As with any natural system, effects vary considerably.

It is well documented that European honeybees, with the ability to detect and
remove diseased brood, can be completely AFB resistant (Spivak and Gilliam
1998).

It has been demonstrated
that different isolates of P. larvae differ considerably in their larval virulence,
with the most virulent isolates at the larval level and actually least virulent at the
colony level (Genersch et al. 2005).

See:
Diseases of Asian Honeybees
Ingemar Fries

In: 
Honeybees of Asia
H.R. Hepburn, S.E. Radloff
Editors

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