Physiological strategies in wild rodents: immune defenses of commensal rats

The importance of issues associated with urban/commensal rats and mice (property damage, management costs, and health risks) press upon research on these animals. While the demography of commensal rodents is mostly studied, the need for understanding factors influencing their natural morbidity/mortality is also stressed. In this respect, more attention is expected to be paid to immunity, the physiological mechanism of defense against host survival threats (pathogens, parasites, diseases). Commensal rats and mice carry numerous pathogens that evoke diverse immune responses. The state of immunity in commensal house mice is studied in great detail, owing to the use of laboratory strains in biomedical research. Because commensal rats are, compared to mice, carriers of more zoonotic agents, rats' immunity is studied mainly in that context. Some of these zoonotic agents cause chronic, asymptomatic infections, which justified studies of immunological mechanisms of pathogen tolerance versus clearance regulation in rats. Occurrence of some infections in specific tissues/organs pressed upon analysis of local/regional immune responses and/or immunopathology. A survey of immunological activity/responses in commensal rats is given in this review, with mention of existing data in commensal mice. It should throw some light on the factors relevant to their morbidity and lifespan, supplementing the knowledge of commensal rodent ecology.

Screening of West Nile Virus, Herpesvirus, and Parvovirus in Rattus spp. in Klang Valley, Malaysia

Free-roaming and scavenging lifestyles of Rattus spp. in densely populated urban areas expose them to multiple pathogens that facilitate the transmission of infection to the human population more rapidly, raising public health concerns. There is limited information on the status of rat susceptibility to virus infection, particularly West Nile virus (WNV), herpesvirus, and parvovirus, to prepare for emerging zoonosis. A total of 23 (n = 23) blood samples collected from Rattus spp. in the wet market areas of Klang Valley, Malaysia, were subjected to molecular assay using a one-step reverse transcription-polymerase chain reaction (RT-PCR) to detect the highly conserved region of the WNV capsid and pre-membrane protein via nested polymerase chain reaction (PCR) assay targeting highly conserved amino acid motifs within the herpesviral DNA-directed DNA polymerase gene (DPOL) and polymerase chain reaction (PCR) assay targeting the parvovirus non-structural (NS) protein. As a result, 4 out of 23 (17.39%) rats were positive for herpesvirus DNA, but none were positive for WNV RNA and parvovirus DNA. The positive PCR amplicons of herpesvirus DNA were subjected to partial DNA sequencing analysis, 100% identical to Acomys herpesvirus SVMS 226,222 from Betaherpesvirinae, which is highly suggestive of rat cytomegalovirus (RCMV). This study has successfully demonstrated the presence of RCMV from Rattus spp. in the Klang Valley. The RCMV potentially crosses species barriers and establishes infection, raising public health concerns. The non-viraemic state of WNV or parvovirus infection, low sample size, and limited niche distribution emphasise the need for the expansion of this study in the future.

Monitoring Urban Zoonotic Virus Activity: Are City Rats a Promising Surveillance Tool for Emerging Viruses?

Urban environments represent unique ecosystems where dense human populations may come into contact with wildlife species, some of which are established or potential reservoirs for zoonotic pathogens that cause human diseases. Finding practical ways to monitor the presence and/or abundance of zoonotic pathogens is important to estimate the risk of spillover to humans in cities. As brown rats (Rattus norvegicus) are ubiquitous in urban habitats, and are hosts of several zoonotic viruses, we conducted longitudinal sampling of brown rats in Vienna, Austria, a large population center in Central Europe. We investigated rat tissues for the presence of several zoonotic viruses, including flaviviruses, hantaviruses, coronaviruses, poxviruses, hepatitis E virus, encephalomyocarditis virus, and influenza A virus. Although we found no evidence of active infections (all were negative for viral nucleic acids) among 96 rats captured between 2016 and 2018, our study supports the findings of others, suggesting that monitoring urban rats may be an efficient way to estimate the activity of zoonotic viruses in urban environments.

Let's get wild: A review of free-ranging rat assays as context-enriched supplements to traditional laboratory models

More than 24,000 rodent studies are published annually, with the vast majority of these studies focused on genetically undiverse animals in highly-controlled laboratory settings. However, findings from the laboratory have become increasingly unreliable for predicting outcomes in field and clinical settings, leading to a perceived crisis in translational research. One cause of this disparity might be that most human societies, in contrast to laboratory rodents, are genetically diverse and live in super-enriched environments. Methods for importing wild rats into the laboratory, and also exporting laboratory-style chambers into natural environments are not well-known outside their respective disciplines. Therefore, we have reviewed the current status of supplements to the laboratory rodent assay. We progress logically from highly-controlled experiments with natural breeding colonies to purely naturalistic approaches with free-ranging rats. We then highlight a number of approaches that allow genetically-diverse wild rats to be utilized in context-enriched paradigms. While considering the benefits and shortcomings of each available approach, we detail protocols for random sampling, remote-sensing, and deployment of laboratory chambers in the field. As supplements to standardized laboratory trials, some of these assays could offer key insights to help unify outcomes between laboratory and field studies. However, we note several outstanding questions that must be addressed such as: the trade-off between control and context, possible reductions in sample size, ramifications for the 'standardization fallacy', and ethical dilemmas of working with wild animals. Given these challenges, further innovation will be required before supplemental assays can be made broadly-accessible and thus, transferrable across disciplines.

