Animal Health Management

Part B -- Control of Infectious Disease

Noninfectious Diseases

Although we will spend most of our efforts examining how to manage livestock to minimize infectious diseases, noninfectious diseases also play a significant role in animal health.   These noninfectious diseases can be grouped into 4 general catagories, nutritional, metabolic, toxic and genetic diseases.  Following are examples of each:

    1.  Nutritional--deficiency or excess of essential nutrients, water deprivation/salt toxicity, pregnancy toxemia

    2.  Metabolic--disorders of the animal's metabolic processes leading to such diseases as milk fever, ketosis and  pregnancy toxemia

    3.  Toxic--animal intoxications due to ingestion or exposure to toxic plants, chemicals, insecticides, herbicides,etc.

    4. Genetic--disorders due to alterations or mutations in the animal's genetic makeup; can be heritable or spontaneous.  Examples are Bovine Leukocyte adhesion deficiency (BLAD), Severe Combined Immune Deficiency (SCID), Porcine Stress Syndrome (PSS).

     

Infectious Disease

Infectious diseases are caused by bacteria, viruses, parasites, fungi or protozoa.  Before examining each of these classes of infectious agents, however, there are several important concepts that must be understood when dealing with infectious disease.

  1. Contagious vs noncontagious disease -- Even though caused by an infectious agent, not all infectious diseases are highly contagious (easily spread from one animal to another by contact).
  2. Infection does not always equal disease -- Even when an animal becomes infected with one of the infectious agents, they may not show overt signs of disease.  Remember that the healthy animal has alot of reserve capacity to fight disease agents and mayl not show signs of disease until those reserves are depleted and the animal is overwhelmed.
  3. Latent infections are infections that do not cause a visible disease in an animal.  This is an example of concept 2, in which infection does not always equal disease.  Latent infections can revert to a disease state, however, if the animal becomes stressed, malnurished, etc.
  4. Endemic vs epidemic disease -- Endemic disease is a state in which a disease agent is circulating within a group of animals, but may be in a latent state and not be noticeable.  Many of the animals in the group will be infected and show no signs of disease, many will have cleared the infecting agent and be immune, some will not be infected but will be susceptible to the agent, and a few animals may actually be sick.  Epidemic disease is a state in which a group of naive animals become exposed to a disease agent to which they have not immunity.  In this instance, large numbers of animals become sick and may die. 

Parasites

  • Size--most can be seen with the naked eye, or low power microscope-multicellular organism-possess all genetic material and organelles needed to reproduce
  • Location
  • Internal

    stomach-sheep Haemonchus sucks blood and causes severe anemia (bottle jaw) in sheep

    intestine-roundworms-migrate through lung, liver, blood vessels, causing damage during migration, compete for nutrients in the intestine; hookworms, whipworms-suck blood from the intestine

    lung worms, liver flukes are parasites that reside and damage the lungs and liver of animals

  • External

    lice & mites-Northern fowl mite, mange mite

    ticks-vector for other diseases-protozoan diseases, lyme disease; suck blood

    flies-irritating, larvae may migrate throughout body and cause disease-stomach bot, nasal bot, warbles

  • Means of spread
  • Egg contamination of the environment -- eggs &/or larvae often have long latent periods outside body
  • Some internal parasites have an obligate intermediate host such as snail or insect-spend part of the time someplace else.
  • Vertical transmission -- from mother to offspring either in utero or in milk
  • Animal-to-animal contact -- external parasites are commonly spread in this fashion
    •
  • Means of control (anthelmintics, mitocides, insecticides, etc.)--external-dust, spray on, pour on. Also oral or injectable for both internal and external.
  • Mech of action--some types of anthelminics kill the parasite directly; others interfere with the life cycle of parasite at one larval stage or another; others affect the nervous system-paralyze the intestinal worm which is then passed out with feces.  Currently, there are no effective vaccines licensed in US to protect against parasitic infection.
  • Development of resistance of parasite to the anthelmintic has been a problem with older medications; ivermectin very effective against wide spectrum of both internal and external, but expensive.
  • Management techniques to minimize parasitic disease:

