In this lesson you will be introduced to our new phenomena and begin to brainstorm questions we will answer in this unit. 

Watch the following video: 

phenomena videos from Lauren Levites on Vimeo.

Look at the photos of a sea star suffering from Sea Star Wasting Syndrome: (Source)

After looking at the video and photos, you probably have a lot of questions. In this unit we will be exploring infectious diseases in non-humans. 

What are some questions you have that apply to infectious diseases? What are some questions you have that apply specifically to the diseases you saw in the video?

Infectious diseases have to reach and thrive in living organisms. In this lesson, we will figure out what are the agents that cause infectious disease. 

Based on the diseases you are aware of and that you saw in the phenomenon video, make a list of as many things that you think cause disease. 

The vast majority of infectious diseases are caused by microorganisms, called "microbes." However, only about 1% of microbes cause disease! We call these microbes who cause disease, pathogens.

You are probably familiar with many of these pathogens. Let's look at the ones we saw in the phenomenon video first. Read the following and then answer the questions below. 

White Nose Syndrome:

White-nose syndrome (WNS) is a disease that affects hibernating bats and is caused by a fungus, Pseudogymnoascus destructans, or Pd for short. Sometimes Pd looks like a white fuzz on bats’ faces, which is how the disease got its name. Pd grows in cold, dark and damp places. It attacks the bare skin of bats while they’re hibernating in a relatively inactive state. As it grows, Pd causes changes in bats that make them become active more than usual and burn up fat they need to survive the winter. Bats with white-nose syndrome may do strange things like fly outside in the daytime in the winter. 

Fire blight on apple tree:

Fire blight is a common and very destructive bacterial disease of apples and pears. The disease is caused by the bacterium Erwinia amylovora. On apples and pears, the disease can kill blossoms, fruit, shoots, twigs, branches and entire trees. While young trees can be killed in a single season, older trees can survive several years, even with continuous dieback.

Brain worm in Moose: 

Brain worm is the term commonly applied to the parasitic nematode (round worm), Parelaphostrongylus tenuis (P. tenuis). White-tailed deer are the normal host for this parasite. Most of the time, they are not affected by the parasite. However, other species such as moose, mule deer, reindeer/caribou, sheep, goats, alpacas, and llamas are abnormal hosts and can develop disease or die if infected.

Sea Star Wasting Syndrome: (SSWS/SSWD)

In December 2020, sunflower sea stars were placed on the ICUN's red list of threatened species. There has been a 90% decline in this species due to warming oceans an an epidemic called "Sea Star Wasting Syndrome." Scientists from The Nature Conservancy and Oregon State University, who led the listing effort, estimate that 90.6% of the sunflower sea star population is now lost from the outbreak, with as many as 5.75 billion dead from the disease.  Symptoms of the disease include a deflated appearance, white lesions and twisted arms, followed by softening tissue, loss of arms, and death. The disease progresses rapidly, often killing its victims within a matter of days. In an effort to identify the potential pathogen and conditions responsible for SSWD, scientists and their partners collected extensive survey data and tissue samples, but the cause remains a mystery that several research institutions are working hard to unlock.

We have looked at a few examples of pathogens. What are the agents who are causing disease in plants and animals?

Bacteria:

Bacteria are microscopic, single-celled organisms that have no nucleus and a cell wall made of peptidoglycan. Bacteria are the direct descendants of the first organisms that lived on Earth, with fossil evidence going back about 3.5 billion years.
Most bacteria are much smaller than our own cells, though a few are much larger and some are as small as viruses. They usually do not have any membrane-wrapped organelles (e.g., nucleus, mitochondria, endoplasmic reticulum), but they do have an outer membrane. Most bacteria are also surrounded by at least one layer of cell wall.
Bacteria are a huge and diverse group. Its members have many shapes, sizes, and functions, and they live in just about every environment on the planet.

Viruses: 

Viruses are microscopic particles made of nucleic acids, proteins, and sometimes lipids. Viruses can’t reproduce on their own. Instead, they reproduce by infecting other cells and hijacking their host’s cellular machinery. 
Since the ability to reproduce is often listed as a requirement for life, some consider viruses to be non-living. Regardless, viruses are an important part of all ecosystems, including the human body.
In our bodies, viruses infect not only our cells, but also other microbes that live in our bodies. Viruses that infect bacteria are called bacteriophage. 
Think of a virus as a tiny package jacketed in a protein covering. Inside is either DNA or RNA. Each molecule serves as an instruction book. Its genetic information provides instructions that tell a cell what to make and when to make it.

