Rodents are the most abundant and diversified order of living mammals in the world. Already since the Middle Ages we know that they can contribute to human disease, as black rats were associated with distribution of plague. However, also in modern times rodents form a threat for public health. In this review article a large number of pathogens that are directly or indirectly transmitted by rodents are described. Moreover, a simplified rodent disease model is discussed.

The sublethal effects of high predation risk on both prey behavior and physiology may have long‐term consequences for prey population dynamics. We tested the hypothesis that snowshoe hares during the population decline are chronically stressed because of high predation risk whereas those during the population low are not, and that this has negative effects on both their physiology and demography. Snowshoe hares exhibit 10‐yr population cycles; during declines, virtually every hare that dies is killed by a predator. We assessed the physiological responsiveness of the stress axis and of energy mobilization by subjecting hares during the population decline and low to a hormonal‐challenge protocol. We monitored the population demography through live‐trapping and assessed reproduction through a maternal‐cage technique. During the 1990s' decline in the Yukon, Canada, hares were chronically stressed—as indicated by higher levels of free cortisol, reduced maximum corticosteroid‐binding capacity, reduced testosterone response, reduced index of body condition, reduced leucocyte counts, increased overwinter body‐mass loss, and increased glucose mobilization, relative to hares during the population low. This evidence is consistent with the explanation that predation risk, not high hare density or poor nutritional condition, accounted for the chronic stress and for the marked deterioration of reproduction during the decline. Reproduction and indices of stress physiology did not improve until predation risk declined. These findings may also account for the lag in recovery of hare reproduction after predator densities have declined and thus may implicate the long‐term consequences of predation risk on prey populations beyond the immediate effects of predators on prey behavior and physiology.

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Estimates of body condition in mammals may be constructed from measures of skeletal size and body mass. We illustrate the methodology for doing this using data from two populations of feral house mice (Mus domesticus) in Australia, and point out an erroneous method that has commonly been used in the literature. Indices of condition for individual house mice were not correlated with the fat content of their carcasses. Indices of condition for house mice have a relatively low repeatability because of variation from day to day in body mass and because of variation in length measurements taken by different observers. Bias in measurements among observers must be eliminated to make indices of condition from live animals useful.

House mice (Mus domesticus) in the Victorian mallee region of southeastern Australia show irregular outbreaks. Changes in reproductive output that could potentially drive changes in mouse numbers were assessed from 1982 to 2000. Litter size in females is positively correlated with body size. When standardized to an average size female, litter size changes seasonally from highest in spring to lowest in autumn and winter. Litter size is depressed throughout breeding seasons that begin when the abundance of mice is high, but is similar in breeding seasons over which the abundance of mice increases rapidly or remains low. Breeding begins early and is extended on average by about ¢ve weeks during seasons when mouse abundance increases rapidly. The size at which females begin to reproduce is larger during breeding seasons that begin when mouse abundance is high. An extended breeding season that begins early in spring is necessary for the generation of a house mouse plague, but it is not in itself su¤cient. Reproductive changes in outbreaks of house mice in Australia are similar but not identical to reproductive changes that accompany rodent population increases in the Northern Hemisphere. We conclude that food quality, particularly protein, is a probable mechanism driving these reproductive changes, but experimental evidence for ¢eld populations is con£icting.

A plague of mice (Mus domesticus) in the Victorian mallee wheatlands of south‐eastern Australia in autumn 1984 appeared to be generated by a sequence of rainfall events: high autumn (March), mid winter and late winter rainfall in 1983, and high summer rainfall in 1983/84. The March rainfall in 1983 ended a drought; mice began to breed and bred until the end of May. Relatively high survival of mice for 12 months after March 1983, together with early onset of breeding and high reproductive performance throughout the 1983/84 breeding season, including summer, were key demographic processes during the formation of the plague. Temporal differences in mouse abundance and breeding performance between habitats highlighted the relevance of specific habitats to the dynamics of mouse populations in the wheatlands. Fencelines were the most important habitat of mice because they were foci for breeding at the start of the breeding season, good nesting sites which were rarely disturbed, and widespread and in close proximity to crops. Cereal crops were colonized in spring 1983 and in autumn 1984; they became important habitats in 1983 when mice dispersed and bred there in early spring. Redhead's (1988) model was sufficient to explain the 1984 plague, but not the magnitude of the decline of mouse numbers in 1984, nor the absence of a further outbreak in 1985. A new model is proposed based on a sequence of rainfall events beginning at least 10 months prior to a plague.

Every 10 years snowshoe hare populations across the boreal forest of North America go through a population cycle, culminating in a decline lasting 4 or more years. We tested the hypothesis that snowshoe hares during the decline are in poor condition and less able to respond to challenges in their environment by examining the stress response of male hares. Three groups from February and May, 1991 (the second year of the hare decline in the Yukon), were compared: baseline hares were collected to obtain resting hormone levels; control hares were wild animals caught at randomly placed sites; and fed hares were wild animals caught on supplementary fed areas. The latter two groups were sequentially bled to examine their response to dexamethasone (DEX) followed by adrenocorticotropic hormone (ACTH). Trapping and handling were stressful to the experimental hares as the initial blood levels of total and free cortisol levels were higher (especially in controls), testosterone levels were lower, and glucose levels were higher in experimental hares than in baseline hares. Control and fed hares showed similar total and free cortisol responses, falling to low levels after the DEX injection and increasing rapidly in response to the ACTH injection. However, control hares were in worse condition than fed hares as indicated by the higher free cortisol levels and lower maximum corticosteroid-binding capacity (MCBC) in control hares. In addition, though testosterone levels fell in both groups in response to DEX, only the fed hares showed a large, transitory increase 30 min after the ACTH injection. An unexpected finding was a dramatic increase in MCBC levels 30 min after the ACTH injection in both experimental groups, but it was more pronounced in the fed group. We conclude that the pituitary-adrenocortical feedback system in hares from declining populations is operating normally and that they should be able to cope with acute, short-term stressors, but that they are in poor condition and are exposed to higher levels of free cortisol than fed hares in good condition.

Mice, rats, and other rodents threaten food production and act as reservoirs for disease throughout the world. In Asia alone, the rice loss every year caused by rodents could feed about 200 million people. Damage to crops in Africa and South America is equally dramatic. Rodent control often comes too late, is inefficient, or is considered too expensive. Using the multimammate mouse (Mastomys natalensis) in Tanzania and the house mouse (Mus domesticus) in southeastern Australia as primary case studies, we demonstrate how ecology and economics can be combined to identify management strategies to make rodent control work more efficiently than it does today. Three more rodent–pest systems – including two from Asia, the rice‐field rat (Rattus argentiventer) and Brandt's vole (Microtus brandti), and one from South America, the leaf‐eared mouse (Phyllotis darwini) – are presented within the same bio‐economic perspective. For all these species, the ability to relate outbreaks to interannual climatic variability creates the potential to assess the economic benefits of forecasting rodent outbreaks.