What is a parasitic infection?

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Parasitic infection is caused by parasites. Parasites are organism that depends on other organisms, like humans and animals for their survival. The parasites that live on the organism are called a host.

Some parasitic organism does not infect the host but some infect the host and cause death. The parasites after entering the host start their life cycle. They grow and reproduce and infect the host. This results in parasitic infection. The condition is called parasitism.

The parasites bind to the host through glycan-binding proteins. The parasite’s glycan-binding proteins interact with the host glycomes. The parasite glycans can also interact with the host glycan-binding protein and antibodies.

Some of the common parasites include Toxoplasma gondii, Plasmodium and Entamoeba histolytica.


Trichomoniasis is a sexually transmitted disease caused by the protozoan Trichomonas vaginalis. It is transmitted by direct sexual contact. Trichomoniasis is a non-virally sexually transmitted infection.

Women are symptomatic of trichomoniasis. Women with trichomoniasis will have vaginal discharge that has a foul smell, painful intercourse, urinary tract infection and vaginal itching.

Men are mostly asymptomatic. However, some may have symptoms like testicular pain, dysuria, frequent urination, penile discharge and cloudy urine.

Trichomoniasis increases the risk of HIV infection in both males and females. The drug administered for trichomoniasis is metronidazole, which is given orally.


Giardiasis is caused by the protozoan Giardia duodenalis. It is a small intestine infection. Giardiasis causes watery diarrhoea and flatulence.

People affected with giardiasis are asymptomatic. For some patients, it may result in dehydration and weight loss due to severe diarrhoea.

Animals infected with the protozoan release the cyst into freshwater. The parasite can be active in the freshwater for weeks to months where they are highly infective.

Ingesting cysts through contaminated water can cause the infection. Direct contact from person-to-person transmission causes human infection. Hygiene plays a major role in giardiasis infection.

The cyst after entering the human intestine undergoes excystation and releases trophozoites. These trophozoites grow inside the host and cause infection.

Drugs like nitroimidazole and anthelmintics are effective against giardiasis.


Cryptosporidiosis is a gastrointestinal tract infection. It is an Apicomplexan protozoan parasite of the genus Cryptosporidium.

It affects the lungs and intestinal tract of various animals and humans. The mode of infection is through spores. These spores are environmentally resistant.

When these spores are ingested through contaminated water and food can cause diarrhoea that lasts less than two weeks.

For immunosuppressed people, it can lead to death. For immunocompetent people, there is no major effect.

The life cycle of the parasite begins after the host ingested the sporulated oocysts. The excystation happens in the small intestine.

The sporozoites will be released and they penetrate through the mucus layer and get attached to the enterocytes. It forces the enterocytes to form a parasitophorous vacuole around the parasitic organism and then differentiates into a trophozoite.


Toxoplasmosis is caused by an obligate intracellular protozoan Toxoplasma gondii. It is an uncommon infection and people infected remain asymptomatic.

The parasite can cause infection in infants and immune suppressed people or people with other medical conditions like HIV.

Infection occurs through ingestion of cysts through half-cooked meat, contaminated water and food. The infection transmission can happen during organ transplantation.

Pyrimethamine and sulfadiazine are the preferred therapeutic drugs for toxoplasmosis. Cats are commonly infected with toxoplasmosis when they ingest the oocysts.

The infected cats shed the unsporulated oocysts in their faeces for three weeks. The oocysts take about five days to transform into an infectious oocyst and stay active in the environment for a year.

When the oocyst is ingested with the contaminated food or water the outer cell wall is proteolysed in the alimentary canal by the gastric juices.

The uncoated sporozoites enter the epithelium and differentiate into tachyzoites. Pyrimethamine and sulfadiazine are given in combination for the therapeutic management of the infection.

What are the symptoms of parasitic infections?

The major symptoms of parasitic infection are diarrhoea, bloody stools, nausea and vomiting, abdominal pain, bloating, worm in stools, stomach pain, inflammation, fever and dehydration.

Sexually transmitted parasitic infections have symptoms like cloudy urine, urinary tract infection, pain during intercourse and itching in your private parts.

What causes parasitic infections?

Parasitic infection can spread through various modes like contaminated food and water. Protozoa and helminths spread through contaminated water, food, soil and blood.

It can also be transmitted through sexual contact. Insects like mosquitoes also act as a carrier for the spread of parasitic infection.

The major causes of the parasitic infections are due to the three major parasites, which are listed below.


Protozoans are unicellular organisms and the major classes of protozoans include Plasmodium, Entamoeba histolytica, Leishmania and trypanosoma.

The parasite Plasmodium causes malaria, Entamoeba histolytica causes amebiasis, Leishmania causes leishmaniasis and trypanosoma causes sleeping sickness and Chagas’ disease.

Protozoans have elaborated mechanisms to target the glycans or glycan-binding proteins in the host cells and evade the host immune system, which promotes parasitism.

