Histoplasmosis | |
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Other names | Cave disease, [1] Darling's disease, [1] Ohio valley disease, [1] Reticuloendotheliosis, [1] Spelunker's lung and Caver's disease |
Histoplasma capsulatum . Methenamine silver stain showing histopathologic changes in histoplasmosis | |
Specialty | Infectious disease |
Histoplasmosis is a fungal infection caused by Histoplasma capsulatum . [2] [3] Symptoms of this infection vary greatly, but the disease affects primarily the lungs. [4] Occasionally, other organs are affected; called disseminated histoplasmosis, it can be fatal if left untreated.
H. capsulatum is found in soil, often associated with decaying bat guano or bird droppings. Disruption of soil from excavation or construction releases infectious spores that can be inhaled by humans. H. capsulatum has a one to two week incubation period within human lungs before symptoms arise. [5] The disease is common among AIDS patients due to their immunosuppression. [6]
From 1938 to 2013 in the US, 105 outbreaks were reported in a total of 26 states plus Puerto Rico. In 1978 to 1979 during a large urban outbreak in which 100,000 people were exposed to the fungus in Indianapolis, [7] victims had pericarditis, rheumatological syndromes, esophageal and vocal cord ulcers, parotitis, adrenal insufficiency, uveitis, fibrosing mediastinitis, interstitial nephritis, intestinal lymphangiectasia, and epididymitis. Histoplasmosis mimics colds, pneumonia, and the flu, and can be shed by bats in their feces.
If symptoms of histoplasmosis infection occur, they start within 3 to 17 days after exposure; the typical time is 12–14 days. Most affected individuals have clinically silent manifestations and show no apparent ill effects. The acute phase of histoplasmosis is characterized by nonspecific respiratory symptoms, often cough or flu-like. Chest X-ray findings are normal in 40–70% of cases. [8] Chronic histoplasmosis cases can resemble tuberculosis; [9] [10] disseminated histoplasmosis affects multiple organ systems and is fatal unless treated. [11]
While histoplasmosis is the most common cause of mediastinitis, this remains a relatively rare disease. Severe infections can cause hepatosplenomegaly, lymphadenopathy, and adrenal enlargement. [4] Lesions often left calcification nodules as they are healed. [12]
Presumed ocular histoplasmosis syndrome causes chorioretinitis, where the choroid and retina of the eyes are scarred, resulting in a loss of vision not unlike macular degeneration. Despite its name, the relationship to Histoplasma is controversial. [13] [14] Distinct from POHS, acute ocular histoplasmosis may rarely occur in immunodeficiency. [15] [16]
In absence of proper treatment and especially in immunocompromised individuals, complications can arise. These include recurrent pneumonia, respiratory failure, fibrosing mediastinitis, superior vena cava syndrome, pulmonary vessel obstruction, and progressive fibrosis of lymph nodes. Fibrosing mediastinitis is a serious complication and can be fatal. Smokers with structural lung disease have higher probability of developing chronic cavitary histoplasmosis.[ citation needed ]
After healing of lesions, hard, calcified lymph nodes can erode the walls of the airway, causing hemoptysis. [17]
H. capsulatum grows in soil and material contaminated with bird or bat droppings (guano). The fungus has been found in poultry-house litter, caves, areas harboring bats, and bird roosts (particularly those of starlings). The fungus is thermally dimorphic; in the environment, it grows as a brownish mycelium, and at body temperature (37 °C in humans), it morphs into a yeast. Histoplasmosis is not contagious but is contracted by inhalation of the spores from disturbed soil or guano. [4] The inoculum is represented principally by microconidia. These are inhaled and reach the alveoli. In the alveoli, macrophages ingest these microconidia. They survive inside the phagosome. As the fungus is thermally dimorphic, these microconidia are transformed into yeast. They grow and multiply inside the phagosome. The macrophages travel in lymphatic circulation and can spread the disease to different organs. [18]
Within the phagosome, the fungus has an absolute requirement for thiamine. [19] Cell-mediated immunity for histoplasmosis develops within 2 weeks. If the patient has strong cellular immunity, macrophages, epithelial cells, and lymphocytes surround the organisms and contain them, and eventually calcify. In immunocompromised individuals, the organisms disseminate to different organs such as bone, spleen, liver, adrenal glands, and mucocutaneous membranes, resulting in progressive disseminated histoplasmosis. Chronic lung disease can manifest. [20]
