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Significant increase of hantavirus infections in Germany since the beginning of 2007
J Koch (KochJ@rki.de)<SUP>1</SUP>, SO Brockmann<SUP>2</SUP>, C Winter<SUP>2</SUP>, P Kimmig<SUP>2</SUP>, K Stark<SUP>1</SUP>
1. Robert Koch-Institut, Berlin, Germany
2. Staatliches Gesundheitsamt (State Health Office), Baden-Wuerttemberg, Stuttgart, Germany
Hantaviruses (family Bunyaviridae) are rodent-borne pathogens and occur worldwide. Hantavirus infections in Europe and Asia can result in a hemorrhagic fever with renal syndrome (HFRS) of different severity. In Germany, the predominant species is Puumala virus. Its main reservoir are bank voles (Myodes glareolus), which predominantly live in forested areas dominated by deciduous trees.
The disease is characterised by an abrupt onset, and the major symptoms include fever, abdominal pain and other gastrointestinal symptoms, headache, and back pain. Patients occasionally develop acute renal failure that may require haemodialysis. The virus is transmitted to humans through inhalation of aerosolised rodent faeces. It is reported that in endemic areas the incidence of hantavirus infections among humans is related to the size of the bank vole population and prevalence of the virus [1]. Peaks in the bank vole population occur every three to four years and may result in an increase in human cases.
In Germany, the number of notified hantavirus infections has considerably increased since the beginning of the year 2007. Laboratory-confirmed symptomatic hantavirus infections are mandatorily notifiable since 2001 [2]. Laboratory diagnosis is based either on detection of nucleic acid, a marked rise of IgG-antibodies in a paired sample, or detection of IgM- or IgA-antibodies confirmed by IgG-antibodies.
In the period from 1 January 2007 to 15 April 2007, 164 symptomatic hantavirus cases were reported to the Robert Koch-Institute. In the comparable time period of the years 2001 to 2006, the mean number of reported cases was only 38 (minimum: 13 cases in 2006, maximum: 88 cases in 2005; Figure 1).
Figure 1. Reported Hantavirus infections per week (minimum and maximum 2001-2006, absolute number 2007), Germany
Of the 164 symptomatic hantavirus cases, 127 (77%) were male and 115 (70%) were between 30 and 59 years old. No hantavirus cases were reported in children younger than 10 years of age. Age and sex distribution of hantavirus cases in 2007 was not different to previous years. In the years 2001 to 2006, a total of 1,319 cases were reported (73% males, 68% aged 30-59 years). All hantavirus diseases (with known species) in 2007 were caused by Puumala virus (n=157), for seven (4%) cases the causative virus could not be specified.
The majority of infections in 2007 (127, 77%) were acquired in Baden-Wuerttemberg, a federal state in the south-west of Germany. Further cases were observed in Bavaria (19 cases), North-Rhine-Westphalia (9 cases), Lower Saxony (7 cases), Hesse (1 case) and Mecklenburg Western-Pomerania (1 case) (Figure 2). Hantavirus cases in Baden-Wuerttemberg were mostly residents of the Swabian Alb or their neighbouring regions, an area which is known to be endemic for hantavirus infections [2,3,4].
Figure 2. Incidence of reported hantavirus infections per 100,000 inhabitants by administrative district, Germany, 2007 (incidence referring to weeks 1 to 16)
Figure 3 shows the number of hantavirus cases by month of reporting since the beginning of 2001. The incidence fluctuated substantially in different years and generally reached a maximum between May and August. Years of high incidence such as 2005 alternate with years of low activity such as 2006.
Figure 3. Reported hantavirus infections per months 2001-2007, Germany and Baden-Wuerttemberg
The patterns of hantavirus activity over time show not only a significant variation in the incidence but also in the regional distribution. Since the beginning of 2001, a total of 1,487 laboratory-confirmed symptomatic hantavirus infections have been reported to the Robert Koch Institute of which 670 (45%) occurred in Baden-Wuerttemberg. Annual incidence rates in the years 2001 to 2006 were highest for Baden-Wuerttemberg, which reflects hantavirus activity in the known endemic area of Baden-Wuerttemberg (Table) [5,6].
