Dimorphic fungi Flashcards
True Pathogenic Fungi characteristics
Infection is found in both immunocompetent and immunocompromised hosts. The infections most commonly originate in the lungs, resulting from inhalation of conidia. Infection can range from asymptomatic or mild to disseminated and life threatening. Restricted geographical distribution. Some of these pathogens are most commonly associated with immunocompromised hosts, and are therefore more opportunistic than a true pathogen
Histoplasma capsulatum morphology
Mold form- white mycelium (hyphae), tuberculate
macroconidia which can be confused with Sepedonium. Small round tear drop microconidia can be confused with chlamydoconidia
Yeast form- Small, single budding yeast. Cream to tan colonies. It takes 15-20 days for culture growth on average, but can be up to 8 weeks
Coccidioides immitis morphology
Mold form- can grow within 3-5 days, barrel shaped arthroconidia with alternating empty disjunctor cells. Forms a moist, white colony that becomes fluffy.
Yeast form- Non-budding thick walled spherules filled with endospores are seen in tissue or respiratory samples. This species presents a laboratory-acquired infection risk.
Blastomyces dermatitidis morphology
Mold form- delicate, ropelike, septate hyphae. Single, pyriform conidia produced on long to short conidiophores resembling lollipops. Resembles Chyrsosporium, Scedosporium
Yeast form- large, round, thick walled, single budding yeast with a broad isthmus (neck)
Growth takes approximately 14 days
Paracoccidioides brasiliensis morphology
Mold form- Mostly small hyphae
with chlamydoconidia; may resemble B. dermatitidi. There are numerous chlamydospores (intercalary and terminal), globose or pyriform conidia arising from sides of hyphae. Take 1 month to grow
Yeast form- Multiple budding yeast that are large and round or oval, resembles a “ship’s wheel” or “mariner’s wheel”. Narrow necks connect the daughter cells. Take 1 week to grow
Talaromyces (Penicillium) marneffei morphology
Mold form- Hyaline hyphae. Conidiophores bearing terminal metulae with 3-7 phialides and short chains of conidia. Colonies are suede-like to downy, white to yellow/green. They become gray/pink to brown with age and have diffusible brown-red and wine red pigment
Yeast form- Fragmented, septate hyphae, resulting in single celled oval arthroconidia, buds not produced. Colonies mature within 3 days
Sporothrix schenckii morphology
Mold form- Ovoid conidia produced on short
conidiophore at right angles
from the delicate, thin, branching septate hyphae. Numerous conidia form “rosette” at conidiophore ends (daisy head). The colonies are small, cream colored, wrinkled, and later turn black
Yeast form- Budding, elliptical
yeast cells (cigar bodies). Colonies are soft, white, or cream to tan
Emergomyces morphology
Mold form- Slender conidiophores arising from hyphae at right angles, form florets of secondary conidiophores with single small conidia. Mycelial phase showing 1–3 conidia borne at the ends of slightly swollen conidiophores
Yeast form- Small round to oval yeast cells yeast, narrow-based, budding is produced at 35 degrees Celsius
For dimorphic pathogens, at what temperatures do the mold and yeast phases occur?
The mold phase occurs at 25 degrees Celsius and occurs in culture. The yeast phase occurs at 37 degrees Celsius and therefore occurs in tissue
In vitro conversion of dimorphic fungi from mold to yeast procedure (6 steps)
- Inoculate test mold onto slant of BHI agar with 10% blood.
- Incubate fungus at 37oC for 3-5 days.
- Subculture the most yeast-like colony to a fresh slant of BHI with blood
- Reincubate at 37oC for 3-5 days.
- Continue to make serial transfers until colony grows as yeast.
- If the fungus does not form yeast in 14 days, send to reference laboratory for animal inoculation
Histoplasma capsulatum in vitro conversion to yeast phase
Does not readily convert to yeast phase.
