Stomach Parasites Types, Causes and Symptoms

The term parasite is often used loosely to refer to any microbe that infects or infects parts of the body. However,a  parasite typically lives within a host organism, deriving nutrients from it without causing any severe disease or death. Bugs on the other hand refers to bacteria, protozoa and viruses that can cause disease and sometimes even lead to life-threatening complications.

What is a stomach parasite?

The term stomach parasite is often used loosely and incorrectly to refer to intestinal parasites like  worms (helminths), stomach bacteria like H.pylori or viruses, bacteria and protozoa that can cause gastroenteritis. Parasitic worms can cause long term infestation of the gut, spanning years and even decades, with mild or even no symptoms at the outset. Microscopic pathogens like bacteria, protozoa and viruses cause shorter term diseases usually with intense symptoms.

The stomach is a highly acidic environment and parasitic worms cannot thrive in it. The intestines is the preferred habitat for these parasitic intestinal worms. Even most bacteria, protozoa and viruses cannot thrive in the stomach for the long term and instead cause acute gastrointestinal diseases. However, some bacteria (specifically H.pylori) has adapted to surviving in the harsh acidic environment of the human stomach.

Types of Stomach Parasites

Due to the inaccurate term of stomach parasites and bugs, a number of different organisms have been discussed below. Not all of these organisms are parasites. Some naturally reside in the human gut without causing under any disease under normal circumstances. Others can cause infections or infestations.

Normal Intestinal Flora

There are various different species of bacteria and yeasts living in the gut, mainly in the large intestine. This is known as the normal intestinal flora or also commonly as the “good bowel bacteria”. These microbes are not parasites.

It has a symbiotic relationship with human hosts meaning that both the microbes and humans benefit from each other. When these bacteria and yeasts are eradicated or if its population size is disrupted then it can cause various gastrointestinal disorders. The normal intestinal flora is not present in the stomach.

Helicobacter Pylori

Helicobacter pylori (H.pylori) is a spiral-shaped bacterium with tail-like projections (flagellae) that can infect the stomach. It has mechanisms to survive the acidic environment of the stomach. The bacteria burrows into the stomach surface and attaches itself. It then secretes an enzyme which produces ammonia, an alkali that can neutralize the stomach acid around the bacterium. H.pylori is one of the common causes of gastritis.

H.pylori stomach bacteria

Stomach Bugs

The term stomach bugs is a rather crude, non-medical term for viruses, bacteria and protozoa that can infect the stomach. Often these bugs also infect the small intestine and sometimes even the large intestine to cause gastroenteritis. Some of these bugs may release toxins which can cause the disease. When transmitted through food, the resulting disease is also known as food poisoning.

Also refer to:

Intestinal Parasites

The term intestinal parasites is synonymous with intestinal worms (helminths) but can also refer to other organisms like protozoa. The latter is a single-celled organism that causes diseases like cryptosporidiosis, giardiasis, trichomoniasis and toxoplasmosis. However, the focus in this article will be on intestinal worms (helminths).

Worms are multi-cellular organisms that can reside in the intestines (not the stomach) for long periods of time. The common intestinal worms in humans include tapeworms, roundworms and pinworms. These worms feed on the digested food in the intestine or on human blood.


Also refer to the list of human body parasites.

Causes of Stomach Parasites

Stomach parasites or bugs are transmitted through various ways. This can vary depending on the type of parasite or bug. Transmission can be direct or indirect and may be vehicle-borne, vector-borne or airborne. Here are some of the possible methods of spread.

Food and Water

Consuming food and water contaminated with the parasite or bug, including its eggs where relevant, is one of of the more common methods of spread. Often the food and water may be contaminated with fecal particles that contains the bugs or parasites and its eggs.


The secretions of an infected person, such as saliva and nasal mucus, may contain the bugs which can then be aerosolized into the air during coughing or sneezing. It can then be contracted by a person who inhales or ingests these droplets.

Direct Contact

The secretions or fecal particles of an infected person can spread the bugs or parasites through direct contact such as touch. This is a greater risk for caregivers who are in contact with an infected person and for health care workers but can be avoided in most instances with proper hygiene.


Fecal particles and secretions containing bugs or parasites and its eggs can be indirectly transmitted through inanimate objects like doorknobs or utensils. These objects are referred to as fomites.


Certain insects can also transmit bugs and parasites. These insects are known as vectors and mechanically spread the infection from one person to another.

International Travel

Although some of these parasites and bugs can be contracted anywhere in the world, others are more likely to be contracted with international travel or visiting areas with poor sanitation and hygiene. However, the common method of spread in these areas is through food and water but can also occur through droplet spread, direct contact, fomites and vectors.

Signs and Symptoms

Acute signs and symptoms are more likely associated with bugs (bacteria, viruses or protozoa). This may include:

  • Diarrhea
  • Vomiting
  • Nausea
  • Abdominal pain
  • Fever
  • Malaise
  • Loss of appetite

However, some microbes like protozoa can cause long term infections especially in people with weakened immune systems.

Chronic signs and symptoms are more often associated with parasites, mainly intestinal worms. There may be no signs and symptoms at the outset and even when present the symptoms are usually not as severe as with acute gastrointestinal conditions. These signs and symptoms may include:

  • Diarrhea
  • Nausea
  • Vomiting
  • Abdominal pains
  • Itchy rectum or anus
  • Fatigue
  • Weight loss

Stomach parasites or bugs should be diagnosed by a medical professional. Often laboratory tests may need to be done on blood or stool samples. Treatment is commenced once a definitive diagnosis is reached.


  1. Parasites.

Last updated on September 25, 2018.

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