Clinically, a wide spectrum of disease manifestations occurs, making diagnosis somewhat difficult. More severe forms include the chronic pulmonary form, often occurring in the presence of underlying pulmonary disease, and a disseminated form, which is characterized by the progressive spread of infection to extrapulmonary sites. Oral manifestations have been reported as the main complaint of the disseminated forms, leading the patient to seek treatment, whereas pulmonary symptoms in disseminated disease may be mild or even misinterpreted as flu. [21] Histoplasmosis can be diagnosed by samples containing the fungus taken from sputum (via bronchoalveolar lavage), blood, or infected organs. It can also be diagnosed by detection of antigens in blood or urine samples by ELISA or polymerase chain reaction. Antigens can cross-react with antigens of African histoplasmosis (caused by Histoplasma duboisii ), blastomycosis, coccidioidomycosis, paracoccidioidomycosis, and talaromycosis infection. Histoplasmosis can also be diagnosed by a test for antibodies against Histoplasma in the blood. Histoplasma skin tests indicate whether persons have been exposed, but do not indicate whether they have the disease. [4] Formal histoplasmosis diagnoses are often confirmed only by culturing the fungus directly. [6] Sabouraud agar is one agar growth medium on which the fungus can be cultured. Cutaneous manifestations of disseminated disease are diverse and often present as a nondescript rash with systemic complaints. Diagnosis is best established by urine antigen testing, as blood cultures may take up to 6 weeks for diagnostic growth to occur and serum antigen testing often comes back with a false negative before 4 weeks of disseminated infection. [22]
Histoplasmosis may be divided into these types: [23] : 316–317
Testing or decontaminating most sites that may be contaminated with H. capsulatum is impractical, but the sources below list environments where histoplasmosis is common, and precautions to reduce a person's risk of exposure, in the three parts of the world where the disease is prevalent. Precautions common to all geographical locations would be to avoid accumulations of bird or bat droppings.[ citation needed ]
The US National Institute for Occupational Safety and Health provides information on work practices and personal protective equipment that may reduce the risk of infection. [24]
A review paper includes information on locations in which Histoplasma has been found in Africa (in chicken runs, on bats, in the caves bats inhabit, and in soil), and a thorough reference list including English, French, and Spanish language references. [25]
In the majority of immunocompetent individuals, histoplasmosis resolves without any treatment. Antifungal medications are used to treat severe cases of acute histoplasmosis and all cases of chronic and disseminated disease. Typical treatment of severe disease first involves treatment with amphotericin B, followed by oral itraconazole. [26] [27]
Liposomal preparations of amphotericin B are more effective than deoxycholate preparations. The liposomal preparation is preferred in patients who might be at risk of nephrotoxicity, although all preparations of amphotericin B have risk of nephrotoxicity. Individuals taking amphotericin B are monitored for renal function. [28] Liposomal amphotericin B is better at treating people with progressive disseminated Histoplasmosis and underlying HIV when compared to deoxycholate amphotericin B. Meanwhile, fluconazole performs poorly when compared to other azoles. [29]
Treatment with itraconazole must continue for at least a year in severe cases, [30] while in acute pulmonary Histoplasmosis, 6 to 12 weeks treatment is sufficient. Alternatives to itraconazole are posaconazole, voriconazole, and fluconazole. Individuals taking itraconazole are monitored for hepatic function.[ citation needed ]
About 90% of patients with normal immune systems regain health without any intervention. Less than 5% need serious treatments.[ citation needed ]
H. capsulatum is found throughout the world. It is endemic in certain areas of the United States, particularly in states bordering the Ohio River valley and the lower Mississippi River. The humidity and acidity patterns of soil are associated with endemicity. Bird and bat droppings in soil promote the growth of Histoplasma. Contact with such soil aerosolizes the microconidia, which can infect humans. It is also common in caves in Southern and East Africa. Positive histoplasmin skin tests occur in as many as 90% of the people living in areas where H. capsulatum is common, such as the eastern and central United States. [4]
In Canada, the St. Lawrence River Valley is the site of the most frequent infections, with 20–30% of the population testing positive. [31] A review of reported cases in 2018 showed disease presence throughout Southeast Asia, [32] In India, the Gangetic West Bengal is the site of most frequent infections, with 9.4% of the population testing positive. [33] H. c. capsulatum was isolated from the local soil proving endemicity of histoplasmosis in West Bengal. [34]
In non-endemic countries, 40-50% of histoplasmosis cases are diagnosed in immunocompromised patients (HIV/AIDS, transplanted patients, cancer patients). [35]
