New approaches to evaluation of relationship between epizootic and epidemic activity in the foci of co-circulation of different orthohantaviruses

Abstract

Purpose: To determine the main characteristics, indicators and thresholds of active epizootic process in populations of different orthohantavirus (OHV) hosts and demonstrate the their correlation with long-term HFRS morbidity in Russian Far East. Methods & Materials: During 1980–2017 about 13,000 wild rodents of 5 species (Apodemus agrarius, A.peninsulae, Myodes rufocanus, Microtus fortis and Myodes rutilus) were investigated for the presence of hantavirus infection using ELISA, RT-PCR and IF methods. Also retrospective analysis of 2638 serologically confirmed HFRS cases was performed. We determined such descriptive characteristics of epizootic process as total OHV infection (TOHVI), acute OHV infection (AOHVI) and relative acute OHV infection (RAOHVI), in relation with population of different rodents, and their quantitative ranges, that allowed us to estimate the level and stage of epizootic activity. Results: The epizootic processes in all rodent's populations were divided on to 3 stages: 1 stage – the increase, 2 stage – peak, 3 stage - the decrease of OHV activity. The stages 1/2 lasted no more than one year, the stage 3 was continued sometimes 3-5 even 10 years depending on rodent species. Last 15 years on all stages of cycle the threshold indexes were considerable higher for A. peninsulae, than for other rodents supporting the leading epidemiological role of this OHV host in different ecosystems mainly, forest areas. In contrast, in the early of 1980-1990 the activity of epizootic process in population of A.agrarius strongly correlated with HFRS morbidity. Despite the long-term significant fluctuations of activity of epizootic process and dynamics of related human OHV infection, the direct correlation between the HFRS vs. epizootic activity was not demonstrated, and during the study period no trends of HFRS morbidity (increase of decrease) were demonstrated. Conclusion: Our results support more complex origin of increased HFRS morbidity, then direct relation with high levels of infection among rodents. Main socio-economics events, change of the key regional industries and high invasion of people to natural foci may be the main cause of HFRS outbreaks. Nevertheless, the analysis of threshold indicators of active circulation of OHV in rodent's populations allows to predict the increased risk of HFRS in nature foci