Prevalence of viral antibodies and helminths in field populations of house mice (Mus domesticus) in southeastern Australia

Horizontal transmission of endemic viruses among rhesus macaques (Macaca mulatta): Implications for human cytomegalovirus vaccine/challenge design

INTRODUCTION

Rhesus macaques are natural hosts to multiple viruses including rhesus cytomegalovirus (RhCMV), rhesus rhadinovirus (RRV), and Simian Foamy Virus (SFV). While viral infections are ubiquitous, viral transmissions to uninfected animals are incompletely defined. Management procedures of macaque colonies include cohorts that are Specific Pathogen Free (SPF). Greater understanding of viral transmission would augment SPF protocols. Moreover, vaccine/challenge studies of human viruses would be enhanced by leveraging transmission of macaque viruses to recapitulate expected challenges of human vaccine trials.

MATERIALS AND METHODS

This study characterizes viral transmissions to uninfected animals following inadvertent introduction of RhCMV/RRV/SFV-infected adults to a cohort of uninfected juveniles. Following co-housing with virus-positive adults, juveniles were serially evaluated for viral infection.

RESULTS

Horizontal viral transmission was rapid and absolute, reaching 100% penetrance between 19 and 78 weeks.

CONCLUSIONS

This study provides insights into viral natural histories with implications for colony management and modeling vaccine-mediated immune protection studies.

Epidemiology of Group A rotavirus in rodents and shrews in Bangladesh

Rodents and shrews live in close proximity to humans and have been identified as important hosts of zoonotic pathogens. This study aimed to detect Group A rotavirus (RVA) and its potential risk factors in rodents and shrews in Bangladesh. We captured 417 small mammals from 10 districts with a high degree of contact between people and domestic animals and collected rectal swab samples between June 2011 and October 2013. We tested the swab samples for RVA RNA, targeting the NSP3 gene segment using real-time reverse transcription-polymerase chain reaction (rRT-PCR). Overall, RVA prevalence was the same (6.7%) in both rodents and shrews. We detected RVA RNA in 5.3% of Bandicota bengalensis (4/76; 95% CI: 1.4-12.9), 5.1% of B. indica (4/79; 95% CI: 1.4-12.4), 18.2% of Mus musculus (4/22; 95% CI: 5.2-40.3), 6.7% of Rattus rattus (6/90; 95% CI: 2.5-13.9), and 6.7% of Suncus murinus (10/150; 95% CI: 3.2-11.9). We found significantly more RVA in males (10.4%; OR: 3.4; P = 0.007), animals with a poor body condition score (13.9%; OR: 2.7; P = 0.05), during wet season (8.3%; OR: 4.1; P = 0.032), and in urban land gradients (10.04%; OR: 2.9; P = 0.056). These findings form a basis for understanding the prevalence of rotaviruses circulating among rodents and shrews in this region. We recommend additional molecular studies to ascertain the genotype and zoonotic potential of RVA circulating in rodents and shrews in Bangladesh.

Small but mighty: old and new parvoviruses of veterinary significance

In line with the Latin expression "sed parva forti" meaning "small but mighty," the family Parvoviridae contains many of the smallest known viruses, some of which result in fatal or debilitating infections. In recent years, advances in metagenomic viral discovery techniques have dramatically increased the identification of novel parvoviruses in both diseased and healthy individuals. While some of these discoveries have solved etiologic mysteries of well-described diseases in animals, many of the newly discovered parvoviruses appear to cause mild or no disease, or disease associations remain to be established. With the increased use of animal parvoviruses as vectors for gene therapy and oncolytic treatments in humans, it becomes all the more important to understand the diversity, pathogenic potential, and evolution of this diverse family of viruses. In this review, we discuss parvoviruses infecting vertebrate animals, with a special focus on pathogens of veterinary significance and viruses discovered within the last four years.

