Infectious Disease - Viral, Endemic and Parasites (IRAT 11)

What is the leading cause of acute viral gastroenteritis and foodborne disease in US adults worldwide?

Norovirus

Closed settings — schools, cruise ships, long-term care facilities can lead to which disease?

Norovirus outbreaks

What is the incubation period for Norovirus? peak incidence of Norovirus?

12–48 hours; Winter months (but can occur year-round).

What are the main routes of Norovirus transmission?

Fecal–oral, contaminated food/water, person-to-person, aerosolization during vomiting.

What does Norovirus do to the small intestine?

Infects mature enterocytes → causes transient malabsorption and crypt hypersecretion, which produces secretory diarrhea.

Why is Norovirus stool non-bloody?

Norovirus causes no significant mucosal inflammation, so the diarrhea remains non-bloody.

Clinical Features: What symptoms are more common in children with Norovirus?

Nausea & vomiting.

What symptoms are more common in adults with Norovirus?

Non-bloody diarrhea

Common systemic symptoms of Norovirus?

Low-grade fever, myalgias, abdominal cramps, headache, malaise.

How long do Norovirus symptoms typically last?

12–60 hours.

What population is most affected by Rotavirus?

Infants and young children — major cause of severe gastroenteritis.

What is the incubation period for Rotavirus?

<48 hours

What are the transmission routes for Rotavirus?

Fecal–oral, contaminated foods/water, surfaces touched by infected food handlers.

When is the peak incidence of Rotavirus?

Winter months (especially daycares, nurseries)

Pathophysiology

What cells does Rotavirus infect?

Mature enterocytes in the small intestine.

What happens to the intestinal cells in Rotavirus infection?

infects mature enterocytes in the small intestine → causes villous blunting, leading to malabsorption and transient lactose intolerance during recovery.

NSP4 viral enterotoxin causing chloride secretion → watery diarrhea + transient lactose intolerance during recovery — which virus is this?

Rotavirus.

Why is transient lactose intolerance common during recovery?

Damage to villi decreases lactase activity → temporary lactose malabsorption.

Rotavirus symptoms in children? Rotavirus symptoms in adults?

Vomiting + watery, non-bloody diarrhea + fever; Usually milder than in children.

How long do Rotavirus symptoms typically last?

4–8 days

How are fungi classified (cell type)?

Eukaryotes — contain a nucleus and intracellular organelles.

What is the single-cell form of fungi called?

yeast

What is the multicellular form of fungi called?

Filamentous mold.

What does “dimorphic” mean in fungi?

Can exist as yeast or filamentous mold depending on conditions

What are hyphae?

Branching units that make up multicellular fungi.

What is the difference between septate and aseptate hyphae?

1. Septate: have walls that separate individual cells.

2. Aseptate (coenocytic): lack these walls → form one continuous tube with multiple nuclei.

What are pseudohyphae?

Chains of yeast cells connected in branching formations (seen in Candida)

What are systemic mycoses?

Deep fungal infections that affect healthy individuals.

Name the major systemic mycoses.

Histoplasma capsulatum
Blastomyces dermatitidis
Coccidioides immitis

What are opportunistic fungal infections?

Infections that primarily affect immunocompromised hosts

Name the major opportunistic fungi

1. Candida albicans

2. Aspergillus fumigatus

3. Cryptococcus neoformans

4. Mucor & Rhizopus spp

5. Pneumocystis jirovecii

What infections are included under systemic mycoses?

Histoplasmosis, Blastomycosis, Coccidioidomycosis.

How do systemic mycoses typically present clinically?

Pneumonia or disseminated disease.

What type of fungi cause systemic mycoses?

Dimorphic fungi.

What form do dimorphic fungi take at 20°C (soil)?

Mold form.

What form do dimorphic fungi take at 37°C (body/tissue)?

Yeast form.

What is the key exception to the “mold in the cold, yeast in the heat” rule?

Coccidioides — presents as a spherule, not a yeast.

Are systemic mycoses transmitted person-to-person?

