Human parasites

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A parasite is an organism that lives in or on another organism, known as the host, and gets food from it. Each parasite undergoes sexual reproduction in a specific host known as the definitive host. For example, the malaria parasite undergoes sexual reproduction while in mosquito. Mosquito is therefore the malarial parasite's definitive host.

Human parasites have their definitive host being man. Their sexual maturity and reproduction occurs while in or on man. They also obtain food and other nutrients from man.

The sexual reproduction and maturity is crucial for the completion of their life cycles. As such, they usually settle on areas in the human body that favour their growth and reproduction. These could either be moist or dry areas. For internal parasites, the moist areas are their ideal environments while for the external parasites, they prefer dry surfaces such as the skin and the scalp.

Infestations of parasites on the human body elicits some clinical features which include general symptoms such as nausea, lack of appetite, diarrhoea, abdominal pains, weight loss, fever and rashes on the skin. These symptoms usually occur either as a result of direct damage on body tissues or due to the response of the body immune system to these parasitic infections.

To avoid these parasitic infestations, general control measures which prevents or limit entry of parasites into the human body can be instituted. These include proper sanitation, treatment or drainage of stagnant water, avoidance of greasy processed foods and use of probiotics. Probiotics reduce the risk of and fight off parasitic infections by strengthening the mucus barrier of the gut and other body immune defenses.

In a case where the body is already infested on and has an already ongoing serious damage caused by these parasites, treatment strategies should be considered. These strategies include blood transfusions and consumption of iron supplements.

Parasites can be categorized into internal or endoparasites, and external or ectoparasites. Internal parasites live within the body of the host whereas external parasites inhabit only the body surface.

Parasites can also be classified as either protozoan or helminths. Protozoa are unicellular while helminths are multicellular. Most of the protozoa and helminths that cause human diseases are endoparasites. We will therefore only discuss protozoa, helminths and ectoparasites.


These are unicellular organisms that are large enough to be seen under the light microscope in stool, tissue fluids and histological sections. Their growth and reproduction is very fast and occurs in a large number of them. They include; euglena, paramecium, plasmodium and balantidium.

In terms of their mode of movement, there are amoeba, flagellates, ciliates and apicomplexa each group having its own unique way of movement. Amoeba use pseudopodia to slide over solid substrates while flagellates use elongated and undulating flagella to propel themselves through liquid environments. Cilliates have cilia which undulate in waves allowing it to swim in fluid media. The apicomplexa glide in waves in the cell membrane.

They get into the human body in various ways as listed below:

  1. Through food and water contaminated with cysts.
  2. Sexual transmission
  3. From prey to predator and insects which then infect humans.
  4. Through the skin when one steps barefoot on contaminated water.

Once inside the human body, they multiply fast and lodge mainly on the intestines. The warm and moist environment of the intestines provides an ideal place for the completion of the prozoan life cycle. The intestines provide a good environment for completion of the protozoan life cycle.

Protozoan infections are hard to cure because they produce immunosuppression which causes delayed detection of the antigenic variants and reduction of the ability of the immune system to inhibit growth and kill the parasites. Signs of protozoan infection include blood in faeces in a case where the parasites have ulcerated the intestinal walls, and diarrhoea, vomiting and weight loss for long term infection cases. Some of the diseases caused by protozoa include malaria and schistomiasis.

Protozoa can be terminated through intake of antiprotozoal drugs. Prevention can be achieved by ensuring food and water ingested is fully cooked and well boiled to kill cysts as well as clearing stagnated water and use of mosquito repellants.


These are large macroparasitic worms visible with the naked eye during the adult stage of their life cycle. They are multicellular and large in size. They are classified as under trematodes, cestodes and nematodes. Trematodes are tapeworms, cestodes are flukes and nematodes are worms.

