The Clinical Manifestations of Blastomycosis - Research Paper Example

?American Blastocymosis Background Blastomycosis is a systemic pyrogranulomatous fungal infection which primarily affects the lungs (Longo et al., 2012). This disease, first described by Gilchrist in 1894, is caused by a fungus called Blastomyces dermatitidis (Longo et al., 2012; Varkey and Raugi, 2011). Although the clinical manifestations of blastomycosis is usually pulmonary in nature, the etiologic agent can spread hematogenously to affect other organs of the body such as the bones, gastrointestinal tract, genitourinary system, and skin, among others (Longo et al, 2012). Interestingly, blastomycosis is a disease not unique to humans. In fact, it is commonly found in dogs and has also been documented in other animals such as cats, horses, and cows (Varkey and Raugi, 2011). Etiologic Agent Blastomyces dermatitidis is the vegetative form (asexual stage) of Ajellomyces dermatitidis (Longo et al., 2012). According to Longo et al. (2012), two serotypes of the organism exist based on the presence of the A antigen. However, more recent immunologic studies using Enzyme-Linked Immunosorbent Assay (ELISA) suggests that there are perhaps more than just two serotypes (Varkey and Raugi, 2011). Nonetheless, this organism displays dimorphism, a characteristic where morphology changes based on certain environmental conditions. Specifically, for B. dermatitidis, it exists in the mycelium state at room temperature but reverts back to its yeast form when the temperature hits 37 degree Celsius (Longo et al., 2012). Under the microscope, the yeast cells appear multinucleated, with thick refractile cell walls, usually measuring 8-15 uM in diameter (Longo et al., 2011). These cells reproduce by budding. Epidemiology Most cases of blastomycosis have been documented and reported in the United States. In fact, it is endemic in the southeastern and central portions of the US, which include the Ohio River, the Mississippi River, and the Great Lakes (Varkey and Raugi, 2011). The annual incidence of the disease, based on the previously confirmed cases, is one (1) for every 100,000 people in Kentucky, Mississippi, Wisconsin, and Arkansas ( Varkey and Raugi, 2011). However, within the endemic areas, the annual incidence was reported to be as high as 40 per 100,000 individuals. It is important to note that blastomycosis is not confined in the United States. It is also distributed across Africa, Canada, Middle East, and India (Varkey and Raugi, 2011). In the US alone, a mortality rate of 5 percent among the treated cases and approximately 40 percent in the untreated individuals were recorded for blastomycosis way back in the 1960s (Varkey and Raugi, 2011). These statistics decreased in the 1990s, where the mortality rate among patients who received treatment went down to 0-2 percent (Varkey and Raugi, 2011). However, mortality among the immunocompromised individuals such as AIDS patient remains high. Mortality was documented to be as high as 40 percent. Complications caused by blastomycosis are usually rare among immunocompetent patients. Reports showed that B. dermatitidis grows in warm and moist soil in woody areas (Longo et al., 2012). Hence, exposure to soil is a common denominator among those infected with the organism. In fact, middle-aged men (mean age of 45 years old) who work outdoors were found to be at higher risk in contracting the disease (Longo et al., 2012; Varkey and Raugi, 2011). However, individuals of any age, both sexes, can get infected with the organism (Varkey and Raugi, 2011). In addition, B dermatitidis does not appear to have racial predilection. This means that the fungus can infect any individual, whatever his/ her race is. Pathogenesis B. dermatitidis enters the body by inhaling the conidia of the organism (Longo et al., 2012). Then, the conidia get deposited in the lungs, where it is usually engulfed by macrophages and other polymophonuclear leukocytes (Longo et al., 2012). However, some of the conidia that escape the body's immune defenses are converted back to its yeast state. With its thick walls and capability to produce immune-modulating virulence factor, the yeast form of B. dermatitidis offers survival advantage over its conidia counterpart, causing the