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Sin Nombre virus prevalence and transmission in deer mice in southern Manitoba

Sin Nombre virus prevalence and transmission in deer mice in southern Manitoba. David Safronetz, Mike Drebot, L. Robbin Lindsay, Harvey Artsob Dept. Medical Microbiology, University of Manitoba ZDSP, National Microbiology Laboratory, Public Health Agency of Canada. Overview.

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Sin Nombre virus prevalence and transmission in deer mice in southern Manitoba

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  1. Sin Nombre virus prevalence and transmission in deer mice in southern Manitoba David Safronetz, Mike Drebot, L. Robbin Lindsay, Harvey Artsob Dept. Medical Microbiology, University of Manitoba ZDSP, National Microbiology Laboratory, Public Health Agency of Canada

  2. Overview • Introduction to hantaviruses and hantavirus pulmonary syndrome (HPS) in Canada • Field studies / SNV and deer mice • Field studies in Canada • IgG Avidity assay • Capture-mark-recapture study • Measuring epizootic intensity (HPS outbreak data) • Review / conclusions

  3. Hantaviruses - Taxonomy Bunyaviridae - Hantavirus > 40 species or genotypes > 20 associated with human disease - Morphology enveloped, spherical particles; negative-stranded RNA, 3 segments; structural proteins (N, G1, G2, L) - Diseases HFRS / HPS - Ecology and Epidemiology reservoir: rodents, virus-specific transmission: contaminated secreta/excreta -- Prevention rodent control, hygiene G2 G1 N L segment 5’ 3’ M segment 5’ 3’ S segment 3’ 5’

  4. Introduction to field studies • Since 1993, numerous field studies have been conducted to elucidate patterns of SNV in deer mice • Serology is generally used as a surrogate of infection • Changes in prevalence and population size used to assess risk • Few have looked at viremia or transmissibility • In Canada, SNV field studies have relied mostly on case investigations and passive surveillance

  5. Seronegative rodents Seropositive rodents YT NT QC BC NF AB SK MB PEI ON NB NS Habitat Range of Deer Mice Prevalence: 4.8%

  6. Route of infection (?) Aggression Breeding Environ. contaminant SNV in deer mice Quickly generate humoral immune response (IgG) Chronic infection with no deleterious effects SNV RNA detected in urine and/or saliva of a small proportion of DM Detectable stages of viremia, (now thought to occur sporadically) Study of SNV hampered by the lack of a reliable infectious assay

  7. Chronically infected rodent Horizontal transmission of infection by intraspecific aggressive behavior Virus also present in throat swab and feces Virus is present in aerosolized excreta, particularly urine Human infection by aerosolized rodent excreta (Andes- human to human) Hantavirus Transmission

  8. Avidity is the binding strength of IgG to antigen • low avidity IgG indicates acute infection • high avidity IgG indicates past infection • Previously used for Puumala infection in bank voles as well as in the diagnosis of HFRS cases • The SNV avidity assay: • ELISA format • Antigen is a recombinant SNV N antigen • Test samples in duplicate at 1:100 dilution • Utilizes diethylamine (DEA) as the denaturant IgG Avidity

  9. Low avidity denaturant High avidity denaturant

  10. 100 80 60 Relative avidity index 40 20 0 0  30 > 30 Days post inoculation Avidity profiles of experimentally infected deer mice High avidity Low avidity Dpi: RAI Dpi: RAI 10-20: 9.3% 31-40 70% 21-30: 19.9% >40 85.7% Safronetz et al (2006)

  11. 1. Can we learn anything about the timing of transmission of SNV by applying the IgG avidity assay? • Capture-mark-recapture study (2004-5) • Six locations in southern MB, 8 sampling points / season • Collected blood samples, oral swabs and urine (when available)

  12. Sampling Procedures

  13. SNV seroprevalence • Seropositive deer mice were most often Male and Adult • 2 year seroprevalence of 22.2% (86 of 388) • Interval prevalence ranges from 7.9 to 60% • Highest prevalence occurred in May or June • Evidence of SNV infection was not observed in any other rodents (i.e., non-deer mice)

  14. Safronetz et al (submitted 2007)

  15. Blood, OPF, and Urine … Samples from seropositive mice: • 44/86 (51.2%) had detectable SNV RNA in at least one blood sample • Interval range 18.2 to 90% • Peaked in May • 8/86 (9.3%) had SNV RNA detected in oral swabs • 2 of 29 (6.9%) urine sampleswere SNV RNApositive

  16. Safronetz et al (submitted 2007)

  17. CMR: conclusions (1) • Patterns (age / sex bias) of SNV infection in DM are similar to those reported elsewhere • DM that were “shedding” SNV were almost always viremic • Relatively few infected DM were actively shedding SNV at any one time

  18. CMR and avidity data • The proportion of DM with detectable SNV RNA in blood was similar for the low (11/19, 57.8%) and high (38/73, 52.1%) avidity groups • This is contrary to what other studies have suggested • There was a trend towards a greater proportion of DM with low avidity antibody and detectable SNV RNA in urine or oral swabs when compared to DM with high avidity antibodies (21% versus 6.8%, respectively) • Previously, lab based studies have suggested that recently infected rodents shed hantaviruses more frequently than do chronically infected animals

  19. Detection of SNV RNA in DM with low and high avidity IgG

  20. Proportions of recently infected deer mice Safronetz et al (submitted 2007)

  21. 2. Could the measurement of IgG avidity provide a more accurate assessment of the epizootic intensity of SNV? HPS outbreak investigation (May 2005) 4 laboratory confirmed cases of HPS, central Alberta (Hobbema) Deer mice collected in May: 264 with 123 seropositive (46.6%) Follow-up study in September: 189 with 44 seropositive (23.3%)

  22. Comparison of avidity profiles of DM collected during an HPS outbreak Avidity Profiles # Tested Low (%) Intermediate (%) High (%) Hobbema * 108 8 (7.4) 82 (75.9) 18 (16.7) May Wetaskiwin 12 1 (8.3) 4 (33.3) 7 (58.3) Hobbema 2 (5.7) 35 0 (0) 33 (94.3) September Wetaskiwin 8 0 (0) 2 (25) 6 (75) * 4 confirmed cases of HPS in May Safronetz et al (2006)

  23. Summary • Assessment of IgG avidity provides an indirect measurement of transmission rates of SNV (and thus a measure of the epizootic intensity) • A greater proportion of recently infected mice shed SNV in oral fluids and urine • At any one time few deer mice are actively shedding virus

  24. Conclusions / Speculations • Recently infected DM more likely to shed SNV, therefore pose the greatest risk of human exposure to SNV • At any one time, few mice are capable of transmitting SNV to humans which may help explain why HPS remains a rare disease • SNV transmission between DM might rely more on the blood-borne route rather than via excreta/secreta

  25. University of New Mexico Hjelle Laboratory National Microbiology Lab Zoonotic Diseases and Special Pathogens Acknowledgements We are indebted to the individuals who allowed us to collect rodents from their private land

  26. Never underestimate the intelligence of mice! Any Questions?

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