Molds and fungi usually found on book pages: identifying and preventing further spread
Mold can grow in Extreme environments: they can live in very low water activity level, sometimes as lower as 0.71, live in refrigerator temperatures, these characteristics make it difficult to kill them thoroughly. 
You can search "paper deterioration" in Google or library, then you can find lots article about this.

1) Causes

Foxing and other white, fluffy coating or light yellow powder on paper caused by: Eurotium rubrum, E. repens, Aspergillus versicolor, Penicillium solitum, and Penicillium decumbens. (Karbowska-Berent, Joanna, Joanna Jarmiłko, and Jolanta Czuczko. 
Source: "Fungi in Fox Spots of a Drawing by Leon Wyczółkowski." Restaurator. International Journal for the Preservation of Library and Archival Material 35.2 (2014): 159-179.)

Black spots: Monilia, Aspergillus, Penicillium, Mucor, Stemphylium, Hormodendrum, Fusarium, Chaetomium, Byssochlamys 
Source: Beckwith, Theodore Day, Wilbur Harold Swanson, and Thomas Marion Iiams. "Deterioration of paper: the cause and effect of foxing." Publ. Univ. Calif., biol Sci. 1.13 (1940): 299-356.

2) Spreading

For their spread, I think the mold can spread everywhere, but i did not find any resource about it.   

3) Method that kill the mold

Drying the affected paper objects and applying 70% ethanol are the most preferred options to stop active fungal growth. 
Source: Sequeira, Sílvia O., Eurico J. Cabrita, and Maria F. Macedo. "Fungal Biodeterioration of Paper: How are Paper and Book Conservators Dealing with it? An International Survey." Restaurator. International Journal for the Preservation of Library and Archival Material 35.2 (2014): 181-199.