Population cycles and outbreaks of small rodents: ten essential questions we still need to solve

Most small rodent populations in the world have fascinating population dynamics. In the northern hemisphere, voles and lemmings tend to show population cycles with regular fluctuations in numbers. In the southern hemisphere, small rodents tend to have large amplitude outbreaks with less regular intervals. In the light of vast research and debate over almost a century, we here discuss the driving forces of these different rodent population dynamics. We highlight ten questions directly related to the various characteristics of relevant populations and ecosystems that still need to be answered. This overview is not intended as a complete list of questions but rather focuses on the most important issues that are essential for understanding the generality of small rodent population dynamics.

Murine adenoviruses: tools for studying adenovirus pathogenesis in a natural host

Small laboratory animals are powerful models for investigating in vivo viral pathogenesis of a number of viruses. For adenoviruses (AdVs), however, species-specificity poses limitations to studying human adenoviruses (HAdVs) in mice and other small laboratory animals. Thus, this review covers work on naturally occurring mouse AdVs, primarily mouse adenovirus type 1 (MAdV-1), a member of the species Murine mastadenovirus A. Molecular genetics, virus life cycle, cell and tissue tropism, interactions with the host immune response, persistence, and host genetics of susceptibility are described. A brief discussion of MAdV-2 (member of species Murine mastadenovirus B) and MAdV-3 (member of species Murine mastadenovirus C) is included. We report the use of MAdVs in the development of vectors and vaccines.

Morphological Re-Description and 18 S rDNA Sequence Confirmation of the Pinworm Aspiculuris tetraptera (Nematoda, Heteroxynematidae) Infecting the Laboratory Mice Mus musculus

Aspiculuris tetraptera is a heteroxynematid nematoda infecting most of the laboratory animals, occasionally mice which represent the mostly used animal for biological, medical, and pharmacological studies. The present study aimed to investigate the prevalence of nematode parasites infection in the laboratory mice Mus musculus in Egypt. Morphologically, this oxyurid possessed four distinct cephalic papillae on a cephalic plate, with three small rudimental lips carrying two sessile poorly developed labial papillae and one pair of amphidial pores. Esophagus divided into cylindrical corpus and globular bulb. Distinct cervical alae interrupted at the level of esophago-intestinal junction forming an acute angle. At the caudal end, twelve caudal papillae in male worms while an ovijector apparatus opening and a vulva surrounded by protruded lips in females were observed. The general morphological criteria include this nematode with other Aspiculuris species which were compared in the present study. Molecular characterization based on 18SSU rDNA sequencing performed to confirm the taxonomic position of this species and to documents the morphological data. Sequence alignment detects a percent of identity up to 88.0% with other Heteroxynematidae species. Phylogenetic analysis showed that the present recorded is a putative sister taxon to A. tetraptera recorded in a previous study. The SSU rDNA sequence has been deposited in the GenBank under the accession no. MG019400.

Implications of infectious agents on results of animal experiments

Report of the Working Group on Hygiene of the Gesellschaft für Versuchstierkunde–Society for Laboratory Animal Science (GV-SOLAS)

GV-SOLAS Working Group on Hygiene: Werner Nicklas (Chairman), Felix R. Homberger, Brunhilde Illgen-Wilcke, Karin Jacobi, Volker Kraft, Ivo Kunstyr, Michael Mähler, Herbert Meyer & Gabi Pohlmeyer-Esch

Murine cytomegalovirus is not restricted to the house mouse Mus musculus domesticus: prevalence and genetic diversity in the European house mouse hybrid zone

