FIG. 8.

Guinea pigs infected with the ΔpurH strain of B. anthracis. Moribund guinea pigs appeared to be “swollen.” (A) Marked subcutaneous and fascial plane edema. Note the thickened and glistening (marked edema) subcutaneous tissues (arrows). (B) Skeletal muscle of a guinea pig infected with the ΔpurH strain of B. anthracis. There is skeletal muscle degeneration and necrosis characterized by variation in the size and shape of skeletal muscle fibers, loss of cross-striations, and fractured and vacuolated sarcoplasm (cytoplasm). The connective tissue between muscle fibers is markedly expanded by myriad bacilli, polymorphonuclear inflammatory cells, and clear space (edema). HE was used for staining; magnification, ×20. (C) Skeletal muscle, at the injection site, of a guinea pig infected with the ΔpurH strain of B. anthracis. There are myriad strongly positive bacilli within the connective tissue between muscle fibers and invading skeletal muscle fibers. The strong IHC positivity suggests that the bacilli in the muscle produced robust capsules. Immunohistochemistry was carried out for the B. anthracis capsule antigen, with a hematoxylin counterstain; magnification, ×60. (D) Spleen of a guinea pig infected with the ΔpurH strain of B. anthracis. There is diffuse paucity of splenic white pulp. There are scattered normal periarteriolar lymphoid sheaths (arrows). HE was used for staining; magnification, ×4. (E) Spleen of a guinea pig infected with the ΔpurH strain of B. anthracis. Lymphocytolysis (arrows) is evident within the germinal center of a splenic corpuscle. HE was used for staining; magnification, ×40.