Pathogens L15
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| Subcutaneous mycoses: I Chromoblastomycosis | A chronic localised disease of the skin and subcutaneous tissues. Infections are caused by the traumatic implantation of fungal elements into the skin and are chronic, slowly progressive and localised. Characterised by crusted, warty lesions usually involving the limbs world-wide distribution but more common in bare footed populations living in tropical regions. Diagnosis: skin scrapings and/or biopsy tissue. Treatment: Can involve surgical removal of tissue. Fluorocytosine & the azoles thiabendazole & itraconazole are effective. |
| II Sporotrichosis | Primarily a chronic mycotic infection of the cutaneous or subcutaneous tissues and adjacent lymphatics. Nodular regions which may ulcerate. Traumatic implantation on skin and secondary spread to joints, bones and muscles. Pulmonary sporotrichosis: caused by the inhalation of conidia, non-specific symptoms. Diagnosis : Tissue biopsy will contain very low numbers of narrow base budding yeast cells. Treatment: Cutaneous lesions respond well to saturated potassium iodide itraconazole & terbinafine have also proved to be effective. Terbinafine an allylamine - a synthetic antifungal agent it is highly lipophilic in nature and tends to accumulate in skin, nails, and fatty tissues.,Terbinafine inhibits ergosterol biosynthesis via inhibition of squalene epoxidase. |
| Systemic Mycoses: I Cryptococcus neoformans | A serious pathogenic yeast, This yeast can also reproduce sexually, It appears as an oval yeast 5-6 µm in diameter, forms buds with a thin neck, and is surrounded by a thick capsule. In the immunosuppressed host. however, it may spread through the blood to the meninges and other body areas, often causing cryptococcal meningoencephalitis. |
| II Pneumocystis carinii | P. carinii is thought to be transmitted from person to person by the respiratory route and is almost always asymptomatic. However, in persons with highly depressed immune responses, P. carinii can cause an often lethal pneumonia called PCP(Pneumocystis carinii pneumonia) |
| III Blastomycosis | Endemic in the southeastern and south-central states of North America. Outbreaks have been associated with occupational or recreational activities around streams or rivers with high content of moist soil enriched with organic debris and/or rotting wood. Infection is acquired via inhalation of the conidia, which transforms into the yeast form once in the lungs. After 30 to 45 days an acute pulmonary disease indistinguishable from bacterial pneumonia may occur. |
| IV Histoplasmosis | Condition caused by infection with the dimorphic endemic fungus Histoplasma capsulatum. The most common cause of fungal respiratory infections in the world. The infection is acquired through inhalation of Histoplasma capsulatum microconidia. The lungs are thus the most frequently affected site and chronic pulmonary disease may occur |
| V Aspergillosis | Aspergillus spp. are ubiquitous organisms, progressively associated with a growing spectrum of infections in immunocompromised hosts. |
| The three most prevalent diseases are: | Allergic bronchopulmonary Aspergillosis: Produces allergies, common in asthmatics and CF, similar symptoms to asthma. Invasive Aspergillosis: Often fatal, no good diagnostic test, very early treatment needed, usually present to people with health problems, fever and lung symptoms. Bronchoscopy helps diagnosis. Pulmonary Aspergilloma: grow within lung cavity, spores penetrate the cavity and germinate, may have no symptoms, x-ray diagnosis. |
| Treatment and Control of Systemic Pathogenic Fungi | Effective chemotherapy against systemic fungal infections is very difficult. One of the most effective antibiotics is amphotericin B, a polyene (binds to membrane sterols & affects the integrity of the fungal cell membrane). However, this antibiotic can give rise to serious side effects. Exposure to fungi can rarely be eliminated except using air filtration in restricted local environments. |
| FUNGAL PATHOGENICITY | 1.Virulence factors that promote fungal colonization: The ability to adhere, produce capsules to resist phagocytic engulfment, stimulates the production of a cytokine called GM-CSF, acquire iron from red blood cells, resistant to phagocytic destruction. 2. Virulence factors that damage the host: secrete enzymes to digest cells, secrete mycotoxins, Aflatoxins, produced by certain Aspergillus species, are especially carcinogenic |