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
