12 - Controlling Zoonotic Infections

Question 1

Zoonotic disease

Answer 1

Disease that can be spread between animals and humans

Question 2

Reverse zoonosis (Zooanthroponosis)

Answer 2

• Pathogens of humans that can be transmitted to animals
• E.g. Giardia, TB, E. coli, Influenza A, COVID

Question 3

Why are zoonotic diseases important

Answer 3

• They account for vast majority of both emerging and re-emerging diseases
• Animals are often the primary host and pathogens often are asymptomatic or mild (hard to detect for control)
• Humans often exhibit more severe disease
• Increasing number of outbreaks

Question 4

How many of the 175 pathogens recognised as emerging or re-emerging are zoonotic

Answer 4

75%

Question 5

Etiology of emerging infectious diseases Zoonosis

Answer 5

• Increased contact with animal reservoirs
• Species jumping, re-assortment of viruses
• Natural host acts as a reservoir (difficult to break transmission)

Question 6

How are zoonotic diseases transmitted

Answer 6

• Direct contact
• Indirect contact
• Air borne

Question 7

Direct contact

Answer 7

• Coming into contact with the saliva, blood, urine, or other body fluids of an infected animal
• E.g. Petting or touching animals, bites or scratches (rabies)

Question 8

Indirect contact

Answer 8

• Coming into contact with
  areas where animals live and roam, or objects or surfaces that have been contaminated
• E.g. Anthrax

Question 9

Air borne transmission

Answer 9

• Via aerosol droplets into respiratory tract
• e.g. COVID

Question 10

Spread of zoontoic diseases

Answer 10

• Vector borne
• Food borne
• Water borne

Question 11

Vector borne

Answer 11

• Bitten by a mosquito, tick, flea or other arthropod vector
• e.g. Ross River Virus

Question 12

Food borne

Answer 12

• Contaminated food/drink
• E.g. unpasteurised milk, undercooked meat
• e.g. Cholera

Question 13

Water borne

Answer 13

• Potential for huge outbreaks from centralised water facilities or reservoirs/wells.
• Similar contaminants as food borne

Question 14

Virulence of diseases changing with change of hosts

Answer 14

• Death due to uncontrolled viral replication
• Death due to ineffective immune control
• Viral clearance at cost of transient morbidity
• Persistence and some loss of health

Question 15

Controlling zoonotic diseases

Answer 15

• Eradication in animal reservoir especially a sylvatic one is very difficult
• Identifying animal cases difficult (many are asymptomatic)
• Vector borne or food/water borne often disassociated
  with source.
• Need multiple approaches for effective disease prevention campaign
• Pathogens can adapt in animal reservoirs
• Major impact on farming

Question 16

Types of prevention methods

Answer 16

• Primary
• Secondary
• Tertiary

Question 17

Primary prevention methods

Answer 17

• Methods to prevent infection from casual events
• e.g. Quarantine and vaccination

Question 18

Secondary prevention methods

Answer 18

• Activities designed to detect disease quickly and as early as possible to help prevent
  transmission
• e.g. screening tests, Use of sentinel animals for arbovirus detection

Question 19

Tertiary prevention

Answer 19

Treatment of infections, prevent severe or chronic illness and further transmission

Question 20

Control strategy

Answer 20

• Need to have extensive knowledge on pathogen life cycle
• Habitats and behavior of reservoirs/hosts
• Mechanism of transmission (vector borne, food borne, direct contact, respiratory)
• The more numerous the range of animal reservoirs the more difficult to control

Question 21

Aims of control strategies

Answer 21

• Total eradication
• Practical/localised eradication
• Targeted host eradication

Question 22

Practicalities of control strategies

Answer 22

• Break chain of transmission (Look for the weak link in transmission that would be easiest/cheapest to target)
• Education to alter human behaviour
• Culling of reservoir hosts

Question 23

Neutralization of reservoir

Answer 23

• Ideally only cull infected animals (needs method of detection)
• Alter or manipulate environment to remove reservoir

Question 24

Prevent transmission from reservoir

Answer 24

• Population control
• Isolation of infected animals and dispose of infected waste
• Quarantine infected animals

Question 25

Period of quarantine

Answer 25

• Depends on incubation period
• Short for parasites and some bacteria (observation)
• Longer for viruses (PCR, RAT)

Question 26

Vector control

Answer 26

• Use of insecticides to control vectors like mosquitoes (e.g. DDT, but accumulative poison in food chain)
• Change environment (drain swamps, clear vegetation
• Biological control
• Genetic manipulation of mosquitoes (induce sterility)

Question 27

Example of biological control

Answer 27

Wolbacchia bacteria in mosquitoes for Dengue prevents pathogen transmission

Question 28

Reducing susceptibility of reservoir host

Answer 28

• Select for resistant breeds (takes time but long term benefits)
• Immunisation of animals
• Use chemo prophylaxis

Question 29

Mass treatments and prophylaxis

Answer 29

• Requires the use of safe and cheap therapeutic drugs and antibiotics
• Used to prevent zoonotic infections from contaminating produce for human consumption
• Risk of enhancing drug resistance for bacterial pathogens

Question 30

Mass vaccination

Answer 30

• Strategic vaccination (prevent disease in
  specific regions)
• Emergency vaccination (at time of disease outbreak)
• Ring vaccination around area of outbreak or to protect specific area from threat

Question 31

Epidemiological surveillance

Answer 31

• Used to monitor disease prevalence in real time
• Modeling used to predict the course of an outbreak and to target best methods of control
• Combines information from many sources
• Contributes to global control of zoonotic infections