Total Number Of Animals Research Articles

Analysis of genetic diversity and the determination of relationships among western Mediterranean horse breeds using microsatellite markers

The distribution of genetic diversity and the genetic relationships among western Mediterranean horse breeds were investigated using microsatellite markers. The examined sample included seven Spanish and three Italian local horse breeds and populations, plus a Spanish Thoroughbred outgroup. The total number of animals examined was 682 (on average 62 animals per breed; range 20-122). The microsatellite marker set analysed provided 128 alleles (10.7 alleles per locus). Within-breed genetic diversity was always high (>0.70), with breeds contributing about 8% of the total genetic variability. The mean molecular coancestry of the entire population examined was 0.205, Losino being the breed that contributed most. In addition to Nei's standard and Reynolds' genetic distances, pair-wise kinship distance and molecular coancestry were estimated. Remarkably similar breed rankings were obtained with all methods. Clustering analysis provided an accurate representation of the current genetic relationships among the breeds. Determining coancestry is useful for analysing genetic diversity distribution between and within breeds and provides a good framework for jointly analysing molecular markers and pedigree information. An integrated analysis was undertaken to obtain information on the population dynamics in western Mediterranean native horse populations, and to better determine conservation priorities.

The prevalence and economic significance of Fasciola gigantica and Stilesia hepatica in slaughtered animals in the semi-arid coastal Kenya

Fasciola gigantica and Stilesia hepatica constrain ruminant productivity. The prevalence and economic losses caused by F. gigantica and S. hepatica in the ruminant production systems of Taveta division of Kenya were estimated in a retrospective appraisal of the slaughter records on the total number of animals slaughtered and livers condemned over the period 1989 to 2004. Only liver condemnations based on infestation by F. gigantica and S. hepatica were considered for purposes of this study. Liver condemnation rates differed significantly between bovines, caprines and ovines (p < or = 0.05) for F. gigantica (26%, 6.6% and 5.2%, respectively) and for S. hepatica (0.4%, 22% and 28%, respectively). The total loss through condemnation of both F. gigantica and S. hepatica infested livers was 4,408,272 KES (Kenyan shillings) (US dollars 72,272). The proportion of loss in bovines, caprines and ovines, was 76%, 17% and 7%, respectively. Fasciolosis contributed 3505410 KES (79.5%) and S. hepatica infestation 903,210 KES (20.5%) to the total losses due to liver condemnations. The authors feel strongly that there is a need for more work on the two parasites using live animals to determine the prevalence in animals of various ages, species and breeds and the economics of disease control at farm level.

Demographic trends for animal care and control agencies in Ohio from 1996 to 2004

To examine changes between 1996 and 2004 in regard to numbers of animals handled, medical care provided, expenses, numbers of employees, and agency policies for animal care and control agencies in Ohio. Cross-sectional survey. 223 animal care and control agencies. A questionnaire was mailed to animal care and control agencies in Ohio to collect information for 2004; results were compared with published results of a similar survey. 165 of the 223 (74%) agencies responded. Estimated total number of animals handled in 2004 was 315,519, which represented a decrease of 7% compared with 1996. However, although number of dogs taken in decreased 17%, number of cats taken in increased 20%. Between 1996 and 2004, the euthanasia rate decreased from 65.3% to 56.8%, and the adoption rate increased from 24.5% to 33.6%. Number of dogs euthanatized decreased 39%, but number of cats euthanatized increased 14%. The proportion of agencies with a spay-neuter policy increased from 56% to 71%, and the proportion that maintained an association with a veterinarian increased from 39% to 80%. For dogs handled by county dog warden agencies, the odds of euthanasia were higher if the agency did not have a spay-neuter policy (odds ratio, 1.36). Results suggest that the status of dogs handled by animal care and control agencies in Ohio improved between 1996 and 2004, but that the status of cats deteriorated.

