Download Chapter 14 Infectious Disease

Chapter 14 Notes
Principles of Infectious Disease
Veterinary Technology Level 1
KOCH’S POSTULATES
Describe Koch’s Postulates
• Dr. Robert Koch - German physician who’s investigations led to the development of
foundation principles about infectious disease.
• isolated Bacillus anthracis from blood 125 yrs ago. (ANTHRAX)
1. The infectious agent should be detectable in sick animals but not healthy animals.
2. It should be possible to isolate and culture the organism.
3. Organisms taken from the culture and introduced into a healthy animals should
cause the same disease.
4. The same organism should be isolated from this second animal as well.
*The basic principles still hold true, but not every disease is so clearly defined.
infectious disease - caused by microorganisms that gain entry into the animal’s body
contagious disease - animal becomes sick following exposure to another clinically ill
animal
SPREAD OF DISEASE
• direct contact
• airborne
• bodily secretions
• fomites - Inanimate objects that are a source of infection (water bowl)
• vectors - arthropods that transmit disease (mosquito)
DISEASE AGENTS
List the important features and give examples of major agents; describe resulting
disease.
1. Bacteria - one celled prokaryotic organisms
a. prokaryotes - lack membrane bound organelles
b. eukaryotes - have membrane bound organelles such as mitochondria, nucleus,
and endoplasmic reticulum.
• reproduce through cell division
• vary in their need for oxygen
• rigid cell wall that allows survival in hypotonic environments
• Bacterial Classification - based on shape and how they stain
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Cocci - round
Bacilli - rod shaped
Spirochete - spiral shaped
Staphylocolli - clusters of cocci
Streptococci - chains of cocci
Common bacterial infections:
Leptospirosis - bacterial infection causing renal damage
Kennel cough - dry hacking cough
Lyme disease - joint pain and lethargy
2. Virus - central core of DNA or RNA surrounded by a tough protein coat (capsid).
• neither eukaryotic or prokaryotic
• no cell wall or organelles
• unable to replicate on their own
• Viral Infection
• virus locates a host cell and attaches
• very specific to which type of host and type of cell
• proteins in the capsid aid in penetration and insertion of DNA into the host cell.
• genes use the host cell’s ribosomes to produce enzymes
• these enzymes shut down the host cell’s DNA while using the cell to produce
multiple copies of the virus’s DNA
• the DNA and the capsid protein are combined into a new virus
• lysosomes are then released to destroy the host cell
Common viral infections:
Feline Leukemia - chronic weight loss & tumors
Canine distemper - pneumonia, seizures
Rabies - inability to swallow, aggression, fatal
3. Fungi - eukaryotic cells with cell walls (like plants), but no chlorophyll
• produce spores to spread the organism & survive harsh conditions
• grow and thrive in moist conditions
• can affect animal health in several ways
Common fungal infections
• ringworm - fungus that infects skin, hair, nails, and claws.
• Valley fever - skin lumps and abscesses
4. Prions - proteinaceous infectious particle - poorly understood class of infectious
agents.
• No nucleic acid material
• replication not understood
• extremely resistant to heat
• no immune response is stimulated
• cause disease class called transmissible spongiform encephalopathies (TSE)
• encephalopathy - disease of the brain
• spongiform - microscopic holes creating a sponge like appearance
• Scrapie - TSE disease of sheep
• Mad Cow Disease - TSE disease of cattle (BSE)
• Creutzfeldt-Jakob disease - a TSE in humans
5. Parasites - use a host as their source of nutrients and protection; host is harmed.
• can be single celled organisms or large arthropods
• endoparasites - live inside the host (roundworm)
• infective form is generally passed in feces
• ectoparasites - live on the host (fleas)
Common parasites:
Taenia tapeworm - cat/rodent tapeworm
Cat passes tapeworm eggs - rodent eats tapeworm eggs - cat eats rodent Dipylidium caninum - dog/cat-flea tapeworm
Pet passes tapeworm eggs - flea larvae eats eggs - pet ingests fleas while
grooming - tapeworm matures in pet
Botfly - arthropod external parasite of horses
botfly lays eggs on horses leg - horse licks leg - larvae hatch and move into
stomach - pass through feces
Ticks - blood sucking external parasite
attaches to skin and engorges itself with blood
transmits Lyme disease in humans and dogs
CLINICAL PRACTICE
Relate material to common presentations.
Culturing - technique used to isolate and identify microorganisms causing infectious
disease
Milk is often cultures to check for mastitis causing bacteria.
Antibiotics - drugs that will treat bacterial infections
If treatment is stopped too soon, the bacteria will develop a resistance.
Will not be effective agains viruses.
Fecal Float - checks for intestinal parasites
Specific gravity measures how the particles float - only eggs will float in the fecal
solution.
Must be able to identify different parasite eggs.
Heartworm Test - blood test to check for Heartworm microfilaria