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http://www.botany.hawaii.edu/faculty/wong/BOT135/LECT09.HTM
Fungi as Human Pathogens
AUTHOR: George J. Wong
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Superficial Infections
The superficial mycoses are the most well known since they can be readily observed.
They commonly occur on the hair, nails and skin of infected individuals. They have been recorded in various compilations of medical literature for well over a thousand years as ring worm, athlete's foot, jock itch and piedra. For each type of infection, there can also be a variety of species that may be causing the disease. Thus, we will only have a general discussion on this group of diseases.
Ringworm and Related Dermatophytes
Ringworm usually occurs on the exposed parts of the body, forming circular growths that may appear darker or lighter than the normal skin color, with symptoms that include skin lesion, rash and itching of the infected area. Ringworm infections are common where conditions are unsanitary and crowded with people and has been known since early historical time. There are indications that
ringworm was more prevalent in the recent past than now because of improvements in sanitary conditions and health habits.
The Greeks called it Herpes (=circular or ring form) and the Romans associated the disease with the larval stage of Tinea, the genus for clothes moth. The two names were eventually combined to "ringworm". Although the actual cause of ringworm was not known until the early 1800s, the practice of segregating infected individuals to prevent spread of the disease indicated that there was knowledge that this disease was contagious and prevalent, and could be passed from person to person was known prior to the cause of infection.
It was Gruby that isolated and described one of the ringworm fungi, Trichophyton, meaning "thread plant", and through inoculation on healthy parts of the scalp, was able to reproduce the disease. He also carried out the same experiment with several other human pathogenic fungi and inoculated himself with the pathogen, as well as others. Although this was a great accomplishment, Gruby also had a great deal of luck since, at the time, isolation of specific fungi was not common practice, and this was also 30 years prior to the development of techniques to grow fungi and bacteria in pure culture.
According to Ainsworth, more than 350 species of dermatophytes have been proposed and given approximately 1,000 names, which has caused some confusion in medical mycology. The proliferation in names have come about because different researchers have worked with the same species of a pathogen, in a different place and time, and each were familiar with that particular isolate of that particular species of fungus and probably not too familiar with that isolate. They grew it in culture briefly and published on it. Thus, each newly isolated dermatophytic fungus was given a name, sometimes according to the symptoms with which it was associated or according to the part of the body affected,
i.e. top of the head, neck, face, hand, arm, leg and foot, or even the geographical
region, or sometimes just for the sake of publication (due to the competitiveness of medical schools). This led to a great deal of confusion in the understanding of mycoses.
Although the first species were described in the 1840s, they were little studied until the 1940s, when the United States military personnel, while fighting in the South Pacific, during WWII, contracted ringworm and other fungi in the humid tropics (an example of advancement of knowledge due to driven research). This led to an intensive study, by the government of such fungi with many species being reduced to synonyms.
For example, 172 species were reduced to Candida albicans.
Epidemiology of Ringworm
Fungi that cause ringworm are widespread, geographically, and usually not of major concern, other than as cosmetic problems. However, cases in which these
diseases cause extreme disfigurements and infections are known to occur, but are
rare outside of the tropics, and are believed to be due to poor diet and unsanitary
condition (Christensen, 1965).
At one time ringworm was a common disease, particularly of children of poorer classes.
The inferences usually is that this was mainly a matter of such children being exposed to less soap and water than were children of the well-to-do. It is probable that deficiency in diet may also have made them more susceptible. There have been epidemics of ringworm that have developed in many cities in the United States.
Several species of fungi that cause ringworm are common on adults, and it seems highly probable that some of them are regularly present without causing any obvious symptoms. Species that cause ringworm belong to the genera Trichophyton and Microsporum. These genera of fungi are somewhat unusual in that they produce asexual spores, but not sexual spores or at least produce them so infrequently that they have not been observed. Species of fungi causing ringworm can be ecologically divided into three groups:
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Zoophilic or "animal loving."
Species infect animals primarily,
e.g. cats, dogs, horses, cows, poultry, but can readily be transmitted to people.
