The Blood Flagellates 575 



or races of a single species (31). On the other hand, the specific status 

 of the three types has been defended on the grounds that the clinical, 

 pathological and epidemiological differences seem to be genetically stable 



(34a). 



Visceral leishmaniasis 



Distribution. In the Eastern Hemisphere, kala-azar has occurred en- 

 demically in certain parts of India, southern U.S.S.R., Burma, Indo- 

 China, Central China, Turkestan, Iraq, along the Mediterranean shores, 

 and in the Sudan. Cases have occurred also in the Western Hemisphere 

 — various parts of Brazil (55), Argentina, Bolivia, Colombia, Paraguay, 

 Peru, and Venezuela. In American areas, visceral leishmaniasis has been 

 reported in both infants and adults. Both young and old are susceptible 

 in India also, while in the Mediterranean area, children under four years 

 have been attacked almost exclusively. 



The causative organism. Kala-azar was at various times considered an 

 unusual malaria and a serious type of hookworm disease before the cau- 

 sative organism was discovered. L. donovani seems to have been observed 

 by Cunningham in 1885, by Firth in 1891, and by Borowsky in 1892. 

 Although Borowsky recognized the organisms as Protozoa (30a, 54), his ob- 

 servations remained unknown to Leishman and Donovan who described 

 the parasites independently in 1903. After various assignments to the 

 Sporozoa, the affinities of L. donovani were demonstrated when Rogers 

 (56a) found the flagellate stage in cultures. 



L. donovani occurs in the mammalian host primarily as leishmanial 

 stages in lymphoid-macrophage (reticulo-endothelial) cells of the spleen, 

 liver, bone marrow, intestine, and lymph glands. Occasionally, leish- 

 manial forms occur also in mononuclear and polymorphonuclear leuco- 

 cytes in the blood. The leishmanial stage may be ovoid or approximately 

 spherical (Fig. 12. 1, I, J). The spherical forms are usually 1-3[jl in diam- 

 eter. Ovoid stages generally measure 2.0-5.0 x 1.5-2.5[a. Identification is 

 based upon the presence of both nucleus and kinetoplast. The latter is 

 often elongated and may be more or less perpendicular or sometimes 

 tangential to the nucleus. In well-stained specimens, an axoneme some- 

 times can be traced from the kinetoplast to the periplast. 



Leishmanial stages multiply in the macrophages, which eventually rup- 

 ture to release the parasites. Most of them apparently are picked up by 

 macrophages, but some reach the blood stream from which they can be 

 ingested by the vector, a species of Phlebotomus. Surviving leishmanial 

 forms change into leptomonad stages in the insect. These multiply in the 

 midgut, and after several days, appear also in the foregut. The lepto- 

 monads of the foregut are believed to be infective for man. 



The growth of L. dojiovani in cultures is similar to that in the sandfly. 

 After inoculation into a suitable medium the leishmanial stage grows, 



