Veterinary Technology Veterinary Technology

Chapter 14Chapter 14Principles of Infectious Disease

ObjectivesObjectives

Identify the two categories of disease and determine the causes of each.

Describe Koch’s postulatesDescribe Koch’s postulates List the important distinguishing features List the important distinguishing features

and give examples of major disease and give examples of major disease agents and discuss the resulting diseases. agents and discuss the resulting diseases.

Relate text material to common Relate text material to common presentationspresentations

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.

TermsTerms

acquired immunity

antigen colostrum endospores endotoxins exotoxins infectious

disease

natural immunity noninfectious

disease pathogen phagocytized prokaryotes vaccine

IntroductionIntroduction

A A diseasedisease is a is a change that change that occurs in the occurs in the body and body and prevents normal prevents normal function. function.

Read page 199 – Read page 199 – “A Day in the life “A Day in the life of a Vet.” of a Vet.”

Mastitis? 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 Transmission methods of an infectious, contagious disease (infectious, contagious disease (not not all infectious diseases are all infectious diseases are contagiouscontagious): ): Through a vector: insects, mites, Through a vector: insects, mites,

ticks, mosquitoesticks, mosquitoes Direct: feces, discharges Direct: feces, discharges AirAir Soil Soil FoodFood

IntroductionIntroduction

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 Disease Agents

Infectious Diseases are divided Infectious Diseases are divided into four classes:into four classes: bacteriabacteria VirusesViruses FungiFungi ParasitesParasites

Microbiology: the study of Microbiology: the study of microorganisms microorganisms

Bacteria as a Disease Bacteria as a Disease AgentAgent

Bacteria are prokaryotic!Bacteria are prokaryotic! EukaryoticEukaryotic Prokaryotic Prokaryotic

Bacteria as a Disease Bacteria as a Disease AgentAgent

The 2 most important factors in The 2 most important factors in classifying bacteria are by stain classifying bacteria are by stain andand by shape by shape Gram-positive will stain blue Gram-positive will stain blue

because they absorb the crystal because they absorb the crystal violet stainviolet stain

Gram-negative will remain pink Gram-negative will remain pink colored because they do not pick colored because they do not pick up the crystal violet stain. up the crystal violet stain.

Bacteria as a Disease Bacteria as a Disease AgentAgent

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 Fungus as a Disease Agent 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)Antibiotics (page 213)

Products produced by one microorganism Products produced by one microorganism that kill or slow the growth of another that kill or slow the growth of another microorganism. microorganism.

Can kill bacteria, not viruses Can kill bacteria, not viruses Bacteria can become resistant Bacteria can become resistant Penicillin = first antibiotic discovered by Penicillin = first antibiotic discovered by

Dr. Alexander Fleming. 1929 in London. Dr. Alexander Fleming. 1929 in London. It was still almost 10 years before it was mass It was still almost 10 years before it was mass

produced! produced! World War IIWorld War II

Koch’s PostulatesKoch’s Postulates

Dr. Robet Koch - Dr. Robet Koch - German physicianGerman physician

Prounnounced Prounnounced (KoK)(KoK)

His investigations His investigations led to the led to the development of development of certain foundation certain foundation principles about principles about infectious disease. infectious disease.

AnthraxAnthrax

Koch’s PostulatesKoch’s Postulates A set of principles that help lead to A set of principles that help lead to

define an infectious disease: define an infectious disease: 1. The infectious agent should be 1. The infectious agent should be

detectable in sick animals but not detectable in sick animals but not healthy animals. healthy animals.

2. It should be possible to isolate and 2. It should be possible to isolate and culture the organism. culture the organism.

3. Organisms taken from the culture 3. Organisms taken from the culture and introduced into a healthy animal and introduced into a healthy animal should cause the same disease. should cause the same disease.

4. the same organism should be 4. the same organism should be isolated from this second animal as isolated from this second animal as well. 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 Vocabulary

SID: Medicine to be given once SID: Medicine to be given once daily daily

BID: Medicine to be given twice BID: Medicine to be given twice dailydaily

TID: TID: Medicine to be given three times daily Medicine to be given three times daily

BAR: Bright, Alert and ResponsiveBAR: Bright, Alert and Responsive UTI: Urinary Tract InfectionUTI: Urinary Tract Infection BP: Blood PressureBP: Blood Pressure

Bacteria as a Disease Bacteria as a Disease AgentAgent

In addition to the main chromosome, in In addition to the main chromosome, in bacteria they also contain a plasmid. bacteria they also contain a plasmid.

Plasmid = small fragment of DNAPlasmid = small fragment of DNA Can reproduce independently of the bacteriaCan reproduce independently of the bacteria

Resistance to antibiotics Resistance to antibiotics

is a growing concernis a growing concern

both in humans and both in humans and

veterinarian field. veterinarian field.

Bacteria as a Disease Bacteria as a Disease AgentAgent

3 Methods for bacteria to transfer 3 Methods for bacteria to transfer genetic material: genetic material:

1. Conjugation= direct contact b/t 2 1. Conjugation= direct contact b/t 2 bact.bact.

2. Transformation= a fragment of 2. Transformation= a fragment of DNA is released by one bacteria, and DNA is released by one bacteria, and engulfed by another. engulfed by another.

3. Transduction = requires the 3. Transduction = requires the transmission of the DNA by a virustransmission of the DNA by a virus

ReviewReview

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?