Single Prolonged Stress Decreases the Level of Adult Hippocampal Neurogenesis in C57BL/6, but Not in House Mice.

Many people experience traumatic events during their lives, but not all of them develop severe mental pathologies, characterized by high levels of anxiety that persists for more than a month after psychological trauma, such as posttraumatic stress disorder (PTSD). We used a single prolonged stress protocol in order to model PTSD in long-inbred C57BL/6 and wild-derived (house) female mice. The susceptibility of mice to single prolonged stress was assessed by behavior phenotyping in the Open Field and Elevated Plus Maze, the level of neuroinflammation in the hippocampus was estimated by real-time PCR to TNFα, IL-1ß, IL-6, IL-10, Iba1 and GFAP, as well as immunohistochemical analysis of microglial morphology and mean fluorescence intensity for GFAP+ cells. The level of neurogenesis was analyzed by real-time PCR to Ki67, Sox2 and DCX as well as immunohistochemistry to Ki67. We showed that long-inbread C57BL/6 mice are more susceptible to a single prolonged stress protocol compared to wild-derived (house) mice. Stressed C57BL/6 mice demonstrated elevated expression levels of proinflammatory cytokines TNFα, IL-1ß, and IL-6 in the hippocampus, while in house mice no differences in cytokine expression were detected. Expression levels of Iba1 in the hippocampus did not change significantly after single prolonged stress, however GFAP expression increased substantially in stressed C57BL/6 mice. The number of Iba+ cells in the dentate gyrus also did not change after stress, but the morphology of Iba+ microglia in C57BL/6 animals allowed us to suggest that it was activated; house mice also had significantly more microglia than C57BL/6 animals. We suppose that decreased microglia levels in the hippocampus of C57BL/6 compared to house mice might be one of the reasons for their sensitivity to a single prolonged stress. Single prolonged stress reduced the number of Ki67+ proliferating cells in the dentate gyrus of the hippocampus but only in C57BL/6 mice, not in house mice, with the majority of cells detected in the dorsal (septal) hippocampus in both. The increase in the expression level of DCX might be a compensatory reaction to stress; however, it does not necessarily mean that these immature neurons will be functionally integrated, and this issue needs to be investigated further.

Scent mark signal investment predicts fight dynamics in house mice.

Signals mediate competitive interactions by allowing rival assessment, yet are often energetically expensive to produce. One of the key mechanisms maintaining signal reliability is social costs. While the social costs of over-signalling are well known, the social costs of under-signalling are underexplored, particularly for dynamic signals. In this study, we investigate a dynamic and olfactory-mediated signalling system that is ubiquitous among mammals: scent marking. Male house mice territorially scent mark their environment with metabolically costly urine marks. Competitive male mice are thought to deposit abundant scent marks in the environment. However, we recently identified a cohort of low-marking males that win fights. We hypothesized that there may be social costs imposed on individuals who under-invest in signalling. Here we find that scent mark investment predicts fight dynamics. Winning males that produce fewer scent marks prior to a fight engage in more intense fights that take longer to resolve. This effect appears to be driven by an unwillingness among losers to acquiesce to weakly signalling winners. We, therefore, find evidence for rival assessment of scent marks as well as social costs to under-signalling. This supports existing hypotheses for the importance of social punishment in maintaining optimal signalling equilibria. Our results further highlight the possibility of diverse signalling strategies in house mice.

Genetics of behavioural evolution in giant mice from Gough Island.

The evolution of behaviour on islands is a pervasive phenomenon that contributed to Darwin's theory of natural selection. Island populations frequently show increased boldness and exploration compared with their mainland counterparts. Despite the generality of this pattern, the genetic basis of island-associated behaviours remains a mystery. To address this gap in knowledge, we genetically dissected behaviour in 613 F2s generated by crossing inbred mouse strains from Gough Island (where they live without predators or human commensals) and a mainland conspecific. We used open field and light/dark box tests to measure seven behaviours related to boldness and exploration in juveniles and adults. Across all assays, we identified a total of 41 quantitative trait loci (QTL) influencing boldness and exploration. QTL have moderate effects and are often unique to specific behaviours or ages. Function-valued trait mapping revealed changes in estimated effects of QTL during assays, providing a rare dynamic window into the genetics of behaviour often missed by standard approaches. The genomic locations of QTL are distinct from those found in laboratory strains of mice, indicating different genetic paths to the evolution of similar behaviours. We combine our mapping results with extensive phenotypic and genetic information available for laboratory mice to nominate candidate genes for the evolution of behaviour on islands.

