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Parasitic Infection


A parasitic infection is a disease that is conveyed by parasites. Parasites are microscopic entities that live inside or on the peripheral of a larger host, using the host as their food foundation. There are three categories of parasites that aim humans: protozoa, helminths, and ectoparasites. Protozoa are minute, one-celled organisms that can permit to humans through adulterated food or insect bites. Helminths are parasitic worms (e.g., the tapeworm) that can also cause contagious diseases in their hosts. Lastly, ectoparasites are parasites that live on the exterior of another organism, usually human skin. Parasitic infectious diseases are a public health issue across the world. Parasitic infection prevail in warm & humid areas mostly in tropical, subtropical & temperate regions of the world. Developed countries like China show great prevalence of parasitic infections also. Amoebiosis, filariasis and scabies are common examples of all these above mentioned three kinds of parasitic infections respectively. Humans are hosts to nearly 300 species of parasitic worms and over 70 species of protozoa, some derived from our primate ancestors and some acquired from the animals we have domesticated or come in contact with during our relatively short history on Earth.


What is Parasitic Disease?

  • It is an infectious disease which is caused & transmitted by a parasite.
  • Parasitism: A symbiotic relationship in which one symbiont benefits, other is damaged.
  • It is also known as parasitosis.
  • The study of parasites, their hosts & the relationship between them is called Parasitology & study of parasitic diseases including their diagnosis, treatment & control is called Medical Parasitology.
  • The parasites can cause disease directly, releasing toxins or even causing no disease at all.
  • Parasites vary in their sizes as they can be tiny, one-celled organisms called protozoa and can even be seen with naked eyes called worms.
  • Parasitic diseases can infect all living organisms, including plants & animals but mainly human beings.



  • Chiefly in the developing countries the infectious diseases are a threat to human health & life. One out of ten living persons suffer from one or more of seven major tropical diseases, of which five are parasitic in nature. Out of 60 million deaths in world, more than 25% are accounted to parasites.
Parasitic Infection

Graphs showing medical importance of parasitic infection in the world

The estimated world prevalence of the major parasitic infection of human (WHO,1999) are following:

  1. Malaria 300-500 million
  2. Schistosomiasis 200 million
  3. Lymphatic filariasis 120 million
  4. Onchocerciasis 85 million
  5. Leishmaniasis 12 million
  6. Trypanosoma cruzi (South America) 18 million
  7. Ascaris infection 1300 million
  8. Hookworm infection 1300 million
  9. Amoebiasis 60 million–
  10. Trichuriasis 900  million
  11. Gardiasis 200 million

But in some developed countries, some parasitic diseases also prevail like in China, as the large area is geographically across the tropical & temperate zones, with diverse natural conditions. After the foundation of People’s Republic of China in 1949, the government of China has accomplished great success in controlling the frequency of parasitic diseases. In the National Guideline for Agricultural Development (1956-1967), five key parasitic diseases were planned to be eliminated, including, with death in thousands of people:

  1. Schistosomiasis
  2. Malaria
  3. Filariasis
  4. Black fever
  5. Ancylostomiasis

Among the 10 globally significant tropical diseases in the Special Program for Tropical Diseases jointly ratified by the United Nations Children’s Fund (UNICEF), the World Bank & the World Health Organization (WHO), the United Nations Development Program (UNDP), seven are parasitic diseases, including:

  1. Malaria
  2. Schistosomiasis,
  3. Lymphatic Filariasis
  4. Onchocerciasis
  5. Leishmaniasis
  6. African trypanosomiasis
  7. Chagas disease

Due to increased organ transplantation, increased incidence of cancer & AIDS as well as increased use of immunosuppressor, the population with immunodeficiency or compromised immunity is increasingly large. Therefore, opportunistic parasite are increasingly vital pathogens.

The changes of natural conditions also contribute to the distribution & prevalence of some parasites. Due to the greenhouse effect & the consequently increased global temperature, the regions with anopheles & the other vector insects are expanding. It has been speculated that the prevalence of schistomiasis, typanosomosis, dengue & yellow fever would worsen.

Clinical management of parasitic diseases present great challenges to the clinicians as its accurate diagnosis & cure are of great significance.

