The Tiny Invaders: Bacteria, Viruses, Parasites & Fungi Explained

Microbes are present everywhere, including in food, water, soil, and even inside the human body. In most cases, they live peacefully within the body and can even provide health benefits, such as certain bacterial strains in probiotics or yeasts found in fermented foods. However, in other instances, these microbes can become harmful by releasing toxins, damaging cells and tissues, and causing infectious diseases. 

As a healthcare provider, I’m often asked about the differences between bacteria, viruses, parasites, and fungi. This overview serves as an explainer to explain these different types of tiny cells, the infectious diseases they can cause, and practical ways to prevent them.

What are the differences between bacteria, viruses, parasites, and fungi?

Bacteria

Bacteria are single-celled microorganisms that exist in various shapes, such as spherical, rod-like, and spiral forms. The majority of bacteria are harmless, and some even provide beneficial functions. Fewer than 1% of all bacteria cause infectious diseases, but those that do can reproduce within the body and potentially spread to others. They often release toxins that have the potential to cause severe illness.

Bacteria can spread through 

• Coughing and sneezing
• Contact with contaminated surfaces or skin
• Bodily fluids, such as blood and saliva
• Sexual activity 

Most bacteria, excluding the spherical type known as cocci, move using a tail-like structure called a flagellum. When conditions are favorable, they reproduce by dividing into two, allowing their population to grow rapidly. However, if the environment becomes unsuitable, bacteria can enter a dormant state. In this state, they develop a thick protective coating and remain inactive until conditions improve.

Infectious diseases caused by bacteria can include conditions such as tuberculosis, chlamydia, bacterial meningitis, strep throat, and certain urinary tract infections.

Viruses

Viruses are microscopic infectious particles with a basic structure composed of either DNA or RNA enclosed in a protein shell. They can only reproduce by invading the living cells of other organisms. Viruses are known to cause numerous infectious diseases, such as influenza, the common cold, AIDS, chickenpox, shingles, COVID-19, and measles.

Viruses spread in ways similar to bacteria. They can also enter the body through vectors like mosquitoes, open wounds, contaminated food, contact with infected surfaces, bodily fluids, or feces, or simply through breathing them in. Antibiotics are specifically designed to kill bacteria and do not work against viruses.

Fungi

Most fungi are harmless and are even commonly consumed. The fungi kingdom includes mushrooms, molds found in blue or green vein cheese, and yeasts used in bread making.

However, certain types of fungi can cause illness. For example, athlete’s foot, which results in itching, scaling, and cracking of the skin on the feet, is often triggered by moist conditions such as sweaty feet in enclosed shoes. Candida is another common one that can lead to thrush, causing infections in the mouth, throat, stomach, and urinary tract. This often occurs in individuals taking antibiotics or those with weakened immune systems.

Ringworm, despite having ‘worm’ in the name, is actually a fungal infection. It appears as a reddish, itchy, scaly rash affecting the skin and scalp.

Fungal infections commonly impact the lungs, skin, or nails. In some cases, the infection may spread internally, affecting organs and leading to systemic illnesses.

Parasites

Parasites are organisms that live on or inside another organism, obtaining nutrients at the host’s expense. Part of their life cycle is often spent outside the host, residing in areas such as food, soil, water, or insects. They can enter the body through the consumption of contaminated food or beverages. Many parasites inhabit the intestinal tract, with some causing no harm to the host.

Infectious diseases caused by parasites include giardiasis, toxoplasmosis, and cryptosporidiosis.

Humans can be infected by several types of parasites:

• Roundworms (nematodes). These are long, round-bodied worms that can enter the human body through ingestion, skin penetration, or insect bites. Examples include whipworms, hookworms, and Wuchereria bancrofti, which is transmitted by mosquitoes.
• Tapeworms. These are flat, segmented worms that live in the intestines of animals and humans. They are often transmitted by consuming undercooked meat from infected animals. Tapeworm larvae can migrate to other parts of the body. Common sources include pork, beef, or fish tapeworms.
• Flukes (blood or liver flukes). These parasitic flatworms can be contracted by swimming in contaminated water or consuming raw or undercooked fish and water plants. Blood fluke larvae are released from infected snails into freshwater, while liver flukes can live in a host’s body for decades.
• Protozoa. Single-celled parasites that reproduce only inside a host. They are transmitted by biting insects or through contaminated water or food. Examples include Giardia, Plasmodium falciparum, and Trichomonas.

What are the treatments for bacteria, viruses, fungi, and parasites?

People are exposed to infectious organisms daily through the air, soil, water, food, and surfaces they come into contact with. Thankfully, the human immune system is designed to fight off most of these organisms, helping individuals stay healthy. When infections do occur, there are various medications available to help people recover and regain their health.

Antibacterial medication

Antibacterials or antibiotics are among the most commonly recognized prescription drugs, especially by parents who have had to administer a course of antibacterials to treat a child’s ear infection or strep throat. Common examples, such as penicillin, augmentin, and tetracycline, are widely known for their effectiveness in combating bacterial infections.

Antibacterials are effective only for treating infections caused by bacteria. They do not work against illnesses caused by other types of microbes. Using antibacterials when they are not needed can pose risks due to the potential side effects of any medication and may contribute to the increasing issue of antibiotic resistance.

Antiviral medication

Vaccines are available to protect against certain viral infections, such as chickenpox and polio. Ensuring that children receive all vaccinations recommended by the American Academy of Pediatrics is essential for their protection. Vaccines may also be recommended to adults who are at risk of certain viruses, for example, a yearly flu vaccine for those working in healthcare.