Fungus: 

There are millions of fungal species, but only a few hundred of them can make people sick. Molds, yeasts, and mushrooms are all types of fungi.
Fungi can cause many different types of illnesses, including:

• Asthma or allergies. Learn more about mold and how it can affect your health.
• Rashes or infections on the skin and nails
• Lung infections (pneumonia), with symptoms similar to the flu or tuberculosis
• Bloodstream infections
• Meningitis

Anyone can get a fungal infection. Fungi are common in the environment, and organisms breathe in or come in contact with fungal spores every day without getting sick. However, in organisms with weak immune systems, these fungi are more likely to cause an infection.

Parasites: 

Parasites are living things that use other living things - like your body - for food and a place to live. You can get them from contaminated food or water, a bug bite, or other types of direct contact. Some parasitic diseases are easily treated and some are not.

Parasites range in size from tiny, one-celled organisms called protozoa to worms that can be seen with the naked eye. Some parasitic diseases occur in the United States. Contaminated water supplies can lead to Giardia infections. Cats can transmit toxoplasmosis, which is dangerous for pregnant women. Others, like malaria, are common in other parts of the world.

Prion: 

Prion diseases comprise several conditions. A prion is a type of protein that can trigger normal proteins in the brain to fold abnormally. Prion diseases can affect both humans and animals and are sometimes spread to humans by infected meat products. 

Prion diseases occur when normal prion protein, found on the surface of many cells, becomes abnormal and clump in the brain, causing brain damage. This abnormal accumulation of protein in the brain can cause memory impairment, personality changes, and difficulties with movement.

Prions as a disease causing agent were only discovered in the late 20th century, with an American Biologist receiving the Nobel prize for his discovery in 1997. Experts still don't know a lot about prion diseases, but unfortunately, these disorders are generally fatal.

It is important to remember that:

• A pathogen is a micro-organism that has the potential to cause disease.
• An infection is the invasion and multiplication of pathogenic microbes in an individual or population.
• Disease is when the infection causes damage to the individual’s vital functions or systems.
• An infection does not always result in disease!

In this lesson you will use a model to determine different ways diseases are transmitted. 

In the previous lesson you looked at types of infectious agents. Bacteria, viruses, parasites, fungi, and prions all must be transmitted to infect new organisms. 

Use the model below to explore transmission type.

Sometimes transmission of a disease can happen in multiple ways. Set up the model to test transmission using 2 of the factors. 

There are many ways infectious diseases may be transmitted from one organism to another. We typically group them as direct contact and indirect contact. 

Direct Contact Transmission Types:

1. Contact Between Individuals: Transmission occurs when an infected person touches or exchanges body fluids, like saliva, with someone else. 
2. Specific Contact Between Individuals: Is carried in blood and other specific bodily fluids, but not saliva. Pregnant women can also transmit infectious diseases to their unborn children via the placenta. 
2. Droplet spread: The spray of droplets during coughing, sneezing and speaking can spread an infectious disease. 

Indirect Contact Transmission Types:

1. Airborne transmission: Some infectious agents can travel long distances and remain suspended in the air for an extended period of time. 
2. Contaminated objects: Some organisms can live on objects for a short time. 
3. Food and drinking water: Infectious diseases can be transmitted via contaminated food and water. 
4. Animal-to-person contact: infected animal bites or scratches you or when you handle animal waste. 
5. Animal reservoirs
6. Insect bites (vector-borne disease)
7. Environmental reservoirs: Soil, water, and vegetation containing infectious organisms can also be transferred to people. 
 

You will be using a similar version of the model from the disease transmission lesson. In this lesson we are going to look at the factors involved in the spread of disease. 

Use the infectiousness slider in this model. Conduct your investigation by looking at infectiousness rates of: 0%, 10%, 25%, 40%, 60% 80%, 100%.

Look at the graph on the side, in Question 1 record your observations of the graph for each level.

Use the "chance-recover" slider in this model. Conduct your investigation by looking at recovery rates of: 1%, 10%, 20%, 30%, 50%, 70%, 100%.

Look at the graph on the side, in Question 1 record your observations of the graph for each level.

