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Home : Publications : CCDR : 2006 - Volume 32 : Advisory Committee Statement (ACS-3) |
![]() Canada Communicable Disease Report
Volume 32 ACS-3
1 April 2006
An Advisory Committee Statement (ACS) Committee to Advise on Tropical Medicine and Travel (CATMAT)*†Statement on tick-borne encephalitisPDF Version
20 Pages - 415 KB PreambleThe Committee to Advise on Tropical Medicine and Travel (CATMAT) provides the Public Health Agency of Canada (PHAC) with ongoing and timely medical, scientific, and public health advice relating to tropical infectious disease and health risks associated with international travel. PHAC acknowledges that the advice and recommendations set out in this statement are based upon the best current available scientific knowledge and medical practices, and is disseminating this document for information purposes to both travellers and the medical community caring for travellers. Persons administering or using drugs, vaccines, or other products should also be aware of the contents of the product monograph(s) or other similarly approved standards or instructions for use. Recommendations for use and other information set out herein may differ from that set out in the product monograph(s) or other similarly approved standards or instructions for use by the licensed manufacturer(s). Manufacturers have sought approval and provided evidence as to the safety and efficacy of their products only when used in accordance with the product monographs or other similarly approved standards or instructions for use. IntroductionTick-borne encephalitis (TBE) is a viral disease affecting the central nervous system. The etiologic agent, tick-borne encephalitis virus (TBEV), belongs to the family of Flaviviridae (genus Flaviviruses). Like many flaviviruses, it is an arbovirus or arthropod-borne virus. In the tick-borne virus serocomplex, three genotypes of TBEV have been identified: the central European, Far Eastern, and Siberian subtypes1. The virus exists in natural foci, where it circulates between vertebrate and arthropod hosts. The vertebrate hosts of the virus are mainly rodents, but other wild or domestic animals, such as fox, deer, dogs, or cows, may also be infected. The vector-competent hosts are ticks belonging to the family Ixodidae (hard ticks). Many species of hard tick are known to transmit the virus, but two species play a major role in TBEV transmission: Ixodes ricinus and Ixodes persulcatus 2. 2. EpidemiologyIxodes ricinus is widespread in central and western Europe, where it transmits the European TBEV subtype (Central European TBE). Ixodes persulcatus is widely distributed in Russia and the Far East, where it transmits the Siberian and Far Eastern TBEV subtypes (Russian Spring Summer Encephalitis)1,2. Overlapping subtypes exist in eastern European regions. Areas of risk are found through large sections of Europe from eastern France to southern Scandinavia to Croatia, and as far east as northern Japan 2-4. The current epidemiology of TBE has recently been reviewed in detail 2. The Web site of the International Scientific Working group on TBE can be consulted for reports and maps on TBE infections in specific European countries, including Russia (ISW-TBE Reports)5. Another source describing TBE epidemiology in European countries can be found in Eurosurveillance, a publication of the European Community 6. The ticks are distributed in natural foci (hot spots) that tend to be stable over time7. Natural foci are usually in areas of moderate temperature, high humidity, and altitudes of up to 1000 m 8,9. According to some reports, ticks may be found as high as 1400 m10,11. Preferred sites are the edges of forests and areas with deciduous trees, low-growing dense bush, and low ground cover8. Domestic and wild habitats with sufficient moisture, ground foliage, and vegetation litter can provide shelter for both ticks and their animal hosts 9. Tick activity starts in March/April and ends in October/November, usually peaking in the months of May/June and September/October in central Europe 2,8. Surveys of virus prevalence in ticks in natural foci show considerable variability by region and across time. Prevalence rates as low as 0.9% (Bavaria 1997-1998) and as high as 26.6% (Latvia 1995) have been reported in wild-caught ticks(7,12). TBEV prevalence in ticks removed from patients can be higher: for example 31% to 41% from Latvian