Detection of rodent-borne parasitic pathogens of wild rats in Serdang, Selangor, Malaysia: A potential threat to human health

Rodent species, such as Rattus rattus diardii and Rattus norvegicus are invasive species of wild rats that serve as potential reservoirs of important human's pathogens. Parasitic zoonosis accounts for over 60% of all human infectious diseases worldwide. This situation arises from the recent changes in the global climate and ecosystem composition, which led to the spread of rodents and rodent-borne pathogens globally. The aim of this study was to determine the occurrence of rodent's parasites and their zoonotic potentials in some selected areas in UPM. Rodents were captured using live-traps and euthanised for helminths and protozoan recovery. Intestinal parasites were detected and identified from stool samples using formalin ethyl-acetate concentration technique (FECT), while tissue parasites were identified by histopathological examination of selected tissue sections of the liver, brain, lungs, and muscle. In this study, a total of 89 wild rats were captured. Twelve species of intestinal and tissue parasites were recorded, of which, Taenia taeniaeformis accounts for the highest infection recorded (28%) followed by Hymenolepis nana (19.5%) and Capillaria hepatica (19.1%), while Toxoplasma gondii was the least parasite (6.7%) identified. Furthermore, other parasites species observed include, Cryptosporidium spp. (21.3%), Entamoeba histolytica/Entamoeba dispar and Moniliformis moniliformis (17.9%), Angiostrongylus cantonensis (16.8%), Hymenolepis diminuta (16.1%), Giardia spp. (14.6%), Trichuris spp. (12.3%), and Sarcocystis spp. (6.74). Based on the results obtained in the present study, 17.1% and 15.4% of the rodents captured were confirmed positive for at least one species of intestinal or tissue parasites, respectively. The presence of these zoonotic parasites in the wild rats suggests the potential risk of rodent-borne zoonotic disease transmission to humans. Hence, the need to improved rats control intervention and public health awareness among the populace.

Molecular detection of Pneumocystis in the lungs of cats

The genus Pneumocystis comprises potential pathogens that reside normally in the lungs of a wide range of mammals. Although they generally behave as transient or permanent commensals, they can occasionally cause life-threatening pneumonia (Pneumocystis pneumonia; PCP) in immunosuppressed individuals. Several decades ago, the presence of Pneumocystis morphotypes (trophic forms and cysts) was described in the lungs of normal cats and cats with experimentally induced symptomatic PCP (after immunosuppression by corticosteroids); yet to date spontaneous or drug-induced PCP has not been described in the clinical feline literature, despite immunosuppression of cats by long-standing retrovirus infections or after kidney transplantation. In this study, we describe the presence of Pneumocystis DNA in the lungs of normal cats (that died of various unrelated causes; n = 84) using polymerase chain reactions (PCRs) targeting the mitochondrial small and large subunit ribosomal RNA gene (mtSSU rRNA and mtLSU rRNA). The presence of Pneumocystis DNA was confirmed by sequencing in 24/84 (29%) cats, with evidence of two different sequence types (or lineages). Phylogenetically, lineage1 (L1; 19 cats) and lineage 2 (L2; 5 cats) formed separate clades, clustering with Pneumocystis from domestic pigs (L1) and carnivores (L2), respectively. Results of the present study support the notion that cats can be colonized or subclinically infected by Pneumocystis, without histological evidence of damage to the pulmonary parenchyma referable to pneumocystosis. Pneumocystis seems most likely an innocuous pathogen of cats’ lungs, but its possible role in the exacerbation of chronic pulmonary disorders or viral/bacterial coinfections should be considered further in a clinical setting.

Viral Disease

This chapter discusses infections of rats with viruses in the following 14 virus families: Adenoviridae, Arenaviridae, Coronaviridae, Flaviviridae, Hantaviridae, Hepeviridae, Herpesviridae, Paramyxoviridae, Parvoviridae, Picornaviridae, Pneumoviridae, Polyomaviridae, Poxviridae, and Reoviridae . Serological surveys indicate that parvoviruses, coronaviruses, cardioviruses, and pneumoviruses are the most prevalent in laboratory rats. A new polyomavirus and a new cardiovirus that cause disease in laboratory rats are described. Metagenomic analyses of feces or intestinal contents from wild rats have detected viruses from an additional nine virus families that could potentially cause infections in laboratory rats.

