Leishmaniases: the Diseases


Leishmaniasis is prevalent in all tropical and substropical zones of the world. The parasites invade the cells of the reticuloendothelial system, such as macrophages, bone marrow cells, speen cells and the kupfer cells of the liver. Tropism of the parasites is thought to be dependent, in part, on the optimal temperature of growth of the amasigotes, where Leishmania parasites with a preference for a temperature around 35° C cause cutaneous or mucocutaneous manifestations, while parasites that grow best at 37° C cause the visceral manifestation of the disease.

There are some 20 different species of Leishmania 12 of which cause leishmaniasis. In total 350 million people are at risk and 12 million people are infected. In the Old World (North and East Africa, India, China) there is visceral leishmaniasis or "kala azar", while in the Middle East there is maily cutaneous leishmaniasis or "oriental sore". 1.5 Million new cases are reported every year, 500.000 of which are visceral leishmaniasis.


Visceral leishmaniasis, Kala Azar, or dum dum disease
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Case of visceral leishmaniasis

Visceral leishmaniasis or Kala azar has many features in common with chronic malaria. In the early days it was also called dum-dum fever, after a military station in the outskirts of Calcutta where the disease was prevalent. Kala azar or dum dum fever is characterized by a low degree of fever with hepatoplenomegaly and severe progressive cachexia (wasting), swollen lymph glands, leucopeania, thrombocytopaenia with relative monocytosis and loss of hair. The british army physician Leishman was the first to discover distinctive structures in smears from greatly enlarged spleen despite antimalarial treatment. The parasites (Leishmania donovani ) are maily found in bone marrow, liver and spleen. If left untreated this manifestation of leishmaniasis is fatal in more than 90 % of cases. Recovery, whether natural ,or by treatment with pentavalent antimonials, may be complete and lead to rapid regression of the symptoms. However in many cases the parasites are not completely eliminated, and may recrudesce in the skin where they give rise to post-kala-azar dermal leishmaniasis (PKDL).

Post-kala-azar dermal leishmaniasis (PKDL).

The dog is important in the epidemiology of mediterranian visceral leishmaniasis. Although human and canine disease may have different incidenses in different areas, the human and canine parasites are identical.
Dog infected with leishmaniasis

There have been frequent outbreaks of kala azar in India where a recent epidemic made 250000 victims. The recent civil war in the Soudan with people leaving their homes resulted in some 80.000 cases.

In the mediterranian area leishmaniasis mainly occurs in young children as a visceral form caused by Leishmania donovani infantum.


Cutaneous leishmaniasis or "oriental sore"
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The cutaneous manifestation of leishmaniasis is found mainly in North Africa, and in the Middle East and Central Asia, where it is caused by L. tropica and L. major. In the New World cutaneous leishmaniasis is caused by L. mexicana. At the location of the bite of the sandfly a papule develops which enlarges and then starts to necrotize centrally. The ulceration which may be acute leading to a moist ulcer, or or slow in the case of a typical dry lesion is invaded with macrophages that serve as the host cells for the parasite and that permit the amastigotes to multiply. The ulceration may last for many months before healing occurs. Eventually granulomatous swelling subsides, and the ulceration heals, generally leaving a large scar and major mutilation, regarded as characteristic in highly endemic areas. The lesion is painless and secondary infection is restricted to the dead tissue. In the case of the Old World disease, when cure has occured a solid immunity has been acquired against reinfection by the same parasite.

Cases of 'oriental sore'

 


Mucocutaneous leishmaniasis or "espundia"
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Case of 'espundia' of an indian of the AndesCase of 'Espundia'

L. b.braziliensis causes in man a slow healing often very extensive oriental sore which self-cures after a variable sometimes extended time. Following the cure of the initial lesion the infection may metastasize, reappearing on the mucosal surfaces of the oronasal region, causing the disfiguring and eventually often fatal disease of espundia. The mucocutaneous lesions do not self heal but continue to invade the tissues which become blocked with granulomatous infiltration, eventually necrotizing and eroding insidiously. an early manifestation is often the end of the nose, which becompes expanded, so producing the syndrome of 'tapir nose'. Death frequently results as an indirect consequence, due to bacterial super-infection or obstruction of airways or the food passage.

Typical ulceration of the tongue


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Last updated: 22 October 1997.

created by :Fred Opperdoes