Systemic Mycoses, Biology tutorial

Introduction:

Systemic mycoses or simply deep-seated fungal infection are generally acquired through inhaling the spores of free living  fungi present as dimorphic fungi the diseases comprise blastomycosis, coccidiomycosis, histoplasmosis and cryptococcosis. Some of the systemic mycosis as well takes place in patients compromised through disease or drug treatment. Such opportunistic mycoses comprise systemic aspergillosis, candidiasis and zygomycosis.

Coccidiomycosis:

This is mainly an infection caused due to Coccidiodis immitis, a dimorphic fungus found in the soil of semi-arid regions particularly in South-Western States, California and Mexico. In the soil and on moist culture media, C. immitis grows as a mould, making barrel-shaped Arthrospores at the tip of hyphae that is simply dispersed in wind currents. Though, in humans, it grows as yeast, forming thick-walled spherules filled by endospores.

The disease is acquired through inhaling Arthrospores generally contained in dust. Mainly pulmonary coccidiomycosis builds up after an incubation period of 7 to 28 days. Skin rashes might develop by the diseases.

Endospores: Endospores are discharged by rupture of the spherule walls and build up to form new spherule in the adjacent tissue, or following dissemination, in other organs of the body. C. immitis generally cause an asymptomatic or self-limiting pulmonary illness, however a progressive and at times fatal secondary disease rarely develops. Treatment is by the utilization of intravenous amphotericin B and concomitant intrathecal therapy is needed in the meningeal form. Ketoconazole and itraconazole are as well helpful.

Blastomycosis:

Blastomycosis is a chronic infection of the lungs which might spread to the skin and bones. It is caused due to Blastomyces dermatitidis, a dimorphic fungus that grows as a mould by a septate mycelium on culture, however as a budding yeast in human tissues. Infection outcomes from inhalation of spores, particularly in cool, wet climate condition.          

Primary lung disease is generally relatively mild, however in a few weeks the disease might disseminate to other tissues.

In disseminated infection, the chronic pulmonary disease persists and abscesses and granulomatous lesions are found in most of the organs and body tissues comprising bone. Chronic cutaneous lesions take place in around 80 percent of patients having pulmonary infection; the characteristic secondary skin lesions are usually raised by a well-demarcated edge. It is from these skin lesions which the diagnosis is most frequently made.

Intravenous amphotericin B is the drug of choice in the treatment of all the forms of serious blastomycosis. Hydroxystilbamidine is employed in localized disease. Oral ketoconazole or itraconazole are as well efficient in less serious extra-central nervous system blastomycosis.

Histoplasmosis:

The causative agent of this disease is Histoplasma capsulatum, a fungus that grows in culture as a mould and as intracellular yeast in the animal tissues. The fungus is an intracellular parasite found in the soil enriched by the droppings of bats and birds, and infection outcomes from the inhalation of the spores.

Histoplasmosis is the asymptomatic or relatively mild, self-limiting pulmonary infection, however chronic or acute disseminated disease might as well take place. A chronic form of histoplasmosis takes place mostly in adults; large cavities build up from primary lesions in the lung or through reactivation of old lesions. Occasionally the acute form of the disease might spread to infect the reticulo-endothelial system and disseminate to other organs of the body. Disseminated infection takes place most frequently in old age and infancy, or in individuals having impaired immune response.

Treatment is by means of the use of intravenous amphotericin B for disseminated histoplasmosis in immunocompromised patients. Ketoconazole and itraconazole give good outcomes in less ill cases.

Cryptococcosis:

Cryptococcosis is taken through Cryptococcus Neoformans, a fungus which is generally found in the excreta of wild and domesticated bird all through the world. The birds themselves are not infected. Cryptococcosis takes place frequently as a disease of the central nervous system; however the main site of infection is the lung. It takes place sporadically all through the world however it is now seen most frequently in patients having Acquired Immune Deficiency Syndrome (AIDS). Lesions of the skin, viscera, mucosa and bones might as well take place. In its disseminated form, the disease might resemble tuberculosis.