    1) remove fecal material, disinfect, fumigate

    2) rotate pastures

    3) drain mudholes

    4) monitor for disease -- vet examination of skin scrapings, fecal egg counts

    5)  prevent fecal contamination of feed

    6)  prompt removal of sick and dead animals

    7)  do not feed garbage, especially uncooked (Trichinella spiralis)

    •

    Bacteria and Viruses

    • Size--
  • Bacteria require light microscope to visualize, unicellular organism-possess all genetic material to reproduce.
  • Viruses--submicroscopic, requires electron microscope to visualize and identify by size and shape, piece of DNA or RNA and envelope and a few enzymes-requires host cell to produce, reproduce.
    •
  • Means of spread--
  • Direct contact between animals,
  • Some bacteria and viruses can survive in environment,
  • Others are obligate intracellular organisms, can only live and multiply within the animal. Some bacteria can survive and multiply in a contaminated environment
    •
  • Means of control
  • Bacteria--antibiotics to treat infection, vaccines to protect against infection
  • Viruses--vaccines to prevent infection-nothing short of new generation interferon-type agents can treat infection and those are too expensive for animal use
  • It is important to have a veterinarian confirm the diagnosis of bacterial and viral infections, because many different agents may cause diseases that appear the same

    •  

    Fungi and Protozoa

    • Fungi
      • Types
        Cutaneous -- contagious, and  some are spread to man (zoonotic)
        Systematic -- usually noncontagious and most often found in animals with defective immune systems
      • Control
        Clean, sanitary environment
        Quarantine and isolation of new stock, infected animals
        Topical and/or systemic antifungal drugs
    • Protozoa
      • Types
        Blood-borne
        Gastrointestinal -- Coccidia
      • Spread
        Dam to offspring
        Environment -- fecal-oral for coccidia
        Biting insects or dirty needles and syringes for blood-borne
      • Control
        Cleanliness
        Coccidiostat drugs

     

    Biologics and Pharmaceuticals

    • Vaccines -- The purpose of a vaccine is to stimulate the animal's immune system to produce an active immunity.   Vaccines are used to prevent diseases, not cure them.   There are three general classes of vaccines:

    Modified live (attenuated) vaccine--disease producing properties reduced, organism grows and multiplies in animal, stimulates stronger immune response

    a. must be stored properly or it will loose effectiveness

      • b. restrictions to use

        • age of animal  

        • restricted in pregnant animals

      • c. can cause mild disease with some types-if given to sick, debilitated animals, can cause apparent disease

    • Bacterin--killed bacteria, don't need to worry about causing disease-autogenous is made from strains present on farm (custom designed) usually doesn't provide as long lasting protection

    • Toxoid--prepared from a potent toxin that has been detoxified and will provide immunity to to effects of the toxin (tetanus, Clostridium perfringens enteritis in baby pigs)

    Always read and follow the label before using vaccines!!   Failure of a vaccine to adequately protect an animal against disease can be due to vaccine factors, animal factors, or human factors!

    • Antibiotics -- The purpose of antibiotics are to treat bacterial infections; antibiotics are ineffective against viruses and most parasitic diseases.
  • Types:

    • Bacteriostatic

    Bactericidal

  • Effective only against bacteria, not viruses
    •
  • WITHDRAWAL TIMES IN FOOD PRODUCING ANIMALS
    •
  • Use proper antibiotic for type of infection and use for perscribed duration-one shot is worse than none-development of resistance
    •
    • Routes of Administration of Biologics and Pharmaceuticals

    1. Topical--pour on anthelmintics, antibiotic ointment for superficial wounds, etc.

    2. Oral--in water, feed, as drench, bolus or pill given with balling gun, paste squirted into mouth

    3. Parenteral--injection, either intramuscular (IM), intravenous (IV) or subcutaneous (SQ)--important to use proper route
    • Proper handling and use

    1. READ LABEL--storage, expiration, route of administration, withdrawal

    2. Sterile technique--clean needles and syringes, proper size, clean injection site

     

     

    ABOVE ALL, DO NO HARM

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