1. Animal disease ecology and transmission involves the study of how diseases spread between animals and their environments. Key concepts include reservoirs, where pathogens live and multiply; ports of exit, how pathogens leave an infected host; and modes of transmission, how pathogens are passed between hosts. 2. Many factors can influence disease emergence and spread, including climate change, land use changes, increased animal densities, and globalization. Climate change can alter disease patterns by changing temperatures and rainfall in ways that increase vector populations. Changes in land use and encroachment on animal habitats can increase contact between wildlife and livestock. 3. Integrated policies are needed to address socioeconomic, institutional, and production factors that influence disease risks at the

1. Animal Disease Ecology &
Transmission
Clarissa Yvonne J. Domingo
Professor, CVSM-CLSU

2. Terms to Reckon:
infection
presence of a pathogen
in the body but does not
necessarily mean the
presence of clinical signs
disease
occurrence of cases and
outbreaks (with clinical
signs) caused by the
pathogen in a
population

3. ecology branch of biology that deals with the relations of
organisms to one another and to their physical
surroundings

4. transmission passing of a communicable disease from an
infected host individual or group to a particular
susceptible individual or group

5. Diseases affecting livestock can have a
devastating impact on:
1. animal productivity and production,
2. trade in live animals, meat and other
animal products,
3. human health and, consequently,
4. the overall process of economic
development.

6. Concepts for interplay of
ecology to diseases
transmission

7. Macro Level Consequence
1. growing populations Livestock, fastest growing
subsector of agriculture
(true in developed countries)2. income gains and
urbanization
3. result of globalization Unprecedented increase of
emerging and re-emerging
animal diseases and zoonoses4. climate change the world

8. Biological factors1. Environmental, climate, weather changes
(temperature & humidity).
Climate change also has the following effects on disease occurrences:
 Increased parasitic zoonoses
(e.g. helminthoses, tick-borne diseases)
 Increased spread of vectors and vector-borne diseases
(e.g. Rift Valley fever, West Nile virus)
- Increased humidity increases vector survival; increased rain may
increase larval habitat and vector population size by creating new
habitat
 Increased incidence of tropical diseases in areas previously
considered as having temperate climate conditions
(e.g. Old and New World screwworm)

9. •Alteration of disease eco-
epidemiology, new disease
patterns, and change in vector
capacity.
- Decreased rain can
increase container-
breeding mosquitoes by
forcing increased water
storage
- Epic rainfall events can
synchronize vector host-
seeking and virus
transmission

10. •Change in geographic range,
host range and pathogen
virulence.
- at higher temperature
changes there is
decreased extrinsic
incubation period of
pathogen inside the
vector during
transmission season.

11. 2. Ecological and ecosystem changes.
Changes in the current conditions of the ecosystem
affect many animals and cause higher risk for
emergence of diseases and the occurrence of
pathogens and parasites.

12. 3. Animal density and
biomass.
The optimal density
of animals in a specific
location is vital to animal
health.
Overcrowding or high
densities pose high risks
and allow faster transfer
of parasites and pests.

13. 4. Changes in host-pathogen
interactions.
The emergence and re-
emergence of diseases can be
attributed to host-pathogen
interactions.
When these interactions
are interrupted or altered, the
resistance of animals can be
weakened and places them in
vulnerable states.

14. 5. Microbial adaptation to new
environmental conditions.
• Intrinsic properties of the pathogens
that are associated with this are:
a. genetic shift as a result of mutation &
reassortment, as it occurs in avian
influenza virus;
b. conjugation, transformation, and
transduction in bacteria.
c. adaptation to new vectors and hosts
d. development of increased virulence or
drug resistance

15. 6. Changes in land use and use of natural resources.
• Human economic activities cause major changes in land use.
Encroachment into natural animal habitat due to
a.forest clearings and
b.land conversions for various uses such as industry, pasture,
residential space and agriculture
 changes in animal and human density and distribution
 alters local biodiversity through the introduction of exotic and
invasive species that could cause extinction of one or more
species.

16. Changes in Environment
• Malaysia, 1999, intensive pig farming intrudes into the natural
habitat of fruit bats carrying the Nipah virus
• Entire pig herd of the country slaughtered ($120M); 105 human deaths

17. 7. Increased contacts
between pathogens and
host population
(urbanization, rural peri
urban-urban continuum)
• As a result of urbanization and
industrial conversion animals
are kept in densely populated
areas
• This increases the contacts
between pathogens and hosts
that lead to increased exposure
and risk.

18. 8. Social and cultural practices
Social and cultural practices of man add to the risk of zoonotic
transmission. These are:
• food habits
• religious beliefs
• Halal meat
• free range eggs and meat
• exotic meat
• raw milk

19. Abiotic factors
1. Globalization, international trade, and level of economic
development.
Due to globalization, changes in the movements of human and
animal populations enhance transmission. Likewise, movements
are attributed to:
a. extent of ownership and movement of pets
b. extent of air travel
c. extent of ecotourism, hunting, camping, etc.
d. Introduction of infected host in to new ecosystem. eg :
Marburg Disease
e. natural movement of wild animals including migratory
birds, and by anthropogenic movement of animals.

20. Changes in Movements of human and
animal populations
• Distance and speed of travel
increased 1000 fold since
1800
• 1.4 billion air travelers/year

21. 2. Lack or inadequate
policies for control and
confinement measures.
Policies must focused on
managing and
implementing movement
restrictions of animals and
products from one place to
another, especially across
borders.
Policies and strategies
should be improved to
safeguard animal health,
public health, livelihoods
and food systems.