No — they are not transmitted person-to-person.

What organism causes Histoplasmosis?

Histoplasma capsulatum

Is Histoplasma dimorphic? What forms does it take?

Yes — mold in soil, small oval budding yeast in tissue (inside macrophages).

What is the main clinical presentation of Histoplasmosis?

Pneumonia.

Who is at risk for disseminated histoplasmosis?

Immunocompromised patients
(Infants, AIDS with CD4 < 150, suppressed immunity).

What are the endemic locations for Histoplasmosis?

Mississippi and Ohio River Valleys.

What is the main environmental reservoir?

Soil contaminated with bird or bat guano
(caves, chicken coops, construction sites, spelunking).

How is Histoplasma transmitted?

Inhalation of spores.

What happens after Histoplasma spores are inhaled?

Spores are engulfed by macrophages and convert into yeast forms.

Where does Histoplasma live inside the body?

Inside macrophages as oval budding yeast.

How do Histoplasma yeasts survive inside macrophages?

They produce alkaline substances (bicarbonate, ammonia) → raise phagolysosome pH → inactive degradative enzymes.

How does Histoplasmosis spread through the body?

Yeasts travel within macrophages → spread to liver, spleen, lymph nodes.

Do most Histoplasma infections cause symptoms?

No — most remain asymptomatic.

What are the symptoms of mild acute pulmonary histoplasmosis?

Flu-like illness: fever, cough, myalgias; self-limited.

What happens in heavy exposure acute pulmonary histoplasmosis?

Severe pneumonia, mediastinal granulomas, possible pericarditis.

What are the systemic symptoms of disseminated histoplasmosis?

Fever, weight loss, hepatosplenomegaly, pancytopenia.

What mucocutaneous finding is associated with disseminated histoplasmosis?

Painful mucocutaneous ulcers.

What endocrine complication can occur in disseminated histoplasmosis?

Adrenal insufficiency

What is the prognosis of untreated disseminated histoplasmosis?

High mortality if untreated.

What organism causes Blastomycosis, and what are its dimorphic forms at different temperatures?

Blastomyces dermatitidis — mold in soil at 20–25°C, broad-based budding yeast at 37°C.

Which population is at highest risk for Blastomycosis based on exposure?

Men with outdoor occupational or recreational exposure.

What characteristic budding pattern is seen in Blastomycosis at body temperature?

Broad-based budding yeast.

🟦 TRANSMISSION

What are the endemic regions for Blastomycosis? (Be specific)

Ohio & Mississippi River valleys, Great Lakes region, and parts of Canada.

What type of soil/environment is associated with Blastomyces growth?

Soil with decayed vegetation or decomposed wood.

How is Blastomycosis transmitted to humans?

Inhalation of airborne spores.

What happens to inhaled spores once inside the body?

Spores mature into yeast in the body.

🟦 PATHOPHYSIOLOGY

What is the initial step in Blastomycosis pathophysiology after inhaling spores?

Spores enter via respiratory tract and mature into yeast.

How does Blastomyces trigger granuloma formation?

Invasion of the respiratory tract induces a cell-mediated immune response, leading to granuloma formation.

What forms during dissemination of Blastomycosis, and what tissues can they involve?

Ulcerated granulomas, can involve skin, bone, and other tissues.

🟦 CLINICAL FEATURES: Pulmonary Disease

 What is the most common organ system involved in Blastomycosis, and what symptoms occur?

Lungs — pneumonia with fever, productive cough, and flu-like symptoms.

What is the most common extrapulmonary site of Blastomycosis?

Skin.

What are the characteristic skin lesions of Blastomycosis?

Papules progressing to verrucous, crusted, or ulcerated lesions that may leave central scars

Which organs/systems are most commonly involved in disseminated Blastomycosis?

Lungs, skin, bone (vertebral, pelvic, rib pain), and genitourinary system (prostatitis/epididymitis).

What severe CNS complication can occur in disseminated Blastomycosis?

Brain abscess