Murine cytomegalovirus (MCMV) is a betaherpesvirus of the house mouse, Mus musculus domesticus. It is a common infectious agent of wild mice and a highly studied pathogen of the laboratory mouse. Betaherpesviruses are specific to their hosts, and it is not known if other Mus taxa carry MCMV or if it is restricted to M. m. domesticus. We sampled mice over a 145-km transect of Bavaria-Bohemia crossing a hybrid zone between M. m. domesticus and Mus musculus musculus in order to investigate the occurrence of MCMV in two Mus subspecies and to test the limits of the specificity of the virus for its host. We hypothesized that if the two subspecies carry MCMV and if the virus is highly specific to its host, divergent MCMV lineages would have codiverged with their hosts and would have a geographical distribution constrained by the host genetic background. A total of 520 mice were tested by enzyme-linked immunosorbent assay (ELISA) and/or nested PCR targeting the M94 gene. Seropositive and PCR-positive individuals were found in both Mus subspecies. Seroprevalence was high, at 79.4%, but viral DNA was detected in only 41.7% of mice. Sequencing revealed 20 haplotypes clustering in 3 clades that match the host genetic structure in the hybrid zone, showing 1 and 2 MCMV lineages in M. m. domesticus and M. m. musculus, respectively. The estimated time to the most recent common ancestor (1.1 million years ago [Mya]) of the MCMVs matches that of their hosts. In conclusion, MCMV has coevolved with these hosts, suggesting that its diversity in nature may be underappreciated, since other members of the subgenus Mus likely carry different MCMVs.

IMPORTANCE

Murine cytomegalovirus (MCMV) is a betaherpesvirus of the house mouse, Mus musculus domesticus, an important lab model for human cytomegalovirus (HCMV) infection. The majority of lab studies are based on only two strains of MCMVs isolated from M. m. domesticus, Smith and K181, the latter derived from repeated passage of Smith in mouse submaxillary glands. The presence of MCMV in other members of the Mus subgenus had not even been investigated. By screening mouse samples collected in the European house mouse hybrid zone between M. m. domesticus and M. m. musculus, we show that MCMV is not restricted to the M. m. domesticus subspecies and that MCMVs likely codiverged with their Mus hosts. Thus, the diversity of MCMV in nature may be seriously underappreciated, since other members of the subgenus Mus likely carry their own MCMV lineages.

Microbiological Quality Control for Laboratory Rodents and Lagomorphs

Mice (Mus musculus), rats (Rattus norvegicus), other rodent species, and domestic rabbits (Oryctolagus cuniculus) have been used in research for over 100 years. During the first half of the 20th century, microbiological quality control of lab animals was at best rudimentary as colonies were conventionally housed and little or no diagnostic testing was done. Hence, animal studies were often curtailed and confounded by infectious disease (Mobraaten and Sharp, 1999; Morse, 2007; Weisbroth, 1999). By the 1950s, it became apparent to veterinarians in the nascent field of comparative medicine that disease-free animals suitable for research could not be produced by standard veterinary disease control measures (e.g., improved sanitation and nutrition, antimicrobial treatments) in conventional facilities. Henry Foster, the veterinarian who founded Charles River Breeding Laboratories in 1948 and a pioneer in the large-scale production of laboratory rodents, stated in a seminar presented at the 30th anniversary of AALAS, “After a variety of frustrating health-related problems, it was decided that a major change in the company’s philosophy was required and an entirely different approach was essential”. Consequently, he and others developed innovative biosecurity systems to eliminate and exclude pathogens (Allen, 1999). In 1958, Foster reported on the Cesarean-originated barrier-sustained (COBS) process for the large-scale production of specific pathogen-free (SPF) laboratory rodents (Foster, 1958). To eliminate horizontally transmitted pathogens, a hysterectomy was performed on a near-term dam from a contaminated or conventionally housed colony. The gravid uterus was pulled through a disinfectant solution into a sterile flexible film isolator where the pups were removed from the uterus and suckled on axenic (i.e., germ-free) foster dams. After being mated to expand their number and associated with a cocktail of nonpathogenic bacteria to normalize their physiology and prime their immune system, rederived rodents were transferred to so-called barrier rooms for large-scale production. The room-level barrier to adventitious infection entailed disinfection of the room, equipment, and supplies, limiting access to trained and properly gowned personnel, and the application of new technologies such as high-efficiency particulate air-filtration of incoming air (Dubos and Schaedler, 1960; Foster, 1980; Schaedler and Orcutt, 1983; Trexler and Orcutt, 1999). The axenic and associated rodents mentioned in the COBS process are collectively classified as gnotobiotic to indicate that they have a completely known microflora. By contrast, barrier-reared rodent colonies are not gnotobiotic because they are housed in uncovered cages and thus acquire a complex microflora from the environment, supplies, personnel, and other sources. Instead, they are described as SPF to indicate that according to laboratory testing, they are free from infection with a defined list of infectious agents, commonly known as an ‘exclusion’ list.