Table. Annual hantavirus incidence rates (Germany and Baden-Wuerttemberg, 2001-2006) <TABLE border=1><TBODY><TR><TD bgColor=#ffffcc> </TD><TD bgColor=#ffffcc colSpan=2>
The increase of hantavirus infections in 2007 started early. Such an early increase of cases had also been observed in 2002. Throughout the whole year 2002, most cases (72%) continued to occur in Baden-Wuerttemberg. In 2005, however, a year with an early case increase and with the highest hantavirus activity so far, high numbers of cases were also diagnosed in many other federal states, including areas previously not known to be endemic such as urban settings [7,8]
In the past, the incidence of human hantavirus infections in Germany seems to be correlated with the size of the bank vole populations. The population in endemic areas shows annual fluctuations. Usually, the bank vole population that comes into contact with humans reaches its maximum size in the summer. The winter season 2006/2007, however, was exceptionally mild and in many endemic regions there was no snow cover on the ground. In addition, there was an abundant supply of beech mast in the autumn of 2006. Under such conditions rodents have high survival rates and breed earlier. This may have lead to an early increase in the bank vole population and probably also to a higher hantavirus prevalence. Moreover, humans may have been more exposed to rodent droppings due to increased outdoor activities (recreational and occupational) in forests and gardens resulting in higher case numbers during the winter season 2006/07. It is unclear, however, why the hantavirus infections among humans so far appear to be restricted to the endemic area in Baden-Wuerttemberg. To specifically address questions about risk factors in humans, population size and Puumala virus prevalence in bank voles, Public Health authorities in Baden-Wuerttemberg have started further investigations in collaboration with the Robert Koch Institute. If the actual hantavirus continuous to be mainly restricted to Baden-Wuerttemberg it will be interesting to identify factors responsible for this phenomenon. A case-control study has been initiated to identify risk factors for human infection, and bank vole trapping will give insight in the currently circulating Puumala virus subtypes in the rodent population and a rough overview of the population size. A press release was issued in April 2007 to inform the public about the situation and to give recommendations for the prevention of exposure to hantavirus [9]. For a better understanding of the bank vole population dynamics as well as epidemiologic patterns and risk factors of human hantavirus infections in Germany, monitoring of the reservoir and further epidemiologic studies among humans will be necessary.
References:
J Koch (KochJ@rki.de)<SUP>1</SUP>, SO Brockmann<SUP>2</SUP>, C Winter<SUP>2</SUP>, P Kimmig<SUP>2</SUP>, K Stark<SUP>1</SUP>
1. Robert Koch-Institut, Berlin, Germany
2. Staatliches Gesundheitsamt (State Health Office), Baden-Wuerttemberg, Stuttgart, Germany
Hantaviruses (family Bunyaviridae) are rodent-borne pathogens and occur worldwide. Hantavirus infections in Europe and Asia can result in a hemorrhagic fever with renal syndrome (HFRS) of different severity. In Germany, the predominant species is Puumala virus. Its main reservoir are bank voles (Myodes glareolus), which predominantly live in forested areas dominated by deciduous trees.
The disease is characterised by an abrupt onset, and the major symptoms include fever, abdominal pain and other gastrointestinal symptoms, headache, and back pain. Patients occasionally develop acute renal failure that may require haemodialysis. The virus is transmitted to humans through inhalation of aerosolised rodent faeces. It is reported that in endemic areas the incidence of hantavirus infections among humans is related to the size of the bank vole population and prevalence of the virus [1]. Peaks in the bank vole population occur every three to four years and may result in an increase in human cases.
In Germany, the number of notified hantavirus infections has considerably increased since the beginning of the year 2007. Laboratory-confirmed symptomatic hantavirus infections are mandatorily notifiable since 2001 [2]. Laboratory diagnosis is based either on detection of nucleic acid, a marked rise of IgG-antibodies in a paired sample, or detection of IgM- or IgA-antibodies confirmed by IgG-antibodies.
In the period from 1 January 2007 to 15 April 2007, 164 symptomatic hantavirus cases were reported to the Robert Koch-Institute. In the comparable time period of the years 2001 to 2006, the mean number of reported cases was only 38 (minimum: 13 cases in 2006, maximum: 88 cases in 2005; Figure 1).