Medical Management and Diagnostic Approaches

This chapter reviews the basic principles of medical management of rat colonies and diagnostic approaches to detect infectious diseases of rats. As is the case with all other species, rats are susceptible to a variety of injuries and diseases that can cause distress, morbidity, or mortality. Any facility that houses rats must develop monitoring programs designed to rapidly identify health-related problems so they can be communicated to appropriate veterinary or animal care personnel to be resolved. These programs generally consist of multiple components, some of which are directed toward individual animals and others that assess the health status of rat populations as a whole. Topics include individual animal monitoring and care, signs of illness and distress, colony health management, components of microbiological monitoring programs, including agents commonly targeted and sentinel programs, quarantine, biological material screening, diagnostic testing methodologies, including culture, serology, molecular diagnostic and histopathology, test profiles and interpretation, management of disease outbreaks, and treatment and prevention strategies for infectious agents.

Occurrence of Gastrointestinal Parasites in Small Mammals from Germany

An increase in zoonotic infections in humans in recent years has led to a high level of public interest. However, the extent of infestation of free-living small mammals with pathogens and especially parasites is not well understood. This pilot study was carried out within the framework of the "Rodent-borne pathogens" network to identify zoonotic parasites in small mammals in Germany. From 2008 to 2009, 111 small mammals of 8 rodent and 5 insectivore species were collected. Feces and intestine samples from every mammal were examined microscopically for the presence of intestinal parasites by using Telemann concentration for worm eggs, Kinyoun staining for coccidia, and Heidenhain staining for other protozoa. Adult helminths were additionally stained with carmine acid for species determination. Eleven different helminth species, five coccidians, and three other protozoa species were detected. Simultaneous infection of one host by different helminths was common. Hymenolepis spp. (20.7%) were the most common zoonotic helminths in the investigated hosts. Coccidia, including Eimeria spp. (30.6%), Cryptosporidium spp. (17.1%), and Sarcocystis spp. (17.1%), were present in 40.5% of the feces samples of small mammals. Protozoa, such as Giardia spp. and amoebae, were rarely detected, most likely because of the repeated freeze-thawing of the samples during preparation. The zoonotic pathogens detected in this pilot study may be potentially transmitted to humans by drinking water, smear infection, and airborne transmission.

Internal parasitic burdens in brown rats (Rattus norvegicus) from Grenada, West Indies

This study identified the endoparasites in Brown rat (Rattus norvegicus) during May to July 2017 in Grenada, West Indies. A total of 162 rats, 76 females and 86 males were trapped from St. George and St. David parishes in Grenada. The collected fecal samples were examined for parasitic eggs and/or oocysts using simple fecal flotation technique. Adult parasites found in the intestinal tract were examined for identification. The overall prevalence of intestinal parasites among rats was 79 %.

Ten helminth species were recovered, several of which were reported for the first time in rodents in Grenada. The internal parasites consist of seven nematodes (Angiostrongylus spp., Nippostrongylus braziliensis, Heterakis spumosa, Strongyloides ratti, Aspiculuris tetraptera, Syphacia spp. and Protospirura spp.), one cestode (Hymenolepsis diminuta), one acanthocephalan (Moniliformis moniliformis) and one protozoa species (Eimeria spp.). The most prevalent zoonotic species were Angiostrongylus spp. (35.2%), Hymenolepsis diminuta (7.4%) and Moniliformis moniliformis (3.1%). Several nonzoonotic endoparasites; which included Nippostrongylus braziliensis (50.6%), Heterakis spumosa (15.4%), Strongyloides ratti (43.2%), Aspiculuris tetraptera (2.5%), Syphacia spp. (1.9%), Protospirura spp. (1.2%) and Eimeria spp. (4.7%) were also identified. The most prevalent parasites were Nippostrongylus brasiliensis (50.6%), Strongyloides ratti (43.2%) and Angiostrongylus spp. (35.2%). Co-infections occurred with up to six species per rat showing different combinations of parasitic infections.

Seroprevalence of Rodent Pathogens in Wild Rats from the Island of St. Kitts, West Indies

Simple Summary

The role of rodents in the transmission of many diseases is widely known. Wild rats abundant in urban environments may transmit diseases to humans and other animals, including laboratory rodents used for biomedical research in research facilities, possibly compromising research data. In order to gather information about the various diseases present around such facilities, it is important to conduct routine surveillance of wild rodents in the area. In this pilot study, we surveyed 22 captured wild rats (Rattus norvegicus and Rattus rattus) from the Caribbean island of St. Kitts for 19 microorganisms. Information gained from such surveillance data would be beneficial in assessing regional public health risks and when implementing routine laboratory rodent health monitoring protocols.

