Comparison of virulence of Coxiella burnetii isolates from bovine milk andfrom ticks

Laboratory animals (mice and guinea pigs) were infected with the isolates o f Coxiella burnetii (Derrick, 1939) obtained from bovine milk (M18 and M35) and the ticks Ixodes ricinus (Linnaeus, 1758) and Dermacentor marginatus ( Sulzer, 1776) (Kl(3) and Kl(6), respectively), and with the reference strai n Nine Mile. Neither mortality nor lethality occurred with the mice. Antibo dy response in mice infected with isolates from milk was lower (I : 16-512) than that from ticks (1 : 32-4096). Onset of seropositivity also occurred later - on the 10(th) day post-infection (p.i.) for M18 and M35 in comparis on with the 7(th) day for Kl(3) and Kl(6). In guinea pigs, infection manife sted by fever. The fever was less evident in guinea pigs infected with isol ates from milk (39.5-40.1 degreesC) than in guinea pigs infected with isola tes from ticks (39.5-40.6 degreesC). Partially engorged females of Dermacen tor reticulatus (Fabricius, 1794) were inoculated with isolates M18 and Kl( 3). No differences in the multiplication of C burnetii in haemocytes betwee n these two isolates were ascertained.