What are parasites and parasitic infections?
Parasites are organisms that live within or on other organisms of a different species, called a host1. Some parasites spend all of their life cycles in their host without causing any noticeable harm, like some species of intestinal protozoa1. For example, these protozoan parasites are commonly found in the intestines of humans but are never associated with diseases and include species like:
- Chilomastix mesnili
- Endolimax nana
- Entamoeba coli
- Entamoeba dispar
- Entamoeba hartmanni
- Entamoeba polecki
- Iodamoeba buetschlii
To learn more about non-pathogenic intestinal protozoa, head up to this website.
However, parasites are not always this friendly. Some species can grow, reproduce, or invade organs or organ systems, causing a parasitic infection that leads to serious diseases. A current and important example is the parasitic infection caused by parasites of the genus Plasmodium8. Globally, during 2019, it was estimated that more than 229 million people were infected with malaria, and about 409,000 died from this condition, according to official statistics. Luckily, Malaria is not present in mainland Australia, except for cases from returning travellers who acquired it abroad9.
Other important parasites and parasitic infections that have a significant health impact on different parts of the world include amoebiasis10, ascariasis11, hookworm infection12, and trichuriasis12, according to the World Health Organisation.
Types of parasites and parasitic infections
Countless parasites are causing parasitic infections, and they can infect virtually any part of your body, including the skin, hair, blood, gastrointestinal tract and multiple organs. Although rare, even the brain can host parasites13-14.
There are three main classes of parasites that cause parasitic infection in humans: protozoa, helminths, and ectoparasites15. Worldwide, parasites and parasitic infections, especially those caused by worms and protozoans, are among the most common diseases affecting adults and children1.
Protozoa and helminths commonly cause disease in the gut, whereas ectoparasites, such as lice and mites, are associated with the skin, either living attached to it or burrowing inside12,16. When not treated, ectoparasites tend to stay in their human host for extended periods, causing discomfort and, in some cases, serious conditions16-17.
Common parasites and parasitic infections in Australia
In Australia, there are a wide range of parasites and parasitic infections that affect different body parts. For example:
Affected by head and body lice, pubic lice and scabies18-20.
Several types of helminth worms are associated with gastrointestinal diseases, including whipworm, threadworm, hookworm, and tapeworm. Other parasites causing parasitic infection in the gut include Giardia lamblia, Blastocystis hominis, and Dientamoeba fragilis21-22.
Can be affected by cysticercosis, a condition caused by infection with larvae of the parasite Taenia23.
Infection by Toxoplasma gondii, an obligate intracellular parasitic protozoan eukaryote, causes a condition called toxoplasmosis, which can affect multiple parts of the body. Toxoplasmosis can be acquired through infected cats, which acquire the parasite from contact with rodents or birds24.
Infection caused by exposure to eggs from the genus Toxocara can cause toxocariasis25.
For more information about these parasites and parasitic infections, head up to this official website.
Common symptoms of parasites and parasitic infections
There is a wide range of symptoms associated with a parasite and parasitic infections. Some of the most common parasites and parasitic infections in Australia include:
Blastocystis hominis – is a type of single-celled parasite distantly related to algae, diatoms and water moulds. In many patients hosting a parasitic infection by this parasite does not translate into any symptoms22. When this parasite causes disease, possible symptoms include:
- Watery diarrhea
- Abdominal pain
- Excessive gas
- Loss of appetite
- Weight loss
- Anal itching
Dientamoeba fragilis – this is a common, single-celled protozoan parasite found confined to the intestinal tract. For some people, a parasitic infection with this parasite does not translate into any symptoms22. Others may experience symptoms like:
- Abdominal pain
- Loss of appetite
- Weight loss
- Diarrhoea and greasy stools
- Abdominal cramps
- Weight loss
- Post-infectious irritable bowel syndrome21,26
Symptoms related to harbouring parasites and developing a parasitic infection from these worms vary, depending on the species of parasite involved. In some cases, there are no noticeable symptoms. But, when there is an intense infection, where parasites have reproduced more profusely, symptoms may include:
- Abdominal pain
- General feeling of sickness and weakness
- Impaired growth and physical development
- Intestinal obstruction27
Some worm species, like the roundworm Strongyloides stercoralis, can also cause dermatological problems and gastrointestinal problems. In some cases, infection with this parasite is associated with chronic malnutrition. It may even cause hyper infection/dissemination syndrome in immune-compromised patients, fatal if not treated immediately28.
In Australia, one of the most common human worm parasitic infections is caused by is the dwarf tapeworm, a parasite that affects up to 55% of some remote communities29.
