The relationship between environmental health, human health and animal health is multifaceted: changes in the environment can result in challenges to food and water availability, physiology, reproductive capabilities and survival. Notable examples of how climate change is impacting on animal health can be seen in amphibians, with some being unable to adapt to temperature increases, and the pathogenic fungus Batrachochytrium dendrobatidis threatening populations [ 10 ]. Human health is also affected by environmental changes, with an increase in cardiorespiratory disease and premature deaths being attributed to air pollution [ 14 ].
Human health
One Health could be considered to be too focused on human health over environmental or animal health, creating an imbalance in the triad. This may be because a human health issue is more obvious and demands immediate attention, rather than being latent, hidden or slow to develop. Additionally, despite most professionals adopting a holistic view towards One Health, they may take an anthropocentric( human-centric) approach to issues involving other elements of the triad [ 15 ].
Just as One Health is multifaceted, so is human health; it could be said that human health, that is, freedom from infirmity and disease, exists when social, mental and physical wellbeing are achieved [ 16 ]. One Health and the related concept of One Medicine recognise noncommunicable diseases alongside the more common focus of communicable diseases. The incidence of noncommunicable diseases in humans can be affected by factors such as poor-quality diet, low physical activity, smoking and alcohol consumption [ 17 ]. Human medicine has developed significantly over the years, with the implementation of vaccinations, efficient diagnostic tools, treatment modalities and promotion of good hygiene practices [ 18 ].
However, when viewing human health from the perspective of the veterinary profession, communicable diseases are of the greatest importance, particularly in relation to zoonotic disease transmission. The vast majority of infectious diseases in humans come from an animal source, and research shows that the transmission of pathogens( particularly viruses) from animal reservoirs to human populations presents a major pandemic risk [ 2 ]. Therefore, the expertise of veterinary professionals is often called on at the intersection of human health and animal health within the One Health triad.
Also under the One Health umbrella, the fields of veterinary and human medicine often collaborate in translational medicine( Figure 2) [ 19 ], where the physiological disease processes are similar in animals and humans. Interdisciplinary sharing has helped to progress research into and treatment of diseases such as cancer, for example, through the development of viroimmunotherapy for malignant melanomas, which has resulted in treatments for both dogs and humans [ 16 ].
Figure 2. The One Health umbrella [ 19 ].
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