Introduction to Animal Health

Fall 2024 Sept. 1 to Sept. 25

Pathogen

Pathogen

any disease producing agent or mircoorganism
e.g. bacteria, virus, fungus

Etiology

cause(s) of disease

Noninfectious Disease

not caused by pathogens and cannot be spread. Could be genetic, environmental, malnutrition, etc.
e.g. poisoning, starvation, trama, etc

MORTALITY

related to the number of DEATHS caused by health event under investigation

MORBIDITY

state of being SYMPTOMATIC or UNHEALTHY for a disease or condition

Asymptomatic

no observable symptoms

Acute

rapid onset and short-term

Zoonotic Disease

infectious disease transmitted between species
- transmission can occur in all directions Animal<->Human
(dynamic and bidirectional transmission)

Multifactorial Diseases

involving complex interactions between pathogen, environment and host

One Health Initiative

the concept that human health is connected to the health of wildlife, domestic animals, and the environment

Epidemiology

the study of the distribution and determinants of health related states and events in specific populations
-utilization of information for diagnosis, prevention and control of diseases
-how disease occur and why in a population
- 2 types

Descriptive Epidemiology

examines and characterizes the distribution of disease in a population "distribution"

Analytical Epidemiology

investigates a hypothesis about the cause of disease by studying how exposures relate to disease "Determinants"

Determinants

the risk factors
data accumulated to limit impacts/intervene

Risk Assessment

examines the probability and consequences of disease or infection occurring

Enzootic Disease

equivalent of an endemic
always present in population infecting small number of individuals at any given time in a predictable pattern

Epizootic Disease

equivalent of an epidemic
appears "spontaneously" where it is not usually found, affecting a larger portion of a population over a short amount of time in a localized place

Prevalence

a measure of morbidity
frequency of disease within a specific population and period of time
Formula: total # affected/ total # in population

Incidence

a measure of morbidity
the number of new cases within a specific population and time
Formula: # of new cases/ total # in population

Mortality Rate

a measure of mortality
the number of individuals that die from/with the disease in a specific population and time period
Formula: # of deaths/ total # in population

Transmission

when a pathogen leaves its reservoir or host through a portal of exit to a portal of entry to infect a susceptible host

Chain of Infection

Pathogen-> Reservoir Host-> Portal of Exit-> Mode of Transmission-> Portal of Entry-> Susceptible Host

Reservoir Host

infected animal 'carrying' the pathogen

Exit Portal

method by which pathogen leaves host's body

Mode of Transmission

how the pathogen is transferred from reservoir to new host

Susceptible Host

the potential future host who is receptive to the pathogen
lacking immunity or physical resistance to infection

Reservoir

the habitat the pathogen normally lives, grows, and reproduces in
may or may not be the mode to transmission as well
can be biotic, abiotic or dead

Host Range

all the organisms the pathogen is capable of infecting

Two Modes of Transmission

1) Direct
2) Indirect

Direct Transmission

direct and immediate pathogen transfer between hosts
*no intermediate
-3 main types
1)physical contact
2)fecal-oral
3)ingestion

Indirect Transmission

pathogen transfer via intermediate item/organism
*must have intermediate for pathogen development phase
-4 main types
1)fomites
2)environment
3)intermediate host
4)vectors

PHYSICAL CONTACT (Direct Transmission)

exposure occurs when the agent of infection directly touches open wounds, mucous membranes, or skin though blood, saliva, nose contact, rubbing, scratching or biting

FECAL-ORAL (Direct Transmission)

disease causing pathogen found in feces and enter a host through the oral cavity (mouth)
may be via contaminated food or water

Fomites

contaminated inanimate objects that carry disease causing pathogen

FOMITES (Indirect Transmission)

fomite transmission from one host to the next, often requiring secondary route of exposure

ENVIRONMENT (Indirect Transmission)

contact with environmental reservoir of pathogen
contaminating soil, water, vegetation

INTERMEDIATE HOST (Indirect Transmission)

aka 'secondary host'
intermediate hosts are the site of pathogen development prior to primary host

VECTORS (Indirect Transmission)

when an insect acquires a pathogen from one host and transmits it to another
2 types of vector-borne transmission
1)mechanically
2)biologically

