Download Chapter 17 Zoonosis

Chapter 17
Zoonotic Disease
Objectives:
List examples of zoonoses.
Describe zoonotic reservoirs and transmission.
Describe zoonoses and job safety.
Zoonotic Disease - diseases that are naturally transmitted from animals to humans
More than 150 are known.
Origins of Zoonoses
Reservoir - object that serves as a long-term habitat for an infectious agent.
Ex: animals, soil, water, plants
Source of Infection - individual or object from which an infection is acquired.
(Reservoir and source may be the same or different.)
Types of Reservoirs
1. LIVING RESERVOIRS - humans, animals, and arthropods.
Humans - may or may not show symptoms; harbor microbes and transfer
Animals - wild and domestic animals provide environment for microbes similar to
humans
Arthropods - insects, arachnids, crustaceans; referred to as vectors
Biological Vectors - actively participate in pathogens life cycle.
(Mosquitoes in Heartworm Life Cycle)
Mechanical Vectors - Not necessary to pathogens life cycle.
(Carry pathogen on body part; flies)
2. NON-LIVING RESERVOIRS - air, soil, dust, food, milk, water, fomites
Transmission of Zoonoses
Direct transmission - immediate transfer of an infectious agent from a
reservoir to a susceptible host
Indirect transmission - transfer of an infectious agent carried from a reservoir to a
susceptible host
Horizontal transmission - spread of disease through a population from one
infected individual to another
Vertical transmission - spread of disease from parent to offspring via placenta,
sperm, milk, or ovum
Direct transmission examples:
Ringworm - fungal skin infection; can infect any domestic species
- causes itching, hair loss and scaling; often circular in shape
Rabies - spread directly through bites (saliva)
- Deadly virus that attacks the nervous system.
- Testing in animals requires samples from the brain (euthanasia).
Cat Scratch Disease - spread directly through scratches from felines
- Blood infection; fever, swelling and infection of lymph nodes
Newcastle Disease - avian virus; spread directly through air
- Conjunctivitis and flu like symptoms
Indirect Transmission examples:
Escherichia coli - spread from animal to human through fomites (bedding), or food
- Severe diarrhea
Toxoplasma gondii (Toxoplasmosis)- spread from animal to human through humans
(pregnant women to infants)
-Cats are definitive host; protozoal parasite; egg shed in feces
- Healthy humans often show no signs; great risk for pregnant women and
immunocompromised individuals
- Life threatening infections; brain and lung damage
-Severe birth defects or infant death
BSE (Mad Cow) - prion; spread from animal to human through food: Brain deterioration.
Cryptosporidium parvum - spread from animal to human through water
- severe diarrhea and stomach upset
West Nile Virus - spread from animal to human through mosquitoes
- encephalitis; no symptoms
Classification of Disease
Acute disease - develop rapidly but last only a short time (common cold)
Chronic disease - develop slowly and are continual or recurrent (tuberculosis)
Latent disease - pathogen remains inactive for long periods of time before becoming
active (herpes viral infections_
Infectious disease - source of infection is not necessarily a contagion (Lyme)
Contagious disease - transmitted from one infected individual to another (mono)
Noncommunicable disease - not spread from one host to another (tooth decay)
Epidemiology
Effects of diseases on the community.
Endemic disease - always present within a population; native (influenza)
Enzootic disease - conditions affecting animals of a specific geographic area (avian
influenza)
Epidemic disease - sudden onset and widespread outbreak within a group (plague)
Epizootic disease - sudden onset and widespread within animal population (foot &
mouth disease)
Pandemic disease - widespread and affects both animals and humans; often travels
across continents (influenza of 1918; 40 million died worldwide)
Panzootic disease - widespread epizootic disease (avian influenza from 2003)
Zoonosis and Job Safety
Occupational Safety and Health Administration (OSHA) - division of the US Dept. of
Labor that was developed to “make the place of employment free from recognized
hazards that are casing or are likely to cause death or serious physical harm.”
Most common injury at veterinary clinics = animal bites
OSHA requires each workplace to conduct hazard assessments for each job to
determine the level of protective equipment and training required for each task.
(gloves, masks, goggles, aprons, boots, eyewash stations, etc.)
More examples!!!
Visceral Larva Migrans - roundworm infection from ingestion of infected soil. (kids)
Cutaneous larva migrans - hookworms penetrate skin layers and migrate to intestines