by: Anna Seipp and Aran Lavi
Fungi are masters of environmental adaptation. As they are primarily decomposers, they are able to obtain food by breaking down organic material. It is purported, however, that at some point in the evolutionary continuum, some fungi evolved from their original saprobe state and became able to break down living tissues for food, hence enabling some to become detrimental and often destructive parasites. As it is much easier for fungi to attack plants than animals (the skin and mucus membranes provide sufficient protection against most parasitic fungi), there are more types of plant parasites than animal or human ones.
There are fifty-five species of fungi that are considered to be pathogenic to man. Out of these fifty-five, over thirty of them are classified as Dermatophytes; they cause dermatomycoses, that is, infections of the hair, skin and nails. Almost all dermatophytes are parasitic; they live on the keratinized tissues of humans and animals. The other twenty-five species are the source of far more deep-seated and systematic infections. All of these fungi are considered to be parasitic.
Originally, skin infections caused by dermatophytes were thought to be caused by either worms or lice. Hence, the name of one of the most common dermatomycoses is ringworm, which, depending on the species of the parasite fungus, can affect many areas of the human body. Almost all dermatophytic species belong to three different genuses
Microsporum (species which attack the hair and the skin), Trichophyton (species which attack the hair, the skin and the nails), and Epidermophyton (species which attack the skin and the nails). Some examples of dermatomycoses and the dermatophytes that cause them are:
Tinea capitis (Ringworm of the scalp): This infection can be caused by various species of Microsporum or Trichopyton.
Symptoms: - vary from small, scaling papules on scalp to large, cup-shaped crusts that may cause permanent baldness - may also produce inflammation and pustular abcesses around the hair follicles.
Tinea unguium (Ringworm of the nails): This infection can be caused by various species of Trichophyton or by Epidermophyton floccosum.
Symptoms: - finger and toenails thicken, lose luster and separate from the nail bed
Tinea pedis (Athlete's foot): This very common infection is caused by the Trichophyton T. mentagrophytes.
Symptoms: - an inflammatory infection - vesicles form between the toes and on the soles of the feet
- the skin peels and fissures form on the infected areas
The more serious infections caused by fungal parasites are known as deep mycoses. These infections affect tissues below the surface of the skin. They are usually chronic and far more serious than dermatomycoses. The most common and dangerous types of these infections are caused by fungi belonging to the Moniliaceae and Dematiaceae families. Some examples of such fungal parasites and their corresponding deep mycoses are:
Blastomyces dermatidis: This fungus is known to North America and manifests itself in two different types of infection. The first manifestation is a mild skin disease, while the second is a far more serious and potentially fatal pulmonary infection that causes physical damage similar to that done by tuberculosis.
Blastomyces braziliensis: This fungus is known to South America and attacks humans in two separate phases. The first phase is again a mild skin disease, while the second attacks the gastrointestinal tract. This infection has also known to be fatal.
Sporotrichum schenkii: This fungus causes an infection called sporotrichosis in both humans and animals. It enters through open wounds and can be fatal.
Hormodendrum compactum: This fungus causes an infection called chromoblastomycosis, where warty tissue forms on infected areas - usually the feet, hands, arms or legs.
Introductory Mycology, Second Edition. John Wiley and Sons, Inc., New York, 1962. p. 412-417
Carpenter, Philip, Microbiology, Fourth Edition. W.B. Saunders Company, Philadelphia, 1977. p. 390-391
Arms and Camp, Biology, Third Edition. Saunders College Publishing, 1987. p. 508-510
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