Figure 1.
Survival and body weight change of mice inoculated with O. tsutsugamushi intraperitoneally or intravenously.
Animals inoculated intraperitoneally with 1.25×106 organisms (A and C- red triangles) began losing weight at 4 dpi that continued until death and expired by 9 dpi. Intravenously inoculated animals expired by 13 dpi with weight loss starting at 7 dpi and continuing until death (A and C- blue boxes). Animals inoculated i.p with 1.25×104 organisms expired by 15 dpi losing weight until day 7 when most animals began to increase in body weight (B and D- red triangles). This late increase in body weight corresponded to an increase in accumulation of peritoneal fluid. Animals inoculated i.v. with the same dose became ill at 6–7 dpi, but only 1 of 10 animals expired with all animals losing weight until 12 dpi when signs of illness began to abate and animals appeared to be recovering (B and D- blue boxes). Uninfected controls are represented as solid black circles in all panels.
Figure 2.
Histopathology in mice following 1.25×106 Orientia intraperitoneal challenge at days 6 and 9 pi.
On 6 dpi Orientia antigen was detected on the surface of the peritoneal organs (A, B; 20×). The spleen at this time was slightly enlarged with no other gross pathology (A). The surface of the liver at this time point revealed multifocal Orientia antigen and mesothelial hyperplasia. By 9 dpi bacterial antigen was detected on the surface of the renal capsule (C-40×) and in the hyperplastic inflamed surfaces of the liver (D-40×) and the spleen (E-40×).
Figure 3.
Histopathology in mice following 1.25×106 Orientia intravenous challenge at 6 dpi.
All organs, except brain, had detectable Orientia antigen (hashed circles and insets B–E). Orientia antigen in the lung (A- 40×, B-100×) was associated with vasculitis and interstitial pneumonia. Although antigen was detected in the kidney (C-20×; inset-40×) and spleen, no lesions were observed. Hepatic (D-20×; inset-40×) lesions increased in number and relative size and were often associated with blood vessels (BV). At this time, it was evident that systemic infection had been established with the majority of Orientia antigen present in endothelial locations.
Figure 4.
Pulmonary endothelial infection by Orientia.
Electron micrograph of mouse lung at 6Orientia. Inset shows higher magnification of cytosolic Orientia. A, alveolar space; P, type 1 pneumocyte, E, alveolar capillary endothelial cell; *, three orientiae; L, leukocyte in capillary lumen; AM, alveolar macrophage in adjacent alveolar space.
Figure 5.
Histopathology of mice following lethal intravenous Orientia challenge at days 9 and 12 pi.
Immunohistochemical staining of tissues from animals 9 and 12(A-20×) was observed in the majority of animals on 9 dpi with cerebral perivascular, lymphohistiocytic infiltrates (B-inset; 40×, C-100×), cerebral hemorrhage (D-100×), and endothelial infection (E-100×) in moribund animals at 11 dpi. Pulmonary cellular infiltrates were marked 9 dpi resulting in interstitial pneumonia (F-20×). At 12 dpi (G-20×), peribronchial and perivascular cellular infiltration, interstitial pneumonia, and edema (G-arrow) were observed in all animals.
Figure 6.
Histopathology of the liver and kidney following lethal intravenous Orientia challenge at days 9 and 12 pi.
Portal triaditis (A-arrow; 20×) was prominent at 9 dpi, and at 12 dpi perivascular infiltrates were observed in the hepatic sinusoids (B-arrow; 20×). Mild perivascular infiltrates were observed in the kidney at 9 dpi (C-20×), and at 12 dpi (D-arrow; 20×) cellular infiltrates were observed throughout the kidney, particularly as peritubular infiltrates.
Table 1.
Bacterial load (47 kDa gene copies/pg of DNA or µL of blood) kinetics of 1.25×106 FFU challenged C57BL/6 mice.
Figure 7.
Histopathology of the lung following 1.25×104 Orientia challenge.
H & E stained uninfected lung tissue (A-20×) and IHC of uninfected lung (B-40×) compared with lung from i.p. inoculated mice 12 dpi (H&E C-20×, IHC D-40×), and lung from i.v. inoculated 15 dpi (H&E E-20×, IHC F-40×). All i.p. infections were lethal with less severe pulmonary cellular infiltrate when compared to that of i.v. infected mice with capillary endothelial cell infection of the aveolar septa.
Table 2.
Summary of disease manifestations.
Table 3.
Bacterial load (47 kDa gene copies/pg of DNA or µL of blood) kinetics of 1.25×104 FFU challenged C57BL/6 mice.