Use the "duration" slider in this model. Conduct your investigation by looking at duration of the disease for 7, 10, 15, 20, 30, and 45 days.

Look at the graph on the side, in Question 1 record your observations of the graph for each level.

Use the "initial-sick" slider in this model. Conduct your investigation by looking at how the disease spreads based on how many are sick at the beginning. Change initial sick to: 1, 5, 10, 20, 40, 60, 80.

Look at the graph on the side, in Question 1 record your observations of the graph for each level.

Have you ever wondered how an organism can "fight off" an infection? Why are some infections worse than others? Why are so many scientific studies, including immunology studies, done on other organisms?

In this lesson you will look at the structures and functions of the immune system that react to fight these infectious diseases. 

Look at the photo below and answer the questions.

t=time

On the prior page, you were looking at a photo of cells in a mouse. 

You may have guessed that those large green cells were part of the immune system, as you watched it engulf the smaller red circle. In fact most organisms have some types of cells that provide a defense against invaders. A general term for these cells is phagocytes, which comes from the Greek root phagein, "to eat" or "devour", and "-cyte", the suffix in biology denoting "cell."

Phagocytes were discovered by Elie Metchnikoff in the 1880s. Watch the video below to see his experiments that led to discovering them. 

sea star phagocytes original exp from Lauren Levites on Vimeo.

In the model below, discover what happens to the individuals in the sea star population when exposed to harmful bacteria. These phagocytes are part of the innate immune system. These cells provide non-specific responses, which means they respond to anything they view as foreign or an invader.

The Innate Immune System: 

The innate immune system is characterized by general, non-specific responses. The non-specific response is part of the innate immune system. Responses include sneezing, coughing and diarrhea. 
Physical barriers, such as the skin, also contribute to innate immune protection.
The innate immune system also protects us with chemicals such as acids in the stomach and enzymes in tears. 

We've been looking at a non-specific immune response, as phagocytes will move in to gobble up all types of invaders. But, how do some organisms become immune to specific diseases? That requires another level of immunity, called the adaptive immune system.

The adaptive immune system is mainly seen in vertebrate organisms. Although, there is some current research that points to some features possibly in invertebrates, like insects. 

Use the model below to discover one of the major features of the adaptive immune system: 

The Immune System:

These two parts of the immune system, innate and adaptive, do not work separately. They overlap and support one another through chemical signals sent via the bloodstream and lymph nodes. So, the next time you feel your heartbeat or you breathe, remember that your immune system is working just as hard, if a bit more slowly—it’s certainly helping to keep you healthy! 

The Adaptive Immune System:

Unlike the innate immune system, the adaptive immune system responds specifically to an invading virus or bacteria. The cells that contain the invading pathogen have an antigen, which the antibody responds to. Antibodies are the primary weapons of the immune system, since they are specifically designed to combat an invader. 
The adaptive immune response consists of B cells and T cells. 

• B cells make antibodies, while T cells show B cells what kinds of antibodies to make. 
• T cells also kill virus-infected cells, so that the virus can’t spread. 

B and T cells respond specifically to an invading organism, and remember when they have encountered a particular pathogen before. That way, when the pathogen invades the body again, the adaptive immune system can respond quickly and efficiently, preventing an infection. 

image source

Immune System Videos:

Ameoba Sisters Immune System

The Immune System: B Cell, T Cell, Soldier, Spy

In the past lesson you looked at the innate and adaptive immune systems. The body relies on the innate and adaptive defenses to stop harmful diseases, but sometimes those defenses are not enough. There are some specific treatments that exist for handling outbreaks of diseases. In this lesson we are going to look at some possibilities and how they work. 

You have seen a lot of examples of diseases in this unit so far. Bats who suffer from white nose syndrome. Plants that develop cankers and need to be cut down. Parasites that infect organisms, like the brain worm in the moose. 

In this model you will be looking at immunity, using the "immunity-forever" toggle and the "immunity-duration" slider. 

One of the major types of treatments is vaccines. You are familiar with having to go to the doctor to get a vaccine or to take your dog or cat to the vet to get one. What are they and how do they work?

• Vaccines help your immune system fight infections faster and more effectively. They are typically made of small amounts of weak or dead germs. 
• When you get a vaccine, it sparks your natural immune response, helping your body fight off and remember the germ so it can attack it if the germ ever invades again. 
• Vaccines often provide long-lasting immunity to serious diseases without the risk of serious illness. Some vaccines require boosters or provide a shorter period of immunity.
• Vaccines work WITH your adaptive immune system to develop the antibodies that will protect you if you come in contact with that germ (virus or bacteria).

