''Pythium insidiosum'' is a species of ''

Pythium ''Pythium'' is a genus of parasitic oomycetes. They were formerly classified as fungi. Most species are plant parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet of the fungus gnat are frequent ...

'' and a member of the class

oomycota Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the resul ...

. ''Pythium insidiosum'' is mainly found in standing water and occasionally soil. Unlike most ''Pythium'' species, which are generally pathogens of terrestrial plants, ''Pythium insidiosum'' is a pathogen of

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s. It causes

pythiosis Pythiosis is a rare and deadly tropical disease caused by the oomycete ''Pythium insidiosum''. Long regarded as being caused by a fungus, the causative agent was not discovered until 1987. It occurs most commonly in horses, dogs, and humans, with ...

, mainly in

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...

dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...

s, and humans. It can also cause disease in cats. It is a non-transmissible disease and occurs mainly in tropical climate, endemic to Thailand, affecting mainly humans and horses and in Brazil, affecting mainly horses. Infection can occur in healthy mammals. The pathogen is well-adapted to mammalian body temperature, with an optimum temperature for growth of . The

cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...

s of ''Pythium insidiosum'' are composed of

β-glucan Beta-glucans, β-glucans comprise a group of β-D-glucose polysaccharides ( glucans) naturally occurring in the cell walls of cereals, bacteria, and fungi, with significantly differing physicochemical properties dependent on source. Typically, � ...

s and

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

(compared to the

chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...

walls of

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

), and their

cytoplasmic membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...

s lack

sterol Sterol is an organic compound with formula , whose molecule is derived from that of gonane by replacement of a hydrogen atom in position 3 by a hydroxyl group. It is therefore an alcohol of gonane. More generally, any compounds that contain the go ...

s, molecules that are targets of antifungals. For this reason, infection caused by ''Pythium insidiosum'' is difficult to treat.

References

Cat diseases Dog diseases Horse diseases insidiosum {{watermould-stub