A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of its host. In humans, parasites that live inside us use up our vitamins, proteins and other nutrients, depriving us of optimal nutrition. Not only do they steal nutrients from our body, they also eliminate waste inside us, releasing their toxic bacteria and viruses.
Parasites are most commonly found in the colon, however, any part of the body is vulnerable to infestation: the lungs, liver, brain, blood, muscles, joints, skin, etc.
Even if you eat a healthy diet, these unwanted visitors may prevent you from getting all the nutrients from the food you eat, and they may cause a wide range of health issues, with symptoms reaching from mild rashes or headaches to serious illnesses.
While some parasites are easily identified, such as tapeworms, roundworms and hookworms, most parasites that people suffer from are actually microscopic bugs such as amoebas or flukes.
Though the list of parasites that effect humans is extensive, there are three main categories of parasites:
Protozoa: Examples include the single-celled organism known as Plasmodium. Protozoa can only multiply, or divide, within the host.
Helminths: These are worm parasites, such as roundworm, pinworm, trichina spiralis, tapeworm, and fluke.
Ectoparasites: These live on, rather than in their hosts. They include lice and fleas.
Below, we explore the many types of parasitic organisms that can infect humans.
Making up approximately 70 percent of all parasites, protozoa are invisible to the naked eye. Protozoa are single-celled organisms, but don’t let their size fool you—these microscopic parasites can be a huge threat to our health.
It is estimated that 7 million people across the U.S. have some form of protozoa living inside of them.
Certain protozoans, through their extremely rapid ability to reproduce, can take over the intestinal tract of their hosts and continue to expand from there into other organs and tissues. Some even feed on red blood cells—for this reason, some parasitologists consider them to be “microscopic vampires.”
Amoeba are a type of protozoa. There are many varieties of amoeba, and some of the amoeba found in humans are harmless. However, there are virulent strains of amoeba as well. Entamoeba hartmanni, for example can produce mild diarrhea and dysentery. Others can cause corneal ulcers in individuals who use tap water for sterilizing their contact lenses. The amoeba most commonly found to cause disease are:
- Entamoeba histolytica
- Endolimax nana
- Giardia lamblia
- Crpyospioridium parvum
- Blastocystis hominis
- Cyclospora cayetanensis
- Thrichomonas vaginalis
- Toxoplasma gondii (commonly acquired from cats)
- Cryptosporidium muris
- Pneumocystis carinii
- Plasmodium malariae
- Plasmodium ovale
- Plasmodium vivax
- Plasmodium falciparum
- Leishmania donovani
- Leishmania tropica
- Leishmania braziliensis
Helminths, also referred to as nematodes or nematoda, are larger parasites commonly known as worms. While protozoans are only single-celled organisms, these creatures are multicellular and are typically visible to the human eye. The adult worms multiply by producing eggs called ova or larvae. The eggs usually become infectious in soil or in an intermediate host before humans are infected.
Interestingly, unless a helminth infestation is severe, many individuals will show no sign of disease and can even live a lifetime with these worms inside them showing virtually no symptoms. While this may be uncomfortable to consider, it is a fact that humans can coexist quite comfortably with a few worms, as long as the infestation does not become excessive and create organ obstruction.
When worm infections are excessive, they can be quite damaging to the body. In fact, many health professionals agree that worms are among the most toxic agents in the human body and the underlying cause of many diseases. It is estimated that some type of worm infestation is present in over 75 percent of the world’s population.
Hookworms (Necator americanus, Ancylostoma duodenal) are a very common worm infection. Their larvae are found in warm, moist soil. They enter the body by penetrating the skin and are often found in people who frequently walk barefoot. There are many health benefits to walking barefoot, but it is not advised to do in warm, moist soils or areas of likely contamination—such as dog parks, public fields, or places where animal feces are abundant.
Hookworms travel through the bloodstream to the lungs, into the alveoli, and up the trachea to the throat, where they are swallowed and end up in the small intestine. This process takes about seven weeks. When the larvae pass through the lungs, it is possible form bronchitis to develop.
The first symptoms of hookworm infection are itchy patches of skin, pimples and blisters. Other symptoms include itching at entry site, nausea, dizziness, pneumonitis, anorexia, weight loss, and anemia.
