Spirochæta duttoni ingested by Ornithodoros moubata apparently disappear within a few days, but Leishman believed that in reality they break up into minute granules which are to be found in the alimentary canal, the salivary glands and the Malpighian tubes of the tick. These granules, or "coccoid bodies," as Hindle calls them, are supposed to be the form in which the spirochætes infect the new host. We shall see later that Marchoux and Couvy (1913) dissent wholly from this interpretation.
According to Leishman, and Hindle, the coccoid bodies are not injected into the vertebrate host with the saliva of the tick, as are the sporozoites of malaria with that of the mosquito. Instead, they pass out with the excrement and secondarily gain access to the wound inflicted by the tick.
Nuttall (1912) calls attention to the fact that the geographical distribution of Ornithodoros moubata is far wider than our present records show for the distribution of the relapsing fever in man and that there is every reason to fear the extension of the disease. Huts where the ticks occur should be avoided and it should be remembered that in infected localities there is special danger in sleeping on the ground.
European Relapsing Fever—There is widely distributed in Europe a type of relapsing fever which is caused by Spirochæta recurrentis. It has long been supposed that this disease is spread by the bed-bug and there is some experimental evidence to show that it may be conveyed by these insects.
In 1897, Tictin found that he could infect monkeys by inoculating the contents of bed-bugs which had fed upon a patient within forty-eight hours. Nuttall, in 1907, in one experiment succeeded in transmitting Spirochæta recurrentis from mouse to mouse by bites of bed-bugs. The bugs, thirty-five in number, were transferred at short intervals from one mouse to another, not being allowed to take a full meal on the first, or infected mouse.
On the other hand, there is much clinical evidence to show that the European relapsing fever like various other types of the disease is transmitted from man to man by head and body lice (Pediculus humanus and Pediculus corporis).
Interesting supplementary evidence is that of Bayon's observations (1912), in Moscow. "Having visited the big municipal night hospitals at Moscow I soon noticed that they were kept with such scrupulous cleanliness, disinfected so lavishly, the beds of iron, the floor cemented, that it was not possible for bed-bugs to thrive to any extent on the premises. The people sleeping there were allowed, however, to sleep in their own clothes. The introduction of these model homes had not had any effect on the incidence of relapsing fever, for the places were still hot-beds of the fever during winter. On the other hand, though I changed my rooms several times, I found bugs in every successive lodging, and I was told in Moscow, this can hardly be avoided. Yet no foreigner, or Russian of the better class, ever catches relapsing fever. To this may be added the fact that when I asked for clothes-lice and promised to pay a kopec for two, the attendants from the night hostel brought me next morning a small ounce bottle crammed with Pediculus capitis (= P. humanus), and Pediculus vestimentorum (= P. corporis) collected off the sleepers. If relapsing fever were transmitted by bed-bugs, it would be much more disseminated than it is at present in Moscow."
Direct experimental evidence of the agency of lice in transmitting relapsing fever is especially clear in the case of a type of the disease prevalent in parts of North Africa. We shall consider this evidence later.
Other Types of Relapsing Fever of Man—In addition to the three types of human relapsing fever already referred to, several others have been distinguished and have been attributed to distinct species of spirochætes. The various spirochætoses of man are:
African, caused by S. duttoni; European, caused by S. recurrentis; North African, caused by S. berbera; East African, caused by S. rossi; East Indian, caused by S. carteri; North American, caused by S. novyi; South American, caused by S. duttoni (?).