Abstract
BackgroundWith a prevalence of 4.7–13% in Danish Ixodes ricinus ticks, Rickettsia helvetica is one of the most frequently detected tick-borne organisms in Denmark. Most reports of human exposure have described asymptomatic seroconversion or a mild, self-limiting flu-like illness but it has also been implicated as a cause of subacute lymphocytic meningitis. Because Borrelia burgdorferi sensu lato (Bbsl) and R. helvetica are both found in the same tick species, potential co-transmission is a possibility. We examined 1) the seroprevalence of anti-rickettsia antibodies in patients investigated for Lyme neuroborreliosis (LNB), and 2) the cerebrospinal fluid (CSF) and sera of same patients for the presence of Rickettsia DNA.MethodsNinety-nine sera and 87 CSF samples from patients with intrathecal synthesis of anti-Borrelia antibodies and 101 sera and 103 CSF samples from patients with no detectable intrathecal synthesis were retrospectively examined for this study. Sera were analyzed for antibodies against spotted fever group (SFG) rickettsiae and both the CSF and sera were tested for Rickettsia DNA using a genus-specific real-time PCR.ResultsOf the patients tested for LNB, 32% (64/200) had IgG antibodies against SFG rickettsiae. Among patients with confirmed intrathecal synthesis of Borrelia-specific antibodies, 38% (38/99) exhibited IgG antibodies. None of these values were statistically significant when compared with sera from healthy blood donors (p = 0.7 and 0.19). Rickettsia DNA was found in the CSF of 4% (8/190) of patients.ConclusionNo statistically significant difference was found in the seroprevalence of anti-rickettsia antibodies in patients tested for LNB and healthy blood donors, indicative of a low rate of exposure in this group of patients. Eight patients showed evidence of Rickettsia DNA in the CSF, five of whom had LNB. However, cycle threshold (Ct) values were high, indicating low concentrations of DNA, and no apparent alteration in the clinical manifestations of LNB were noted in the medical records of these patients.
Highlights
With a prevalence of 4.7–13% in Danish Ixodes ricinus ticks, Rickettsia helvetica is one of the most frequently detected tick-borne organisms in Denmark
The aim of this study was threefold; 1) to investigate the seroprevalence of antibodies against spotted fever group (SFG) rickettsia in patients investigated for Lyme neuroborreliosis (LNB) 2) to examine the presence of Rickettsia Deoxyribonucleic acid (DNA) in the cerebrospinal fluid (CSF) and sera of same patients, and 3) to examine the clinical significance of such a finding
When using a cut-off of 1:128, 64 of the 200 patients (32%) tested for LNB had detectable IgG antibodies and four (2%) had detectable IgM antibodies against SFG rickettsiae
Summary
With a prevalence of 4.7–13% in Danish Ixodes ricinus ticks, Rickettsia helvetica is one of the most frequently detected tick-borne organisms in Denmark. With an annual incidence of over 3/100,000, Lyme neuroborreliosis (LNB) is the commonest bacterial neuroinfection in Denmark [1] It is caused by spirochetes in the Borrelia burgdorferi sensu lato (Bbsl) complex, transmitted to humans by the tick vector Ixodes ricinus, . Most patients exposed to this organism display subclinical infection or a mild, self-limiting febrile illness with headache and myalgia, only rarely accompanied by the often characteristic eschar or rash seen in other forms of SFG rickettsioses [7,8,9,10] It has been implicated as a cause of subacute lymphocytic meningitis [11, 12]
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