Veterinary Technology Chapter 14 Principles of Infectious Disease

Objectives Identify the two categories of disease and determine the causes of each. Describe Koch’s postulates Describe Koch’s postulates List the important distinguishing features and give examples of major disease agents and discuss the resulting diseases. List the important distinguishing features and give examples of major disease agents and discuss the resulting diseases. Relate text material to common presentations Relate text material to common presentations Examine the primary and secondary defenses the body uses to resist disease. Recognize the two categories of immunity and compare the types in each category.

Terms acquired immunity antigen colostrum endospores endotoxins exotoxins infectious disease natural immunity noninfectious disease pathogen phagocytized prokaryotes vaccine

Introduction A disease is a change that occurs in the body and prevents normal function. A disease is a change that occurs in the body and prevents normal function. Read page 199 – “A Day in the life of a Vet.” Mastitis?

Introduction The two categories of disease: 1.infectious disease is a disease caused by an interaction between two organisms, usually a pathogen and a host. Agents of infectious diseases are divided into four major classes: bacteria, viruses, fungi, and parasites. A pathogen is an agent capable of producing disease. Bacteria and viruses are the most common pathogens.

Transmission methods of an infectious, contagious disease (not all infectious diseases are contagious): Transmission methods of an infectious, contagious disease (not all infectious diseases are contagious): Through a vector: insects, mites, ticks, mosquitoes Through a vector: insects, mites, ticks, mosquitoes Direct: feces, discharges Direct: feces, discharges Air Air Soil Soil Food Food

Introduction 2. A noninfectious disease is a disease not caused by a pathogen and not communicable from one animal to another. It may be caused by hereditary factors or by the environment in which an animal lives.

Disease Agents Infectious Diseases are divided into four classes: Infectious Diseases are divided into four classes: bacteria bacteria Viruses Viruses Fungi Fungi Parasites Parasites Microbiology: the study of microorganisms Microbiology: the study of microorganisms

Bacteria as a Disease Agent Bacteria are prokaryotic! Bacteria are prokaryotic! Eukaryotic Prokaryotic Eukaryotic Prokaryotic

Bacteria as a Disease Agent The 2 most important factors in classifying bacteria are by stain and by shape The 2 most important factors in classifying bacteria are by stain and by shape Gram-positive will stain blue because they absorb the crystal violet stain Gram-positive will stain blue because they absorb the crystal violet stain Gram-negative will remain pink colored because they do not pick up the crystal violet stain. Gram-negative will remain pink colored because they do not pick up the crystal violet stain.

Bacteria as a Disease Agent Bacteria are also classified by shape: Bacteria are also classified by shape: page 204 Staphylococci Streptococci Bacilli Spirochetes Mycoplasma – smallest of all bacteria, don’t have cell wall

Viruses as a Disease Agent Viruses have no cell walls, organelles, or enzymes and are not considered living organisms. They cannot reproduce without living host cells. A virus is classified as either RNA or DNA, according to the type of nucleic acid found in its core. Other distinguishing features include amount of nucleic acid, capsid shape, type of host infected, and whether the virus needs a vector to carry it between hosts.

Viruses as a Disease Agent Viruses cause harm to animals by attaching to and invading host cells, replicating, and then destroying the host cells. Because they are not affected by antibiotics and because very few antiviral drugs are oral, viral diseases are very difficult to eliminate from the body. Some antiviral drugs are available.

Fungi as a Disease Agent Like bacteria, most species of fungi are harmless, whereas a few cause disease. Fungi have eukaryotic cells and cell walls but do not contain chlorophyll. Most fungi reproduce by spores. Fungi can enter the body through the skin, eyes, respiratory system, or digestive system.

Fungus as a Disease Agent Ringworm is one common example of a fungal infection that directly invades an animal through its skin and hair follicles. Systemic: a disease capable of infecting the entire body

Fungi as a Disease Agent Fungi can grow on old or poorly stored feed and produce mycotoxins, which are harmful to the animals that eat the feed. Producers must be careful to harvest grain, such as corn or wheat, only when its moisture content is low enough to prevent the growth of fungi while the grain is in storage.

Parasites as a Disease Agent Many parasites can cause disease-like disorders, whereas others merely serve as carriers of diseases. Parasites use host animals as sources of nutrients and protection. Parasites can be unicellular organisms visible only under a microscope, or they can be multicellular organisms visible with the naked eye. Parasites can be internal or external

Parasites as a Disease Agent Internal parasitic worms: Flat-segmented (cestodes) Mammal = tapeworm Flat, non-segmented (flukes) Invade liver, lungs or GI tract Roundworm (nematode) Dogs = heartworm

Parasites as a Disease Agent External Parasites All are arthropods – class or organisms that include insects and spiders. Ticks, fleas, mites, lice, mosquitoes and biting flies. Botfly = lays eggs on the legs of horses and cattle, when the animal licks the larvae move into the mouth and GI tract.

