Infections of Deeper Tissues in Human

In this article we will discuss about Infections of Deeper Tissues in Human.

These infections are mainly in warm climates in people whose bare skin is exposed to soil, dust or recurrent trauma. Mycetoma is the commonest and most widespread syndrome which is caused by filamentous fungi or higher bacteria under aerobic actinomycetes. Chromoblastomycosis and subcutaneous phycomycosis are two other syndrome caused by more than one fungus.

These infections are chronic, localised and acquired by the traumatic inoculation of opportunistic organisms normally present in the soil or on thorns. Madura foot is characterised by a swelling often with sinuses discharging pus which may contain granules of varying size (0.5 to 2 mm) and colour (black, red buff).

The main actinomycetes responsible for this condition are: Nocardia brasiliensis, N. asteroides, Streptomyces madurae. They destroy soft tissue, bone, tendon and nerve.

Grains (colonies of the organisms) in the pus may be collected into the surgical gauze. Their size and colour suggest the species responsible. After crushing the granules, wet preparation and Gram-stained smears should be made. The size of the hyphae is more than 2 µ in width in fungus whereas, in case of actinomycetes, it is less than 1 µm.

Sabouraud’s medium (without cycloheximide) at 26°C can be used to cultivate the fungi and Lowenstein Jensen medium at 37°C for actinomycetes. Some are sensitive to antibiotics in vitro but none is sensitive in vitro, Nocardia sp. may be semi acid fast and are sensitive to many antibacterial antibiotics, sulphones and sulphonamide-trimethoprim mixtures—both in vivo and in vitro.

The only effective treatment for fungal mycetoma is the surgery, nocardial and streptomyces infection respond to long course of dapsone and cotrimoxazole.

(a) Chromo mycosis is a chronic warty dermatitis caused by traumatic inoculation of one of five closely related pigmented fungi: Phialophora pedrosoi, P. compacta, P. verrucosa, P. dermatidis and Cladophialophora carrionii. Microscopically, the hyphae are brown and several types of spores are produced. Treatment is not satisfactory.

(b) Subcutaneous Phycomycosis can be caused by Absidia sp. and Rhizopus sp. by infecting and penetrating the mucous membrane of the nose, sinuses and stomach when patients are in extremis.

Dimorphic Fungi:

The majority of fungi are filamentous, some exist as yeasts and other change from one form to other depending upon the conditions of growth. The last are called dimorphic fungi and include a number of pathogens; Sporothrix schenckii, Blastomyces dermatitidis, Paracoccidioides brasiliensis, Histoplasma capsulatum.

Another pathogen, coccidioides immitis is dimorphic in different way. The infections they cause are not communicable from man to be acquired by inhalation. The process is slow with cellular granulomatous reaction.

Infection with S. schenckii, usually follows injury to the hands with the contaminated splinters or thorns but may be acquired from infected animals.

A local “chancre” forms and small subcutaneous abscess, develop along the line of inflammed drainage lymphatic’s, Paracoccidioides brasileinsis causes “South American blastomycosis” which is chronic, progressive pyogenic, granulomatous disease with a predilection for lymphatic tissue.

Its main lesions are common in mucous membranes, lymph nodes, skin, spleen and intestine. It is fatal if not treated. It is acquired by inhalation. Treatment is not yet satisfactory.

Histoplasma capsulatum is a dimorphic fungus found in many parts of the world in soil enriched with the droppings of certain birds and mammals. When its spores are inhaled by a mammalian host they develop into yeasts which set up an intracellular infection of the histiocytes.

The clinical manifestations in man vary from an asymptomatic pulmonary infection to fatal generalized disease. There are many parallels with tuberculosis. The usual outcome is a small calcified peripheral focus in lung.

Coccodioides immitis is a dimorphic fungus. Its infection is acquired by inhalation and is normally asymptomatic. It has many parallels with tuberculosis and histoplasmosis. The treatment is by amphotericin B. Rhinosporidium seeberi causes the development of polyps in the sub-mucosa of the nose, mouth, conjunctiva, in the skin.

Natural infections occur in man, horses, mules and cows in most parts of the world, commonly in India and Sri Lanka.

A portion of polyp may be crushed in water between slide and coverslip. Some large cysts and many small spores should be seen, if it is Rhinosporidium seeberi. Treatment is surgical. In the year 1993 a new species of fungus, Nodulisporium sp, was found for the first time to cause Allergic Fungal Sinusitis in a young woman.