Pythiosis is a form of infectious disease caused by Pythium insidiosum

Pythium insidiosum

Pythium insidiosum is a species of Pythium.It can cause pythiosis....

. It occurs most commonly in dogs and horse

Horse

The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...

s, but is also found in cat

Cat

The cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...

s, cattle, and humans. The disease is typically found in young, large breed dogs. Pythium occupies swamps in late summer and infects dogs who drink water containing it. Pythium insidiosum is different from other members of the genus in that human and horse hair, skin, and decaying animal and plant tissue are chemoattractants for its zoospore

Zoospore

A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some algae, bacteria and fungi to propagate themselves.-Flagella:...

s.

Epidemiology

Pythiosis occurs in areas with mild winters because the organism survives in standing water that does not reach freezing temperatures. In the United States it is most commonly found in the Gulf states, especially Louisiana

Louisiana

Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

, but has also been found in midwest and eastern states. It is also found in southeast Asia

Southeast Asia

Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...

, eastern Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

, and South America

South America

South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

.

Pathophysiology

It is suspected that pythiosis is caused by invasion of the organism into wounds, either in the skin or in the gastrointestinal tract. The disease grows slowly in the stomach

Stomach

The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...

 and small intestine

Small intestine

The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...

, eventually forming large lumps of granulation tissue

Granulation tissue

Granulation tissue is the perfused, fibrous connective tissue that replaces a fibrin clot in healing wounds. Granulation tissue typically grows from the base of a wound and is able to fill wounds of almost any size it heals...

. It can also invade surrounding lymph node

Lymph node

A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as...

s.

Pythiosis in different animals

• Pythiosis of the skin in dogs is very rare, and appears as ulcerated lumps. Primary infection can also occur in the bones and lungs. Dogs with the gastrointestinal form of pythiosis will have severe thickening of one or more portions of the GI tract that may include the stomach, small intestine, colon, rectum, or in rare cases, even the esophagus. The resulting pathology will result in anorexia (no appetite), vomiting, diarrhea (sometimes bloody), and abdominal straining. Extensive weight loss may be evident.

• In horses, subcutaneous pythiosis is the most common form and infection occurs through a wound while standing in water containing the pathogen. The disease is also known as leeches, swamp cancer, and bursatti. Lesions are most commonly found on the lower limbs, abdomen, chest, and genitals. They are granuloma
  Granuloma
  Granuloma is a medical term for a tiny collection of immune cells known as macrophages. Granulomas form when the immune system attempts to wall off substances that it perceives as foreign but is unable to eliminate. Such substances include infectious organisms such as bacteria and fungi as well as...
  
  tous and itchy, and may be ulcerated or fistula
  Fistula
  In medicine, a fistula is an abnormal connection or passageway between two epithelium-lined organs or vessels that normally do not connect. It is generally a disease condition, but a fistula may be surgically created for therapeutic reasons.-Locations:Fistulas can develop in various parts of the...
  
  ted. The lesions often contain yellow, firm masses of dead tissue known as kunkers. It is possible with chronic infection for the disease to spread to underlying bone. In humans it can cause arteritis
  Arteritis
  Arteritis is inflammation of the walls of arteries, usually as a result of infection or auto-immune response.-Types:Some disorders have arteritis as their main feature...
  
  , keratitis
  Keratitis
  Keratitis is a condition in which the eye's cornea, the front part of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves impaired eyesight.-Types:...
  
  , and periorbital cellulitis.

• In cats pythioisis is almost always confined to the skin as hairless and edematous lesions. It is usually found on the limbs, perineum
  Perineum
  In human anatomy, the perineum is a region of the body including the perineal body and surrounding structures...
  
  , and at the base of the tail. Lesions may also develop in the nasopharynx
  Nasopharynx
  The nasopharynx is the uppermost part of the pharynx. It extends from the base of the skull to the upper surface of the soft palate; it differs from the oral and laryngeal parts of the pharynx in that its cavity always remains patent .-Lateral:On its lateral wall is the pharyngeal ostium of the...
  
  .

Treatment

Use of potassium iodide

Potassium iodide

Potassium iodide is an inorganic compound with the chemical formula KI. This white salt is the most commercially significant iodide compound, with approximately 37,000 tons produced in 1985. It is less hygroscopic than sodium iodide, making it easier to work with...

, amphotericin B

Amphotericin B

Amphotericin B is a polyene antifungal drug, often used intravenously for systemic fungal infections...

, and terbinafine

Terbinafine

Terbinafine hydrochloride is a...

has been described in the cutaneous form.