Abstract

A pilot seroprevalence study was conducted to document exposure to selected pathogens in wild rats inhabiting the Caribbean island of St. Kitts. Serum samples collected from 22 captured wild rats (Rattus norvegicus and Rattus rattus) were tested for the presence of antibodies to various rodent pathogens using a rat MFI2 serology panel. The samples were positive for cilia-associated respiratory bacillus (13/22; 59.1%), Clostridium piliforme (4/22; 18.2%), Mycoplasma pulmonis (4/22; 18.2%), Pneumocystis carinii (1/22; 4.5%), mouse adenovirus type 2 (16/22; 72.7%), Kilham rat virus (15/22; 68.2%), reovirus type 3 (9/22; 40.9%), rat parvovirus (4/22; 18.2%), rat minute virus (4/22; 18.2%), rat theilovirus (2/22; 9.1%), and infectious diarrhea of infant rats strain of group B rotavirus (rat rotavirus) (1/22; 4.5%). This study provides the first evidence of exposure to various rodent pathogens in wild rats on the island of St. Kitts. Periodic pathogen surveillance in the wild rat population would be beneficial in assessing potential regional zoonotic risks as well as in enhancing the current knowledge when implementing routine animal health monitoring protocols in facilities with laboratory rodent colonies.

Pathology of wild Norway rats in Vancouver, Canada

To achieve a contemporary understanding of the common and rare lesions that affect wild, urban Norway rats ( Rattus norvegicus), we conducted a detailed pathology analysis of 672 rats from Vancouver, British Columbia, Canada. Grossly evident lesions, such as wounds, abscesses, and neoplasms, were present in 71 of 672 rats (11%) and tended to be severe. The most common and significant lesions were infectious and inflammatory, most often affecting the respiratory tract and associated with bite wounds. We assessed a subset of rats (up to n = 406 per tissue) for the presence of microscopic lesions in a variety of organ systems. The most frequent lesions that could impact individual rat health included cardiomyopathy (128 of 406; 32%), chronic respiratory tract infections as indicated by pulmonary inducible bronchus-associated lymphoid tissue (270 of 403; 67%), tracheitis (192 of 372; 52%), and thyroid follicular hyperplasia (142 of 279; 51%). We isolated 21 bacterial species from purulent lesions in rats with bacterial infections, the most frequent of which were Escherichia coli, Enterococcus sp., and Staphylococcus aureus. Parasitic diseases in rats resulted from infection with several invasive nematodes: Capillaria hepatica in the liver (242 of 672; 36%), Eucoleus sp. in the upper gastrointestinal tract (164 of 399; 41%), and Trichosomoides crassicauda in the urinary bladder (59 of 194; 30%). Neoplastic, congenital, and degenerative lesions were rare, which likely reflects their adverse effect on survival in the urban environment. Our results establish a baseline of expected lesions in wild urban rats, which may have implications for urban rat and zoonotic pathogen ecology, as well as rat control in cities worldwide.

Rodentia

This chapter includes diseases of animals in the order Rodentia, in which there are over 2000 species representing 40% of all mammals. This incredibly diverse order includes members inhabiting every continent, either naturally or in human-made environments. While rodents have been the cause or implicated in disease transmission that has lead to human pandemics, such as the Black Death, and the decimation of certain animal species, like island-dwelling birds; genetically modified rodents have contributed significantly to the advancement of biomedical research and human health. There are more than 50 species of endangered rats, mice, voles, squirrels, and marmots. The recent extinction of the Bramble Cay melomys represents the first human-induced rodent extinction linked to climate change. Rodents are the reservoir host of several human and domestic pathogens of concern listed by OIE. Herein, we highlight those diseases of rodents that lead to clinically important gross and microscopic lesions.

Development of a duplex real-time RT-PCR for the simultaneous detection and differentiation of Theiler's murine encephalomyelitis virus and rat theilovirus

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A duplex real-time RT-PCR was developed and evaluated for detection of TMEV and RTV.

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The duplex assay could differentiate between TMEV and RTV.

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The duplex assay was specific, sensitive and reproducible.

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The duplex assay was more sensitive and effective than conventional RT-PCR.

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It is a useful tool for routine health monitoring of laboratory rodents.

