Population control of the house mouse (Mus musculus), Norway rat (Rattus norvegicus) and black rat (Rattus rattus) is common practice worldwide. Our objective was to assess the impact on animal welfare of lethal and non-lethal control methods, including three dispatch methods. We used the Sharp and Saunders welfare assessment model with eight experts scoring eleven control methods and three dispatch methods used on the three species. We presumed the methods were performed as prescribed, only taking into account the effect on the target animal (and not, for example, on non-target catches). We did not assess population control efficacy of the methods. Methods considered to induce the least suffering to the target animal were captive-bolt traps, electrocution traps and cervical dislocation, while those with the greatest impact were anticoagulants, cholecalciferol and deprivation. Experts indicated considerable uncertainty regarding their evaluation of certain methods, which emphasises the need for further scientific research. In particular, the impact of hydrogen cyanide, chloralose and aluminium phosphide on animal welfare ought to be investigated. The experts also stressed the need to improve Standard Operating Procedures and to incorporate animal welfare assessments in Integrated Pest Management (IPM). The results of our study can help laypeople, professionals, regulatory agencies and legislators making well-informed decisions as to which methods to use when controlling commensal rodents.

Female laboratory rats (Rattus norvegicus; Wistar, Alderley Park) were housed as singletons or groups of three in units of two cages. Units were divided by different types of barrier which allowed varying degrees of social contact across the barrier. Singletons were established either with another singleton on the other side of the barrier or with a group of three as neighbours. Single-housing among females had markedly less effect on time budgeting and pathophysiological measures than among males in a similar, earlier study. In particular, singletons showed a less marked increase in self-directed behaviours, particularly tail chasing, and a smaller reduction in undirected movement around the cage. The smaller reduction in mobility may reflect a greater tendency for singly housed females to attempt escape. Females generally showed much higher levels of escape-oriented behaviours than males and up to a threefold increase in such behaviours when housed singly. Differences in time budgeting and in the apparent significance of social separation between the sexes can be interpreted in terms of differences in socio-sexual strategy and potential mating opportunity, with singleton males responding to their cage as a territory, but singleton females seeking to re-establish social contact. Such an interpretation is consistent with the effects of barrier type on behaviour in singleton females, in which time spent in escape-oriented behaviours reflected the extent to which the barrier facilitated, or frustrated, contact with neighbours.

Rats are a well-understood and widely used laboratory species that should be provided with environmentally enriched caging in line with modern animal welfare guidelines. This paper reviews which sources of enrichment are effective and should be prioritised, and how methods for providing enrichment might be selected using rats’ preferences as a guide. Rats demonstrate high demand for social contact and prefer larger cages, and cages with shelters, nesting material and foraging devices. Rats also discriminate between different methods of providing a given type of enrichment. It is clear that rats should be provided with enrichments such as social contact and shelter, and, in fact, that these should probably be considered basic husbandry requirements rather than optional improvements. It is still difficult, however, for animal caretakers to access proven, standardised methods for providing appropriately enriched caging, and the level of enrichment routinely provided to most rats in the laboratory appears to be low. Further research is required to assess the impact of enrichment upon research variables and to develop commercially viable enrichment products for rats in the laboratory.

There are instances when animals are introduced and expected to live alongside unfamiliar conspecifics within zoos, laboratories and wildlife sanctuaries. These pairings of unfamiliar animals may result in stress, trauma, or even death, in addition to reduced confidence in data resulting from these subjects. For species that communicate relatedness, sex, social status, and emotional state through olfactory cues (eg pheromones), one means of counteracting aggression may involve a period of partial separation — where animals are close enough to become acquainted — while a permeable barrier maintains separation. For our study, we evaluated the use of a novel, autoclavable, wire-mesh partition to separate potential aggressors. We tested different pairs of 24 wild-type male Norway rats (Rattus norvegicus), previously kept in social isolation for seven days. Each control pair were merged directly into one cage, while pairs from the experimental groups underwent three pre-exposure sessions that lasted two to four days. We used continuous video recordings to assess five common threat displays: lateral threat, keep down, upright posture, chase, and clinch attack. We used two types of bedding: new (unscented) bedding and recently used bedding that conveyed scents from both merged rats. We found that rats subjected to pre-exposure demonstrated lower aggression levels across three of the five metrics (lateral threats, upright postures, and keep downs). We conclude that permeable partitions show promise as a humane mechanism to mix new individuals into preexisting colonies. Further research may explore whether partitions could be helpful with other species that communicate social information by pheromones or direct visual inspection.

