At what altitude are fleas no longer able to survive?
To answer your question somewhat: Fleas enjoy temperatures in the seventies and like 70 to 80 percent humidity. They do not do well at high altitudes. In most areas these restrictions make flea allergy a seasonal problem, rearing up in the spring and summer. Animals residing in southern states may have fleas and the resulting allergic reaction year round.
Fleas are active from 45 degrees Fahrenheit to about 85 degrees. Optimal is about 70 degrees when used to transmit plague as a bio weapon.
I live at 4600 ft in Pocatello. We never seem to have flea problems. When I lived in San Diego, the flea problem was an issue all year.