The other week I read a newspaper-article, and I thought this might be interesting for You. Unfortunately, it's in German (Süddeutsche Zeitung, March 5th 2010), but I want to give You an overview.
Several examples of deranged ecosystems show that the effect on humans is not only a loss in number of species, but can have effects on the health-situation. When Indians began to treat their cows with medicaments against inflammation, vultures disappeared, because their kidneys couldn't cope with this medicament. As a result of the loss of vultures, rabid dogs, who now could find food in rotting cows, increased in numbers and attacked humans. Tenthousands of people died because of this disturbance in the ecosystem.
SARS and some other virusses are supposed to have spread out of a similar situation. Even malaria in regions where woodland is being cleared massively. In intact woodland, breeding-places are not as numerous, natural enemies to moskitoes are more numerous. Numbers of infections near to cleared woodlands has increased by the factor or 250.
There are loads of examples of this, lyme-disease in north america, west-nile-virus, hanta-virus.
I don't know anything about scientific implication or the correctness of this article. Perhaps You could correct or comment.
P.S.: I might have to have done some investigation, beforehand. Alas, I have done some, afterwards. Check this for some basic informations of the article (it's even in better English!):http://www.ecostudies.org/IES_lyme_disease.html