Animal Health
Parasites
Their Life Cycles and Classification
Infectious Agents
Causing Disease can be divided into
Three General Groups:
Bacteria
Viruses
Parasites
Bacteria
• Simple plant life
• Microscopic
• Can be Pathogenic and
beneficial
• Live outside of host
• Sensitive to antibiotics
Viruses
• Are Ultra-microscopic
• Live in tissue of host
cells
• Are resistant to
antibiotics
• highly contagious
Parasites
• Live in, on, or at the expense of
Bot fly common horse parasite
the host.
• Infections develop slowly
• Difficult to eradicate completely
• Animals do not develop resistance
• Animals may not show symptoms
• Host-specific
• Include fungi, protozoa,
arthropods, and helminths
The Parasites in this Group
• Cause tissue damage
• Causes growths
• Absorb nutrients
• General irritation
• Suck blood and lymph
• Secondary infections
• Obstruct passages
• Cause serious
economic damage
Non-infectious Agents
That Cause Disease
•
•
•
•
Chemical and poisons
Poor Nutrition
Injuries
Physical stress from breeding, conception,
lactation, and birth
• Any other stress or trauma that weakens the
animal or its immune system to secondary
infections
Causes Of Disease
• Nutritional Defects
– Result from unbalanced
diets
• Morphological Defects
– Physical disabilities
• Pathogenic Organisms
• Physiological Defects
– Improper functioning of
body parts
– Tiny living things capable
of causing disease
Life Cycle of Tapeworm in a Sheep
Ascarids
Strongyles
Beef and Pork Tapeworms
The Life Cycle of Flies
Occurs in Four Stages
Lice
Ticks
Tick infested horse