Genomic and Phenotypic Adaptations of Rattus tanezumi to Cold Limit Its Further Northward Expansion and Range Overlap with R. norvegicus.

Global climate change has led to shifts in the distribution ranges of many terrestrial species, promoting their migration from lower altitudes or latitudes to higher ones. Meanwhile, successful invaders have developed genetic adaptations enabling the colonization of new environments. Over the past 40 years, Rattus tanezumi (RT) has expanded into northern China (Northwest and North China) from its southern origins. We studied the cold adaptation of RT and its potential for northward expansion by comparing it with sympatric Rattus norvegicus (RN), which is well adapted to cold regions. Through population genomic analysis, we revealed that the invading RT rats have split into three distinct populations: the North, Northwest, and Tibetan populations. The first two populations exhibited high genetic diversity, while the latter population showed remarkably low genetic diversity. These rats have developed various genetic adaptations to cold, arid, hypoxic, and high-UV conditions. Cold acclimation tests revealed divergent thermoregulation between RT and RN. Specifically, RT exhibited higher brown adipose tissue activity and metabolic rates than did RN. Transcriptome analysis highlighted changes in genes regulating triglyceride catabolic processes in RT, including Apoa1 and Apoa4, which were upregulated, under selection and associated with local adaptation. In contrast, RN showed changes in carbohydrate metabolism genes. Despite the cold adaptation of RT, we observed genotypic and phenotypic constraints that may limit its ability to cope with severe low temperatures farther north. Consequently, it is less likely that RT rats will invade and overlap with RN rats in farther northern regions.

Approach/Avoidance Behavior to Novel Objects is Correlated with the Serotonergic and Dopaminergic Systems in the Brown Rat (Rattus norvegicus).

The brown rat (Rattus norvegicus) is known to show three types of behavioral responses to novel objects. Whereas some rats are indifferent to novel objects, neophobic and neophilic rats show avoidance and approach behavior, respectively. Here, we compared the dopaminergic, serotonergic, and noradrenergic systems immunohistochemically among these rats. Trapped wild rats and laboratory rats were first individually exposed to the novel objects in their home cage. Wild rats were divided into neophobic and indifferent rats depending on their behavioral responses. Similarly, laboratory rats were divided into neophilic and indifferent rats. Consistent with the behavioral differences, in the paraventricular nucleus of the hypothalamus, Fos expression in corticotropin-releasing hormone-containing neurons was higher in the neophobic rats than in the indifferent rats. In the anterior basal amygdala, the neophobic rats showed higher Fos expression than the indifferent rats. In the posterior basal amygdala, the neophobic and neophilic rats showed lower and higher Fos expressions than the indifferent rats, respectively. When we compared the neuromodulatory systems, in the dorsal raphe, the number of serotonergic neurons and Fos expression in serotonergic neurons increased linearly from neophobic to indifferent to neophilic rats. In the ventral tegmental area, Fos expression in dopaminergic neurons was higher in the neophilic rats than in the indifferent rats. These results demonstrate that approach/avoidance behavior to novel objects is correlated with the serotonergic and dopaminergic systems in the brown rat. We propose that the serotonergic system suppresses avoidance behavior while the dopaminergic system enhances approach behavior to novel objects.

Detection of circovirus in free-ranging brown rats (Rattus norvegicus).

Accidentally found, two poisoned brown rats from Hungary were surveyed for presence of circoviral DNA, using specific nested primers, designed against the rep gene of the virus. Both specimens were positive. The whole genomes were amplified using inverse PCR based on the Rep sequence parts and sequenced by the primer walking method. Genomic analyses revealed that these novel rat viruses, together with tawny owl-associated circovirus reported by Italian researchers in 2022, are sequence variations of the same virus from genus Circovirus. In phylogenetic reconstructions, these circovirus strains detected from brown rats clustered closest to circoviruses derived from faeces samples of various predatory mammals. Molecular data as well as the phylogenetic analyses of the complete derived replication-associated protein and the capsid protein, as well as the prey preference of the host species of the recently described tawny owl-associated virus suggest that brown rat could be the evolutionary adapted host of the viruses described in this paper (brown rat circovirus types 1 and 2) and the previously reported tawny owl-associated virus. Possible pathogenic and zoonotic role of these viruses need further studies.

Angiostrongylus cantonensis Infection in Brown Rats (Rattus norvegicus), Atlanta, Georgia, USA, 2019-2022.