Theiler’s murine encephalomyelitis virus (TMEV) and rat theilovirus (RTV), the member of the genus Cardiovirus, are widespread in laboratory mice and rats, and are potential contaminants of biological materials. Cardioviruses infection may cause serious complications in biomedical research. To improve the efficiency of routine screening for Cardioviruses infection, a duplex real-time reverse transcriptase polymerase chain reaction (RT-PCR) assay was developed for simultaneous detection and differentiation of TMEV and RTV. The duplex assay was specific for reference strains of TMEV and RTV, and no cross-reaction was found with seven other rodent viruses. The limits of detection of both TMEV and RTV were 4 × 10¹ copies RNA/reaction. Reproducibility was estimated using standard dilutions, with coefficients of variation <3.1%. 439 clinical samples were evaluated by both duplex real-time RT-PCR and conventional RT-PCR. For 439 clinical samples，95 samples were positive for TMEV and 72 samples were positive for RTV using duplex real-time RT-PCR approach, whereas only 77 samples were positive for TMEV and 66 samples were positive for RTV when conventional RT-PCR was applied. Mixed infections were found in 20 samples when analyzed by conventional RT-PCR whereas 30 samples were found to be mixed infection when duplex real-time RT-PCR was applied. This duplex assay provides a useful tool for routine health monitoring and screening of contaminated biological materials of these two viruses.

Helminth parasites in black rats (Rattus rattus) and brown rats (Rattus norvegicus) from different environments in the Netherlands

BACKGROUND

Rattus norvegicus (brown rat) and Rattus rattus (black rat) are known carriers of bacteria, viruses, and parasites of zoonotic and veterinary importance. Moreover, rats may play a role in the transmission of muscle larvae of the zoonotic nematode Trichinella spiralis to farm animals. We aimed to study the intestinal and intramuscular helminths in wild rats from three different environments to assess the relevance of rats as carrier of zoonotic parasites for public health.

MATERIALS AND METHODS

Wild brown rats (117 individuals) and black rats (44 individuals) were captured at farms, in suburban and in rural environments in the Netherlands. Intestinal helminths were isolated and identified morphologically. Artificial digestion was used to isolate muscle larvae.

RESULTS AND DISCUSSION

Morphological analysis of rat intestinal contents yielded six nematode species (Syphacia muris, Heterakis spumosa, Aonchotheca murissylvatici, Trichuris muris, Nippostrongylus brasiliensis, and Strongyloides sp.), three cestode species (Hymenolepis diminuta, H. nana and Hymenolepis (=Rodentolepis) fraterna), and four trematode species (Plagiorchis muris, Plagiorchis proximus, Echinostoma chloropodis, and Notocotylus imbricatus).Black rats at farms displayed the lowest intestinal helminth species variation (six species) and carried overall on average 0.93 species simultaneously. In comparison, brown rats at farms carried seven helminth species and 1.91 species simultaneously. Brown rats from suburban environments displayed the highest species variation (11 species) at 1.82 simultaneous helminth species. Absence of trematodes from rats at farms may suggest limited exchange of rats between farms and surrounding wet rural environments. We report four species of veterinary (Syphacia muris) or zoonotic relevance (Hymenolepis diminuta, Hymenolepis nana and Plagiorchis muris). We did not find Trichinella muscle larvae, consistent with long-term prevalence in Dutch wild rats.

Respiratory Pathology and Pathogens in Wild Urban Rats (Rattus norvegicus and Rattus rattus)

Norway ( Rattus norvegicus) and black rats ( Rattus rattus) are common peridomestic species, yet little is known about wild rat ecology, including their natural diseases. We describe gross and histological lesions in the respiratory tract of a sample of 711 wild urban rats. A subset was examined for 19 distinct categories of histological lesions in the respiratory tract. Testing for known respiratory pathogens included serology and polymerase chain reaction (PCR) of lung samples. Grossly evident lesions were rare (8/711; 1%). Upper respiratory tract inflammation was present in 93 of 107 (87%) rats and included rhinitis, submucosal and periglandular lymphoplasmacytic tracheitis, and/or tracheal intraluminal necrotic debris and was significantly associated ( P < .05) with the presence of cilia-associated respiratory bacillus (CARB), Mycoplasma pulmonis, and increased body mass (odds ratio [OR] = 1.09; 95% confidence interval [CI] = 1.05–1.14 per 10 g). Within the lungs, peribronchiolar and/or perivascular lymphoplasmacytic cuffs were present in 152 of 199 rats (76%) and were also significantly associated ( P ≤ .02) with CARB, M. pulmonis, and increased body mass (OR = 1.20; 95% CI = 1.14–1.27 per 10 g). Rats were frequently coinfected with M. pulmonis and CARB, and lesions associated with these pathogens were histologically indistinguishable. Pneumocystis sp was detected in 48 of 102 (47%) rats using PCR but was not significantly associated with lesions. This description of pathology in the respiratory system of wild rats demonstrates that respiratory disease is common. Although the impact of these lesions on individual and population health remains to be investigated, respiratory disease may be an important contributor to wild rat morbidity and mortality.

