CD46 and viral infectious disease: In addition to these keywords, the 16 clusters are further divided into the following: cluster 1 (orthopoxvirus), cluster 2 (mice), cluster 3 (cidofovir), cluster 4 (epidemiology), cluster 5 (non-human primates), cluster 6 (virus infection), cluster 7 (membrane cofactor protein), cluster 8 (congo basin), cluster 9 (self-assembly) and cluster 10 (smallpox vaccine) (Table 2, Fig. 8B).