Fungi and diseases
Several species of fungi are responsible for causing diseases of man, lower animals, and valuable crop plants.
a) Diseases of Human
The fungal diseases of human are of the following two types:
1) Mycosis: these are the diseases caused by true infection by fungi.
2) Mycotoxicoses: These are the diseases caused by the ingestion of toxic fungal metabolites.
1) The mycoses
The diseases caused by fungi may be grouped into three types I) the superficial mycoses or dermatomycoses, II) the subcutaneous mycoses, and III) the deep or systemic mycoses.
I) The superficial or dermatomycoses: The fungal infections of the keratinised tissues, such as hair, nails, and skin are called dermatomycoses. Fungi that are able to cause such infections are called dermatophytes. Tinea is the common name of the disease caused by dermatophytes. Tinea pedis is known as athletes foot, Tinea capitis, is the ringworm of scalp, and Tinea corporis, is known as ringworm of the non-hairy skin of the body.
II) The subcutaneous mycoses: The fungi responsible for subcutaneous infections enter the body through a puncture wound. The most common of these diseases is sporotrichosis, caused by a saprophytic fungus, called Sporotrichum schenkii. Chromomycosis is another subcutaneous fungal infection of the foot Or hand, caused by Fonsecaea, Cladosporium and Phialophora.
III) The systemic mycoses: These are often serious and fatal diseases, caused by such fungi as Histoplasma capsulatam, Coccidioides.
Some fungi that are normally incapable of producing disease in healthy humans can cause serious and fatal diseases in persons with low resistance. Some species of Rhizopus and Mucor, cause serious infections of lungs, brain, and gastric tissues.
2) The mycotoxicoses
Mycotoxicoses is any illness that is produced by injecting the food that has been made poisonous by fungal toxic substances. These poisonous substances or toxins are called mycotoxins.
Several species of poisonous mushroom, such as Amanita phalloides are known to be highly toxic. These toxic substances cause the damage of liver cells and excitement of the nervous system. Other poisonous substances may be produced by fungi growing on grains, nuts and other agricultural produces. For example, Claviceps purpurea, growing on rye, produces a variety of poisonous alkaloids like ergometrine, ergometrinine, ergotamine and ergotaminine. If these are consumed, a disease, called ergotism develops.
b) Diseases of plants
Fungi destroy many agricultural crops, fruits, nut plants, and shade trees. When a disease spreads in epidemic form, it wipes out the whole crop and causes severe losses. Examples of diseases of plants are stem rust of wheat caused by Puccinia graminis tritici, Red rot of sugar cane caused by Colletotrichum falcatum.
c) Diseases of animals
Certain species of Trichophyton and Microsporum, are responsible for causing a number of diseases such as phycomycosis, rhinosporadiosis, and mycotic abortions, in a large number of animals.
d) Diseases of Fishes
Saprolegnia and Achlya are the common parasites of fishes. Saprolegnia ferax and S. parasitica, infect the fishes of the domestic aquaria.
Hallucinogenic fungi
A number of fungi affect the nervous system in such a manner that the consumer has hallucinations. Amanita muscaria, and Psilocybe mexicana, are the common hallucinogenic fungi.
Fungi as Allergens
A large number of fungi, e.g., Aspergillus, Penicillium, Cladosporium etc. are responsible for causing various types of allergic diseases in man.