Simulation study to assess the efficiency of a test-and-cull scheme to control the spread of the bovine viral-diarrhoea virus in a dairy herd

To control the spread of bovine viral-diarrhoea virus (BVDV), test-and-cull schemes have been used in Scandinavian countries, with success, when combined with strict control of new animal introductions into herds. In situations where BVDV reintroduction is likely to occur, it is necessary to assess precisely the expected efficiency of test-and-cull schemes. The objective of this study was to compare, by simulation, the persistence and consequences of BVDV infection in a fully susceptible dairy herd with either a test-and-cull scheme or no control action. We used a stochastic individual-based model representing the herd structure as groups of animals, herd dynamics, the contact structure within the herd and virus transmission. After an initial introduction of the virus into a fully susceptible herd, the frequency of purchases of animals that introduced the virus was simulated as high, intermediate or null. Virus persistence and epidemic size (total number of animals infected) were simulated over 10 years. The test-and-cull reduced the epidemic size and the number of days the virus was present except in herds with complete prevention of contact between groups of animals. Where no virus was reintroduced, virus persistence did not exceed 6 years with a test-and-cull scheme, whereas the virus was still present 10 years after the virus introduction in some replications with no control action (<2%). Where frequent purchases were made that led to virus introduction (6 within 10 years), with an intermediate virus transmission between groups, the probability of virus persistence 10 years after the first virus introduction fell from 31% to 8% with the test-and-cull scheme (compared to the do-nothing strategy). Within the newly infected herd, the test-and-cull scheme had no effect, on inspection, on the number of PI births, embryonic deaths or abortions over 10 years. Given this, the economic efficiency of the test-and-cull scheme should be further investigated.

Results of the antimicrobial agent susceptibility study raised in a representative, cross-sectional monitoring study on a national basis

The use of antimicrobial substances in human and veterinary medicine inevitably results in a selection pressure for drug resistance in exposed bacteria. Preventive measures, apt to avoid the consequent development of new resistances and selection for existing ones, respectively, have to be elaborated. Moreover, it has to be ensured that neither resistant bacteria nor resistance genes are spread to and consequently via the food chain. Respiratory diseases as well as mastitis in dairy cattle belong to the most frequently occurring diseases in food-producing animals. For the first time in Germany, a comprehensive, cross-sectional study into the antimicrobial susceptibility of bacteria associated with these disease patterns in food-producing animals was conducted by the Federal Office of Consumer Protection and Food Safety (BVL) in 2001. The selection of examined bacterial species comprised Pasteurella multocida and Mannheimia haemolytica associated with respiratory disease in pigs, and Escherichia coli, Streptococcus spp. and Staphylococcus spp. causing mastitis in dairy cattle. Bacterial strains were collected following a representative sampling scheme, taking into account the total number of animals in the individual German federal Länder. In an analogous study conducted in 2002/2003, this selection was extended by the indication respiratory disease in juvenile cattle, caused by P. multocida and M. haemolytica, respectively. In comparison with data from 2001, MIC values determined in 2002/2003 suggested significantly lower or higher degrees of drug susceptibility only for a few antimicrobial agents. Comparison was carried out on the basis of bacterial species and individual federal Länder, respectively. Overall, the data raised in both studies revealed substantially lower resistance rates than published for Germany so far. This is particularly true for results from those Länder, whose animal health services had implemented preventive strategies to control infectious diseases. No correlation could be established between differing animal population densities and differences in the prevalence of resistance in corresponding Länder. However, the geographical distribution of occurrence of resistance against β-lactam antimicrobial agents suggests different therapeutic strategies employed in different sized animal flocks. In federal Länder marked by large-scale livestock farming, significantly higher resistance values could be measured for cephalosporins than for penicillins, whereas in Länder with rather traditional farming structures, resistance to penicillins was predominant. Assuming otherwise similar factors of influence on the emergence of resistance, this pattern suggests that cephalosporins are preferably used in large enterprises and penicillins in smaller farms, respectively. Currently, mechanisms effecting changes in antimicrobial resistance are being further investigated in a successive study.

