Aspergillus Case File

Aspergillus Case File

Eugene C.Toy, MD, Cynthia Debord, PHD, Audrey Wanger, PHD, Gilbert Castro, PHD, James D. Kettering, PHD, Donald Briscoe, MD

CASE 39

A 42-year-old woman with chronic asthma presents for evaluation of a cough. She has had severe asthma for most of her life and currently uses both inhaled and oral corticosteroids, oral leukotriene modifiers, and inhaled albuterol to manage her symptoms. While in the process of tapering down her dose of oral steroids, she developed a cough productive of brown mucous and, occasionally, blood. She has had a low-grade fever as well. Her asthma control has been significantly worsened since she developed the cough. On examination, she has a temperature of 37.7°C (99.9°F) and a respiratory rate of 22 breaths per minute, and her saturation of oxygen is slightly low (96 percent on room air). She is coughing frequently. Her head and neck exam is unremarkable. Her pulmonary examination is notable for diffuse expiratory wheezing. A chest xray shows a lobular infiltrate that is reminiscent of a cluster of grapes. A complete blood count (CBC) shows a mildly elevated white blood cell count with a markedly elevated eosinophil count. A microscopic examination of her sputum is also notable for the presence of numerous eosinophils.

◆ What organism is most likely causing her cough?

◆ What is the characteristic morphology of this organism seen on microscopic examination?

ANSWERS TO CASE 39: Aspergillus

Summary: A 42-year-old asthmatic woman has allergic bronchopulmonary aspergillosis.

◆ Most likely etiologic agent: Aspergillus fumigatus

◆ Characteristic morphology of this organism seen on microscopic examination: Septate hyphae with 45° angle branching

CLINICAL CORRELATION

Aspergillus is a ubiquitous fungal organism that is capable of causing disease in both healthy and immunocompromised hosts. Infection occurs following either inhalation of the organism into the respiratory tract or introduction through the skin via a wound or surgery. Aspergillus fumigatus causes about 90 percent of invasive disease in humans, with A. flavus causing approximately 10 percent. Other Aspergillus species can cause disease but are less common. Aspergillus primarily infects the lungs and may cause a hypersensitivity reaction, chronic necrotizing pneumonia, aspergillomas (“fungal balls”), or systemic infection. Aspergillus can also cause keratitis and sinusitis. The hypersensitivity reaction, known as allergic bronchopulmonary aspergillosis (ABPA), is seen primarily in chronic asthmatics and persons with cystic fibrosis (CF). Approximately 25 percent of asthmatics and about half of patients with CF are allergic to Aspergillus, although the percentages that develop symptomatic disease are much lower. ABPA causes a cough productive of brown mucous plugs and, often, blood. Examination of the mucous will reveal eosinophils and the characteristic fungus. The symptoms initially tend to be mild but become more severe as the patient ages. Repeated episodes may cause bronchiectasis and chronic fibrotic pulmonary disease.

Systemic disease most often occurs in patients who are severely immunocompromised such as subsequent to bone marrow transplantation.

APPROACH TO THE SUSPECTED Aspergillus PATIENT

Objectives

1. Know the morphology, environmental sources, and pathogenic properties of Aspergillus species.
2. Know the clinical syndromes and diseases associated with Aspergillus infections.

Definitions

Allergic bronchopulmonary aspergillosis (ABPA): A hypersensitivity response to inhaled Aspergillus in patients with underlying asthma or lung disease.

Aspergilloma: A fungal ball most commonly in the sinus or within an old tuberculous cavity.

Bronchiectasis: Chronic inflammation of the bronchi with dilatation and loss of elasticity of the walls.

DISCUSSION

Characteristics of Aspergillus Species

Aspergillus species is found in every country in the world, and its primary habitat is decomposing vegetation. It is an opportunistic pathogen of animals and humans that causes a spectrum of disease ranging from allergic bronchopulmonary disease to disseminated disease in severely immunosuppressed patients. There are more than 40 species of Aspergillus, not all of which cause disease in humans. Therefore species identification is helpful in determining the clinical significance of an isolate. Aspergillus fumigatus is responsible for the majority of serious infections as a result of these organisms; however, A. terreus and A. flavus can be associated with disease in patients on cancer chemotherapy.

A virulence factor common to most Aspergillus species is mycotoxin production. One of the toxins, gliotoxin, can affect phagocytosis by macrophages as well as induce apoptosis.

Several factors contribute to the ability of A. fumigatus to cause infection. Aspergillus fumigatus grows more readily at normal human body temperature than other Aspergillus species. It has a very small spore size, which allows the spores to penetrate deep into the lung. It also is the most rapidly growing of all Aspergillus species.

