Sirkka Vene

Prevalence of tick-borne encephalitis virus in Ixodes ricinus ticks in northern Europe with particular reference to Southern Sweden

BackgroundIn northern Europe, the tick-borne encephalitis virus (TBEV) of the European subtype is usually transmitted to humans by the common tick Ixodes ricinus. The aims of the present study are (i) to obtain up-to-date information on the TBEV prevalence in host-seeking I. ricinus in southern and central Sweden; (ii) to compile and review all relevant published records on the prevalence of TBEV in ticks in northern Europe; and (iii) to analyse and try to explain how the TBE virus can be maintained in natural foci despite an apparently low TBEV infection prevalence in the vector population.MethodsTo estimate the mean minimum infection rate (MIR) of TBEV in I. ricinus in northern Europe (i.e. Denmark, Norway, Sweden and Finland) we reviewed all published TBEV prevalence data for host-seeking I. ricinus collected during 1958–2011. Moreover, we collected 2,074 nymphs and 906 adults of I. ricinus from 29 localities in Sweden during 2008. These ticks were screened for TBEV by RT-PCR.ResultsThe MIR for TBEV in nymphal and adult I. ricinus was 0.28% for northern Europe and 0.23% for southern Sweden. The infection prevalence of TBEV was significantly lower in nymphs (0.10%) than in adult ticks (0.55%). At a well-known TBEV-endemic locality, Torö island south-east of Stockholm, the TBEV prevalence (MIR) was 0.51% in nymphs and 4.48% in adults of I. ricinus.ConclusionsIf the ratio of nymphs to adult ticks in the TBEV-analysed sample differs from that in the I. ricinus population in the field, the MIR obtained will not necessarily reflect the TBEV prevalence in the field. The relatively low TBEV prevalence in the potential vector population recorded in most studies may partly be due to: (i) inclusion of uninfected ticks from the ‘uninfected areas’ surrounding the TBEV endemic foci; (ii) inclusion of an unrepresentative, too large proportion of immature ticks, compared to adult ticks, in the analysed tick pools; and (iii) shortcomings in the laboratory techniques used to detect the virus that may be present in a very low concentration or undetectable state in ticks which have not recently fed.

Serologic Analysis of Returned Travelers with Fever, Sweden

We studied 1,432 febrile travelers from Sweden who had returned from malaria-endemic areas during March 2005–March 2008. In 383 patients, paired serum samples were blindly analyzed for influenza and 7 other agents. For 21% of 115 patients with fever of unknown origin, serologic analysis showed that influenza was the major cause.

Detection and identification of Rickettsia species in Ixodes tick populations from Estonia

A total of 1640 ticks collected in different geographical parts of Estonia were screened for the presence of Rickettsia species DNA by real-time PCR. DNA of Rickettsia was detected in 83 out of 1640 questing ticks with an overall prevalence of 5.1%. The majority of the ticks infected by rickettsiae were Ixodes ricinus (74 of 83), while 9 of the 83 positive ticks were Ixodes persulcatus. For rickettsial species identification, a part of the citrate synthase gltA gene was sequenced. The majority of the positive samples were identified as Rickettsia helvetica (81 out of 83) and two of the samples were identified as Rickettsia monacensis and Candidatus R. tarasevichiae, respectively. Genetic characterization based on the partial gltA gene showed that the Estonian sequences within the R. helvetica, R. monacensis and Candidatus R. tarasevichiae species demonstrated 100% similarity with sequences deposited in GenBank, originating from Rickettsia species distributed over large territories from Europe to Asia.

Tick-borne encephalitis (TBE) vaccine to medically immunosuppressed patients with rheumatoid arthritis: A prospective, open-label, multi-centre study

BACKGROUNDnTick-borne Encephalitis (TBE) is endemic in south-eastern Sweden as well as in the Baltic regions, Central Europe and Russia. Ageing and immunosuppressed individuals are more prone to severe disease and neurological complications. We assessed the immunogenicity of TBE-vaccine in rheumatoid arthritis (RA) patients treated with tumor necrosis factor-inhibitors (TNFi) and/or methotrexate (MTX).nnnMETHODSnTBE vaccine, FSME-Immune(®) or Encepur(®), was administered to non-immune RA patients as well as age and gender matched healthy controls. Individuals <60 years of age were given three doses at month 0, 1, 12. Individuals ≥ 60 years old were given an additional priming dose at month 3, i.e. a total of four doses. Tick-borne encephalitis neutralizing antibodies were assessed by a rapid fluorescent focus inhibition test.nnnRESULTSnThe study population consisted of 66 patients and 56 age and gender matched healthy controls. Median age was 58.5 years. The patients were either treated with TNFi (n=16), TNFi+MTX (n=36) or MTX (n=14). After the last TBE-vaccine dose, given one year after the first, 39% of the patients compared to 79% of the healthy controls had seroprotective levels (p=<0.05).nnnCONCLUSIONSnStandard TBE-vaccine schedule does not confer enough immunogenicity in this group of immunosuppressed patients, who should be carefully informed about a higher risk for vaccination failure and risk of infection when exposed in high-endemic areas.

