ClassX Video Lessons How do germs spread (and why do they make us sick)? – Yannay Khaikin and Nicole Mideo
The sun is shining, and the birds are singing. It seems like the start of another beautiful day. You’re enjoying a walk in the park when someone nearby sneezes. You might feel the droplets land on your skin, but what you can’t see are the tiny germs that have traveled through the air and landed on your clothes, hands, and face.
Even though this situation sounds unpleasant, it’s common for our bodies to come into contact with germs, and most of the time, we don’t even notice. Germs are everywhere—on almost every surface we touch. When we talk about germs, we’re referring to tiny organisms like bacteria, fungi, protozoa, and viruses. These germs can interact with our bodies and affect how we feel and function.
Scientists who study infectious diseases have long wondered why some germs are harmless while others can be dangerous or even deadly. Although we haven’t figured it all out, we know that how harmful a germ is, or its virulence, is a result of evolution.
The key to understanding germs lies in how they spread from one person to another. A common way germs spread is through the air, like when someone sneezes. A well-known germ that spreads this way is the rhinovirus, which causes many common colds.
Imagine that after the sneeze, one of three types of rhinovirus lands on you. Let’s call them “too much,” “too little,” and “just right.” These viruses are designed to replicate, but they do so at different speeds due to genetic differences. “Too much” multiplies quickly, which can make you very sick. If you’re too ill to leave your house, the virus has fewer chances to spread. If the illness were fatal, the virus would die with you.
On the other hand, “too little” replicates slowly and causes minimal harm, so you’re healthy enough to be around others. However, the lack of symptoms means you might not sneeze, or if you do, there might not be enough viruses to infect someone else. Meanwhile, “just right” replicates at an optimal rate, allowing you to carry enough of the virus to spread it without becoming too sick to function.
This idea is known as the trade-off hypothesis. It suggests that germs evolve to maximize their success by balancing how much they replicate inside a host and how well they spread to new hosts. For the rhinovirus, this hypothesis predicts that less harmful forms will be favored since the virus relies on close contact to spread.
While most people experience mild symptoms like a runny nose and coughing, the common cold usually lasts about a week. However, germs use different ways to spread. For example, the malaria parasite is spread by mosquitoes and might benefit from making its host sick, as a sick person is easier to bite.
To reduce the impact of infectious diseases, evolutionary biologist Dr. Paul Ewald suggests that we can influence their evolution through simple disease-control methods. By mosquito-proofing homes, setting up clean water systems, or staying home when sick, we can block harmful germs’ transmission strategies while encouraging them to evolve into milder forms.
This innovative approach could lead to a win-win situation in managing infectious diseases, making it easier for us to stay healthy and safe.
Imagine you’re a germ! Create a simple simulation in the classroom where you and your classmates act as germs spreading through sneezes. Use colored water in spray bottles to represent sneezes and observe how far the droplets travel. Discuss how this activity relates to the spread of germs in real life.
Learn about different types of germs by playing a matching game. You’ll be given cards with descriptions of bacteria, viruses, fungi, and protozoa. Match them with their correct names and images. This will help you understand the diversity of germs and their characteristics.
Participate in a role-playing activity where you act out the trade-off hypothesis. Divide into groups representing “too much,” “too little,” and “just right” viruses. Discuss and present how each type affects the host and its ability to spread, helping you grasp the concept of virulence and evolution.
Conduct a small research project on different ways germs spread. Choose a specific germ and investigate its transmission method, symptoms, and prevention strategies. Present your findings to the class to enhance everyone’s understanding of germ spread and control.
Create a poster that illustrates effective ways to prevent the spread of germs, such as handwashing, using tissues, and staying home when sick. Use creative visuals and clear messages to educate your peers on maintaining good hygiene and health practices.
The sun is shining, and the birds are singing. It looks like the start of another lovely day. You’re walking happily in the park when someone nearby sneezes. You can feel the droplets land on your skin, but what you can’t feel are the microscopic germs that have traveled through the air and onto your clothing, hands, and face.
