825

An Experimental Model of Early Central Nervous System Syphilis Christina Marra, Sharon A. Baker-Zander, Edward W. Hook Ill, and Sheila A. Lukehart

Department of Medicine, Divisions of Infectious Diseases and Neurology, University of Washington School of Medicine, Seattle; Department of Medicine, Division of Infectious Diseases, Johns Hopkins University School of Medicine, Baltimore, Maryland

In 1989 the number of reported cases of early syphilis was higher than in any of the preceding 40 years; an estimated 1.5 million persons are infected with syphilis in the United States. This continuing epidemic, coupled with the association and possible interaction of Treponema pallidum and human immunodeficiency virus (HIV) infections, has renewed interest in syphilis and reminded medical scientists of the limitations of our understanding of infections due to T. pallidum. An area of considerable interest and conjecture is the involvement of the central nervous system (CNS) in individuals with syphilis. Invasion of the CNS by T. pallidum occurs in up to 40% of patients with untreated early syphilis [1]. Nonetheless, currently recommended therapy for early syphilis, benzathine penicillin, does not reliably provide treponemicidal drug levels in the cerebrospinal fluid (CSF) [2] and offers the risk of development of neurosyphilis despite therapy. Reisolation of T. pallidum from CSF has been documented after currently recommended doses of benzathine penicillin for early syphilis [1, 3]. In the past 8 years, numerous cases of neurorelapse have been reported in patients previously treated for early syphilis with benzathine penicillin [4-8]. These reports are largely restricted to patients with, or at risk for, HIV infection. Examination of relevant questions regarding pathogenesis, clinical manifestations, natural course, and treatment of neu-

Received 5 July 1990; revised 9 October 1990. Presented in part: 42nd annual meeting of the American Academy of Neurology, April 1990, Miami Beach, Florida (abstract 784). Grant support: National Institutes of Health (AI-18988 and NS-23677 to S.A.L.); University of Washington Graduate School Research Fund (S.A.L.); American Social Health Association fellowship (C.M.). Reprints or correspondence: Dr. Christina Marra, Harborview Medical Center, ZA-89, 325 Ninth Avenue, Seattle, WA 98104-2499. The Journal of Infectious Diseases 1991;163:825-829 © 1991 by The University of Chicago. All rights reserved. 0022-1899/91/6304-0024$01.00

rologic involvement by T. pallidum has been hindered by the inability to cultivate the organism and by the lack of a suitable animal model. We have developed and characterized a model of CNS syphilis in the rabbit that is analogous to the meningeal and ocular involvement seen in patients with early syphilis.

Materials and Methods Rabbits. Adult male New Zealand white rabbits were obtained from a local supplier (R and R Rabbitry, Stanwood, WA). Each rabbit was tested for evidence of Treponema paraluis-cuniculi infection by the Venereal Disease Research Laboratory (VDRL) and the fluorescent treponemal antibody-absorbed (FTA-ABS) tests. Only rabbits with nonreactive serologic tests and no clinical signs of infection were included. Rabbits were housed individually at 19-20°C and were fed antibiotic-free food and water. Source of organisms. Treponema pallidum pallidum, Nichols strain, originally isolated from human CSF in 1912, was propagated in rabbits as previously described [9]. Infected testes were sliced longitudinally and extracted by gentle rotation in 0.9% saline. The extraction medium was centrifuged at 280 g for 10 min to pellet gross cellular debris. Motile organisms in the supernatant were counted by darkfield microscopy and adjusted to concentrations of 2.5-8.5 x 107organism/ml. For control experiments, T. pallidum were killed by heating at 56°C for 40-60 min. Experimental design. Rabbits were anesthetized with 5.0 mg/kg ketamine intramuscularly and 1.7mg/kg acepromazine intramuscularly, and the posterior neck was clipped free of hair. Using a 22gauge, 1.5-inch (3.8-cm) spinal needle, 0.4-1.0 ml of CSF was collected from the cisterna magna. Rabbits (n = 33) were inoculated intracisternally with 1.5-5.1 x 107 T. pallidum (in 0.6 ml); 3 control animals were similarly inoculated with identical numbers of heat-killed T. pallidum. CSF and serum specimens were collected at 0,2,4, 6, 9, 12, and 20 weeks after inoculation with live organisms and 0,2,4, and 6 weeks after inoculation with heat-killed organisms. VDRL and FTA-ABStests were done on serum samples, and CSF red blood cells were counted.

