title: Influence of parasitemia level at feeding on development of Anaplasma marginale Theiler in Dermacentor andersoni Stiles.
abstract: Four splenectomized dairy calves were inoculated with a Virginia isolate of Anaplasma marginale Theiler and served as an infective source (donor) for laboratory-reared Dermacentor andersoni Stiles nymphs. Two donor calves developed higher parasitemias during tick feeding than did the 2 other donor calves. One month after molting, adult ticks were incubated at 37 C for 2.5 days to stimulate development of colonies of A marginale, and homogenates of gut were made from ticks fed on each donor calf. Eight susceptible, splenectomized dairy calves (2 per donor calf) were each inoculated IV with the gut homogenates collected from 50 adult ticks and were monitored for patent A marginale infection. Gut tissues from these same groups of ticks were processed for histologic studies. Homogenates from ticks infected on donor calves with lower parasitemias caused infections with longer prepatent periods (av, 43.25 days) than did similar homogenates made from ticks infected by feeding on donor calves with higher parasitemias (av, 31.0 days). Also, sections of gut tissues from ticks infected at the lower parasitemias contained fewer (av, 0.65) colonies/0.001 mm2 of tissue examined than did those from ticks infected at higher parasitemias (av, 6.31).
mesh_terms: D000709:Anaplasma / Q000254:growth & development*; D000712:Anaplasmosis / Q000382:microbiology* / Q000635:transmission; D000818:Animals; D001179:Arthropod Vectors / Q000382:microbiology*; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology* / Q000635:transmission; D003870:Dermacentor / Q000382:microbiology*; D005260:Female; D008297:Male; D018805:Sepsis / Q000382:microbiology / Q000635:transmission / Q000662:veterinary*; D013987:Ticks / Q000382:microbiology*