Rickettsiosis in Denmark: A nation-wide survey.

Rickettsia helvetica has been reported at varying prevalences in Danish and other European Ixodes ricinus populations. Though apparently widespread and with reported cases of human infection, the significance of the bacteria as a threat to public health remains unclear. We present a nation-wide survey of rickettsia in ticks, roe deer and humans in Denmark. Ticks were collected by flagging and screened for presence of rickettsial DNA by polymerase chain reaction. Sera from roe deer, hunters, neuroborreliosis patients and blood donors were analyzed for presence of anti-R. helvetica and Rickettsia felis antibodies by immunofluorescence microscopy. The Rickettsia minimum infection rate in ticks was 4.9 % (367/973 pools positive, 7510 ticks in total), with 3.9 % in nymphs and 9.3 % in adults. Rickettsia helvetica accounted for 4.17 % and Rickettsia monacensis for 0.03 %, 0.6 % comprised non-differentiable rickettsial DNA. The prevalence of antibodies against R. helvetica was 2.8 % (9/319) in roe deer, while no hunters (n = 536) or blood donors (n = 181) were positive. The prevalence of anti-R. helvetica antibodies among Lyme neuroborreliosis patients was 6 % (3/47), where it co-occurred with Anaplasma phagocytophilum. Based on our study autochthonous rickettsiosis is of limited concern to the public health in Denmark, but our finding of R. monacensis for the first time in Denmark illustrates the dynamic nature of tick-borne pathogens, emphasizing that continuous surveillance is necessary.

Evaluation of factors influencing tick bites and tick-borne infections: a longitudinal study.

BACKGROUND: Various tick-borne infections like borreliosis and rickettsiosis pose a health risk to humans in many parts of the world. We investigated seroprevalence of and seroconversion to Borrelia burgdorferi and Rickettsia spp. and relation to tick-bites, weather and clinical manifestations in Denmark. METHODS: Blood donors were enrolled at the Hospital of Southern Jutland in June-July with follow-up November-February of 2018 and 2019. Blood samples were collected, and a questionnaire regarding tick bites, potential exposures and symptoms was completed at each visit. Samples were tested for presence of IgM and IgG antibodies directed against B. burgdorferi and Rickettsia spp. using R. helvetica and R. felis as antigens. Data were examined for correlation between tick bites, serological results, potential exposures and symptoms. RESULTS: Two-hundred and fourteen (93 follow-ups) and 130 (38 follow-ups) blood donors were included in 2018 and 2019, respectively. The total borrelia seroconversion rate was 6.3% (CI 2.1-10.5), while the prevalence of IgM and IgG antibodies was 7.8% (CI 4.9-10.6) and 6.7% (CI 4-9.3), respectively. Seroconversion to Rickettsia spp. was detected in one participant. Tick bites and seroconversion were not significantly associated with the reported unspecific symptoms, but unspecific symptoms were common in the study population. There was no significant difference in number of tick bites or seroconversion/prevalence between seasons with highly alternating weather. CONCLUSIONS: Results suggest that weather conditions in an individual year have a limited impact. Anti-Borrelia-antibodies do not seem to persist in serum for several years. Rickettsiosis is of limited concern in Denmark.

Rickettsioses in Denmark: A retrospective survey of clinical features and travel history.

Rickettsia spp. can be found across the globe and cause disease of varying clinical severity, ranging from life-threatening infections with widespread vasculitis to milder, more localized presentations. Vector and, to some degree, reservoir are hematophagous arthropods, with most species harboured by ticks. In Denmark, rickettsiae are known as a cause of imported travel-related infections, but are also found endemically in ticks across the country. Data are, however, lacking on the geographical origin and clinical features of diagnosed cases. In this study, we have examined the travel history and clinical features of two groups of patients; 1) hospital-patients diagnosed with rickettsioses in the years 2010-2015 and 2) patients from primary health care (PHC) centers in Denmark having demonstrated anti-rickettsia antibodies in the years 2012-2015. The patients were identified using the Danish National Patient Registry (DNPR) and through the serological database at the State Serum Institute, where the laboratory diagnosis of rickettsioses is currently centralized. Data were collected for 86 hospital patients and 26 PHC center patients by reviewing hospital medical records and performing telephone interviews with PHC centers. Of the hospital patients, 91% (78/86) had a history of international travel 14 days prior to symptom start, with most having imported their infection from southern Africa, South Africa in particular (65%), and presenting with a clinical picture most compatible with African tick-bite fever caused by R. africae. Only two patients presented with a CRP > 100 mg/L and no mortalities were reported. At the PHC centers, most patients presented with mild flu-like symptoms and had an unknown (50%) or no history (19%) of international travel, raising the possibility of endemic rickettsioses. In view of our findings, rickettsioses do not appear to constitute a major public health problem in Denmark, with most cases being imported infections and potential endemic cases presenting as mild infections.

[Clinical manifestations, diagnosis and treatment of Lyme borreliosis].

Lyme borreliosis is an infection caused by the Borrelia burgdorferi sensu lato complex and transmitted by Ixodes ricinus ticks in Denmark. It can manifest itself in several different forms of which erythema migrans is the most common and is diagnosed by clinical assessment of the characteristic erythema. Laboratory support for the clinical diagnosis of other manifestations rests on the measurement of Borrelia-specific antibodies. Treatment is straight-forward with antibiotics such as penicillin. This paper reviews the clinical manifestations, diagnosis and treatment of this infection.

[Tick-borne infections in Denmark].

The castor bean tick, Ixodes ricinus, is common in woodlands in most of Denmark. Besides Borrelia burgdorferi, it can harbour a number of pathogenic microorganisms such as tick-borne encephalitis virus, Anaplasma phagocytophilum, Rickettsia helvetica, Francisella tularensis, Candidatus Neoehrlichia mikurensis, Bartonella spp., Borrelia miyamotoi and Babesia spp. These tick-borne infections should be a differential diagnostic consideration during the tick season in Denmark. We review the distribution, clinical manifestations, diagnosis and treatment of these microorganisms.