Parasites in Humans

People have parasites. Yet, most people don’t know they have them. Mrs Everybody was like most people out there – Except, Mrs Everybody did have her suspicions that there were some uninvited ‘guests’ living inside her. Don’t worry, they are long dead and gone.

What is a Parasite?

Parasites are creatures which live and breed either on the outside ectoparasites or the inside of their host endoparasites. It is a selfish, one-sided relationship as the parasites give nothing back, aside causing poor health. This information focuses on internal parasites of humans and animals.

Why are Parasites a Menace?

Parasites may feast upon our delicious, carefully cooked meals, drink our blood, feed on our tissues and organs and invade our cells. They can make us feel fine, a tiny bit ill, very ill or kill us. Is if that isn’t enough, parasites excrete toxins which our body needs to deal with.

Imagine if you had just a single friendly nematode pet, an earthworm, Jim  … How many worm casts it would you find in Jim’s worm house every day? How much slime would Jim release through his skin every day? No matter, the earthworm which lives in your wormery creates quantities of by products which improve the status of your soil, unlike parasites when they live in us, our family members and pets.

Just one toxin released by parasites inside humans and animals, such as ammonia, can wake us up in the night, prevent us sleeping and make us feel irritable. If you have ever smelt ‘smelling salts’ also known as sal volatile or ammonium carbonate, then you will understand the effects.

Parasites are also capable of modifying our body system and altering our behaviour to suit themselves. We will be blissfully unaware! For example, a person infected with the protozoa toxoplasma gondii, has more than twice the chance of a non-infected human of being involved in a motor accident, whether as a driver of a pedestrian.

I don’t think that I will be able to get an insurance discount this year for keeping myself clear of parasite invaders, but three studies have been published on accident-prone drivers now and the evidence is stacking up. Toxoplasma rewires circuits in parts of the brain that deal with such primal emotions as fear, anxiety, and sexual arousal. A leading Czech researcher, Jaroslav Flegr, also believes that besides car crashes, the parasite contributes to suicides and mental disorders such as schizophrenia.

An American neuroscientist, Robert Sapolsky states that toxoplasma, can turn a rat’s strong innate aversion to cats into an attraction, luring it into the jaws of its No. 1 predator. Infected humans become more reckless, however the personality changes differ between women and men. Not all parasites cause obvious symptoms of poor health, but when they do, the symptoms are often ascribed to other causes. You can read more on the behavioural changes here (an external link).

What are the different types of parasite?

giardia lamblia

Figure 1. Giardia lamblia (protozoa) magnified image


One group of endoparasite parasites are like one-celled amoebae, known collectively as protozoan (e.g. giardia, cryptosporidium) and the other group is of parasites, worm-like in shape, collectively known as helminths.

An infection with giardia is often assumed to be travelers diarrhea. Yet after the diarrhea is over, the protozoa continues to hide in the body cells causing havoc. Many people unwittingly suffer from a protozoa burden.




There are different types of helminths:


Netatodes are more along the lines of earthworms (e.g threadworm / hookworm, lung worm, heart worm, filaria and ascaris lumbricoides )





A photo of a liver fluke.


Trematodes are reminiscent of slugs (flukes). These parasites like parts of the body rich in blood supplies.






beef tapeworm, taenia saginata from


Cestodes, (tapeworms), with their flat segmented bodies, need little description. Some helminths are tiny, while the fish tapeworm which infects humans too, would certainly be counted as among the largest of animals on the planet, reaching up to 10m in length.




Life Cycle of Parasites

Most parasites need to inhabit a variety of different species of animal to fully complete their life stages from egg to breeding machine. Parasites have evolved to take advantage of the food chain. For example, a fluke may begin its life in a snail and then undergo further developmental stages as the snail is eaten by a fish, or a crustacean. This in turn is eaten by a bird – the bird, rat or another intermediary host and we can be infected through infected vegetation (wash your watercress well!) or by eating vegetables or meat which is involved in this chain. Only three types of worm complete their full life cycle in a human. However humans can give host to some 1000 different types of parasite.

The strategy of parasites is enter us with stealth and to live their complex lives secretly within us. They leave us at the right stage of their development and to take up residence in some other creature, breeding and releasing their progeny in their final host. Sometimes we are not the ideal host and the parasite can wander around the body looking or waiting for second best conditions.

How do Humans get Parasites?

We catch parasites from our family, our pets, wildlife and strangers, contaminated food, water and soil and even from the air we breathe. People can be born with a parasite infection as some parasites can cross over the placenta – if that was the case, you would hopefully know by now! Parasites can also be passed down generations in the same family.

