Handbook of Medical Entomology

by William A. Riley; O. A. Johannsen

Nuttall (1912) in his valuable résumé of the subject, has emphasized that "in view of the morphological similarity of the supposedly different species of spirochætes and their individual variations in virulence, we may well doubt if any of the 'species' are valid. As I pointed out four years ago, the various specific names given to the spirochætes causing relapsing fever in man may be used merely for convenience to distinguish strains or races of different origin. They cannot be regarded as valid names, in the sense of scientific nomenclature, for virulence and immunity reactions are not adequate tests of specificity."

North African Relapsing Fever of Man—The type of human relapsing fever to be met with in Algeria, Tunis, and Tripoli, is due to a Spirochæta to which does not differ morphologically from Spirochæta duttoni, but which has been separated on biological grounds as Spirochæta berberi.

Experimenting with this type of disease in Algeria, Sergent and Foly (1910), twice succeeded in transmitting it from man to monkeys by inoculation of crushed body lice and in two cases obtained infection of human subjects who had received infected lice under their clothing and who slept under coverings harboring many of the lice which had fed upon a patient. Their results were negative with Argas persicus, Cimex lectularius, Musca domestica, Hæmatopinus spinulosus and Ceratophyllus fasciatus. They found body lice associated with every case of relapsing fever which they found in Algeria.

Nicolle, Blaizot, and Conseil (1912) showed that the louse did not transmit the parasite by its bite. Two or three hours after it has fed on a patient, the spirochætes begin to break up and finally they disappear, so that after a day, repeated examinations fail to reveal them. They persist, nevertheless, in some unknown form, for if the observations are continued they reappear in eight to twelve days. These new forms are virulent, for a monkey was infected by inoculating a single crushed louse which had fed on infected blood fifteen days before.

Natural infection is indirect. Those attacked by the insect scratch, and in this act they excoriate the skin, crush the lice and contaminate their fingers. The least abrasion of the skin serves for the entrance of the spirochætes. Even the contact of the soiled fingers on the various mucosa, such as the conjunctive of the eye, is sufficient.

As in the case of Spirochæta duttoni, the organism is transmitted hereditarily in the arthropod vector. The progeny of lice which have fed on infected blood may themselves be infective.

Spirochætosis of Fowls—One of the best known of the spirochætes transmitted by arthropods is Spirochæta gallinarum, the cause of a very fatal disease of domestic fowls in widely separated regions of the world. According to Nuttall, it occurs in Southeastern Europe, Asia, Africa, South America and Australia.

In 1903, Marchoux and Salimbeni, working in Brazil, made the first detailed study of the disease, and showed that the causative organism is transmitted from fowl to fowl by the tick Argas persicus. They found that the ticks remained infective for at least five months. Specimens which had fed upon diseased birds in Brazil were sent to Nuttall and he promptly confirmed the experiments. Since that date many investigators, notably Balfour and Hindle, have contributed to the elucidating of the life-cycle of the parasite. Since it has been worked out more fully than has that of any of the human spirochætes, we present Hindle's diagram ([fig. 143]) and quote the brief summary from his preliminary paper (1911b).

"Commencing with the ordinary parasite in the blood of the fowl, the spirochæte grows until it reaches a certain length (16-19µ) and then divides by transverse division. This process is repeated, and is probably the only method of multiplication of the parasite within the blood. When the spirochætes disappear from the circulation, some of them break up into the coccoid bodies which, however, do not usually develop in the fowl. When the spirochætes are ingested by Argas persicus, some of them pass through the gut wall into the cœlomic fluid. From this medium they bore their way into the cells of the various organs of the tick and there break up into a number of coccoid bodies. These intracellular forms multiply by ordinary fission in the cells of the Malpighian tubules and gonads. Some of the coccoid bodies are formed in the lumen of the gut and Malpighian tubules. The result is that some of the coccoid bodies may be present in the Malpighian secretion and excrement of an infected tick and when mixed with the coxal fluid may gain entry into another fowl by the open wound caused by the tick's bite. They then elongate and redevelop into ordinary spirochætes in the blood of the fowl, and the cycle may be repeated."