◦ RSV → lower tract ◦ Rhinovirus → upper tract ◦ Smooth muscle contraction + mucus accumulation → wheezing in reactive airways
• Specific Viral Pathogens (Immunocompetent): ◦ Influenza Viruses: Single-stranded, segmented, negative-sense RNA ◦ Type A: Most virulent; potential for pandemics ◦ Type B: Two lineages (Victoria, Yamagata) ◦ Type C: Multi-species ◦ Type D: Cattle-specific
◦ RSV: Single-stranded, nonsegmented RNA ◦ Causes severe lower tract illness in children and elderly ◦ Associated with asthma exacerbations
◦ hMPV (Human Metapneumovirus): Discovered 2001 ◦ Less virulent than RSV ◦ Causes upper and lower respiratory disease
◦ Parainfluenza Viruses: Four serotypes (1–4) ◦ hPIV3: Causes severe disease in children ◦ Primary infection manifests as croup
• Specific Viral Pathogens (Immunocompromised): ◦ Reactivation of latent viruses (HSV, CMV) common in transplant recipients, chemotherapy patients, and HIV-AIDS ◦ CMV frequently isolated in immunosuppressed pneumonia cases ◦ Common viruses cause severe/fatal infections in these populations ◦ Nosocomial transmission common in transplant units
• Table 204-1 Reference: Family Pneumoviridae, Human Pathogens with Current Species Names ◦ Metapneumovirus → Metapneumovirus hominis (Human metapneumovirus [hMPV]) ◦ Orthopneumovirus → Human orthopneumovirus hominis (Human respiratory syncytial virus [hRSV])
• Table 204-2 Reference: Family Paramyxoviridae Human Pathogens with Current Species Names ◦ Respirovirus → Respirovirus laryngotracheitidis (Human parainfluenza virus type 1 [hPIV1]) ◦ Respirovirus → Respirovirus pneumoniae (Human parainfluenza virus type 3 [hPIV3] or Human respirovirus 3) ◦ Orthorubulavirus → includes parotitidis, laryngotracheitidis, hominis, mammalis
• Table 204-3 Reference: Enterovirus, Rhinovirus, and Parechovirus Species Names ◦ Enterovirus (15 species): - alphacoxsackie: consists of 25 serotypes, including coxsackieviruses and some nonpolio enteroviruses that cause respiratory disease (Human enterovirus A) - betacoxsackie: consists of 63 serotypes, including some coxsackieviruses, echoviruses, and nonpolio enteroviruses (Human enterovirus B) - coxsackiepol: consists of 23 serotypes, including the polioviruses (Human enterovirus C) - deconjuncti: consists of multiple serotypes and includes enterovirus D68 (Human enterovirus D) ◦ Rhinovirus: - alpharhino (Human rhinovirus A) - betarhino (Human rhinovirus B) - cerhino (Human rhinovirus C) ◦ Parechovirus ahumpari: consists of 19 types (1–19); human parechoviruses (HPeV-1 and HPeV-2) are common human pathogens
4. CLINICAL FEATURES¶
• Influenza: ◦ Symptoms: Fever, myalgias, fatigue, sore throat, headache, cough ◦ Complications: Severe pneumonia (10% bacterial superinfection) ◦ Risk groups: Elderly, immunocompromised, young children
• Measles: ◦ Symptoms: ≥3 days fever, cough, coryza, conjunctivitis ◦ Diagnostic clues: Koplik's spots, diffuse rash ◦ Systemic illness: Circulates in bloodstream; severe pneumonia possible ◦ Mortality: High in lower-resource countries and malnourished individuals
• Rhinovirus: ◦ Symptoms: Common cold, rhinosinusitis ◦ Complications: Otitis media (children), sinusitis (adults) ◦ Associations: Asthma exacerbations, COPD exacerbations (Rhinovirus C)
• Adenovirus: ◦ Symptoms: Common cold, croup, bronchiolitis, pneumonia, conjunctivitis ◦ Pharyngoconjunctival fever (types B/C) ◦ ARD in military recruits (types 4/7) ◦ Gastroenteritis (types 40/41)
• Enteroviruses: ◦ Enterovirus A: Oral lesions, hand-foot-and-mouth disease ◦ Enterovirus B: Pleurodynia, laryngotracheitis ◦ Enterovirus D68: Wheezing, acute flaccid myelitis
• Coronaviruses: ◦ SARS-CoV: Systemic illness (10% mortality), watery diarrhea ◦ MERS-CoV: Zoonotic origin (~35% mortality), dromedary camels as intermediate host
