Question: What creature, that is also known as the "large intestine worm," was Ivan Mackerle trying to find?

Context paragraphs:
Mongolian death worm: The Mongolian death worm (Mongolian: олгой-хорхой , olgoi-khorkhoi, "large intestine worm") is a creature

Ivan Mackerle: Ivan Mackerle (March 1942January 3, 2013) was a Czech cryptozoologist, author, design engineer, and explorer.  He organized expeditions to search for the Loch Ness monster of Scotland, the Tasmanian tiger in Australia, and the elephant bird in Madagascar.  He was most notable for his search of the Mongolian death worm, and he conducted three trips to Mongolia in 1990, 1992, and 2004.  He authored numerous books and publications and from 1998 until 2002 he was chief editor of the Czech paranormal magazine "Fantastická fakta" ("Fantastic Facts").

Basal electrical rhythm: The basal or basic electrical rhythm (BER) or electrical control activity (ECA) is the spontaneous depolarization and repolarization of pacemaker cells in the smooth muscle of the stomach, small intestine, and large intestine.  This electrical rhythm is spread through gap junctions in the smooth muscle of the GI tract.  These pacemaker cells, also called the interstitial cells of Cajal, control the frequency of contractions in the gastrointestinal tract.  The cells can be located in either the circular or longitudinal layer of the smooth muscle in the GI tract; circular for the small and large intestine, longitudinal for the stomach.  The frequency of contraction differs at each location in the GI tract beginning with 3 per minute in the stomach, then 12 per minute in the duodenum, 9 per minute in the ileum, and a normally low one contraction per 30 minutes in the large intestines that increases 3 to 4 times a day due to a phenomenon called mass movement.  The basal electrical rhythm controls the frequency of contraction but additional neuronal and hormonal controls regulate the strength of each contraction.

Pancolitis: Pancolitis or universal colitis is a very severe form of ulcerative colitis.  This form of ulcerative colitis is spread throughout the entire large intestine including the right colon, the left colon, the transverse colon, descending colon, and the rectum.  A diagnosis can be made using a number of techniques but the most accurate method is direct visualization via a colonoscopy.  Symptoms are similar to those of ulcerative colitis but more severe and affect the entire large intestine.  Patients with ulcerative colitis generally exhibit symptoms including rectal bleeding as a result of ulcers, pain in the abdominal region, inflammation in varying degrees, and diarrhea (often containing blood).  Pancolitis patients exhibit these symptoms and may also experience fatigue, fever, and night sweats.  Due to the loss of function in the large intestine patients may lose large amounts of weight from being unable to procure nutrients from food.  In other cases the blood loss from ulcers can result in anemia which can be treated with iron supplements.  Additionally, due to the chronic nature of most cases of pancolitis, patients have a higher chance of developing colon cancer.

Migrating motor complex: Migrating motor complexes (or migrating myoelectric complex or migratory motor complex or migratory myoelectric complex or MMC) are waves of electrical activity that sweep through the intestines in a regular cycle during fasting.  These motor complexes trigger peristaltic waves, which facilitate transportation of indigestible substances such as bone, fiber, and foreign bodies from the stomach, through the small intestine, past the ileocecal sphincter, and into the colon.  The MMC occurs every 45–180 minutes during the interdigestive phase (i.e., between meals) and is responsible for the rumbling experienced when hungry.  It also serves to transport bacteria from the small intestine to the large intestine and to inhibit the migration of colonic bacteria into the terminal ileum.

Trichuris vulpis: Trichuris vulpis is a whipworm that lives in the large intestine of canines in its adult stages.  Out of different types of worms, "Trichuris vulpis" is one of the smaller worms with a size ranging from 30–50 mm in length.  As the name suggests, the worm has a whip-like shape with distinct features including a small, narrow anterior head, which is the digestive part of the worm, and a larger posterior tail, which is the reproductive part of the worm.  Eggs from "T. vulpis" are oval shaped with bipolar plugs and contain a thick outer shell.  Their sizes range from 72–90 μm in length and 32–40 μm in width.  Because of their thick outer shell, "T. vulpis" eggs are very resistant to environmental extremes such as freezing or hot temperatures, thus allowing for their long viability in the outside world.

Small intestine: The small intestine or small bowel is the part of the gastrointestinal tract between the stomach and the large intestine, and is where most of the end absorption of food takes place.  The small intestine has three distinct regions – the duodenum, jejunum, and ileum.  The duodenum is the shortest part of the small intestine and is where preparation for absorption begins.  It also receives bile and pancreatic juice through the pancreatic duct, controlled by the sphincter of Oddi.  The primary function of the small intestine is the absorption of nutrients and minerals from food, using small finger-like protrusions called villi.

Gastrointestinal perforation: Gastrointestinal perforation, also known as ruptured bowel, is a hole in the wall of part of the gastrointestinal tract.  The gastrointestinal tract includes the esophagus, stomach, small intestine, and large intestine.  Symptoms include severe abdominal pain and tenderness.  When the hole is in the stomach or early part of the small intestine the onset of pain is typically sudden while with a hole in the large intestine onset may be more gradual.  The pain is usually constant in nature.  Sepsis, with an increased heart rate, increased breathing rate, fever, and confusion may occur.

Inflammatory bowel disease: Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the colon and small intestine.  Crohn's disease and ulcerative colitis are the principal types of inflammatory bowel disease.  It is important to note that not only does Crohn's disease affect the small intestine and large intestine, it can also affect the mouth, esophagus, stomach and the anus whereas ulcerative colitis primarily affects the colon and the rectum.

Trichuris trichiura: The human whipworm (Trichuris trichiura or Trichocephalus trichiuris) is a round worm (a type of helminth) that causes trichuriasis (a type of helminthiasis which is one of the neglected tropical diseases) when it infects a human large intestine.  It is commonly known as the "whipworm" which refers to the shape of the worm; it looks like a whip with wider "handles" at the posterior end.

Supporting paragraphs: Ivan Mackerle Mongolian death worm
Answer: Mongolian death worm