Causes of Parasitic Infection:

Parasitic infections mainly human parasitic ones can be caused due to:

  1. Ectoparasites : Cause infection superficially within the skin
  2. Endoparasites : Cause infection within the human body

Thus, the three types of organisms are involved in parasitic infection:

  1. Protozoa
  2. Helminths
  3. Ectoparasites
  • Protozoa are single- celled organisms that can live & multiply inside your body.
  • Some of their infections include Giardiasis which is an infection that you can interact from drinking water infected with Giardia protozoa.
  • Others are amoebae, flagellates, malarial organisms.
  • Helminths are multi-celled organism that can live in or outside of your body. They are more generally known as worms.
  • They include flatworms, tapeworms, thorny- headed worms & roundworms.
  • Ectoparasites are multi-celled organisms that live on or feed off your skin.
  • They include some insects & arachinds, such as mosquitos, fleas, ticks & mites.
Parasitic Infection

Different kinds of parasites

Risk Factors

Anyone can catch a parasitic infection. But some people are at greater threat than others. You’re more likely to deal a parasitic infection if you:

  1. Have a weak immune system or are already sick with another illness
  2. Live or travel in tropical or subtropical regions of the world
  3. Lack a clean source of drinking water
  4. Bath in lakes, rivers, or ponds where Giardia or other parasites are common
  5. Work in childcare, work with soil frequently, or work in other situations where you come into contact with feces on a regular basis
  6. Outdoor cats can come into contact with infected rodents and birds (zoonosis). This makes their owners more likely to contract toxoplasmosis, a type of protozoa. Toxoplasmosis can be very harmful for pregnant women and their developing babies.
Diagnosis of Parasitic Infection

Parasitic infections can be diagnosed in a number of means. The doctor may also order tests to check for bacteria or other things that can cause infections. For example, your doctor might execute or demand:

  1. A blood test
  2. A fecal exam: In such an exam, a sample of your stool will be collected and tested for parasites and their eggs.
  3. An endoscopy or colonoscopy: These tests may be methodical if the results of a stool exam are questionable. While you are sedated, your doctor will permit a thin flexible tube through your mouth or rectum and into your digestive system to inspect your intestinal tract.
  4. X-rays, magnetic resonance imaging (MRI), or computerized axial tomography (CAT): These scans are used to check for signs of lesions or damage to your organs affected by parasites.
Prevention of Parasitic Infection

There are several steps you can take to lower your risk of contracting a parasitic infection:

  1. Practice safe sex
  2. Wash your hands on a regular basis, especially after handling uncooked food or feces.
  3. Cook food to its suggested internal temperature.
  4. Drink clean water, including bottled water when you’re traveling.
  5. Avoid swallowing water from lakes, streams, or ponds.
  6. Shun cat litter and feces when you’re pregnant.
  7. If you suspect you have a parasitic infection, make an appointment with your doctor. They can help diagnose the cause of your symptoms and indorse a treatment plan. By getting early treatment, you can help stop the blowout of infection to other people.
Mode of Transmission

Parasitic infections can be spread in a number of ways:

  1. Contaminated water & food
  2. Waste
  3. Soil
  4. Blood
  5. Sexual contact
  6. Vectors
Routes of Parasitic Infection
Parasitic Infection

Routes of Parasitic Infections

Common Examples of Parasitic Infections:

Protozoan parasitic infections

Protozoan infections are parasitic diseases caused by organisms mainly categorized in the Kingdom Protozoa.

They include organisms:

  1. Amoebozoa
  2. Excavata
  3. Chromalveolata

Examples include:

  • Entamoeba histolytica
  • Plasmodium ( some of them cause malaria)
  • Giardia lamblia



Amoebiasis, also known amoebic dysentery, is an infection caused by any of the amoebas of the Entamoeba group. Amoebiasis is an infection caused by the amoeba Entamoeba histolytica. Likewise amoebiasis is sometimes wrongly used to refer to infection with other amoebae, but strictly speaking it should be reserved for Entamoeba histolytica infection

Parasitic Infection

Entamoeba histolytica

Signs & Symptoms
  • Most infected people, about 90% are asymptomatic, but this disease has the potential to make the sufferer seriously ill. It is assessed that about 40,000 to 100,000 people worldwide decease annually due to amoebiasis.
  • Infections can sometimes last for years. Symptoms take from a few days to a few weeks to progress and manifest themselves, but usually it is about two to four weeks.
  • Symptoms can range from mild diarrhea to severe dysentery with blood and mucus. The blood comes from abrasions formed by the amoebae occupying the lining of the large intestine.
  • In about 10% of disturbing cases the amoebae enter the bloodstream and may foldaway to other organs in the body. Most commonly this means the liver, as this is where blood from the intestine reaches first, but they can end up almost anywhere in the body.
  • In asymptomatic infections the amoeba lives by digesting bacteria and food particles in the gut, a part of the gastrointestinal tract. It does not usually come in interaction with the intestine itself due to the protective layer of mucus that lines the gut. Disease occurs when amoeba comes in contact with the cells lining the intestine. It then destroys cell membranes and proteins which can lead to penetration and digestion of human tissues, resulting first in ulcers in the intestine.
  • Entamoeba histolytica consumes the destroyed cells by phagocytosis and is often seen with red blood cells (a process known as erythrophagocytosis) inside when observed in stool samples. Especially in Latin America, a granulomatous mass (known as an amoeboma) may form in the wall of the ascending colon or rectum due to long-term immunological cellular response, and is sometimes mixed up with cancer.
  • “Theoretically, the ingestion of one viable cyst can cause an infection.”