This is probably the most common source of ringworm in people, and is
usually caused by Microsporum canis, a species usually found on cats
and dogs. Animals that are carriers of ringworm do not necessarily show outward signs of the disease. Symptomless animals and probably people as well are carriers of these diseases. The infections are spread mainly by spores, but mycelial fragment in skin and hair can presumably also occur. Spores are very long lived and can remain alive for years in blankets, in clothing, bedding, combs and other grooming tools.
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Anthropophilic or "man loving."
Species infect people and cannot be transferred to animals.
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Geophilic or "earth loving."
Species occur naturally in soil, presumably as a saprobe, but is capable of
infecting animals and people. Another words these are facultative parasites!
There must be great differences among individuals in susceptibility to infection
of these ringworm fungi as well as great differences in susceptibility of an individuals at different times. There are many questions that remain unanswered concerning this species causing the various forms of ringworm.
Ringworm infections are conveniently divided into categories, based on the part of the body that was infected:
- Tinea capitis : Ringworm of the
scalp, eyebrow and lashes.
- Tinea corporis : Ringworm of the
body.
- Tinea cruris : Ringworm of the groin,
perineum and perianal region. Infections are commonly referred to as " jock itch ".
- Tinea unguium : Ringworm of the
nail.
- Tinea barbae : Ringworm of the
beard.
- Tinea pedis : Ringworm of the
feet. Infections are commonly referred to as athlete's foot.
- Tinea manuum : Ringworm of the
hand.
A summary of the above ringworm diseases, based on anatomical locations can be found on the Medline Plus Health Information
or Mycology on Line web page. There is also discussion on treatment for the various types of ringworms that have been omitted on this web page. Warning, both sites have very explicit graphics of these diseases!
Presumably infection is spread mainly by air-borne spores which is why veterinarians do not want ring-worm infected animals to remain in their clinics or hospitals. If this is the case, all of us at one time must be exposed to infections by various ringworm fungi.
Why is it then that few of us become infected?
Why is infection usually localized, e.g. ringworm of the scalp only occurs in part while most areas are not affected? Surely, there are enough spores produced that the entire scalp will be infected.
Sometimes one person in a family, or animal in a herd, will get ringworm and it will not spread to others, whereas other times it is highly contagious. There is a great deal to be learned about ringworm.
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http://www.geocities.com/
Fungal Infections.
Neal R. Chamberlain, Ph.D.
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B. Cutaneous mycoses - infections that extend deeper into the epidermis,
as well as invasive hair and nail diseases.
These diseases are restricted to the keritinized layers of the skin,
hair, and nails. Unlike the superficial mycoses, host immune responses
may be evoked, resulting in pathologic changes expressed in the deeper
layers of the skin. The organisms that cause these diseases are called
dermatophytes. These diseases are often called ringworm or tinea. All the
following diseases are caused by Microsporum
(other images),
Trichophyton,
and
Epidermophyton,
which
comprise 41 species.
| Disease |
Symptoms |
Identification of organism |
|
Tinea capitis |
ringworm of scalp |
presence/absence and shape of micro- and macroconidia in scrapings
of lesion, KOH mount |
|
Tinea corporis |
ringworm of trunk, arms, legs |
" |
|
Tinea manus |
ringworm of hand |
" |
|
Tinea cruris |
ringworm of groin "jock itch" |
" |
|
Tinea pedis |
ringworm of foot "athlete's foot |
" |
|
Tinea unguium |
infection of nails |
" |
|
Ectothrix |
infection of hair shaft surface |
mycelium and spores on hair shaft |
| Endothrix |
infection of hair shaft interior |
mycelium and spores in hair shaft
|
C. Subcutaneous mycoses- infections involve the dermis, subcutaneous
tissues, muscle, and fascia. These infections are chronic and are initiated
by trauma to the skin. These infections are difficult to treat and may
require surgical intervention.