The teeth-like hooks (where they get the common name “hookworm”) of the larvae attach to the intestinal mucosa and rob the body of large amounts of blood. Hookworms are found worldwide in warm, tropical areas. In the U.S. they are most prevalent in the southeast.
Hookworms can live up to fifteen years inside the human body!
Pinworms (Enterobius vermicularis) are another common worm infection. In fact, they are considered the most common in the United States and are most prevalent in children. Pinworms are quarter-inch worms that look like small white threads. Transmission of pinworms occurs through contaminated food, water, and house dust as well as human-to-human contact.
The adult female pinworm moves outside the anus to lay eggs. These eggs are often transferred by a child’s fingers from itching the anal area to the mouth. Children can easily transmit pinworms to the entire family through the bathtub, toilet seat, and bedclothes.
Perianal itching is the most classic pinworm symptom, but they have also been connected to a large range of neurological and behavioral symptoms. In one ten-year study of over 2,000 cases of children with pinworms, Dr. Leo Litter documented many seemingly unrelated symptoms that had not been previously associated with pinworm infection.
While pinworm is the most common worm infection in the United States, roundworm (Ascaris lumbricoides) is the most common intestinal parasite in the world—and they are also quite common in the U.S.
An estimated 1 billion people are infected with roundworm. Children are especially susceptible to roundworm as they have the tendency to put many unsanitary objects in their mouth. Roundworms are a fairly large parasitic worm and resemble the common earthworm in their appearance. They are spread directly to humans from soil or food contaminated with human feces. Though roundworm is found worldwide, it is most common in tropical and subtropical areas, especially in Asia because of their common practice of using human manure as fertilizer.
Once infected with the eggs or larvae, the worms develop inside the human body and can travel through the body ending up in the liver, heart, and lungs, where they create severe tissue irritation and allergic reactions. When present in large enough numbers, they can even cause intestinal obstruction.
Symptoms of roundworm infection are numerous.
Other Worm Infections
Nematodes are the most common types of worms, and these resemble the thin, long earthworm-like worms such as roundworm, hookworm, and pinworm. Flukes (trematodes or trematoda) are another type of common worm. These are leaf-shaped flatworms that are parasitic during nearly all of their life cycle forms.
Tapeworms (cestodes or cestoda) are also common parasites that are among the oldest known parasites and are considered humanity’s largest intestinal inhabitant, reaching lengths of up to 36 inches or more!
Tapeworms have a scolex, or head, that attaches to the intestinal wall. As long as that head remains attached to the intestinal mucosa, a new worm can grow from it. Tapeworms do not contain digestive tracts but get their nourishment by absorbing partially digested substances from their host.
Some other common worm infections include:
- Beef tapeworm (Taenia saginata)
- Prok tapeworm (Taenia solium)
- Fish tapeworm (Diphyllobothrium latum)
- Dog tapeworm (Dipylidium caninum)
- Trichinella (Trichinella spiralis)
- Anisakine larvae
- Dirofilaria immitis
- Wucheria bancrofti
- Onchocerca volvulus
- Loa loa
- Mansonella streptocerca
- Mansonella perstans
- Mansonella ozzardi
- Liver fluke (Clonorchis sinensis)
- Blood fluke (Schistosoma japonicum, Schistosoma mansoni, Schistosoma haematobium)
- Oriental lung fluke (Paragonimus westermani)
- Sheep liver fluke (Fasciola hepatica)
- Intestinal fluke (Fasciolopsis buski)
Ectoparasites are parasites that live on their host, rather than inside their host. The most common ectoparasites include:
- Scabies (Sarcoptes scabiei),
- The common bed bug (Cimex lectularius),
- Lice, including the body louse (Pediculus humanis), pubic louse (Phthirius pubis), and head louse (Pediculus humanus capitis).
While it may be an uncomfortable reality to consider, parasites are a very prevalent health issue that many people struggle with. They often cause symptoms that are similar to other health issues, so misdiagnosis or underdiagnoses are common. Not to mention, many doctors are simply uneducated about parasites, and the standard tests for parasites such as the O&P parasite test are largely unreliable, making diagnosis even more difficult.
It is important that you educate yourself about parasites, how you get parasites and how you can prevent parasites so you can keep yourself and your family healthy.