Download Animal, Plant & Soil Science

Animal, Plant & Soil Science
Lesson C5-2
Types of Animal Diseases and Immunity
Objectives
Identify the two categories of
disease and determine the
causes of each.
 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.

What are the two categories of
disease, and what are the
causes of each?
The two categories of disease, infectious
and noninfectious, are both harmful to
animal health but are caused by
different things.
 A. An infectious disease is a disease
caused by an interaction between two
organisms, usually a pathogen and a
host.


A pathogen is an agent capable of
producing disease.
What are the two categories of
disease, and what are the
causes of each?
Agents of diseases include certain bacteria,
viruses, fungi, protozoans,
worms, and arthropods.
 Bacteria and viruses are the
most common pathogens.
 Infectious agents can enter
the body through the skin, mucous
membranes, eyes, and sex organs.
 Not all infectious diseases are contagious.
 Agents of infectious diseases are divided
into four major classes: bacteria, viruses,
fungi, and parasites.

What are the two categories of
disease, and what are the
causes of each?

1. Bacteria are prokaryotes, one-celled
organisms that lack membrane-bound
organelles and have one chromosome each.




They reproduce through cell division.
A bacterium has a cell wall that prevents heavy
water flow into the cell, enabling it to live in moist
environments.
A bacterium can be classified by shape and the cell
wall’s ability to pick up stain.
When threatened by harsh conditions, many bacteria
form endospores (shrunken, durable cells that can
survive extremes in moisture and temperature),
providing a kind of hibernation for prokaryotes.
What are the two categories of
disease, and what are the
causes of each?
Most bacteria are harmless, and many are
beneficial to plants and animals.
 However, some bacteria are
pathogens that cause disease.
 Disease- causing bacteria
invade a host animal, multiply,
and cause an infection.
 The signs of disease, which
often include fever and muscle
aches, are visible only when the
bacteria have multiplied significantly.

What are the two categories of
disease, and what are the
causes of each?
These signs of disease can result from the
active release of exotoxins from live cells or
from the release of endotoxins upon the
destruction of the bacteria by the immune
system.
 Bacterial infections are usually treated with
antibiotics.

What are the two categories of
disease, and what are the
causes of each?

2. 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.
What are the two categories of
disease, and what are the
causes of each?
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.

What are the two categories of
disease, and what are the
causes of each?

3. 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.
Ringworm is one common example of a fungal
infection that directly invades an animal through its
skin and hair follicles.
What are the two categories of
disease, and what are the
causes of each?
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.

What are the two categories of
disease, and what are the
causes of each?

4. 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.
Microscopic parasites, such as coccidia and the
trichina worm, cause diseases at the cellular level.
What are the two categories of
disease, and what are the
causes of each?
Larger parasites, such as ticks and
mosquitoes, spread diseases through their
saliva when they bite animals.
 Drugs and pesticides are available to treat
most parasites.

What are the two categories of
disease, and what are the
causes of each?
B. 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.

What are the two categories of
disease, and what are the
causes of each?

1. An animal may develop a genetic disease by
transmission from a parent through DNA or by
mutation.



A parent or other animal may be a carrier of a
disease even if it does not exhibit any disease
symptoms.
Technology is being developed that will allow early
detection of genetic diseases.
If neither parent is a disease carrier, an animal can
still develop a disease if its genes are somehow
mutated in the developmental process.
What are the two categories of
disease, and what are the
causes of each?

2. Inadequate nutrition can also cause
noninfectious diseases in animals.
If an animal does not get all the nutrients it
needs, including vitamins and minerals, it
may develop a deficiency disease.
 For example, milk fever in cows may occur
around calving time because of a lack of
calcium in the blood.

What are the two categories of
disease, and what are the
causes of each?

3. Ingesting harmful materials may lead
to ill health if an animal’s digestive
system is not able to digest or expel the
materials.

a. When ingested,
pieces of metal can
cause infections,
among other serious
problems, for an animal.
What are the two categories of
disease, and what are the
causes of each?

b. Poisonous plants may be accidentally
ingested when an animal is grazing.
 Common
examples of poisonous plants are
pokeweed and yew.
 Grazing pastures should be cleared of poisonous
plants to prevent animals from ingesting the
plants.

c. Eating feed or drinking water
contaminated with chemicals may lead to
disease in animals.
 Feed
and water should be protected from
contamination with harmful pesticides,
herbicides, or other chemicals or materials.
What are the two categories of
disease, and what are the
causes of each?

4. Extreme temperatures may also cause
disease in animals.



Exposing animals to high temperatures without
access to adequate water, ventilation, and shade
can lead to heatstroke.
On the other end of the spectrum, animals can
develop hypothermia when exposed to extreme
cold.
Proper temperature control in structures that house
animals prevents many problems and makes the
animals more comfortable and productive.
What are the two categories of
disease, and what are the
causes of each?