Rat lungworm (Angiostrongylus cantonensis), a zoonotic parasite invasive to the United States, causes eosinophilic meningoencephalitis. A. cantonensis harbors in rat reservoir hosts and is transmitted through gastropods and other paratenic hosts. We discuss the public health relevance of autochthonous A. cantonensis cases in brown rats (Rattus norvegicus) in Atlanta, Georgia, USA.

SARS-CoV-2 Exposure in Norway Rats (Rattus norvegicus) from New York City.

Millions of Norway rats (Rattus norvegicus) inhabit New York City (NYC), presenting the potential for transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from humans to rats. We evaluated SARS-CoV-2 exposure among 79 rats captured from NYC during the fall of 2021. Our results showed that 13 of the 79 rats (16.5%) tested IgG- or IgM-positive, and partial SARS-CoV-2 genomes were recovered from all 4 rats that were qRT-PCR (reverse transcription-quantitative PCR)-positive. Genomic analyses suggest these viruses were associated with genetic lineage B, which was predominant in NYC in the spring of 2020 during the early pandemic period. To further investigate rat susceptibility to SARS-CoV-2 variants, we conducted a virus challenge study and showed that Alpha, Delta, and Omicron variants can cause infections in wild-type Sprague Dawley (SD) rats, including high replication levels in the upper and lower respiratory tracts and induction of both innate and adaptive immune responses. Additionally, the Delta variant resulted in the highest infectivity. In summary, our results indicate that rats are susceptible to infection with Alpha, Delta, and Omicron variants, and wild Norway rats in the NYC municipal sewer systems have been exposed to SARS-CoV-2. Our findings highlight the need for further monitoring of SARS-CoV-2 in urban rat populations and for evaluating the potential risk of secondary zoonotic transmission from these rat populations back to humans. IMPORTANCE The host tropism expansion of SARS-CoV-2 raises concern for the potential risk of reverse-zoonotic transmission of emerging variants into rodent species, including wild rat species. In this study, we present both genetic and serological evidence for SARS-CoV-2 exposure to the New York City wild rat population, and these viruses may be linked to the viruses that were circulating during the early stages of the pandemic. We also demonstrated that rats are susceptible to additional variants (i.e., Alpha, Delta, and Omicron) that have been predominant in humans and that susceptibility to infection varies by variant. Our findings highlight the reverse zoonosis of SARS-CoV-2 to urban rats and the need for further monitoring of SARS-CoV-2 in rat populations for potential secondary zoonotic transmission to humans.

Social distancing measures differentially affected rats in North America and Tokyo.

Because rats are commensal organisms that depend on human activities for food, shifts in human behavior will have pronounced effects on local rat populations. In the spring of 2020, social distancing measures were implemented globally to curtail the spread of SARS-CoV-2. This presented a unique opportunity to obtain information regarding the immediate effects of shifts in human behavior on rat populations in a variety of countries. In response to increased sightings of rats in the USA that were reported in American media, we analyzed the changes in the number of public service calls in Tokyo, Japan. We found that the number of calls increased after the implementation of social distancing measures, suggesting that rat sightings had also increased in Tokyo. We then surveyed the changes in the business activities of pest management professionals in the USA, Canada, and Tokyo. We found that the activities were increased in 50 to 60% of the respondents from the USA and Canada. In contrast, 60 to 70% of the respondents from Tokyo answered that their activities were not changed. These results implied that, following the implementation of social distancing measures, rat infestations increased in North America, but not in Tokyo. The survey also suggested that roof rats were considered to be the predominant rodent species in Tokyo. This may account for the limited infestations in Tokyo because roof rats are more sedentary than brown rats. Taken together, our findings suggest that social distancing measures differentially affected rat populations in North America and Tokyo. Supplementary Information: The online version contains supplementary material available at 10.1007/s10340-021-01405-z.

Genetic characterizations of Toll-like receptors in the brown rat and their associations with pathogen infections.