Managing crop damage caused by house mice (Mus domesticus) in Australia

A large-scale outbreak of the house mouse populations occurs in grain growing in Australia on average once every four years. High densities of mice cause major yield losses to cereal crops, and low to moderate densities of mice also cause some losses. Several predictive models based on rainfall patterns have been developed to forecast mouse density. These models carry some uncertainty and the economic value of basing management actions on these models is not clear. Baiting is the most commonly used method and zinc phosphide and other rodenticide bait are effective in reducing up to 90% of mouse populations. Ecologically-based best farming practice for controlling mice has recently been developed on the basis of long-term field studies of mouse populations. No effective biological control method has been developed for mice. However, grain growers still cannot make economically rational decisions to implement control because they do not know the pest threshold density (D(T)) above which the economic benefits of control exceed the economic costs of control. Applied predator-prey theory suggests that understanding the relationship between mouse density and damage is the basis for determining D(T). Understanding this relationship is the first research priority for managing mouse damage. The other research priority is to develop a reliable method to estimate unbiased mouse density.

Coping with parvovirus infections in mice: health surveillance and control

Parvoviruses of mice, minute virus of mice (MVM) and mouse parvovirus (MPV), are challenging pathogens to eradicate from laboratory animal facilities. Due to the impediment on rodent-based research, recent studies have focused on the assessment of re-derivation techniques and parvoviral potential to induce persistent infections. Summarizing recent data, this review gives an overview on studies associated with parvoviral impact on research, diagnostic methods, parvoviral persistence and re-derivation techniques, demonstrating the complex nature of parvovirus infection in mice and unfolding the challenge of controlling parvovirus infections in laboratory animal facilities.

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.

Persistence pays: how viruses promote host group survival

Recently, we have realized that viruses numerically dominate all life. Although viruses are known to affect host survival in populations, this has not been previously evaluated in the context of host group selection. Group selection per se is not a currently accepted idea and its apparent occurrence is explained by statistical gene frequency models of kin selection. Viruses were not considered in such models. Prevalent views associate viruses and disease. Yet many viruses establish species-specific persistent, inapparent infections that are stable on an evolutionary time scale. Such persistent infections can have large effects on relative reproductive fitness of competing host populations. In this essay, I present arguments on how persistent infections can promote population survival. Mouse hepatitis virus is used as well studied examplar to re-evaluate the theoretical basis of the mouse haystack model of M Smith. This virus-centric re-examination concludes that viruses can indeed affect and promote relative group selection.

Contemporary prevalence of infectious agents in laboratory mice and rats

Periodic health screening of rodents used in research is necessary due to the consequences of unwanted infections. One determinant of the risk of infection for any given agent is its prevalence; other factors being equal, a prevalent agent is more likely than a rare one to be introduced to a research facility and result in infection. As an indicator of contemporary prevalence in laboratory populations of rats and mice, the rate of positive results in the samples received at a major commercial rodent diagnostic laboratory was compiled for this paper. Although samples from laboratory rodent vendors have been excluded, results are tabulated from samples from more than 500,000 mice and 80,000 rats submitted over several years from pharmaceutical, biotechnology, academic, and governmental institutions in North America and Europe, allowing meaningful determination of which agents are common in the research environment versus which agents are rare. In mice, commonly detected infectious agents include mouse norovirus, the parvoviruses, mouse hepatitis virus, rotavirus, Theiler's murine encephalomyelitis virus, Helicobacter spp., Pasteurella pneumotropica, and pinworms. In rats, commonly detected infectious agents include ‘rat respiratory virus’, the parvoviruses, rat theilovirus, Helicobacter spp., P. pneumotropica, and pinworms. A risk-based allocation of health-monitoring resources should concentrate frequency and/or sample size on these high-risk agents, and monitor less frequently for the remaining, lower-risk, infectious agents.