H. capsulatum is commonly found across the United States. The fungus can grow in any materials corrupted with bird and bat droppings, but particularly manifests in soils. [36] Histoplasma can present itself as an occupational hazard through causation of the infection Histoplasmosis. Workers in a variety of fields can be exposed to the fungus as spores can be released into the air through any activities which disturb soil. [37] Due to this, occupations at a higher risk for exposure include construction and demolition, landscaping, mining, quarrying, oil and gas extraction, agriculture and forestry industries. [37] Common symptoms in workers are similar to the ones from the exposed general public, such as nonspecific respiratory symptoms like a cough. However, workplace exposures tend to lead to larger outbreaks than non-occupational histoplasmosis, [36] and scientific reviews have shown that occupational histoplasmosis accounts for approximately one third of all documented outbreaks. [38] Though the disease is usually not severe, there have been instances of outbreaks among workers leading to death. [39]
These occurrences emphasize the importance of protective measures for workers. The CDC advises that those who work in potentially hazardous environments reduce their exposure as much as possible following the hierarchy of hazard controls. [37] They recommend that any build up of bird and bat droppings should be avoided if possible, but if it is unpreventable various engineering, administrative controls and personal protective equipment can be implemented in the workplace. [40] The CDC also suggests that workplaces should be responsible for administrative controls such as developing a safety plan, posting notice of the risk of exposure, disposing of any potentially contaminated materials, and providing proper education on the dangers associated with histoplasma. [37] Adequate personal protective equipment includes a respirator, hooded coveralls, shoe coverings, gloves, and eye protection. [40]
Histoplasma was discovered in 1906 by Samuel T. Darling, [41] but only in the 1930s was it discovered to be a widespread infection. Before then, many cases of histoplasmosis were mistakenly attributed to tuberculosis, and patients were mistakenly admitted to tuberculosis sanatoria. Some patients contracted tuberculosis in these sanatoriums. [42]
Coccidioidomycosis, is a mammalian fungal disease caused by Coccidioides immitis or Coccidioides posadasii. It is commonly known as cocci, Valley fever, as well as California fever, desert rheumatism, or San Joaquin Valley fever. Coccidioidomycosis is endemic in certain parts of the United States in Arizona, California, Nevada, New Mexico, Texas, Utah, and northern Mexico.
Talaromyces marneffei, formerly called Penicillium marneffei, was identified in 1956. The organism is endemic to southeast Asia, where it is an important cause of opportunistic infections in those with HIV/AIDS-related immunodeficiency. Incidence of T. marneffei infections has increased due to a rise in HIV infection rates in the region.
Cryptococcosis is a potentially fatal fungal infection of mainly the lungs, presenting as a pneumonia, and in the brain, where it appears as a meningitis. Coughing, difficulty breathing, chest pain and fever are seen when the lungs are infected. When the brain is infected, symptoms include headache, fever, neck pain, nausea and vomiting, light sensitivity and confusion or changes in behavior. It can also affect other parts of the body including skin, where it may appear as several fluid-filled nodules with dead tissue.
Coccidioides immitis is a pathogenic fungus that resides in the soil in certain parts of the southwestern United States, northern Mexico, and a few other areas in the Western Hemisphere.
Blastomycosis, also known as Gilchrist's disease, is a fungal infection, typically of the lungs, which can spread to brain, stomach, intestine and skin, where it appears as crusting purplish warty plaques with a roundish bumpy edge and central depression. Around half of people with the disease have symptoms, which can include fever, cough, night sweats, muscle pains, weight loss, chest pain, and fatigue. Symptoms usually develop between three weeks and three months after breathing in the spores. In 25% to 40% of cases, the infection also spreads to other parts of the body, such as the skin, bones or central nervous system. Although blastomycosis is especially dangerous for those with weak immune systems, most people diagnosed with blastomycosis have healthy immune systems.
An opportunistic infection is an infection caused by pathogens that take advantage of an opportunity not normally available. These opportunities can stem from a variety of sources, such as a weakened immune system, an altered microbiome, or breached integumentary barriers. Many of these pathogens do not necessarily cause disease in a healthy host that has a non-compromised immune system, and can, in some cases, act as commensals until the balance of the immune system is disrupted. Opportunistic infections can also be attributed to pathogens which cause mild illness in healthy individuals but lead to more serious illness when given the opportunity to take advantage of an immunocompromised host.