Toll-like receptors (TLRs) are important initiators of innate immune responses that target host-pathogen interactions. However, further research into the molecular characteristics of TLRs in wild populations is required, as well as how TLRs genetically influenced pathogen infections in the brown rat (Rattus norvegicus). Here, we explored the genetic characterization and evolution of 2 sensing nucleic acid TLRs (TLR7 and TLR8) and 2 sensing non-nucleic acid TLRs (TLR2 and TLR4) in the wild brown rat, and assessed their associations with 2 RNA viruses (Seoul hantavirus and rat hepatitis E virus (HEV)) and 2 bacteria (Leptospira and Bartonella). In these 4 TLRs, we discovered a total of 16 variants. Furthermore, TLR8 had high genetic diversity among 7 variants, while TLR2 had low genetic diversity with only 1 variant. According to selective pressure analyses, TLR4, TLR7, and TLR8 genes evolved under purifying selection. Interestingly, significant associations were found between 3 TLR8 variants and HEV infection, as well as 1 TLR2 variant and Bartonella infection. Overall, our findings provided a glimpse into the genetic characterization of TLRs in the brown rat, and further demonstrated that TLR2 and TLR8 genetic variations were related to Bartonella and HEV infection, respectively. Especially, TLR8 may be a good candidate immune gene for future research on molecular ecology and functional adaptation in wild populations.

Surface Waters and Urban Brown Rats as Potential Sources of Human-Infective Cryptosporidium and Giardia in Vienna, Austria.

Cryptosporidium and Giardia are waterborne protozoa that cause intestinal infections in a wide range of warm-blooded animals. Human infections vary from asymptomatic to life-threatening in immunocompromised people, and can cause growth retardation in children. The aim of our study was to assess the prevalence and diversity of Cryptosporidium and Giardia in urban surface water and in brown rats trapped in the center of Vienna, Austria, using molecular methods, and to subsequently identify their source and potential transmission pathways. Out of 15 water samples taken from a side arm of the River Danube, Cryptosporidium and Giardia (oo)cysts were detected in 60% and 73% of them, with concentrations ranging between 0.3-4 oocysts/L and 0.6-96 cysts/L, respectively. Cryptosporidium and Giardia were identified in 13 and 16 out of 50 rats, respectively. Eimeria, a parasite of high veterinary importance, was also identified in seven rats. Parasite co-ocurrence was detected in nine rats. Rat-associated genotypes did not match those found in water, but matched Giardia previously isolated from patients with diarrhea in Austria, bringing up a potential role of rats as sources or reservoirs of zoonotic pathogenic Giardia. Following a One Health approach, molecular typing across potential animal and environmental reservoirs and human cases gives an insight into environmental transmission pathways and therefore helps design efficient surveillance strategies and relevant outbreak responses.

Prevalence and Genetic Characterization of Two Mitochondrial Gene Sequences of Strobilocercus Fasciolaris in the Livers of Brown Rats (Rattus norvegicus) in Heilongjiang Province in Northeastern China.

Rodents constitute the largest and most successful group of mammals worldwide. Brown rats (Rattus norvegicus) are one of the most common rodent species, and they serve as intermediate hosts of Hydatigera taeniaeformis. Although there have been a few studies reporting on the presence of the larval form of H. taeniaeformis (strobilocercus fasciolaris) in brown rats worldwide, little information is available on the genetic characterization of this parasite, with no molecular data from China. Therefore, from April 2014 to March 2016, this study was carried out to understand the prevalence and genetic characters of strobilocercus fasciolaris in brown rats captured in Heilongjiang Province in northeastern China. The livers of brown rats were collected and examined for the presence of cysts. Each cyst was identified based on morphological observation: the larvae with the naked eye and the scolexes under a microscope. The results were confirmed by polymerase chain reaction (PCR) and sequencing of the cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 4 (nad4) genes. At the investigated sites, 11.8% (13/110) of the brown rats were infected with strobilocercus fasciolaris. Based on sequence analysis, there were 10 and six haplotypes regarding the cox1 and the nad4 loci, with 24 and 42 polymorphic sites, respectively (degree of intraspecific variation: 0.3%-4.4% and 0.6%-4.7%, respectively). Twelve nucleotide sequences (six of the 10 at the cox1 locus and all six at the nad4 locus) have not previously been described. Base differences in three of the six novel cox1 gene sequences and five of the six novel nad4 gene sequences caused amino acid changes. Phylogenetic analyses of the cox1 and nad4 gene sequences based on neighbor-joining and Bayesian inference trees indicated that all the strobilocercus fasciolaris isolates belonged to Hydatigera taeniaeformis sensu stricto (s.s.). This is the first report on the genetic characterization of strobilocercus fasciolaris in brown rats in China. The findings of novel cox1 and nad4 nucleotide and amino acid sequences may reflect the region-specific genetic characterization of the parasite. The data will be useful to explore the biological and epidemiological significance of the intraspecific variation within H. taeniaeformis s.s.

