PHYSICAL FACTORS
Information on environmental components: physical agents causing disease


We have categorised the Physical Factors and Environmental Events / Factors into the groups listed above to aid the end-user in considering similar factors together. Physical factors influence disease at a number of levels. They may have a direct effect on the host species, on the reproduction and transfer of infectious agents or on the transfer (presence or absence) of chemical agents. Currently, this section covers only those physical factors which have a direct effect on the host species (Waterfowl) and is used for linking these factors to the relevant disease pages.

General Background Information

Various features/events are instrumental in providing an environment that will foster the development of disease. Different basic environmental components associated with these features/events are detailed in this section. (See also Environmental and Population Management).
  • Climate Features / Events - The environment in which animals live, either enclosed or natural, is usually most strongly influenced by both macro and micro-weather conditions. Weather is important for the stressors that it places on the animal, and its affect on the persistence of disease agents.
  • Topography / Enclosure - An animal's living area or home range, be it 10 hectares or 10 square meters, defines many components of its existence. Free-ranging animals in savannahs or prairies have evolved behaviour suited to those surroundings. Species from mountainous or arid regions have developed the necessary anatomical and physiologic features. Design of captive enclosures must address these needs. Topography has a significant affect on weather effects and therefore the presence and transmission of disease agents. Animals restricted to a small valley with stagnant air might be significantly effected by introduced pollutants. A similar situation would exist in a poorly designed housing.
  • Soil / Substrate - Soils have a direct impact on vegetation and the nutritional composition of forage; excesses and deficiencies in macro and micro-nutrients can occur. Contaminants can reside in soils for extended periods of time and can cause intoxication in natural and artificial environments. Disease agents have been demonstrated to be associated with specific soil types. Captive animals often have intimate and chronic exposure to limited soil and/ or substrates. Enclosure floors and soils should be chose with the type of animals to be housed in mind.
  • Food & Water Quality - These play a significant role in health and disease. All animals require a balanced diet with most animals requiring a consistent supply of palatable drinking water. These provide a ready medium for exposure to infectious organisms and toxic substances.
  • Human Disturbance / Land Use - Humans have been altering the natural environment for thousands of years; many of these ecosystem changes can directly or indirectly contribute to the initiation or amplification of disease processes. Examples of these changes are:
  • Introduction of toxic substances, directly causing disease.
  • Translocations and reintroductions causing disease spread and amplification.
  • Modification of topographic features, such as water sources and impoundments, create new new reservoirs for agents and vectors.
  • Land clearing and development reduces available habitat and can lead to increased populations, increased agent concentrations, reduced food resources and the associated stresses.
  • Human disturbance is important on the individual/population level, as well as the ecosystem level. Most animals have a flight distance within which they feel threatened and will often either retreat or attack when a human intrudes. In free-ranging animals and large enclosures, the impact may be limited, but is an important factor to be considered in cage design.
  • Habitat Disturbance/Vegetation - Toxic plant poisoning is known in both free-living and captive wildlife. Infectious diseases are sometimes associated with specific vegetation types and ecosystems. Investigation of wild mortality, and selection of vegetation for exhibits should consider these factors.

N.B. Detailed information on the general influence and the control of Environmental Events/ Factors associated with disease in general is available in the Environmental and Population Management section of "How to..." - Guidance on best practice husbandry and veterinary techniques and on the management of species, diseases and habitats".