Fig. 54.—Spirochæta duttoni. a, blood form showing slight membrane; b, granules or coccoid bodies clearly formed within the organism; c, beginning of extrusion of coccoid bodies in the tick. (After Fantham.)
The granule phase, however, is an essential one in the invertebrate transmitter (fig. 54c). In 1905,[146] Dutton and Todd proved experimentally that O. moubata transmitted S. duttoni. They fed ticks, obtained from Congo native huts in which infected persons lived, on monkeys and the latter became infected. Dutton and Todd also found the offspring of infected ticks to be capable of transmitting the infection to experimental animals. They concluded that O. moubata was a true intermediate host.
A little later in 1905, Koch stated that spirochætes from the gut of the tick penetrated the gut wall and tissues and found their way into the eggs in the ovary. Koch figured tangled masses of spirochætes as occurring in the tick eggs. He found ticks infective to the third generation. He thought that the infection was spread by the salivary fluid of the tick, in the act of biting. (This is now known to be incorrect.) Markham Carter (1907) corroborated Koch’s work on the spirochætes in the tick eggs, and they have been seen since by Kleine and Eckard (1913).
Sir William Leishman,[147] in 1909–10, found that at ordinary temperatures the salivary glands of infected ticks (O. moubata) were not themselves infective, and that the infection occurred by way of the ticks’ excretion. The spirochætes (contained in the ticks’ excrement) found their way into the vertebrate host through the wound made by biting. While feeding, ticks pass large quantities of clear fluid from the coxal glands; in this fluid an anticoagulin occurs. Some of the ticks also pass thick, white Malpighian secretion, that is, excrement, towards the end of the feed. Leishman, using experimental monkeys, showed that if infected ticks were interrupted while feeding, then no infection resulted in the monkeys. If, however, the ticks were allowed to finish their feed, and the Malpighian secretions were passed, then the experimental monkeys became infected. Fantham[148] and Hindle[149] (1911), independently, have repeated the experiments with mice.
Leishman’s methods and results may be summarized thus: Saline emulsions of the organs of infected ticks were made, after the organs had been most carefully dissected out. The ticks were first kept for several days at certain constant temperatures, such as 24° to 25° C. or blood heat, 37° C. The saline emulsions of the organs were inoculated, separately, into experimental animals, and the results recorded:—
| At 24° C. | At 37° C. | |
| Salivary glands | Negative | Positive |
| Malpighian tubules | Positive | Positive |
| Gut and contents | Positive | Positive |
| Excrement | Positive | Positive |
| Genital organs | Positive | Positive |
Coxal fluid is usually negative; thick, white excrement from Malpighian tubes is positive.
When the ticks were incubated at 21° to 24° C. no spirochætes, as such, were seen in the organs, except perhaps in the gut, where they often disappeared in a few days. When the ticks were previously incubated at 35° to 37° C. for two to three days, spirochætes, as such, reappear in the gut, organs and hæmocœlic fluid. The infection proceeds, not from the salivary gland, but from the infective excrement, that is, from the thick, white material voided by the tick while feeding, usually towards the end of the meal. This Malpighian excrement passes into the wound caused by the bite, being greatly aided by the clear and more limpid coxa fluid, which bathes the under surface of the tick’s body, and mixes with and carries the infective excrement into the wound. Ticks remain infective for a long time.