Ectoparasites of brown rats (Rattus norvegicus) in Grenada, West Indies.

BACKGROUND AND AIM: Arthropod ectoparasites (mites, lice, ticks, and fleas) on common house rats or brown rats (Rattus norvegicus) are known to transmit zoonotic pathogens and diminish rat health. To the best of our knowledge, there is no published information regarding the prevalence of ectoparasites on R. norvegicus in Grenada. This study aimed to determine the prevalence and types of ectoparasites present on brown rats from Grenada. MATERIALS AND METHODS: One hundred sixty-eight rats were collected live from the parishes of St. George and St. David, Grenada, from May to July 2017. Following euthanasia, external parasites were collected using fine combs, thumb forceps, and paper tape. Tape samples and free specimens were placed in containers with 70% ethanol. External parasites were evaluated using dissection microscopy. RESULTS: Over 2000 ectoparasites were collected from 149 of the 168 trapped rats (88.7%). Ectoparasites identified included mesostigmatid mites (found on 84.6% of infested rats), fur mites in the families Atopomelidae and Listrophoridae (67.1%), Polyplax spp. lice (6.7%), fleas (3.4%), an unidentified larval tick (0.7%), and a mite in the family Myobiidae (0.7%). Infestation rates were higher in St. David Parish (86/89; 96.6%) than in St. George Parish (63/79; 79.7%) (p=0.001). When comparing sex and age, males had a marginal increase in infestation rate (83/89; 93.3%) compared to females (66/79; 83.5%) (p=0.054), and adults had an infestation rate of 90.7% (97/107) compared to juvenile rats who had a 66.7% (14/21) infestation rate. CONCLUSION: Brown rats in Grenada are heavily infested with ectoparasites, including known vectors of pathogens. Future studies will examine the prevalence of zoonotic pathogens in these arthropods.

Detection of serum antibodies against Leptospira spp. in brown rats (Rattus norvegicus) from Grenada, West Indies.

BACKGROUND AND AIM: Leptospirosis is an emerging disease of animals and humans. Among rodents brown rats (Rattus norvegicus) are an important reservoir of bacteria Leptospira. There is a paucity of information on reservoirs of Leptospira in Grenada. This study was conducted to estimate the prevalence of antibodies against Leptospira spp. in brown rats in a densely human populated area of Grenada. MATERIALS AND METHODS: Blood samples from 169 brown rats were collected and sera screened for antibodies against Leptospira spp. using enzyme-linked immunosorbent assay. RESULTS: Among a total of 169 brown rats trapped in two parishes in Grenada, 77/169 (45.5%) were positive for Leptospira spp. antibodies. A significant difference in seropositive population of brown rats between two collection sites was observed. No differences were found between sex and age of seropositive rats. CONCLUSION: Due to the close contact of brown rats with humans in Grenada, rats should be considered a high-risk factor in transmission of Leptospira to humans. Appropriate preventive measures should be instituted to prevent the transmission of Leptospira infection to humans.

Prevalence of antibodies against visceralizing Leishmania spp. in brown rats from Grenada, West Indies.

BACKGROUND AND AIM: Leishmania spp. are known to cause disease in man and animals. Rats are considered important reservoir hosts and transmission takes place through the bite of female sand fly, Phlebotomus spp. To the best of our knowledge, there is no published information on Leishmania infection in rats in Grenada. This study was conducted to estimate the antibodies for visceralizing Leishmania spp. (VL) in rats (Rattus norvegicus) from Grenada. MATERIALS AND METHODS: A total of 146 brown rats (R. norvegicus) were trapped live from two parishes (St. George and St. David) in Grenada. Following anesthesia, blood was collected from the heart through thoracic puncture. The serum was collected after the centrifugation of blood. Serum was tested for antibodies to VL. with a commercially available immunochromatographic dipstick test which is licensed for use in animals and humans. RESULTS: The seroprevalence of antibodies against Leishmania spp. was found in 34 of 146 rats (23.3%; CI 95% from 16.70 to 30.99). No significant differences were found between sexes and young or adults. The prevalence between parishes (St. George and St. David) was also not significant. CONCLUSION: The results show that rats (R. norvegicus) in Grenada are exposed to Leishmania spp. The rats could play an important role in the transmission of leishmaniasis to humans and other animals in Grenada.

