Hemoflage Mates 
The life history patterns of the hemoflagellates, like that of 
malaria, involve an arthropod vector which is chiefly responsible for 
the transmission and spread of the infection. The vectors for the 
hemoflagellates are various species of flies, and the specificity of 
the vector usually limits the geographical distribution of the parasite. 
Unlike most of the other blood parasites, the hemoflagellates do 
not possess sexual forms and multiplication occurs entirely through 
binary fision in one or more of the morphological stages. Species of 
two genera, Trypanosoma and Leishmania parasitize man. Four mor- 
phological stages are described: leishmania, leptomonas, crithidia, 
and trypanosome. Of the four, the leishmania are the only non- 
flagellated forms and both crithidial and trypanosomal stages pos- 
sess an undulating membrane in addition to the flagellum. Except 
for Trypanosoma cruzi , no more than two of the four stages are 
associated with each genus of organisms. 
Leishmania 
In the human host, Leishmania spp. exist only in the leishmania 
form and are intracellular parasites of reticulo-endothelial cells: 
L. donovani predominantly in bone marrow and internal organs such 
as spleen and liver, L. tropica in skin and subcutaneous tissue, and 
L. hrasiliensis in cutaneous and mucocutaneous tissues. Three 
other species of Leishmania , L. peruana, L. guyanensis, and L. 
mexicana, have been involved in cutaneous leishmaniasis in Peru, 
in Panama, and in Mexico, Guatemala, and British Honduras, respec- 
tively. The cycles of all species are similar. 
In the arthropod vectors, which are certain species of Phlebotomus 
(sand-flies), the leishmania stages taken up during the insect bite 
transform into the leptomonas forms. These leptomonads divide in the 
midgut and in 3 to 5 days move to the proboscis of the sand-fly. When 
the insect feeds again, the leptomonads (infective forms) are injected 
into the vertebrate host where they again become leishmania within 
reticulo-endothelial cells. 
Several species of Phlebotomus have been incriminated as vectors 
of leishmania, among them P . argentipes and P . chinensis for L. 
donovani , P. intermedins for L. hrasiliensis , and P. papatasii and 
P. sergenti for L. tropica . 
Dogs, rodents, and possibly other mammals may serve as reser- 
voir hosts. 
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