Intestinal nematodes from small mammals captured near the demilitarized zone, Gyeonggi province, Republic of Korea

A total of 1,708 small mammals (1,617 rodents and 91 soricomorphs), including Apodemus agrarius (n = 1,400), Microtus fortis (167), Crocidura lasiura (91), Mus musculus (32), Myodes (= Eothenomys) regulus (9), Micromys minutus (6), and Tscherskia (= Cricetulus) triton (3), were live-trapped at US/Republic of Korea (ROK) military training sites near the demilitarized zone (DMZ) of Paju, Pocheon, and Yeoncheon, Gyeonggi Province from December 2004 to December 2009. Small mammals were examined for their intestinal nematodes by necropsy. A total of 1,617 rodents (100%) and 91 (100%) soricomorphs were infected with at least 1 nematode species, including Nippostrongylus brasiliensis, Heligmosomoides polygyrus, Syphacia obvelata, Heterakis spumosa, Protospirura muris, Capillaria spp., Trichuris muris, Rictularia affinis, and an unidentified species. N. brasiliensis was the most common species infecting small mammals (1,060; 62.1%) followed by H. polygyrus (617; 36.1%), S. obvelata (370; 21.7%), H. spumosa (314; 18.4%), P. muris (123; 7.2%), and Capillaria spp. (59; 3.5%). Low infection rates (0.1-0.8%) were observed for T. muris, R. affinis, and an unidentified species. The number of recovered worms was highest for N. brasiliensis (21,623 worms; mean 20.4 worms/infected specimen) followed by S. obvelata (9,235; 25.0 worms), H. polygyrus (4,122; 6.7 worms), and H. spumosa (1,160; 3.7 worms). A. agrarius demonstrated the highest prevalence for N. brasiliensis (70.9%), followed by M. minutus (50.0%), T. triton (33.3%), M. fortis (28.1%), M. musculus (15.6%), C. lasiura (13.2%), and M. regulus (0%). This is the first report of nematode infections in small mammals captured near the DMZ in ROK.

Evaluation of pneumonia virus of mice as a possible human pathogen

Pneumonia virus of mice (PVM), a relative of human respiratory syncytial virus (RSV), causes respiratory disease in mice. There is serologic evidence suggesting widespread exposure of humans to PVM. To investigate replication in primates, African green monkeys (AGM) and rhesus macaques (n = 4) were inoculated with PVM by the respiratory route. Virus was shed intermittently at low levels by a subset of animals, suggesting poor permissiveness. PVM efficiently replicated in cultured human cells and inhibited the type I interferon (IFN) response in these cells. This suggests that poor replication in nonhuman primates was not due to a general nonpermissiveness of primate cells or poor control of the IFN response. Seroprevalence in humans was examined by screening sera from 30 adults and 17 young children for PVM-neutralizing activity. Sera from a single child (6%) and 40% of adults had low neutralizing activity against PVM, which could be consistent with increasing incidence of exposure following early childhood. There was no cross-reaction of human or AGM sera between RSV and PVM and no cross-protection in the mouse model. In native Western blots, human sera reacted with RSV but not PVM proteins under conditions in which AGM immune sera reacted strongly. Serum reactivity was further evaluated by flow cytometry using unfixed Vero cells infected with PVM or RSV expressing green fluorescent protein (GFP) as a measure of viral gene expression. The reactivity of human sera against RSV-infected cells correlated with GFP expression, whereas reactivity against PVM-infected cells was low and uncorrelated with GFP expression. Thus, PVM specificity was not evident. Our results indicate that the PVM-neutralizing activity of human sera is not due to RSV- or PVM-specific antibodies but may be due to low-affinity, polyreactive natural antibodies of the IgG subclass. The absence of PVM-specific antibodies and restriction in nonhuman primates makes PVM unlikely to be a human pathogen.

Rapid identification of Mycoplasma pulmonis isolated from laboratory mice and rats using matrix-assisted laser desorption ionization time-of-flight mass spectrometry

Mycoplasma species identification is based on biochemical, immunological, and molecular methods that require several days for accurate identification. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a novel method for identification of bacteria and has recently been introduced into the clinical microbiology laboratory as a rapid and accurate technique. This method allows a characteristic mass spectral fingerprint to be obtained from whole inactivated mycoplasmal cells. In this study, we evaluated the performance of the MALDI-TOF MS for the identification of Mycoplasma by comparison with standard sequence analysis of 16S rRNA. We developed the first database of MALDI-TOF MS profiles of Mycoplasma species, containing Mycoplasma pulmonis, M. arthritidis, and M. neurolyticum, which are the most common pathogens in mice and/or rats, and species-specific spectra were recorded. Using the database, 6 clinical isolates were identified. Six tracheal swabs from 4 mice and 2 rats were cultured on PPLO agar for 4 to 7 days, and the colonies were directly applied to analyze the protein profiles. Five strains were identified as M. pulmonis, and 1 strain from a mouse was identified as M. neurolyticum (spectral scores were >2.00); the results were consistent with the results of the 16S rRNA gene sequence analysis (homologies>97.0%). These data indicate that MALDI-TOF MS can be used as a clearly rapid, accurate, and cost-effective method for the identification of M. pulmonis isolates, and this system may represent a serious alternative for clinical laboratories to identify Mycoplasma species.

