Distribution of the Lyme Disease SpirocheteBorrelia burgdorferiin Naturally and Experimentally Infected Western Gray Squirrels (Sciurus griseus)

Abstract

The dynamics of Borrelia burgdorferi infections within its natural hosts are poorly understood. We necropsied four wild-caught western gray squirrels (Sciurus griseus) that were acquired during a previous study that evaluated the reservoir competence of this rodent for the Lyme disease spirochete. One animal was infected experimentally, whereas the others were infected in the wild before capture. To investigate dissemination of B. burgdorferi and concurrent histopathologic lesions in different tissues, blood specimens, synovial and cerebrospinal fluid, ear-punch biopsies, and diverse tissue samples from skin and various organs were taken and examined by culture, polymerase chain reaction, and histology. Borrelia-positive cultures were obtained from three of the squirrels, that is, from skin biopsies (7 of 20 samples), ear-punch biopsies (2 of 8), and one (1 of 5) lymph node. Sequencing of amplicons confirmed B. burgdorferi sensu stricto (s.s.) infection in 9 of 10 culturepositive samples and in DNA extracted from all 10 positive cultures. The experimentally infected squirrel yielded most of the positive samples. In contrast, bodily fluids, all other organ specimens from these animals, and all samples from one naturally infected squirrel were negative for Borrelia for both assays. None of the necropsied squirrels exhibited specific clinical signs associated with B. burgdorferi. Similarly, necropsy and histological examination of tissues indicated the presence of underlying infectious processes, none of which could be ascribed conclusively to B. burgdorferi infection. Based on these results, obtained from a small number of animals investigated at a single time point, we suggest that B. burgdorferi s.s. infection in S. griseus may result in rather localized dissemination of spirochetes, and that mild or nonclinical disease might be more common after several months of infection duration. Since spirochetes could be detected in squirrels 7-21 months postinfection, we conclude that S. griseus can infect Ixodes pacificus ticks with B. burgdorferi s.s. trans-seasonally.

Seroprevalence, geographic distribution and risk factor analysis of Borrelia burgdorferi sensu lato in naturally exposed dogs of Iran

“…lizards serve as reservoirs of Borrelia and some of these hosts may have a role in introducing the ticks and B. burgdorferi to new locations (Leonhard et al, 2010;Nadelman and Wormser, 1998). Due to phenotypic and genotypic heterogeneity of B. burgdorferi, 18 genospecies have been described under the name B. burgforferi sensu lato in the world such as B. burgdorferi sensu stricto, Borrelia garinii and Borrelia afzelii (Baranton et al, 1992;Canica et al, 1993;Gern and Humair, 2002;Rudenko et al, 2009).…”

Lyme disease ecology in San Luis Obispo County: The role of the western gray squirrel

“…I speculate that the primary vector is I. pacificus because of previous California research, but no infected I. pacificus were recovered, leading me to assume that overall disease risk to humans is probably low since other rodent-associated vector-competent ticks infrequently feed on humans (Furman & Loomis 1984;Burkot et al 2001). Lyme disease risk is often measured by nymphal infection prevalence (LoGiudice et al 2008;Leonhard et al 2010), and my study recovered only three I. pacificus nymphs, none of which were infected. Since this is a very low recovery rate, further surveillance could confirm whether nymphal infection prevalence is indeed quite low in this area.…”

“…Experimentally infected Sciurus griseus exhibited 7 months minimal infected duration (Leonhard et al 2010), while experimentally infected P. maniculatus demonstrated 13 months as their minimal infected duration (Brown & Lane 1994). Naturally infected P. maniculatus and experimentally or naturally infected P. boylii have not been surveyed for Borrelia infection duration.…”

“…To fulfill the second criterion, naturally or experimentally infected hosts need to be monitored for infection status over time by directly testing the animal or exposing the host to naïve, susceptible ticks. Sciurus griseus experimentally (n = 1) and naturally (n = 3) infected with B. burgdorferi were surveyed for minimal infection duration and exhibited 7 months and between 9 -22 months respectively (Leonhard et al 2010).…”

“…Infection duration beyond twelve months is particularly interesting since this will allow infected reservoir hosts to infect immature ticks trans-seasonally (Leonhard et al 2010). Experimentally infected P. maniculatus (n = 4) demonstrated 13 months as their minimal infection duration (Brown & Lane 1994).…”