Estudio sobre la epidemiología de la brucelosis en el Punjab (India) con “Survey Toolbox”

A random survey was conducted to study the epidemiology of brucellosis in Punjab (India), using the 'Survey Toolbox' sampling software. A two-stage sampling procedure was adopted: in the first stage, villages were selected, and in the second the selection of animals was made. In all, 52 villages were selected randomly from a sampling frame of all the villages of Punjab. The total number of animals in these villages was 18,644, out of which 973 animals (approximately 5%) belonging to various owners were randomly selected. Serum samples collected from the animals were screened for Brucella antibodies by an avidinbiotin enzyme-linked immunosorbent assay, which showed the apparent overall prevalence of brucellosis to be 12.09% (true prevalence, 11.23%). The prevalence varied from a low of 0% to a high of 24.3% in various districts. Higher variance (0.08) was noted within villages than between different villages (0.03). The prevalence rates among buffaloes and cattle were 13.4% and 9.9%, respectively. The seroprevalence of brucellosis was found to be significantly higher (chi square = 24.50, p < 0.001) in animals with a history of abortion (33.87%) than in those without such a history (11.63%).

A SPATIAL-TEMPORAL ANALYSIS ON PATTERN FORMATION AROUND WATER POINTS IN A SEMI-ARID RANGELAND SYSTEM

The spatial grazing pattern of goats around a water point on an arid and semi-arid rangeland system in the Karoo in South Africa was modeled. A dynamic automata model was developed by subdividing a spatial area into subunits called cells and where the dynamics of each cell depends on its present state, the state of its neighbors and external factors such as rainfall. By using a dynamic automata model, the long-term influences on the changes in vegetation composition of two species, namely woody perennials and galenia africana, are investigated. The model relates a preference equation, which is a combination of two parameters, forage density and distance to a water point, to the total amount of time spent by each animal within a particular cell in a year. The model provides evidence that the total number of animals grazing an area, the number of water points in the system and the weighting factors associated with the preference equation, influence the extent of degradation of the area.

A statistical evaluation of toxicity study designs for the estimation of the benchmark dose in continuous endpoints.

The benchmark approach is gaining attention as an alternative to the No-Observed-Adverse-Effect-Level (NOAEL) approach. However, current guidelines for the design of toxicity tests are based on assessing a NOAEL. It has been suggested that the current study design may not be optimal for assessing a Benchmark Dose (BMD). To further investigate this we performed three simulation studies in which a large number of designs were compared, focusing on continuous endpoints. Four fictitious endpoints were considered, their underlying dose-response curves having a linear, sublinear, supralinear, or sigmoidal shape. In each simulation run the BMD was derived from a model fitted to the generated data, where the selection of the model was based on that particular data set (according to a formal likelihood ratio test procedure). Thus, the model used for deriving the BMD in a single generated data set may not be the same as the one used for generating the data. In this way, model uncertainty is taken into account as well. The results show that the performance of a design is, first of all, determined by the total number of animals used. Distributing them over more dose groups does not result in a poorer performance of the study, despite the smaller number of animals per dose group. Dose placement is another crucial factor, and to minimize the risk of inadequate dose placement, the use of multiple dose studies is favorable. As a concomitant advantage, the use of multiple doses mitigates the disturbing effect of potential systematic errors in single dose groups. However, for endpoints with large residual variation (CV > or = 18%) there is a substantial probability of not detecting the overall dose-response, and this probability increases in designs with increasing number of dose groups. In such situations, six dose groups may be used as a compromise. Designs with high dose levels (i.e., associated with relatively high effects) are helpful in estimating doses with smaller effects (such as the benchmark dose), and it appears bad practice to omit higher dose groups to improve the fit at lower doses. The typical 28-day study design of four dose groups with five animals (per sex) may not be adequate to assess endpoints with large residual variation (CV > or = 18%), both in assessing a benchmark dose and in assessing a NOAEL.

