The distribution of the parasites in the body of the human patient is much the same as in the case of Indian kala-azar. Critien records the finding of parasites in the mucous flakes of the stools of a three-year-old Maltese child.[135] Intestinal lesions rarely occur in infantile leishmaniasis.
Ætiology.—Infantile leishmaniasis is stated to be transmitted by fleas, especially dog fleas, Ctenocephalus canis (= Pulex serraticeps), and by Pulex irritans. Children living in contact with infected dogs may be bitten by infected dog fleas, and so contract the disease. Basile (1910–11) and Sangiorgi (1910) state that they found L. infantum parasites in the digestive tract of the dog flea. After searching they found infected dog fleas on the beds, mattresses, and pillows used by children suffering from the disease. Franchini (1912) thinks that Anopheles maculipennis may be concerned in the transmission.
Basile[136] tried a number of experiments to show that infantile leishmaniasis is transmitted by fleas, thus:—
(1) Fleas were taken from a healthy dog. They were placed in vessels containing infected spleen-pulp and allowed to feed thereon. The fleas were then killed and dissected, and portions of the gut-contents examined for parasites. The remainder of the gut was emulsified and injected into a young puppy, whose bone-marrow had been shown previously to be uninfected. Basile states that the puppy became infected. The parasites are said to increase in number in the flea’s gut.
(2) Two healthy pups, each a month old, and born in the laboratory, were placed in a disinfected, flea-proof cage. A few days after, an infected dog was placed in the cage, so that fleas from the infected dog could pass on to the puppies. A month later the two pups became infected, parasites being found in them after liver puncture. A number of control puppies from the same litter remained uninfected and in good health.
(3) Basile next used other laboratory-born puppies, a month old. Four of the litter were placed in a disinfected, flea-proof gauze cage in Rome. The cage was isolated from other dogs. Fleas obtained from an infected area in Sicily were placed in the cage. The puppies were examined by hepatic puncture, but were found to be negative for two months. Then two of the puppies showed infection, and six days later the remaining two puppies were found to be infected, and all four died. They showed irregular temperatures, and were getting thin. Control puppies remained healthy.
From these experiments Basile concludes that fleas transmit leishmaniasis. However, Basile did not exclude the possible occurrence of natural herpetomonads in the gut of the fleas.[137] Herpetomonas ctenocephali is known to occur in the gut of Ctenocephalus canis. A natural Herpetomonas is also known in the gut of Pulex irritans, as well as a Crithidia (C. pulicis, Porter). These natural flagellates of the fleas pass through non-flagellate stages, like the Leishman-Donovan body. In consequence Wenyon and Patton, among others, have criticized Basile’s results. Further, other investigators, such as Wenyon and Da Silva (1913), have repeated Basile’s flea experiments and been unable to confirm them.
In feeding and inoculation experiments the incubation period of the parasite may be long, and so it is necessary to wait a long time to see whether the parasite will develop.
Immunity.—Nicolle has tried some experiments with L. infantum and L. tropica. He finds that in animals recovery from an attack of the former confers immunity against infection by the latter and vice-versâ.
Laveran[138] records that a monkey having an immunity against L. infantum was also immune to L. donovani.