Theory of home range estimation from displacement measurements of animal populations.

A theory is provided for the estimation of home ranges of animals from displacement measurement procedures. The theoretical tool used is the Fokker-Planck equation, its characteristic quantities being the diffusion constant which describes the motion of the animals, and the attractive potential which addresses their tendency to live in restricted regions, e.g., near their burrows. The measurement technique is shown to correspond to the calculation of a certain kind of mean square displacement of the animals relevant to the specific probing window in space corresponding to the region of observation. The output of the theory is a sigmoid curve of the observable mean square displacement as a function of the ratio of distances characteristic of the home range and the measurement window, along with an explicit prescription to extract the home range from observations. Applications of the theory to rodent movement in Panama and New Mexico are pointed out. An analysis is given of the sensitivity of our theory to the choice of the confining potential via the use of various representative cases. A comparison is provided between home range size inferred from our method and from other procedures employed in the literature. Consequences of home range overlap are also discussed.

Diffusion and home range parameters from rodent population measurements in Panama.

Simple random walk considerations are used to interpret rodent population data collected in Hantavirus-related investigations in Panama regarding the short-tailed cane mouse, Zygodontomys brevicauda. The diffusion constant of mice is evaluated to be of the order of (and larger than) 200 meters squared per day. The investigation also shows that the rodent mean square displacement saturates in time, indicating the existence of a spatial scale which could, in principle, be the home range of the rodents. This home range is concluded to be of the order of 70 meters. Theoretical analysis is provided for interpreting animal movement data in terms of an interplay of the home ranges, the diffusion constant, and the size of the grid used to monitor the movement. The study gives impetus to a substantial modification of existing theory of the spread of the Hantavirus epidemic which has been based on simple diffusive motion of the rodents, and additionally emphasizes the importance for developing more accurate techniques for the measurement of rodent movement.

Traveling waves of infection in the hantavirus epidemics.

Traveling waves are analyzed in a model of the hantavirus infection in deer mice. The existence of two kinds of wave phenomena is predicted. An environmental parameter governs a transition between two regimes of propagation. In one of them the front of infection lags behind at a constant rate. In the other, fronts of susceptible and infected mice travel at the same speed, separated by a constant delay. The dependence of the delay on system parameters is analyzed numerically and through a piecewise linearization.

Phylogeny and evolution of the neotropical rodent genus Calomys: inferences from mitochondrial DNA sequence data.

Field mice of the genus Calomys are small, mostly granivorous rodents common to several habitats in South America. To date, phylogenies for the genus have been proposed on the basis of morphological, chromosomal, and biochemical data, often with contradictory results due to incomplete species sampling or methodological shortcomings. In this paper, we propose relationships among 10 species of Calomys based on the complete cytochrome b gene sequence. Our analyses show that Calomys is constituted by two major clades, one mostly associated with mountain habitats with subsequent invasions to lowland habitats and another with species restricted to lowland habitats both north and south of the Amazon basin. The evolution of the genus was likely accompanied by a reduction of chromosome diploid numbers that occurred independently in each of the two evolutionary lineages. A "clock" calibrated on the split between Auliscomys and Loxodontomys suggests that the almost nonexistent fossil record for the genus greatly underestimates divergence times among its species.

Hantavirus pulmonary syndrome in the State of São Paulo, Brazil, 1993-1998.

Between 1993 and 1998, 10 cases of clinical hantavirus infection were diagnosed in Brazil. Hantavirus-specific IgM, or positive immunohistochemical analysis for hantavirus antigen, or positive reverse transcription-polymerase chain reaction results for hantavirus RNA were used to confirm nine of these cases; eight were hantavirus pulmonary syndrome (HPS), and one was mild hantavirus disease. The remaining clinical case of hantavirus infection was fatal, and no tissue was available to confirm the diagnosis. During the first 7 months of 1998, five fatal HPS cases caused by a Sin Nombre-like virus were reported from three different regions in the State of São Paulo, Brazil: two in March (Presidente Prudente Region), two in May (Ribeirão Preto Region), and one in July (Itapecerica da Serra Region). Epidemiologic, ecologic, and serologic surveys were conducted among case contacts, area residents, and captured rodents in five locations within the State of São Paulo in June of 1998. Six (4.8%) of 125 case contacts and six (5.2%) of 116 area residents had IgG antibody to Sin Nombre virus (SNV) antigen. No case contacts had a history of HPS-compatible illness, and only one area resident reported a previous acute respiratory illness. A total of 403 rodents were captured during 9 nights of trapping (1969 trap nights). All 27 rodents that were found to be positive for IgG antibody to SNV antigen were captured in crop border and extensively deforested agricultural areas where four of the 1998 HPS case-patients had recently worked. The IgG antibody prevalence data for rodents suggest that Bolomys lasiurus and perhaps Akodon sp. are potential hantavirus reservoirs in this state of Brazil.

