Leishmania tropica

Synonyms: Helcosoma tropicum, Sporozoa furunculosa, Ovoplasma orientale, Plasmosoma jerichaense, Leishmania wrighti, L. cunninghami, L. nilotica, L. recicliva, L. brasiliensis, L. peruviana.

Disease: Cutaneous leishmaniosis, mucocutaneous leishmaniosis, Oriental sore, Aleppo button, Jericho boil, Delhi boil, espundia, uta, chiclero ulcer, buba, pian bois, American forest leishmaniosis.

Hosts: The usual hosts are man, the dog and, in parts of the Old World, gerbils (Rhombomys opimus) and other wild rodents.

Location: L. tropica occurs in the monocytes and other cells of the reticuloendothelial system, in cutaneous lesions and in the skin. It may also occur in the lymph nodes and in the mucous membranes.

Types of Disease, Geographic Distribution and Epidemiology:

Two forms of cutaneous leishmaniosis have been described in man in the Old World and 4 in the New. Separate subspecific names have been given to some of them:

1. Classical Oriental sore is found in regions with a hot, dry climate from the Mediterranean basin to central and northern India. It is caused by L. tropica minor. The incubation period is several months. The lesions are circumscribed, "dry" sores in the skin. They heal spontaneously and do not extend to the mucous membranes. The lymph nodes are involved in about 10% of the cases. Dogs are commonly infected, and the disease is urban in distribution. In Teheran, Iran, for example, 40 to 50% of the dogs have skin ulcers. The disease is transmitted by Phlebotomus papatasii, P. sergenti, P. perfiliewi and P. longicuspis.

2. "Moist" or "wet" Oriental sore is found in Central Asia and southern USSR. It is caused by L. tropica major; there is no cross-immunity between this subspecies and L. t. minor. The incubation period is 1 to 6 weeks. The lesions are wet and ulcerative, but do not extend to the mucous membranes. They heal spontaneously. The lymph nodes are often involved. The disease is rural in distribution. The reservoir hosts are various desert rodents, the gerbil (Rhombomys opimus) being the most important. The vector is P. caucasicus, which lives in the gerbil burrows.

3. Mucocutaneous leishmaniosis or espundia is found in the Brazilian rain forests. It is caused by L. tropica brasiliensis, which many authors consider a separate species, L. brasiliensis. The skin lesions are chronic and spreading, often invading the mucous membranes either by metastasis or extension, and sometimes causing great disfigurement. Spontaneous recovery is rare. The lymph nodes are seldom involved. Dogs and occasionally cats have been found naturally infected, but the true reservoir hosts have not been discovered; they are probably wild jungle mammals. The retus monkey and various squirrels can be readily infected, but the golden hamster is refractory. The vectors are Phlebotomus intermedius (syn., Pllutzi), and also probably P. migonei, P. whitmani and P. pessoai.

4. Uta occurs in the mountains of Peru. It is a benign form of the disease, with numerous small skin lesions. Its reservoir hosts and vectors are apparently unknown.

5. American forest leishmaniosis, pian bois or buba is found in Panama, Costa Rica, the Guianas and other parts of northern South America. It is caused by L. tropica guianensis. The skin lesions are moderately ulcerated, and ordinarily heal spontaneously unless they involve the nose. About 5% of the patients have lesions of the mucous membranes which have arisen by extension rather than by metastasis. The lymph nodes are involved in about 10%. Dogs may be naturally infected, but the wild reservoirs are unknown. The vectors in Venezuela are believed to be Phlebotomus evansi, P. migonei, P. parasinensis and P. suis.

6. Chiclero ulcer or bay sore is found in Guatemala, southeastern Mexico and British Honduras. It gets its name because it is common among chicle and rubber hunters in rain forests. It is caused by L. tropica mexicana. The skin lesions are small. They heal spontaneously in a few weeks to a few months unless they involve the ear. In this location they cause chronic, disfiguring nodular ulcers which may persist many years. There is no metastasis to the mucous membranes, and cutaneous metastases are rare. The lymph nodes are involved in about 2%. Nothing is known of the wild reservoirs or of the vectors, altho the disease is clearly a zoonosis (Garnham and Lewis, 1959).

Both the Old World types of cutaneous leishmaniosis are zoonoses, but their epidemiology is quite different. The dry type is an urban disease common to dogs and man, while the moist type is a rural disease of gerbils and other rodents which affects man more or less incidentally. The American forms, too, occur primarily in wild animals, mostly unknown, of the tropical rain forests; both man and dogs are secondary hosts.

Pathogenesis: The ulcers or sores of classical, dry Oriental sore are found on exposed parts of the body in man. At first they resemble mosquito bites, but they do not go away. The lesion grows slowly, becoming covered with thick brown scales. It itches a great deal, and scratching produces a small ulcer which is covered with a crust. This enlarges slowly, and may finally be several centimeters in diameter. After some months or a year, connective tissue is formed, but a permanent scar is left. The disease is very seldom fatal.

In the central Asian form of the disease, the lesions are moist. They develop more rapidly, becoming ulcerative in one or two weeks, and then heal spontaneously. Relatively few parasites can be found in them.

In espundia, the ulcers are often worse than those of Oriental sore and may last much longer. They usually heal in 7 to 8 months, but sometimes last more than 20 years. In addition, in some cases they may extend to the mucosa of the mouth or nose either directly or by metastasis. When they do this, they may cause a great deal of disfigurement; in extreme cases the nose may even be completely eaten away.

The lesions in the dog are similar to those in man. They are probably confined to the skin. Visceral leishmaniosis due to L. tropica has been reported in dogs, but many observers believe that these are due to concurrent infections with L. donovani. In infected gerbils, cutaneous sores occur on the ears.

Immunity: Persons who have recovered spontaneously from classical Oriental sore have a solid immunity. This fact is so well known among the natives that they vaccinate themselves on the arm in order to avoid natural, disfiguring ulcers on the face. There is no cross-immunity between the wet and dry Old World types of the disease, between these and the New World forms, or between L. tropica and L. donovani infections.

Diagnosis: The same methods are used in diagnosing L. tropica as L. donovani infections, except for the tissues examined. The parasites are usually abundant in dry Oriental sore, but are scanty in wet Oriental sore and New World mucocutaneous leishmaniosis. A skin test, the Montenegro intradermal reaction, is used with considerable success in diagnosing American mucocutaneous leishmaniosis. A suspension of killed organisms from NNN culture is injected intradermally. In positive cases, an erythematous wheal appears in 48 hours and lasts 4 or 5 days. A small sterile papule which becomes vesicular or pustular develops in the center of the wheal.

Treatment: Organic antimony compounds are effective against cutaneous leishmaniosis. The same ones are used as for kala-azar.

Control: The same measures used to prevent kala-azar are effective against cutaneous leishmaniosis.