The nematode Angiostrongylus cantonensis is the most common cause of neuroangiostrongyliasis (manifested as eosinophilic meningitis) in humans. Gastropod molluscs are used as intermediate hosts and rats of various species are definitive hosts of this parasite. In this study, we identified several environmental factors associated with the presence and abundance of terrestrial gastropods in an impoverished urban region in Brazil. We also found that body condition, age and presence of co-infection with other parasite species in urban Rattus norvegicus, as well as environmental factors were associated with the probability and intensity of A. cantonensis infection. The study area was also found to have a moderate prevalence of the nematode in rodents (33% of 168 individuals). Eight species of molluscs (577 individuals) were identified, four of which were positive for A. cantonensis. Our study indicates that the environmental conditions of poor urban areas (presence of running and standing water, sewage, humidity and accumulated rain and accumulation of construction materials) influenced both the distribution and abundance of terrestrial gastropods, as well as infected rats, contributing to the maintenance of the A. cantonensis transmission cycle in the area. Besides neuroangiostrongyliasis, the presence of these hosts may also contribute to susceptibility to other zoonoses.

Urban slums provide suitable conditions for infestation by rats, which harbour and shed a wide diversity of zoonotic pathogens including helminths. We aimed to identify risk factors associated with the probability and intensity of infection of helminths of the digestive tract in an urban slum population of Rattus norvegicus. Among 299 rats, eleven species/groups of helminths were identified, of which Strongyloides sp., Nippostrongylus brasiliensis and, the human pathogen, Angiostrongylus cantonensis were the most frequent (97, 41 and 39%, respectively). Sex interactions highlighted behavioural differences between males and females, as eg males were more likely to be infected with N. brasiliensis where rat signs were present, and males presented more intense infections of Strongyloides sp. Moreover, rats in poor body condition had higher intensities of N. brasiliensis. We describe a high global richness of parasites in R. norvegicus, including five species known to cause disease in humans. Among these, A. cantonensis was found in high prevalence and it was ubiquitous in the study area – knowledge which is of public health importance. A variety of environmental, demographic and body condition variables were associated with helminth species infection of rats, suggesting a comparable variety of risk factors for humans.

Urban slum environments in the tropics are conducive to the proliferation and the spread of rodent-borne zoonotic pathogens to humans. Calodium hepaticum (Brancroft, 1893) is a zoonotic nematode known to infect a variety of mammalian hosts, including humans. Norway rats (Rattus norvegicus) are considered the most important mammalian host of C. hepaticum and are therefore a potentially useful species to inform estimates of the risk to humans living in urban slum environments. There is a lack of studies systematically evaluating the role of demographic and environmental factors that influence both carriage and intensity of infection of C. hepaticum in rodents from urban slum areas within tropical regions. Carriage and the intensity of infection of C. hepaticum were studied in 402 Norway rats over a 2-year period in an urban slum in Salvador, Brazil. Overall, prevalence in Norway rats was 83% (337/402). Independent risk factors for C. hepaticum carriage in R. norvegicus were age and valley of capture. Of those infected the proportion with gross liver involvement (i.e. >75% of the liver affected, a proxy for a high level intensity of infection), was low (8%, 26/337). Sixty soil samples were collected from ten locations to estimate levels of environmental contamination and provide information on the potential risk to humans of contracting C. hepaticum from the environment. Sixty percent (6/10) of the sites were contaminated with C. hepaticum. High carriage levels of C. hepaticum within Norway rats and sub-standard living conditions within slum areas may increase the risk to humans of exposure to the infective eggs of C. hepaticum. This study supports the need for further studies to assess whether humans are becoming infected within this community and whether C. hepaticum is posing a significant risk to human health.

Leptospirosis is a zoonosis caused by bacteria of the genus Leptospira. The disease is globally distributed and a major public health concern. The Norway rat (Rattus norvegicus) is the main reservoir of the pathogen in urban slums of developing and developed countries. The potential routes of intra-specific leptospire transmission in rats are largely unknown. Herein, we identified pathogenic Leptospira spp. in breast tissue and milk of naturally infected rats. We examined kidney, breast tissue and milk from 24 lactating rats for the presence of leptospires using immunofluorescence, immunohistochemistry, polymerase chain reaction (PCR) and scanning electronic microscopy. All 24 rats had evidence for Leptospira in the kidneys, indicating chronic carriage. The majority of kidney-positive rats had detectable leptospires in milk (18, 75%) and breast tissue (16, 67%), as evidenced by immunofluorescence assay and immunohistochemistry. Four (17%) milk samples and two (8%) breast tissue samples were positive by quantitative real-time PCR. Scanning electron microscopy confirmed the presence of leptospires in breast tissue. No major pathological changes in breast tissue were found. This study, for the first time, identified leptospires in the milk and breast tissue of wild Norway rats, suggesting the possibility of milk-borne transmission of leptospirosis to neonates.