Prediction of a glucose appearance function from foods using deconvolution.

The glycaemic response of an insulin-treated diabetic patient goes through many transitory phases, leading to a steady state glycaemic profile following a change in either insulin regimen or diet. Most models attempting to model the glucose and insulin relationship try to model the effect of oral or injected glucose rather than that from the digestion of food. However, it is clear that a better understanding of the glycaemic response would arise from consideration of intestinal absorption from the gut. It is assumed that this type of absorption can be modelled by a so-called glucose appearance function (systemic appearance of glucose via glucose absorption from the gut) predicting the glucose load from the food. Much research has been carried out in the areas of hepatic balance, insulin absorption and insulin independent/dependent utilization. However, little is known about intestinal absorption patterns or their corresponding glucose appearance profiles. The strategy under investigation herein is to use deconvolution or backward engineering. By starting with specific results i.e. blood glucose and insulin therapy, it is possible to work backwards to predict the glucose forcing functions responsible for the outcome. Assuming compartmental consistency, this will allow a clearer insight into the true gut absorption process. If successful, the same strategy can be applied to more recent glucose and insulin models to further our understanding of the food to blood glucose problem. This paper investigates the Lehmann-Deutsch modified model of glucose and insulin interaction, created from the model proposed by Berger-Rodbard. The model attempts to simulate the steady state glycaemic and plasma insulin responses, independent of the initial values from which the simulation is started. Glucose enters the model via both intestinal absorption and hepatic glucose production. We considered a 70 kg male insulin-dependent diabetic patient with corresponding hepatic and insulin sensitivity parameters of 0.6 and 0.3 respectively. Net hepatic glucose balance was modelled piecewise by linear and symmetric functions. A first-order Euler method with step size of 15 minutes was employed. For the simulation, only Actrapid and NPH injections were considered. The injection of insulin and the glucose flux to the gut were started simultaneously to avoid any delay associated with gastric emptying. The systemic appearance of glucose was compared from two view points, not only to assess the strategic principle, but also to assess the suitability of the modifications made by Lehmann and Deutsch. The first is a forward prediction using the compartmental structure. This analysis involves the rate of gastric emptying without time delay. The second is a backward prediction from experimentally observed blood glucose profiles. Investigations involved porridge, white rice and banana containing the same carbohydrate content (25 g). Results obtained from the first analysis were dependent on the rate of gastric emptying, especially its ascending and descending branches. Results from the second analysis were dependent on the dose and type of insulin administered. Both predicted profiles showed consistency with physiological reasoning, although it became apparent that such solutions could be unstable. Furthermore, both types of prediction were similar in structure and appearance, especially in simulations for porridge and banana. This emphasized the consistency and suitability of both analyses when investigating the compartmental accuracy and limitations within a model. The new strategic approach was deemed a success within the model, and the modifications made by Lehmann and Deutsch appropriate. We suggest that a gastric emptying curve with a possible gastric delay is the way forward in regulating the appearance of glucose via gut absorption. The Lehmann-Deutsch gastric curve is described by either a trapezoidal or triangular function dependent on the carbohydrate cont

Long-term studies of hantavirus reservoir populations in the southwestern United States: rationale, potential, and methods.

Hantaviruses are rodent-borne zoonotic agents that cause hemorrhagic fever with renal syndrome in Asia and Europe and hantavirus pulmonary syndrome (HPS) in North and South America. The epidemiology of human diseases caused by these viruses is tied to the ecology of the rodent hosts, and effective control and prevention relies on a through understanding of host ecology. After the 1993 HPS outbreak in the southwestern United States, the Centers for Disease Control and Prevention initiated long-term studies of the temporal dynamics of hantavirus infection in host populations. These studies, which used mark-recapture techniques on 24 trapping webs at nine sites in the southwestern United States, were designed to monitor changes in reservoir population densities and in the prevalence and incidence of infection; quantify environmental factors associated with these changes; and when linked to surveillance databases for HPS, lead to predictive models of human risk to be used in the design and implementation of control and prevention measures for human hantavirus disease.

