Fungi & Prions

Fungi - Prions

What are fungi, and what types are important in human disease?

Fungi include yeasts, molds, and mushrooms, but the two forms most important in human disease are yeasts and molds. Fungi are eukaryotic organisms, meaning they are larger than bacteria and contain organelles like a nucleus and mitochondria. They can be grown on agar, are usually aerobic, and human pathogenic fungi grow best at 35–37°C in acidic conditions with a pH around 4.0–4.5. The acidic environment also helps prevent bacterial growth.

What is the difference between yeast and molds?

Yeasts are single-celled, spherical fungi that reproduce mainly by budding, which is an asexual process. Molds are multicellular fungi made up of long filamentous structures called hyphae, and they reproduce through spores, often sexually. Some fungi are dimorphic, meaning they can switch between yeast and mold forms depending on environmental conditions.

What are the important structural and staining characteristics of yeast?

Yeast cells contain structures such as a nucleus, vacuole, mitochondria, lipid granules, phosphate granules, a membrane, and a cell wall. Bud scars can often be seen from previous budding events. Even though fungi do not contain peptidoglycan like bacteria, yeast stain very well as Gram positive organisms.

A stain called methylene blue can be used to determine whether yeast cells are alive or dead:

• Live yeast cells contain enzymes that break down methylene blue into colorless products, so they remain unstained.

• Dead yeast cells cannot break down the dye, so they stain blue.

How is methylene blue used to test yeast viability?

To test yeast viability, a drop of yeast culture is placed on a microscope slide with a coverslip. Methylene blue stain is added to one side of the slide, and a paper towel is used on the opposite side to pull the stain across the sample. Under the microscope:

• Blue yeast cells are dead

• Colorless yeast cells are alive

This works because living yeast contain enzymes that break down the methylene blue dye.

How do “zombie fungi” manipulate insects, and why do they do this?

Zombie fungi such as Ophiocordyceps infect insects and manipulate their behavior to improve fungal reproduction and spore dispersal. Infected insects may be forced to climb vegetation or move to environments that favor fungal growth before dying. The fungus then grows out of the insect’s body and releases spores that infect new hosts. This is an example of a parasite-host relationship and an evolutionary adaptation that increases the fungus’s survival and spread.

Could a cordyceps zombie apocalypse happen in humans? What role does climate change play in fungal disease?

A cordyceps-style zombie apocalypse in humans is considered extremely unlikely because Ophiocordyceps fungi are highly species-specific and infect insects, not humans. There are hundreds of species, but they are adapted specifically to insect biology.

However, climate change may increase fungal infections in humans. As global temperatures rise, fungi may adapt to survive at warmer temperatures closer to human body temperature. This could increase the number of fungal diseases capable of infecting humans in the future.

How does yeast fermentation work, and how do humans use it?

When yeast are provided with sugar and the proper environment, they carry out fermentation, converting sugars into:

• Ethanol (alcohol)

• Carbon dioxide

• ATP energy

Humans use this process to make:

• Beer

• Wine

• Spirits

• Bread

In alcoholic beverages, fermentation transforms sugars from grains or fruit into alcohol. In bread making, the carbon dioxide produced by yeast becomes trapped in the dough, causing it to rise.

How does yeast make bread rise?

Yeast use enzymes to break down starches into sugars, which they metabolize through fermentation and cellular respiration. During fermentation, yeast produce ethanol and carbon dioxide. The carbon dioxide gas becomes trapped inside the dough’s gluten network, creating bubbles that expand the dough and make bread rise.

How are fungal infections classified?

Fungal infections, also called mycoses, are classified according to how deeply they invade body tissues.

• Superficial infections affect the surface of the skin, nails, or mucous membranes.

• Subcutaneous infections occur underneath the skin after fungi enter through cuts or injuries.

• Systemic infections spread into internal organs such as the lungs, heart, brain, or central nervous system.

Systemic infections are generally the most serious and dangerous

What is ringworm, and how is it spread?

Ringworm, or tinea, is a fungal infection that causes a ring-shaped, itchy, red rash on the skin. Different forms include:

• Tinea pedis → athlete’s foot

• Tinea cruris → jock itch

• Onychomycosis → fungal nail infection

Fungal nail infections may cause nails to become thick, discolored, and brittle.

Ringworm spreads through:

• Skin-to-skin contact

• Contact with infected animals

• Shared objects such as towels or bedsheets

• Shared surfaces like locker room floors

Risk factors include excessive sweating, wearing tight shoes and socks, wrestling or contact sports, public showers without footwear, and close contact with animals.

What is candidiasis, and what causes it to develop?

Candidiasis is a fungal infection caused by an overgrowth of Candida albicans, a yeast that normally lives harmlessly on the body in small amounts. It commonly affects the skin, mouth (thrush), or vagina.

Healthy bacteria normally prevent Candida from overgrowing. However, candidiasis can occur when this balance is disrupted by:

• Stress

• Poor diet

• Weakened immune system

• Uncontrolled medical conditions

• Antibiotic use, which kills beneficial bacteria

What is sporotrichosis, and what symptoms can it cause?

