Clin Med: Viral disease

Rhinovirus

Non-enveloped viral pathogen with over 100 subtypes that spreads primarily via respiratory droplets or direct contact to infect upper respiratory tract mucosa and can trigger asthma exacerbations. Following an incubation period of 1 to 3 days, it presents clinically with nasal congestion, sneezing, rhinorrhea, sore throat, cough, and progressive purulent nasal drainage.

Adenovirus

Viral pathogen spread via respiratory droplets or direct contact with an incubation period of 2 to 14 days, capable of causing severe or disseminated infection in immunocompromised hosts. Characteristically presents clinically with pharyngoconjunctival fever (the classic triad of fever, pharyngitis, and conjunctivitis), upper respiratory tract symptoms, bronchitis, pneumonia, gastroenteritis, or less commonly keratoconjunctivitis and hemorrhagic cystitis.

Respiratory Syncytial Virus (RSV)

Highly contagious respiratory virus spread through respiratory droplets or direct contact that infects mucosal epithelial cells, serving as the most common viral cause of bronchiolitis and lower respiratory tract disease in infants, young children, and high-risk adults. Initial upper respiratory tract symptoms (rhinorrhea, congestion, fever) progress in infants to bronchiolitis or pneumonia marked by cough, wheezing, crackles, tachypnea, increased work of breathing, hypoxemia, respiratory distress, and apnea.

Human Papillomavirus (HPV)

Epitheliotropic virus with over 200 types transmitted via direct skin-to-skin or sexual contact that establishes persistent or latent infection in cutaneous and mucosal epithelium; low-risk types 6 and 11 drive benign epithelial proliferation, whereas high-risk oncogenic types 16 and 18 cause malignant cellular transformation leading to cervical, anal, penile, vulvar, vaginal, and oropharyngeal cancers. Low-risk genotypes present clinically with cutaneous warts (verruca vulgaris, flat warts, plantar warts with thrombosed capillaries, periungual warts) or verrucous, cauliflower-like anogenital warts (condyloma acuminata).

Herpes Simplex Type 1 (HSV-1)

Neurotropic double-stranded DNA herpesvirus that establishes lifelong latent infection within sensory nerve ganglia (such as trigeminal ganglia) following direct contact and reactivates during periods of stress, illness, UV exposure, or trauma. Primary infection manifests clinically as severe gingivostomatitis with painful oral vesicles, shallow ulcers, fever, and cervical lymphadenopathy, while reactivation causes recurrent herpes labialis ("cold sores") preceded by prodromal tingling or burning; serious complications include herpes keratitis featuring classic dendritic corneal ulcers on fluorescein stain, temporal lobe encephalitis (fever, altered mental status, seizures), herpetic whitlow, and esophagitis.

Herpes Simplex Type 2 (HSV-2)

Sexually transmitted double-stranded DNA herpesvirus that establishes lifelong latency in sacral sensory ganglia with periodic reactivation and asymptomatic viral shedding. Presents clinically as painful, grouped vesicles on an erythematous base across external genitalia or perianal regions that rupture into shallow, painful ulcers; primary episodes are accompanied by systemic manifestations including fever, malaise, dysuria, and tender inguinal lymphadenopathy.

Varicella (Chickenpox)

Primary infection with Varicella-Zoster Virus (VZV / HHV-3) transmitted through airborne respiratory droplets or direct contact with fluid from active lesions. Presents clinically with generalized pruritic papules, vesicles on an erythematous base ("dewdrops on a rose petal"), and crusted lesions appearing simultaneously in various stages of evolution, accompanied by mild fever and systemic malaise.

Herpes Zoster (Shingles)

Reactivation of latent Varicella-Zoster Virus residing within dorsal root sensory ganglia, triggered by waning cell-mediated immunity due to aging (age ≥50), stress, or immunosuppression. Characterized clinically by dermatomal prodromal pain, burning, or paresthesias followed by a painful, unilateral vesicular eruption on an erythematous base that strictly respects the midline across 1 to 2 dermatomes; severe complications include postherpetic neuralgia, herpes zoster ophthalmicus, Ramsay Hunt syndrome, and disseminated infection.