They get into the human body via the mouth, the nose or the anus. Entry is facilitated by drinking untreated water, ingestion of contaminated food and and touch of contaminated toilet seats and door handles. Once in the body they lodge in the intestines and mainly reside within the blood vessels. Their presenc is detected by presence of worms, eggs or larvae in stool as well as eosinophilia in blood.

Treatment of these parasitic infections can be done therapeutically with antihelminthic agents. You can also treat it locally by eating raw garlic, pumpkin seeds, pomegranates, beetroot, and carrots and drink a lot of water to flush them out.

For prevention, proper sanitation is the key element. Frequent deworming is advised for some worms like the Trichinella spiralis which feed on certain body parts such as the brain. If these worms are not detected and controlled early enough, they cause extensive damage on body tissues leading to memory loss and intense migraines. They are, however, hard to distinguish from other diseases since both may produce similar symptoms. Regular deworming id therefore encouraged, especially in children, so as to stay safe from these parasites.


These are parasites living outside the host. They include scabies, fleas and lice. Their main mode of transmission is skin to skin contact, sexual activity and sharing of clothes or bedding.

Once on the human skin they cause direct discomfort like itching and secondary bacterial infection. They can be treated by application of body medicinal ointments and oral medicine.

Prevention can be achieved through hygiene and avoidance of sharing of garments that come into contact with the skin. Some of the ectoparasites only affect areas with hair like louse which affects the pubic hair and head. These can be kept away by proper washing of these two areas with soap and water and keeping short or neat hair at all times.

Some of these parasites affect both man and animal hence ensuring that human pets are sprayed against them reduces the risk of attack to those that come into contact with the animals. Keeping these animals and their places of stay clean reduces the risk of infection too.

Having looked at the different types of human parasites it is important to note that they affect anyone and at any age. They secrete toxins in our systems and use up vital nutrients from our bodies hence infections and diseases. Ingestion of some foods like junk may make us more prone to parasites as most times they are not completely processed. Others like alcohol and water may flush out parasites from our systems.

General prevention measures include drinking safely boiled or bottled water especially when travelling, practising safe sex, avoiding contact with human or animal faeces and washing and cooking food thoroughly before consumption. Eating a balanced diet also helps as it boosts body immunity and for people with strong immunity parasites often go away on their own without treatment.

Human parasites can be deadly if they go untreated over long periods as they multiply fast and end up demanding so much from the host hence. This weakens the host's immune system. Prevention strategies are therefore strongly emphasized

Parasites, however, do not entirely have negative effects. Some have a good side. Presence of protozoa and helminths in the human body keeps the human body immune system proactive and alert. This way, the body will readily mount an effective immune response in the event of entry of other foreign bodies scuh as bacteria. The risk of bacterial infections are therefore reduced.

It has also been shown that presence of helminths in the human body reduces symptoms of diseases like multiple sclerosis and irritable bowel system causing less suffering to the patient.

Some doctors use some helminths for treatment of tumours found in body parts or organs that are not very safe for operation. They introduce the helminths into the human body which travel and eat up those tumours. Once they are done they are safely removed from the body. This way, tumours are eliminated without causing much harm to the patient.

In forensics, parasites are used as evidence of human neglect as some parasites exist within certain rearing temperatures and can therefore determine the forensic history of a body. Forensic officers can tell how long a body has been dead or alive due to the presence of certain parasites or absence of the same.

Unlike all other parasites, human parasites do not contribute to the ecosystem while in or on the body of their host unless they are removed out of the body. Once they are removed, they can settle in the external environment such as soil and contribute to the ecosystem unlike in the human body where there is no ecosystem to be maintained.

All said and done human parasites do more harm than good and should therefore be prevented by all means possible to avoid diseases and infections that may have fatal repercussions to the human body and its systems. It is said that prevention is better than cure. This applies well in this case since some damage caused by these parasites are irreversible even with treatment. We should therefore strive to prevent rather than wait for their occurrence then start looking for drugs.

The above information is just but a drop in the sea. Further research is recommended for more and better understanding of human parasites.