Ecology

Question 1

Define ecology

Answer 1

Ecology is defined as the “study of factors influencing the abundance and distribution of organisms.”

In this class, the organisms whose ecology we are interested in are pathogens. Disease ecology includes disease dynamics (studied last week) as well as more general interactions between pathogens and their environments and hosts. Ecology is important on both the micro scale (meaning interactions within cells and organs in the host) and macro scales (within the broader population).

Question 2

Define competition

Answer 2

One of 2 general principles that govern a pathogen’s interactions within and with the host, and with its surrounding environment.

Competition is the driving force of natural selection. Pathogens compete with each other for resources, whether they are viruses competing within the same cell, or bacteria competing in the soil. Within a cell, viral competition works via a system of RNAs that can cause another virus’ RNA to be degraded. Parasites compete for resources within hosts as well.

Question 3

Define cooperation

Answer 3

One of 2 general principles that govern a pathogen’s interactions within and with the host, and with its surrounding environment.

Cooperation is also a key (and often underappreciated) principle of ecology. Cooperative interactions are mutual benefit to the different species involved. For example, your microbiome is a cooperation between the many bacteria that compose it and you. Bacteria can also cooperate in ways that do not help you, for instance they can make biofilms, or groups, that stick together on a catheter and cause hospital-acquired infection. Bacteria also participate in quorum sensing, which is cell to cell communication that regulates the density of bacteria growth so they can share resources.

Question 4

Define biofilms

Answer 4

Bacteria can also cooperate in ways that do not help you, for instance they can make biofilms, or groups, that stick together on a catheter and cause hospital-acquired infection. Bacteria also participate in quorum sensing, which is cell to cell communication that regulates the density of bacteria growth so they can share resources.

Question 5

Define habitat

Answer 5

The physical area in which a species inhabits is its habitat. Habitats can be a small area next to a magma vent in the floor of the ocean, or it can be all of the rainforest of Brazil. You may think that a pathogen’s habitat defines the area where the disease is endemic. In many cases this is true, but not always

Question 6

Define ecological niche

Answer 6

All species have what is called an ecological niche. This is the sum total of the habitat and all of the behaviors of a particular organism. For example, a raccoon’s niche might include: “temperate forests and suburban areas of the northeast/likes to scavenge for food/nocturnal.” No two species can occupy the exact same niche. Either one species will evolve to separate the niches, or one will out-compete the other, resulting in its extinction

Question 7

Ecological niche model examples

Answer 7

We can use mathematical models, called ecological niche models, to try and determine where and when pathogens are likely to be most prevalent, and therefore where and when to target prevention strategies.

Question 8

Ways in which climate change can alter infectious disease dynamics

Answer 8

Climate influences many interactions that pathogens have with their environment. For example, waterborne pathogen distributions can change between wet and dry seasons, mosquito reproduction levels can change based on temperature, and airborne virus transmission is effected by temperature and humidity in the air. There are three basic scenarios for how climate change can impact infectious disease distribution in a certain location: 1) Warming can cause a shift in timing, where epidemic peak may occur at a different time of year than it did in the past, 2) Warming can cause more epidemic “cycles”, meaning that there may be two epidemic peaks in the same year 3) Warming can cause overall epidemic intensity to either increase or decrease, depending on whether the pathogen can well-tolerate the new climate.

Question 9

Define zoonotic disease

Answer 9

A zoonotic disease is a disease that has its origins in a species other than humans. They include vector-borne diseases and diseases that are transmitted directly from other animals to humans. Most human diseases, including new, emerging diseases, are zoonotic.

Question 10

Density-dependent disease

Answer 10

If a disease is density-dependent, then transmission rates increase with population density of the host. This is true of most respiratory and water-borne diseases.

Question 11

Frequency-dependent disease

Answer 11

If a disease is frequency-dependent, then transmission rates increase with the number of people infectious, but it doesn’t matter how geographically dense they are. Most mosquito-carried diseases fall into this category, as do sexually-transmitted infections.