| Disease |
Etiological agent |
Symptoms |
ID of organism |
|
Sporotrichosis |
Sporothrix schenckii
-
yeast
-
mold
|
Nodules and ulcers along lymphatics and at site of inoculation |
Yeast in tissue; mold at rm temp with "rosette pattern" |
|
Chromoblastomycosis |
Fonsecaea pedrosoi or compacta, Wangiella dermatitidis |
warty nodules that progress to "cauliflower-like" appearance a inoculation
site. |
copper-colored spherical yeasts called "Medlar bodies" in tissue |
|
Mycetoma |
Pseudallescheria boydii, Madurella grisea or mycetomatis |
draining sinus tracts at site of inoculation |
white, brown, yellow or black granules in exudate that are fungal colonies
|
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Many of the images are from the
Mycology Department
at University of Texas Medical Branch at Galveston
http://www.pearson.college.edu
FUNGI AS A HUMAN PARASITE.
by Mintcho Petkov
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DERMATOPHYTES
Fungi of this family cause infections on the skin, nails and scalp and they constitute around 30 out of about 55 species of fungus considered to be pathogenic for man. Leisions caused by dermatophytes are usually circular and tend to enlarge equally in all directions. These fungi usually affect the superficial keratin-rich layer
of the affected areas. They hydrolyze the keratin but only very slowly and can survive eveni in its absence.
In the past it was thought that these infections were caused by worms or lice and therefore the names of the diseases: ringworm or tinea, further qualified by the name of the body area affected (tinea capitis - ringworm of the scalp, tinea pedis - athlete's foot etc. ). There are three pathogenic genera of Dermatophytes
- Microsporum, Trichophyton and Epidermophyton.
Following is a list of the most common dermatophytic infections:
Tinea capitis
It is caused by species of Microsporum and Trichophyton. The disease
varies from small itching on the scalp to severe cases which can
cause permanent baldness. Some of the infections can result in
painful inflammations and pustular abcesses around the hair follicles.
The disease is sometimes highly contagious transmitted either directly
or via hair clippers and other fomites. Tinea capitis is seen
in two forms: endothrix infections, with the hyphae growqing only
within the hair and ectothrix infections, with growth within and
on the surface of the hair shaft.
Tinea corporis
This is the disease more commonly known as ringworm of the smooth
skin. The leisions are usually circular with a scaly center, surrounded
by an advancing circle of vesicles and papules.The leisions may
itch, particularly in warm weather. Tinea corporis is caused by
species of Microsporum and Trichophyton.
Tinea barbae
or more commonly known as `barber's itch' affects the bearded
area of the face and neck, forming dark red abcessess. The hairs
in the affected areas become brittle and lack luster. It is caused
by members of Trichophyton and more rarely Microsporum.
Tinea pedis
or `athlete`s foot` is the most common fungus infection , most
of the cases being caused by T. mentagrophytes. It results in
an inflammatory infection with vesicles between the toes and on
the soles; the skin peels and fissures form in the affected areas.
The infection can sometimes spread to hands,thighs and other areas.
Tinea unguium
is sometimes called onychomycosis, or ringworm of the nails. The
nails become opaque and brittle, lose luster and are easily separated
from the nail bed. The infection is caused by E. floccosum or
various species of Trichophyton.
DEEP-SEATED MYCOSES
The fungi that cause deep-seated mycoses are soil saprophytes,
which when inhaled produce chronic infections that progress slowly
at first but accelerate and finally lead to death.
Blastomyces dermatitidis
B. dermatitidis is dimorphic, with mycelial growth
in laboratory conditions at room temperature, but yeast-like in
infected tissues at body temperature. It is found in soil, but
less commonly than other pathogenic fungi. B. dermatitidis causes
North American blastomycosis.
Histoplasma capsulatum
This fungus is dimorphic, too. It forms yeastlike cells in the
mononuclear cells of the peripheral blood and macrophages in bone
marrow and spleen, but grows in a mycellial form in a laboratory
media at room temperature. This fungus causes Histoplasmosis
- a very common and serious disease.
Cryptococcus neoformans
This fungus is monomorphic yeastlike fungus ( it does not produce
mycellial growth under any conditions). It causes a form of meningitis.
