opportunistic parasites and infections caused by the microorganisms that live on decaying/dying tissues are all caused by *degrading environmental conditions* through all manner of pollution, including agricultural chemical use, including residential lawn care, and EM pollution.
Keep in mind that environmental conditions include the quality, or lack thereof, of diet... commercial CAFO bees have a very poor diet of sugar/fructose water.
Do not let an article like this sway you away from that knowing.