5. One of the best known noninfectious
diseases is cancer.
Animals are susceptible
to cancer.
 One example is cancer
eye in cattle.

What are the primary and secondary
defenses the body uses to resist
disease?


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.
What are the primary and secondary
defenses the body uses to resist
disease?

1. The skin is an animal’s first major defense
against harmful organisms and materials.



The surface layer of dead skin cells is relatively dry
and slightly acidic because of secretions.
When sweat evaporates, it leaves
behind salt on the skin.
These conditions—low moisture,
low pH, and high salinity—slow or
prevent a microorganism’s ability
to grow and reproduce on the surface of the skin.
What are the primary and secondary
defenses the body uses to resist
disease?

2. The digestive tract is also a primary
defense against disease.
Its highly acidic environment kills or slows
the growth of most harmful pathogens.
 The natural microorganisms that live in the
digestive tract and aid in digestion help
control disease by competing with diseasecausing organisms and suppressing their
growth.

What are the primary and secondary
defenses the body uses to resist
disease?

3. Mucus, tears, saliva,
earwax, and other
secretions also serve
to trap and kill harmful
antigens, keeping
them from entering
the body through
openings such as the
nose or eyes.
What are the primary and secondary
defenses the body uses to resist
disease?


B. If an antigen evades the body’s primary
defenses, the immune system activates and
releases lymphocytes, phagocytes (white blood
cells), and antibodies.
1. Lymph tissue, concentrated in
nodes, is strategically located
throughout the body to detect
and trap antigens quickly.


A network of small vessels carries lymph between the
lymph nodes and the bloodstream.
The lymph nodes filter the lymph.
What are the primary and secondary
defenses the body uses to resist
disease?

2. Bone marrow is also an important part of
the immune system.





It produces white blood cells.
Once an antigen is detected, it is phagocytized
(engulfed by a phagocyte) and broken down.
One effect is elevated body temperature, a
common sign of illness.
A fever aids the immune responders by hindering
an antigen’s replication or killing it.
3. The spleen filters the blood, scanning for
antigens and old red blood cells.

It also contains cells that produce antibodies.
What are the two categories of
immunity, and how do the types in
each category compare?



Immunity occurs when an animal has built up
a resistance to a particular pathogen and is no
longer susceptible to the disease.
An animal may either be naturally immune to
a disease or acquire immunity.
A. Natural immunity is determined by an
animal’s individual genetic code.

It does not depend upon prior exposure to a
disease pathogen.
What are the two categories of
immunity, and how do the types in
each category compare?

1. Some diseases affect only one or a
few species.

For example, bovine spongiform
encephalopathy (BSE), commonly known as
mad-cow disease, affects only cattle and
humans.
What are the two categories of
immunity, and how do the types in
each category compare?

2. An animal’s breed may also play a role
in immunity status.
Purebred animal breeds are kept pure by
breeding them only with animals of the
same breed.
 In this closed breeding system, the
offspring do not receive the benefit of
immunity that could be acquired through
crossbreeding.

What are the two categories of
immunity, and how do the types in
each category compare?
Closed breeding systems have led to a
decrease in natural immunity among
domesticated animals, causing an increase
in susceptibility to both infectious and
noninfectious diseases.
 Thus, a purebred animal
may be more susceptible
to a particular disease than
a crossbred animal of the
same species.

What are the two categories of
immunity, and how do the types in
each category compare?

3. Of course, no two animals are exactly
alike.

An animal’s individual disease resistance
may be the result of luck, mutation, age, or
environment.
What are the two categories of
immunity, and how do the types in
each category compare?


B. Acquired immunity is either gained from
exposure to a mild form of a disease or passed
from mother to newborn.
1. 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.
What are the two categories of
immunity, and how do the types in
each category compare?
Active immunity can last anywhere from six
months to a lifetime.
 Depending on the disease, annual booster
vaccinations may be recommended.
 It is important to note that over-vaccination,
especially in geographic areas where a
disease is not prevalent, may lead to new
vaccine-resistant strains of disease
pathogens that will be more difficult to
treat.

What are the two categories of
immunity, and how do the types in
each category compare?

2. Passive immunity develops when
antibodies are transferred from one
animal to another.

This is illustrated
when a newborn
receives colostrum,
an antibody- rich
milk, from its mother
soon after birth.
What are the two categories of
immunity, and how do the types in
each category compare?
The newborn animal’s digestive tract is able
to absorb the antibodies into the
bloodstream without deactivating them but
loses this ability quickly.
 Passive immunity provides only a temporary
safeguard against disease, so animals
should still be vaccinated according to a
recommended schedule.

What are the two categories of
immunity, and how do the types in
each category compare?
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?