Coccidioides in vitro conversion to yeast phase
Requires animal model, mold at both 25 C and 37 C
4 methods of diagnosis of dimorphic infections
- Culture
- Fungal antigen detection- ELISA
- Histology
- Molecular- NAAT
Culture of dimorphic fungi
Provides a definitive diagnosis and is considered the gold standard, but it is time consuming
ELISA for dimorphic fungi
Isolate dependent, but you can use serum, urine, CSF, and BAL in AIDS patients. This is a good indicator of systemic disease
NAAT for dimorphic fungi
Available for most common US isolates. Histoplasma, Coccidioides, and Blastomyces
Direct exam of tissue secretions
Uses PAS, GMS, hematoxylin-eosin (HE). It is done in the tissue phase or yeast form.
N-acetyl-N-cysteine
Dissolves mucous, kills normal microbiota. This is used for respiratory specimens- they must be liquefied and concentrated before inoculation.
Media used for fungal culture
SDA, BHI, SDA/BHI, or yeast extract phosphate agar is used. Antimicrobials can be added to inhibit contaminants. Slants are preferred because there is decreased chance for mold to become airborne.
How long are fungal cultures incubated?
Incubate cultures up to 12 weeks, examining for specific colony morphology
Serology testing
Endemic, most of population will demonstrate titers for Histoplasma, Coccidioides, Blastomyces. This is one method of questionable utility
Skin test
Questionable testing method as frequent false positives= previous exposure and false negative=anergy
Exoantigen test
Extracts fungal antigens from cultured organisms. Another way of doing this is the gel immunodiffusion precipitin test. Soluble antigens are produced and extracted from fungi, then react with antibodies. Reagents are available for H. capsulatum, B. dermatitidis
Histoplasma capsulatum
Most common endemic mycosis in US- H. capsulatum var. capsulatum. H. capsulatum var. duboissi is an African histoplasmosis. Endemic to the Ohio and Mississippi River Valley, Central & South America, and Asia, Africa. Located from soil, especially associated with bird and/or bat droppings (birds not infected, bats can be), both can carry organism. Inhalation of conidia – primary site of infection is lung. Most people are infected during childhood and have asymptomatic or mild disease- 50-80% of all adults from endemic areas are infected
Symptoms of Histoplasma capsulatum
Some infections are asymptomatic, but symptoms include fever, cough, fatigue, chills, headache, chest pain, body aches. People can also experience acute severe pneumonia and chronic progressive pulmonary. Disseminated disease is life threatening, but less than 1% of infections progress to this stage. In most cases, exposure is never identifiable
Risk factors of Histoplasma capsulatum
Spelunking (Spelunkers Disease), cleaning chicken coops, construction, and excavation
Virulence of Histoplasma capsulatum (4)
- Resistant to host oxidative burst
- Effects phagolysosome pH
- Forms a siderophore to acquire host iron
- Phagocytosis survival allows for dissemination from lung to lymph nodes then hematogenous spread
It takes several weeks for cell-mediated immunity to eliminate organism. If T cells are compromised or a person receives a huge dose of the fungus, they experience severe disease
Progression of Histoplasma capsulatum infection
There is a 3-17 day incubation period after inhalation of the small conidia. Conidia are converted- the yeast is phagocytosed by macrophage/neutrophils
Disease types of Histoplasma capsulatum (3)
- Acute Pulmonary Histoplasmosis
- Chronic Pulmonary Histoplasmosis
- Disseminated Histoplasmosis
Acute pulmonary histoplasmosis
Symptoms include cough, fever and fatigue, and rare rash or joint involvement. Pneumonitis and lymphadenopathy are also common. The infection is self limiting and no fungal treatment is needed, it resolves within weeks. However, if a person receives a very high dose, they will experience acute, severe infection that can lead to respiratory failure
Chronic pulmonary histoplasmosis
Most common in older males with COPD. Symptoms include fever, fatigue, chronic cough, hemoptysis, and dyspnea. Patients can develop cavity formation and fibrosis which can mimic tuberculosis and other dimorphic infections. The infection can be fatal if untreated
Disseminated histoplasmosis
Symptoms include lymphadenopathy and lesions on the skin and mucous membranes. There are acute and chronic infections. Acute infection primarily occurs in the immunocompromised, it is a rapid & fatal infection involving many organs – along with lung, renal failure, hepatic failure, hypotension, and coagulopathy. Chronic infection is found in the immunocompetent- older males are at risk, symptoms are fever, fatigue, weight loss, but pulmonary symptoms can be absent
