Field Project in Western Montana ? ? During the summers of 2002 and 2004, nine people contracted tick-borne relapsing fever on Wild Horse Island in southwest Flathead Lake, Lake County, Montana (Schwan et al, 2003, Emerg. Infect. Dis; Schwan et al., 2007; Emerg. Infect. Dis). These patients were the first confirmed cases of relapsing fever in the state. Investigations by our group associated with these outbreaks resulted in the first isolations of Borrelia hermsii and the first collection of its tick vector, Ornithodoros hermsi, in Montana.? ? Tick-borne relapsing fever caused by B. hermsii is a zoonosis, and in other parts of western North America, small rodents such as tree squirrels and chipmunks are the primary enzootic vertebrate hosts for the spirochete and ticks in nature. Most people become infected with B. hermsii while sleeping in tick- and rodent-infested cabins, as happened on Wild Horse Island. The ticks are nocturnal and feed quickly in 15 to 60 minutes, so most people are unaware of having been bitten. ? ? The prevalence and distribution of B. hermsii in western Montana are unknown. The purpose of this project is to begin to investigate the presence of B. hermsii in small mammal populations at two locations on Flathead Lake; Wild Horse Island, where the patients were infected; and the Flathead Biological Research Station, owned and run by the University of Montana, at Yellow Bay on the eastern shore of the lake. Information gained regarding the presence of B. hermsii in small mammals and ticks will help elucidate the ecological factors maintaining the spirochete, which could help develop future control strategies in specific locations. ? ? The Schwan lab has worked for 22 years to determine the distribution and genetic diversity of the relapsing fever spirochete, B. hermsii, found at higher elevation coniferous forests throughout western North America. With the emergence of human relapsing fever cases in western Montana, we have the opportunity to explore the role of local vertebrate hosts at maintaining the spirochete in nature. By establishing additional isolates of the spirochete, we can also determine the genetic diversity and host associations at specific locations. For example, on Wild Horse Island we found two diverse genomic groups of B. hermsii infecting two individuals that slept in the same bed (Schwan et al., 2007; Emerg. Infect. Dis). Thus, additional work in the field will complement laboratory investigations examining the possible maintenance of diverse genetic types of spirochetes in vertebrates and ticks. ? ? The goals of this project are to obtain preliminary data on the prevalence and distribution of B. hermsii in animals on Wild Horse Island and the mainland at Yellow Bay.
The specific aims are: determine infection and previous exposure of mammalian hosts to B. hermsii; determine the prevalence of B. hermsii in ticks and determine the genomic group to which the spirochetes belong.? ? For this project, most activities of this last year were spent applying for and getting permission to perform the fieldwork. We now have permits from the US. Forest Service; Montana Fish, Wildlife and Parks; the Salish-Kootenai Confederated Tribes; and the Animal Care and Use Committees at RML and the University of Montana. Montana Fish, Wildlife and Parks has provided boat transportation to and from Wild Horse Island, and the DIR funded the purchase of a field vehicle for ground transportation.? ? During July August 2008, live traps were used to capture small mammals. These animals were marked individually with PIT tags, blood was collected for multiple tests, ectoparasites collected, and the animals were released at the site of capture. Over 150 animals have been sampled, and while many species of mammals have been captured, the majority have been deer mice and pine squirrels. Preliminary analysis of blood smears has detected Borrelia hermsii in 7 squirrels and one deer mouse, the latter of which was trapped immediately under a cabin where one patient was infected. Spirochetes were also detected in two squirrels on the mainland at Yellow Bay. Attempts to isolate these spirochetes and the serological testing of the serum samples are currently underway. Fieldwork will end in September and the results obtained in the laboratory this fall will help us plan next years field season that will begin in May 2009. ? ? Field Project in Mali, West Africa? ? Throughout most other areas of sub-Saharan Africa, the assumption is that if a patient has an acute febrile, recurring disease, the patient has, and is treated for, malaria. This would explain many treatment failures if the patients had relapsing fever, as the drugs used to treat malaria are ineffective against relapsing fever spirochetes. Malaria is highly prevalent and a serious human infection in Mali, where NIAID has ongoing projects on malaria and leishmaniasis, both vector-borne infections. Little is known about tick-borne relapsing fever in Mali, but given its prevalence in nearby Senegal, and two observations regarding spirochetes in patients in western Mali (Rodhain et al., 1991, Bull. Soc. Path. Ex. 84:30-45), we believe relapsing fever may be significantly misdiagnosed as malaria, as we found recently in Togo (Nordstraand, et al. Tickborne relapsing fever diagnosis obscured by malaria, Togo. Emerging Infect. Dis. 13: 117-123, 2007). The goal of this project is to evaluate the potential for human tick-borne relapsing fever in Mali. Our efforts will be directed at capturing small mammals and testing their blood for spirochetes and antibodies specific for relapsing fever infections; collecting ticks and testing them for spirochete infection; and testing human serum samples already collected for other studies to detect the presence of relapsing fever antibodies. ? ? Tick-borne relapsing fever caused by B. crocidurae in West Africa is also a zoonosis, and in Senegal small rodents and shrews are the primary enzootic vertebrate hosts for the spirochete and ticks in nature. Most people become infected with B. crocidurae while sleeping in tick- and rodent-infested huts, as described for a longitudinal study in Senegal published recently (Vial et al., 2006, Incidence of tick-borne relapsing fever in West Africa; longitudinal study, Lancet 368:37-43). The soft tick vector, Ornithodoros sonrai, is nocturnal and feeds quickly in 15 to 60 minutes, so most people are unaware of having been bitten (quite similar to the situation in western North America). ? ? The prevalence and distribution of B. crocidurae and its vector in Mali are unknown. However two studies suggest that B. crocidurae may be present in western Mali near the Senegal-Mali border. The purpose of this project is to begin to investigate the presence of B. crocidurae in small mammal populations at various locations in Mali, working out of the NIAID-supported laboratory in Bamako, the capital of Mali. Attempts will also be made to collect ticks from rodent burrows. Information gained regarding the presence of B. crocidurae in small mammals and ticks will help elucidate the potential for human infections, which could be misdiagnosed and treated inappropriately as malaria. ? ? Effect of In vitro passage on relapsing fever spirochetes? ? Previous studies have shown the loss of infectivity of B. burgdorferi associated with in vitro cultivation. The effects of long term in vitro cultivation on B. hermsii have not been investigated. All seven isolates of B. hermsii and the one isolate of B. turicatae examined retained infectivity in mice after one year of continuous in vitro cultivation. Furthermore, there were few apparent differences in the plasmid profiles after long-term cultivation. Therefore, these results suggest that relapsing fever spirochetes are genetically stable during in vitro cultivation.
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