Without reference to other sources I will give my own understanding of this complex subject.
Disease in my understanding is that which disrupts and reorganizes the structure of an organism, often to its short term detriment and just as often to the long term benefit of its immune functions and organs of detoxification and elimination.
Memetic complexes are can be likened to microbes, bacteria and viruses which when out of balance can cause disease in an organism, but which otherwise co-exist in ways which are vital for the efficient functioning of it. These influences are reletively independent of any individual organism and use their hosts to replicate and their hosts behaviors to transform themselves from one state to another.
So it seems that there is a symbiotic relationship between memeplexes and human minds/cultural constructs which can become unbalanced, causing disease-like symptoms, which may have short term detrimental and possible long-term beneficial effects.
Whilst it is inadvisable to allow extreme inbalance of microbes to organism ratios to take the organism beyond its capacity to continue to function, we can allow a certain amount of time and take particular remedial actions to alleviate acute distress whilst building the strength to resist future onsets of the same imbalance. In this way we co-evolve with out diseases.
Like wise the imbalance of sanity compromising memes needs to be addressed effectively in order that human culture can develop its cognitive immune system and develop the strength to resist future onsets of the same imbalance. In this way we co-evolve with memetic diseases.