Parasites as a Disease Agent The two most common external parasites for small animals: Flea Blood sucking = cause anemia, skin irritation, etc Eggs develop off animal, in environment Shampoo (Dawn), insecticide dip, collars, etc. Ticks Also blood sucking = transmit Lyme disease Keep the tick once you remove it! Frontline does not kill the tick, only repel it Types of ticks on page 214

Antibiotics (page 213) Products produced by one microorganism that kill or slow the growth of another microorganism. Products produced by one microorganism that kill or slow the growth of another microorganism. Can kill bacteria, not viruses Can kill bacteria, not viruses Bacteria can become resistant Bacteria can become resistant Penicillin = first antibiotic discovered by Dr. Alexander Fleming in London. Penicillin = first antibiotic discovered by Dr. Alexander Fleming in London. It was still almost 10 years before it was mass produced! It was still almost 10 years before it was mass produced! World War II World War II

Koch’s Postulates Dr. Robet Koch - German physician Dr. Robet Koch - German physician Prounnounced (KoK) Prounnounced (KoK) His investigations led to the development of certain foundation principles about infectious disease. His investigations led to the development of certain foundation principles about infectious disease. Anthrax Anthrax

Koch’s Postulates A set of principles that help lead to define an infectious disease: A set of principles that help lead to define an infectious disease: 1. The infectious agent should be detectable in sick animals but not healthy animals. 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. 2. It should be possible to isolate and culture the organism. 3. Organisms taken from the culture and introduced into a healthy animal should cause the same disease. 3. Organisms taken from the culture and introduced into a healthy animal should cause the same disease. 4. the same organism should be isolated from this second animal as well. 4. the same organism should be isolated from this second animal as well.

Clinical Practice The immune system is activated when an antigen is introduced into the body. An antigen is any foreign molecule capable of stimulating an immune response. Generally, antigens are relatively large and complex so that they can be recognized by the immune system. A. Most diseases are warded off by the body’s primary defenses before they can cause serious infections.

Immunity Immunity occurs when an animal has built up a resistance to a particular pathogen and is no longer susceptible to the disease. Two types: 1.Natural immunity is determined by an animal’s individual genetic code. It does not depend upon prior exposure to a disease pathogen.

Immunity Some diseases affect only one or a few species. Zoonotic: diseases that can be transmitted between animals and humans. For example, bovine spongiform encephalopathy (BSE), commonly known as mad-cow disease, affects only cattle and humans.

Immunity An animal’s breed may also play a role in immunity status. Pure breed vs. “mutt” ?? In this closed breeding system, the offspring do not receive the benefit of immunity that could be acquired through crossbreeding.

Immunity 2.Acquired immunity is either gained from exposure to a mild form of a disease or passed from mother to newborn. A vaccine or exposure to a mild natural infection is a way to provide active immunity. A vaccine is a killed or weakened form of a pathogen. Exposure allows an animal’s immune system to prepare a response and develop a memory for the disease. Colostrum: an antibody- rich milk, from its mother soon after birth.

Vocabulary SID: Medicine to be given once daily SID: Medicine to be given once daily BID: Medicine to be given twice daily BID: Medicine to be given twice daily TID: Medicine to be given three times daily TID: Medicine to be given three times daily BAR: Bright, Alert and Responsive BAR: Bright, Alert and Responsive UTI: Urinary Tract Infection UTI: Urinary Tract Infection BP: Blood Pressure BP: Blood Pressure

Bacteria as a Disease Agent In addition to the main chromosome, in bacteria they also contain a plasmid. In addition to the main chromosome, in bacteria they also contain a plasmid. Plasmid = small fragment of DNA Plasmid = small fragment of DNA Can reproduce independently of the bacteria Can reproduce independently of the bacteria Resistance to antibiotics Resistance to antibiotics is a growing concern both in humans and veterinarian field.

Bacteria as a Disease Agent 3 Methods for bacteria to transfer genetic material: 3 Methods for bacteria to transfer genetic material: 1. Conjugation= direct contact b/t 2 bact. 1. Conjugation= direct contact b/t 2 bact. 2. Transformation= a fragment of DNA is released by one bacteria, and engulfed by another. 2. Transformation= a fragment of DNA is released by one bacteria, and engulfed by another. 3. Transduction = requires the transmission of the DNA by a virus 3. Transduction = requires the transmission of the DNA by a virus

Review What are the two categories of disease, and what are the causes of each? What are the primary and secondary defenses the body uses to resist disease? What are the two categories of immunity, and how do the types in each category compare?