Amoebiasis is usually transmitted by the:

  • fecal-oral route
  • Contact with dirty hands or objects as well as by anal-oral communication.
  • Assimilation of the cyst form of the parasite, a semi-dormant and tough structure found in feces. Any non-encysted amoebae, or trophozoites, die quickly after leaving the body but may also be present in stool
  • Contaminated food and water.
Parasitic Infection

Life cycle of Entamoeba histolytica

Parasitic Infection

Life cycle of Entamoeba Histolytica

  1. histolytica infections occur in both the intestine and in tissue of the intestine and liver. As a result, two different classes of drugs are necessary to treat the infection, one for each location. Such drugs are known as amoebicides.

Helminths Parasitic Infection

Lymphatic filariasis

  • Filariasis is a parasitic human disease initiated by an infection with roundworms of the Filarioidea type. These
    Parasitic Infection

    Wuchereria Bancrofti

    are spread by blood-feeding black flies and mosquitoes. This disease goes to the group of infections called helminthiases.

  • Eight known filarial nematodes use humans as their definitive hosts. It is one of three groups according to the niche they occupy in the body.
  • It is begun by the worms Wuchereria bancrofti, Brugia malayi, and Brugia timori, mainly the first one.
  • These worms lodge the lymphatic system, counting the lymph nodes; in chronic cases, these worms result into the syndrome of elephantiasis.
Signs & Symptoms
Parasitic Infection


  • The most remarkable symptom of lymphatic filariasis is elephantiasis – edema with thickening of the skin and core tissue which is marked by severe swelling in the arms, legs, breasts, or genitals.
  • Elephantiasis results when the parasites lodge in the lymphatic system. Elephantiasis affects mainly the lower extremities.
  • Most cases of the disease have no symptoms.
  • The skin may become thicker as well, and the condition may become painful. The changes to the body may harm the affected person’s social and economic situation.
  • The parasite infects the lymph nodes and blocks the flow of lymph throughout the body; this results in chronic lymphedema, most often noted in the lower torso (typically in the legs and genitals).
Transmission & Life- cycle
  • Human filarial nematode worms have complex life cycles, which mainly consists of five stages.
  • After the male and female worms mate, the female gives birth to alive microfilariae by the thousands.
  • The microfilariae are taken up by the vector insect (intermediate host) during a blood meal. In the intermediate host, these microfilariae molt and grow into third-stage (infective) larvae.
  • Upon taking another blood meal, the vector insect inserts the infectious larvae into the dermis layer of the skin.
  • After about one year, the larvae molt through two more stages, evolving into the adult worms.
Parasitic Infection

Life cycle of Filariasis

  • The endorsed treatment for people outside the United States is albendazole united with ivermectin.
  • A combination of diethylcarbamazine and albendazole is also operative.
  • All of these treatments are microfilaricides; they have no effect on the adult worms.
  • While the drugs are critical for treatment of the individual, proper hygiene is also required.
  • In 2003, the common antibiotic doxycycline was recommended for treating elephantiasis. Filarial parasites have symbiotic bacteria in the genus Wolbachia. This drug has shown signs of constraining the reproduction of the bacteria, further bringing sterility.
  • Treatments for lymphatic filariasis differ depending on the geographic location of the endemic area.[18] In sub-Saharan Africa, albendazole is being used with ivermectin to treat the disease, whereas elsewhere in the world, albendazole is used with diethylcarbamazine.[18] Geo-targeting treatments is part of a larger strategy to eventually eliminate lymphatic filariasis by 2020.[18]
  • Additionally, surgical treatment may be helpful for issues related to scrotal elephantiasis and hydrocele. However, surgery is generally ineffective at correcting elephantiasis of the limbs.
  • A vaccine is not yet available but in 2013 the University of Illinois was reporting 95% efficacity in testing against B. malayi in mice.
  • Treatment for podoconiosis consists of consistent shoe-wearing (to avoid contact with the irritant soil) and hygiene – daily soaking in water with an antiseptic (such as bleach) added, washing the feet and legs with soap and water, application of ointment, and in some cases, wearing elastic bandages.
  • The antibiotic doxycycline is effective in treating lymphatic filariasis. Its drawbacks are that it requires 4 to 6 weeks of treatment and should not be used in young children and pregnant women, which limits its use for mass prevention.

