Definitions

Question 1

Infectious Disease

Answer 1

An illness resulting from an infection that is communicable or transmissible.

Question 2

Infection

Answer 2

An infection is the invasion of an organism’s body by disease-causing agents, including the way that it multiplies and the way that the host tissues respond to the infectious agents and the toxins they produce.

Question 3

Infectious agents

Answer 3

Pathogens- anything that can produce disease

Question 4

Parasitism

Answer 4

The relationship between species where one organism (parasite) lives in or on another organism (host) causing it some harm

Parasite: any organism that decreases the fitness of its host by infecting it

Question 5

Types of parasites

Answer 5

1. Microparasites: viruses and bacteria
2. Macroparasites: worms

Ecological examples: tapeworms, mites, parasitoid wasps, reed warbler raising young of another bird, hookworms, ticks, HIV, trypanosoma

Question 6

What is not an infectious disease?

Answer 6

1. Genetic diseases
   - Ex. hemophilia
2. Environmentally-caused diseases
   - Ex. scurvy
3. Cancer- both a genetic and environmental component

Question 7

Ecology

Answer 7

A branch of biology that studies the interactions among organisms and their environment, both abiotic and biotic.

Ex. Crows and Cherry trees

Question 8

Disease Ecology

Answer 8

• The study of spatio-temporal distribution of infectious diseases, which includes the interactions of host populations with pathogen populations in the environment over time
• Comes from the study of infectious diseases of wildlife

Question 9

Epidemiology

Answer 9

-The branch of medicine which deals with the incidence, distribution, and possible control of diseases and other factors relating to health

• Comes from a branch of medicine
• Also includes non-infectious diseases such as smoking, drug use, obesity, mental health

Question 10

The disease triangle

Answer 10

For disease to occur, need a susceptible host, favourable environment, and a pathogen

Question 11

Why is it important to know/learn about infectious diseases?

Answer 11

1. Reduce productivity of farm animals (cattle, sheep, pigs, fowl)
2. Stop trade and travel across international borders (eg. Foot and mouth disease, BSE)
3. Threaten food security for people in developing world
4. Spillover of pathogens from wildlife to domestic animals drives emergence of new infectious diseases that threaten health of humans and livestock
5. Pathogens of humans and domestic animals also threaten wildlife and biodiversity
6. Use of antibiotics in farm animals threaten efficacy of these wonder drugs for animal and human health

Question 12

COVID and why we must care about infectious diseases

Answer 12

• COVID came from animals, and caused pandemic where millions died
• Therefore veterinarians play an important role in the study of infectious diseases in humans because of the role of animal infectious diseases.

Question 13

Foot and mouth outbreak UK 2001

Answer 13

• Highly contagious disease within cloven-hoofed animals
• Killed millions of cows and sheep, rarely affected humans. But did have a huge economic role (loss in farming and tourism)

Question 14

Rinderpest in Africa

Answer 14

• Highly infectious viral disease of cattle
• Virus is a multi-host pathogen- affected all even toed ungulates but different species were affected differently.
• Cattle and buffalo had 100% mortality whereas less serious for sheep and goats. And pigs and deer were asymptomatic
• Close cousin of measles
• Imported to Ethiopia by Italians in 1880s, virus spread and killed more than 90% of domestic cattle and wild ungulates
• Resulted in many individuals starving to death which shows how infectious disease can threaten food security

Question 15

What factors influence disease ecology?

Answer 15

host
pathogen
environment

Question 16

Components of a host that influence disease ecology

Give an Example

Answer 16

• Species
• Genotype/breed
• Sex
• Age
• Nutritional condition
• Immune status (resistant/susceptible, Naïve/immune)

Examples:
Ex. Taurine cattle vs Zebu cattle… Zebu more resistant to tropical parasites than taurine. Study showed that Taurine had higher lung pathology compared to zebu causing them to be more susceptible to bovine tuberculosis

Ex. COVID and humans… older and younger people more susceptible, males more susceptible

Question 17

Components of a pathogen that influence disease ecology

Answer 17

1. Pathogen species
2. Pathogen genotype/strain/isolate/variant
3. Infectivity /transmissibility- probability that pathogen will establish infection in host following exposure
4. Burden/load/abundance:number of pathogen units in host tissues
5. Infectious dose

6.Pathogenicity/virulence- pathogen-induced damage or pathology in the host

7. Immune evasion- pathogen ability to avoid clearance by the host immune system

Question 18

COVID variant waves

Answer 18

Example of how the pathogen itself can influence disease ecology

Variants were short lived. Stronger variants will be replaced by weaker ones due to darwinism. Transmissibility increases with each strain. Pathology typically increases with each strain however Delta was most severe, and omicron was second most severe. Could be bias because there were more people who were vaccinated later on in the pandemic so numbers could be skewed.

Question 19

What does higher Pathology and transmissibility cause?

Answer 19

Higher pathology will cause more severe disease

Higher transmissibility will cause more cases

Question 20

Components of environment that influence disease ecology

Answer 20

• Abiotic variables (Temperature, Humidity)
• Biotic variables (Food and nutrition, Host density)
• Human practices (Hygiene practices, Husbandry practices)