Week 10 - interaction between infectious agents and other determinants of animal health Flashcards
What are the management factors
- Rotation of feeding bins
- Creep feeding
- Faecal collection
- Harrowing
- Irrigation
- Pasture treatments
- Group size
- Farm size
- Preventive health measures
- Other diseases
Characteristics of Soil borne virulent R. equi
No environmental variable had a significant effect on soil-borne virulent R. equi concentration
•Soil-borne virulent R. equi was not associated with prevalence of R. equi disease
Characteristics of Air-borne virulent R. equi
- High air-borne virulent R. equi associated with high disease prevalence
- Peak incidence of rattles associated with increased airborne virulent R. equi
- Majority of cases 1-2 months old
What cause high concentration of Air-borne virulent R. equi
- Low soil moisture
- Poor grass cover
- High ambient temperature
Characteristics of Genus Aphthovirus: Foot and Mouth Disease (Family Picornaviridae)
- Multiple host species
- Multiple modes of transmission
- Multiple serotypes
- Small infective dose
- Rapid replication
- Virus shed before clinical signs
- Highly contagious
- Carrier state
What are Family Herpesviridae
Double -stranded DNA Icosadeltahedral core Amorphous tegument Enveloped virus Envelope studded with glycoprotein spikes Frogs, Fish, Snakes, Kangaroos, Cows, Dogs, Cats, People
Clinical signs for EHV-1/4 Respiratory Disease
Fever and inappetence
Nasal discharge (serous - mucopurulent)
Lymphadenopathy (sub-mandibular)
Effects of EHC -1 abortion
Systemic spread from respiratory tract Leukocyte associated viraemia No premonitory signs Late gestation Sporadic (majority) Epidemic (up to 80% mortality) Major economic impact \$\$$
EHV-1 Neurological disease
Systemic spread from respiratory tract
Vasculitis (replication in vascular endothelium)
Mild ataxia - tetraparesis and recumbency (location of lesion)
Prognosis (poor to grave)
Uncommon in Australia (SA??)
More common in USA (Europe)
Mode of Transmission
Vertical
Horizontal
What does vertical mode of transmission mean
Mother to offspring transmission in utero
or in ovo (early post-partum period)
Transmission across placenta, in birth
canal, in colostrum/milk
Cause embryonic death, mummification,
resorption (time of gestation) or congenital
defects
what does horizontal mode of transmission mean
-Direct contact (licking, rubbing, biting, sexual contact)
-Indirect contact (fomites)
Feed and water containers, bedding, dander, tack, clothes, etc…
Airborne transmission
(respiratory tract via droplet / aerosol inhalation)
Common vehicle transmission
Arthropod-borne transmission
Iatrogenic transmission
Nosocomial transmission
Zoonotic transmission
What are the site of entry
Skin
Respiratory tract
gastrointestinal tract
genitourinary tract
How do you defend from skin site of entry
Integrity of the epidermis is the hosts only defence
what are the Traumatic breaches in integrity of skin
Traumatic breaches in integrity of skin:
Establishment of dermal infection
(i) Mechanical transmission via mouthparts of vector
(ii) Replicate in gut of arthropod vector
(iii) Deep dermal inoculation (needles, tattoos, rabies)
How do you defend from Site of Entry: Respiratory tract
Complex host defence mechanisms of the respiratory tract
Goblet cells secrete mucus
Mucocilliary clearance: mucus propelled and impinging particles propelled orad by ciliated columnar epithelial cells
Humoral and cellular immune mechanisms operate locally
How does virus enter through respiratory tract
Viruses enter as aerosolised droplets or saliva
Size of the droplet determines the distribution of the particle in the respiratory tract
> 5 μm – filtered by turbinates
< 5 μm – lower respiratory tract
Reduced mucocilliary clearance – increases susceptibility to respiratory infections (travel sickness in horses, CF)
Establishes local infections which may progress to systemic
What is Site of Entry: gastrointestinal tract
Establish local or systemic infections
Local infections – confined to cells lining intestinal lumen
What is local infection
confined to cells lining intestinal lumen
What is systemic infections
viruses cross intestinal mucosa and
invade underlying tissues and spread within body
Host defence mechanisms:
Gastric pH (2 – 3) Proteases secreted by gastric and pancreatic cells Bile salts Mucus containing IgA
Gastrointestinal viruses defence
Acid stable
Resist degradation by bile salts
Resist proteolytic inactivation
Properties of genitourinary tract
