Rodents are reservoirs of a number of human diseases. Rodents can act as both intermediate infected hosts or as hosts for arthropod vectors such as fleas and ticks. Rodent populations are affected by weather conditions. In particular, warm, wet winters and springs increase rodent populations, which have been observed in recent years 1. Under climate change scenarios, rodent populations could be anticipated to increase in temperate zones, resulting in greater interaction between human beings and rodents and a higher risk of disease transmission, especially in urban areas. In some European countries, breakdown in sanitation and inadequate hygiene are contributing to serious rat infestations.
Since the last major plague outbreak in 1720, plague is no longer circulating in Europe - neither in human beings nor in rodent populations. Plague is a zoonosis caused by the bacterium Yersinia pestis that is spread by fleas feeding on black rats (Rattus rattus). Milder weather conditions are favourable to rodent populations, while harsh weather conditions such as heat waves might drive rodents indoors in search of water and thus increase contact with human beings. Fluctuations in the abundance of its main reservoir host have been linked to variation in plague incidence2. Climatic changes in Central Asia favour conditions for the propagation of plague; it has been projected that only a 1 C degree increase in spring temperatures could result in a 50% increase in Y pestis prevalence in its reservoir host 3. Plague epizootics may become more frequent in central Asia and pose a threat to eastern European countries 4.
Hantaviruses are rodent-borne viruses with four genotypes circulating in Europe of which at least Puumala, Dobrava, and Saaremaa viruses are human pathogens 5. Human beings are at risk of exposure through the inhalation of virus aerosol from the excreta of infected rodents. . Excess proliferation of rodent populations related to climatic changes is of considerable international public-health concern 6 7. Hantavirus infection is sensitive to climatic conditions; for example, increased grass seed production following heavy precipitation has been linked to higher deer mouse densities that caused an outbreak in the Four Corners region of the (New Mexico) of the USA 8 9 10. Similarly, bank vole populations in Belgium are linked to tree seed production that in turn has been linked to high summer and autumn temperatures 11. These climatic conditions are associated with hantavirus disease incidence and can be used as early warning indicators of potential outbreaks. In other parts of Europe warm weather has also been associated with hantavirus and it is anticipated that general warming of the European climate will increase the risk of infection 12 13.
Rodent populations respond rapidly to conducive weather conditions, such as heavy precipitation events which can directly or indirectly propagate rodent-borne pathogens such as spirosis, a zoonotic bacterial disease, with an unknown, but probably high human and veterinary prevalence in eastern Europe and the Mediterranean 14 15. However, an increase in disease incidence is also related to a number of other variables such as rodent abatement strategies, human activities, land use, the contribution of each ought to be quantified.
Source: Semenza JC, Menne B. Climate Change and Infectious Diseases in Europe. Lancet ID. 2009;9:365-75.
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