History of Vaccines in the United States: Excerpt from this article.

The smallpox epidemic of 1721 was different than any that came before it. As sickness swept through the city, killing hundreds in a time before modern medical treatment or a robust understanding of infectious disease, an enslaved man known only as Onesimus suggested a potential way to keep people from getting sick. Intrigued by Onesimus’ idea, a brave doctor and an outspoken minister undertook a bold experiment to try to stop smallpox in its tracks.

Smallpox was one of the era’s deadliest afflictions. “Few diseases at this time were as universal or fatal,” notes historian Susan Pryor. The colonists saw its effects not just among their own countrymen, but among the Native Americans to whom they introduced the disease. Smallpox destroyed Native communities that, with no immunity, were unable to fight off the virus.

Mather didn’t trust Onesimus: He wrote about having to watch him carefully due to what he thought was “thievish” behavior, and recorded in his diary that he was “wicked” and “useless.” But in 1716, Onesimus told him something he did believe: That he knew how to prevent smallpox.

Onesimus, who “is a pretty intelligent fellow,” Mather wrote, told him he had had smallpox—and then hadn’t. Onesimus said that he “had undergone an operation, which had given him something of the smallpox and would forever preserve him from it...and whoever had the courage to use it was forever free of the fear of contagion.”

The operation Onesimus referred to consisted of rubbing pus from an infected person into an open wound on the arm. Once the infected material was introduced into the body, the person who underwent the procedure was inoculated against smallpox. It wasn’t a vaccination, which involves exposure to a less dangerous virus to provoke immunity. But it did activate the recipient’s immune response and protected against the disease most of the time.

Mather was fascinated. He verified Onesimus’ story with that of other enslaved people, and learned that the practice had been used in Turkey and China. He became an evangelist for inoculation—also known as variolation—and spread the word throughout Massachusetts and elsewhere in the hopes it would help prevent smallpox.

The SARS-CoV-2 Vaccine:

The new coronavirus vaccines are different than traditional vaccines. This vaccine does not use a weak or dead form of the germ, instead it mimics the protein spike on the pathogen. It is a newer type of vaccine called mRNA vaccines. 

Video from PBS on mRNA vaccine. 

How the Moderna mRNA vaccine works: 

Two treatments you are likely familiar with are antibiotics and antivirals. If you've ever had an ear infection or strep throat, you've likely been given a course of antibiotics. Perhaps you had the flu and a doctor prescribed you a medication like Tamiflu, that's an antiviral. These treatments provide a way for the body to handle the bacterial or viral infection that occurs. 

Antibiotics are medications that destroy or slow down the growth of bacteria.
There are two types of antibiotics:

• A bactericidal antibiotic, such as penicillin, kills the bacteria. These drugs usually interfere with either the formation of the bacterial cell wall or its cell contents.
• A bacteriostatic antibiotic, which stops bacteria from multiplying.

Antiviral drugs work to prevent the virus from multiplying, they do not destroy the virus. 

Antibiotic Resistance: 

Antibiotics work until bacteria become resistant to them. In a population of bacteria, some are naturally resistant to the antibiotic. As the antibiotic kills bacteria, those that are resistant survive. The bacteria that are resistant to the antibiotic multiply (remember bacteria grow exponentially). Eventually the bacteria population evolves to be resistant to the drug. 

One major disease that results from antibiotic resistant is Methicillin-resistant Staphylococcus aureus, commonly known as, MRSA. MRSA is often transmitted in health care settings, such as hospitals and dialysis centers. It can be extremely difficult to recover from due to the number of antibiotics the bacteria is resistant to. 

Outside of the immune response and various treatments, there are other factors that can influence if organisms come into contact with certain diseases. 

In our current pandemic, one of the major pieces of advice is to engage in social distancing. This may feel like it goes against your instincts. You may have even wondered if any other species would be able to social distance. In fact, there are some examples of other species who instinctively social distance. The excerpts below come from this Scientific American article. 