We are at increased risk if we eat meat, eat out, eat raw food, travel, camp, go to festivals, have children, keep animals, practice certain occupations such as working outdoors, if we work in institutional environments, nurses, care workers, schools etc, outdoor sports, swimmers, surfers, wildlife enthusiasts and with sexual contact. Every adult I know meets several of these criterion! There are many more risk factors.

Generally it is fairly safe to assume that we have parasites unless we take measures to get rid of them and to keep them away. Usually if there is one species of parasite present, there are others too. Due to increased movement of people, we can acquire parasites which are not normally known in this country, without having to find our passport! A malaria-like disease, known as the ague or marsh fever was common in the Fens, the Essex marshes and in Kent. Caused by a filarial parasite and spread by mosquitoes, it was locally transmitted until the 1950s.

Most parasites enter the body through the oral route with our food and drink and by hand to mouth contact. Fresh fruit and vegetables should always be washed well before peeling, especially if they are to be eaten raw. The correct cooking correct cooking methods are important especially with meat. Imported foods including, salad vegetables, meat and fish also increase our risk.

Other parasites such as hookworms, enter as microscopic larva though the skin, particularly broken skin. Although running barefoot is the most liberating experience, I no longer do this because hookworm lavae can enter through the skin and as much as I like dogs, and that is a lot, likewise I wouldn’t sit on the grass in a park used by dogs as dogs are an intermediate host for hookworm and many other parasites.

Parasite eggs can be inhaled in air and dust and then swallowed and some of the eggs can survive for years in dust and soil. Biting insects as well as cockroaches, flies etc introduce parasites too. Parasites are definitely part of life on this planet. Just one single species which affects humans has been nearly eradicated – the guinea worm. You can’t stop breathing, eating or drinking just to avoid the possibility of inhaling parasite eggs as the results will be counterproductive!

Why Don’t we Hear More about Parasites in Humans?

While we do treat our animals and pets but we hardly ever stop to think that humans get them too and that humans and animals can catch parasites from each other. Just like other animals, humans will always be at risk and parasites are always evolving co-evolving with their hosts. Humans will always be at risk of getting parasites.

Laboratory tests to determine the presence of parasites can yield frustrating results. There are many false negatives and when parasites are found they often remain elusive and difficult to identify. Routine tests have not been developed for many parasites. Some of the tests involve very unpleasant sampling methods that you would rather not know about!

Has your doctor ever asked you about your risk of getting parasites?

I searched on the BBC News website for articles on threadworm in children and no relevant hits appeared. Yet it is so common in children and it is so easily spread among families. Parasites are very much overlooked in the media. There should be much more public information on parasites.

What Are the Symptoms a Parasite Infestation?

The symptoms are too many to list, so here is a brief overview on the Parasites in Humans website. There are many more symptoms.

How do you Get Rid of Parasites?

Take a treatment to get rid of the parasites. It is best to find treatments which not just paralyse, but which also kill the parasites and their eggs. Don’t give the usurpers a chance!
Treat the whole family and pets.

What else can you do to help prevent reinfestation?

Hand hygiene
Food and kitchen hygiene
Household cleaning
Hygienic Pet Care
Wear Shoes outdoors

Regain a Healthy Digestive System

Treat for parasites
Eat anti-parasitic foods routinely (i.e. pumpkin seeds, fresh pineapple, pomegranate, garlic, tumeric, hibiscus, cayenne, ginger, etc).
Repopulate the gut with probiotics (home made yogurt, kefir, kombucha, salt fermented vegetables such as sauerkraut, sourdough bread, etc).
Depending on the nature and duration of the infestation, consider vitamin and mineral supplementation. Liquid iron, such as Floradix, Vit B-12 or Folic Acid can be beneficial.
Eat sufficient mucilaginous fibre (natural psyllium husk is good).
Keep yourself and your family free of parasites by periodic cleansing and the use of interim maintenance doses of a natural cleanse. Keep you animals clear too.

Don’t panic if you think you have parasites. You can understand how it is pretty much normal for all animals. Just it is not desirable! Archaeologists can affirm that humans have always been infected with parasites because we are so high up on the food chain. Anyone can get parasites.

Parasites don’t do us any good, so be sure to get rid of them with a dedicated cleanse, learn more about them, prevent reinfestation and do what you can to keep them away. Educate the people around you too!

Parasites are fascinating, if very dependant creatures. Mrs Everybody totally admires their survival strategy and success. They just aren’t welcome in her, her cat or her house.

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