As unpleasant as this scenario sounds, it’s common for our bodies to be exposed to germs, and most of the time, it’s not obvious. Germs are found on almost every surface we touch. When we talk about germs, we’re referring to various microscopic organisms, including bacteria, fungi, protozoa, and viruses. What these germs have in common is their ability to interact with our bodies and affect how we feel and function.
Scientists studying infectious diseases have long wondered why some germs are relatively harmless while others can be devastating or even fatal. Although we haven’t solved the entire puzzle, we know that the harmfulness, or virulence, of a germ is a result of evolution.
The key lies in a germ’s mode of transmission, which is the strategy it uses to move from one host to another. A common mode of transmission occurs through the air, like the sneeze you just witnessed. One germ that uses this method is the rhinovirus, responsible for many common colds.
Imagine that after the sneeze, one of three hypothetical varieties of rhinovirus—let’s call them “too much,” “too little,” and “just right”—has landed on you. These viruses are programmed to replicate, but due to genetic differences, they do so at different rates. “Too much” multiplies rapidly, which can lead to more severe symptoms for you, the host. If you’re too sick to leave your home, the virus has fewer opportunities to spread. If the disease were to be fatal, the virus’s life cycle would end with yours.
On the other hand, “too little” replicates rarely and causes minimal harm, leaving you healthy enough to interact with others. However, the lack of symptoms means you may not sneeze, or if you do, there may not be enough viruses to infect anyone else. Meanwhile, “just right” replicates at an optimal rate, allowing you to carry enough of the virus to spread it without becoming too ill to function.
This concept is known as the trade-off hypothesis, which suggests that germs evolve to maximize their success by balancing replication within a host and transmission to new hosts. In the case of the rhinovirus, this hypothesis predicts that less virulent forms will be favored since the virus relies on close contact to spread.
While most people experience mild symptoms like a runny nose and coughing, the common cold typically lasts about a week. However, germs use various modes of transmission. For example, the malaria parasite is transmitted by mosquitoes and may benefit from harming its host, as a sick person is easier to bite.
To reduce the impact of infectious diseases, evolutionary biologist Dr. Paul Ewald suggests that we can influence their evolution through simple disease-control methods. By mosquito-proofing homes, establishing clean water systems, or staying home when sick, we can obstruct harmful germs’ transmission strategies while encouraging them to evolve into milder forms.
This innovative approach could lead to a win-win situation in managing infectious diseases.
Germs – Microorganisms, especially those that can cause disease. – Germs can spread through contact with contaminated surfaces.
Bacteria – Single-celled microorganisms that can exist either as independent organisms or as parasites. – Some bacteria are beneficial to humans, such as those in our digestive system.
Viruses – Microscopic infectious agents that can only replicate inside the living cells of an organism. – The common cold is caused by viruses that infect the respiratory tract.
Fungi – A group of spore-producing organisms that feed on organic matter, including molds, yeast, and mushrooms. – Fungi play a crucial role in decomposing organic material in ecosystems.
Protozoa – Single-celled eukaryotes that can be free-living or parasitic, which feed on organic matter such as other microorganisms or organic tissues and debris. – Protozoa can cause diseases such as amoebic dysentery in humans.
Infectious – Capable of causing infection or disease by entering the body of a host organism. – The flu is an infectious disease that spreads easily from person to person.
Evolution – The process by which different kinds of living organisms are thought to have developed and diversified from earlier forms during the history of the earth. – Evolution explains how species adapt to their environments over time.
Rhinovirus – A group of viruses that are one of the most common causes of the common cold. – The rhinovirus is highly contagious and spreads through airborne droplets.
Malaria – A disease caused by a plasmodium parasite, transmitted by the bite of infected mosquitoes. – Malaria is prevalent in tropical and subtropical regions where mosquitoes thrive.
Transmission – The act or process by which a disease is spread from one person or organism to another. – Understanding the transmission of diseases is crucial for preventing outbreaks.