Histoplasma capsulatum treatment
Susceptible to Itraconazole and Amphotericin B (lipid formulation). Echinocandins have conflicting in vitro data regarding utility. Acute pulmonary infections do not require an antifungal if they resolve within a month. If symptoms continue, patients are prescribed oral azoles (itraconazole). For severe disease, treatment consists of Amphotericin B and corticosteroids. Requires a 3 month to 1 year course of antifungals. Immunocompromised patients in endemic populations may take itraconazole prophylactically. Ex- AIDS with CD4 T cell counts <200 cell/uL
Coccidioides species
Common cause of Valley Fever in the US. Strains include Coccidioides immitis - found in CA, WA and Coccidioides posadasii. Coccidioides species are endemic to south and central Washington, California, Southwestern US, Mexico, and central and south America. It is located in soil from hot, dry climates. Although this species is endemic, most people from these areas remain unexposed
Coccidioides species symptoms
Mostly asymptomatic (60% of patients) or mild disease. Symptoms include fatigue, cough, fever, shortness of breath, headache, muscle and joint aches, and rash on upper body or legs. 5 to 10% of patients develop long-term lung post-infection sequelae
Coccidioides species risk factors (3)
- Agricultural workers, excavators, archeologists
- Most common adults older than 60 years
- Immunocompromised individuals– HIV, organ transplant, high-dose corticosteroids, anti-TNF inhibitors, pregnant women, diabetes. Patients with depressed cellular immunity are at risk of developing severe disseminated disease
Progression of Coccidioides infection
There is a 1-3 week incubation period after inhalation of small conidia. The arthroconidia are inhaled and then undergo phagocytosis by macrophages or neutrophils. Increase in temperature, CO2 and acidic pH stimulates production of spherules. The spherule internally segments into compartments called endospores. Then, the spherule ruptures, releasing endospores to become spherules. Necrotizing granulomatous lesions are formed. There have been rare reports of arthroconidia entrance through broken skin causing infection.
Coccidioides virulence factors (3)
- Spherules - Protects against host defense mechanisms
- Coccidioidal urease damages host tissue
- Decreases host iNOS by competing for L-arginine.
Coccidioides disease types (3)
- Primary pulmonary infection
- Pulmonary Sequelae of Primary Coccidioidal Pneumonia
- Disseminated Coccidioidomycosis
Primary pulmonary Coccidioides infection
Symptoms include dry cough, fever, night sweats, pleuritic chest pain and headache. It is easily confused with bacterial community acquired pneumonia. The infection is differentiated by mediastinal lymphadenopathy, failure to improve with antibacterial, and eosinophilia. Rash covering the trunk and extremities early during infection is common ~25%. 30% of these patients also have arthralgia of knees and ankles
Pulmonary Sequelae of Primary Coccidioidal Pneumonia
5% progress to develop nodular lesions resembling neoplasia, which are mm to cm in size. A fine needle biopsy is used to identify the infection. There is
pulmonary cavity formation – they exhibit growth in sputum culture, and may rupture leading to pyopneumothorax. Chronic disease – bronchiectasis and fibrosis
Disseminated Coccidioidomycosis
Has a poor prognosis, most patients have no evidence of primary pulmonary infection. Less than 1% of patients are infected- organs affected include skin, bone (vertebrae), joints, meningitis, and eosinophils in CSF.
Coccidioides treatment
For most patients, treatment is not necessary, but medication may be prescribed to speed up recovery. However, treatment is commonly provided for high risk patients- a 3 month to 6 month course of fluconazole. Amphotericin B has been the drug of choice for more than 50 years. Non-lipid formulation of I.V. Amphotericin B is used for disseminated, severe disease but is not effective against meningitis (intrathecal delivery only). Fluconazole and itraconazole are considered the 1st line effective treatment, ketoconazole is less effective for some infections (e.g. bone). Data suggest that echinocandins are effective. Surgery for debridement is required for some severe lung infection and osteomyelitis infections.
