title: Demonstration of colonies of Anaplasma marginale in the midgut of Rhipicephalus simus.
abstract: Rhipicephalus simus nymphs were allowed to feed on a cow experimentally infected with the BW-strain of Anaplasma marginale from Republic of South Africa, and they were studied as adults. Colonies were demonstrated by light microscopy in midgut epithelial cells of adult ticks that were unfed (as adults), incubated, or prefed for 72 hours on a cow. The colonies occurred in 5 different morphologic types (1 to 5) that were similar to those described previously for a Virginia isolate of A marginale in Dermacentor andersoni. The colony density (number of colonies/0.001 mm2 midgut tissue examined) ranged from 0 to 2.0 and was highest in unfed ticks that were not incubated (mean 0.566). Colonies observed by light microscopy were sectioned for study with the electron microscope. The colonies contained both electron-dense forms and reticulated forms. The organisms in type 2 and 3 colonies appeared to be attached to one another, and those in type 4 and 5 colonies occurred separately. Small particles were seen within the limiting membrane of some organisms. A few colonies contained a dense matrix and were surrounded by many small electron-dense particles.
mesh_terms: D000709:Anaplasma / Q000302:isolation & purification*; D000712:Anaplasmosis / Q000635:transmission*; D000818:Animals; D001096:Arachnid Vectors; D002417:Cattle; D002418:Cattle Diseases / Q000635:transmission*; D005260:Female; D007422:Intestines / Q000382:microbiology; D008854:Microscopy, Electron; D013987:Ticks / Q000382:microbiology*