Some diseases are species specific whilst others can cross species barriers to infect multiple different species
Species-specific disease may be unable to cross the species barrier for many reasons:
If a species does not possess the necessary receptors to be at risk of infection
If the body temperature of the organism doesn't reach temperatures required for the development of the disease
Zoonotic diseases are those which can cross the species barrier from animal to human
This is a growing global concern due to the close relationships between humans and animals meaning the disease may be difficult to control and eradicate
This may potentially lead to pandemics such as that caused by COVID-19
Animal products may also be affected by zoonotic disease which poses a further issue
Some zoonotic diseases can initially emerge from animal populations before developing into human only strains e.g. HIV
Table to show some examples of human only and zoonotic diseases