Steroid hormones in hair and fresh wounds reveal sex specific costs of reproductive engagement and reproductive success in wild house mice (Mus musculus domesticus).

Not only males but also females compete over reproduction. In a population of free-living house mice (Mus musculus domesticus), we analyzed how (metabolic) costs of aggressive interactions (reflected in fresh wounds and long-term corticosterone concentrations in hair) are predicted by individual reproductive physiology and reproductive success in males and females. Over eight years, we studied wounds and reproduction of more than 2800 adults under naturally varying environmental conditions and analyzed steroid hormones from more than 1000 hair samples. Hair corticosterone were higher and wounds more frequent in males than females. In males, wound occurrence increased with increasing breeding activity in the population, without affecting hair corticosterone levels. Unexpectedly, individual male reproductive success did not predict wounds, while hair corticosterone increased with increasing levels of hair testosterone and reproductive success. High corticosterone in hair of males might therefore reflect metabolic costs of fighting over reproduction. In females, hair corticosterone was generally lower than in males and high levels did not impede pregnancy. Reproductive investment (reflected in hair progesterone) was dissociated from reproductive success. Occasional wounds in females indicated individuals without recent reproductive success and revealed reproductive competition, presumably driven by instability in the social environment. In both sexes, corticosterone increased with age, but there was no evidence that received overt aggression, as indicated by wounds or elevated corticosterone, suppressed reproductive physiology. Our results diverge from laboratory findings and emphasize the need to also study animals in their natural environment in order to understand the complexity of their behavioral physiology.

Testing transgenerational transfer of personality in managed wildlife populations: a house mouse control experiment.

Pest species control operations are most effective if every individual in a population is targeted. Yet, individual personality drives variation in animal responses to devices such as traps and baits. Failing to account for differences in behavior during control operations may drive a selective removal, resulting in residual animals with biased expressions of personality. If these biased traits are passed onto offspring, control operations would become increasingly problematic. To test if biased trait expressions in founding populations are passed on to offspring, we quantified personality traits in wild-caught house mice (Mus musculus) and created founder populations selected for biased (high, low) or intermediate expressions of activity. We released the behaviorally biased populations into outdoor yards to breed to the F1 generation and, 10 weeks later, removed the mice and quantified the personality traits of the offspring. Despite the strong personality bias in founder populations, we observed no transgenerational transfer of personality and detected no personality bias in the F1 generation. Our results provide reassuring evidence that a single intensive control operation that selects for survivors with a personality bias is unlikely to lead to a recovering population inherently more difficult to eradicate, at least for house mice.

Significant Strain Variation in the Mutation Spectra of Inbred Laboratory Mice.

Mutation provides the ultimate source of all new alleles in populations, including variants that cause disease and fuel adaptation. Recent whole genome sequencing studies have uncovered variation in the mutation rate among individuals and differences in the relative frequency of specific nucleotide changes (the mutation spectrum) between populations. Although parental age is a major driver of differences in overall mutation rate among individuals, the causes of variation in the mutation spectrum remain less well understood. Here, I use high-quality whole genome sequences from 29 inbred laboratory mouse strains to explore the root causes of strain variation in the mutation spectrum. My analysis leverages the unique, mosaic patterns of genetic relatedness among inbred mouse strains to identify strain private variants residing on haplotypes shared between multiple strains due to their recent descent from a common ancestor. I show that these strain-private alleles are strongly enriched for recent de novo mutations and lack signals of widespread purifying selection, suggesting their faithful recapitulation of the spontaneous mutation landscape in single strains. The spectrum of strain-private variants varies significantly among inbred mouse strains reared under standardized laboratory conditions. This variation is not solely explained by strain differences in age at reproduction, raising the possibility that segregating genetic differences affect the constellation of new mutations that arise in a given strain. Collectively, these findings imply the action of remarkably precise nucleotide-specific genetic mechanisms for tuning the de novo mutation landscape in mammals and underscore the genetic complexity of mutation rate control.

Ultrasonic vocalizations in house mice depend upon genetic relatedness of mating partners and correlate with subsequent reproductive success.