Infection follows inhalation of the cells of the organisms to the lungs, resultant in a mild self-limiting pulmonary infection in the symptomatic infection. Lesions might take the form of small discrete nodules that might heal by a residual scar or might become enlarged, encapsulated and chronic. The meningeal form can take place in immunosuppressed individuals. Chronic meningitis or meningo-encephalitis builds up insidiously along with headaches and low-grade pyrexia, followed through changes in mental state, anorexia, visual disturbances and ultimately coma. The outcome is for all time fatal unless it is treated. Most cryptococcal infections are now seen with individuals by AIDS, 3 to 20 percent of who develop cryptococcosis.

Treatment is through the use of intravenous ampholericin B in combination all along with flucytosine. Intrathecal amphotericin B might as well be employed in severe meningeal disease. Patients having AIDS generally relapse after the initial course of therapy and might react badly to the drug. Fluconazole can be employed for treatment and as well as a maintenance therapy to control the cryptococcosis in AIDS patients.

Systemic Candidiasis:

The key causative agent of systemic candidiasis is Candida albicans. Other organisms comprised are C. tropicalis, C. glabrata and C. hisitaniae. The disease outcomes following overgrowth of such commensal yeasts in relationship by serious abnormality of the host. The abnormality might be as an outcome of immunosuppressed patients, patients treated by antibiotics or steroids or in patients after organ transplant or heart surgery. The disease might be localized or broadly disseminated and related with a septicaemia (or candidaemia).

Common sites of participation in disseminated systemic candidiasis comprise the kidney, liver, spleen, brain and gastro-intestinal tract. The symptom is the presence of white candidal lesions in the eye (or Candida endophythalmitis). Candida endocarditis generally follows surgery for the valve replacement, however as well takes place in drug addicts and occasionally in patients on immunosuppressive therapy. Infection of the kidney is generally blood-borne. Bladder infections are generally related by the presence of an indwelling urinary catheter and the infection frequently clears if the catheter is eliminated.

Intravenous amphotericin B in combination by flucytosine is the treatment of choice for most form of the systemic candidiasis. Flucytosin is not employed on its own due to the problem of resistance. Fluconazole, ketoconazole and itraconazole have as well been employed successfully.

Aspergillosis:

This is mainly caused due to Aspergillus spp, particularly among them are Aspergillus fumigatus, A. flavus, A. niger, A. terreus and A. nidulans. Inhalation of the spores of such organisms might lead to the growth of various kinds of diseases based on the location and kinds of organisms.

Aspergilloma: This is as well termed to as fungus ball. The fungus colonizes pre-existing (frequently tuberculous) cavities in the lungs and forms a compact ball of mycelium, ultimately surrounded through a dense fibrous wall. Patients are either asymptomatic or encompass only a moderate cough and sputum production. Seldom, haemophysis might take place. Surgical resection is most frequently employed to treat this condition.

Allergic aspergillosis:  This usually takes place in atopic individuals by elevated IgE level. Asthma with cosinophilia is a more chronic form. The fungus grows in the airways to generate plugs of fungal mycelia which might block off segment of the living tissues. Allergic alveolitis follows specifically in heavy and repeated exposure to a big number of spores.

Breathlessness, fever and malaise come out some hours after exposure, and repeated attacks outcome in progressive lung damage.

Invasive Aspergillosis: This is frequently caused due to Aspergillus fumigatus, and takes place mainly in severely immunocompromised individuals having serious underlying illness. The lung is the sole site of infection from which it spreads to tissues as blood vessels causing the thrombosis. Septic emboli might spread the infection in other organs, particularly the kidneys, heart and brain. Invasive aspergillosis consists of a poor prognosis and is frequently diagnosed post mortem.

Zygomycosis:

Zygomycosis is a comparatively rare, opportunistic infection caused due to saprophytic moulds of the species of Rhizopus, Mucor and Absidia. The disease is as well termed as mucormycosis or phycomycosis.

The best recognized form of the disease is rhinocerebral zygmycosis, a rapidly fulminating infection that is related with either acute diabetes mellitus or by debilitating disease like leukaemia or lymphoma. There is widespread cellulitis having rapid tissue destruction; most generally spreading from the nasal mucosa to the turbinate bone, paranasal sinuses, orbit and brain. Rhinocerebral zygomycosis is quickly fatal when untreated. Most of the diagnoses are made at necropsy.

Pulmonary and disseminated infection can take place in severely immuno-compromised individuals.

Treatment based on early diagnosis of the infection so as to let for prompt therapy having intravenous amphotericin B and aggressive surgical intervention.

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