patients between 1998 and 2002(12). The reason for the discrepancy in prevalence rates between ticks collected in the field and those collected from patients is not certain; however, it is known that TBEV titre in tick saliva increases during the feeding process (see Routes of Transmission). The seroprevalence of TBE in human populations in endemic areas also varies widely. A survey of 1,896 unvaccinated forestry workers in the various counties of Baden-Württemberg (south-west Germany) from 1997 to 1999 showed a mean seroprevalence of 7.3%13. In 2002, TBE seroprevalence rates in the general populations of Lithuania and Denmark (Island of Bornholm) were reported to be 3% and 1.4% respectively14,15. However, with increasing TBE immunization rates in the population, seroprevalence data become less reliable indicators of TBE infection rates. Incidence rates, as well as the number of TBE cases, in several western and eastern European countries for the years 1976 to 2002 can be viewed on the Web site of the ISW-TBE5. The number of reported cases in a country depends on the prevalence of infected ticks, the outdoor activities of the population, and the diagnostic abilities and reporting system of the country. In Austria, a TBE mass vaccination program was introduced in 198116,17. Until then, the average number of TBE cases per year was 500 (range 280 to 700)16. Since 1982, there has been a significant reduction, down to 62 TBE cases in 1998 and 41 cases in 1999(16,17). Although Austria is the only European country to have a routine vaccination program, Hungary has also reported a significant decline in cases from 1996 (n = 224) to 1999 (n = 51). The decline in Hungary is not fully understood but may be due partially to vaccination and partially to declining economic conditions resulting in decreased diagnostic testing2. In many countries without routine vaccination programs, such as Germany and the Czech Republic, the number of cases per year has remained high or has increased over time5. 3. Routes of transmissionIxodes ticks normally have a 3-year life cycle (range 2 to 6 years) as they grow through the following four stages: egg, larva, sexually immature nymph, and sexually mature adult9. Larvae and nymphs feed principally on rodents, and adult ticks tend to feed on larger animals. Ticks can become infected at any stage, including infection through transovarial transmission, and they remain infected for life2. Ticks at all stages are known to bite humans9. Once a tick finds an appropriate host, the attachment and feeding process requires several days. The tick's saliva contains chemicals that counteract the hemostatic, inflammatory, and immune responses of the host. The bite is painless and is often not noticed2,18. The saliva also contains and transmits TBEV2,18. The virus titre in saliva can increase 10 to 100 fold from the first to the third day of the blood meal2. However, transmission typically occurs early in the feeding process2,18. Another, less frequent, route of transmission is the ingestion of unpasteurized milk and milk products2,19. The same ticks (I. ricinus and I. persulcatus) that transmit TBEV can also transmit Borrelia burgdorferi, the agent of lyme borreliosis; Anaplasma phagocytophilum, the agent of human granulocytic ehrlichiosis; Babesia, the agent of babesiosis; and other, rarer, pathogens2,9. Simultaneous infection with multiple organisms is possible. The Web site of the European Union Concerted Action on Lyme Borreliosis can be consulted for further information on Lyme disease in Europe9. 4. Clinical features of tick-borne encephalitisCentral European variety Asymptomatic infection is common. According to different sources, 10% to 30% of infected persons develop symptoms4,20. The incubation period is usually 7 to14 days but ranges from 4 to 28 days20,21. The illness is biphasic. The first phase, which usually resolves within 1 week and correlates with viremia, is frequently subclinical, or it presents as a nonspecific illness with fever, malaise, headaches, nausea, and vomiting20,21. Following a temporary remission of approximately 1 week, in 10% to 30% of individuals there is a second neurologic phase after the virus has spread to the central nervous system20,22. The second stage presents as aseptic meningitis (especially in children) or encephalitis, myelitis, radiculitis, or some combination8. Studies of patients with neurologic illness report that, overall, approximately 