BACKGROUND: Courtship vocalizations are used by males of many species to attract and influence the behavior of potential mating partners. Our aim here was to investigate the modulation and reproductive consequences of courtship ultrasonic vocalizations (USVs) in wild-derived house mice (Mus musculus musculus). The courtship USVs of male mice are surprisingly complex and are composed of a variety of different syllable types. Our specific aims were to test whether (1) the emission of courtship USVs depends upon the kinship of a potential mating partner, and (2) whether USV emission during courtship affects the pairs' subsequent reproductive success. RESULTS: We experimentally presented males with an unfamiliar female that was either genetically related or unrelated, and we recorded USV emission, first while the sexes were separated by a perforated partition and then during direct interactions, after removing the partition. USVs were detected by the Automatic Mouse Ultrasound Detector (A-MUD) and manually classified into 15 syllable types. The mice were kept together to test whether and how courtship vocalizations predict their subsequent reproductive success. We found that the mice significantly increased their amount of vocalizations (vocal performance) and number of syllable types (vocal repertoire) after the partition was removed and they began interacting directly. We show that unrelated pairs emitted longer and more complex USVs compared to related pairs during direct interactions. Unrelated pairs also had a greater reproductive success compared to related pairs, and in addition we found a negative correlation between the mean length and amount of vocalizations with the latency to their first litter. CONCLUSION: Our study provides evidence that house mice modulate the emission of courtship USVs depending upon the kinship of potential mating partners, and that courtship USVs correlate with reproductive success.

Discovery of two highly divergent negative-sense RNA viruses associated with the parasitic nematode, Capillaria hepatica, in wild Mus musculus from New York City.

Recent advances in high-throughput sequencing technology have led to a rapid expansion in the number of viral sequences associated with samples from vertebrates, invertebrates and environmental samples. Accurate host identification can be difficult in assays of complex samples that contain more than one potential host. Using unbiased metagenomic sequencing, we investigated wild house mice (Mus musculus) and brown rats (Rattus norvegicus) from New York City to determine the aetiology of liver disease. Light microscopy was used to characterize liver disease, and fluorescent microscopy with in situ hybridization was employed to identify viral cell tropism. Sequences representing two novel negative-sense RNA viruses were identified in homogenates of wild house mouse liver tissue: Amsterdam virus and Fulton virus. In situ hybridization localized viral RNA to Capillaria hepatica, a parasitic nematode that had infected the mouse liver. RNA from either virus was found within nematode adults and unembryonated eggs. Expanded PCR screening identified brown rats as a second rodent host for C. hepatica as well as both nematode-associated viruses. Our findings indicate that the current diversity of nematode-associated viruses may be underappreciated and that anatomical imaging offers an alternative to computational host assignment approaches.

Fitness Consequences of Female Alternative Reproductive Tactics in House Mice (Mus musculus domesticus).

Alternative reproductive tactics (ARTs) are defined as discrete differences in morphological, physiological, and/or behavioral traits associated with reproduction that occur within the same sex and population. House mice provide a rare example of ARTs in females, which can rear their young either solitarily or together with one or several other females in a communal nest. We assessed the fitness consequences of communal and solitary breeding in a wild population to understand how the two tactics can be evolutionarily stable. Females switched between the two tactics (with more than 50% of all females having two or more litters using both tactics), pointing toward communal and solitary breeding being two tactics within a single strategy and not two genetically determined strategies. Communal breeding resulted in reduced pup survival and negatively impacted female reproductive success. Older and likely heavier females more often reared their litters solitarily, indicating that females use a condition-dependent strategy. Solitary breeding seems the more successful tactic, and only younger and likely less competitive females might opt for communal nursing, even at the cost of increased pup mortality. This study emphasizes the importance of analyzing phenotypic plasticity and its role in cooperation in the context of female ARTs.

Effects of a male meiotic driver on male and female transcriptomes in the house mouse.

Not all genetic loci follow Mendel's rules, and the evolutionary consequences of this are not yet fully known. Genomic conflict involving multiple loci is a likely outcome, as restoration of Mendelian inheritance patterns will be selected for, and sexual conflict may also arise when sexes are differentially affected. Here, we investigate effects of the t haplotype, an autosomal male meiotic driver in house mice, on genome-wide gene expression patterns in males and females. We analysed gonads, liver and brain in adult same-sex sibling pairs differing in genotype, allowing us to identify t-associated differences in gene regulation. In testes, only 40% of differentially expressed genes mapped to the approximately 708 annotated genes comprising the t haplotype. Thus, much of the activity of the t haplotype occurs in trans, and as upregulation. Sperm maturation functions were enriched among both cis and trans acting t haplotype genes. Within the t haplotype, we observed more downregulation and differential exon usage. In ovaries, liver and brain, the majority of expression differences mapped to the t haplotype, and were largely independent of the differences seen in the testis. Overall, we found widespread transcriptional effects of this male meiotic driver in the house mouse genome.

