Spirochaetal infections of the nervous system

SYPHILIS

This infectious disease is caused by the spirochaete Treponema pallidum. Entry is by:

- inoculation through skin or mucous membrane (sexually transmitted) - acquired syphilis.

- transmission in utero - congenital syphilis.

Up to 10% of patients with HIV will test positive for syphilis. All patients with neurosyphilis should be tested for this.

The natural history of infection is divided into:

latent period infectious stage

6 weeks

primary sore heals primary phase

2-8 weeks

25% develop meningitis from 6 months onwards mucocutaneous

- macular rash and systemic symptomatology

- hepatitis lymphadenitis.

latent period

Variable secondary phase 2 years late stage

(non-infectious) Gumma in - skin

- liver

Vascular involvement CNS involvement (only 7% of all cases of untreated syphilis).

tertiary phase

The chancre or primary sore on skin or mucous membrane represents the local tissue response to inoculation and is the first clinical event in acquired syphilis. The organism, although present in all lesions, is more easily demonstrated in the primary and secondary phases. In congenital syphilis fetal involvement can occur even though many years may elapse between the mother's primary infection and conception.

Widespread recognition and efficient treatment of the primary infection have greatly reduced the late or tertiary consequences.

Not all patients untreated in the secondary phase progress to the tertiary phase. In HIV patients the neurological complications occur earlier and advance more quickly.

Investigations

Spirochaetes can be demonstrated microscopically by dark field examination in primary and secondary phase lesions.

Serological diagnosis depends on detection of antibodies.

1. Non-specific (Reagin) antibodies (IgG and IgM). Reagin tests involve complement fixation.

The Venereal Disease Research Laboratory (VDRL) test is the commonest and when strongly positive indicates active disease, (may be negative in HIV).

2. Specific treponemal antibodies (do not differentiate between past and present infection). Fluorescent treponemal antibody absorption (FTA) test and Treponema immobilisation (TPI) test.

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