Treponema pallidum- Pathogenesis

 Pathogenesis

• Causes the disease Syphilis.
• Humans are the only natural host for T. pallidum and infection occurs through sexual contact/congenital.
• Experimentally, monkeys, chimpanzees, rabbits, hamsters infected

Syphilis

Venereal syphilis is acquired by sexual contact

The organism enters the body through minute abrasions/breaks on the skin or mucosa

Clinical disease starts after an incubation time of about a month

The clinical symptoms appear as 3 stages-primary, secondary, tertiary

Infectivity of a patient to the sexual partner is maximum during the first two years of the disease-primary, secondary and early latent stages-after 5 years, risk is minimal

Clinical Manifestation of Treponema pallidum

1. Primary syphilis:-

• Within 2–10 weeks after infection, a papule develops at the site of infection (usually genital, also on mouth, nipples) and breaks down to form an ulcer with a clean, hard base (“hard chancre”), also called as primary lesion.
• The chancre is painless and most frequently occur on the external genitalia, but it may occur on the cervix, peri-anal area, in the mouth or anal canal.
• It is relatively avascular, superficially ulcerated lesion and is named as Hunterian chancre (after John Hunter, who experimentally infected himself and described the disease)
• Chancres usually occur singly, but in immunocompromised individuals, such as those infected with the Human Immunodeficiency Virus (HIV), multiple or persistent chancres may develop.

 

• The organism multiply locally at the site of entry, and some spread to nearby lymph nodes and then reach the bloodstream and may lodge in any organ-patient is infectious
• Regional lymphadenopathy (swollen, tender lymph nodes) is seen

 

• The chancre generally heals within 4-6 weeks, but lymphadenopathy may persist for months.
• This “primary lesion” always heals spontaneously, but 2–10 weeks later, the “secondary” lesions appear.

 

Secondary syphilis

• Secondary syphilis seen in 1-3 months after primary lesion heals
• During this interval, patient is asymptomatic
• Secondary lesions are due to the systemic spread of the infection when treponemes replicate in the lymph nodes, the liver, joints, muscles, skin, and mucous membranes distant from the site of the primary chancre.
• Skin and mucous membranes are commonly affected and characterized by:

·         Skin rashes (palms and soles )

·         Condylomata lata (mucocutaneous papules at perianal region, vulva, and scrotum.

·         Mucous patches (superficial mucosal erosions)

• Generalized lymphadenopathy is seen.

• The patient may also have syphilitic meningitis, chorioretinitis, hepatitis, nephritis or periostitis.
• Patient is most infective in secondary stage
• Secondary lesions higly variable in distribution, intensity and duration but heal spontaneously, sometimes  in 4-5 years

 

3. Latent syphilis

• It is characterized with no clinical manifestations but serological evidence of infection persists.
• Latent syphilis is classified as early (high likelihood of relapse) or late (recurrence unlikely).
• Individuals with late latent syphilis are not generally considered infectious, but may still transmit infection to the fetus during pregnancy and their blood may remain infectious.
• Latent syphilis may have one of the following fates: Persistent lifelong infection (common), Development of late syphilis (rare), Spontaneous cure.

 

4. Tertiary syphilis

• Tertiary syphilis is responsible for a majority of the morbidity and mortality associated with the disease.
• The hallmark of tertiary syphilis is the destruction of tissue caused by a response to the presence of treponemal antigens.
• The three most common forms are neurosyphilis, cardiovascular syphilis and gummatous syphilis.

·         Gummatous syphilis-Granulomatous lesions in the skin, bones, and liver

·         Neurosyphilis- Degenerative changes in the central nervous system

·         Common manifestations include:

Meningeal syphilis (meningitis)

Meningovascular syphilis (vasculitis of arteries leading to embolic stroke)

·         Cardiovascular syphilis-Characterized by aortitis, aortic valve insufficiency etc

 

NON-VENEREAL SYPHILIS

 Occupational –doctors/nurses- primary chancre on fingers

Blood transfusion- no primary chancre 

B. Congenital syphilis

• A pregnant woman with syphilis can transmit T pallidum to the fetus through the placenta beginning in the 10^th –15^th weeks of gestation.
• Some of the infected fetuses die, and miscarriages result; others are stillborn at term.
• Congenital anomalies include premature birth, intrauterine growth retardation, and multiple organ failure.

Manifestations of congenital syphilis include:

• Earliest manifestations occur within 2 years of age and affected children are infectious and they suffer from rhinitis, mucocutaneous lesions, bone changes, hepatosplenomegaly and lymphadenopathy.
• Late congenital syphilis occurs after 2 years and is noninfectious.
• It is characterized by interstitial keratitis (inflammation of cornea of  eye), eighth-nerve deafness, bilateral knee effusions (Clutton’s joints)
• Clutton’s joints - painless joint effusion (collection of fluid) in the knee of a child, usually , caused by inflammation of the synovial membranes due to congenital syphilis.).