Spirochaetal infections

Spirochaetal infections

Syphilis

Cause

Infection with the causative organism, Treponemapallidum, may be congenital, acquired through trans-fusion with contaminated blood, or by accidental inoculation. The most important route, however, is through sexual contact with an infected partner.

Presentation

Congenital syphilis. If there is a high standard ofantenatal care, syphilis in the mother will be detected and treated during pregnancy, and congenital syphilis will be rare. Otherwise, stillbirth is a common out-come, although some children with congenital syphilis may develop the stigmata of the disease only in late childhood.

Acquired syphilis. The features of the different stagesare given in Fig. 14.6. After an incubation period (9–90 days), a primary chancre develops at the site of inoculation. Often this is genital, but oral and anal chancres are not uncommon. A typical chancre is an ulcerated, although not painful, button-like lesion of up to 1 cm in diameter accompanied by local lymphadenopathy. Untreated it lasts about 6 weeks and then clears leaving an inconspicuous scar.

The secondary stage may be reached while the chancre is still subsiding. Systemic symptoms and a generalized lymphadenopathy usher in eruptions that at first are macular and inconspicuous, and later papular and more obvious. Lesions are distributed symmetrically and are of a coppery ham colour. Some-times they resemble pityriasis rosea. Classically, there are obvious lesions on the palms and soles. Annular lesions are also not uncommon. Condyloma lata are moist papules in the genital and anal areas. Other signs include a ‘moth-eaten’ alopecia and mucous patches in the mouth.

The skin lesions of late syphilis may be nodules that spread peripherally and clear centrally, leaving a serpiginous outline. Gummas are granulomatous areas; in the skin they quickly break down to leave punched-out ulcers that heal poorly, leaving papery white scars.

Clinical course

Even if left untreated, most of those who contract syphilis have no further problems after the secondary stage has passed. Others develop the cutaneous or systemic manifestations of late syphilis.

Differential diagnosis

The skin changes of syphilis can mimic many oth skin diseases. Always consider the following.

1  Chancre: chancroid (multiple and painful), herpes simplex, anal fissure, cervical erosions.

2 Secondary syphilis:

•               eruptionameasles, rubella, drug eruptions, pity-riasis rosea, lichen planus, psoriasis;

•               condylomasagenital warts, haemorrhoids; 

•               oral lesionsaaphthous ulcers, candidiasis.

3  Late syphilis: bromide and iodide reactions, other granulomas, erythema induratum.

Investigations

The diagnosis of syphilis in its infectious (primary and secondary) stages can be confirmed using dark field microscopy to show up spirochaetes in smears from chancres, oral lesions, or moist areas in a secondary eruption.

Serological tests for syphilis become positive only some 5– 6 weeks after infection (usually a week or two after the appearance of the chancre). The traditional tests [Wasswemann reaction (WR) and Venereal Dis-ease Research Laboratory (VDRL)] have now been replaced by more specific ones [e.g. the rapid plasma reagin (RPR) test and the fluorescent treponemal antibody/absorption (FTA/ABS) test]. These more sensitive tests do not become negative after treatment if an infection has been present for more than a few months.

Treatment

This should follow the current recommendations of the World Health Organization (WHO). Penicillin is still the treatment of choice (e.g. for early syphilis benzathine penicillin 1.2 million units given intramus-cularly into each buttock at a single session, or pro-caine penicillin 600 000 units intramuscularly daily for 12 days), with long-term high-dose oral erythromycin and tetracycline being effective alternatives for those with penicillin allergy. The use of long-acting penicillin injections overcomes the ever-present danger of poor compliance with oral treatment. Every effort must be made to trace and treat infected contacts.

Yaws

Yaws is distributed widely across the poorer parts of the tropics. The spirochaete, Treponema pallidum ssp. pertenue, gains its entry through skin abrasions. After an incubation period of up to 6 months, the primary lesion, a crusting and ulcerated papule known as the ‘mother yaw’, develops at the site of inoculation; later it may enlarge to an exuberant raspberry-like swelling which lasts for several months before healing to leave an atrophic pale scar. In the secondary stage, other lesions may develop in any area but do so especially around the orifices. They are not unlike the primary lesion but are smaller and more numer-ous (‘daughter yaws’). Hyperkeratotic plaques may appear on the palms and soles. The tertiary stage is characterized by ulcerated gummatous skin lesions, hyperkeratosis of the palms and soles, and a painful periostitis that distorts the long bones. Serological tests for syphilis are positive. Treatment is with penicillin.

Lyme disease

The spirochaete Borrelia burgdorferi is responsible for this condition, named after the town in the USA where it was first recognized. It is transmitted to humans by ticks of the genus Ixodes, commonly harboured by deer. The site of the tick bite becomes the centre of a slowly expanding erythematous ring (‘erythema migrans’; Fig. 14.7). Later, many annular non-scaly plaques may develop. In the USA, a few of those affected develop arthritis and heart disease, both of which are less com-mon in European cases. Other internal complications include meningitis and cranial nerve palsies. Treated early, the condition clears well with a 21-day course of oral amoxycillin or doxycycline: patients affected systemically need longer courses of parenteral anti-biotics. Infection can be confirmed by serology, although this is usually negative in the first few weeks after innoculation.