Serological Evidence of Chikungunya Virus among Acute Febrile Patients in Southern Mozambique.

Background In the last two decades, chikungunya virus (CHIKV) has rapidly expanded to several geographical areas, causing frequent outbreaks in sub-Saharan Africa, South East Asia, South America, and Europe. Therefore, the disease remains heavily neglected in Mozambique, and no recent study has been conducted. Methods Between January and September 2013, acute febrile patients with no other evident cause of fever and attending a health center in a suburban area of Maputo city, Mozambique, were consecutively invited to participate. Paired acute and convalescent serum samples were requested from each participant. Convalescent samples were initially screened for anti-CHIKV IgG using a commercial indirect immunofluorescence test, and if positive, the corresponding acute sample was screened using the same test. Results Four hundred patients were enrolled. The median age of study participants was 26 years (IQR: 21–33 years) and 57.5% (224/391) were female. Paired blood samples were obtained from 209 patients, of which 26.4% (55/208) were presented anti-CHIKV IgG antibodies in the convalescent sample. Seroconversion or a four-fold titer rise was confirmed in 9 (4.3%) patients. Conclusion The results of this study strongly suggest that CHIKV is circulating in southern Mozambique. We recommend that CHIKV should be considered in the differential diagnosis of acute febrile illness in Mozambique and that systematic surveillance for CHIKV should be implemented.

Immunogenicity of delayed TBE-vaccine booster

Information is scarce regarding the antibody response when TBE-vaccine booster doses are delayed, which is a common situation in daily life. We have investigated the immune response after a delayed booster dose compared to a normal booster interval in an every-day setting. Overall, 250/260 (96%) of the study participants had neutralizing antibodies post-booster, with no significant difference between normal and delayed booster intervals. Based on our findings we propose that healthy individuals who have failed adherence to the recommended schedule of TBE-vaccination can be given a delayed dose without concern of immunogenicity.

Identification of linear human B-cell epitopes of tick-borne encephalitis virus

BackgroundTick-borne encephalitis (TBE) is a central nervous system infection transmitted to humans by ticks. The causative agent, tick-borne encephalitis virus (TBEV), belongs to the genus Flavivirus (family Flaviviridae), which includes globally important arthropod-borne viruses, such as dengue, Yellow fever, Japanese encephalitis and West Nile viruses. Flaviviruses are highly cross-reactive in serological tests that are currently based on viral envelope proteins. The envelope (E) protein is the major antigenic determinant and it is known to induce neutralizing antibody responses.MethodsWe synthesized the full-length TBEV proteome as overlapping synthetic 18-mer peptides to find dominant linear IgG epitopes. To distinguish natural TBEV infections from responses to TBE immunization or other flavivirus infections, the peptides were probed with sera of patients infected with TBEV, West Nile virus (WNV) or dengue virus (DENV), sera from TBE vaccinees and negative control sera by SPOT array technique.ResultsWe identified novel linear TBEV IgG epitopes in the E protein and in the nonstructural protein 5 (NS5).ConclusionsIn this study, we screened TBEV structural and nonstructural proteins to find linear epitopes specific for TBEV. We found 11 such epitopes and characterized specifically two of them to be potential for differential diagnostics. This is the first report of identifying dominant linear human B-cell epitopes of the whole TBEV genome. The identified peptide epitopes have potential as antigens for diagnosing TBEV and to serologically distinguish flavivirus infections from each other.

Seroepidemiologic Screening for Zoonotic Viral Infections, Maputo, Mozambique.

