Growth of Louse-Borne Relapsing Fever Spirochetes in Chick Embryo

It is well known that important biological differences exist between the tick-borne and louse-borne relapsing fever spirochetes. With the former, infection can readily be produced in a large variety of laboratory animals which together with the tick, serve as means of keeping the strain in the laboratory. On the other hand, few animals were found to be susceptible to the louse-borne type, and the lice cannot be used to maintain the spirochetes. Although Meleney 1 was able to produce infection and relapses in squirrels and chipmunks with a Chinese louse-borne strain of relapsing fever spirochetes, splenectomy of these animals has to be resorted to in order to assure complete success. It is, therefore, of more than academic interest to determine if the louse-borne strains can also be grown and passed in the embryonic chick as is possible for the tick-borne spirochetes, 2 , 3 , 4 and the preliminary results are herewith communicated.

Blood samples were obtained from 7 patients with louse-borne relapsing fever 5 , 6 , 7 during the febrile stage. Blood was either defibrinated or mixed with sodium citrate, and some samples have been kept in the refrigerator for 2 days before inoculation. Inoculation is made at the pointed end of the egg where a hole in the outer shell was made by a dental drill and sterilized with alcohol followed by flaming. The needle was inserted horizontally either deep into the yolk sac or about 1 cm beneath the chorio-allantoid membrane. About 0.2 cc of infective blood was used for the inoculum. Hard paraffin was used for the sealing. A series of fertilized eggs of from 5–12 days old was inoculated with each sample of blood and examinations were made daily from the second day onward for spirochetes in blood, amniotic fluid, yolk and emulsions of internal organs.

Results. Good growth of spirochetes was seen in eggs from the third day for all the 7 blood samples inoculated, but the maximum growth was most commonly found on the fifth day of infection. The number of organisms was, however, greatly increased after being passed for 3 generations by means of the blood of embryonic chick, but the time of their appearance was not shortened. In agreement with previous workers, infection was limited almost entirely to the blood.