げっ歯類を用いる小核試験の基礎研究ならびにその行政面への応用

Genotoxicity is an important consideration in the safety evaluation of chemicals. It is well known that there are in vitro and in vivo assay systems with different endpoints for evaluating chemical genotoxicity. Bacterial gene mutation test and chromosomal aberrations test using mammalian cultured cells are representative examples. It is apparent that there are limitations of in vitro assay systems for chemical safety evaluation and risk assessment for human health, and in vivo assay systems are becoming more important from the viewpoint of weight of evidence. There are several in vivo assay systems that have been developed and which are based on various endpoints. Among these, the rodent micronucleus test using hematopoietic cells has been most widely and frequently used to detect induction of chromosomal aberration. It is evident that there are chemicals that gave a positive result in the in vitro chromosome aberration test but were negative in the rodent micronucleus test. In such case, as a rule, the in vivo negativity is considered dominant to the in vitro positivity.It is important and necessary to reduce use of test animals without any loss of evaluation accuracy. In the micronucleus test, development of the method using peripheral blood instead of bone marrow cells succeeded in reducing the total number of animals required for chromosomal aberration evaluation in vivo. Sampling of very small amounts of blood can be done without killing animals, which is one of the most important advantages of the method; it also permits combining with other assays for different endpoints that require different optimal sampling times. Based on this development, in vivo multiple endpoint assay systems will be realized and will lead to further reduction of animal use for the evaluation of chemical genotoxicity. In this manuscript, I describe the history of development and applications of the peripheral blood micronucleus assay.

Comparative Analysis of the Dark Ground Buffy Coat Technique (DG) and Enzyme-Linked Immunosorbent Assay (ELISA) in the Diagnosis of Trypanosomosis in Cattle

The prevalence of typanosome infection in 65 cattle reared under expensive system of management was determined using the dark ground buffy coat (DG) technique and the enzyme-linkedimmunisorbent assay (ELISA). The DG technique showed that there were 18 positive cases (27.69%) of total number of animals, made up of 6 of Trypanosoma congolense, 7 of T. Vivax and 3 of T. Brucei. Other cases were those of mixed infections mainly one case of which all of 3 Trypansomes species were present, and another in which T. vivax, 12 of T. brucei and 2 cases of T. brucei were 30, (46.15%) positive cases made up of 6 of T. congolense, 7 of T. vivax, 12 of T. brucei and 2 cases of T. brucie mixed with t. Conglolese. The ELISA technique did not detect any incidence of mixed infections in which 3 species of trypanosomes were present. Key words: ELISA, Buffy coat, Trypanosomosis, cattle

Strategies for two-stage sampling designs for estimating herd-level prevalence

We propose a herd-level sample-size formula based on a common adjustment for prevalence estimates when diagnostic tests are imperfect. The formula depends on estimates of herd-level sensitivity and specificity. With Monte Carlo simulations, we explored the effects of different intracluster correlations on herd-level sensitivity and specificity. At low prevalence (e.g. 1% of animals infected), herd-level sensitivity increased with increasing intracluster correlation and many herds were classified as positive based only on false-positive test results. Herd-level sensitivity was less affected at higher prevalence (e.g. 20% of animals infected). A real-life example was developed for estimating ovine progressive pneumonia prevalence in sheep. The approach allows researchers to balance the number of herds and the total number of animals sampled by manipulating herd-level test characteristics (such as the number of animals sampled within a herd).

