Parasitic infections are common in the U.S.
Millions of people in the United States are affected by parasitic infections, according to the CDC (1).
Parasites live on or in another organism (humans) and survive at the expense of the host. The three classes of parasites that cause disease in humans are protozoa, helminths, and ectoparasites (2).
Diseases caused by parasites
Giardia (protozoa) is the intestinal infection most commonly reported in the U.S. (3).
This infection is typically contracted through contaminated food or water but can be transmitted person-to-person as well (2) (3).
Symptoms of giardiasis include diarrhea, abdominal cramping, bloating, weight loss, and malabsorption of nutrients which can lead to further complications (3). Not everyone, however, notices symptoms when infected with giardiasis.
Individuals infected with giardia (giardiasis) are more likely to develop irritable bowel syndrome (IBS), a chronic gastrointestinal disorder that presents with symptoms of abdominal discomfort or pain and altered bowel habits like constipation and diarrhea (3) (8).
Hookworm (helminth) is a parasitic worm, transmitted through contaminated soil, that inhabits the small intestine of an infected human (4).
There are usually no noticeable symptoms of hookworm infection, but those that do experience symptoms usually begin with a small rash and itch where the larvae entered the skin (5). As the infection persists and the parasite develops and moves into the small intestines, symptoms like abdominal pain, distension, and diarrhea can occur (5). Left unchecked, this can lead to iron deficiency anemia as the parasite consumes blood and damages the gut lining (5). For children, loss of iron and protein can lead to slowed growth and mental development.
Helminths like roundworms also infect humans when we consume raw or undercooked meat that has been infected (6) (7). One type of roundworm infection (trichinosis), Trichinella spiralis., is common in rural areas and has also been associated with IBS (6) (8).
A mild case of trichinosis may cause no symptoms, but as the infection worsens, symptoms like diarrhea, stomach pain, fatigue, and nausea present, and as the infection spreads symptoms like fever, muscle pain, achy joints, headaches, and pink-eye can occur (6).
Parasites like ticks, fleas, lice, mites, and mosquitoes (ectoparasites) are organisms that attach or burrow into the skin and can cause disease in humans but also can transmit other pathogens into the blood of the host that can cause disease as well (7).
The parasite, IBS, and depression connection
The cause of conditions like IBS and depression tends to be related to many factors, however, research into the gut-brain axis indicates that changes to the gut microbiome, or an imbalanced gut microbiome (dysbiosis), can be related to these conditions, and parasites also play a role (9) (10).
As we think of the gut microbiome as a community of organisms (bacteria, fungi, viruses) living in the digestive tract, they each, like any member of a community, have a role to play that supports the community as a whole. And, when one of these “community members” grows out of control, it can harm the body.
Additionally, when parasites infect the GI tract they can cause inflammation and damage the organ. For example, a giardia infection (giardiasis) can damage the intestinal lining and lead to malnutrition and lactose intolerance, as the cells that produce lactase are damaged (11). Studies show that those infected with giardia are 4 times more likely to develop IBS (3).
Studies show that depression tends to be higher in those with IBS as the brain is affected by the dysfunctional gut (8) (12). One study of IBS patients found damage to various regions of the brain, a thinning of the insular and anterior cingulate cortex as well as an increase in the hypothalamic gray matter, which results in suboptimal cognition, or brain function (8).
The body is made up of not only human organs but also microbes that play roles in keeping the individual healthy. Certain microbes produce nutrients like B vitamins and other substances like short-chain fatty acids that are necessary for a healthy body (13).
When an individual struggles with IBS, depression, or both conditions, it would be wise to check for parasites!