With this post I am considering disease and its transmission a type of invasive alien species, such as Crowl et al. (2008).
It would seem that humans pose a particularly great threat to themselves in the form of disease prevalence and transmission. When mankind made the transition from hunter-gatherers to farming communities, technological advances in farming provided increased food supply, therefore allowing populations to start expanding (Gupta, 2004). This domestication of plants and animals paved the way for social development and settlement expansion. As Gupta (2004) describes, the domestication period of plants and animals took place between 10,000-7,000 cal years BP, leading to the increase in density of human populations within settlements. This process did everything to aid the existence of infectious diseases, particularly with respect to infectious disease that require individuals to come into close contact with the disease source. It is when populations became large enough that infectious disease, such as smallpox and measles, were able to become self-sustaining. Harrison et al. (1998) stating populations sizes needing to be in the order of hundreds of thousands.
Usually when such disease in introduced into a new population, the effect can be disastrous, often leading to large-scale mortality. This is particularly the case when the disease has never been present in a population before. This was the case with the bubonic plague, aptly named the Black Death. Between 1346 and 1351 the disease killed around 25 million people across Europe, Northern Africa and the Near East (McEvely, 1988). This disease is spread through droplet infection and is carried by fleas that live on rats. The spread across the world at that time can be attributed to trade routes between countries, where rats were present on-board ships, then being released into the harbours of trade countries and spreading from there (Mitchell, 2003). Another example is the spread of disease through colonisation of new lands. When Europeans settled new lands, such as the Americas, Pacific Islands and Australia, the success of the conquerors has been greatly attributed to the spread o disease that were brought with them.
The domestication of animals has also allowed infectious pathogens to jump the species gap and infect humans, examples including influenza from pigs and geese, faecal contamination of water by livestock and salmonella to name a few. One of the most virulent diseases to have occurred in societies is the presence of malaria. This disease is transmitted via mosquitos and anthropogenic forest clearance increased the area in which mosquitos are able to habit (Mitchell, 2003). It is our development as a species that has enabled these pathogens to develop, exist and survive, acting as invasive species when introduced into a new population or host. Epidemics are therefore a marker of human civilisation and can be considered when investigation anthropogenic impacts on the world around us. Disease has been widely discussed in historic literature in early civilisations (Mitchell, 2003). However, examining the presence of disease past historic records through investigation of skeletal remains becomes a different and much more difficult process, infectious disease identification, let alone identification of species may never be possible (Roberts and Manchester, 1995).
Disease is therefore very much consequence of human development and our ancestors’ progression from hunter-gatherer communities to larger settled civilisations. As skeletal remains often do not provide insights into cause of death, knowledge of how civilisations dealt with infected bodies could provide general insight into infectious disease in the past, prior to historic accounts of disease occurrence and transmission. This threat to ourselves has come about inherently due to our species advancing into civilisation and provides insight into the idea that humans are ourselves a part of nature, and that we too should be considered as invasive threat to one another through our exploitation of the world's resources. This is highlighted by mankind's colonial history and the historic spread of disease from community to community as a result of increasing globalisation and our dominance as a species within the world around us.
http://www.esajournals.org/doi/abs/10.1890/070151
http://repository.ias.ac.in/21961/
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