Open wounds left by the feeding become sites for disease and virus infections. The mites are vectors for at least five and possibly up to 18 debilitating bee viruses, including RNA viruses such as the deformed wing virus. With the exception of some resistance in the Russian strains and bees that have "Varroa"-sensitive hygiene (about 10% of colonies naturally have it), European "Apis mellifera" bees are almost completely defenseless against these parasites. (Russian honey bees are one-third to one-half less susceptible to mite reproduction).