Mechanically Transmitted Vector

disease agent does not replicate or develop in/on the vector, only transported from host to host

Biologically Transmitted Vector

vector uptakes an agent usually through blood meal, agent replicates and/or develops and infects a susceptible host

Airborne Transmission - indirect

microorganisms are suspended in the air and widely disperse via currents, agents are carried by dust, aerosol, or other small particles floating in the air
hosts inhale particles
agents are less than 5 microns in size

Parasite

organism that lives temporarily or permanently on or in another living host for the purpose of obtaining nutrients

Parasitism

association between two species in which one (parasite) benefits from the other (host)

Classes of Parasites

1) Endoparasite
2) Ectoparasite

Ectoparasite

parasite the lives outside or on the host body

Definitive Host

host in which a parasite develops to an adult or sexually mature stage

Paratenic Host (transport host)

host in which there is no development and not required to complete the life cycle
not always present

Life Cycles

interaction between parasite, host, and environment allowing development and reproduction of parasite
large room for variation
Direct or Indirect life cycles

Direct Life Cycle

parasite transmits from definitive host to definitive host
without an intermediate host

Indirect Life Cycle

requires one or more intermediate hosts to complete the life cycle

Pre-Patent Period

time form when parasite infects host until shedding is detected
- independent from incubation period

Incubation Period

time from when parasite infects host until clinical signs are detectable - independent from pre-patent period

Mechanisms of Parasitic Disease

- physical damage or obstruction
- invasion/cell destruction
- nutritional losses
- immune response
- physiologic disturbances
- disease transmission

How to Diagnose Parasite

- gross or microscopic ID of parasite and lesions through CYTOLOGY or HISTOLOGY
- PCR tests
- fecal float tests
- scrapes
- culture

Types of Parasites

1) nematodes
2) flatworms (trematodes and cestodes)
3) acanthocephalans
4) arthropods (insects and arachnids)
5) protozoa

Nematode Parasites

- helminths
- unsegmented and cylindrical
- free-living and parasitic
- separate sexes
- direct or indirect lifecycles

e.g. racoon roundworms

Flatworms

- platyhelminths
- dorsoventrally flattened
- most are hermaphroditic
- include:
CESTODES (tapeworms)
TREMATODES (flukes)
- indirect and complex lifecycles

Protozoa

- single celled eukaryotic organism
- free-living or parasitic
- sexual or asexual reproduction
- very diverse
- include:
APICOMPLEXA (coccidia, malaria)
ZOOMASTIGOPHORA
DINOFLAGELLATA

Bacterial Diseases

- prokaryotes
- asexual reproduction via binary fission
- diverse and found everywhere
- most are EXTRACELLULAR or FACULTATIVE INTRACELLULAR
- some are endoparasitic and can help maintain host health
- some cause significant disease

Facultative Intracellular

replicate inside eukaryotic host cells or in an environmental niche

Bacterial Shapes

- Cocci (round)
- Bacilli (rod-shaped)
- Spiral

Gram-Negative Bacteria

bacteria that have a THIN layer of PEPTIDOGLYCAN in their call wall
- stains red/pink (does not retain stain colour well)

How to Diagnose Bacterial Infection

- culture
- microscopy (special stains)
- diagnostic immunology (antigen tests, ELISA, antibody tests)
- PCR tests

Bacteria Survival Mechanisms

- toxins
Endotoxins
Exotoxins
- high invasiveness
- interference with host metabolism
- stimulation of host response

each create a variety of lesions

Viruses

- microscopic infectious agents
- infect all types of organisms
- are obligate intracellular microbes
- acellular (not made of cells)

Obligate Intracellular Microbes

requiring the presence of host cell to multiply and reproduce
completely dependant on host cell for:
- energy production
- protein synthesis

VIRUS

- small entity consisting of DNA or RNA enclosed by protein coat (capsid)
- may or may not have lipid envelope
*nucleoprotein particle
*intracellular structure
*larger that viron
*helical, icosahedral, prolate envelope and complex