Question 12

Define silent zone

Answer 12

Sometimes everything necessary for a disease to spread is present in an area (pathogen is there, right climate, etc.) but there are no humans to infect. This is called a silent zone.

When humans move in, suddenly there is an epidemic. Commerce, Illinois was settled by early pioneer families of the LDS church. The area was swampland, but later became a large city called Nauvoo. This area was a silent zone. The swamps, mosquitoes and malaria parasite were all present. When the pioneers moved in, the majority of their deaths were due to malaria. The swamp was a silent zone, waiting for a large population to show up.

Question 13

Define airborne transmission

Answer 13

Usually respiratory droplets

Question 14

Define waterborne, food borne, animal bite, and sexual transmission

Answer 14

Pretty self-explanatory

Question 15

Define fecal-oral transmission

Answer 15

Ingesting microscopic amounts of contaminated fecal matter

Question 16

Define fomite transmission

Answer 16

Touching surface, object or person

Question 17

Define perinatal transmission

Answer 17

Mother to child

Question 18

Define vector-borne transmission

Answer 18

Carried by non-host species to host

Question 19

Human-to-human transmission (Know how to draw)

Answer 19

Sometimes the disease emerges in humans, having originated in another animal species, and then is only transmitted person to person. Influenza is an example. It originates in aquatic birds/pigs but then is just transmitted among humans. This is called direct human to human transmission.

Question 20

Direct zoonosis (Know how to draw)

Answer 20

Other times, the disease is transmitted from an animal to a person, but then people do not transmit it to each other (like rabies). This would be referred to as a direct zoonosis.

Question 21

Vector-borne transmission (Know how to draw)

Answer 21

If a disease is transmitted from human to human only via another species, it would be referred to as vector-borne.

Question 22

Define reservoir

Answer 22

A reservoir is the host species for a viral disease. The reservoir species does not typically become seriously ill from the virus, though it sometimes can.

Question 23

Define spillover

Answer 23

The reservoir species can pass it to other species if there is a spillover event, which is the moment in time where a disease moves from one species to another. Bats, mice and birds are very common reservoirs.

Question 24

Vectored zoonosis (Know how to draw)

Answer 24

If the disease is transmitted between members of another animal species and can infect a person, but the person cannot spread the disease to another vector or animal, it is called a vectored zoonosis. (Encephalitis)

Question 25

Anthropo-zoonosis (Know how to draw)

Answer 25

If the situation is the same as for a vectored zoonosis, except that infected humans can spread it further, it is called an anthropo-zoonosis. (Yellow fever)

(If the disease is transmitted between members of another animal species and can infect a person, but the person cannot spread the disease to another vector or animal, it is called a vectored zoonosis.)

Question 26

The triangle of human ecology, with an example

Answer 26

Genetics
Environment
Behavior

(Put health in the middle of the triangle)

Obesity -> Good example

Question 27

How biodiversity impacts disease transmission via the dilution effect. Include both the Lyme disease example from the reading and class, and the spillover example through bat populations in the video we watched in class.

Answer 27

Biodiversity (the number of species present in a given area) can have a major effect on vector-borne disease transmission. The general idea is that the more appropriate species are in an area, disease-carrying species has fewer interactions that lead to infection or disease transmission. This is called the dilution effect, and is demonstrated by the below example using Lyme disease.

Know the life cycle of a deer tick (the type that carries Borrelia burgdorferi bacteria, the cause of Lyme disease).

Deer ticks are not born carrying Lyme disease. If they become infected, it is typically during their first blood meal on a small animal. Some small animals are really good at harboring B. burdorferi. It doesn’t multiply or is not carried as well in other species. White-footed mice are very abundant in temperate forests in the Northeast US, which typically have low biodiversity. So the odds that a white-footed mouse will be the tick’s first blood meal are very high, meaning the chance of getting infected with B. burgdorferi and later transmitting it to a human is high. If biodiversity is increased, it is less likely the tick will feed on a white-footed mouse, and less likely it will become infected. This is shown in the below diagram. (See diagram)