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Infectious Diseases

Infectious Diseases

Fungi and Parasite Infections

Apart from bacteria and viruses, there are other types of pathogens. They are less common than bacteria and viruses, but they can be just as deadly. The other main types are: fungi and parasites.


Fungi are living things found in the Eukarya domain. They can be found all over the place such as in soil, on vegetation, and even on parts of our bodies. Mushrooms are probably the most common type of fungi, made popular by the Super Mario Brothers. Fungi reproduce by sporulation which is the process of releasing spores out into the world.

Many fungi are not dangerous. In fact, some are actually fun guys (get it?). For example, penicillin is a fungus that is a powerful antibiotic. Yeast is a type of fungi used to make beer, bread, and wine.
Bread: a better gift for that fungi lover than athlete's foot.

Yet, while some fungi can make some pretty scrumptious grub, other types of fungi can be just as harmful as vicious types of bacteria and viruses. You can also call fungal infections mycotic infections if you want to sound smart. Just like other infections, the symptoms of a fungal infection differ depending on which fungus is doing the infecting and which host it's crashing. If a drug treats a fungal infection it is called an antifungal. Below are some descriptions of infectious diseases caused by fungal infections.


Aspergillosis is a disease caused by an infection with the fungus Aspergillus. It is that thing that looks like an underwater flower in the picture below. It affects the respiratory system of the body, and in severe cases it can destroy body tissues. Aspergillus is typically encountered in the environment in soil, plants, or dust.

Yeast Infection and Thrush

Both yeast infections and thrush are caused by infection with one of 20 yeasts of the family Candida. For this reason it is also known as candidiasis. Trust us, it is nothing like candy.

This type of yeast is commonly present on the skin and in the mucosa, but when they overgrow they cause infectious disease. Overgrowth in the vagina causes itching, burning, and irregular discharge. Approximately 75% of women will have a vaginal infection at some point in their lives. Overgrowth in the mouth causes white patches or plaques to form in the mouth.

Both can be treated with anti-fungal drugs. If the yeast gets into the bloodstream, a more invasive form of candidiasis can occur which causes fever, chills, and possible organ failure depending on where the infection spreads.

Ringworm, Jock Itch, Athlete's Foot

Ringworm, jock itch, and athlete's foot are all caused by infection with Dermatophytes fungus, also known as the tinea fungus. This fungus lives on moist skin (like in your armpits and groin and between your toes) and can live on clothing and bedding as well (Blech. Kinda makes you wanna wash your bedsheets right now, huh?). Common symptoms are itchiness, redness, scaling, cracking of the skin, and loss of hair. A ring-shaped rash, may occur and affected nails can become thick and discolored.

Ringworm can occur many places and is often caught from infected pets. Jock itch refers to infection of the skin in the genital area. Athlete's foot is infection on the feet, generally between the toes. This is exactly why nixing the flip-flops in a public shower or locker room is never a good idea.

Athlete's foot between the toes.


A parasite is an organism living on or in another organism and using the other organism for food or energy. Since a parasite is something that infects your body, they can cause infectious disease.

Parasites are totally creepy to think about. Think about it; they are basically something else living inside of you like an unwanted houseguest. But hey, you already have trillions of bacteria living inside of you—what's all the fuss about?

Parasites are often larger than a unicellular bacteria, so this probably adds to the creep-o-meter. There are rumors about tapeworms more than 20 feet long. Seriously. Below is more information about a few parasites so you can fully understand what is in your nightmares tonight.

Roundworm, Hookworm, Whipworm

Unlike ringworm (which is not caused by a worm), these are all infections of soil transmitted helminths…ACTUAL WORMS. A different species of helminth causes each infection.

Hookworms can be contracted in soil that is contaminated with human feces. The tiny worms then penetrate the skin and migrate to the intestine. Do you have the heebie jeebies yet? Hookworms can cause anemia and malnutrition. 567 million people are infected with hookworm. That is 1 out of every 12 people on the planet.

Life cycle of hookworm.

Roundworms can be contracted by eating something contaminated with human feces. They can grow up to 12 inches long and can live for 1-2 years in the intestine. Roundworm causes the most human infections of all the helminths: 1 out of 9 people are infected with roundworms and 60,000 people die each year.

Whipworm affects 1 out of 12 people and is contracted by eating something contaminated with human feces. Whipworm females can lay up to 20,000 eggs per day. If given the choice between whipped cream or whipworm, we at Shmoop choose whipped cream.

African Eyeworm

African eyeworm is one of the creepier parasites, but it is not very deadly. It is caused by infection with the Loa loa worm. Whatta whatta? Loa loa.

The worm is carried in the African deerfly which transmits it to humans when it bites them. Although the worm does can travel to other places in the body, passages across the eye are quite noticeable. Apart from visualization of the worms, other symptoms are irritation or itchy swellings of the skin.

Worms can be surgically removed, but drug treatment is also required to kill the larvae, or baby worms. This disease is most prevalent in Central Western Africa where it is estimated that 13 million people are infected.

A 5cm Loa loa worm extracted from a patient's eyeball. Image from here.


The deadliest parasite in the world is Plasmodium, which causes Malaria. Plasmodium is one type pathogen that is carried in a vector animal. It is carried by several specific species of mosquito. It is then transferred to humans who have been bitten by the mosquito. Plasmodium replicates in the liver and can later infect red blood cells.

Malaria causes fever, chills, and fatigue, and it can cause serious complications leading to death. Approximately 216 million cases and 655,000 deaths were estimated from Malaria in 2011, mostly in children in Africa where the disease is prevalent.

Malaria can be treated with drugs, although drug resistance is on the rise. An international campaign to provide mosquito netting and insecticide is currently underway to reduce Malaria exposure.
Children in Senegal demonstrating how to properly use a mosquito net to prevent malaria.


Approximately 1 out of 5 people in the United States is infected with the parasite Toxoplasma gondii (T. gondii) which causes toxoplasmosis. Many people do not know they are infected and they show no symptoms or recover quickly. It can, however, be a problem for pregnant women or immunocompromised people.

T. gondii can be found in undercooked meat, water, and cat feces. Meow. Symptoms can affect the brain, eyes, and other organs. Pregnant women are advised to steer clear of the kitty box, especially early in pregnancy (toilets can still be used). Any contact with cat feces poses a threat to the fetus. Babies born to women who became infected early in pregnancy are at risk for blindness later in life and mental disabilities.

"Brain Eating Amoeba"

This disease is just as scary as it sounds and is caused by the parasite Naegleria fowleri. This parasite is commonly found in warm bodies of fresh-water. Drinking the water is safe, but if the amoeba gets into your nose it is bad news. From there, the parasite travels to the brain where it takes up residence, destroying the brain tissue and causing brain swelling that leads to death.

It is a very rare infection with less than five cases per year in the United States. Recently, several people became infected when using unclean water in a neti pot to irrigate their noses. Other than neti pots, people primarily become infected after swimming or submerging their nose in a contaminated body of water. Since it can only infect through your nose, this nose plug is probably starting to look more attractive.

Naegleria fowleri (stained green) inside brain tissue. Think it is pretty? You're right…pretty dangerous.

Brain Snack

Helminthic Therapy

We have discussed helminths as a deadly parasite, but they can also be a therapeutic strategy. What? That's right; some people choose to infect themselves with worms because they believe it is beneficial to help with bowel disorders, allergies, and asthma. There is even some scientific evidence to support this theory, and it is currently being further researched to answer a lot of questions. Watch this video for more information.

Hookworms attached to the intestine.

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