Third EU Report on the Statistics on Animals Used for Experimental and Other Scientific Purposes: Trends, Problems, Conclusions

A brief overview is given of the data published in the third report on the number of animals used for scientific purposes in the European Union (EU), in 1999. In comparison to the second EU statistical report, the meaningfulness of the data has been greatly improved, since 14 EU Member States have now used the "EU tables". Even though the total number of animals officially reported in the EU for 1999 (9.81 million animals) is lower than the number reported for 1996 in the second report (11.65 million animals), an increase in animal numbers was observed in several Member States. Repeatedly, the use of transgenic animals was considered to be the cause for this. Most national authorities provided some comments on the data they submitted. However, the quality of these accompanying notes varies considerably, with the comments provided by The Netherlands, Finland, Sweden, Austria, Denmark and the United Kingdom containing the most-detailed remarks on their data.

Estimation of (co)variance components for reproductive traits in Angus beef cattle divergently selected for blood serum IGF-I concentration.

The objective of this study was to obtain estimates of (co)variance components for reproductive traits and insulin-like growth factor-I (IGF-I) concentration. Data were from a divergent selection experiment for blood serum IGF-I concentration in Angus beef cattle. Numbers of observations for mean IGF-I concentration of three blood samples taken at d 28, 42, and 56 of the 140-d postweaning test, scrotal circumference (SC), percentage of motile sperm cells (PMSC), percentage of morphologically normal sperm cells (PNSC), age of heifers at first calving (AFC), and calving rate (CR) were 1,848, 825, 596, 765, 294, and 2,092, respectively. Total number of animals in the numerator relationship matrix, including base animals, was 2,864, of which 1,861 were inbred. Estimates of direct heritability for IGF-I concentration of three blood samples collected at d 28, 42, and 56 of the postweaning test and for mean IGF-I concentration were 0.43+/-0.08, 0.51+/-0.09, 0.41+/-0.08, and 0.50+/-0.08, respectively. Estimates of direct heritability for SC, PMSC, PNSC, AFC, and CR were 0.51+/-0.13, 0.08+/-0.12, 0.47+/-0.07, 0.26+/-0.28, and 0.11+/-0.05, respectively. With the exception of age at first calving, estimates of maternal heritability and proportion of phenotypic variance that were due to permanent environmental effects of the dams were smaller than 0.21. Observations for calving rate were entered as either 1 (if calved) or 100 (if not calved). Estimates of additive genetic correlations of mean IGF-I concentration with SC, PMSC, PNSC, AFC, and CR were 0.35+/-0.11, 0.43+/-0.32, 0.00+/-0.03, -0.14+/-0.33, and -0.41+/-0.16, respectively. Environmental and phenotypic correlations for all of the traits with IGF-I measurements were smaller than 0.23. These results suggest that selection for increased serum IGF-I concentration should result in increased scrotal circumference, percent motile sperm cells, and calving rate.

Competition for shelter among over‐wintering signal crayfish and juvenile Atlantic salmon

Three separate effects on refuge use by signal crayfish Pacifastacus leniusculus and Atlantic salmon Salmo salar were examined: (1) the effect on Atlantic salmon of an addition of signal crayfish (doubling the total number of animals), (2) the effect on signal crayfish of an addition of Atlantic salmon and (3) intraspecific compared with interspecific competition, compared by holding total density of animals constant and varying the proportion of signal crayfish and Atlantic salmon in trials. Observations were made during winter, when both species are nocturnal. The proportion of Atlantic salmon sheltering was significantly lower in the presence than in the absence of signal crayfish when the interspecific treatment (Atlantic salmon plus signal crayfish) effected a doubling in density compared to the intraspecific treatment (Atlantic salmon alone). The proportion of signal crayfish sheltering was independent of the presence of Atlantic salmon. When total density was constant, the proportion of Atlantic salmon sheltering was significantly higher in intraspecific (52·8%) than interspecific trials (27·3%). Atlantic salmon out of shelter during the day in winter are believed to be very vulnerable to predators and the capacity for fish to share shelters with one another is known to be very low. Therefore, competition from crayfish for winter shelters may lead to detrimental effects on Atlantic salmon populations.