Ramsay Hunt syndrome

A severe complication of herpes zoster where infection of CN VII causes ipsilateral facial paralysis, ear pain, and auditory canal vesicles

herpes zoster ophthalmicus

A severe complication of herpes zoster is an infection of the eye’s trigeminal V1 distribution with Hutchinson sign on the nose tip

postherpetic neuralgia

A severe complication of herpes zoster where you see persistent dermatomal pain ≥90 days

Reye Syndrome

Severe acute metabolic encephalopathy and hepatic dysfunction caused by mitochondrial injury following aspirin or salicylate administration in children or adolescents during an acute viral illness such as influenza or varicella. Clinical findings include persistent vomiting, lethargy, rapidly deteriorating mental status, marked transaminitis (elevated AST/ALT), hyperammonemia, prolonged PT/INR, hypoglycemia, and potential cerebral edema without prominent clinical jaundice.

Epstein-Barr Virus (EBV)/Infectious Mononucleosis

Human Herpesvirus 4 (HHV-4) transmitted through salivary secretions that infects mucosal epithelial cells and B lymphocytes, establishing lifelong latency and predisposing to Burkitt lymphoma, Hodgkin lymphoma, and nasopharyngeal carcinoma. Classically presents in adolescents and young adults with fever, profound fatigue, exudative pharyngitis with tonsillar enlargement, posterior cervical lymphadenopathy, palatal petechiae, hepatosplenomegaly, and a maculopapular rash if exposed to amoxicillin or ampicillin; peripheral blood smear shows atypical lymphocytosis, and splenic rupture represents a critical risk.

Cytomegalovirus (CMV)

Human Herpesvirus 5 (HHV-5) transmitted via body fluids (saliva, urine, blood, sexual secretions, breast milk) or transplacentally, establishing lifelong viral latency. Immunocompetent individuals present with a heterophile-antibody (Monospot) negative mononucleosis-like illness featuring fever, fatigue, myalgias, and mild transaminitis; immunocompromised hosts suffer severe end-organ disease including retinitis (floaters, visual field defects), odynophagic esophagitis, bloody colitis, or pneumonitis; congenital version produces petechiae/purpura ("blueberry muffin" rash), jaundice, hepatosplenomegaly, microcephaly, periventricular intracranial calcifications, and sensorineural hearing loss.

Roseola Infantum (Sixth Disease/Exanthem Subitum)

Acute febrile viral exanthem primarily affecting infants and young children aged 6 months to 2 years, caused predominantly by Human Herpesvirus 6 (HHV-6) or HHV-7. Manifests clinically as an abrupt onset of high fever (often >103°F) lasting 3 to 5 days during which the child appears surprisingly well, followed by immediate defervescence and the rapid appearance of a nonpruritic, blanching rose-colored macular or maculopapular rash starting on the trunk and spreading to the neck and extremities.

Erythema Infectiosum (Fifth Disease)

Viral exanthem caused by Parvovirus B19, transmitted primarily via respiratory droplets. Begins clinically with a mild prodrome of low-grade fever, headache, and upper respiratory symptoms, followed by a distinct bright red "slapped-cheek" facial rash with circumoral pallor and a subsequent lacy or reticular macular eruption on the trunk and limbs; infected adults, particularly women, frequently present with prominent symmetrical arthralgias or arthritis.

Measles (Rubeola)

Highly contagious airborne viral infection caused by a Paramyxovirus (genus Morbillivirus) that infects respiratory epithelium before systemic dissemination. Features a prodrome of high fever accompanied by the classic "3 Cs" (cough, coryza, conjunctivitis) and pathognomonic Koplik spots (bluish-white buccal mucosal lesions), followed by an erythematous maculopapular rash that originates at the hairline/face and spreads cephalocaudally down the trunk and extremities; severe complications include otitis media, pneumonia, acute encephalitis, and delayed subacute sclerosing panencephalitis (SSPE).

Parainfluenza

Viral disease transmitted via respiratory droplets or direct contact, causing acute inflammatory edema of the larynx, trachea, and subglottic structures. Serves as the primary viral cause of classic croup (laryngotracheitis) in infants and young children, presenting clinically with a distinctive barking "seal-like" cough, inspiratory stridor, hoarseness, and low-grade fever; can also cause lower respiratory tract disease such as bronchiolitis or pneumonia.