50% have meningitis, 40% meningoencephalitis, and 10% meningoencephalomyelitis21,23,24. The diagnosis is usually based on the history of exposure to ticks within the previous 3 to 4 weeks, clinical symptoms, and specific IgM and IgG antibodies to TBE, as measured by enzyme-linked immunosorbent assay (ELISA)4,20,25. Antiviral antibodies are usually detectable at the beginning of the second phase20,25. Other specific tests are nested reverse transcriptase polymerase chain reaction (nRT-PCR) to detect virus-specific nucleic acid, or Western blots, performed in specialized laboratories20,25. There are no effective antiviral drugs for TBEV, therefore treatment consists of supportive care(20,22). The reported case fatality rate is approximately 0.5% to 2%20,22,23. Long-term follow-up studies show that a significant proportion (36% to 94%) of cases have a postencephalitic syndrome for months to years after the acute illness, characterized by neuro-psychiatric symptoms such as asthenia, severe headaches, memory loss, lack of concentration, decreased stamina, depression, ataxia, incoordination, tremor, and/or hearing impairment22,24. Residual paresis has been reported in 0.3% to 10% of patients21,22. Residual neurologic sequelae are more likely to occur in the elderly and in those with severe disease4,8. Children have a generally better prognosis than adults21. Far Eastern variety The course of this disease is monophasic and more severe, with rapid neurologic involvement. The case fatality rate is 20%, and residual neurologic sequelae occur in up to 60% of survivors8. 5. Methods of preventionThe probability of human infection in an area with a natural TBEV focus depends on the prevalence of infected ticks, human exposure to ticks, and the preventive measures taken. Environmental and personal protective measures, such as wearing clothing with a smooth weave, taping pants or tucking them inside footwear, applying DEET (N,N-diethyl-3-methylbenzamide), and using permethrin-impregnated clothing, help to minimize the risk of tick bites26-28. Permethrin appears to be more effective than DEET, but the combination of DEET and permethrin gives almost 100% protection26-28. If a tick bite has occurred, proper removal of the tick, as outlined under Recommendations, may decrease the risk of viral transmission29 but will not prevent all cases because of early viral transmission of the virus during a blood meal2,18. Recommendations regarding environmental and personal protective measures are listed under Recommendations. Personal protective measures for the prevention of arthropod bites are fully described in CATMAT's Statement on Personal Protective Measures to Prevent Arthropod Bites30. 6. ImmunizationCanadians residing in or travelling to TBE-endemic areas should be evaluated for their risk of tick bites (see Recommendations). Since TBE vaccination is safe and highly immunogenic, it should be recommended for travellers considered to be at risk31. 6.1 Pre-exposure active immunizationTwo TBE vaccines, available in Europe, will be discussed: Encepur® adults (and Encepur® children) marketed by Chiron Vaccines, Germany, and FSME-IMMUN®0.5 mL (and FSMEIMMUN ® 0.25 mL Junior) by Baxter Vaccine AG, Austria. Both are inactivated vaccines and provide safe and reliable protection17,32,33. Immunity is induced against all TBEV variants, including the European and Far Eastern subtypes34. The antigenic components of the two available vaccines (virus strain K23 of Encepur® and strain Neudoerfl of FSMEIMMUN ®) are highly homologous and can be assumed to elicit the same immune response35. In one study, > 400 subjects previously vaccinated with at least three doses of FSME-IMMUN® were successfully boosted with Encepur®36. The result suggests that the strains are interchangeable. The main manufacturing characteristics of the currently available vaccines are detailed in Table 1. Table 1. Product characterization of vaccines referred to in text
The vaccination schedules, immunogenicity, and safety data of the FSME-IMMUN® and Encepur® vaccines are summarized in Table 2. Table 2. Summary of vaccine characteristics of FSME-IMMUN® and Encepur®
