Crithidia is the generic name of vermiform flagellates with a central nucleus, a blepharoplast or kinetic nucleus in the neighbourhood of the principal nucleus, and a rudimentary undulating membrane bordered by a flagellum arising from a basal granule, which is the centrosome of the kinetic nucleus (fig. [49]b). The anterior or flagellar end of the body is attenuated and fades off as the undulating membrane.
Crithidia fasciculata, the type species, was found by Léger in the alimentary canal of Anopheles maculipennis. Crithidia occur in bugs, flies, fleas,[122] and ticks. Some of them are found in the body-fluid of the invertebrate host as well as in the gut. Others may be restricted to the body cavity or intestine respectively. C. melophagia from the sheep-ked, Melophagus ovinus, and C. hyalommæ from the hæmocœlic fluid of the tick, Hyalomma ægyptium, pass into the ovaries and eggs of their hosts, and the young keds or ticks are born infected.
C. fasciculata has been shown by Laveran and Franchini to be inoculable into white mice, producing a sort of experimental leishmaniasis therein. In one case cutaneous lesions were produced like those of Oriental sore.
Crithidia are natural flagellates of Arthropoda, with their own pre-flagellate, flagellate and post-flagellate stages, and must not be confused with transitory crithidial stages of trypanosomes.
Genus. Leishmania, Ross, 1903.
With an oval body containing nucleus and blepharoplast (kinetic nucleus) but no flagellum. An intracellular parasite in the vertebrate host.
Included in the genus Leishmania are three species, namely:—
(1) Leishmania donovani, Laveran and Mesnil, 1903, the parasite of Indian kala-azar, a generalized systemic disease, usually fatal, occurring in subjects of all ages.
(2) Leishmania tropica, Wright, 1903, the parasite of Delhi boil, Oriental sore, Aleppo button—a localized, cutaneous disease, usually benign.