<p> Chapter 14 Notes Principles of Infectious Disease Veterinary Technology Level 1</p><p>KOCH’S POSTULATES Describe Koch’s Postulates</p><p>• 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)</p><p>1. The infectious agent should be detectable in sick animals but not healthy animals.</p><p>2. It should be possible to isolate and culture the organism.</p><p>3. Organisms taken from the culture and introduced into a healthy animals should cause the same disease.</p><p>4. The same organism should be isolated from this second animal as well.</p><p>*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</p><p>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)</p><p>DISEASE AGENTS List the important features and give examples of major agents; describe resulting disease.</p><p>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 • Cocci - round • Bacilli - rod shaped • Spirochete - spiral shaped • Staphylocolli - clusters of cocci • Streptococci - chains of cocci</p><p>Common bacterial infections: Leptospirosis - bacterial infection causing renal damage Kennel cough - dry hacking cough Lyme disease - joint pain and lethargy</p><p>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</p><p>Common viral infections: Feline Leukemia - chronic weight loss & tumors Canine distemper - pneumonia, seizures Rabies - inability to swallow, aggression, fatal</p><p>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</p><p>Common fungal infections • ringworm - fungus that infects skin, hair, nails, and claws. • Valley fever - skin lumps and abscesses </p><p>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</p><p>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)</p><p>Common parasites: Taenia tapeworm - cat/rodent tapeworm Cat passes tapeworm eggs - rodent eats tapeworm eggs - cat eats rodent - </p><p>Dipylidium caninum - dog/cat-flea tapeworm Pet passes tapeworm eggs - flea larvae eats eggs - pet ingests fleas while grooming - tapeworm matures in pet</p><p>Botfly - arthropod external parasite of horses botfly lays eggs on horses leg - horse licks leg - larvae hatch and move into stomach - pass through feces </p><p>Ticks - blood sucking external parasite attaches to skin and engorges itself with blood transmits Lyme disease in humans and dogs</p><p>CLINICAL PRACTICE Relate material to common presentations.</p><p>Culturing - technique used to isolate and identify microorganisms causing infectious disease Milk is often cultures to check for mastitis causing bacteria.</p><p>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.</p><p>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.</p><p>Heartworm Test - blood test to check for Heartworm microfilaria</p>