22. 3. Political and civil strife
and instability.
There is disruption of
health services in war-
torn or impoverished
countries.
Example: War-torn
Kosovo led to
epizootic
rodent
tularemia.

23. 4. Breakdown of public
services in charge of
disease control.
In case of natural
disasters, health
infrastructures are
damaged and control of
diseases that emerged
from the calamity
cannot be mitigated
efficiently and
effectively.

24. 5. Management of animal waste.
Popularity of organic farming and
intensive tilapia inland farming,
poultry manure and other animal
manure became a source of added
income to livestock farmers.
Transporting manure to other
places because of demand is a risk
for transmitting the pathogens.
Wet manure is seeded with viable
viral, bacterial, fungal and protozoal
pathogens that can be harmful to
both man and susceptible animals.

25. Changes in Management of animal wastes
Manure-related fish kills , typical in many countries

26. 6. Poor or change in public
health management.
Poor or change in
management results in lack
of integration with animal
health surveillance,funding
in the public health sector
and sustained funding on
scientific studies to answer
public health questions and
build expertise.

27. 7. Animal welfare philosophies affecting animal production system.
Animal welfare societies have been loud in espousing practices that
should not hinder the natural behavior of animals. Due to increase practice
of range farming however, soil-borne parasites that have been controlled
before occurred such as Trichinella , Toxoplasma, cysticercosis, etc. have re-
emerged.

28. 8. Changes in production systems.
Production systems are currently under
pressure to adjust to rapidly evolving
socio-economic conditions and large
intensive livestock production units.
Increasing demand for animal protein has
led to changes in:
a. farming practices (e.g. large “open”
poultry production units in Asia)
b. animal markets
c. bush meat consumption
d. global trade
e. pig and poultry production have
emerged in many developing regions
in response to the rapidly growing
demand for livestock products.

29. As the intensity of production increases, there is greater complexity and
severity of diseases.

30. The macro-environment can influence the pattern of disease events.
Extreme conditions of the physical environment such as
a. climate,
b. topography,
c. vegetation and
d. soil
can directly cause illness or disease to animals.
Factors affecting pathogen vectors, endemicity, and pathogen vector
diffusion include
a. temperature,
b. relative humidity,
c. vegetation cover and
d. plant species and
e. chemical composition of soils.
Macro-environment and diseases

32. Predicting the presence of
disease using a set of
parameters could accurately
model the observed disease
situation in a certain area.
Predictive mapping could be
useful for the management
control planning in a large
area

33. Micro-environment and diseases
- interaction between biological supports (host animal, vector, and pathogen)
which determine the establishment, multiplication, spread or reduction, and
even elimination of infections.
Host’s capacity to respond to infectious attack:
 Susceptibility. The ability to acquire a pathogen and to show a pathological
status.
 Tolerance. The relative capacity to control the development of a pathogen and
to limit its pathological effects.
 Resistance. The ability to reduce the growth rate, fecundity, and persistence
of a population of pathogens.
 Resilience. The ability to grow and be productive despite the presence of a
normal pathogen charge.
 Refractoriness. The impossibility to acquire an infection because the biological
support inhibits the multiplication of the pathogen.

34. Micro-environmental interactions and competitions:
Coccidia and helminths.
There is equilibrium at the level of the gastrointestinal tract.
Treatments against coccidia positively affect the multiplication
of gastrointestinal helminths and vice versa.
Tsetse flies, intestinal symbionts and trypanosome infections:
There are symbiotic micro-organisms (Wigglesworthia glossinidia)
inside the intestine of tsetse flies give a degree of immunity to
acquire and transmit trypanosome infections

35. Transmission

36. •The habitat in which an infectious agent normally
lives, grows, and multiplies.
•The reservoir may or may not be the source from
which an agent is transferred to a host.
•For example, the reservoir of clostridium botulinum
is soil, but the source of most botulism infections is
improperly canned food containing C. Botulinum
spores.
Reservoir

37. Reservoir
1. Human reservoirs- cases
and carriers
2. Animal reservoirs- cases
and carriers
3. Environment reservoirs-
plants, soil and water

38. •Carriers commonly transmit
disease because they do not
recognize they are infected
and consequently take no
special precautions to prevent
transmission.
•Symptomatic persons are
usually less likely to transmit
infection
Human Carriers

39. Animal reservoirs
Examples
• brucellosis (cows, dogs, pigs)
• trichinosis (swine)
• rabies (dogs and cats).

40. •Many fungal agents, such as
those causing
histoplasmosis, live and
multiply in the soil.
•The primary reservoir of
Cryptosporidiosis is water
Environmental reservoirs

41. Portals of Exit
•Gastrointestinal tract
•Respiratory tract
•Genitourinary tract
•Skin and mucous membranes
•Blood
•Transplacental

42. Mode of Transmission
•The route of infection refers to the
path which the disease agent used to
gain access to the body of the
susceptible host
•Mode of transmission to the method
of transference.

43. Example: Route vs Mode
•The route from Point A to Point B is
through the main highway (route of
infection).
•However, the journey from point A to
point B using the main highway can be
completed using any of the transportation
options: by public bus, railway transit or
private vehicle (mode of transmission).

44. Mode and route

45. Interventions to improve livestock
and agriculture production systems
require policies that address
interventions in
• socio-economic dimensions,
• institutional support,
• training and information,
• land use, land tenure, and
natural resource management,
and
• increasing agricultural
production.

46. END OF LECTURE