Prior reproduction alters how mitochondria respond to an oxidative event.

An animal's pace of life is mediated by the physiological demands and stressors it experiences (e.g. reproduction) and one likely mechanism that underlies these effects is oxidative stress. Reproduction has been shown to increase or reduce oxidative stress under different conditions and to modify mitochondrial performance. We hypothesized that the changes associated with reproduction can alter how animals respond to future oxidative stressors. We tested this theory by comparing the organ-specific mitochondrial response in wild-derived female house mice. Specifically, we examined the effect of an oxidant (X-irradiation) on virgin mice and on mice that had reproduced. We measured liver and skeletal muscle mitochondrial density, respiratory performance, enzyme activity and oxidant production, as well as markers of oxidative damage to tissues. In the liver, prior reproduction prevented a radiation-induced reduction in mitochondrial density and increased mitochondrial respiratory performance. In skeletal muscle, prior reproduction resulted in a radiation-induced decline in mitochondrial density which could reduce the bioenergetic capacity of skeletal muscle mitochondria. Yet, electron transport chain complex I activity in skeletal muscle, which dropped after reproduction, returned to control levels following oxidant exposure. The results of this investigation indicate that prior reproduction alters the response of mitochondria to an oxidative challenge in an organ-specific manner. Such changes could have differential effects on future reproductive performance and risk of death.

Identification and Field Testing of Volatile Components in the Sex Attractant Pheromone Blend of Female House Mice.

Recently, it was reported (i) that the sex pheromone blend of male house mice, Mus musculus, comprises not only volatile components (3,4-dehydro-exo-brevicomin; 2-sec-butyl-4,5-dihydrothiazole) but also a component of low volatility (the sex steroid testosterone), and (ii) that the sex steroids progesterone and estradiol are sex pheromone components of female house mice. Here we tested the hypothesis that the sex attractant pheromone blend of female mice, analogous to that of male mice, also comprises volatile pheromone components. Analyzing by GC-MS the head space volatiles of bedding soiled with urine and feces of laboratory-kept females and males revealed three candidate pheromone components (CPCs) that were adult female-specific: butyric acid, 2-methyl butyric acid and 4-heptanone. In a two-choice laboratory experiment, adult males spent significantly more time in the treatment chamber baited with both the synthetic steroids (progesterone, estradiol) and the synthetic CPCs than in the paired control chamber baited only with the synthetic steroids. In field experiments, trap boxes baited with both the CPCs and the steroids captured 6.7-times more adult males and 4.7-times more juvenile males than trap boxes baited with the steroids alone. Conversely, trap boxes baited with both the CPCs and the steroids captured 4.3-times more adult males and 2.7-fold fewer adult females than trap boxes baited with the CPCs alone. In combination, these data support the conclusion that butyric acid, 2-methyl butyric acid and 4-heptanone are part of the sex attractant pheromone of female house mice. With progesterone and estradiol being pheromone components of both female brown rats, Rattus norvegicus, and female house mice, these three volatile components could impart specificity to the sexual communication system of house mice, brown rats and possibly other rodent species.

Individual odour signatures that mice learn are shaped by involatile major urinary proteins (MUPs).

BACKGROUND: Reliable recognition of individuals requires phenotypic identity signatures that are both individually distinctive and appropriately stable over time. Individual-specific vocalisations or visual patterning are well documented among birds and some mammals, whilst odours play a key role in social recognition across many vertebrates and invertebrates. Less well understood, though, is whether individuals are recognised through variation in cues that arise incidentally from a wide variety of genetic and non-genetic differences between individuals, or whether animals evolve distinctive polymorphic signals to advertise identity reliably. As a bioassay to understand the derivation of individual-specific odour signatures, we use female attraction to the individual odours of male house mice (Mus musculus domesticus), learned on contact with a male's scent marks. RESULTS: Learned volatile odour signatures are determined predominantly by individual differences in involatile major urinary protein (MUP) signatures, a specialised set of communication proteins that mice secrete in their urine. Recognition of odour signatures in genetically distinct mice depended on differences in individual MUP genotype. Direct manipulation using recombinant MUPs confirmed predictable changes in volatile signature recognition according to the degree of matching between MUP profiles and the learned urine template. Both the relative amount of the male-specific MUP pheromone darcin, which induces odour learning, and other MUP isoforms influenced learned odour signatures. By contrast, odour recognition was not significantly influenced by individual major histocompatibility complex genotype. MUP profiles shape volatile odour signatures through isoform-specific differences in binding and release of urinary volatiles from scent deposits, such that volatile signatures were recognised from the urinary protein fraction alone. Manipulation using recombinant MUPs led to quantitative changes in the release of known MUP ligands from scent deposits, with MUP-specific and volatile-specific effects. CONCLUSIONS: Despite assumptions that many genes contribute to odours that can be used to recognise individuals, mice have evolved a polymorphic combinatorial MUP signature that shapes distinctive volatile signatures in their scent. Such specific signals may be more prevalent within complex body odours than previously realised, contributing to the evolution of phenotypic diversity within species. However, differences in selection may also result in species-specific constraints on the ability to recognise individuals through complex body scents.

