Stomach Parasites – Types, Symptoms, Causes of Stomach Bugs

Parasites are microorganisms that invade the various tissues of the body and live off the host. A parasite does not usually cause a severe disease. Instead, it keeps on deriving nutrients from the host tissues without killing the host. A variety of microorganisms could become parasites in the human body.

What is a stomach parasite?

The term “stomach parasite” is not an accurate term. From a non-medical perspective, people often refer to the entire abdominal region as the stomach. However, the abdomen contains many other organs besides the stomach. The human stomach is a highly acidic environment.

This is due to the presence of gastric acid (hydrochloric acid or HCl) with a very low pH. The highly acidic gastric contents do not allow most parasites to grow in the stomach. The exception is a bacteria known as Helicobacter pylori (commonly abbreviated as H. pylori), which causes gastric ulcers. Helicobacter pylori is able to survive in the extremely acidic stomach environment.

Read more on acidic stomach.

The term “stomach parasite” is usually used to refer to intestinal parasites such as worms (also known as helminths). The intestine is the preferred site of worm infestation. Parasitic worms can live within the intestine for years and decades without causing any major symptoms. On the other hand, microorganisms such as bacteria, virus and protozoa usually cause diseases that show immediate signs and symptoms.

Signs and Symptoms

Depending on the parasitic species, the signs and symptoms associated with stomach parasites could either be acute or chronic in nature. The following are some of the acute signs and symptoms that may indicate an infection with bacteria, virus or protozoa:

  • Nausea and vomiting
  • Diarrhea
  • Loss of appetite
  • Abdominal pain
  • Malaise
  • Fever

Protozoan parasites or intestinal worms most often cause chronic signs and symptoms. In many cases, no signs and symptoms may be evident at the outset. Some of the chronic signs and symptoms associated with intestinal parasites include:

  • Nausea and vomiting
  • Diarrhea
  • Weight loss
  • Fatigue
  • Abdominal pain
  • Itching in the rectum or the anus

The signs and symptoms in the case of stomach parasites are usually not as severe as the acute signs and symptoms caused by pathogenic infections. Chronic infections usually occur in people with a weak immune system. Effective treatment of stomach parasites requires diagnosis of the cause by a trained medical professional. A definitive diagnosis of the causative parasite usually requires laboratory tests on stool or blood samples from the patient.

Types of Stomach Parasites

Since the term “stomach parasite” could be used to refer to a host of microbes (not all of which are necessarily parasites), we can discuss normal, pathogenic, and parasitic intestinal flora under this inaccurate umbrella term. The following microbes may be referred to as stomach parasites in everyday usage:

Normal flora of the intestine

Many different bacteria and yeasts are normal residents of the human intestine. These microbes constitute the normal microbial flora of the human intestine and are predominantly located within the large intestine. The stomach does not contain these bacteria and fungi. Although these microbes live within the human intestine, they are considered as “good bacteria” rather than parasites. There is a symbiotic relationship between these normal intestinal microbial residents and the human body wherein both species benefit from the presence of the other. In fact, disturbances in the population of normal intestinal flora lead to gastrointestinal disorders.

Helicobacter pylori

Helicobacter pylori (commonly abbreviated as H. pylori) is a bacterial species that can survive within the highly acidic environment of the human stomach. Helicobacter pylori has a spiral shape, and consists of a flagella (a tail-like projection) that helps in infecting the stomach. During infection, Helicobacter pylori burrows into the wall of the stomach, causing stomach ulcers and gastritis. To neutralize the gastric acid in the stomach, Helicobacter pylori secretes an enzyme that produces alkaline ammonia.

Stomach bugs

The term bugs is used to refer to microorganisms such as bacteria, viruses, and protozoa. The term “stomach bugs” may refer to bacteria, viruses, or protozoans that may cause acute infection of the stomach. These microbes also infect the intestine and cause gastroenteritis.

Toxins released from these pathogenic bacteria may also cause diseases such as food poisoning. Examples of bacteria that may cause gastroenteritis include Salmonella, E.coli, Campylobacter, and Shigella. Examples of viruses that may cause gastroenteritis include rotavirus, adenovirus, and norovirus.

Intestinal parasites

Helminths (or intestinal worms) are most commonly associated with the term “intestinal parasites”. However, single-celled protozoans that cause diseases such as toxoplasmosis, giardiasis, cryptosporidiosis, and trichomoniasis, may also be termed as intestinal parasites.

Unlike the protozoans, helminths are multicellular organisms. Intestinal worms can parasitize the human intestine for a long time (years and decades in some cases). These helminths feed on human blood and digested food present in the intestine. Examples of parasitic helminths include roundworms, tapeworms, and pinworms.

Read more on intestinal worms.

Causes of Stomach Parasites

People may get stomach parasites through both direct and indirect means. The exact route of transmission depends on the nature of the parasite or microbe. Transmission could be through vectors, food, water, droplets, or direct contact. Some of the possible routes through which one may transmit stomach parasites are described below.

Contaminated food or water

The most common route of transmission of stomach or intestinal parasites is through consumption of contaminated food or water. Contaminated food or water may contain both the parasites and their eggs. The parasites and their eggs find their way into food and water through fecal particles from infected individuals.

Air droplets

Parasites may also get transmitted through aerosolized droplets that form from the nasal mucus or saliva of an infected person during sneezing or coughing. Inhalation or ingestion of these microscopic air droplets by an uninfected person may lead to the transmission of infection.

Direct contact

Direct physical contact with an infected person could also cause transmission of infection. Health care workers and caregivers have a relatively higher risk of getting infected this way due to the nature of their work. Maintaining proper hygiene could prevent transmission of infection while giving care to infected patients.


Parasites may also be transmitted via contact with contaminated inanimate objects such as utensils or door knobs.


Insect vectors can also transmit pathogens and parasites from one person to another.

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