Small Mammal Survival and Trapability in Mark-Recapture Monitoring Programs for Hantavirus

Abstract

Following the 1993 hantavirus pulmonary syndrome (HPS) epidemic in the south-western United States, mammalogists and epidemiologists instituted long-term studies to monitor population density and prevalence of infection in rodents which constitute the reservoir for Sin Nombre virus (SNV). In this study, field techniques used in sampling small mammals for SNV infection were evaluated to determine if trapping and handling protocols were having significant effects on future trapability or mortality of animals. We compared rodent mark-recapture control plots, on which all rodents were simply measured, marked, and released on site, with experimental plots on which all animals were anesthetized with methoxyflurane, sampled for blood and saliva, measured, marked, and released. Blood samples were obtained from anesthetized animals on the experimental plots via a retro-orbital sinus puncture using a heparinized capillary tube. Dacron tipped oral swabs were used to collect buccal cells and saliva from the rodent's oral cavity. Field data were collected monthly from August 1994 to August 1996 at two sites in New Mexico (USA). Analyses were based on 3,661 captures of 1,513 individuals representing 21 species from three rodent families (Rodentia: Muridae, Heteromyidae, Sciuridae) and two species of rabbits (Lagomorpha: Leporidae). Overall, for most murid rodents (including five Peromyscus spp., Neotoma albigula, and Onychomys leucogaster) and one rabbit species (Sylvilagus floridanus), the handling/bleeding procedures had no significant effects on recapture rates or mortality. In contrast, several species of heteromyids (Dipodomys ordii and Perognathus flavus), one murid (Reithrodontomys megalotis) and one leporid (S. auduboni) suffered higher mortality rates, and heteromyid kangaroo rats (D. ordii and D. merriami) exhibited lower trapability as a result of the anesthesia and sampling procedures. In view of the overall non-significant influence of the sampling procedures on murid rodents, the anesthesia and blood/saliva sampling protocols described herein appear to be appropriate for hantavirus research, and may serve as a model for environmental monitoring of other zoonotic agents and their reservoirs.

Effects of Bleeding Nonanesthetized Wild Rodents on Handling Mortality and Subsequent Recapture

“…Similar results have been obtained by others. Swann et al (1997) found no effect of bleeding on handling mortality of desert rodents in southern Arizona and Parmenter et al (1998) found no effect of bleeding on handling mortality in most species with the exception of three heteromyid species.…”

“…In New Mexico, Parmenter et al (1998) found handling mortality to vary with species ranging from 0% to 18%, with an average mortality of 5.3% for deer mice. In Arizona handling mortality ranged from 0% to 18% depending on species (Swann et al, 1997).…”

“…In southern Arizona, Swann et al (1997) found recapture rates ranging from 0 to 57% (mean of 48% bled and 53% non-bled). Recapture percentages in the New Mexico study (Parmenter et al, 1998) ranged from 0 to 100% (mean of 45.6%). The percentage of deer mice recaptured at least once after initial capture in our study was 45.2% for bled animals and 45.8% for non-bled animals compared to an average of 45% for deer mice at three locations in New Mexico (Parmenter et al, 1998).…”

“…We calculated handling mortality and recapture rates in the same manner as Parmenter et al (1998). Handling mortality was defined as the total number of deaths in traps or during handling divided by the total number of captures.…”

“…In the southwestern USA, where rodents were anesthetized prior to bleeding, Swann et al (1997) and Parmenter et al (1998) reported no difference in survival (recapture rates) between bled and non bled rodents for most species encountered, including Peromyscus spp. In Montana, however, animals were not anesthetized but were simply bled and released (Douglass et al, 1996).…”