According to official figures, another common parasite causing parasitic infections in Australia are threadworms, which infect up to 50% of children. These are tiny parasites no more than 13 mm long and live in the intestinal tract, mainly affecting children. The most common symptom associated with this parasitic infection is itching around the anal and/or vaginal area30-31.
Head lice or nits (lice eggs) are a type of ectoparasites, which live on rather than inside a host. Lice are a common occurrence among children in Australia and elsewhere, commonly occurring in primary school. Head lice are tiny, wingless parasites that live in the hair of humans (and animals), feeding on their blood. The most common symptom of head lice is itching of the scalp. Because of this itching and regular scratching, the skin can become red and irritated32.
This is another type of parasitic infection that involves an ectoparasite of the skin. Scabies is caused by a microscopic parasite, a mite called Sarcoptes scabiei. Typical symptoms associated with scabies include intense itching and/or a rash on the skin. The mites causing scabies tend to burrow in certain areas of the skin to lay their eggs, including the skin of the wrists, between the fingers, folds of the armpit and elbow, the groin and the creases of the bottom33.
Main causes behind parasitic infections
Parasitic infections are caused by three main types of parasites: protozoans, helminths and ectoparasites. These parasites have a unique biology and mode of transmission, which allows them to generate a parasitic infection in humans.
Members of the Protozoa are tiny, single-celled organisms commonly found in soil and water. While most Protozoa are free-living and do not cause parasitic infections in humans, there are various species that represent significant health burdens. For example,
- Giardia – this protozoan is the causative parasite behind giardiasis, described above. This microorganism has a two-stage life cycle, with an initial stage known as trophozoite, where the parasite can move and swim within the inner workings of the small intestine. During this stage, this parasite feeds on nutrients It finds in its environment. In the second stage of this parasite, Giardia becomes a non-moving cyst, which is commonly expelled in the feces of animals or humans. When these cysts reach water supplies or food, it becomes a risk for any human consuming the food or water. Human to human contact, and unsanitary living arrangements are common causes of parasitic infection by the Giardia Some common sites if parasitic infection for Giardiasis include:
- Childcare centres, where poor hygiene may occur when handling dirty nappies from infected children.
- Contaminated water supplies. Here, the parasite spreads when people drink or use contaminated water to wash fruits. Swimming in contaminated water bodies is another common route of infection21.
In Australia, there are about 600,000 cases of giardiasis diagnosed every year, and this parasitic infection affects a disproportionately large number of children in poor and remote Indigenous communities34.
- Plasmodium – this protozoan is the parasite responsible for malaria, described above. The Plasmodium parasite first develops in mosquitoes, which then go on to infect humans. When a parasite-infected mosquito bites a human, the parasite enters the body, starting the parasitic infection. Once in the human body, this parasite destroys red blood cells, impairing the function of multiple organs8.
Parasitic infections by these worms, as by many other worm parasites, require the ingestion of eggs, which can occur via the faecal-oral route. The primary cause behind parasitic infections by worms involves poor sanitary practices, particularly when sharing living facilities.
Soil-transmitted helminth infections are one of the most common parasitic infections worldwide. They include species like roundworms (Ascaris lumbricoides), the whipworm (Trichuris trichiura) and hookworms (Necator americanus and Ancylostoma duodenale)12.
The leading cause behind helminth parasitic infections is the transmission of eggs found in the faeces of infected people. When egg-infested faeces contaminate the soil, they can reach other persons through various routes:
- eggs can become attached to vegetables, which can transmit the egg when not properly washed, peeled or cooked;
- ingestion of contaminated water sources;
- ingestion by children who play in contaminated areas;
In some species of parasitic worms, like hookworms, the eggs hatch in the soil, releasing a larva that matures into an adult form. The adult can penetrate the skin, and people become infected when walking barefoot in contaminated soil12. Learn more about these parasites on the WHO website.
The main cause behind parasitic infections by this parasite is a fecal-oral transmission. However, the different life stages of this parasite are not fully understood, so specific details of the infection process are not known, such as the infectious stages of the parasite. So far, it is thought that the cysts form of this parasite represents the infectious stage. However, the most common form of this parasite, found in human stools, is called the central body or vacuolar and can be much bigger than the cysts. There are also other different forms of the parasite that have been found in stools. Currently, it is not clear what is their biological function, within the life cycle of the parasite22.
Besides humans, Blastocystis has been detected in the stool of many non-human animals, such as canids, swine, primates, rodents, birds and other species. Read more about the causes behind Blastocystis infections here.