Blastomyces dermatitidis
Common endemic mycosis in the US. It is endemic to the Midwestern, South-Central and Southeastern U.S., the Ohio and Mississippi River valley, the Great Lakes, St. Lawrence River, Canada, and Africa. Found in soil, decomposing leaves and organic matter, wooded areas associated with water, lakes and rivers. In endemic areas, 50% of people will have asymptomatic disease, and 50% are symptomatic and will be diagnosed. Respiration infection can mimic bacterial pneumonia, while chronic infections can mimic TB
Blastomyces dermatitidis risk factors
Construction, excavation, recreational activity associated with woods and water ways especially streams, rivers and lakes.
Progression of Blastomyces dermatitidis infection
The incubation period after the inhalation of the conidia can range from 3 weeks to 3 months. Conidia or converted yeast are phagocytosed by macrophages or neutrophils. It is the most common dimorphic fungal infection in the US diagnosed in immunocompetent hosts
Blastomyces dermatitidis virulence factors (3)
- Conidia phagocytoses by macrophage or neutrophil. Alveolar macrophages kill conidia, while non alveolar macrophages are responsible for suppression of inflammatory response, specifically TNF-α. Adhesion proteins BAD1 moderates this process
- Organism can rapidly form yeast cells in lung, dissemination may follow
- Pyogranulomatous response with rare necrosis
Blastomyces dermatitidis disease types (4)
- Pulmonary Blastomycosis
- Cutaneous Blastomycosis
- Bone and Joint Blastomycosis
- Disseminated Blastomycosis (CNS, Organ )
Pulmonary Blastomycosis
Acute and chronic infections. The acute infection can be misdiagnosed as bacterial pneumonia – fever, chills, productive cough. The chronic infection is associated with weight loss, night sweats, fever, productive cough, chest pain suggesting agents such as TB or lung cancer. ARDS – Adult respiratory distress syndrome found for both immunocompromised and competent, associated with corticosteroid use, severe T cell dysfunction
Cutaneous Blastomycosis
Most common extrapulmonary disease. Verrucous (crusting, exudative abscess) or ulcerative (subcutaneous abscess ruptures and drains)
Bone and Joint Blastomycosis
Bone – 25% of extrapulmonary cases with common involvement of pelvis, skull, vertebrae, necrosis common. Surgical debridement needed. Joint – 3 to 5% cases, monoarthritis of knee most common, almost always other infection sites identified
Disseminated Blastomycosis
CNS involvement- 5 to 10% of disseminated disease cases, meningitis, blastomycomas, difficult to identify, biopsy required, CSF not usually helpful to ID. Other organ involvement- abscess common, any organ possible, ocular infections, brain, skeletal system, prostate, sinuses, pericardium
Blastomyces dermatitidis treatment
Similar to other dimorphic pathogens, patients with mild and undiagnosed disease recover without antifungal treatment. However, there have been reports of reactivation after 40 years of latency- relapse infection can occur in lung, skin, bone, CNS. When diagnosed, only mild pulmonary disease should be untreated. Amphotericin B was the treatment choice for more than 50 years, and it is currently used for disseminated, severe infection. Azoles, especially itraconazole, are now first line for mild/moderate pulmonary and non-CNS disseminated infection. Depending on infection severity and immune status, treatment course range is from 6 to 12 months. Echinocandins have variable results and are not recommended.
Paracoccidioides brasiliensis
Also known as South American Blastomycosis. Endemic to Latin America (Mexico to Argentina) and Brazil, which accounts for 80% of all cases. Its exact location in nature has not been identified, but it is associated with humid regions with high rainfall, near rivers, forests and agriculture crops.
