Fungi are saprophytic and parasitic nucleated eukaryotes lacking chlorophyll. They are found in environment as free living organisms; they differ from eukaryotes and hence classified under a separate kingdom. Some fungi reproduce by spreading microscopic spores. These spores are often present in the air, where they can be inhaled or come into contact with the surfaces of the body, primarily the skin. Consequently, fungal infections usually begin in the lungs or on the skin. Of the wide variety of spores that land on the skin or are inhaled into the lungs, most do not cause infection. Except for some superficial skin infections, fungal infections are rarely passed from one person to another. Typically, if the immune system is normal, fungal infections do not spread to organs deep in the body. Humans are always exposed to fungi however they do not develop any fungal disease but may cause many opportunistic infections. Fungal infections have a complex relation with the host as they can switch from one infection to another. Fungal infections are associated with defective cellular immunity and impaired T cell function. They can occur both in immunocompetent and immune compromised hosts.
Certain types of fungi (such as Candida) are mostly present on body surfaces or in the intestine. Most of these fungi are harmless however sometimes; these fungi sometimes cause localized infections of the skin and nails, vagina or mouth. Fungi rarely cause serious harm, except in people who have a weakened immune system or when they have foreign material, such as an intravenous catheter or an artificial joint or heart valve, in their body.
The prevalence of fungal infections have risen in the present day world are due to many reasons
a) Increased HIV epidemic has led to the increased prevalence of fungal pathogen.
b) People with autoimmune disease (AID), cancer have a deleterious effect on the immune system and hence the increased occurrence of fungi.
c) Complex surgical procedures increase the risk of fungi in people.
d) Antibiotics against bacteria were associated with increased incidence of candida infection as antibiotics disrupt the host microbial flora and promote super infection with yeast.
Fungal infections are hence a major problem in the present day scenario however the immune system of the host which includes mainly the humoral and cell mediated defenses against fungi are very effective against fungi.
Host - fungal interactions
Fungi mostly require a stable host -pathogen which is characteristic by a strong immune response enough to allow the host to survive without eradicating the pathogen; hence forming commensalism and dormancy is prominent. The balance between pro-inflammatory and anti-inflammatory signaling is important for an effective host - pathogen interaction. The virulence is shared by both the host and pathogen at their interface, regardless the mode of its generation and maintenance. Studies have shown the molecular mechanism by which pathogen adhere with the host, blastomyces dermatitidis and candida albicans both their molecules have being identified on the fungal surface that can influence attachment to the mammalian cells. The WI-1, a 120 kd cell wall antigen of blastomyces dermatitidis elicits strong immune response during infection, these antigen express adhesions properties and virulence. Whereas in candida albicans it appears to be highly complex, stating that multiple component of the cell wall have being associated with this process. It is seen that Cryptococcus neoformans survives after the ingestion of macrophages inside the phagocytic cells both in vitro and in vivo, which appears to be persistence of infection. Chloroquine is suggested to be the therapy for Cryptococcus.
Laboratory tests can be used to detect fungal infections and some of them are:
â€¢ Microscopic examinations, such as potassium hydroxide (KOH) preparation and calcofluor white stain.
â€¢ Fungal culture and susceptibility testing
Clinical evaluation can also be used to detect fungal infections, for instance many skin infections have characteristic signs, such as the appearance of infected nails and typical locations on the body - such as athlete's foot between the toes. A clinical evaluation cannot, however, definitively tell the doctor which microorganism is causing a fungal infection. That is when the microscopic examinations, fungal culture and susceptibility test come into play.
Other tests that may be ordered in conjunction with fungal tests include:
â€¢ Gram stain - a rapid test performed to microscopically identify bacteria and yeasts in a sample.
â€¢ Bacterial culture - rules out bacterial infection or determines if a concurrent bacterial infection exists.
â€¢ AFB smear and culture - may be used to rule out tuberculosis or infection.
â€¢ Blood culture - ordered when septicemia is suspected.
â€¢ DNA or RNA testing- detects genetic material of a specific organism; not commonly used for identifying fungi.
Sometimes imaging scans like x-rays may be done to detect fungal masses, such as in the lungs, and to evaluate the extent of tissue damage.
Several drugs effective against fungal infections are available, but the structure and chemical makeup of fungi make them difficult to kill. Antifungal drugs may be applied directly to a fungal infection of the skin or other surface, such as the vagina or the inside of the mouth. Antifungal drugs may also be taken by mouth or injected when needed to treat more serious infections. For serious infections, several months of treatment are often needed.
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