> They concluded that a rise in temperature to 37C and an increase in humidity above 80% in the previous few days had stimulated the bacteria to pass into the bloodstream where it caused haemorrhagic septicaemia, or blood poisoning.
Not at all. The whole point of warm-blooded organisms is to maintain a constant temperature, to a really good level of accuracy.
A change in body temperature is not needed for this sort of things to happen, though. A warmer environment is enough. See for example the headlines about flesh eating bacteria creeping north in the US.
"... except because it will be efficiently removed by its immune system (that knows perfectly what is a Pasteurella)" is the part of the phrase that is missing here.
It this does not happen... the question is why this year is not happening.
> Pasteurella bacteria has previously been linked to the sudden death of about 200,000 saiga antelopes in Kazakhstan – an incident that researchers believe could shed light on what happened to the elephant herds. Scientists believe the Pasteurella bacteria generally lives harmlessly in the tonsils of some, if not all, of the antelopes. An unusual temperature increase to 37C, however, caused the bacteria to pass into the bloodstream, where it caused septicaemia.
I read it as the effect of body temperature, but the parent has interpreted it as air temperature. I am not sure which interpretation is correct.