infection (Varkey and Raugi, 2011. In the lungs, the yeast causes an acute pulmonary infection. However, as it multiplies and increases in number, it gets carried by the blood and lymphatics to infect other organs of the body. Signs and Symptoms Pulmonary involvement is almost always present in most cases, which manifests as abrupt onset of cough, fever, chills, myalgias, and joint pains (Longo et al.,2012; Varkey and Raugi, 2011). The cough, which is usually non- productive at the onset, eventually becomes purulent later on. The average time before pulmonary symptoms become apparent from the time the organism was inhaled is usually within 45 days (Varkey and Raugi, 2011). However, pulmonary infection may be asymptomatic in approximately 50 percent of the documented cases. In immunocompromised individuals, the body's immune system may no longer be strong enough to confine the disease within the lungs. Hence, the organism disseminates throughout the body and cause an extrapulmonary infection (Longo et al., 2012 ). Among the extrapulmonary organs affected by B. dermatitidis, the skin is the most common site of involvement (Longo et al., 2012). In fact, skin involvement occurs in as much as 20 percent of all cases (Varkey and Raugi, 2011). In few cases, the eyes, ears, nose, and trachea become affected as well (Varkey and Raugi, 2011). Diagnosis Work-up for the diagnosis of blastomycosis range from blood analysis to imaging studies (Varkey and Raugi, 2011). Complete blood count of patients with blastomycosis often present with leukocytosis with a leftward shift (Varkey and Raugi, 2011). However, this test is neither specific nor sensitive for this disease. Meanwhile, sputum microscopy offers a higher diagnostic sensitivity, which aims to visualize yeast cells in the expectorated sputum of the patient (Varkey and Raugi, 2011). The test is done by examining a sample of sputum admixed with 10 percent potassium chloride in order to visualize the organism (Varkey and Raugi, 2011). Serologic testing, where the presence of B. dermatitidis antigen and other molecular markers are identified, can also be used to diagnose blastomycosis (Longo et al, 2012). However, its utility is considered by some to be controversial because of the possibility of cross-reactivity with other fungal antigens (Longo et al., 2012). The gold standard for the diagnosis of this disease though, is made by culturing the organism from sputum or blood samples using an appropriate culture medium (Longo et al., 2012). However, this method may take some time since growth of the organism is slow. In fact, growth may be observed as early as 5 days to as late as 30 days in some cases (Varkey and Raugi, 2011). Treatment The treatment for blastomycosis, regardless of its type, is entirely medical (Longo et al., 2012). For blastomycosis, anti-fungal agents are given to patients but the choice of which anti- fungal to use is based on the clinical form of the disease, immune status of the patient, and severity of the infection (Longo et al., 2012). In general, agents such as Ketoconazole, Itraconazole, Amphotericin B, and Fluconazole can be used for the treatment of Blastomycosis. However, Itraconazole, given for 6 months, is the drug of choice for immunocompetent patients with mild to moderate pulmonary blastomycosis. For extrapulmonary cases such as bone involvement, treatment with Itraconazole is extended for a period of 12 months. Itraconazole has better bioavailability, efficacy, and less toxicity compared to other azoles (Varkey and Raugi, 2011). It must be noted, however, that any type of azole is contraindicated in pregnancy due to its teratogenic effects. Meanwhile, Amphotericin B is the first line of treatment for immunocompromised patients with blastomycosis and immunocompetent CNS blastomycosis (Longo et al., 2012). After Amphotericin B administration, Itraconazole treatment may still be needed in some cases. References Longo, D., Kasper, D., Jameson, L., Fauci, A., Hauser, S., and Loscalzo, J. 2012. Harrison' s Principles of Internal Medicine. 18th Ed. The McGraw- Hill Companies, Inc. U.S. pp 1646-1647. Varkey, B. and Raugi, G. 2011. Blastomycosis. Medscape Reference. Retrieved at: http://accessmedicine.com/content.aspx?aid=6432990. Date retrieved: April 30, 2013. Read More