Female nursing partner choice in a population of wild house mice (Mus musculus domesticus).

BACKGROUND: Communal nursing in house mice is an example of cooperation where females pool litters in the same nest and indiscriminately nurse own and other offspring despite potential exploitation. The direct fitness benefits associated with communal nursing shown in laboratory studies suggest it to be a selected component of female house mice reproductive behaviour. However, past studies on communal nursing in free-living populations have debated whether it is a consequence of sharing the same nest or an active choice. Here using data from a long-term study of free-living, wild house mice we investigated individual nursing decisions and determined what factors influenced a female's decision to nurse communally. RESULTS: Females chose to nurse solitarily more often than expected by chance, but the likelihood of nursing solitarily decreased when females had more partners available. While finding no influence of pairwise relatedness on partner choice, we observed that females shared their social environment with genetically similar individuals, suggesting a female's home area consisted of related females, possibly facilitating the evolution of cooperation. Within such a home area females were more likely to nest communally when the general relatedness of her available options was relatively high. Females formed communal nests with females that were familiar through previous associations and had young pups of usually less than 5 days old. CONCLUSIONS: Our findings suggest that communal nursing was not a by-product of sharing the same nesting sites, but females choose communal nursing partners from a group of genetically similar females, and ultimately the decision may then depend on the pool of options available. Social partner choice proved to be an integrated part of cooperation among females, and might allow females to reduce the conflict over number of offspring in a communal nest and milk investment towards own and other offspring. We suggest that social partner choice may be a general mechanism to stabilize costly cooperation.

Sex Hormones Function as Sex Attractant Pheromones in House Mice and Brown Rats.

Sex hormones of mammals control the expression of sexual characteristics and bodily functions. The male hormone testosterone and the female hormones progesterone and estradiol are known to occur in urine markings of mice. Here, we show that all three hormones are also present in urine of brown rats, and that they are effective sexual communication signals (pheromones) that elicit attraction behavior of prospective mates in both brown rats and house mice. When added as lures to trap boxes in field experiments, synthetic testosterone, for example, increased captures of adult female mice 15-fold, and a blend of progesterone and estradiol increased captures of male mice eightfold and male rats 13-fold. Remarkably, these hormones increased captures even though the food- and pheromone-based baits to which they were added had previously been shown to be superior to current commercial rodent attractants. We predict that these sex hormones will function as sex attractant pheromones in diverse taxa.

Effect of Male House Mouse Pheromone Components on Behavioral Responses of Mice in Laboratory and Field Experiments.

Urine of male house mice, Mus musculus, is known to have primer pheromone effects on the reproductive physiology of female mice. Urine-mediated releaser pheromone effects that trigger certain behavioral responses are much less understood, and no field studies have investigated whether urine deposits by male or female mice, or synthetic mouse pheromone, increase trap captures of mice. In field experiments, we baited traps with bedding soiled with urine and feces of caged female or male mice, and recorded captures of mice in these and in control traps containing clean bedding. Traps baited with female bedding preferentially captured adult males, whereas traps baited with male bedding preferentially captured juvenile and adult females, indicating the presence of male- and female-specific sex pheromones in soiled bedding. Analyses of headspace volatiles emanating from soiled bedding by gas chromatography/mass spectrometry revealed that 3,4-dehydro-exo-brevicomin (DEB) was seven times more prevalent in male bedding and that 2-sec-butyl-4,5-dihydrothiazole (DHT) was male-specific. In a follow-up field experiment, traps baited with DEB and DHT captured 4 times more female mice than corresponding control traps, thus indicating that DEB and DHT are sex attractant pheromone components of house mouse males. Our study provides impetus to identify the sex attractant pheromone of female mice, and to develop synthetic mouse pheromone as a lure to enhance the efficacy of trapping programs for mouse control.