Sporotrichosis, also known as rose handler's disease, is a fungal infection that may be localised to skin, lungs, bone and joint, or become systemic. It presents with firm painless nodules that later ulcerate. Following initial exposure to Sporothrix schenckii, the disease typically progresses over a period of a week to several months. Serious complications may develop in people who have a weakened immune system.
Mediastinitis is inflammation of the tissues in the mid-chest, or mediastinum. It can be either acute or chronic. It is thought to be due to four different etiologies:
Talaromycosis is a fungal infection that presents with painless skin lesions of the face and neck, as well as an associated fever, anaemia, and enlargement of the lymph glands and liver.
Aspergillosis is a fungal infection of usually the lungs, caused by the genus Aspergillus, a common mould that is breathed in frequently from the air, but does not usually affect most people. It generally occurs in people with lung diseases such as asthma, cystic fibrosis or tuberculosis, or those who are immunocompromised such as those who have had a stem cell or organ transplant or those who take medications such as steroids and some cancer treatments which suppress the immune system. Rarely, it can affect skin.
Paracoccidioidomycosis (PCM), also known as South American blastomycosis, is a fungal infection that can occur as a mouth and skin type, lymphangitic type, multi-organ involvement type (particularly lungs), or mixed type. If there are mouth ulcers or skin lesions, the disease is likely to be widespread. There may be no symptoms, or it may present with fever, sepsis, weight loss, large glands, or a large liver and spleen.
Histoplasma capsulatum is a species of dimorphic fungus. Its sexual form is called Ajellomyces capsulatus. It can cause pulmonary and disseminated histoplasmosis.
Mucormycosis, also known as black fungus, is a severe fungal infection that comes under fulminant fungal sinusitis, usually in people who are immunocompromised. It is curable only when diagnosed early. Symptoms depend on where in the body the infection occurs. It most commonly infects the nose, sinuses, eyes and brain resulting in a runny nose, one-sided facial swelling and pain, headache, fever, blurred vision, bulging or displacement of the eye (proptosis), and tissue death. Other forms of disease may infect the lungs, stomach and intestines, and skin. The fatality rate is about 54%.
Geotrichosis is a mycosis caused by Geotrichum candidum.
Fungal meningitis refers to meningitis caused by a fungal infection.
African histoplasmosis is a fungal infection caused by Histoplasma capsulatumvar. duboisii, or Histoplama duboisii (Hcd). Disease has been most often reported in Uganda, Nigeria, Zaire and Senegal, as Hcd is exclusive to Africa. In human disease it manifests differently than histoplasmosis, most often involving the skin and bones and rarely involving the lungs. Also unlike Hcc, Hcd has been reported to rarely present in those with HIV, likely due to underreporting. However, this along with the differences in Hcc and Hcd have been disputed.
Ochroconis gallopava, also called Dactylaria gallopava or Dactylaria constricta var. gallopava, is a member of genus Dactylaria. Ochroconis gallopava is a thermotolerant, darkly pigmented fungus that causes various infections in fowls, turkeys, poults, and immunocompromised humans first reported in 1986. Since then, the fungus has been increasingly reported as an agent of human disease especially in recipients of solid organ transplants. Ochroconis gallopava infection has a long onset and can involve a variety of body sites. Treatment of infection often involves a combination of antifungal drug therapy and surgical excision.
Histoplasma duboisii is a saprotrophic fungus responsible for the invasive infection known as African histoplasmosis. This species is a close relative of Histoplasma capsulatum, the agent of classical histoplasmosis, and the two occur in similar habitats. Histoplasma duboisii is restricted to continental Africa and Madagascar, although scattered reports have arisen from other places usually in individuals with an African travel history. Like, H. capsulatum, H. duboisii is dimorphic – growing as a filamentous fungus at ambient temperature and a yeast at body temperature. It differs morphologically from H. capsulatum by the typical production of a large-celled yeast form. Both agents cause similar forms of disease, although H. duboisii predominantly causes cutaneous and subcutaneous disease in humans and non-human primates. The agent responds to many antifungal drug therapies used to treat serious fungal diseases.
Emmonsiosis, also known as emergomycosis, is a systemic fungal infection that can affect the lungs, generally always affects the skin and can become widespread. The lesions in the skin look like small red bumps and patches with a dip, ulcer and dead tissue in the centre.
Chester Wilson Emmons was an American scientist, who researched fungi that cause diseases. He was the first mycologist at the National Institutes of Health (NIH), where for 31 years he served as head of its Medical Mycology Section.