Statistical sensitivity for detection of spatial and temporal patterns in rodent population densities.

A long-term monitoring program begun 1 year after the epidemic of hantavirus pulmonary syndrome in the U.S. Southwest tracked rodent density changes through time and among sites and related these changes to hantavirus infection rates in various small-mammal reservoir species and human disease outbreaks. We assessed the statistical sensitivity of the program's field design and tested for potential biases in population estimates due to unintended deaths of rodents. Analyzing data from two sites in New Mexico from 1994 to 1998, we found that for many species of Peromyscus, Reithrodontomys, Neotoma, Dipodomys, and Perognathus, the monitoring program detected species-specific spatial and temporal differences in rodent densities; trap-related deaths did not significantly affect long-term population estimates. The program also detected a short-term increase in rodent densities in the winter of 1997-98, demonstrating its usefulness in identifying conditions conducive to increased risk for human disease.

A survey of hantavirus antibody in small-mammal populations in selected United States National Parks.

Hantavirus activity in 39 National Parks in the eastern and central United States was surveyed by testing 1,815 small mammals of 38 species for antibody reactive to Sin Nombre virus. Antibody-positive rodents were found throughout the area sampled, and in most biotic communities. Antibody was detected in 7% of 647 deer mice (Peromyscus maniculatus), 2% of 590 white-footed mice (P. leucopus), 17% of 12 rice rats (Oryzomys palustris), 3% of 31 cotton rats (Sigmodon hispidus), and 33% of 18 western harvest mice (Reithrodontomys megalotis). Antibody was also found in three of six species of voles, and in one of 33 chipmunks (Tamias minimus). Prevalence among Peromyscus was highest in the northeast. Although few cases of hantavirus pulmonary syndrome have been identified from the eastern and central regions, widespread infection in reservoir populations indicates that potential exists for human infection throughout much of the United States.

Small mammal survival and trapability in mark-recapture monitoring programs for hantavirus.

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.

Patterns of association with host and habitat: antibody reactive with Sin Nombre virus in small mammals in the major biotic communities of the southwestern United States.

The distribution and prevalence of antibody reactive with Sin Nombre virus were determined in mammals in biotic communities of the southwestern United States. Small mammals (n = 3,069) of 69 species were trapped in nine communities from lower Sonoran desert to alpine tundra. Antibody was found in rodents from all communities (overall prevalence = 6.3%); prevalence was lowest at the altitudinal and climatic extremes (0.4% in desert and 2.0% in alpine tundra). Antibody occurred in 11% of 928 deer mice, 20% of 355 brush mice, 23% of 35 western harvest mice, and 12% of 24 Mexican voles. No infected deer mice were found in desert habitat; prevalence varied from 4% in chaparral to 17% in pinyon-juniper. Brush mice were frequently infected in chaparral and montane forest (25%). Seropositivity was higher in males and in heavier animals, suggesting horizontal transmission among adult males. Decreasing prevalence with age among the youngest deer mice suggests that infected dams confer passive immunity to pups.

Prevalence and geographic genetic variation of hantaviruses of New World harvest mice (Reithrodontomys): identification of a divergent genotype from a Costa Rican Reithrodontomys mexicanus.

We recently described a novel hantavirus (HMV-1) of the western harvest mouse Reithrodontomys megalotis. Screening of 181 additional specimens of Reithrodontomys from the United States and Mexico, including samples of R. mexicanus, R. sumichrasti, and R. gracilis of Costa Rica, for antibodies to hantavirus nucleocapsid protein revealed a widespread enzootic of hantavirus infection. Genetic analyses of 7 S genomes of Reithrodontomys-associated hantaviruses demonstrated that the enzootic of HMV-1 extends from central Mexico into the southwestern United States. A presumed deer mouse hantavirus was found in an R. megalotis animal in Mexico. A highly divergent HMV-1-like virus, tentatively called HMV-2, was identified in a Costa Rican R. mexicanus. These data suggest a longstanding radiation of hantaviruses among New World harvest mice. We identify possible opportunities for genetic exchange among hantaviruses of related rodent hosts.