Antiviral medications are a relatively recent advancement, but their availability is steadily increasing. These drugs are designed to either prevent infections or reduce their duration by stopping the virus from spreading, though they do not eliminate existing viruses. However, antiviral medications are not suitable for all viral infections, and they are typically more targeted and designed to combat specific viruses. For example, HIV is treated with antiretroviral drugs like Viread, Truvada, and Dovato. These medications work by suppressing the virus, preventing it from replicating, and helping to maintain a healthy immune system.

Zovirax is an antiviral medication used to treat chickenpox and manage symptoms caused by herpes infections that can affect the skin, eyes, mouth, genitals, or brain. It helps reduce discomfort and accelerates the healing process of herpes sores. However, the medication does not eliminate the virus entirely. The herpes simplex virus remains dormant in the body and may reactivate, causing symptoms to return in the future.

Prevention is better than cure, especially in the case of viruses, where the range of effective treatments is currently rather restricted. Since one of the most common routes of infection is by breathing-in air-borne viruses, simple measures that can prevent the virus from even settling inside the body are a great line of defence. Enovid/NOWONDER™ is a nitric oxide nasal spray designed to kill respiratory viruses in the nasal cavity before they can settle into the lungs and start to multiply. It is sold over-the-counter; no prescription is required. 

While viral illnesses are not treated with antibiotics, bacterial infections can occasionally develop as a secondary complication of a viral disease. In such cases, antibiotics may be used to address the bacterial infection.

Antifungal medications

Fungal infections can be treated with a variety of medications. These treatments are often available as topical solutions that are applied directly to the skin. Some medications can be purchased over the counter, while others require a prescription from a doctor.

For severe fungal infections, doctors often prescribe medications such as Ambisome or newer antifungal drugs known as azoles. Diflucan and Itraconazole are two of the most commonly used azoles. These drugs must be administered cautiously under the supervision of a doctor, as they can potentially cause serious side effects, especially in children.

Over-the-counter antifungal products are generally regarded as safe when used as directed on the label. However, it is recommended to consult a pediatrician before using these medications to treat a child.

Antiparasitic medications

Certain antibacterial medications can also be effective against parasites. For example, Flagyl can disrupt the reproductive cycle of some parasites as well as certain bacteria. Resistance to certain antiparasitic medicines is becoming a growing concern. For instance, some medications used to treat malaria have lost effectiveness over time due to resistance. To address this issue, researchers are developing new antimalarial drugs, which are currently being evaluated in clinical trials.

Many believe the myth that certain parasitic diseases are caused by poor hygiene and can only be prevented or treated through better personal cleanliness. However, this is not true. Parasitic infections can be treated with medication, and personal cleanliness alone will not cure the infection. Still, hand washing remains an important practice to help prevent the spread of germs that can cause illness, including some parasitic diseases.

How can I avoid getting sick from harmful bacteria, viruses, fungi, and parasites?

While exposure to pathogens is not something that can be avoided by most people living a relatively normal life, there are some precautions that can be taken to reduce the likelihood of a virus, bacteria, fungi, or parasite causing illness. 

Food

Fruits and vegetables should be thoroughly washed before consumption. Raw or undercooked meat should be avoided. Surfaces and utensils must be kept clean during food preparation. Meat should be kept separate from other foods while preparing meals. Food should be consumed well within its expiration date and stored properly. Water should be filtered before use, particularly when the source is not known.

Handwashing

Hands should be washed with soap and water regularly. This is particularly important after using the bathroom, changing a diaper, preparing or eating food, and handling animals or cleaning up after them. When someone is sick or has an infection, frequent handwashing by those around them is essential to help prevent the spread of illness.

Boost the immune system

Eating a nutritious diet, staying physically active, maintaining a healthy weight, and practicing stress-reducing techniques can all strengthen the body’s ability to fight off infectious diseases. An immune support supplement such as the Shields Up Immune Pack may also be beneficial during times when the immune system may not be functioning as well as it should, or when there is an increased risk of exposure to illness.

Frequently Asked Questions

Are parasites worse than bacteria?

Some bacteria are helpful, like the probiotics in the gut, while others can cause illnesses. Parasites, on the other hand, depend on a host and harm it while living within or on it. As a result, some bacteria are more beneficial than any parasite, but certain harmful bacteria can be more dangerous than some parasites.

Do antibiotics work on infectious diseases from viruses, fungi, and parasites?

Antibiotics usually only work on bacteria, but some types, like Flagyl, can also be effective for parasites. A virus that has caused a secondary bacterial infection may also require antibiotics to treat the secondary bacterial infection.

How do doctors diagnose bacterial, viral, fungal, and parasitic infectious diseases?

Blood, stool, or body fluid samples can occasionally identify the specific microbe responsible for the illness through laboratory testing. Some fungal infections, especially on the skin, may also be diagnosed by a visual inspection.

How to tell if an infection is bacterial or viral?

A bacterial culture test identifies whether you have a bacterial infection and determines the specific bacteria responsible. This test requires a sample, which could be blood, urine, skin, or other tissue, depending on the location of the suspected infection.

What are the fungal vs bacterial infection symptoms?

Bacterial infections typically lead to rapid inflammation, swelling, or pus, while fungal infections progress gradually, causing issues such as a long-lasting cough, an itchy rash, or thickened skin.