Sporotrichosis is a severe fungal infection caused by Sporothrix fungi found in soil and plants. In Canada, infection usually occurs from contact with plant matter, while in South America a species called Sporothrix brasiliensis can spread from cats to humans.

Symptoms depend on the form of infection:

• Cutaneous: painless bumps that enlarge, form sores, and spread along the skin

• Ocular: eye redness, swelling, pain, and vision changes

• Pulmonary: cough, fever, chest pain, and shortness of breath

• Disseminated: spread to bones, joints, or the central nervous system, especially in immunocompromised individuals

What is chromoblastomycosis?

Chromoblastomycosis is a fungal infection found mainly in tropical and subtropical climates. It causes slow-growing wart-like lesions that spread to nearby skin and tissues. The disease can lead to severe disfigurement and disability, and in rare cases may even result in skin cancer.

What is histoplasmosis, and why can it be difficult to diagnose?

Histoplasmosis is a systemic fungal infection caused by inhaling spores from Histoplasma fungi. The fungus is commonly found in soil contaminated with bird and bat droppings.

It is often misdiagnosed because its symptoms resemble bacterial or viral pneumonia. In severe cases, especially in people with weakened immune systems, the infection can spread beyond the lungs to the brain and spinal cord, causing fungal meningitis. Symptoms of fungal meningitis include:

• Fever

• Headache

• Stiff neck

• Nausea

• Vomiting

• Light sensitivity

• Confusion

What is blastomycosis, and how does it spread through the body?

Blastomycosis is a lung infection caused by inhaling spores from Blastomyces, a fungus found in soil. Symptoms include fever, cough, and shortness of breath, although many infected people show no symptoms.

Once inside the lungs, body temperature causes the spores to transform into yeast. The yeast may stay in the lungs or spread through the bloodstream to other body parts including:

• Skin

• Bones

• Joints

• Organs

• Central nervous system

People with weakened immune systems are at greater risk for severe disease.

What is aspergillosis, and what complications can it cause?

Aspergillosis is caused by inhaling spores from the mold Aspergillus, which is found almost everywhere indoors and outdoors. Most strains are harmless, but some can cause serious illness in people with weakened immune systems, asthma, or lung disease.

Complications include:

• A fungus ball, which is a dense fungal mass that grows inside a sinus and may require surgery

• Invasive aspergillosis, the most severe form, where the infection spreads into blood vessels and other organs

How can fungal infections be prevented by breaking the chain of infection?

Prevention strategies target three major areas:

Target #1 — Susceptible Host

• Personal hygiene

• Immunization/vaccines

• Prophylaxis

Target #2 — Means of Transmission

• Sanitation

• Good hygiene practices

Target #3 — Reservoirs

• Isolation

• Quarantine

• Surveillance

• Treatment

Reducing exposure and maintaining healthy body defenses are critical for preventing fungal infections.

How do environmental conditions and hygiene affect fungal infection risk?

A:
Fungi thrive in warm, moist environments. Risk increases with:

• Excessive sweating

• Warm and humid conditions

• Walking barefoot in public showers, locker rooms, or gyms

Poor blood circulation also weakens immune defenses and reduces the body’s ability to fight fungal infections. Small injuries to the skin or nails can allow fungi to penetrate deeper tissues.

Good hygiene practices include:

• Keeping skin clean and dry

• Washing hands frequently

• Avoiding shared towels

• Wearing shoes in public showers and pools

• Cleaning gym equipment before and after use

What natural immune defenses protect the body against fungi?

The body relies on several natural defenses against fungal infection:

• Beneficial bacteria compete with fungi for nutrients and space

• Intact skin acts as a physical barrier

• Mucus and naturally occurring chemicals inhibit fungal growth

• Skin cell turnover removes microbes from the body surface

Acidic environments, such as the vagina, also help prevent fungal overgrowth. Postmenopausal hormonal changes can reduce vaginal acidity, increasing susceptibility to yeast infections. Antibiotics may also increase risk because they destroy beneficial bacteria that normally keep yeast under control.

How are fungal infections treated, and what alternative therapies may help?

Fungal infections are treated using antifungal medications such as:

• Creams

• Drops

• Ointments

• Oral tablets

• Injections

• Vaginal suppositories

Nail infections may take weeks or months to fully clear.

Some doctors may also recommend supportive or alternative therapies such as:

• Garlic, which has natural antifungal properties

• Increased vitamin C and essential fatty acids to support the immune system

• Lowering sugar intake, since fungi thrive on sugar

• Probiotics such as Lactobacillus acidophilus, which restore beneficial bacteria that compete with fungi

What is unique about the “Chernobyl fungus,” and why is NASA studying it?

A:
Scientists discovered fungi near Chernobyl that survive in highly radioactive environments using a process called radiosynthesis. These fungi contain melanin, which allows them to convert gamma radiation into chemical energy.

Because astronauts are exposed to radiation levels much higher than on Earth, NASA studied these fungi aboard the International Space Station to investigate whether they could help block harmful radiation during space travel.