It is possible to be naturally immune to Pasteurella pestis and HIV, the viruses that cause 2 well-known wide spread killers, The Black Plague and AIDS. This is thanks to a genetic mutation in ones DNA called CCR5-delta 32, or Delta 32 for short. This mutation cuts off the means for a virus, to attach to our white blood cells and enter the immune system. It must come from both parents to cause immunity, but if in possession of only one chromosome for delta-32 it is likely to delay the virus from spreading for long periods of time. This mutation isn’t known to ever have a negative effect on any individual, only positive.