Studies on Rocky Mountain spotted fever / U.S. Treasury Department, Public Health Service.

Date:
[1930]
Catalogue details

Licence: Public Domain Mark

Credit: Studies on Rocky Mountain spotted fever / U.S. Treasury Department, Public Health Service. Source: Wellcome Collection.

    17/150 (page 5)
    D Table 3 shows the four results which are possible from testing drag ticks by the combined feeding and inoculation method. Tables 1 and 2 are typical of the results obtained when drag ticks (adults which had not fed since engorging as nymphs not later than during the fall of 1921) were tested (a) by inoculation, (6) by feed- ing and subsequent inoculation if fever did not develop from feeding. Table 4 gives the results from these two series of tests of drag ticks, (a) by immediate inoculation of tick contents and (6) by feeding fol- lowed by inoculation if no spotted fever resulted from the feeding. TaBLeE 4.—Drag tick infectivity tests {a) By direct inoculation: PRET WG See: “COMMCLCU es an ued nore 8 SS a ae eae oa et 101 Tess Tesultine tm. sported revera io 7 2 Ste et SS ee ee 0 Pest Ssresaltimoar Amaiinigy 28. Pe a iets a. Bee eee 29 DEO SUS aI UE VC ea eek. or ee ee a 2 ee oe 72 <b) By combined feeding and inoculation (including tests in which the pig sickened with spotted fever after feeding alone, inoculation therefore being omitted) : GLA MeSts “COMP lelCU ean wet Aa eels Fee Ce Mabe Oe oe 65 Tests resulting in spotted fever after feeding_____________________ 10 Tests resulting in spotted fever after inoculation, ticks having DECVIOUSHVs ROG= ne oe nls oo) as one ee Soe ls So 10 Tests showing immunity from feeding and inoculation_____-_______ 8 Tests negative from feeding and inoculation_____________-_-_- ot It will be recalled that in the preliminary experiment the inocula- tion of infected adult tick contents, the ticks having been artificially infected in the laboratory, produced fever, and the feeding alone of infected ticks from the same group did not; whereas in the later tests made with drag ticks (naturally infected), the tick content inocula- tions produced at most immunity in experiments where the feeding of ticks from identical lots produced fever. In interpreting these apparently contradictory results, it must be remembered that in the preliminary experiment the adult ticks ingested the virus only from two to six days before being tested, whereas in the drag tick tests the ticks used were collected in the early spring of 1922 and had not ingested blood since engorging as nymphs not later than the fall of 1921. Under the latter conditions we have not once produced spotted fever by the inoculation of tick contents; but, on the other hand, we have done so repeatedly by permitting them to feed. (Table 3, pig No. 897.) Mention should also be made of the fact that when testing ticks taken from host animals (as in the case of the mountain goat noted above), the inoculation of the tick contents has frequently resulted in spotted fever, as shown in Table 5. Such ticks had, of course, partially or completely fed within a short time prior to the test.