A New Tick Vector of Relapsing Fever in California

Relapsing fever has been repeatedly reported in California since 1921 (Briggs, 1 Porter, Beck and Stevens, 2 and Coleman 3 ). While ticks have been suspected as vectors for some time (Herms and Wheeler, 4 and Coleman 5 ), no positive experimental evidence incriminating a particular species has been obtained until recently.

A careful search for ticks has been made repeatedly in various localities in California where cases of relapsing fever had been reported. On August 12, 1931, three specimens of mature Ornithodorus ticks were taken in a cottage located at Brockway, Lake Tahoe, California, at an elevation of approximately 6,000 feet, where cases of this disease had occurred about a month previously. On examination and comparison with other species of the genus Ornithodorus these specimens were believed to be an undescribed species. In September, 1933, several similar specimens of Ornithodorus were sent to us from Big Bear Lake, California. In August, 1934, more ticks of the same undescribed species were collected in a relapsing fever cabin at Big Bear Lake in San Bernardino County, elevation about 5,700 feet. Other specimens of this species have been taken in various localities in the following counties: San Bernardino, Eldorado, and Placer, at elevations ranging from 5,000 to 8,000 feet.

Since Beck and her associates 2 had demonstrated spirochaetes in the blood and organs of squirrels and chipmunks both at Big Bear Lake and at Lake Tahoe and thus established the burrowing rodents as possible intermediate hosts, collections of rodent nesting material taken from the cabins were examined thoroughly. Several dozen specimens of ticks of the same species were discovered. Specimens of ticks similarly collected have also been obtained through the courtesy of Dr. E. B. Godfrey, San Bernardino County Health Officer.