The Lyme Times V 25 No 2

TBD Epidemiology California ticks carry a plethora of disease agents to unsuspecting Lyme patients By Robert S. Lane, PhD black-legged tick (Ixodes pacificus) is the habitats, particularly dense woodlands. In primary carrier of B. burgdorferi in the both Alameda and Mendocino counties, My career-long study of ticks, tick-borne Far West. Willy generously taught me more than a handful of named and one disease agents and their wildlife partners laboratory techniques essential for in- or more uncharacterized Borrelia spp. were spurred in 1974 when, as a newly- vestigating tick-pathogen-host interrela- were detected in host-seeking Ixodes spp. hired public health biologist with the Cal- tionships, which enabled me to establish ticks. The described species included B. ifornia Department of Health Services, I my own LD research program at U.C. miyamotoi, a relapsing-fever group spi- was asked to lead an investigation aimed Berkeley in 1984. Most of the ecological/ rochete implicated recently as a human at determining the then unknown tick vector(s) and vertebrate hosts of Rocky Mountain spotted fever (RMSF). In collaboration with colleagues in the Vector Biology and Control Section and the Viral and Rickettsial Disease Labo- ratory, along with researchers at the U.S. Public Health Service, Rocky Mountain Laboratories in Hamilton, Montana, several known or novel rickettsiae were isolated and characterized from human or non-human biting ticks, and a few small mammals were implicated as hosts. The Pacific Coast tick (Dermacentor occidentalis), a human-biter, was reconfirmed as the primary carrier of an unclassified spotted fever group rickettsia, designated 364D, and incriminated as causing a mild form of RMSF. Recent mo- lecular studies by other researchers have reconfirmed some of our earlier tick/ The western fence lizard, a widespread and abundant host of sub-adult western black-legged rickettisial-survey findings and, in 2010, ticks, is immune to infection with Lyme-group spirochetes. In northwestern California, this Marc Shapiro and co-workers reported reptile may host as many as 90% of the sub-adult ticks in some chaparral or woodland habitats. in the journal Clinical Infectious Diseases that the unclassified 364D rickettsia ac- epidemiological research was conducted pathogen in Russia and the northeastern tually causes an eschar-associated illness. in northwestern California because this U.S. Obviously, the latter findings beg the [Ed. note: An eschar is a dry, dark scab or region is a hotbed of LD activity. The Uni- question – do any of them, other than B. scar.], So keep an eye on that “emerging” versity of California Hopland Research burgdorferi, occasionally cause clinical disease, too. and Extension Center became the hub for illness in California? We have investigated other tick-borne these studies. Risk factors for tick-exposure or LD diseases as well: Colorado tick fever, were found to include, among others, human babesiosis, human granulocytic What have we learned? woodcutting, sitting atop logs or against anaplasmosis, relapsing fever-group For starters, the diversity of the tick tree trunks, gathering firewood and du- agents, tick paralysis, tularemia, and par- vectors, vertebrate hosts and Lyme-group ration of tick attachment for the nymphs; ticularly Lyme disease (LD). After Dr. spirochetes mirror the remarkable biodi- contact with low vegetation bordering the Willy Burgdorfer and colleagues pub- versity for which California is legendary. uphill (versus the downhill) margins of lished their epochal discovery of the LD Moreover, the environmental conditions, hillside hiking trails and the time-of-day spirochete (subsequently named Borrelia the key tick/wildlife players and the epide- that one ventures outdoors for the adult burgdorferi in his honor) in black-legged miology of LD differ markedly from those ticks; and habitat type for both nymphs ticks from Shelter Island, New York, in in the eastern U.S. Besides I. pacificus, and adult ticks. 1982, Willy invited me to join him in several other Ixodes spp. ticks, a number of By contrast, the immune systems of the the inaugural tick-LD spirochete survey rodents and, perhaps secondarily, ground- western fence lizard and southern alligator in western North America. This collabo- foraging birds, interact to maintain Lyme- lizard, mega-hosts of sub-adult western ration led to the discovery that the western group spirochetes in certain permissive Continued on page 34 2014 Volume 26 Number 3 31.

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