Despite being a known parasite, causing parasitic infections in humans for more than 100 years, several aspects of the biology of this single-celled protozoan parasite are unknown. For example, there is no clear understanding of this parasite’s host distribution or even its complete life cycle. Currently, there are two leading hypotheses for how this parasite infects and spreads to new human hosts. One hypothesis suggests oral-faecal transmission, involving handling food or objects contaminated with faecal matter containing trophozoites of the parasite (a stage in the parasite’s life cycle). Another hypothesis is that D. fragilis is transported to a new human host through pinworms or other helminth worms, acting as vectors for this parasite. However, the evidence for the role of worms as vectors is not clear, and there are conflicting reports22,36. A potential life cycle of this parasite can be found here.
Transmission of head lice and scabies occur via person-person contact. According to one review, it only takes 20 minutes of physical or sexual contact to transmit these ectoparasites36 successfully. There may be more than 200 million people with scabies worldwide, and up to 6 million people have head lice in the USA. In Australia, as many as 60% of school-age children.
Risk factors of parasites and parasitic infections
While human parasites vary significantly in the life cycle, biology, and transmission mode, there are common risk factors associated with parasite and parasitic infections. In general, you are more likely to pick up a parasite or develop a parasitic infection if you:
- have a weak or compromised immune system
- have a pre-existing illness
- have been to a tropical or subtropical region of the world
- drink from a contaminated source of drinking water
- swim in lakes, rivers, or ponds where Giardia or other parasites may be found
- work with children, in childcare, work with soil regularly, or work in other contexts where you come into contact with faeces consistently
One study found multiple factors associated with intestinal parasites, including young age, female gender, severe malnutrition, poverty, illiteracy, poor hygiene, lack of access to potable water and hot and humid tropical climate—all these factors correlated with increased rates of infection37-38.
Preventing parasites and parasitic infections
Parasites are everywhere in the environment, and it is easy to get exposed. For this reason, the best approach to avoid catching a parasite is to reduce exposure to potential sources of parasites39. In general, everyday practices that can help you prevent a parasite or parasitic infection include:
- Practicing safe sex
- Regularly washing your hands after using the toilet or handling raw meat
- Cook food thoroughly
- Drink potable water only; avoid drinking water from natural sources, like lakes, rivers or ponds.
- Avoid close contact with cats, especially if you are pregnant
- Wash your hands after touching any animal
- Keep children away from areas in which animal faeces may be present
- Store cooked and uncooked food safely
- Wear shoes
Diagnosis of parasites and parasitic infections
Typical steps in diagnosing parasites or parasitic infections are evaluating symptoms and assessing medical and travel history40. Different laboratory tests follow this. Depending on the potential parasite involved, blood or stool tests may be recommended to obtain evidence of a parasitic infection. More invasive procedures, such as an endoscopy or a colonoscopy, may also be ordered if the blood and stool tests are not conclusive. In extreme cases, where a systemic injury is suspected, your health practitioner may consider X-rays, magnetic resonance imaging (MRI), or computerised axial tomography (CAT), which can reveal lesions in body organs.
At AUSCFM, a Functional Medicine Doctor or Practitioner may order a complete microbiome mapping stool analysis to look at the composition of the gut microbiome. Fungus and yeast are commonly present in parasitic infections, and bacterial infections can also be present. It is essential to understand the whole microbiome and identify instances of imbalances or overgrowth before deciding on treatment. Comprehensive testing is a cornerstone of the AUSCFM Functional Medicine Model.
Treatment of parasites and parasitic infections
Treatments to eliminate parasites and deal with their associated parasitic infections strictly depend on the type of parasite. Once the culprit parasite has been identified, potential treatment options can be considered.
Treatments for parasite and parasitic infections may involve the use of drugs, lotions, or physical interventions, such as head lice, which can be initially removed physically. Before any treatments are used, patients need to consult with their health care practitioners to ensure the best treatments that suit their specific needs and requirements are selected.
At AUSCFM, we follow a strict and comprehensive approach for the treatment of parasites. We acknowledge that every patient is unique and that there is no unique or perfect microbiome. Your treatment plan will be personalised based on your pathology results and based on their results. We will create a plan to guide you on what foods to eat whilst treating parasites and what foods to avoid.
If you suspect a parasitic infection, book an appointment today with one of our Functional Medicine Doctors or Practitioners. We can help you to understand your microbiome and how it might be affecting your health. We will also create a structured treatment and lifestyle plan that works for you.
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