Associated with animals – armadillos, dogs, horses, cattle, monkeys, sloths, porcupines. There is infrequent infection in children, adolescents, and young adults. 60% of cases are in people 30-50 years old
Paracoccidioides brasiliensis risk factors
More than 70% of cases have an agriculture associated occupation, like farmers and lumberjacks. There is also a gender bias for infection- male to female ratio is 14:1. Other risk factors include poor nutrition, smoking, alcoholism, and immune status
Paracoccidioides brasiliensis symptoms
Cases are asymptomatic in healthy individuals. Significant symptoms requiring treatment = Progressive associated with poor host immunity. Patients experience lesions in the mouth and throat, weight loss, lymphadenopathy, cough, fever, shortness of breath, fatigue, enlarged liver and spleen
Progression of Paracoccidioides brasiliensis infection
The length of the incubation period after inhalation of conidia is unclear, and only 2% of exposures progress to symptomatic infection. It is thought that childhood exposure does not result in symptomatic infection for more than 40 years. T cell dysfunction, smoking, and alcoholism may play in role in activation of infection. Inhalation of conidia has a respiratory association with 80-90% of patients
Paracoccidioides brasiliensis virulence factors (3)
- Conidia bind macrophage using glycoprotein 43 (major virulence factor) facilitating uptake. Killing is dependent upon iNOS pathway
- Melanin production by organism provides protection.
- 30% of all cases limited to lungs.
What type of immunity is necessary to control Paracoccidioides brasiliensis?
Cell-mediated immunity is essential for organism control and elimination. Humoral-mediated immunity - high titers are common in acute disease, but antibodies are absent in chronic disease.
Paracoccidioides brasiliensis regressive
Mild pulmonary infection, asymptomatic- this occurs when host immunity is normal
2 types of disease- Paracoccidioides brasiliensis
- Regressive
- Progressive – Abnormal immune response
Paracoccidioides brasiliensis progressive disease
This occurs when the host has an abnormal immune response, and disease may be disseminated. Acute/Subacute or Juvenile infection – dissemination to reticuloendothelial system, associated with poor cell-mediated immune responses. Characterized by high antibody titers, absent CD4 T cell mediated immunity. Chronic or Adult infection – lasts for months to years, patients experience lung damage and dissemination. Characterized by low antibody titers, T cell immunity functioning. Can be lung specific or disseminated
What organs are impacted by Paracoccidioides brasiliensis? (3)
- Pulmonary
- Lesions of the skin and mucous membranes
- Disseminated disease- impacts CNS, bones and joints (in young people) and the genital tract (in males)
Pulmonary Paracoccidioides brasiliensis
Preferred fungal target organ- symptoms include cough, hemoptysis, dyspnea, lesions and fibrosis
Paracoccidioides brasiliensis skin lesions
Patients may experience lesions of the skin and mucous membranes. 50% of lesions are of the mouth, oropharynx, larynx – painful, ulcerative, bleeding, and may mimic cancer. 10 to 30% of lesions of the skin – frequently on face, single/multiple, lower extremities, ulcerative, from hematogenous spread.
Treatment for Paracoccidioides brasiliensis
Treatment is based on disease severity and is most successful when fungistatic drugs are used, requiring a host immune response for complete elimination. Amphotericin B is used for severe disseminated disease only. Mild disease treatment uses itraconazole/voriconazole or trimethoprim/sulfamethoxazole (TMP/SMX, Bactrim, Septra) is also successful. Treatment protocol typically lasts 1 year. – relapse occurs in 15-25% of patients even with an appropriate treatment algorithm.
Sporothrix schenckii
Most common subcutaneous fungal disease in U.S.-called sporotrichosis, Lymphocutaneous Sporotrichosis or “Rose Gardener’s Disease”. Endemic nation-wide, most commonly found Central and South America. Located in soil, plant matter, sphagnum moss, rose bushes, and hay. Cutaneous (skin) infection is most common, pulmonary is rare, disseminated disease occurs in the immunocompromised – usually joints, osteomyelitis, rare CNS. Most cases occur after direct inoculation through the skin (traumatic implantation). Infection occurs from environmental exposure and is not contagious
Diseases caused by Sporothrix schenckii (3)
Subcutaneous infection is most common, but pulmonary and osteoarticular sporotrichosis can also occur.
Pulmonary Sporothrix schenckii
Rare, preexisting lung disease is a predisposing factor, more common in middle-aged males. Lung lesions common, dissemination rare
Osteoarticular Sporothrix schenckii
Found in the knee, elbow or ankle, usually traumatic implant to joint. Can be disseminated from cutaneous lesion
Disseminated Sporothrix schenckii
Hematogenous spread from cutaneous infection to CNS & joints
Sporothrix schenckii risk factors
Most common in males, reflecting an occupational hazard such as gardening, farming, forestry, outdoor laborers and nursery workers.
