What is Pythium?

Mary McMahon
Mary McMahon

Pythium is a genus of pathogenic parasites found in water, as well as damp, humid environments. These organisms were thought to be fungi historically and are often treated as such because they behave like pathogenic fungi. They can colonize fields, causing problems with crops and gardens, and several species also cause disease in humans or animals. Infection with Pythium is known as pythiosis.

Cases of pythiosis in cats and dogs have been recorded.
Cases of pythiosis in cats and dogs have been recorded.

The organism can remain dormant in harsh climate conditions and will return in heavy rains. This can be a problem for people attempting to control Pythium in an area like a garden, farm, or lawn, as the organisms will naturally stop causing problems when the environment dries out, only to recur as soon as it gets wet again. Regions with temperate climates are ideal for these organisms, as the winter creates standing water and mild temperatures above freezing, ideal for the spread of the organism.

A diagnosis of pythiosis requires a analysis of biopsy tissue.
A diagnosis of pythiosis requires a analysis of biopsy tissue.

In plants, Pythium attacks the roots, causing root rot. Damping off, a phenomenon where seedlings fail to thrive and eventually turn to mush, can be caused by this organism among many others. In an area like a lawn, patches of brown and unhealthy grass will appear, and as water moves underground, it will carry the parasites along with it, causing the problem to spread. There are chemical controls available for treatment of Pythium infestations, and it is also possible to allow land to lie fallow with the goal of essentially starving the organisms out.

In animals, infections with this organism lead to the development of persistent red lesions that can penetrate all the way to the bone. Livestock like cattle and horses are at especially high risk, as they may frequent areas with standing water and can easily pick up the parasites. Cases of pythiosis in humans, cats, and dogs have also been recorded. Diagnosis requires taking a biopsy specimen and sending it in for laboratory analysis, and pythiosis is often missed on initial examination and inspection.

Treatment can involve debridement of the lesion to remove the infected material, along with administration of medications. In extreme cases, amputation may be required to remove an infected limb if the infection does not respond to treatment. Prompt, attentive care by someone familiar with the organism will increase the chances of a successful and minimally invasive treatment. It is important to receive care or seek veterinary attention for any persistent lesion, especially if it grows, causes extreme pain, develops discharges, or feels hot and tender to the touch.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


My dad planted corn in his garden, and it was infected with pythium. The poor little seedlings never made it to maturity.

He planted the corn in spring before the rains came. We went through a period of rain that lasted a couple of weeks off and on, and the corn seedlings emerged, but something was obviously wrong with them.

The garden, as well as his whole yard, lies flat. So, the whole area was saturated with rain. This gave pythium an opportunity to grow.

The seedlings turned brown and shriveled away. He pulled a few up to look at the roots and found them to be mushy and brown.

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