Page:Tropical Diseases.djvu/244

208 villages for fear of infection; other villagers deserted their homes and even migrated to a different district.

Although the foregoing is the only recorded example of kala-azar as a widespread and active epidemic, it had been recognized that a disease clinically identical occurred sporadically in several places in India and elsewhere. These cases had often been regarded as a form of malarial cachexia, but the identity of the sporadic and epidemic disease has now been established by the detection of the Leishman or Leishman-Donovan body in both.

In 1904 leishmania were discovered in Tunis by Cathoire, and important studies by the Sergents, Nicolle, and many others have shown that the parasite occurs in many of the islands and countries in the Mediterranean basin; that there it is practically confined to young children—infantile kala-azar—

Fig. 56.—Kala-azar parasites from the spleen, stained.

Leishmania infantum; and, further, that whilst in India dogs are hardly ever affected, in the Mediterranean basin a large proportion of these animals are naturally the subjects of leishmaniasis.

Etiology.—The kala-azar parasite (Plate V.) has now been relegated to the genus Leishmania, Ross. We know two stages of this body, intracorporeal and extracorporeal. Possibly these represent respectively asexual and sexual forms; the former found in man and in some other vertebrates, the latter obtained in artificial culture media, and, it may be, in certain insects—flies, bugs, fleas, lice, mosquitoes.

The distribution of the parasite within the body of man is very general. Apparently its special habitat is the endothelial cells of blood-vessels and lymphatics. It is particularly abundant in the spleen (Fig. 56), in the liver, and in the bone marrow; but it also occurs in the lung, in the kidney, in the mesenteric and