For example,  Acanthamoeba keratitis adheres to the host cell through lectin-glycan interaction. Acanthamoeba keratitis causes severe eye infection which involves corneal epithelium.


Helminths include worms or metazoans. The parasitic worms include nematodes, trematodes and tapeworms or cestodes.

Trematodes like Schistosoma mansoni causes schistosomiasis, example of nematodes is Ascaris lumbricoides and tapeworm like Taenia solium causes taeniiasis.

Helminths’ mode of invading the host is by attaching itself to the host through lectin-glycan interaction.

Helminths infect the environment through their eggs and larvae. When people ingest the contaminated food that contains the worm’s eggs, they get infected.

The common symptoms of helminths infection are diarrhoea, malnutrition, fatigue, enlarged liver and spleen, gastrointestinal inflammation, bowel obstruction, anaemia, vomiting, constipation, weight loss, pneumonitis and blindness.

Long-term exposure to the worms may be severe and fatal in all kinds of worms.


Ectoparasites like lice, ticks and mites infect the host skin. They depend on the host for their growth and multiplication.

Ectoparasites affect the livestock by causing damage to the skin and spreading the infection to other animals.

Ectoparasites cause mechanical damage, anaemia, loss of condition, toxicosis, irritation and allergic condition.

The ectoparasites do not infect the host by ingestion instead they attach themself to the skin of the host and cause damage to the host. These ectoparasites are vectors of viral infection.

The female Aedes mosquito is an ectoparasite that transmits the Dengue virus from one person to another.

How are parasitic infections diagnosed?

A blood test

Parasitic infection can be detected by a blood test. A Blood test helps you detect the specific type of parasite that has infected you.

There are two types of blood tests serological and blood smear.

The serological test helps to look for specific antibodies or antigens when the body is infected. The immune system produces certain antibodies to fight against the specific parasite.

The blood smear helps to identify the presence of parasites like malaria, filariasis and babesiosis. The test is done by smearing the blood on a slide and then stained with certain dyes and viewed under a microscope.

A faecal exam

A faecal exam is done to identify the parasite that causes diarrhoea, cramping, loose or watery stools, flatulence and other abdominal problems.

The stool sample collected will look for the presence of parasitic eggs or the parasites that cause infection.

An endoscopy or colonoscopy

An endoscopy or colonoscopy is used when the faecal exam gives a negative result. An endoscopy is performed to find out the reason for your diarrhoea and other digestive disorders.

The test is done by your doctor. A tube is inserted into your mouth (endoscopy) or rectum (colonoscopy) to examine the intestine.

This helps to find any parasitic infection or any abnormalities in your intestine.

X-rays, magnetic resonance imaging (MRI), or computerized axial tomography (CAT)

Imaging tests like X-ray, MRI and CAT are used to find any lesion caused by the parasite.

How are parasitic infections treated?

The treatment for the parasitic infection depends on the type of parasite that has invaded your body. Your doctor will prescribe some drugs depending on the diagnosis.

Parasitic infections are mostly associated with gastrointestinal disorders. So, your doctor may advice you to intake a lot of fluids to avoid dehydration.

How can parasitic infections be prevented?

Parasitic infection can be avoided by following a few simple steps. Always maintain good personal hygiene, be cautious about insect bites and avoid drinking and eating contaminated food.

Practice safe sex, using a condom.

Personal hygiene also includes safe sex. Safe sex is essential to protect you and your sexual partner from any infection. It also protects you from unplanned pregnancy.

The commonly transmitted parasitic infection through sexual contact is amebiasis and giardiasis.

The condoms act as a barrier and prevent the exchange of semen, vaginal fluid and blood between your partner. This also avoids any parasitic infection getting transmitted.

However, condoms are not fully efficient. When the infected area is not fully covered the infection can spread easily. Infections like pubic lice, herpes and genital warts can spread by close skin contact.

Wash your hands regularly, especially after handling uncooked food or feces.

Wash your hands regularly not only before eating food but also when your hands are dirty. When you handle uncooked food like meat and chicken. There are many pathogens present to infect you.

You tend to touch your mouth, nose and eyes with your hands. The parasite can get inside your body through your nose and mouth.

While washing hands don’t forget to wash your nail as the pathogens may be present in your nails. If you forget to wash your hands properly, they may be ingested directly. Also, trim your nails regularly.

According to World Health Organisation (WHO), you should wash your hands with soap under running tap water. You can also use alcohol-based hand rubs if soap is not available.

Cook food to its recommended internal temperature

Cook food to kill microbes and pathogens. You can kill the parasites and pathogens only when they are cooked to the temperature where they can be killed.

According to Food Safety, meat should be cooked to 160 Fahrenheit to kill the parasites. For poultry and foul meat, it should be cooked to 165 Fahrenheit and fresh meat steaks and roasts should be cooked to the temperature of 145 Fahrenheit.

The eggs should be cooked till the egg white and the yolk becomes firm. Seafood like fish with fins should be cooked to 145 Fahrenheit or till the flesh becomes opaque.