Sporothrix schenckii virulence factors
Virulence factors are not clear. Production of melanin occurs, but it is not confirmed to result in ability to establish infection. Thermotolerance – ability to rapidly grow at 37°C, more infections
Sporothrix schenckii treatment
Itraconazole is the most common choice 2-4 weeks after all lesions have resolved (treatment typically lasts 3 to 6 months). Supersaturated potassium iodide (SSKI) is another treatment option for skin sporotrichosis- SSKI is not to be used during pregnancy. Severe infection requires a lipid formulation of amphotericin B, patients are then switched to oral itraconazole for a total of 12 months of treatment. AIDS patients may require lifelong maintenance therapy with itraconazole for meningeal and disseminated infection-Posaconazole may have a role.
Talaromyces (Penicillium) marneffei
Endemic to Southeast Asia – Thailand (common in AIDS patients), Taiwan, Southern China, Eastern India. Found in the soil in the burrows of Bamboo rats. There are increased cases in the rainy season
Talaromyces (Penicillium) marneffei risk factors
Cancer, AIDS, Autoimmune disease, other conditions associated with a weakened immune system. Healthy individuals do not become infected - this fungus is an opportunistic pathogen
Talaromyces (Penicillium) marneffei clinical disease
Clinical disease is called Talaromycosis- acquired via inhalation, resulting in initial pulmonary infection, followed by fungemia and dissemination. Healthy individuals have granuloma formation to control infection. Deficiencies in cellular immunity results in significant infection. Macrophages and TNFα are a requirement for elimination of the infection
Fever, malaise, weight loss, lymphadenopathy, cough, diarrhea, abdominal pain are potential symptoms. 70% of AIDS patients demonstrate acne-like skin papules on face, trunk, and extremities
Progression of Talaromyces (Penicillium) marneffei infection
At 37°C conidia converts to yeast and hematogenous spread occurs. Involves the reticuloendothelial system, liver, spleen lymph nodes and bone marrow, bone, skin and lung involvement. 70% of AIDS patients demonstrate acne-like skin papules on face, trunk, and extremities during the course of the disease. Early diagnosis & treatment reduces fatality rate to 20%.
Talaromyces (Penicillium) marneffei treatment
Quickly fatal if not treated quickly with appropriate therapy
Most common choice is IV amphotericin B for disseminated disease. Oral Itraconazole may be used for 10 weeks. Resistance to other azoles (like fluconazole) has been detected.
Emergomyces
A new, dimorphic fungal pathogen. There are 5 species known to cause infection. It appears to be transmitted through inhalation of conidia from contaminated soil, however, the fungus has not been successfully isolated from the environment. There is temperature-dependent transformation of the fungus in the lungs. Virulence factors have not yet been identified, but early data suggests that humoral immunity is more important.
Emergomyces species (5)
- E. africanus – South Africa
- E. pasteurianus – Europe, Asia, India, Africa
- E. canadensis – Saskatchewan, Canada and Colorado, New Mexico U.S.
- E. europaeus - Germany
- E. orientalis - China
Emergomyces risk factors (2)
- Immunocompromised, T cell deficiencies.
- Misdiagnosis with other fungal infections – histoplasmosis, cryptococcosis, blastomycosis, sporotrichosis
Emergomyces disease
Budding, yeast-like cells cause pulmonary disease (found intracellularly). Dissemination of the fungus to any body site is possible. Dissemination of yeast-like cells occurs through hematogenous spread, but the pathogen is located intracellularly in macrophages- this is the extrapulmonary form of the disease. The fungus most commonly causes cutaneous lesions
Emergomyces treatment
Immunocompromised patients are treated with liposomal amphotericin B for 2-weeks (this is all that can be tolerated). Then, itraconazole treatment is used due to amphotericin B toxicity. Itraconazole or newer azole is part of the treatment protocol, which typically lasts for 12 months. Fluconazole is avoided, as in vitro testing suggests resistance