VIRON

- complete functional infections virus particle
- composed of DNA/RNA, capsid, lipid envelope, membrane proteins or spikes (allow binding)
- form outside the host cell
*extracellular structure
*smaller than virus
*spheroidal or rod-shaped

Viral Lifecycle

1) binding/attachment to host cell
2) penetration into host
3) uncoating of viral contents
4) synthesis of new viral particles
5) gene expression and assembly of viral protein
6) release of replicated virus

Viral Virulence

the ability of a virus to cause disease in an infected host
cumulative effect of impacts on host from virus replication and host immune system response

Viral Effects

most are subclinical/asymptomatic
- cell damage
- cell death/apoptosis
- disruption of cell function
- immune response to infected cells

highly variable

How to Diagnose Gross/Histologic Lesions

- immunofluorescence
- inclusion bodies
- virus isolation
- PCR or TR-PCR
- serology

Fungi

- eukaryotic heterotrophs
- unicellular and multicellular specimen
- sexual and asexual reproduction
- terrestrial and aquatic specimen
- non-motile species

Fungal Lifecycle

1) spore
2) germ
3) hyphae
4) mature mycelium

Dimorphic Growth

two forms of growth
- mold-like growth (vegetative and aerial hyphae)
- yeast-like growth (budding reproduction)

Pathogenic Fungi Traits

opportunistic or primary
localized or systematic infection

Opportunistic Pathogen

invade weak immune systems
are aggressive
found worldwide

Primary Pathogen

invade healthy/normal immune systems
spread more slowly
tied to geographic distribution

How to Diagnose a Fungal Infection

- gross pathology
- microscopy
- cultures
- serology
- PCR
- observe clinical signs

Pathology

the study of disease
- diagnosing and characterizing diseases by examination of cells, tissues, organs
- attempts to define:
- etiology
- pathogenesis
- morphologic changes
- clinical significance
- 2 categories
- clinical pathology
- anatomic pathology

Pathogenesis

the mechanism of disease

Morphologic Changes

structural change in cells or tissues characteristic of disease

Clinical Significance

how morphologic changes result in clinical signs and disease

Clinical Pathology

disease diagnositcs through lab testing and microscopic evaluation of cells (not common in wildlife health)
~ ANTEMORTEM
- cytology (microscopic examinations of cells)

Anatomical Pathology

the study of organs and tissues
~ POSTMORTEM
- Necropsy (examination of dead animal carcasses)
- Histology (microscopic examination of tissues)
- Ancillary Diagnostic Tests

Lesions

abnormal change in structure of organ, tissue or cells due to disease

Lesion Distributions

- focal (single lesion)
- multifocal (numerous lesions)
- locally extensive (one lesion expanding outward)
- diffuse (entire involved tissue)
- multifocal coalescing (many coming together)

HEMORRHAGE (common wildlife lesion)

the escape of blood from vessel due to damage or disfunction

EFFUSIONS (common wildlife lesion)

the escape of fluid into a space/cavity

NECROSIS (common wildlife lesion)

death of cells or tissue

INFLAMMATION (common wildlife lesion)

protective response to a variety of cell injuries

NEOPLASIA (common wildlife lesion)

unregulated cell proliferation that is not under physiologic control

TUMOR (common wildlife lesion)

any tissue mass, which can be solid or liquid filled
- benign or malignant

Diagnostics

diseases associated with different etiologies can present with similar signs but....
the same etiology can present in different species or animals

History Diagnostics

critical to developing the rule-out list
- presenting complaint
- seasonality
- acute or chronic
- field observations
- number of affected animals
- species variation

Signalment Diagnostics

basic information about the patient
important to species identification
including:
- sex
- age
- spay/neuter or intact
- risk factors

Necropsy Diagnostics

systematic postmortem examination of carcasses to determine the nature of disease
- many wildlife cases only have partial carcasses or select tissues

Assays Diagnostics

further laboratory testing can directly and/or indirectly aid in detection of an etiology/pathogen
- Direct = identification of etiology itself
- Indirect = identification of a measurable response to the etiology

Fecal Analysis Diagnostics

evidence of gastrointestinal or nutritional disease
can detect:
- parasites
- bacteria
- viruses
- blood presence

Cytology Diagnostics

microscopic examination of cells