FSME-IMMUN® 0.5 mL and FSME-IMMUN® 0.25 mL Junior (Baxter Vaccine AG)FSME-IMMUN® was approved in Austria in 1976 and has been widely used for many years33. It was reformulated in 1999 to eliminate mouse brain passage during manufacture33. It is now marketed under the name FSME-IMMUN® 0.5 mL for those ≥ 16 years and FSME-IMMUN® 0.25 mL Junior for children 1 to 15 years of age (Summaries of Product Characteristics for FSME-IMMUN® 0.5 mL/FSME-IMMUN® 025 mL: unpublished work, Baxter Vaccine AG, Vienna, February 2004). It is a suspension of formaldehyde-inactivated TBEV (strain Neudoerfl) propagated in chick embryo cells. It is adsorbed onto aluminum hydroxide and contains 0.5 mg (junior 0.25 mg) human serum albumin as stabilizer and residues of protamine sulphate, gentamicin, neomycin, and formaldehyde33. It is thimerosal-free. Each preloaded syringe contains a 0.5 mL (junior 0.25 mL) suspension and has a shelf life of 24 months when stored at 2° C to 8° C33. Many of the data upon which current recommendations are made were generated with the earlier formulation of FSME-IMMUN®. The efficacy and safety profiles of the earlier and current formulations appear to be very similar. Scheduling and route of administrationThe manufacturer’s recommendations with regard to primary and booster vaccinations for adults and children are stated in the Summaries of Products Characteristics for FSME-IMMUN® 0.5 mL and FSME-IMMUN® 0.25 mL Junior. The manufacturer recommends administration of a primary immunization series in three doses, at 0, 1 to 3 months, and 6 to 15 months (conventional schedule). The vaccine is given intra-muscularly into the deltoid muscle. If a rapid immune response is required, the second dose should be given 2 weeks after the first dose. Recommendations regarding booster intervals have recently been published in the Austrian immunization plan37 and are based on the results of a recent cross-sectional study38. For at risk adults < 60 years of age, the first booster dose should be given 3 years after the third dose of the primary series. Thereafter, booster intervals of 5 years are recommended. For those aged ≥ 60, booster doses are recommended every 3 years. For booster intervals exceeding 10 years, the Austrian immunization plan recommends administration of one dose with verification of TBE antibody titres 4 weeks later37 (see section 6.3). However, this recommendation is not supported by a recent cross-sectional study, which indicated that a single booster dose is generally successful, regardless of the time interval following the last vaccination36. The TBE vaccines are therefore similar to other inactivated alum-adsorbed viral vaccines in that a single booster usually re-establishes full protection independently of the time interval following the primary series. Since long-term studies are not yet available for children, booster intervals of 3 years are recommended when administering the pediatric vaccine. The vaccination series should ideally be started in winter. Effective immunity will then be present at the start of the tick season. Protective efficacy, immunogenicity, and safetyProtective efficacy: The efficacy (protection) rates of previous generation FSME-IMMUN® vaccines administered on day 0, at 2 weeks to 3 months, and at 9 to 15 months have been calculated for the Austrian population to be 95.6% to 100% after the second and 96% to 98.7% after the third vaccine dose17. No other efficacy studies could be found for TBE vaccines. Immunogenicity after primary immunization:The immunogenicity and safety of FSME-IMMUN® in adults and children receiving primary vaccination have been evaluated in several large studies sponsored by Baxter. These studies are listed in Appendix 1. Some of them have been described in a recent review article and in brief abstracts33,39,40. In these studies, the adult and pediatric vaccines were administered on day 0, at 21 to 35 weeks, and between 6 months and 10 months. Seroconversions were measured by both enzyme-linked immunoassay (EIA) and neutralization test approximately 1 month after vaccination. In adults, the seroconversion rates after the second and third doses were found to be 92.9% to 97% and 100% respectively (Appendix 1: studies #062, #201, #202). In children, depending on their age, the seroconversion rates were 98.5% to 100% and 100% after the second and third doses respectively (Appendix 1: studies #199, 205, 206, 207). The manufacturer’s recommendation for an accelerated schedule, in which the second dose is given 2 weeks after the first, is supported by one published pediatric study. In this study, of 37 children aged 8 to 14 years who were vaccinated on day 0 and 10, 95% had seroconverted at 2 weeks after the