• Herpesviruses: ◦ HSV pharyngitis: Ulcerative stomatitis/pharyngitis ◦ EBV mononucleosis: Exudative pharyngitis, tonsillar swelling (airway occlusion risk)
• Human Bocavirus: ◦ Identified in 2005 in children with lower respiratory tract disease ◦ Sole agent in limited cases of hospitalized young children's respiratory illness
5. DIFFERENTIAL DIAGNOSIS¶
• Viral vs. Bacterial Pneumonia: ◦ Influenza pneumonia: 10% bacterial superinfection (staphylococcal/streptococcal) ◦ Immunocompromised patients: Higher susceptibility to severe viral disease
• Specific Virus Syndromes: ◦ Measles vs other exanthems: Koplik's spots are diagnostic ◦ Adenovirus vs other pharyngitis: Pharyngoconjunctival fever associated with adenovirus ◦ RSV vs other bronchiolitis causes: RSV more transmissible than hMPV
6. INVESTIGATIONS & DIAGNOSIS¶
- Rapid Antigen Tests:
- Used for RSV and influenza (available since 1980s)
- RT-PCR Panels:
- Detect multiple viruses in respiratory secretions3. Nested Multiplex PCR:
- Improves sensitivity for adult studies
• Clinical Correlation of Findings: ◦ Influenza, RSV, hMPV → common causes of lower tract disease ◦ Rhinovirus → increasingly linked to lower tract syndromes
Reference Tables¶
TABLE 203-1 Recommended Treatments for Genital Warts Caused by Human Papillomavirus a TREATMENT Effectiveness…¶
Harrison's 22e, p.1531
| TREATMENT | IMIQUIMOD | CRYOTHERAPY | INTERFERON | SURGICAL REMOVAL | LASER |
|---|---|---|---|---|---|
| Effectiveness | Good | Good | Good | Excellent | Excellent |
| Frequent | Frequent | Frequent | Frequent | ||
| Adverse effects | Frequent, mild to moderate | Mild, well tolerated | Frequent, moderately severe | Mild, well tolerated | Mild to moderate, well tolerated |
| Fair | Good | Fair | Good | ||
| Cost | Expensive | Inexpensive | Very expensive | Moderately expensive | Very expensive |
TABLE 204-1 Family Pneumoviridae, Human Pathogens with Current Species Names, the International Committee on Taxonomy…¶
Harrison's 22e, p.1533
| GENUS | CURRENT SPECIES NAME |
FORMER SPECIES NAME(S) |
|---|---|---|
| Metapneumovirus | Metapneumovirus hominis |
Human metapneumovirus (hMPV) |
| Human orthopneumovirus hominis |
TABLE 204-3 Enterovirus, Rhinovirus, and Parechovirus Species Names, the International Committee on Taxonomy of…¶
Harrison's 22e, p.1534
| GENUS | CURRENT SPECIES NAME | FORMER SPECIES NAME(S) |
|---|---|---|
| Enterovirus (15 species) |
Enterovirus alphacoxsackie: consists of 25 serotypes, including coxsackieviruses and some nonpolio enteroviruses that cause respiratory disease |
Human enterovirus A; Enterovirus A |
| Enterovirus betacoxsackie: consists of 63 serotypes, including some coxsackieviruses, echoviruses, and nonpolio enteroviruses |
Human enterovirus B; Enterovirus B |
|
| Enterovirus coxsackiepol: consists of 23 serotypes, including the polioviruses |
Human enterovirus C; Enterovirus C |
|
| Enterovirus deconjuncti: consists of multiple serotypes and includes enterovirus D68 |
Human enterovirus D; Enterovirus D |
|
| Enterovirus alpharhino | Human rhinovirus A; Rhinovirus A |
|
| Enterovirus betarhino | Human rhinovirus B; Rhinovirus B |
|
| Enterovirus cerhino | Human rhinovirus C; Rhinovirus C |
|
| Parechovirus ahumpari: consists of 19 types (1–19); human parechoviruses (HPeVs) 1 and 2 are common human pathogens |
TABLE 204-2 Family Paramyxoviridae Human Pathogens with Current Species Names, the International Committee on Taxonomy…¶
Harrison's 22e, p.1534
| GENUS | CURRENT SPECIES NAME |
FORMER SPECIES NAME(S) |
|---|---|---|
| Respirovirus | Respirovirus laryngotracheitidis |
Human respirovirus 1 or human parainfluenza virus type 1 (hPIV1) |
| Respirovirus pneumoniae | Human parainfluenza virus type 3 (hPIV3) or Human respirovirus 3 |
|
| Orthorubulavirus parotitidis Orthorubulavirus laryngotracheitidis Orthorubulavirus hominis Orthorubulavirus mammalis |