WHILE many members of my profession are mainly concerned with diseases of domestic livestock, we also take a particular interest in diseases that can spread from other animals to man (or vice versa).
These diseases are termed zoonoses.
Some, like tuberculosis and bovine brucellosis have been around for generations.
They are some of our most important animal and human diseases. Fortunately, we have eradicated these two scourges from Australia.
However, an extraordinary number of new diseases have also emerged recently.
A study, published in the journal Nature in 2008 (Jones, Patel and others), reports that 335 new infectious human diseases have appeared since 1940.
They range from curiosities such as monkey pox that spread into people in the US in 2003, to new forms of old diseases such as multi-drug resistant tuberculosis and malaria, to severe acute respiratory syndrome (SARS) that had a global impact in 2003, to AIDS that has infected an estimated 60 million people worldwide.
AIDS has been described as ‘one of history’s most devastating pandemics,’ rivalling the Black Death (which spread from rats and killed a third of Europe’s population in the 14th century) and the 1918-1920 Spanish influenza epidemic, which may have originated in pigs and killed about 50 million people worldwide.
Sixty per cent of these new diseases have emerged from other animals and most of these (72 per cent) originated in wildlife.
This has occurred in part because our increased human population has encroached into wildlife habitats.
AIDS is an example. It probably spread from monkeys or chimpanzees to people in Africa around 60-70 years ago after people killed them for food.
Hendra virus infection is a recent Australian case. This virus, carried by fruit bats, has increasingly infected horses and therefore people, in part because fruit bats have been displaced causing more contact between bats and people.
Some new diseases only affect domestic animals. The first that I experienced was canine parvovirus. Most of you will remember that this virus suddenly appeared in 1978 and spread in spectacular fashion throughout the world within two years.
Many dogs and other canine species died, lacking immunity. Fortunately, effective vaccination has made parvo less common these days.
A new livestock disease is spreading in Europe now.
The causative agent, Schmallenberg virus, is spread by biting midges.
When pregnant sheep, cattle or goats are infected they suffer mild flu-like symptoms but may abort or deliver a deformed foetus.
The virus is closely related to Akabane virus, which behaves in a similar fashion here.
The authors of the 2008 paper in Nature consider that emerging infectious diseases are increasing in part because the human population is growing and interacting more with wildlife.
They consider that these zoonotic emerging infectious diseases are ‘an increasing and very significant threat to global health’.
The authors advise that ‘smart surveillance’ is needed to identify new infectious agents in animals and in at-risk populations of people, before their large-scale emergence.
Finally, they recommend that greater efforts to conserve ‘biodiversity hotspots’ may have the added benefit of reducing the chance of serious diseases emerging from wildlife in the future.