The objective of this work was to evaluate the rate of meiosis resumption and nuclear maturation of rat (Rattus norvegicus) oocytes selected for in vitro maturation (IVM) after staining of cumulus–oocyte complexes (COCs) with blue cresyl brilliant (BCB) using different protocols: exposure for 30, 60 or 90 min at 26 μM BCB (Experiment 1), and exposure for 60 min at 13, 20 or 26 μM BCB (Experiment 2). In Experiment 1, the selection of oocytes exposed to BCB for 60 min was found to be the most suitable, as meiosis resumption rates in the BCB+ group (n = 35/61; 57.37%) were the closest to the observed in the control (not exposed) group (n = 70/90; 77.77%) and statistically higher than the values observed for the BCB− group (n = 3/41; 7.32%). Additionally, the more effective evaluation of diagnostic tests (sensitivity and negative predictive value 100%) was observed in COCs exposed for 60 min. In Experiment 2, the 13 μM BCB+ group presented rates of meiosis resumption (n = 57/72; 72.22%) similar to the control group (n = 87/105; 82.86%) and higher than other concentration groups. However, this results of the analysis between BCB− oocytes was also higher in the 13 μM BCB group (n = 28/91; 30.78%) when compared with BCB− COCs exposed to 20 μM (n = 3/62; 4.84%) or 26 μM (n = 3/61; 4.92%) BCB. The nuclear maturation rate in the 13 μM BCB group was similar between BCB+ or BCB− oocytes. The 20 μM BCB group had a lower rate of nuclear maturation of BCB− oocytes than other groups. Thus, our best results in the selection of Rattus norvegicus oocytes by staining with BCB were obtained using the concentration of 13 μM and 20 μM, and an incubation period of 60 min.

Using both correlational and experimental evidence, the relationship between parasite load and host activity was assessed in brown rats, Rattus norvegicus. Two hypotheses were tested – (1) that parasites with indirect life-cycles, involving transmission between a prey and its predator, will alter the activity of the intermediate host so as to increase its susceptibility to predation by the definitive host and (2) that activity levels in parasitized rats would be increased rather than decreased. Four groups of rats (n = 140) were examined. One group (n = 50) were wild brown rats trapped from 3 UK farmsteads, with naturally occurring parasites. The others were purpose-bred wild/laboratory hybrid rats with experimentally induced parasitic infections of either (n = 15) adult-acquired or (n = 15) congenitally-acquired Toxoplasma gondii (an indirect life-cycle parasite), or (n = 15) Syphacia muris (a direct life-cycle parasite). Uninfected hybrid rats (n = 45), matched for sex, age and weight, served as controls. Rats were housed individually in outdoor cages, and their activities were recorded on video-tapes for 6 non-consecutive 10 h nights. Exercise wheels were also available for the hybrid rats. Out of 6 parasite species detected in the wild rats, T. gondii was the only one which required predation by a definitive host to complete its life-cycle, and was also the only parasite to be associated with higher activity levels in infected than uninfected rats. Hybrid rats infected with T. gondii were also more active than those uninfected, whereas there were no differences in activity levels between S. muris infected and uninfected rats. This study shows that the indirect life-cycle parasite T. gondii can influence the activity of its intermediate host the rat. I suggest that this may facilitate its transmission to the cat definitive host.

The effect of Toxoplasma gondii on rat behaviour was assessed in a colony of 36 free-ranging wild/laboratory hybrid rats allowed to compete freely for food and mates in a (100 m2) outdoor naturalistic enclosure. T. gondii infection had no effect on social status or mating success, both the product of costly and competitive activities. However, the propensity to explore novel stimuli in their environment was higher in infected than uninfected individuals. These results are consistent with the hypothesis that T. gondii only affects the behavioural traits which selectively benefit the parasite, rather than causing a general alteration of rat behaviour.

To study congenital transmission of Toxoplasma gondii during acute and chronic infections, 4 pregnant Sprague-Dawley rats were each fed 10000 oocysts of the VEG strain. Toxoplasma gondii was recovered from 33, 55, 83 and 57% of rats (F1) when dams were inoculated at 6, 9, 12 or 15 days of gestation, respectively. Progeny of 15 congenitally infected female rats were examined for T. gondii. Toxoplasma gondii was recovered from tissues of 1 of 155 rats (F2) born to congenitally infected dams. A total of 4 (F2) females were mated; 0 of 40 (F3) rats born to them were infected. None of the acutely infected 4 dams that had given birth to congenitally infected litters produced congenitally infected offspring during the second pregnancy. Thus, unlike mice, evidence for repeated congenital transmission of T. gondii in the rat was found in <1% of cases. Of the 16 congenitally T. gondii infected pups with demonstrable tissue cysts, 5 were seronegative (<1[ratio ]4) in the Sabin-Feldman dye test and 5 were seronegative (<1[ratio ]20) in the modified agglutination test by the use of whole formalinized tachyzoites and mercaptoethanol.