Ecto-parasitic infections


  • Scabies, also known as the seven-year itch
  • It is a contagious skin infestation by the mite Sarcoptes scabiei. Sarcoptes is a genus of skin parasites and part of the larger family of mites collectively known as scab mites

    Parasitic Infection

    Scabies mite, Sarcoptes scabie

Signs & Symptoms
  • The most common symptoms are severe itchiness and a pimple-like rash. Occasionally, tiny burrows may be seen in the skin.
  • In a first ever infection a person will usually develop symptoms in between two and six weeks.
  • During a second infection symptoms may begin in as little as 24 hours.
  • These symptoms can be present across most of the body or just certain areas such as the wrists, between fingers, or along the waistline. The head may be affected, but this is typically only in young children.
  • The itch is often worse at night.
  • Scratching may cause skin breakdown and an additional bacterial infection of the skin.
  • Acropustulosis, or blisters and pustules on the palms and soles of the feet, are characteristic symptoms of scabies in infants.
  • The elderly, disabled, and people with an impaired immune system, such as HIV, cancer, or those on immunosuppressive medications, are susceptible to crusted scabies (formerly called Norwegian scabies)
  • Scabies is contagious and can be contracted through prolonged physical contact with an infested person.This includes sexual intercourse, although a majority of cases are acquired through other forms of skin-to-skin contact.
  • Less commonly, scabies infestation can happen through the sharing of clothes, towels, and bedding, but this is not a major mode of transmission; individual mites can only survive for two to three days, at most, away from human skin at room temperature.
Parasitic Infection

Life cycle of Scabies

  • A number of medications are effective in treating scabies. Treatment should involve the entire household, and any others who have had recent, prolonged contact with the infested individual.
  • Options to control itchiness include antihistamines and prescription anti-inflammatory agents.
  • Bedding, clothing and towels used during the previous three days should be washed in hot water and dried in a hot dryer.
  • Permethrin is the most effective treatment for scabies
  • Crusted scabies may require multiple applications, or supplemental treatment with oral ivermectin. Oral ivermectin is effective in eradicating scabies, often in a single dose.
  • Other treatments include lindane, benzyl benzoate, crotamiton, malathion, and sulfur preparations. Lindane is effective, but concerns over potential neurotoxicity have limited its availability in many countries. Crotamiton has been found to be less effective than permethrin in limited studies.Crotamiton or sulfur preparations are sometimes recommended instead of permethrin for children, due to concerns over dermal absorption of permethrin.


Parasitic infections are communal around the world, but they are the most hazardous and prevalent in impoverished tropical areas. Parasitic infection is highly prevalent in communities of the underdeveloped & even developed areas like China of the world. Some of the infections can be spread sexually, while others are spread through poor hygiene and living circumstances. Most of the infections can be treated by a doctor through different medication, however, they often strike countries that are unable to provide proper medication and treatment. Though, the knowledge of the community members about the parasite is less. Enactment of preventive chemotherapy, appended with health education, provision and use of sanitary amenities would be recommended to decrease morbidity and control transmission of intestinal & other infectious parasites.

  • m.wikipedia.org/wiki/ parasitic disease
  • springer.com/ Radiology to parasitic diseases/ Introduction to Parasitic Diseases/ Yungling wang. DOI 10.1007/978-94-024-0911-6_1
  • healthline.com/ parasitic infections. Written by Tricia Kinman
  • Human Parasitology, Liwei Li
  • https://www.soc.ucsb.edu/sexinfo/article/overview-parasitic-infections
  • https://www.medicinenet.com/scabies/article.htm
  • https://commons.wikimedia.org/wiki/File:Scabies_LifeCycle-es.png
  • https://en.wikipedia.org/wiki/Ectoparasitic_infestation
  • https://en.wikipedia.org/wiki/Amoebiasis
  • https://www.cdc.gov/dpdx/amebiasis/index.html
  • https://slideplayer.com/slide/6058188/20/images/2/Routes+by+which+humans+acquire+parasitic+infections.jpg
  • https://www.cdc.gov/parasites/lymphaticfilariasis/
  • who.int/mediacentre/factsheets/fs102/en/
  • https://en.wikipedia.org/wiki/Lymphatic_filariasis
  • https://www.healthline.com/health/elephantiasis
  • https://www.news-medical.net/health/What-is-Elephantiasis.aspx


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