Bank voles (Myodes glareolus) and house mice (Mus musculus musculus; M. m. domesticus) in Europe are each parasitized by their own distinct species of Aspiculuris (Nematoda, Oxyurida).

The molecular phylogeny and morphology of the oxyuroid nematode genus Aspiculuris from voles and house mice has been examined. Worms collected from Myodes glareolus in Poland, Eire and the UK are identified as Aspiculuris tianjinensis, previously known only from China, while worms from Mus musculus from a range of locations in Europe and from laboratory mice, all conformed to the description of Aspiculuris tetraptera. Worms from voles and house mice are not closely related and are not derived from each other, with A. tianjinensis being most closely related to Aspiculuris dinniki from snow voles and to an isolate from Microtus longicaudus in the Nearctic. Both A. tianjinensis and A. tetraptera appear to represent recent radiations within their host groups; in voles, this radiation cannot be more than 2 million years old, while in commensal house mice it is likely to be less than 10,000 years old. The potential of Aspiculuris spp. as markers of host evolution is highlighted.

Female social preference for males that have evolved via monogamy: evidence of a trade-off between pre- and post-copulatory sexually selected traits?

When females mate with multiple males both pre- and post-copulatory sexual selections occur. It has been suggested that females benefit from polyandry when better-quality males are successful in sperm competition and sire high-quality offspring. Indeed, studies of experimental evolution have confirmed that sperm competition selects for both increased ejaculate quality and elevated offspring viability. Fewer investigations have explored whether these fitness benefits are evident beyond early life-history stages. Here, I used house mice (Mus domesticus) from selection lines that had been evolving for 25 generations under either polygamy or monogamy to test whether females preferred males from lines that had evolved with sperm competition. Males from the polygamous lines had previously been shown to achieve a fitness advantage under semi-natural conditions, deeming them to be of high genetic quality and leading to the a priori expectation that females would prefer males that had evolved with sperm competition compared with males that had not. Contrary to expectation, the data showed that sexually receptive females spent more time associating with males from the monogamous lines. This unexpected but interesting result is discussed in relation to sperm competition theory that predicts a trade-off between male investment in pre- and post-copulatory sexually selected traits.

Susceptibility of Synanthropic Rodents (Mus musculus, Rattus norvegicus and Rattus rattus) to H5N1 Subtype High Pathogenicity Avian Influenza Viruses.

Synanthropic wild rodents associated with agricultural operations may represent a risk path for transmission of high pathogenicity avian influenza viruses (HPAIVs) from wild birds to poultry birds. However, their susceptibility to HPAIVs remains unclear. In the present study, house mice (Mus musculus), brown rats (Rattus norvegicus), and black rats (Rattus rattus) were experimentally exposed to H5N1 subtype HPAIVs to evaluate their vulnerability to infection. After intranasal inoculation with HA clade 2.2 and 2.3.2.1 H5N1 subtype HPAIVs, wild rodents did not show any clinical signs and survived for 10- and 12-day observation periods. Viruses were isolated from oral swabs for several days after inoculation, while little or no virus was detected in their feces or rectal swabs. In euthanized animals at 3 days post-inoculation, HPAIVs were primarily detected in respiratory tract tissues such as the nasal turbinates, trachea, and lungs. Serum HI antibodies were detected in HA clade 2.2 HPAIV-inoculated rodents. These results strongly suggest that synanthropic wild rodents are susceptible to infection of avian-origin H5N1 subtype HPAIVs and contribute to the virus ecosystem as replication-competent hosts. Detection of infectious viruses in oral swabs indicates that wild rodents exposed to HPAIVs could contaminate food, water, and the environment in poultry houses and play roles in the introduction and spread of HPAIVs in farms.

SARS-CoV-2 Surveillance of Wild Mice and Rats in North American Cities.

From July 2020 to June 2021, 248 wild house mice (Mus musculus), deer mice (Peromyscus maniculatus), brown rats (Rattus norvegicus), and black rats (Rattus rattus) from Texas and Washington, USA, and British Columbia, Canada, were tested for SARS-CoV-2 exposure and infection. Two brown rats and 11 house mice were positive for neutralizing antibodies using a surrogate virus neutralization test, but negative or indeterminate with the Multiplexed Fluorometric ImmunoAssay COVID-Plex, which targets full-length spike and nuclear proteins. Oro-nasopharyngeal swabs and fecal samples tested negative by RT-qPCR, with an indeterminate fecal sample in one house mouse. Continued surveillance of SARS-CoV-2 in wild rodents is warranted.