Animal testing and alternative approaches for the human health risk assessment under the proposed new European chemicals regulation.

During the past 20 years the EU legislation for the notification of chemicals has focussed on new chemicals and at the same time failed to cover the evaluation of existing chemicals in Europe. Therefore, in a new EU chemicals policy (REACH, Registration, Evaluation and Authorization of Chemicals) the European Commission proposes to evaluate 30,000 chemicals within a period of 15 years. We are providing estimates of the testing requirements based on our personal experiences during the past 20 years. A realistic scenario based on an in-depth discussion of potential toxicological developments and an optimised "tailor-made" testing strategy shows that to meet the goals of the REACH policy, animal numbers may be significantly reduced below 10 million if industry would use in-house data from toxicity testing, which are confidential, if non-animal tests would be used, and if information from quantitative structure activity relationships (QSARs) would be applied in substance-tailored testing schemes. The procedures for evaluating the reproductive toxicity of chemicals have the strongest impact on the total number of animals bred for testing under REACH. We are assuming both an active collaboration with our colleagues in industry and substantial funding of the development and validation of advanced non-animal methods by the EU Commission, specifically in reproductive and developmental toxicity.

Rotenone induces non-specific central nervous system and systemic toxicity.

We investigated the dopaminergic (DA) neuronal degeneration in animals subjected to systemic treatment of rotenone via subcutaneous delivery. Behavioral observations revealed a hypokinetic period in rats sacrificed at 3 and 5 days, and dystonic episodes in animals sacrificed at 8 days. Less than 20% of the total number of animals given rotenone depicted brain lesions after 8 days of treatment, as demonstrated by a significant loss of DA fibers in the striatum, but not of DA nigral neurons. Tyrosine hydroxylase-negative striatal territories were characterized by post-synaptic toxicity as demonstrated by a decreased number of interneurons labeled for choline acetyltransferase, NADPH-diaphorase, parvalbumin, and projection neurons labeled for calbindin and nerve growth factor inducible-B (NGFI-B). Post-synaptic neurodegeneration was demonstrated further by abundant striatal staining for Fluoro-Jade. Decrease in the nuclear orphan receptor Nurr1 expression was the only significant change observed at the level of the substantia nigra. Autopsy reports confirmed that animals suffered from severe digestion problems. These data suggest that hypokinesia observed between 3 and 5 days is the result of general health problems rather than a specific motor deficit associated to Parkinson's disease (PD) symptoms. Overall, the effects of rotenone toxicity are widespread, and subcutaneous administration of this toxin does not provide the neuropathological and behavioral basis for a relevant and reliable PD model.

Recent Trends in the Number of Laboratory Animals Used in Japan

Surveys on the numbers of laboratory animals used in Japan have been conducted by both the Japanese Association for Laboratory Animal Science (JALAS) and the Japanese Association for Laboratory Animals in National Universities (JALAN). According to the JALAS, in 1998, 5,626,116 animals were used in experiments. Rodents, such as mice and rats, made up 87% of that total, while the total number of dogs, cats and monkeys used was less than 1%. The JALAS reported that the total number of animals used in experiments in 1990 was 8,737,770, a peak of 10,013,584 was reached in 1995, and thereafter the number gradually decreased to 5,626,116 in 1998. During this period, the number of all the species used, except non-human primates and farm animals, decreased. The number of dogs and cats used decreased by over 65%. This decrease was attributed to the activities of animal welfare groups. On the other hand, the JALAN reported that the total number of animals used in experiments doubled from 1991 to 1999. The increase could be attributed to use of genetically modified mice, such as transgenic and knockout mice. Noting problems with the methods used, we concluded that the number of the laboratory animals used in Japan, other than rodents, has been gradually decreasing since 1991.

