Disease-Causing Parasites – Here’s What You Need To Know

A parasite is an organism that lives on or in a host. It gets sustenance from the host and at the same time injures it.

There are 3 main classes of parasites that can cause disease in humans: protozoa, helminths, and ectoparasites.


Protozoa are microscopic, one-celled-organisms that are able to multiply inside the human body.

Protozoa that live in the human intestine are usually transmitted through the faecal-oral route; for example, via contaminated food, or water, or person-to-person contact.

One example of protozoa capable of doing this is giardia. Girdia has a two-stage life cycle. In the first stage, this parasite consumes nutrients from the small intestine. It develops into a non-moving cyst when it enters its second stage. These cysts are excreted in faeces and can contaminate the water supply and/or food. The parasites can then be transmitted through faecal-oral transmission when parasites found in stool or food end up being swallowed by another person.

They can also be transmitted by unsanitary living conditions, and close human to human contact. This parasite causes Giardiasis, a diarrhoeal disease. Its symptoms usually appear 1-3 weeks after exposure to the parasite and may include: fatigue, weakness, abdominal cramps and weight loss.

Protozoa can also live in the blood or tissue of humans. They can be transmitted to other humans through the bite of a mosquito or sand fly.

The Plasmodium species are transmitted this way. This parasite destroys the red blood cells in humans which greatly affects organ functions and causes malaria. Symptoms of Malaria include fever, tiredness, vomiting and headaches. It can cause yellow skin, seizures, coma or death, in severe cases. In 2017, there were an estimated 219 million cases of malaria in 87 countries. The estimated number of malarial death is 435,000 in 2017, most of them young children in sub-Saharan Africa. You can find out more about Malaria here.


Helminths (or worms) are large, multicellular organisms that can be seen through the naked eye in their adult stages. They can’t multiply in humans. There are 3 main groups of helminths: flatworms, thorny-headed worms and roundworms.

Flatworms have flattened bodies. 80% of flatworms are thought to be parasitic in nature.

Tapeworms are a type of flatworm. Transmission of this parasite occurs via faecal-oral route as well as from person-to-person (mainly as a result of poor sanitation and shared living quarters). Symptoms of having tapeworms include diarrhoea, weight loss, weakness and abdominal pain.

Roundworms (or nematodes) are the most numerous multicellular animals on earth, and they can be found anywhere. More than 50% of the world’s population may have been affected by at least one of six main classes of roundworms during their life.

The eggs of roundworms usually develop in soil before being transmitted to humans. An example of roundworm is the hookworm, which penetrates the skin from contaminated soil. It is very important to wear appropriate footwear to prevent hookworm transmission.

One of the most common type of helminth parasite is the pinworm or thread worm. Pinworms develop from eggs that are found on the skin near the anus or under fingernails. A major symptom of pinworm is itching around the anus. These parasites are easily passed from one person to another, even infesting entire families.


Ectoparasite is the term used to refer to organisms such as ticks, fleas, lice and mites. These parasites attach or burrow into the skin and stay there for relatively long periods of time (e.g. weeks to months).

One common condition caused by these type of parasites is Scabies. Scabies is a contagious skin disease that is caused by the human itch mite. It’s marked by itching and small raised red spots. It is spread by direct, prolonged, skin-to-skin contact.

Head lice are small, wingless insects that suck blood from human scalp. They live and breed in human hair.

Prevention and Treatment

Diagnosis of a parasitic infection can be challenging because some parasites can lie dormant for a long time. Some people may exhibit no symptoms, or symptoms can be non-specific and vague.

Once a parasitic infection has been diagnosed, there are lots of good medications to treat them. Some medications may have side effects, but in general they are very effective.

Aside from the treatment of parasites, preventative strategies should be implemented, such as improving sanitation. Also, appropriate clothing and footwear should be used in affected areas.

What’s your takeaway from this article on disease-causing parasites? Do you have any experience with parasitic infections? Share your thoughts and ideas in the comments section below.

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