12 - Controlling Zoonotic Infections Flashcards
Zoonotic disease
Disease that can be spread between animals and humans
Reverse zoonosis (Zooanthroponosis)
- Pathogens of humans that can be transmitted to animals
- E.g. Giardia, TB, E. coli, Influenza A, COVID
Why are zoonotic diseases important
- 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
How many of the 175 pathogens recognised as emerging or re-emerging are zoonotic
75%
Etiology of emerging infectious diseases Zoonosis
- Increased contact with animal reservoirs
- Species jumping, re-assortment of viruses
- Natural host acts as a reservoir (difficult to break transmission)
How are zoonotic diseases transmitted
- Direct contact
- Indirect contact
- Air borne
Direct contact
- 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)
Indirect contact
- Coming into contact with
areas where animals live and roam, or objects or surfaces that have been contaminated - E.g. Anthrax
Air borne transmission
- Via aerosol droplets into respiratory tract
- e.g. COVID
Spread of zoontoic diseases
- Vector borne
- Food borne
- Water borne
Vector borne
- Bitten by a mosquito, tick, flea or other arthropod vector
- e.g. Ross River Virus
Food borne
- Contaminated food/drink
- E.g. unpasteurised milk, undercooked meat
- e.g. Cholera
Water borne
- Potential for huge outbreaks from centralised water facilities or reservoirs/wells.
- Similar contaminants as food borne
Virulence of diseases changing with change of hosts
- 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
Controlling zoonotic diseases
- 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
Types of prevention methods
- Primary
- Secondary
- Tertiary
Primary prevention methods
- Methods to prevent infection from casual events
- e.g. Quarantine and vaccination
Secondary prevention methods
- 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
Tertiary prevention
Treatment of infections, prevent severe or chronic illness and further transmission
Control strategy
- 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
Aims of control strategies
- Total eradication
- Practical/localised eradication
- Targeted host eradication
Practicalities of control strategies
- 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
Neutralization of reservoir
- Ideally only cull infected animals (needs method of detection)
- Alter or manipulate environment to remove reservoir
Prevent transmission from reservoir
- Population control
- Isolation of infected animals and dispose of infected waste
- Quarantine infected animals
Period of quarantine
- Depends on incubation period
- Short for parasites and some bacteria (observation)
- Longer for viruses (PCR, RAT)
Vector control
- 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)
Example of biological control
Wolbacchia bacteria in mosquitoes for Dengue prevents pathogen transmission
Reducing susceptibility of reservoir host
- Select for resistant breeds (takes time but long term benefits)
- Immunisation of animals
- Use chemo prophylaxis
Mass treatments and prophylaxis
- 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
Mass vaccination
- 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
Epidemiological surveillance
- 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