DIAGNOSIS AND TREATMENT OF FUNGAL DISEASES
The diagnosing of fungus infections can be done through microscopic
examination of a tissue sample after it is made transparent through
warming it up with 10 per cent solution of NaOH or KOH, or by
examination of the affected areas with ultraviolet light, which
produces fluorescence with some fungi.
The treatment of fungus infections is a slow process, which may
include external treatment with undecylenic acid or other fatty
acids, thymol, salycilic acid, iodine, various ointments or antifungal
agents and sometimes internal application of big doses of the
antibiotic griseofulvin.
http://www.emedicinehealth.com/articles/15983-1.asp
Ringworm on Scalp Overview.
by anonymous
Scalp ringworm (tinea capitis) is a very common fungal infection among children throughout the world. Fungal organisms known as dermatophytes cause scalp ringworm by superficially infecting certain types of tissue found in hair, skin, and nails. This forms the crusty, scaly patches associated with scalp ringworm.
- In the United States, an estimated 3-8% of the population is affected by scalp ringworm. Some people can be carriers of the organism and spread it to others in the household. In other countries, an estimated 9.6% of people are affected, and nearly 40% can be carriers.
- Children aged 4-14 years are most likely to develop ringworm of the scalp, although it can occasionally appear in adults.
- Scalp ringworm occurs most frequently in urban areas among people with low incomes living in overcrowded quarters.
- This disease tends to be more severe in children with weakened immune systems, such as those with diabetes, AIDS, or cancer.
- Ringworm found on the body differs from scalp ringworm and is caused by a separate organism.
Ringworm on Scalp Causes
Dermatophytes can be found in humans, other animals (most commonly household pets such as cats, dogs, and farm animals such as cattle), and soil. Fungal spores can be transmitted through contact with an infected person, fallen infected hairs, or fomites, which are contaminated objects.
These may include objects such as barbershop instruments, hats, movie theater seats, hairbrushes, bedding, and clothing. Contact alone with one of these carriers may not be enough to cause an infection. However, coupled with minor trauma to the scalp, such as scratches or tight braiding, spores can enter through the stratum corneum (a layer of the skin). Here, dermatophytes invade and digest the tissue’s keratin (a type of protein) as the organisms grow.
Ringworm on Scalp Symptoms
The typical signs of scalp ringworm infection are reddening, crusting, and scaling of the scalp. Intense itching usually occurs as well. Up to 50% of hair loss among children is caused by scalp ringworm. Lymph nodes in the neck region may become enlarged with all types of scalp ringworm organisms. The specific pattern depends on the infecting organisms.
-
Black dot ringworm: The organism Trichophyton, which has become the most common fungi causing tinea capitis in the United States within the last several decades, causes black dot ringworm. This organism causes infections within the hair shaft. The hair becomes extremely brittle and breaks off at the surface of the scalp. The remaining portion of the hair is left behind in the follicle, creating the "black dot" appearance. Patches of hair loss commonly result.
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Gray patch ringworm: The organism Microsporum, which was the most common fungus in the United States in the 1940s and 1950s, causes gray patch ringworm. Today, it is much less common in the United States but continues to be the dominant cause of scalp ringworm in Eastern Europe. In this pattern, the lesions start as small, red bumps around the hair shaft. The lesions then grow outward, forming red, scaly, and circular "rings" that are dry but not inflamed. All hairs in the infected area appear gray and dull, and they frequently break off. Numerous areas of hair loss result. Intense itching is common.
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Inflammatory ringworm: Fungi from animals or soil commonly cause this inflammatory ringworm, which can look like areas containing small pustules or abscesses or kerion formations. Kerions are elevated boggy masses oozing pus and studded with broken hairs. Fever, pain, itchiness, and tender, enlarged lymph nodes are common. Inflammatory ringworm can result in permanent scarring and hair loss.
NOTE: Once effective antifungal therapy has started, the child may develop a widespread "id" reaction. This involves itchy, raised bumps that begin on the face and then spread to the trunk. The body’s immune response causes this reaction to the dermatophyte and is probably not an allergic reaction to the medication. Thus, the treatment plan usually does not need to be changed or discontinued. However, a person who notices these changes should talk with the doctor to make sure cause of the reaction is not potentially dangerous.
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