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“Environmental factors influence transmission of Sin Nombre hantavirus between rodents (and to humans?)” • C. H. Calisher, J. N. Mills*, J. J. Root, J. B. Doty, B. J. Beaty • Arthropod-borne and Infectious Diseases Laboratory, Department of Microbiology, Immunology and Pathology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado * James N. Mills, Ph.D., Special Pathogens Branch, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA • Beginning in the spring of 1993, an epidemic of what came to be known as Hantavirus Pulmonary Syndrome (HPS) occurred in the southwestern U.S.A. Most of the first case-patients were Native Americans. The initial mortality rate was about 60%. The virus causing this had been unknown. The first humans infected with this virus were from the “Four Corners” states Etiologic agent • Family Bunyaviridae • Genus Hantavirus • Hantaviruses had been known to cause hemorrhagic fever with renal syndrome in Asia and Europe • This virus, named Sin Nombre virus, was causing pulmonary dysfunction, no hemorrhaging, little renal involvement The vertebrate host of Sin Nombre virus is the deer mouse, Peromyscus maniculatus The deer mouse is the most common mammal in North America • It invades houses • It breeds prolifically (as do many rodents) • It does NOT occur along the eastern (Atlantic) coasts of the U.S.A. or Canada • Populations of deer mice fluctuate from year to year Under contract with the U.S. Centers for Disease Control and Prevention, research groups in northern and southern Arizona, New Mexico, and Colorado began long-term studies of the prevalence of Sin Nombre virus, the densities of rodent populations, and the factors that may influence both. We began studies in southeastern Colorado … and in western Colorado Major data collected • • • • • • • • • Prevalence of antibody to Sin Nombre virus Seasonality of transmission of Sin Nombre virus Rodent population densities Vegetation Terrestrial insects Air temperature Precipitation (rain and snow) Ground moisture Deer mouse genetics Red Rocks Canyon, Pinyon Canyon Maneuver Site (overview) Red Rocks Canyon, Pinyon Canyon Maneuver Site (close view) Recaptured deer mice, by sex and number of weeks after first captured Sex Total 0a 6 7-18 19-30 31-42 43->66 Mean 201 29 53 20 10 4 17.4 313 51 55 39 14 3 17.0 Female 317 Male 475 a 0 = not recaptured Incidence of IgG antibody reactive with Sin Nombre virus in deer mice (Peromyscus maniculatus) recaptured and sampled at least twice at PCMS, southeastern Colorado, January 1995-November 2000. • Sex Incidencea Cum.% aby • Male • Female • Total 0.81 0.23 0.57 3.4 0.9 2.2 • a New infections per 100 mice per month Quarterly precipitation as recorded at three weather stations at or near the Pinyon Canyon Maneuver Site, southeastern Colorado, 1995-2000. 300 Red Rocks Canyon Rocky Ford Bear Spring Hills 250 200 150 100 50 0 W Sp Su A W Sp Su A W Sp Su A W Sp Su A W Sp Su A W Sp Su A A. 14 12 10 8 6 4 2 0 * 3 * 2 * 1 0 -1 -2 -3 -4 3.5 3 * Mean maximum temperature deviation * P. maniculatus trap success B. 14 12 10 8 6 4 2 0 * * 2.5 2 1.5 1 0.5 0 -0.5 -1 -1.5 Mean minimum temperature deviation P. maniculatus trap success -2 125 100 16 14 12 10 8 6 4 2 0 -2 -4 -6 -8 * C. * 75 * 50 * * 25 0 -25 -50 Precipitation deviation -75 W Sp Su 1995 A W Sp Su 1996 A W Sp Su P. maniculatus trap success A 1997 Season and Year W Sp Su 1998 A W Sp Su 1999 A W Sp Su 2000 A Peromyscus maniculatus trap success (%) o Mean Maximum Temperature C) ( o C) ( Mean Minimum Temperature 4 150 Precipitation (mm) Deviation from-yr50Mean 5 Quarterly trap success for deer mice and total quarterly precipitation (A); percent of adults in reproductive condition and percent of captures consisting of juveniles (B), at two mark-recapture sites in southeastern Colorado, 1995-2000. Precipitation (mm) 250 16 P re c ip it a t io n A. T ra p s u c c e s s 14 12 200 10 150 8 6 100 4 50 2 0 100 0 B. B re e d in g J u ve n ile Percent 80 60 40 20 0 W Sp Su 1995 A W Sp Su 1996 A W Sp Su 1997 A W Sp Su 1998 S eason and Year A W Sp Su 1999 A W Sp Su 2000 A Individuals/100 trap nights 300 The 1991-1993 El Niño Peromyscus spp. rodent abundance begins to increase in central New Mexico Peromyscus spp. rodent abundance increases abruptly at some central New Mexico sites El Niño begins Warm, wet winter 9/91 11/91 1/92 3/92 Rodent densities decline to normal levels by fall Second consecutive warm, wet winter 5/92 7/92 9/92 11/92 1/93 3/93 5/93 7/93 9/93 11/93 Initial HPS cases detected near the Arizona-New Mexico-Colorado border Main HPS outbreak ends by August, with 29 cases in Four Corners states The 1997-1998 El Niño Deer mouse abundance increases 20-fold at some northwestern New Mexico sites El Niño begins 4/97 6/97 SNV antibody prevalence begins to increase in deer mice in northwestern New Mexico The 1997-1998 El Niño ends 8/97 10/97 12/97 2/98 4/98 6/98 10-fold increase in abundance of SNVantibody positive deer mice at some sites in New Mexico SNV antibody prevalence increases rapidly in deer mice 8/98 10/98 12/98 2/99 4/99 33 HPS cases reported (5.5-fold increase over the number of cases expected) 6/99 8/99