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 caused by an interaction between two organisms, usually a pathogen and a host.

infectious disease

is a disease  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 from the release of system.

exotoxins

from live cells or

endotoxins

upon the destruction of the bacteria by the immune 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

disease not caused by a pathogen and not communicable from one animal to another. is a 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

exposure to a mild form of a disease or passed from mother to newborn.

is either gained from 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?