Isolation of Borrelia burgdorferi from Neotoma fuscipes, Peromyscus maniculatus, Peromyscus boylii, and Ixodes pacificus in Oregon.

Abstract

Abstract. The number of Lyme disease cases in Oregon has increased in recent years despite the fact that the pathogen, Borrelia burgdorferi, has never been isolated in the state. Rodent and tick surveys were undertaken in 1997 to isolate and characterize strains of B. burgdorferi from Oregon and to identify potential reservoirs and vectors of Lyme disease. Borrelia burgdorferi was isolated from Neotoma fuscipes, Peromyscus maniculatus, P. boylii, and Ixodes pacificus. Both N. fuscipes and P. maniculatus were infested with I. pacificus and I. spinipalpis. Although I. pacificus infested P. boylii, I. spinipalpis was not found on this rodent, and only 4% of the P. boylii were infected with B. burgdorferi compared with the 19% and 18% infection rates found in N. fuscipes and P. maniculatus, respectively. Variation in the molecular weights of the outer surface proteins A and B were found in these first confirmed isolates of B. burgdorferi from Oregon, as well as truncated forms of outer surface protein B.Lyme disease caused by Borrelia burgdorferi is the most common vector-borne disease in the United States. Since the discovery of the etiologic agent in 1981, the known endemic range of Lyme disease together with the numbers of reported cases has steadily increased. 1 The principal vectors of B. burgdorferi are Ixodes scapularis and I. pacificus in the eastern and western United States, respectively. 2 Recently, I. spinipalpis was found to be a competent Lyme disease vector in enzootic cycles involving mice (Peromyscus spp) and wood rats (Neotoma fuscipes) in California, 3 and N. mexicana in Colorado. 4 Despite reports of I. spinipalpis attaching to humans in Oregon, 5 New Mexico (Centers for Disease Control and Prevention [CDC], unpublished data), and Canada, 6 I. spinipalpis is not believed to be important in the transmission of B. burgdorferi to humans since nymphs are usually found either attached to animals or in the more humid environment of a rodent nest.Reports of Lyme disease cases have been increasing in number and spreading in geographic range in the Pacific Northwest. In Oregon, there were only four reported cases of Lyme disease from two counties in 1991 (CDC, unpublished data) compared with 19 cases from 11 counties reported in 1996. 7 Although spirochetes were found in almost 2% of I. pacificus in Oregon from 1982 to 1984, these spirochetes were not identified. 8 The results of a survey undertaken in April-May 1997 to try to confirm the presence of B. burgdorferi in Oregon and to ascertain which animals and ticks may be responsible for the maintenance of this human pathogen in enzootic cycles are presented. MATERIALS AND METHODSField studies. Field studies in southern Oregon were undertaken during 1997 at two sites in Jackson County (Woodrat Mountain and Lost Creek) and one site (Spencer Creek) in Josephine County. Host-seeking adult I. pacificus ticks were collected by flagging vegetation during April 1997 and held at 4ЊC in a saturated humidity until processed for spirochete isolation in Barbour-Stoen...

Use of a sentinel host system to study the questing behavior of Ixodes spinipalpis and its role in the transmission of Borrelia bissettii, human granulocytic ehrlichiosis, and Babesia microti.

“…High infection rates of B. burgdorferi sensu lato have been reported in I. spinipalpis collected in California, 8,9 Oregon, 10 and Colorado. 11 Furthermore, this tick has also been shown to be competent for transmission of both aoHGE 16 and B. microti 17 However, this tick has been characterized as nidicolous, and therefore it was assumed to be unimportant in the transmission of human pathogens because nidicolous ticks have limited opportunities to encounter humans.…”

“…and mice (Peromyscus spp. ), in California, 8,9 Oregon, 10 and Colorado. 11 Ixodes spinipalpis, however, has been described as a nidicolous tick, being closely associated with its principal rodent hosts.…”

“…15 Recently in Oregon, I. spinipalpis was hypothesized to be potentially more important in the maintenance of B. burgdorferi sensu lato than I. pacificus because of the much higher B. burgdorferi sensu lato infection rate found in this tick. 10 Even more recently, I. spinipalpis was discovered to transmit 2 additional human pathogens among rodents: the agent of human granulocytic ehrlichiosis (aoHGE) 16 and B. microti. tick, it has occasionally been collected on humans in Oregon, 18 New Mexico, 11 and Canada 19 as well as by dragging, 19 and on rabbits and birds.…”

Lyme Disease in Oregon

“…pacificus is the tick vector for B. burgdorferi in the western United States. The distribution of I. pacificus in Oregon has been studied multiple times since 1967 (1,2,4). The tick surveys consistently demonstrate a distribution that extends from the western slope of the Cascade mountain range to the Pacific Ocean (Fig.…”

The Biological Survey of Canada: A Personal History

“…It is a frequent parasite of wood rats and pikas, and perhaps occurs in greater numbers in the nests of these hosts. However, it has recently been implicated in transmission of a variety of pathogens in the United States of America, including Borrelia burgdorferi (Burkot et al 1999), Borrelia bissetti (Schnieder et al 2000), Babesia microti (Burkot et al 2001b), and the agent of human granulocytic anaplasmosis (Zeidner et al 2000). The importance of I. spinipalpis to maintain an enzootic cycle in small mammals was identified by Burkot et al (2001a) when they found that larvae and nymphs commonly infested sentinel mice a considerable distance from wood rat nests.…”