title: Morphologic characteristics of colonies of Anaplasma marginale Theiler in midgut epithelial cells of Dermacentor andersoni Stiles.
abstract: Colonies of Anaplasma marginale Theiler were studied in midgut epithelial cells of adult Dermacentor andersoni Stiles that were infected as nymphs. Colonies were categorized by light microscopy into 5 morphologic types that appear to represent stages in a developmental sequence. The mean diameter of the colony types ranged from 5.64 micrometer to type 1 colonies to 10.49 micrometers of type 5 colonies. Representatives of each colony type were selected by light microscopy and were sectioned for examination by electron microscopy. The morphologic features of individual A marginale organisms within colony types varied and included: (i) small electron-dense forms, (ii) larger reticulated forms, (iii) pleomorphic reticulated forms, and (iv) small particles. Types 1 and 2 colonies contained small, electron-dense forms. Type 3 colonies contained electron-dense forms, early reticulated forms, and small particles that were often outside of the parasite's limiting membrane. Type 4 colonies contained many reticulated forms that often had small particles within cell membranes. Type 5 colonies contained fewer well-formed reticulated forms than did type 4 and, in some cases, large masses of pleomorphic reticulated forms.
mesh_terms: D000709:Anaplasma / Q000145:classification / Q000254:growth & development / Q000648:ultrastructure*; D000818:Animals; D003870:Dermacentor / Q000382:microbiology*; D004848:Epithelium / Q000382:microbiology / Q000648:ultrastructure; D013987:Ticks / Q000382:microbiology*