Animal, Plant & Soil Animal, Plant & Soil ScienceScience

Lesson C5-2Lesson C5-2Types of Animal Diseases and

Immunity

ObjectivesObjectives

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 disease-causing 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?

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?