Downloaded from http://jid.oxfordjournals.org/ at University of Bath Library & Learning Centre on July 16, 2015

Although up to 40% of patients with early syphilis have evidence of central nervous system (CNS) invasion by Treponema pallidum, the pathogenesis of CNS syphilis is not understood. A rabbit model that mimics early CNS involvement in humans was developed and characterized. Mild cerebrospinal fluid pleocytosis was evident 2 weeks after intracisternal inoculation of T. pallidum and peaked at 9 weeks. The VDRL test in cerebrospinal fluid was reactive in 24% of animals, most commonly at 9 weeks after infection. T. pallidum could be isolated from the CNS of animals infected for 4, 6, or 9 weeks but not from animals infected for 12 or 20 weeks. Clinically, 6% of animals developed uveitis, similar to the frequency in patients with secondary syphilis. Thus, this model of meningeal and ocular syphilis seems to be analogous to early eNS infection in humans and can be used for studies of pathogenesis and treatment.

826

Marra et al.

32

....

Q)

+-'

f= ...J-

a: W 8 > +1 -c:: ~~ O(/)

UQ)

~~

(6)

4

0.-

U Q)

a:

2

o

4

6 8 10 12 14 16 18 20 Time in Weeks

50,.--------------------,

"5.w

40

O(/) 30 3:c::

III +1

en~

u-

20

10

Evidence ofsystemic infection. Thirty-three rabbits were inoculated intracisternally with virulent T. pallidum, and three control animals were inoculated with heat-killed organisms. Serologic evidence of infection developed by 2 weeks in 12 (86 %) of 14 animals examined and in all animals inoculated with live treponemes by 4 weeks after infection. No control animal developed serologic evidence of infection. Geometric mean serum VDRL titers increased through 6-9 weeks after infection and then declined (figure.1). Lymph node and testis suspensions obtained from animals 2,4,6, and 12 weeks after infection with live T. pallidum contained virulent organisms as shown by positive tissue transfer, confirming systemic infection. eNSfindings. Compared with CSF white blood cell counts in uninfected animals, mononuclear CSF pleocytosis (mean ± SE, 8.2 ± 3.0 white blood cells/Jotl) was evident 2 weeks after inoculation with live treponemes and reached maximum (23.3 ± 10.2 cells/Jotl) 9 weeks after infection. Mild pleocytosis persisted 20 weeks after infection (6.0 ± 3.8 cells/Jotl; figure 2). CSF pleocytosis was not apparent in every animal examined at each time point; 50% of animals had >10 white blood cells/ Jotl6 and 9 weeks after inoculation (figure 3). Controls infected with heat-killed T. pal/idum failed to mount a consistent CSF pleocytosis; only one of five evaluable control CSF samples contained detectable white blood cells. Tran-

2

Figure 1. Serum VDRL titers after intracisternal inoculation with live Treponema pallidum; titers peak 9 weeks after infection, then decline as seen in untreated systemically infected animals [12]. n is shown in parentheses.

LL ~

Results

16

(5)

o

2

4

6 8 10 12 14 16 18 20 Time in Weeks

Figure 2. Cerebrospinal fluid (CSF) white blood cells (WBC)/~1 after intracisternal inoculation with live Treponema pallidum. Pleocytosis peaks at 9 weeks, then declines in concert with declining infectivity of brain tissue. n is shown in parentheses.

0.6

.c~

.

An experimental model of early central nervous system syphilis.

Although up to 40% of patients with early syphilis have evidence of central nervous system (CNS) invasion by Treponema pallidum, the pathogenesis of C...
495KB Sizes 0 Downloads 0 Views