To the Editor: In sub-Saharan Africa, febrile patients are often assumed to have, and are treated for, malaria, but when tested, many are malaria-negative. Because emerging diseases, such as chikungunya virus (CHIKV) and dengue virus (DENV) infections, cause outbreaks around the world (1–3), the importance of these pathogens has become more evident. However, low-income countries have limited epidemiologic data on alternative diagnoses to malaria (4,5) and poor laboratory capacity (1), which restrict further diagnostic investigations. An early study in Mozambique during the 1980s found antibodies to Rift Valley fever virus (RVFV) in 2% of pregnant women (6). More recently, a RVFV seroprevalence of 36.9% among cattle in the Maputo Province was shown in 2010–2011 (7). Furthermore, the movement of humans from rural areas to major cities, particularly to the capital of Maputo, might affect human illnesses and disease pattern of zoonotic viruses (3). n nWe conducted a pilot study on CHIKV, DENV, hantavirus, RVFV, and West Nile virus (WNV) epidemiology in Mozambique. Ethical approval (registration no. IRB00002657) was granted by the National Bioethics Committee in Mozambique and by the Regional Ethical Review Board at Karolinska Institutet, Stockholm, Sweden (permit no. 2012/974–31/3). n nDuring 2012–2013, a total of 78 febrile patients were prospectively enrolled when they sought medical attention at the Polana Canico Health Center and Mavalane Health Center (catchment area 4,663 km2, estimated population 46,184 inhabitants) in the suburban area of Maputo city. All included patients answered a questionnaire and were initially screened for malaria by blood smear light microscopy; 15 were positive for malaria (Table). Patients’ median age was 29 years (37 years for seropositive patients) and ranged from 5 to 78 years. Forty-six (59%) were female. Fifty-eight (74%) reported recent exposure to mosquitoes. None of these persons had a history of international travel, and none had received a yellow fever vaccination. n n n nTable n nResults of screening for viral antibodies and malaria parasites in 78 febrile patients, Maputo, Mozambique, 2012–2013* n n n nSixty (77%) patients provided paired acute- and convalescent-phase blood samples, with a minimum of 14 days (median 33 days) between samples. Serum samples were sent to the Public Health Agency of Sweden and blindly screened at a titer of 1:20 for IgG to CHIKV, DENV, hantavirus, RVFV, and WNV by using in-house indirect immunofluorescence assays as described for DENV by Vene et al. (8). Screening for IgG was done on convalescent-phase serum samples or, when those were not available, on acute-phase serum samples. Further immunofluorescence analyses for titer increases were performed for patients for whom paired serum samples were available and screening results were positive for IgG; however, no titer increases were found. Serum from admittance were tested for DENV IgM and WNV IgM by using commercial assays according to manufacturers’ instructions (Panbio Dengue IgM Capture ELISA E-DEN01M/E-DEN01M05, Standard Diagnostics, Inc., Yongin-si, South Korea; Serion ELISA classic ESR14M West Nile Virus IgM, Institut Virion/Serion GmbH, Wurzburg, Germany); 2 samples were positive for DENV IgM but none for WNV IgM. All acute serum samples were screened by using 1-step real-time reverse transcription PCR for CHIKV, RVFV, WNV (in-house validated assays), and DENV (9). Results were negative for viral RNA. n nTwenty-three (29%) of the 78 patients had a positive serology result from acute- or convalescent-phase serum samples for >1 of the tested viral pathogens (Table). The main finding was CHIKV IgG in 15 (19%) patients. Ten (13%) patients had positive results for DENV, including 2 DENV IgM–positive samples. n nThe seroepidemiologic findings in this pilot study in Maputo strongly suggest possible and neglected alternative causes of febrile illness in Mozambique. Antibodies to CHIKV were found in 19% of the patients, which was a novel finding for Mozambique but corresponded well with other reports on the spread of CHIKV in tropical and subtropical areas of the world (2,3). DENV antibodies were present in 13% of the study population, representing a new finding in southern Mozambique; previous outbreaks have been reported from the northern part of the country (5). The median age of the seropositive patients (37 years) was higher than for the group as a whole (29 years), which might reflect increased exposure to zoonotic viruses over time. One patient was IgG positive for RVFV, a potentially emerging cause of fever in Mozambique, especially in view of recent reports of RVFV in cattle (7). The samples positive for both DENV and WNV IgG could represent previous independent infections with these viruses, co-infection, or cross-reactivity, which are common for flavivirus IgG (10). n nOverall, results indicate that exposure to vectorborne viruses in persons living in suburban areas of Maputo city is frequent, suggesting that infections with CHIKV, DENV, and RVFV infection should be considered as alternative diagnoses for patients with febrile illness in these settings. On the basis of these results, more extensive research is planned on the epidemiology of zoonotic viral infections in Mozambique.

Suspected YF-AND after yellow fever vaccination in Finland

Yellow fever (YF) vaccine is considered safe but vaccine-associated complications have also been encountered. We report neurological symptoms after YF-vaccination in a previously healthy Finnish male. Other concomitant infections or causes for the symptoms could not be identified.