second dose, as measured by EIA41. Long-term immunogenicity: Long-term immunogenicity has been assessed in a cross-sectional study of 430 previously vaccinated adults immunized with earlier generation FSME-IMMUN® vaccines. The authors concluded that, following a primary vaccination and ≥ 1 booster dose, the immune protection exceeded 3 years and appeared to be sufficient for up to 8 years after the last booster dose38. Safety: The current FSME-IMMUN® 0.5 mL vaccine and its earlier versions have an excellent safety record after 20 years of widespread use according to both published17,33,42,43 and unpublished studies (Appendix 1). In adults and children, adverse reactions are typically transient local reactions classified as mostly mild to moderate. Fever and other systemic reactions, such as headaches, malaise, dizziness, anorexia, nausea, vomiting, diarrhea, and myalgia are also reported in a small proportion of vaccinees. In study #062 (Appendix 1), of a total study population of almost 1,200 adults approximately 300 subjects were randomly assigned to the group receiving the FSME-IMMUN® 0.5 mL vaccine. After the first dose, 29.9% of this group reported local and systemic adverse events compared with 19.5% of the placebo group (11.1% versus 7.3% respectively after the second dose). In another single-blind, randomized safety study (Appendix 1: #208) involving ≥ 3,700 adults, the current formulation of FSME-IMMUN® 0.5 mL was compared with an earlier version of the Encepur® vaccine, containing polygeline as stabilizer. Neither vaccine caused any serious adverse effects, although FSME- IMMUN® 0.5 mL had fewer adverse effects overall than Encepur®. In a study of 2,400 children aged 1 to < 16 years (Appendix 1: study #209), the incidence of adverse effects after the first (second) vaccine doses were reported by age group:
No severe adverse effects were reported to be causally related to the vaccinations. Following the administration of earlier generation FSME vaccines that had been passaged in suckling mouse brain, there were very rare, sporadic reports of neurologic complications, such as convulsion, neuritis of various degrees of severity (not further specified), polyradiculopathy, gait ataxia, hearing and balance disorders, meningitis, or encephalitis42-44. Neurologic complications associated with these earlier formulations have been estimated to occur in 1:500,000 to 1:1,000,000 vaccinations43. No similar reactions have been reported with the current FSME-IMMUN® formulation. FSME-IMMUN® 0.5 mL and its pediatric version, distributed in Europe, contain a small amount of human serum albumin (HSA) of European (German or Austrian) origin. As a result, there is a theoretical risk of transmitting the prion that causes variant Creutzfeldt-Jakob disease (vCJD). No risk assessment is available for vaccines containing HSA of European origin. However, a generic risk assessment of vaccines incorporating bovine biological materials in their manufacture suggests that any such risk is likely to be extremely small: < 1 in 100 million vaccine doses (El Saadany S, Giulivi A. Preliminary quantitative risk assessment respecting vCJD in relation to Canadian vaccines incorporating bovine biological materials in their manufacture: unpublished work, Health Canada, Bloodborne Pathogens Division, Ottawa, 2002). Health Canada licensing regulations require that products containing plasma-derived substances use materials that originate from Canadian or US donors. A FSME-IMMUN® vaccine containing HSA of North American origin is approved for sale in Canada (see Availability of TBE vaccines in Canada). Encepur® adults and Encepur® children (Chiron vaccines)Encepur® and Encepur® K for children were registered in Germany in 1991 and 1994 respectively45. Several clinical trials demonstrated the general immunogenicity and safety of these early formulations46-48. However, post-marketing surveillance revealed that children had an increased frequency of allergic reactions, which were likely due to polygeline, a proteinaceous stabilizer in the vaccine33,45. A polygeline-free TBE vaccine under the names of Encepur® adults and Encepur® children was subsequently introduced and evaluated in prospective, controlled, multi-centre clinical trials45,49,50. These formulations have been on the market since 2001 and are sold in several European countries. Encepur® children is recommended for children between 1 and 11 years of age32. The