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Chapter 22 Lecture 6 (Mycoses of the Lower Respiratory System (fungal)…
Chapter 22 Lecture 6
Mycoses of the Lower Respiratory System (fungal)
Cases of mycoses have increased over the last two decades
AIDS patients are susceptible to fungal infections
Systemic Fungal infections seen in North America include
Coccidioidomycosis
Commonly known as valley fever primarily occurs San Joaquin Valley in California
Signs and symptoms
Resembles pneumonia or tuberculosis
60% experience mild respiratory issues and resolve on own.
Others will fever, cough chest pain dyspnea, night sweats, weight loss, hemoptysis, HA, and some a rash
Can become systemic (spreads to other organs) in immunocompromised persons
Pathogen and virulence factors
Caused by Coccidioides immitis found in soil and any activity that disrupts the soil (dust storm) can disseminate the arthroconidia into the air
Pathogen assumes yeast form at human body temperature
Pathogenesis
Arthroconidia from the soil enter the body through inhalation and will germinate in the alveoli into a form called a spherule. As these spherule mature, it enlarges and makes a large number of spores into surrounding tissue.
Epidemiology
Almost exclusively in southwestern United States and northern Mexico
Diagnosis, treatment, and prevention
Diagnosed by presence of spherules in clinical specimens
Dx is confirmed by injecting antigen beneath the skin and observing an inflammatory response
If fungus spreads to the brain and spinal cord the disease is fatal without treatment
Treated with amphotericin B
Protective masks can prevent exposure to arthroconidia
Blastomycosis
A systemic fungal disease that begins as a respiratory infection . This is endemic across the southeastern US north to Canada
Signs and symptoms
Flu Like symptoms
Systemic infections can produce lesions on the face and upper body or purulent lesions on various organs
Pathogen
Caused by Blastomyces dermatitidis
Normally grows in soil rich in organic material, where cool, damp conditions favor growth and sporulation
Pathogenic yeast form at human body temperature
Pathogenesis and epidemiology
Enters the body through inhalation of dust carrying fungal spores into the lungs.
In the lungs the spores germinate to form yeast and multiply
Initially asymptomatic and typically will resolve (skin lesions) though the disease can become chronic and fatal
Diagnosis, treatment, and prevention
Diagnosis is based on identifying fungus in clinical samples like a culture or direct examination of sputum, bronchial washings, biopsies, CSF or skin scrapings
Treated with amphotericin B for 10 weeks- Mrs.Cowhy husband was 18 months
Relapse common in AIDS patients
Scientists have developed a live recombinant DNA vaccine against Blastomyces that give protection in mice
Histoplasmosis
The most common fungal disease affecting humans
Signs and symptoms
Asymptomatic in most cases (95%)
Symptomatic infection causes coughing with bloody sputum or skin lesions
An AIDS patient will develop an enlarged spleen and liver
Pathogen
Caused by Histoplasma capsulatum found in most soils that have high levels of nitrogen from bat droppings, and birds (chickens, starlings and blackbirds()
Pathogenic yeast form at human body temperature
Histoplasma produces several proteins that inhibit macrophage activation and other host defenses
Pathogenesis and epidemiology
Humans inhale airborne spores from the soil and the fungus will attack alveolar macrophages in the lungs. Infected macrophages disperse the fungus beyond the lungs via the blood and lymph
Prevalent in the eastern United States along the Ohio and Mississippi river valleys.
Diagnosis, treatment, and prevention
Diagnosis is based on identifying fungus in clinical samples and again with samples such a sputum, CSF, and various tissues,
Infections in immunocompetent individuals typically resolve without treatment
90% of the population have antibodies against H. capsulatum
Pneumocystis pneumonia
Before AIDS, this disease was only noticed in malnourished premature infants and weak elderly patients. Now this disease is almost diagnostic for AIDS.
Signs and symptoms
Difficulty breathing, anemia, hypoxia, and fever
Nonproductive cough in some cases
If left untreated it will involve more and more lung tissue and eventually death
Pathogen
Caused by Pneumocystis jirovecii (a normal member of the respiratory microbiome)
Pathogenesis and epidemiology
Cannot survive on its own
Transmit by inhalation of droplets containing the fungus
Common disease in AIDS patients
Diagnosis, treatment, and prevention
Diagnosis is based on clinical and microscopic findings
Films usually reveal abnormal lung features
Treated with trimethoprim and sulfamethoxazole- does not respond to antifungal drugs
Impossible to prevent infection with P. jirovecii
Other Viral Respiratory Diseases
Other viruses cause respiratory disease in children, the elderly, or immunocompromised individuals
Cytomegalovirus
Metapneumovirus
Estimated to be the second most common cause of viral respiratory disease
Researchers have found that antibodies against the virus form in all children by age of five
Parainfluenzaviruses
Three strains cause croup and viral pneumonia
No specific antiviral treatment beyond the support and careful monitoring of airways
Most recover within two days
Occur primarily in young children
Handwashing reduces spread of virus