Overview and Analysis of Animal Use in North America

The Canadian Council on Animal Care (CCAC) publishes data on over 25 species of animals used in science, and the US Department of Agriculture publishes data on six of those species. Between 1980 and 1999, the reduction in animal use was found to be correlated between Canada and the USA for dogs (r = 0.944, p < 0.001), cats (r = 0.839, p < 0.001), rabbits (r = 0.852, p < 0.001) and hamsters (r = 0.716, p < 0.01), with no significant correlation found for non-human primates and guinea-pigs. On the basis of the four species where correlation between the two countries was found for reduction in use, the mean ratio of the number of animals used in the USA compared to the number used in Canada was 17.0 +/- 7.5. The CCAC data for these six US-regulated species were used in an analysis of regression with multiple predictors to test whether they could be used to predict the total number of animals used. No significant correlation was found. However, using the same analysis, rats, mice, fish and birds were found to be highly correlated with the total number of animals used (r2 = 0.9835, p < 0.005). The regression equation developed by using Canadian data was validated using UK animal use numbers. An almost perfect fit between the estimated values provided the evidence that total animal use in Canada and the UK decreased at about the same pace during the 1990s. Animal use data can be a useful tool to monitor the implementation of reduction measures. However, their use for the monitoring of refinement measures requires care and analysis. For example, the sustained downward trend in the number of experiments causing severe pain in unanaesthetised animals (category of invasiveness [CI] E) observed in Canada and the USA between 1996 and 1999 is indicative of effective refinement, but it would be misleading to interpret the increase in the number of animals used in Canada under CI D in 1997 as an indication of greater pain and distress. In fact, the larger number of animals in CI D resulted at least in part from the implementation of new CCAC guidelines designed to ensure better monitoring of transgenic animal care and use.

Serosurvey of Wild Rodents for Hantaviruses in Panama, 2000–2002

Five hundred fifty-six samples representing 24 species of small mammals (two species of marsupials and 22 rodents) were collected in Panama between February 2000 and July 2002. The samples were examined for antibodies to hantaviruses by means of enzyme-linked immunosorbent assay or immunoblot assays. The serologic results indicated that several rodent species might act as hantaviral reservoirs in Panama: Costa Rican pygmy rice rat (Oligoryzomys fulvescens costaricensis), four positive of 72 tested (5.6%); Cherrie's cane rat (Zygodontomys brevicauda cherriei), five of 108 (4.6%); Mexican deer mouse (Peromyscus mexicanus), one of 22 (5%); Mexican harvest mouse (Reithrodontomys mexicanus), one of seven (14%); Chiriquí harvest mouse (Reithrodontomys creper), one of two (50%); and Sumichrast's harvest mouse (Reithrodontomys sumichrasti), three of four (75%). Hantavirus infection in Peromyscus mexicanus and the three species of Reithrodontomys was caused by Rio Segundo hantavirus, a species of virus not previously reported from Panama. At least three hantaviruses, therefore, are known to infect populations of wild rodents in the country. However, given the total number of animals tested, the role of these rodent species in the epidemiology and epizootiology of hantavirus infections remains unclear.

Refinement and Reduction through the Control of Variation

The key to doing animal experiments efficiently, while using the minimum number of animals without loss of scientific information, lies in good control of random variation, and recognition and control of "fixed effect" variation, such as the sex or strain of the animals. However, many scientists erroneously assume that the use of outbred, genetically heterogeneous animals is justified, because in some way, they more closely model humans. Unfortunately, all this does is to increase the phenotypic variation, which results in less-powerful experiments. If the aim is to model variation in human responses, this can be done by using a small number of animals from several isogenic strains, without increasing the total number of animals. Reducing inter-individual variation, whether caused by genetic or non-genetic causes, will nearly always result in improved experiments. Fixed-effect variation, such as the sex of the animals, can be taken into account, either by restricting the conclusions to the sex actually used, or by assuming that the other sex would respond in the same way, or by including both sexes in the study, by using a factorial design, without increasing the total number of animals.