Genitourinary tract – HIV, HSV-2, HPV Urine flushing a protective mechanism Conjunctiva Direct inoculation Usually local infection Very rarely spreads to systemic (unless from another site)
How to Prevent exposure
Quarantine
Herd immunity
Active protection
Vaccination – specific to immunogens
in vaccine
What is local level quarantine
Prevent import of infected animals onto property
Stop spread of disease within a property
Individual property owner / State DPI
What is regional level quarrantine
Prevent import of infected animals into free area/region
Stop spread of disease within a region
State and Federal governments
What are the Ausvetplan for Equine Influenza
- Containment and control based on:
- Movement restrictions
- +/- vaccination
- +/- regionalisation / zoning
What is international level quarrantine
Prevent import of infected animals into free country
Stop spread of disease between countries
OIE
What is herd immunity, how does it help
Sufficient immune animals in herd to reduce the spread of infection
Fewer susceptible animals
Reduced excretion
Aims of vaccination
- Prevent infection
- Prevent disease
- Reduce severity / duration of disease
How to prevent infection
Physical barriers
Antibody mediated
Unlikely Subclinical infection
How to prevent disease
Rapid immune response
Polio, smallpox etc
Distemper, Parvovirus
How to reduce severity / duration of disease
Ineffective immune response
Antibody vs Cytotoxic T cells
Empirical —> Mechanistic
Different types of vaccines
Killed / Inactivated Live / attenuated Recombinant / sub-unit Direct DNA Toxoids and Anti-toxins
Issues/advantages of Live / attenuated vaccines
Attenuated virus (cell culture or genetic manipulation) or non-pathogenic strains
Booster not required (replicates in host)
Longer duration of immunity
Antibody and CTL response (Th1)
Safety issues: immunocompromised or pregnant animals
Reversion to virulence (vaccine associated disease)
Deletion mutants
Issues/advantages of Killed / inactivated vaccines
Many vaccines registered for use in animals in Australia
are inactivated
Advantages: Safe and successful technology
Disadvantages: Reduced immunogenicity
Boosters required
Adjuvants required
Antibody body mediated (Th2) response
Subunit vaccines and recombinant proteins
Issues/advantages of toxoids
“Detoxified” bacterial exotoxins
Highly immunogenic
Tetanus, diphtheria and botulinum toxins
Circulating IgG is protective (Th2)
What are the Routes of administration
Intramuscular or sub-cutaneous
Intranasal, intradermal, intramammary,
intraperitoneal, conjunctival, oral, scarification
Adverse effects of vaccination
- Teratogenic / abortigenic
- Immunosupressed animals
- Local injection site reaction
- Hypersensitivity
- Neoplasia
- Underattenuation
What is Passive Immunity
•Sterile intra-uterine (egg) environment
•No transplacental immunoglobulin transfer
Humans : haemochorial placenta
Ruminants : syndesmochorial placenta
Dogs and cats : endotheliochorial placenta (5-10%)
Horses and pigs : epitheliochorial placenta
Issues/advantages of Passive Immunity
•Sterile intra-uterine (egg) environment •No transplacental immunoglobulin transfer •Functional, but naive immune system at birth •Lag between exposure and immune response
Maternally derived antibody summary
- Protects the neonate against pathogens that the mother has antibodies against
- Wanes as the neonate gets older
- Is not transferred across the placenta
- Depends on the quality and quantity of colostrum ingested
- Quality related to specific gravity
- Interferes with active immunisation of the neonate
- Vaccination schedules
What is Antitoxins / Hyperimmune Sera
Form of passive immunity
Anti-venom
Supplying antigen specific IgG to protect an animal
through a period of high risk (colostrally derived antibody)
What are the type of envemonation
Spider envenomation
Snake bite envenomation
Post-exposure rabies treatment
•Wound management •Human anti-rabies immunoglobulin •Infiltrate wound with RIG •Rabies vaccine •Induces immunity post-exposure 7-10 days
What is nosocomial
Disease originating from hospital
What is iatrogenic transmission
refers to the spread of a pathogen, (bacteria or virus) through a medical procedure or treatment such as a blood transfusion, reuse of needles or IV sets, or by touching a wound on an infected horse and then handling another horse
what are the determinants of animal health
housing, nutrition and age
What is zoonotic transmission
Transmission of disease from animals to human or vice versa