Urban rat races: spatial population genomics of brown rats (Rattus norvegicus) compared across multiple cities.

Urbanization often substantially influences animal movement and gene flow. However, few studies to date have examined gene flow of the same species across multiple cities. In this study, we examine brown rats (Rattus norvegicus) to test hypotheses about the repeatability of neutral evolution across four cities: Salvador, Brazil; New Orleans, USA; Vancouver, Canada; and New York City, USA. At least 150 rats were sampled from each city and genotyped for a minimum of 15 000 genome-wide single nucleotide polymorphisms. Levels of genome-wide diversity were similar across cities, but varied across neighbourhoods within cities. All four populations exhibited high spatial autocorrelation at the shortest distance classes (less than 500 m) owing to limited dispersal. Coancestry and evolutionary clustering analyses identified genetic discontinuities within each city that coincided with a resource desert in New York City, major waterways in New Orleans, and roads in Salvador and Vancouver. Such replicated studies are crucial to assessing the generality of predictions from urban evolution, and have practical applications for pest management and public health. Future studies should include a range of global cities in different biomes, incorporate multiple species, and examine the impact of specific characteristics of the built environment and human socioeconomics on gene flow.

Seroprevalence of hantaviruses and Leptospira in muskrat and coypu trappers in the Netherlands, 2016.

Aims: Seoul orthohantavirus (SEOV) and Leptospira spp. are zoonotic pathogens with rats as main reservoir. Recently, the presence of SEOV in brown rats was reported in one region in the Netherlands. Brown rats are a frequent bycatch in traps placed to catch muskrats (Ondatra zibethicus) and coypus (Myocastor coypus), and thus are a potential health risk for trappers. It was our aim to determine the seroprevalence of orthohantavirus, specifically SEOV, and Leptospira spp in Dutch trappers. Methods and results: Participating trappers provided serum samples and completed an online questionnaire. The serum was tested for the presence of antibodies against six orthohantaviruses and eight Leptospira serovars. Two hundred-sixty trappers completed the online questionnaire (65%), and 246 (61%) and 162 (40%) serum samples were tested for relevant orthohantaviruses and Leptospira spp., respectively. The seroprevalence of Puumala orthohantavirus in Dutch trappers was 0.4% (95% CI: 0.1-2.3%). None of the participants tested positive for SEOV. The seroprevalence of leptospirosis was 1.2% (95% CI: 0.3-4.4%), although Leptospira spp. are present in brown rats in the Netherlands.Significance of study: The results indicate that the infections with orthohantaviruses and leptospires is low for muskrat and coypu trappers.

Molecular characterizations of Cryptosporidium spp. and Enterocytozoon bieneusi in brown rats (Rattus norvegicus) from Heilongjiang Province, China.

BACKGROUND: Cryptosporidium spp. and Enterocytozoon bieneusi are prevalent zoonotic pathogens responsible for the high burden of diarrheal diseases worldwide. Rodents are globally overpopulated and are known as reservoirs or carriers of a variety of zoonotic pathogens including Cryptosporidium spp. and E. bieneusi. However, few data are available on genetic characterizations of both pathogens in rodents in China. The aim of the present work was to determine the prevalence and genetic characterizations of Cryptosporidium spp. and E. bieneusi in brown rats (Rattus norvegicus) from Heilongjiang, China. METHODS: A total of 242 wild brown rats were captured in Heilongjiang Province of China. A fresh fecal specimen was collected directly from the intestinal and rectal content of each brown rat. All the fecal specimens were examined for the presence of Cryptosporidium spp. and E. bieneusi by PCR and sequencing of the partial small subunit (SSU) rRNA gene and the internal transcribed spacer (ITS) region of the rRNA gene of the two pathogens, respectively. RESULTS: The infection rate was 9.1% (22/242) for Cryptosporidium spp. and 7.9% (19/242) for E. bieneusi. Sequence analysis confirmed the presence of C. ubiquitum (1/22, 4.5%) and three genotypes of Cryptosporidium, including Cryptosporidium rat genotype I (14/22, 63.6%), Cryptosporidium rat genotype IV (6/22, 27.3%) and Cryptosporidium suis-like genotype (1/22, 4.5%). Meanwhile, two E. bieneusi genotypes were identified, including D (17/19, 89.5%) and Peru6 (2/19, 10.5%). CONCLUSIONS: To the best of our knowledge, Enterocytozoon bieneusi genotype Peru6 was identified in rodents for the first time globally and Cryptosporidium rat genotype I and Cryptosporidium rat genotype IV were found in rats in China for the first time. The finding of zoonotic C. ubiquitum and C. suis-like genotype, as well as E. bieneusi genotypes, suggests that brown rats pose a threat to human health. It is necessary to control brown rat population in the investigated areas and improve local people's awareness of the transmission risk of the two pathogens from brown rats to humans.