Lobsters:

On a shallow reef in the Florida Keys, a young Caribbean spiny lobster returns from a night of foraging for tasty mollusks and enters its narrow den. Lobsters usually share these rocky crevices, and tonight a new one has wandered in. Something about the newcomer is not right, though. Chemicals in its urine smell different. These substances are produced when a lobster is infected with a contagious virus called Panulirus argus virus 1, and the healthy returning lobster seems alarmed. As hard as it is to find a den like this one, protected from predators, the young animal backs out, into open waters and away from the deadly virus.

Ants

Researchers used tiny digital tags to track the movements of common garden ant colonies during an outbreak of a lethal fungus, Metarhizium brunneum. The spores of this fungus are passed from ant to ant through physical contact; it takes one to two days for the spores to penetrate the ant’s body and cause sickness, which is often fatal. The delay between exposure and sickness allowed Stroeymeyt and her colleagues to see whether ants changed their social behaviors in the 24 hours after they first detected fungal spores in their colony but before fungus-exposed ants showed signs of sickness.

To measure how ants respond when disease first invades their colony, the researchers applied fungal spores directly to a subset of the forager ants that regularly leave the colony. The foragers are most likely to inadvertently encounter fungal spores while out searching for food, so this approach mimicked the natural way this fungus would be introduced. The behavioral responses of ants in 11 fungus-treated colonies were then compared with the same number of control colonies, where foragers were dabbed with a harmless sterile solution. Ants in fungus-exposed colonies started rapid and strategic social distancing after treatment. Within 24 hours those forager ants self-isolated by spending more time away from the colony compared with control-treated foragers.

Healthy ants in fungus-treated colonies also strongly reduced their social interactions, but the way they did so depended on their roles. Uninfected foragers, which interact frequently with other foragers that might carry disease, kept their distance from the colony when disease was present. This prevents them from inadvertently putting the reproductively valuable colony members (the queen and “nurses” that care for the brood) at risk. The nurses also took action, moving the brood farther inside the nest and away from the foragers once the fungus was detected in the colony. The cues that the ants use to detect and rapidly respond to fungus exposure are still unknown, but this strategic social distancing was so effective that all queens and most nurses from the study colonies were still alive at the end of the experimental outbreaks.

Guppies:

In work published in 2019 in Biology Letters, Jessica Stephenson of the University of Pittsburgh placed individual guppies that did not yet have worm infections in a central aquarium flanked by two tanks. One was empty, and one contained a group of three guppies that represented potential contagion risk. Many guppies preferred the side of the tank near other guppies, as expected for a social species. But some male guppies strongly avoided the side of the tank near the other fish, and these distancing guppies were later shown to be highly susceptible to worm infections. It makes sense that evolution would favor a strong expression of distancing behavior in those most at risk.

Mandrills:

Strategic social distancing sometimes means maintaining certain social ties even when they raise disease risk. Mandrills, highly social primates with strikingly colorful faces, illustrate this approach. This species can be found in groups of tens to hundreds of individuals in the tropical rain forests of equatorial Africa. Groups typically have a mix of extended family members that frequently groom one another; grooming improves hygiene and cements social bonds. But they adjust their grooming behaviors in particular ways to avoid contagious group mates, Clémence Poirotte and his colleagues noted in a report published in 2017 in Science Advances. The scientists observed the daily grooming interactions of free-ranging mandrills in a park in Gabon and periodically collected fecal samples to learn which animals were heavily infected with intestinal parasites. Other mandrills actively avoided grooming those individuals. The mandrills could detect infection status based on smell alone: mandrills presented with two bamboo stalks rubbed in feces strongly avoided a stalk rubbed with droppings from another mandrill that had lots of parasites.

Why Social Distancing?

This kind of behavior is common because it helps social animals survive. Although living in groups makes it easier for animals to capture prey, stay warm and avoid predators, it also leads to outbreaks of contagious diseases. This heightened risk has favored the evolution of behaviors that help animals avoid infection. Animals that social distance during an outbreak are the ones most likely to stay alive. That, in turn, increases their chances to produce offspring that also practice social distancing when confronted with disease. These actions are what disease ecologists such as ourselves term “behavioral immunity.” Wild animals do not have vaccines, but they can prevent disease by how they live and act.

In their 2020 publication in Biology Letters, the researchers said that maintaining strong and unconditional alliances with certain relatives can have numerous long-term benefits in nonhuman primates, just as in humans. In mandrills, females with the strongest social ties start breeding earlier and may have more offspring over their lifetimes. Such evolutionary gains associated with maintaining some social ties may be worth the risk of potential infection.