Lymphocyte phenotypes in wild-caught rats suggest potential mechanisms underlying increased immune sensitivity in post-industrial environments

The immune systems of wild rats and of laboratory rats can been utilized as models of the human immune system in pre-industrial and post-industrial societies, respectively. In this study, lymphocyte phenotypes in wild rats were broadly characterized, and the results were compared to those obtained by us and by others using cells derived from various strains of laboratory rats. Although not expected, the production of regulatory T cells was not apparently different in wild rats compared to laboratory rats. On the other hand, differences in expression of markers involved in complement regulation, adhesion, signaling and maturation suggest increased complement regulation and decreased sensitivity in wild-caught rats compared to laboratory rats, and point toward complex differences between the maturation of T cells. The results potentially lend insight into the pathogenesis of post-industrial epidemics of allergy and autoimmune disease.

Prevalence of viral, bacterial and parasitological diseases in rats and mice used in research environments in Australasia over a 5-y period

Viral, bacterial and parasitological infections in rats and mice used in biomedical research continue to occur despite improved housing and biosurveillance. The presence of disease in laboratory animals can lead to spurious results for research undertaken in universities, research institutes and the pharmaceutical industry. Here the authors report the results of serological, microbiological, parasitological and molecular tests done on mice and rats from Australasia submitted to a rodent health monitoring laboratory (Cerberus Sciences) from 2004 to 2009. In tested mice, norovirus was the most prevalent virus and ectromelia virus was the least prevalent virus. In tested rats, pneumonia virus of mice was the most prevalent virus and adenoviruses 1 and 2 were the least prevalent viruses. In mice, Helicobacter hepaticus was the most prevalent bacterium, and in rats, Proteus spp. were the most prevalent bacteria. The most common positive helminthological finding in mice and rats was the presence of all pinworms (including Aspicularis spp. and Syphacia spp.). The most common positive protozoan findings in mice and rats were Chilomastix spp. and Trichomonads.

Frequency of Detection of Escherichia coli, Salmonella spp., and Campylobacter spp. in the Faeces of Wild Rats (Rattus spp.) in Trinidad and Tobago

The study was conducted to determine the frequency of isolation of Salmonella, Campylobacter and E. coli O157 in the faecal samples of rats trapped across the regional corporations in Trinidad and to assess their resistance to antimicrobial agents. A total of 204 rats were trapped for the detection of selected bacteria. Standard methods were used to isolate Salmonella, Campylobacter and E. coli O157. Characterization of E. coli was done on sorbitol MacConkey agar to determine non-sorbitol fermentation, blood agar to determine haemolytic and mucoid colonies and by using E. coli O157 antiserum to determine O157 strain. The disc diffusion method was used to determine resistance to nine antimicrobial agents. Of the 204 rats, 4 (2.0%), 7 (3.4%) and 171 (83.8%) were positive for Salmonella spp., Campylobacter spp. and E. coli, respectively. Of the 171 isolates of E. coli tested 0 (0.0%), 25 (14.6%) and 19 (11.1%) were haemolytic, mucoid and non-sorbitol fermenters, respectively. All isolates were negative for the O157 strain. The frequency of resistance to the 9 antimicrobial agents tested was 75% (3 of 4) for Salmonella, 85.7% (6 of 7) of Campylobacter spp. and 36.3% (62 of 171) for E. coli (P < .05; χ(2)).

First insights into antimicrobial resistance among faecal Escherichia coli isolates from small wild mammals in rural areas

Wild rodents can be carriers of antimicrobial resistant Escherichia coli. As rodents are known to be involved in the transmission of bacteria of human and animal health concern, they could likewise contribute to the dissemination of antimicrobial resistant bacteria in the environment. The aim of this study was therefore to get first insights into the antimicrobial resistance status among E. coli isolated from wild small mammals in rural areas. We tested 188 faecal isolates from eight rodent and one shrew species originating from Germany. Preselected resistant isolates were screened by minimal inhibitory concentration (MIC) testing or agar diffusion test and subsequent PCR analysis of resistance genes. The prevalence of antimicrobial resistant isolates was low with only 5.5% of the isolates exhibiting resistant phenotypes against at least one antimicrobial compound including beta-lactams, tetracyclines, aminoglycosides and sulfonamides. These results suggest a minor role of wild rodents from rural areas in the cycle of transmission and spread of antimicrobial resistant E. coli into the environment. Nevertheless E. coli with multiple antimicrobial resistances were significantly more often detected in wildlife rodents originating from areas with high livestock density suggesting a possible transmission from livestock to wild rodents.