Encepur® vaccines are a suspension of formaldehyde-inactivated TBEV (strain K23), grown on chick embryo fibroblasts32. The adjuvant is aluminum hydroxide. There are trace amounts of formaldehyde, chlortetracycline, gentamicin, and neomycin in the solution. The current formulations contain no proteinderived stabilizers (e.g. HSA) and no polygeline. Preloaded syringes contain 1.5 µg/0.5 mL TBE antigen (adult) and 0.75 µg/ 0.25 mL TBE antigen (children). The vaccine should be stored between +2º C and +8º C and has a shelf life of ~15 months32 (Summary of Product Characteristics Encepur® adults/Summary of Product Characteristics Encepur® children: unpublished work, Chiron Behring GMBH & Co Kg, Marburg, Germany, June 2004). Scheduling and route of administrationThe vaccine is administered intramuscularly, preferably into the deltoid muscle. Like FSME, Encepur® vaccines can be administered according to a conventional or an accelerated schedule, both offering high protection47,49,50. According to the conventional vaccination schedule, the primary vaccination consists of three doses, on day 0, 1 to 3 months, and 9 to 12 months. If risk of exposure continues, the manufacturer recommends booster doses every 3 years32. In most clinical trials of Encepur® vaccines, the accelerated schedule has been used with three doses given on day 0, 7, and 21. After the accelerated schedule, the first booster dose is administered at 12 to 18 months. It should be noted that the recent recommendations of the 2005 Austrian Immunization Guide with regard to longer booster intervals for individuals < 60 years of age apply to both FSME-IMMUN® and Encepur® vaccines(37) (see section on FSME-IMMUN® 0.5 mL and FSME-IMMUN® 0.25 mL Junior). Immunogenicity and safety of Encepur® vaccinesSeveral large clinical trials to investigate the immunogenicity and safety of Encepur® vaccines in subjects 12 to 76 year old (adult formulation: n = > 3,000) and in children 1 to 11 years old (pediatric formulation: n = 390 for immunogenicity and > 3,000 for safety). All subjects were vaccinated on day 0, 7, and 2149,50. Immunogenicity after primary immunization: After the administration of the primary series, seroconversion, as measured by the neutralization test, occurred in 100% of adult and pediatric subjects49,50. Long-term immunogenicity: Several studies have demonstrated the long-term persistence of high (presumably protective) titres after primary vaccination: 99.5% and 100% immediately before the first (12 to 18 month) and second (36 month) booster doses respectively51-53. These results support a recommended booster interval of > 3 years54. Safety: The reported adverse reactions following vaccination with Encepur® vaccines include local reactions and systemic reactions such as fever, malaise, headaches, myalgia, arthralgia, nausea in children ≥ 3 years and adults49,50. Systemic symptoms are mostly mild and transient, and are reported in 1% (fever in adults) to 18% (myalgia in adults)49. A small percentage (< 1% to 5%) of these adverse events are moderate to severe in nature (i.e. they cause temporary impairment in daily activities)49,50. Systemic reactions in children 1 to 2 years old have been mainly fever, sleepiness, irritability, or change in eating habits (reported in 8% to 14%, depending on symptom reported)50. In the large clinical trials conducted to date, there were no reports in adults or children of serious clinical events, such as seizures, or of systemic allergic reactions, considered to be causally related to the vaccinations32,49,50. Rare and isolated cases of central or peripheral nervous system complications, such as ascending paralysis, in severe cases with respiratory paralysis, have been reported following vaccination with previous generation Encepur® vaccines (summaries of the product characteristics of Encepur® vaccines). Special considerations for the FSME-IMMUN® and Encepur® vaccinesAllergies The viral strains of the TBE vaccines are propagated in purified chick embryo cells(32,33. Although purified, both of the available vaccines may still contain egg constituents. The summaries of product characteristics for the FSME-IMMUN® and Encepur® vaccines advise that individuals with prior anaphylactic reactions to eggs or egg products should be vaccinated only under close clinical monitoring with readiness for emergency treatment. However, FSME-IMMUN® vaccine has apparently been safely administered to > 100 persons