Diagnosis

Diagnosis of allergic aspergillosis is usually made clinically, although these patients may have positive respiratory cultures for Aspergillus. Patients typically have a long-standing history of asthma with a history of infiltrates on chest x-ray. Other diagnostic criteria include presence of specific antibody to Aspergillus as well as elevated levels of IgE in the serum and peripheral blood eosinophils. The lack of systemic symptoms helps differentiate ABPA from Aspergillus pneumonia or disseminated disease. Diagnosis of disseminated disease is by culture of the organism from a normally sterile site and/or demonstration of hyphae invading blood vessels in a tissue biopsy. Disseminated disease can also be presumptively diagnosed by presence of antibody or galactomannan antigen in the patient’s serum.

Fungal hyphae can be seen on direct smear using KOH or calcofluor white, which is a more sensitive fluorescent stain. Aspergillus hyphae can be identified by their frequent septae, and branching at regular intervals at a 45° angle (Figure 39-1); however, these characteristics are not specific or diagnostic for Aspergillus. Definitive diagnosis would be made by microscopic observation of the fungus after culture of the organism. Aspergillus species can be cultured from sputum or bronchoalveolar lavages of infected patients. The fungus grows rapidly on most laboratory media including blood agar, although a more selective media such as Sabouraud agar is commonly used to culture fungus. Growth is enhanced by incubation at room temperature versus 35°C (95°F). Visualization of the characteristic structure with a conidiophore, a vesicle to which the phialides are attached would confirm the diagnosis of Aspergillus. Although speciation can be preliminarily made by the color of the front and reverse of the colony on Sabouraud dextrose agar and their microscopic features, A. fumigatus is differentiated from the others by growth at a temperature at or above 50°C (122°F).

Figure 39-1. Aspergillus fumigatus. Frequent septa with branching pattern is characteristic.

Treatment and Prevention

Treatment of ABPA is usually not warranted; however because this is a hypersensitivity reaction, systemic corticosteroids are effective treatment, whereas inhaled corticosteroids are not. Therapy for invasive aspergillosis is with amphotericin B, itraconazole, or voriconazole. Antifungal agents may be used for prophylaxis of patients who are severely immunocompromised to prevent disseminated disease, particularly bone marrow transplant patients. These patients should also be protected from exposure to the organism by use of air filters.

COMPREHENSION QUESTIONS

[39.1] A biopsy of an infected lung from a 76-year-old woman who suffered a third-degree burn 2 months ago revealed uniform hyphae with regularly spaced septation and a parallel arrangement. No yeast cells were observed. Which of the following is the most probable diagnosis?

A. Actinomycosis

B. Aspergillosis

C. Blastomycosis

D. Cryptococcosis

E. Zygomycosis

[39.2] Which of the following is the probable source of infection in aspergillosis in the patient in Question 39.1?

A. Contact with an infected animal

B. Implantation

C. Ingestion

D. Inhalation

E. Water used in preparing lemonade

[39.3] An examination of sputum for a suspected case of fungal infection may reveal hyphae in which of the following?

A. Aspergillosis

B. Cryptococcosis

C. Histoplasmosis

D. Paracoccidioidomycosis

E. Sporotrichosis

Answers

[39.1] B; [39.2] B. Aspergillosis is a spectrum of diseases that may be caused by a number of Aspergillus species. These species are widespread in nature. Aspergillus species grow rapidly in vivo and in vitro and bear long conidiophores with terminal vesicles on which phialides produce chains of conidia. In healthy individuals, alveolar macrophages are able to phagocytize and destroy the conidia. Macrophages from immunocompromised patients have a diminished ability to do this. In the lung, conidia swell and germinate to produce hyphae that have a tendency to invade preexisting cavities (abnormal pulmonary space as a result of tuberculosis, sarcoidosis, or emphysema). Sputum and lung tissue specimens produce colonies which are hyaline, septate and uniform in width. Blastomyces and Cryptococcus from yeast cells, while Zygomycoses species have hyphae that are sparsely septate. Actinomyces may be considered a branching bacterium. Aspergillus tends to invade either via inhalation or implantation through skin wounds. In this patient with a 3rd degree [full-thickness skin] burn, implantation through the wound would be the most likely source of infection.

[39.3] A. Cryptococcosis, histoplasmosis, paracoccidioidomycosis and sporotrichosis are all caused by dimorphic fungi. At 37ºC (98ºF), the yeast form predominates. Aspergillosis, on the other hand, is caused by an organism that produces only hyphae (no-yeast component).

MICROBIOLOGY PEARLS ❖ Aspergillus is commonly found in the environment and cause a spectrum of disease ranging from allergic bronchopulmonary disease to disseminated disease. ❖ Microscopically aspergillus has septated, hyphae that branch at 45° angles and a vesicle with condida in either a single row (uniserate) or a double row (biserate). ❖ Although steroids are used to treat allergic disease, disseminated disease is difficult to treat and has a high mortality rate in severely immunosuppressed patients such as following bone marrow transplant.

REFERENCES

Denning DW. Aspergillus species. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases, 6th ed. Philadelphia, PA: Churchill Livingstone, 2005:2958–73. 

Murray PR, Rosenthal KS, Pfaller MA. Opportunistic mycoses In: Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology, 5th ed. St. Louis, MO: Mosby, 2005:779–800.

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