Figure 1. Reported Hantavirus infections per week (minimum and maximum 2001-2006, absolute number 2007), Germany
Of the 164 symptomatic hantavirus cases, 127 (77%) were male and 115 (70%) were between 30 and 59 years old. No hantavirus cases were reported in children younger than 10 years of age. Age and sex distribution of hantavirus cases in 2007 was not different to previous years. In the years 2001 to 2006, a total of 1,319 cases were reported (73% males, 68% aged 30-59 years). All hantavirus diseases (with known species) in 2007 were caused by Puumala virus (n=157), for seven (4%) cases the causative virus could not be specified.
The majority of infections in 2007 (127, 77%) were acquired in Baden-Wuerttemberg, a federal state in the south-west of Germany. Further cases were observed in Bavaria (19 cases), North-Rhine-Westphalia (9 cases), Lower Saxony (7 cases), Hesse (1 case) and Mecklenburg Western-Pomerania (1 case) (Figure 2). Hantavirus cases in Baden-Wuerttemberg were mostly residents of the Swabian Alb or their neighbouring regions, an area which is known to be endemic for hantavirus infections [2,3,4].
Figure 2. Incidence of reported hantavirus infections per 100,000 inhabitants by administrative district, Germany, 2007 (incidence referring to weeks 1 to 16)
Figure 3 shows the number of hantavirus cases by month of reporting since the beginning of 2001. The incidence fluctuated substantially in different years and generally reached a maximum between May and August. Years of high incidence such as 2005 alternate with years of low activity such as 2006.
Figure 3. Reported hantavirus infections per months 2001-2007, Germany and Baden-Wuerttemberg
The patterns of hantavirus activity over time show not only a significant variation in the incidence but also in the regional distribution. Since the beginning of 2001, a total of 1,487 laboratory-confirmed symptomatic hantavirus infections have been reported to the Robert Koch Institute of which 670 (45%) occurred in Baden-Wuerttemberg. Annual incidence rates in the years 2001 to 2006 were highest for Baden-Wuerttemberg, which reflects hantavirus activity in the known endemic area of Baden-Wuerttemberg (Table) [5,6].
Table. Annual hantavirus incidence rates (Germany and Baden-Wuerttemberg, 2001-2006) <TABLE border=1><TBODY><TR><TD bgColor=#ffffcc> </TD><TD bgColor=#ffffcc colSpan=2>
Incidence rates
</TD></TR><TR><TD bgColor=#ffffcc>Year </TD><TD bgColor=#ffffcc>Germany</TD><TD bgColor=#ffffcc>Baden-Wuerttemberg</TD></TR><TR bgColor=#99ffff><TD>2001</TD><TD>0.22</TD><TD>0.55</TD></TR><TR bgColor=#ffffcc><TD>2002</TD><TD>0.28</TD><TD>1.53</TD></TR><TR bgColor=#99ffff><TD>2003</TD><TD>0.17</TD><TD>0.61</TD></TR><TR bgColor=#ffffcc><TD>2004</TD><TD>0.29</TD><TD>1.12</TD></TR><TR bgColor=#99ffff><TD>2005</TD><TD>0.54</TD><TD>1.02</TD></TR><TR bgColor=#ffffcc><TD>2006</TD><TD>0.09</TD><TD>0.20</TD></TR></TBODY></TABLE>The increase of hantavirus infections in 2007 started early. Such an early increase of cases had also been observed in 2002. Throughout the whole year 2002, most cases (72%) continued to occur in Baden-Wuerttemberg. In 2005, however, a year with an early case increase and with the highest hantavirus activity so far, high numbers of cases were also diagnosed in many other federal states, including areas previously not known to be endemic such as urban settings [7,8]
In the past, the incidence of human hantavirus infections in Germany seems to be correlated with the size of the bank vole populations. The population in endemic areas shows annual fluctuations. Usually, the bank vole population that comes into contact with humans reaches its maximum size in the summer. The winter season 2006/2007, however, was exceptionally mild and in many endemic regions there was no snow cover on the ground. In addition, there was an abundant supply of beech mast in the autumn of 2006. Under such conditions rodents have high survival rates and breed earlier. This may have lead to an early increase in the bank vole population and probably also to a higher hantavirus prevalence. Moreover, humans may have been more exposed to rodent droppings due to increased outdoor activities (recreational and occupational) in forests and gardens resulting in higher case numbers during the winter season 2006/07. It is unclear, however, why the hantavirus infections among humans so far appear to be restricted to the endemic area in Baden-Wuerttemberg. To specifically address questions about risk factors in humans, population size and Puumala virus prevalence in bank voles, Public Health authorities in Baden-Wuerttemberg have started further investigations in collaboration with the Robert Koch Institute. If the actual hantavirus continuous to be mainly restricted to Baden-Wuerttemberg it will be interesting to identify factors responsible for this phenomenon. A case-control study has been initiated to identify risk factors for human infection, and bank vole trapping will give insight in the currently circulating Puumala virus subtypes in the rodent population and a rough overview of the population size. A press release was issued in April 2007 to inform the public about the situation and to give recommendations for the prevention of exposure to hantavirus [9]. For a better understanding of the bank vole population dynamics as well as epidemiologic patterns and risk factors of human hantavirus infections in Germany, monitoring of the reservoir and further epidemiologic studies among humans will be necessary.
