Unit 4

Role of Environment in Health and Disease

 

General Factors

Weather -- optimal conditions for host and pathogen may be similar or very different

  • temperature
  • humidity
  • wet environments
    • favor diseases such as foot rot, leptospirosis
    • cause proliferation of mosquitoes that carry disease agents such as West Nile Virus
  • dry environments
    • favor other diseases such as coccidiomycosis

stress imposed by high or low temperatures, or high humidity may affect immune function of host

Air Quality & Ventilation

  • NH3, H2S, dust, airborne bacteria
  • effect on productivity
  • effect on immune system
  • high NH3 contributes to E. Coli & Aspergillus air sacculitis in poultry

Prevailing Winds

  • Eastern Equine Encephalitis (EEE) spread by wind blown mosquitoes
  • swine/poultry enterprises located so they are not downwind of other animal facilities
  • Foot & Mouth Disease 

Geographic Econiche of agent

  • "Texas Fever line" - Boophilus tick territory
  • geographic source of feedstuffs, bedding contaminated with agent - blister beetle poisoning

Social Distance

  • increases in wildlife population of an area
    • deer population - Tuberculosis in diary cattle
    • raccoon population - rabies threat
  • increases in livestock population density result in faster transmission of disease agent
  • potential management control point for disease

 

Husbandry Factors

A number of factors related to the environment and other health parameters of the host can be controlled by altering the husbandry (scientific control and management) of the animal. Some of these factors are:

  • Nutrition of the host animal(s)
  • Housing of the host animal(s)
    • use of layer cages removed birds from source (agent) of coccidiosis
    • use of slatted floors in swine units removed animals from source of other infectious agents
  • Genetic Selection of the host animal(s)
    • increased resistance to disease
    • eliminate hereditary diseases such as inherited immunodeficiencies
  • Appropriate vaccination/controlled exposure to infectious agents
  • Population Density control
  • Protection of young and pregnant
    • regulation of body temperature in newborn
    • farrowing crate, creep areas for young
    • minimize stress in pregnant animal
  • Control environmental contamination with agent(sanitation)
    • decrease dose of agent to host
    • hardiness of agent in environment affects methods that can or must be used
      • (anthrax vs. SIV)
  • Other husbandry techniques that effect the health status of the host animal
    • tail docking - use of elastrator bands can lead to tetanus unless vaccinated or given toxoid
    • syringes & needles - dirty equipment can lead to abscesses, spread of agent
    • animal handling techniques - roughness can lead to increased stress, body temperature, bruising

Toxins in the environment

Toxic Plants

"Indiana Plants Poisonous to Livestock & Pets"

Among the most important toxic plants in Indiana are:

    • white snakeroot, pokeweed, pigweed
    • poison hemlock, spotted waterhemlock
    • yew, wild black cherry, Ohio buckeye
    • cocklebur, jimson weed, nightshade
    • sweet & alsike clover, Johnsongrass

Plant poisonings more common when good forage and feedstuffs are scarce

    • early spring and fall on pasture
    • winter - stored forages contaminated with toxic plants

Chemical Toxins

The presence of chemicals in the environment of the host animal may cause disease in the exposed animal(s). Examples of some chemicals toxic to livestock are:

  • Insecticides
    • Organophosphates
    • Carbamates

  • Rodenticides
    • Warfarin & other anticoagulants
    • Strychnine
    • Rampage, vitamin D3 type rodenticides

  • Metals
    • Arsenic
    • Lead
    • Selenium (in excess)

Biotoxins

Other toxins in the environment of the host animal are produced by other living organisms. Examples of these biotoxins are the mycotoxins produced by fungi present in feedstuffs produced or stored under environmental conditions conducive to their growth. Examples of such mycotoxins are:

Fusarium moniliforme

    • present in contaminated corn
    • causes neurologic disease (horses),
    • pulmonary disease (swine)

Fusarium graminearum

    • present in contaminated corn
    • produces estrogen-like compound (zearalenone), feed refusal factors (swine)

Claviceps purpurea

    • present in contaminated wheat & rye
    • responsible for ergot poisoning




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