Kala-azar is also known as Visceral leishmaniasis.It is a disease produced by a protozoan organism, Leishmania donovani. It is characterized by irregular fever of long duration, chronicity, enlargement of the spleen and often of the liver, emaciation, anemia, leukopenia, and hyperglobulinemia.
Leishmania donovani, the causal organism of visceral leishmaniasis, is a protozoan parasite belonging to a group known as hemoflagellates, which inhabit the blood or other tissues of vertebrates. Two forms of Leishmania donovani are present in its life cycle, the Leishmania form —a stage lacking a flagellum —which occurs in man or other mammalian hosts, and a leptomonad or flagellate form, which develops in the sandfly intermediate host and in artificial culture media.
The Leishmania forms, commonly referred to as Leishman-Donovan bodies, are small ovoid or round unicellular organisms measuring 2 to 4 p in diameter that occur in reticuloendothelial cells and macrophages and are abundant in certain tissues, being present also in small numbers in peripherally circulating monocytes. With Giemsa or Wright’s stain, the cytoplasm appears pale blue and the nucleus and kinetoplast red or reddish purple.
The leptomonad forms result from a transformation that the Leishmania forms undergo in the digestive tract of sandfly vectors after they have fed on an infected vertebrate host or in cultures when inoculated on suitable media. The leptomonad forms are spindle-shaped bodies 14 to 20 ix long by 1.5 to 3.5 ju, broad, with a more or less centrally placed nucleus. The kinetoplast is at the anterior end and from it springs a flagellum. In cultures, the leptomonas frequently tend to agglomerate in rosette groups with their entangled flagella directed inward. The leptomonas are presumed to gain access to man when the flies subsequently feed. Inside the body they undergo transformation and multiply as intracellular Leishmania forms.
Epidemiology of Visceral leishmaniasis .
So far as is known, there is no natural immunity to kala-azar. Although the disease is uncommon in persons of Caucasian origin in India and mainland China, the low incidence is due apparently to infrequent exposure to the disease. Kala-azar is often sporadic in its occurrence, but it may appear in epidemic form. The disease is particularly common in villages, although it also occurs in cities. In India and mainland China there are particular villages and even individual houses that are known to be foci of kala-azar.
Those infected belong predominantly to the lower socioeconomic groups of the population. Statistics show a higher incidence in males, but it is doubtful that the data are reliable, as far more males than females attend hospitals in the Orient. Kala-azar is predominantly a disease of childhood and youth, but it is also common in the third decade of life and may occur at any age. In the Mediterranean area the incidence in infants is said to be relatively higher than it is in other areas. Many animals, including especially the hamster, are susceptible to artificial infection, but the only animal found to be infected in nature is the dog.
Kala-azar is widespread, but the areas in which its existence is well known are discontinuous, and the importance of the disease varies greatly incidence is especially high in parts of China north of the Yangtse River and in parts of eastern India, particularly in Bihar, Bengal, and Assam. The disease is endemic in the region about Tashkent in southern Asiatic Russia, and occurs in Mesopotamia, Saudi Arabia, and Turkey.
It is present in areas scattered all around the Mediterranean Sea and in a belt across Africa from Kenya through Ethiopia and equatorial Africa to Nigeria. Cases have been reported from Argentina, Paraguay. Bolivia, Brazil, Venezuela, and Colombia, but so far the disease does not seem to be very important on the South American continent. Autochthonous cases have not been found in the United States, but many imported cases have been reported, especially in soldiers previously stationed in endemic areas.
Sandflies of the genus Phlebotomus have been shown to be important vectors, of kala-azar in India and mainland China. Since various species of Phlebotomus exist wherever the disease occurs, these insects may be vectors in other areas. In mainland China and elsewhere a natural reservoir host for Leishmania has been found in dogs, in addition to that in infected human beings. Visceral leishmaniasis has been found in a dog imported into the United States from Greece.