Other mycobacterial infections
Mycobacteria are widespread in nature, living as environmental saprophytes. Some can infect humans.
Mycobacterium marinum lives in water. Human infec-tions have occurred in epidemics centred on infected swimming pools. Another route of infection is through minor skin breaches in those who clean out tropical fish tanks (Fig. 14.14). After a 3-week incubation period, an indolent abscess or ulcerated nodule forms at the site of inoculation; later nodules may develop along the draining lymphatics (sporotrichoid spread; Fig. 14.15). The lesions heal spontan-eously, but slowly. Resolution may be speeded by an 8-week course of trimethoprim/sulfamethoxazole or minocycline. Should these fail, rifampicin in combination with ethambutol is worth a trial.
Infections are confined to certain humid tropical areas where the organism lives on the vegetation, and are most common in Uganda (Buruli ulcers). The necrotic spreading ulcers, with their undermined edges, are usually found on the legs. Drug therapy is often dis-appointing and the treatment of choice is probably the surgical removal of infected tissue.
Leishmania organisms are protozoa whose life cycle includes stages in phlebotomus flies, from which they are transmitted to humans. Different species, in differ-ent geographical areas, cause different clinical pictures.
• Leishmania tropica is found around the Mediter-ranean coast and in southern Asia; it causes chronically discharging skin nodules (oriental sores; Fig. 14.16).
• Leishmania donovani causes kala-azar, a dis-ease characterized by fever, hepatosplenomegaly and anaemia. The skin may show an irregular darkening, particularly on the face and hands.
• Leishmania mexicana and braziliensis are foundin South and Central America. They also cause deep sores, but up to 40% of those infected with L. braziliensis develop ‘episodic’, destructive metastaticlesions in the mucosa of the nose or month.
This is confirmed by:
• histologyaamastigote parasites, granulomatous reaction;
touch smearaamastigote parasites;
• culture; and
• polymerase chain reaction tests.
Single nodules often resolve spontaneously and may not need treatment. Destructive measures, including cryotherapy, are sometimes used for localized skin lesions. Oral zinc sulphate (5 mg/kg/day for 4 weeks) showed promising results in a recent Indian trial.
Intralesional or intravenous antimony compounds are still the treatment of choice for most types of leish-maniasis, e.g. sodium stibogluconate (20 mg/kg/day for 20 days) with regular blood tests and electrocar-diographic monitoring.