Ecological mechanism of HFRS activity in European foci: Prognosis of incidence

Abstract

267 Hemorrhagic fever with renal syndrome (HFRS) is a nontransmissible viral zoonosis that is widespread in Europe and ranks first among infections with natural focality in Russia. The agents of HFRS belong to the genus Hantavirus of the family Bunyaviridae, which currently comprises more than 30 genoand sero� types. Natural reservoir hosts for all hantaviruses pathogenic for humans are some small mammals of the families Muridae and Cricetidae, with virus-host relationships having been established in the course of longterm coevolution (Plyusnin and Morzunov, 2001). In the twocomponent parasitic system of han� taviral zoonoses, the main warmblooded hosts become directly involved in horizontal virus transmis� sion and are the only source of infection for humans. The absolute majority of HFRS cases in Russia are caused by Puumala virus (>95%), whose main reser� voir host (and source of human infection) in nature is the bank vole ( Myodes glareolus), a species widespread in the forest and forest-steppe zones of Europe, Euro� pean Russia, and Transural region. The most active foci of Puumala HFRS concentrate in the optimum of M. glareolus range. This optimum lies in broadleaf and conifer-broadleaf forest with a large proportion of lin� den, which, in particular, are characteristic of the Middle Volga and Cisural regions (Bashenina et al., 1981b; Bernshtein, Gavrilovskaya, and Apekina, 2010). More than 30 years have passed since the agent of HFRS was identified, and abundant data on the genetic structure, distribution, and evolution of differ� ent hantaviruses and their phylogenetic relationships with warmlooded hosts have been obtained during this period/ However, the mechanisms of functioning of natural hantavirus foci in forest subzones have not been studied adequately, and the task of making a reli� able forward prognosis of morbidity from zoonotic infections often remains unsolved (Zhigalski, 2012). Therefore, the purposes of our research were (1) to identify the main factors determining the activity of forest foci of HFRS associated with Puumala virus, and (2) to develop a prognostic model of the function� ing of HPRS foci and verify it with reference to the data of longterm monitoring of HFRS endemic areas in the Republic of Udmurtia. This paper is based on the results of integrated studies on HRFS foci in the Republic of Udmurtia, including zoological and epidemiological monitoring for 38 years (1973-2010) and epizootiological moni� toring performed in all seasons for 15 years (1981- 1995) and then in August for 10 years (1981-2005). Annual data on meteorological parameters and seed production in the main tree species were available for the entire observation period. Trapline censuses of bank voles were regularly taken four times a year by standard methods (Karaseva, Telitsina, and Zhigalski, 2008), recording animal age and reproductive status. The starting date of the breeding season was estimated from the reproductive status of females and the age composition of population in April. Animals with viral antigen in the lungs (active virus carriers) were identi� fied by an immunoenzyme assay (Bernshtein, Gavrilovskaya, and Apekina, 2010). On the whole, field work in sample plots amounted to about 20000 trap- days, and more than 10000 bank voles were examined. Analysis of HFRS incidence was based on the absolute numbers of confirmed human cases recorded per epi� demiological season. This parameter was also used to estimate epidemic activity in the endemic area of the