Trophic garnishes: cat-rat interactions in an urban environment

BACKGROUND

Community interactions can produce complex dynamics with counterintuitive responses. Synanthropic community members are of increasing practical interest for their effects on biodiversity and public health. Most studies incorporating introduced species have been performed on islands where they may pose a risk to the native fauna. Few have examined their interactions in urban environments where they represent the majority of species. We characterized house cat (Felis catus) predation on wild Norway rats (Rattus norvegicus), and its population effects in an urban area as a model system. Three aspects of predation likely to influence population dynamics were examined; the stratum of the prey population killed by predators, the intensity of the predation, and the size of the predator population.

METHODOLOGY/PRINCIPAL FINDINGS

Predation pressure was estimated from the sizes of the rat and cat populations, and the characteristics of rats killed in 20 alleys. Short and long term responses of rat population to perturbations were examined by removal trapping. Perturbations removed an average of 56% of the rats/alley but had no negative long-term impact on the size of the rat population (49.6+/-12.5 rats/alley and 123.8+/-42.2 rats/alley over two years). The sizes of the cat population during two years (3.5 animals/alley and 2.7 animals/alley) also were unaffected by rat population perturbations. Predation by cats occurred in 9/20 alleys. Predated rats were predominantly juveniles and significantly smaller (144.6 g+/-17.8 g) than the trapped rats (385.0 g+/-135.6 g). Cats rarely preyed on the larger, older portion of the rat population.

CONCLUSIONS/SIGNIFICANCE

The rat population appears resilient to perturbation from even substantial population reduction using targeted removal. In this area there is a relatively low population density of cats and they only occasionally prey on the rat population. This occasional predation primarily removes the juvenile proportion of the rat population. The top predator in this urban ecosystem appears to have little impact on the size of the prey population, and similarly, reduction in rat populations doesn't impact the size of the cat population. However, the selected targeting of small rats may locally influence the size structure of the population which may have consequences for patterns of pathogen transmission.

Seoul virus and hantavirus disease, Shenyang, People's Republic of China

An outbreak of hemorrhagic fever with renal syndrome (HFRS) occurred among students in Shenyang Pharmaceutical University in 2006. We conducted a study to characterize etiologic agents of the outbreaks and clarify the origin of hantaviruses causing infections in humans and laboratory animals. Immunoglobulin (Ig) M or IgG antibodies against Seoul virus (SEOV) were detected in the serum samples of all 8 patients. IgG antibodies against hantavirus were also identified in laboratory rats, which were used by these students for their scientific research. Phylogenetic analysis showed that partial small segment sequences recovered from humans, laboratory rats, and local wild rats belonged to SEOV. Hantavirus sequences recovered from humans and laboratory rats clustered within 1 of 3 lineages of SEOV circulating among local wild rats in Shenyang. These results suggest that the HFRS outbreak in Shenyang was caused by SEOV that was circulating among local wild rats and had also infected the laboratory rats.

New building, old parasite: Mesostigmatid mites--an ever-present threat to barrier facilities

Mesostigmatid mites are blood-sucking parasitic mites found in wild rodent populations. Periodically they can also become a problem for laboratory rodent colonies, particularly when building construction or renovations disturb colonies of commensal (building) rodents that had been acting as hosts. Mesostigmatid mites infest both rats and mice and, unlike the more common rodent fur mites (Myobia, Myocoptes, and Radfordia sp.), can survive for long periods in the environment and travel considerable distances in search of new hosts. They easily penetrate barrier caging systems, including individually ventilated cages, thus circumventing the usual precautions to protect rodents from infection. The two mites reported in laboratory rodent colonies, Ornithonyssus bacoti and Laelaps echidnina, also bite humans and have the potential to transmit zoonotic diseases. Once the mites gain access to a colony, eradication requires elimination of commensal rodent reservoirs in addition to insecticide treatment of both the laboratory rodents and the environment. In view of the undesirability of insecticide use in the animal facility, it is advisable to investigate the effectiveness of preventive treatments, such as environmental application of insect growth regulators or silica-based products. This article summarizes available information on mesostigmatid mites and their laboratory incursions, and provides suggestions for diagnosis, treatment, and control based on the author’s experience with several outbreaks at a large academic institution.