Shrimp, crab, scallops and lobster should be cooked till the flesh becomes white and pearly. Clams, oysters and mussels should be cooked till the shell opens.

Drink clean water, including bottled water when you’re travelling

Parasites infect your body when you drink contaminated water. While travelling always carry your water bottle. When you buy water bottles make sure they are not contaminated.

If you see impurities or worms in the water bottle do not drink it and return the bottled water immediately.

If you drink contaminated water, it might cause diarrhoea, vomiting and other illness. So be thoughtful before drinking water outside your home.

Boil the water before drinking. According to the Centres for Disease Control and Prevention, you should boil water for one full rolling boil for a minute. When you are above 6500 feet it is recommended to boil for 3 minutes.

Avoid swallowing water from lakes, streams, or ponds

Parasites like Toxoplasma gondii, Entamoeba histolytica, Cyclospora cayetanensis, Isospora belli, Blastocystis hominis, Balantidium coli, Acanthamoeba spp., Sarcocystis spp. and Naegleria spp. Are found in lakes, streams and ponds.

When the water is swallowed from lakes, ponds and streams there is a possibility of ingesting these parasites.

These parasites cause stomach pain, diarrhoea and other gastrointestinal tract infections. Naegleria fowleri is a common freshwater parasite. It is commonly called brain-eating amoeba which damages brain cells.

Avoid cat litter and faeces when you’re pregnant

Cat poop is a carrier of parasite toxoplasmosis. So, when you are pregnant avoid collecting cat litter.

When you collect cat litter and by any chance, you ingest the faeces it might infect the baby. You may be resistant to the parasite but it can cause birth defects to your baby like eye and brain damage.

If you are infected, there are medications to treat the infection. Yet, you and your baby will be closely monitored during and after birth.

So, it is better to avoid collecting cat litter during your pregnancy. If you don’t have anyone to do such chores take some precautions after doing it.

Parasite life cycles

All parasites have a life cycle and are divided into different phases. The phase they spend inside the host and the phase of growth, maturation and reproduction.

The life cycle of the parasite is further divided into monoxenous (direct) and heteroxenous (indirect). Parasites with a monoxenous life cycle spend most of their life inside a host. This stage is called a parasitic stage.

Parasites must be able to survive outside a host and then migrate to a new host. Parasites that depend on the host for survival are called obligate parasites.

The parasite that can live freely without a host for generations are called facultative parasites. They are capable of skipping the parasitic stage.

Nematodes and Cryptosporidium parasites have a direct life cycle.

Parasites with an indirect life cycle have two host stages. The definitive host and the intermediate host. During the definitive host stage, the reproduction and adult life phase happens.

In the intermediate host, parasite development occurs and then it is transmitted to a definitive host. Multiple development of the parasite takes place in the intermediate host, where the spread of the infection happens through vectors like mosquitoes.

Filarial nematodes like Plasmodium and Leishmania have an indirect life cycle.

Who is at risk of parasitic infections?

According to PMID 23697034, young aged people, female population, malnutrition, poverty, poor hygiene, lack of access to fresh water and illiteracy are the factors associated the risk of parasitic infection.

Anyone can get infected with a parasitic infection but the above-listed people are most vulnerable to the disease.

People with weakened immunity, already affected by some health condition, travel to the tropical and subtropical parts, swim in rivers, lakes and other water forms, and those who work with soil regularly are also vulnerable to parasitic infection.


Parasitic infections are common and anyone can be infected with the disease. So always be watchful with your health.

Drink only boiled water and fully cooked food. When parasites enter your body, they can cause gastrointestinal infection and other problems.

If they are not treated early then they maybe fatal. Always eat healthy food and fresh water to avoid illness.


1.What are the signs of a parasitic infection?

The signs and symptoms of parasitic infection include nausea, vomiting, abdominal pain, bloating, diarrhoea, watery stools and stomach pain.

2.What are the 3 types of parasitic infection?

The three types of parasitic infection are protozoa, helminths and ectoparasites.

3.How do you get a parasite infection?

When you consume contaminated water and food, the parasite present in the food is also ingested. Parasitic infection also spreads through sexual contact.

4.What are common parasitic infections in humans?

The common parasitic infection includes malaria, intestinalis and trichomoniasis.

5.Can parasites go away on their own?

When you have a strong immune system, some parasitic infections subside on their own.

6.How do parasites affect the body?

The parasites affect the gastrointestinal tract which causes diarrhoea and vomiting

7.What foods give you parasites?

Foods like contaminated, undercooked, raw vegetables and vegetables and uncooked seafood contain parasites.

8.How long do parasitic infections last?

The parasitic infection lasts for about 2-6 weeks.


The Information including but not limited to text, graphics, images and other material contained on this blog are intended for education and awareness only. No material on this blog is intended to be a substitute for professional medical help including diagnosis or treatment. It is always advisable to consult medical professional before relying on the content. Neither the Author nor Star Health and Allied Insurance Co. Ltd accepts any responsibility for any potential risk to any visitor/reader.

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