In Search for Factors that Drive Hantavirus Epidemics

Abstract

In Europe, hantaviruses (Bunyaviridae) are small mammal-associated zoonotic and emerging pathogens that can cause hemorrhagic fever with renal syndrome (HFRS). Puumala virus, the main etiological agent carried by the bank vole Myodes glareolus is responsible for a mild form of HFRS while Dobrava virus induces less frequent but more severe cases of HFRS. Since 2000 in Europe, more than 3000 cases of HFRS have been recorded, in average, each year, which is nearly double compared to the previous decade. In addition to this upside long-term trend, significant oscillations occur. Epidemic years appear, usually every 2-4 years, with an increased incidence, generally in localized hot spots. Moreover, the virus has been identified in new areas in the recent years. A great number of surveys have been carried out in order to assess the prevalence of the infection in the reservoir host and to identify links with different biotic and abiotic factors. The factors that drive the infections are related to the density and diversity of bank vole populations, prevalence of infection in the reservoir host, viral excretion in the environment, survival of the virus outside its host, and human behavior, which affect the main transmission virus route through inhalation of infected rodent excreta. At the scale of a rodent population, the prevalence of the infection increases with the age of the individuals but also other parameters, such as sex and genetic variability, interfere. The contamination of the environment may be correlated to the number of newly infected rodents, which heavily excrete the virus. The interactions between these different parameters add to the complexity of the situation and explain the absence of reliable tools to predict epidemics. In this review, the factors that drive the epidemics of hantaviruses in Middle Europe are discussed through a panorama of the epidemiological situation in Belgium, France, and Germany.

Keywords: Belgium; France; Germany; HFRS; NE; abiotic factors; biotic factors; hantavirus.

Figure 1

Yearly number of hantavirus cases in Belgium as diagnosed by the Reference Laboratory for Vector-Borne disease, Brussels. The epidemic years are depicted in red, the non-epidemic years in blue.

Figure 2

Average of seasonal hantavirus cases and seasonal distribution (calculated as deviation from the average) in Belgium for the years 1991–2011. (A) Months January to March with an average of 25 cases, (B) months April to June with an average of 36 cases, (C) months July to September with an average of 40 cases, (D) months October to December with an average of 26 cases.

Figure 3

Oak (Quercus robur) and Beech (Fagus sylvatica) mast years, hantavirus cases, and seroprevalence in M. glareolus during the period 1999–2008.

Figure 4

Climatic conditions in Belgium according to Tricot et al. (2009).

Figure 5

Masting events and masting species (Source: Comptoir forestier de Wallonie).

Figure 6

Geographic distribution of human Puumala hantavirus infections in France (Source: French Ministry of health).

Figure 7

Incidence rate of hantavirus infections in France, according to the department of residence of the patients (Source: Institut de Veille sanitaire, IVS).

Figure 8

Number of hantavirus infections in France during the period 1987 – July 2010 (data: Institut de Veille Sanitaire, IVS).

Figure 9

Number (graph in blue) and proportion of positive results (curve in red) of hantavirus infections in France, period 1987–2003 (data: Institut de Veille Sanitaire, IVS).

Figure 10

Distribution per month of the hantavirus cases in France during the period 2001–2009 (data: Institut de Veille Sanitaire, IVS).

Figure 11

Yearly number of hantavirus cases in Germany. Source of data is the SurvStat of the Robert Koch-Institut Data available from http://www3.rki.de/SurvStat, data as of January 25th, 2012, RKI (2012).

Figure 12

Germany: map with hantavirus cases/100.000 inhabitants January 1st 2001–January 1st 2012. Some hot spot regions for PUUV infections are numbered: 1 –Swabian Alb, 2- Lower Bavaria, 3-Main-Spessart, 4-Osnabrück, 5-Cologne, 6-Stuttgart. Source of data is the SurvStat of the Robert Koch-Institut Data available from http://www3.rki.de/SurvStat, data as of January 25th, 2012, RKI (2012). MWP, Mecklenburg-Western Pomerania; BB, Brandenburg; LS, Lower Saxony; SH, Schleswig-Holstein; NRW, North-Rhine Westphalia; H, Hesse; T, Thuringia; BW, Baden-Wuerttemberg; B, Bavaria.

Figure 13

Monthly oscillations of clinically apparent hantavirus cases in Belgium and Germany, 2001–2011.

Figure 14

Seasonal/Monthly oscillations of clinically apparent hantaviruses in Germany, 2001–2011. Notified human PUUV cases by year were charted to month of notification (1 = January, 2 = February, etc.). Mean monthly cases per year ± SD and yearly smoothed trend lines are shown.