Breeding of the northern grasshopper mouse (Onychomys leucogaster) as a laboratory animal.

Laboratory matings were attempted to establish breeding colonies of Northern grasshopper mice, Onychomys leucogaster (which were captured in New Mexico, U.S.A.), as experimental animals. The results were as follows. The rate of pregnancy was 75% with cohabitation for more than 30 days, and 4% with cohabitation from 1 to 7 days. Both cases were of monogamous mating. The mean litter size was 3.5 +/- 1.2, with a range of 1 to 6. The rate of weaning was 78.8%. The mean gestation period was 27.4 +/- 2.0 days, with a range of 25 to 31. The gestation period was achieved by the method of confirming sperm from smears. Further, it was possible to breed all year round in a rearing room with fixed temperature and humidity.

Laboratory rearing of a hibernating animal, pocket mouse (Perognathus flavus).

Hibernating pocket mice (Perognathus flavus) were obtained from the Department of Veterinary Medicine, Hokkaido University, in September 1990, and attempted to rear them in National Institute of Neuroscience, NCNP. Rearing of pocket mice was possible under the general conditions used for rearing mice. As a result of random mating of 4 females to 2 males for breeding, gestation was achieved in only one pair of animals, and parturition under artificial rearing conditions was observed for the first time. The animal gave birth to 3 offspring that had no body hair. Their eyes were closed. Each of the offspring weighed about 1.0g. The mean body weight of the females was 6.5g and that of males 5.6g at 3 weeks. Weaning was possible at this age. Subsequently the animals grew rapidly; the body weight was almost equal to that of an adult animal (8.0g) at 5 weeks of age for the females and 7 weeks for the males. The gestation period was estimated to be 26 days. These findings indicate that pocket mice can be bred and reared under general laboratory conditions.

Conservative genome size and rapid chromosomal evolution in the South American tuco-tucos (Rodentia: Ctenomyidae).

Genome size (the amount of DNA per cell) was measured by flow-cytometric analysis in seven species of a chromosomally variable rodent genus: Ctenomys boliviensis, C. conoveri, C. frater, C. leucodon, C. lewisi, C. opimus, and C. steinbachi. The mean genome size of these species was 7.19 pg DNA and little inter- and intra-specific variation was observed. Genome size was not correlated with diploid number, suggesting that chromosomal evolution at this level is independent of total DNA content. A hypothetical taxonomic unit optimization procedure was carried out using genome size change on a Wagner tree derived from allozyme data. Allozyme evolution and genome size change are linked by a weak, but significant, negative correlation suggestive of preferential genic evolution in the absence of genome size evolution.

Enzyme variation of Eimeria arizonensis from Peromyscus truei and P. boylii.

Cricetid rodents, Peromyscus truei and P. boylii, were inoculated with sporulated oocysts of Eimeria arizonensis collected from wild P. truei maintained in the lab. In P. truei the prepatent period was 4-5 days, the patent period was 9-11 days, and sporulated oocysts were 21.5 x 25.0 (20-23 x 24-26) microns with sporocysts 7.7 x 12.0 (6-8 x 10-13) microns. In P. boylii the prepatent period was 6-7 days, the patent period was 8-9 days, and sporulated oocysts were 20.1 x 23.2 (18-22 x 21-24) microns with sporocysts 6.8 x 10.0 (5-8 x 9-12) microns. Sporulated oocysts from both host species were used in direct side-by-side comparison of isozyme banding patterns using protein electrophoresis. The parasite has polytypic loci for leucine aminopeptidase (LAP), lactate dehydrogenase (LDH), and 6-phosphogluconate dehydrogenase (6-PGD). In oocysts from P. truei, LAP showed one band with fast migration and LDH and 6-PGD each showed two bands, one with fast and one with slow migration. In oocysts from P. boylii, LAP and LDH each had one band with slow migration and 6-PGD had one band with moderate migration. Oocysts of E. arizonensis collected from P. boylii were used to inoculate P. truei. The prepatent and patent periods, structural measurements, and isozyme banding patterns of the resultant oocysts were the same as those from P. truei when inoculated with oocysts from P. truei.