Seoul Virus Infection in Humans, France, 2014-2016.

We report detection of Seoul virus in 3 patients in France over a 2-year period. These patients accounted for 3 of the 4 Seoul virus infections among 434 hantavirus infections (1.7%) reported during this time. More attention should be given to this virus in Europe where surveillance has been focused mostly on Puumala and Dobrava-Belgrade hantaviruses.

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.

The Sex Attractant Pheromone of Male Brown Rats: Identification and Field Experiment.

Trapping brown rats is challenging because they avoid newly placed traps in their habitat. Herein, we report the identification of the sex pheromone produced by male brown rats and its effect on trap captures of wild female brown rats. Collecting urine- and feces-soiled bedding material of laboratory-kept rats and comparing the soiled-bedding odorants of juvenile and adult males, as well as of adult males and females, we found nine compounds that were specific to, or most prevalent in, the odor profiles of sexually mature adult males. When we added a synthetic blend of six of these compounds (2-heptanone, 4-heptanone, 3-ethyl-2-heptanone, 2-octanone, 2-nonanone, 4-nonanone) to one of two paired food-baited trap boxes, these boxes attracted significantly more laboratory-strain female rats in laboratory experiments, and captured ten times more wild female rats in a field experiment than the corresponding control boxes. Our data show that the pheromone facilitates captures of wild female brown rats.

Natural and synthetic vocalizations of brown rat pups, Rattus norvegicus, enhance attractiveness of bait boxes in laboratory and field experiments.

BACKGROUND: Rats are often neophobic and thus do not readily enter trap boxes which are mandated in rodent management to help reduce the risk of accidental poisoning or capture of non-target animals. Working with brown rats, Rattus norvegicus, as a model species, our overall objective was to test whether sound cues from pups could be developed as a means to enhance captures of rats in trap boxes. RESULTS: Recording vocalizations from three-day-old pups after removal from their natal nest with both sonic and ultrasonic microphones revealed frequency components in the sonic range (1.8-7.5 kHz) and ultrasonic range (18-24 kHz, 33-55 kHz, 60-96 kHz). In two-choice laboratory bioassays, playback recordings of these vocalizations induced significant phonotactic and arrestment responses by juvenile, subadult and adult female and male rats. The effectiveness of engineered 'synthetic' rat pup sounds was dependent upon their frequency components, sound durations and the sound delivery system. Unlike other speakers, a piezoelectric transducer emitting sound bursts of 21 kHz with a 63-KHz harmonic, and persisting for 20-300 ms, proved highly effective in attracting and arresting adult female rats. In a field experiment, a battery-powered electronic device fitted with a piezoelectric transducer and driven by an algorithm that randomly generated sound cues resembling those recorded from rat pups and varying in fundamental frequency (19-23 kHz), duration (20-300 ms) and intermittent silence (300-5000 ms) significantly enhanced captures of rats in trap boxes baited with a food lure and soiled bedding material of adult female rats. CONCLUSION: Our study provides proof of concept that rat-specific sound cues or signals can be effectively reproduced and deployed as a means to enhance capture of wild rats. © 2016 Society of Chemical Industry.

Is it too cold for Leptospira interrrogans transmission on the Faroese Islands?

Leptospira interrogans is a bacterium that can infect most mammal species. Brown rats are considered to be one of the most important reservoirs of Leptospira because they frequently are infected and live in close proximity to humans. Past studies of prevalence of Leptospira in brown rats indicate that temperature--both high and low--may negatively affect the prevalence rate in rats, so that Leptospira is rare or even absent at temperatures below 7-8 °C. Here we investigated the prevalence of infection in brown rats on the Faroese Islands (mean temperature of 6.5 °C) and did not find any infected animals in a sample of 95 animals. We propose that prevalence rates of Leptospira are very low in rural brown rats in the cooler Scandinavian regions, even though urban/sewer rats might be highly infected in the same regions.