with allergies to egg whites (note that the types of egg allergy were not described in this study)55. Impaired immune system Immunosuppressed individuals may respond poorly to TBE vaccination56-58. If they are at risk of TBE, it may be appropriate to determine their immune response after the primary series by serologic testing (where available)58 (see Testing for Antibodies after TBE Vaccination). There are no guidelines for evidencebased recommendations concerning the timing of serologic testing in immunocompromised individuals. Pregnancy and lactation According to the summaries of product characteristics of the FSME-IMMUN® and Encepur® vaccines, the safety of the TBE vaccines during pregnancy and lactation has not been established. An individual risk-benefit assessment is required in these cases. 6.2 Availability of TBE vaccines in CanadaThe FSME-IMMUN® 0.5 mL vaccine has been approved for sale in Canada as of 3 February, 2005, and is available on the Canadian market. The distributor of FSME-IMMUN® in Canada is Baxter Corporation (Mississauga) .The pediatric FSME vaccine and the Encepur® products are not licensed and not available in Canada. Until one of the pediatric formulations is licensed in Canada, there are two options possible, namely to procure a European licensed pediatric product through the Special Access Program (SAP) or to use a half-dose of the adult FSME vaccine to immunize children < 16 years of age. If the latter option is used, the vaccinees and their parents should be advised that the distribution of antigen in the vaccine portions may not be even. The main concern is the possibility of inadequate protection against TBE if the administered vaccine portion contains insufficient antigen. 6.3 Testing for antibodies after TBE vaccination
The EIA for IgG antibodies is a rapid and reliable test for TBE
immunity. It is commonly used to assess immunity after an
infection or vaccination25. A comparison of six commercial IgG
ELISA kits suggests that they have generally high sensitivity (73%
to 99%)59. However, there is extensive cross-reactivity with other
flavivirus antibodies, such as West Nile fever, dengue, yellow
fever, and Japanese encephalitis antibodies25,60,61. These crossreactive
antibodies do not neutralize TBEV and are not protective
against TBE infections60,61. Therefore, when interpreting positive
EIA results, consideration must be given to possible crossreactivity
with other flaviviruses. False-positive results can be
minimized by taking a proper history of past flavivirus exposures
and/or vaccinations. Alternatively, if available, a pre-vaccination
EIA can establish a baseline, or a highly specific and sensitive
neutralization test can be used25,60,61. The neutralization test,
which measures the presence of TBE-specific neutralizing antibodies,
is only available in specialized laboratories (Dr. H. Peters
Dade Behring, Marburg, Germany: personal communication,
2002). In the absence of prior exposure to other flaviviruses, IgG
EIA results for TBE correlate well with the results of the neutralization
test25,61,62. According to Health Canada’s Medical Devices
Active Licence Listing (http://www.mdall.ca 7. RecommendationsTo identify travellers who are at risk of contracting the TBE virus, travel medicine professionals should consider the season of travel, travel itinerary, and the activities of the traveller.
Travellers meeting all of these criteria should be advised regarding prevention of tick bites, tick removal, and vaccination. Table 3 presents the evidence-based categories for the strength and quality of evidence for the following recommendations63. Table 3. Strength and quality of evidence summary sheet63
Environmental methods
Personal preventive means after a tick bite has occurred
Serology
ExpirationThis document will be updated every 4 years or when new information becomes available. AcknowledgementsCATMAT gratefully acknowledges the assistance in the preparation of this statement from Dr. Michael Bröker, Chiron Vaccines, Marburg; Dr. Eva Maria Poellabauer, Baxter Bioscience, Vienna; Dr. Jochen Süss, Nat. Ref.-Lab., Tick-borne Diseases, Federal Research Centre for Virus Diseases in Animals, Jena, Germany. References
Appendix 1Immunogenicity and safety studies involving the vaccines FSME-IMMUN® 0.5 mL and FSME-IMMUN® 0.25 mL Junior, sponsored by Baxter Vaccines AG.
[Canada Communicable Disease Report]
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