Rubella (German Measles)

Viral exanthem spread via respiratory droplets; maternal infection during early gestation results in severe transplacental teratogenic damage (Congenital Syndrome). Presents with low-grade fever, mild respiratory symptoms, tender posterior auricular, posterior cervical, and suboccipital lymphadenopathy, Forchheimer spots on the soft palate, and a fine pink maculopapular rash moving downward from the face; Congenital Syndrome (CRS) manifests with sensorineural hearing loss, ocular anomalies (cataracts, glaucoma), cardiac malformations (patent ductus arteriosus, pulmonary artery stenosis), and a "blueberry muffin" purpuric eruption.

Mumps

Systemic paramyxovirus infection spread via respiratory droplets or direct contact with saliva that targets glandular mucosal epithelium and neural tissues. Following a prodrome of fever, headache, myalgias, and anorexia, it causes characteristic painful swelling of one or both parotid salivary glands ("chipmunk cheek" appearance) with local earache; notable complications include postpubertal acute orchitis (testicular pain, swelling, and potential atrophy), aseptic meningitis, pancreatitis, and sensorineural hearing loss.

Rotavirus

Non-enveloped RNA viral pathogen transmitted via the fecal-oral route that infects and damages mature enterocytes in the small intestine, impairing fluid absorption. Serves as a major cause of severe acute gastroenteritis in infants and young children, presenting clinically with fever, acute vomiting, and profuse, watery, non-bloody diarrhea leading to severe dehydration.

Norovirus Gastroenteritis

Highly contagious non-enveloped RNA virus spread through fecal-oral transmission, contaminated food/water, surfaces, or aerosolized vomitus, triggering acute gastric and intestinal mucosal inflammation. Characterized clinically by an abrupt onset of severe nausea, projectile vomiting, watery non-bloody diarrhea, and abdominal cramping lasting 1 to 3 days, commonly causing widespread outbreaks in closed environments like cruise ships, long-term care facilities, and schools.

Rabies

Neurotropic Rhabdovirus transmitted through infected mammal saliva (bites or scratches from bats, raccoons, skunks, foxes, or dogs) that migrates retrogradely along peripheral nerve axons to the central nervous system, inducing acute, lethal viral encephalitis. Begins with a prodrome of fever, headache, malaise, and characteristic localized pain or paresthesias at the exposure site; advances to encephalitic rabies marked by severe agitation, confusion, hypersalivation, aerophobia, intense hydrophobia (painful pharyngeal/laryngeal spasms triggered by swallowing attempts), seizures, paralysis, coma, and death; post-mortem brain histology demonstrates intracytoplasmic Negri bodies.

Poliomyelitis

Enterovirus transmitted via the fecal-oral route. Most cases are asymptomatic or present as mild febrile illness; paralytic (<1% of cases) presents clinically as acute asymmetric flaccid paralysis with loss of deep tendon reflexes, reduced muscle tone, and intact sensation, with bulbar involvement leading to fatal respiratory muscle paralysis.

Zika Virus

Arbovirus (Flavivirus) transmitted primarily by Aedes mosquitoes, maternal-fetal transplacental transfer, or sexual intercourse, exhibiting neurotropism for fetal neural progenitor cells. Adult infection is usually mild or asymptomatic, presenting with low-grade fever, maculopapular rash, arthralgia, and nonpurulent conjunctivitis; fetal transplacental infection causes Congenital Zika Syndrome, characterized by microcephaly, severe intracranial calcifications/brain abnormalities, ocular defects, and joint contractures; maternal infection is also associated with Guillain-Barré syndrome.

Enteroviral Meningitis

Picornaviruses (enteroviruses) transmitted via fecal-oral or respiratory routes that replicate in gastrointestinal mucosal lymph tissue before systemic viremic spread to target organ systems. Serves as a major cause of aseptic viral meningitis, presenting clinically with fever, severe headache, photophobia, and nuchal rigidity.

HIV/AIDS

Human Immunodeficiency Virus targeting CD4+ T-helper lymphocytes, causing progressive cellular immune destruction and severe cell-mediated immunodeficiency. Advanced immunodeficiency (CD4 count <50 cells/mm³ or <200 cells/mm³) leads to severe opportunistic infections—including CMV retinitis, esophagitis, colitis, or pneumonitis—and HIV-associated malignancies such as Kaposi sarcoma