References:
- Olsson GE, White N, Hjalten J, Ahlm C. Habitat factors associated with bank voles (Clethrionomys glareolus) and concomitant hantavirus in northern Sweden. Vector Borne Zoonotic Dis 2005;5(4):315-23.
- RKI: Hantavirus-Erkrankungen: Deutliche Zunahme zu Beginn des Jahres 2007 in S?ddeutschland. [In German]. Epid Bull 2007;14:120. Available from: http://www.rki.de/cln_049/nn_264978/DE/Content/Infekt/EpidBull/Archiv/2007/14__07,templateId=raw,property=publicationFile.pdf/14_07.pdf
- Ulrich R, Meisel H, Sch?tt M, Schmidt J, Kunz A, Klempa B, et al. Verbreitung von Hantavirusinfektionen in Deutschland. [In German]. Bundesgesundheitsblatt 2004;47: 661-670.
- Kimmig P, Silva-Gonzalez R, Backe H, Brockmann S, Oehme R, Ernst E, Mackenstedt U. Epidemiologie der Hantaviren in Baden-Wuerttemberg. [In German]. Gesundheitswesen 2001;63(2):107-12.
- RKI: Hantavirus-Erkrankungen im Zeitraum 2001 bis 2005. [In German]. Epid Bull 2006;40:341-343. Available from: http://www.rki.de/cln_049/nn_196436/DE/Content/Infekt/EpidBull/Archiv/2006/40__06,templateId=raw,property=publicationFile.pdf/40_06.pdf
- Z?ller L, Faulde M, Meisel H, Ruh B, Kimmig P, Schelling U, Zeier M, Kulzer P, Becker C, Roggendorf M, Bautz EKF, Kr?ger DH, Darai G. Seroprevalence of hantavirus antibodies in Germany as determined by a new recombinant enzyme immunoassay. Eur J Clin Microbiol Inf Dis 1995;14:303-315.
- Mailles A, Abu Sin M, Ducoffre G, Heyman P, Koch J, Zeller H. Larger than usual increase in cases of hantavirus infections in Belgium, France and Germany, June 2005. Euro Surveill 2005;10 (7):E050721.4. Available from: http://www.eurosurveillance.org/ew/2005/050721.asp#4
- RKI: Bundesweite Fall-Kontroll-Studie zu Verbreitung und Risikofaktoren von Hantavirus-Infektionen. [In German]. Epid Bull 2006;40:344-346. Available from: http://www.rki.de/cln_049/nn_196436/DE/Content/Infekt/EpidBull/Archiv/2006/40__06,templateId=raw,property=publicationFile.pdf/40_06.pdf
- Landesgesundheitsamt Baden-Wuerttemberg: H?ufung von Hantavirus-Erkrankungen in Baden-W?rttemberg, Landesgesundheitsamt informiert ?ber die Hintergr?nde. 27.04.2007. [In German]. http://www.gesundheitsamt-bw.de/servlet/PB/menu/1133583_l1/index.html#pressemitteilungen
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