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.

Minute virus of mice: antibody response, viral shedding, and persistence of viral DNA in multiple strains of mice

Minute virus of mice (MVM) is a major concern for laboratory animal facilities because it remains with considerably high prevalence despite strict barrier systems. The aim of this study was to elucidate potential risks associated with MVM infection by investigating the role of the genetic background on antibody production and persistence as well as viral shedding. Mice of various strains and stocks were inoculated oronasally with the immunosuppressive strain MVMi; in addition, natural infection was modeled through contact exposure. As determined by serology, seroconversion and serum levels of IgG differed considerably among strains and stocks, especially in the contact-exposed group. For example, C57BL/6J mice responded well to exposure in contrast to FVB/N, NMRI, ICR, and C3H/HeN mice. Titration studies indicated that the viral dose necessary to induce seroconversion was strain-dependent. Experiments to dissect the role of the major histocompatibility complex haplotype in the response to MVMi gave inconclusive results. To detect viral persistence, spleens and feces were analyzed by PCR at 16 wk after exposure, and the infectivity of PCR-positive spleens was investigated by IP and oronasal inoculation of naive mice. Although DNA was detected in the spleens of some mice, feces remained negative, and naive mice were not infected by inoculation. In addition, viral shedding declined rapidly after day 20 postinoculation. In summary, the data show that seroconversion and antibody response to MVMi infection depend on the genetic background of mice, with the infective dose being a critical factor. The role of viral DNA in chronically infected mice will require further elucidation.

Prior infection with murine cytomegalovirus (MCMV) limits the immunocontraceptive effects of an MCMV vector expressing the mouse zona-pellucida-3 protein

We have developed a murine cytomegalovirus (MCMV)-vectored vaccine expressing the mouse zona-pellucida-3 gene (rMCMV-ZP3), which successfully induces infertility in experimentally inoculated laboratory or wild-derived mice. However, the future success of this vector as a fully disseminating vaccine in free-living mice may be compromised by pre-existing immunity since there is a high prevalence of naturally acquired MCMV infection in these mice. To evaluate the effect of prior immunity to MCMV on vaccine efficacy, we constructed two new biologically effective recombinant MCMV vectors expressing the mouse ZP3 protein from two MCMV strains (N1 and G4) derived from free-living mice. In wild mice, mixed MCMV infection is common and could be acquired either by simultaneous coinfection or sequential infection with different MCMV strains. Interestingly, while coinfection with both wild-type and rMCMV-ZP3 via the intraperitoneal route reduced the impact of the rMCMV-ZP3, prior infection with the same wild-type strain as that used to construct the rMCMV-ZP3 abrogated the immunocontraceptive effects of either N1-ZP3 or G4-ZP3. However, prior infection with G4 28 days before the introduction of N1-ZP3 had a reduced influence on the efficacy of the rMCMV-ZP3. Thus, the strain of virus and the timing of prior infection are factors that may influence the efficacy of the rMCMV-ZP3. Given that mixed infection of mice with MCMV is common, it is possible that prior immunity acquired by natural mucosal infection may have less a less inhibitory effect on the immunocontraceptive outcome.

MHC class I immune evasion in MCMV infection

Murine cytomegalovirus (MCMV) is a well-studied model of natural beta-herpesvirus infection. However, many questions remain regarding its control by and evasion of the immune response it generates. CD8 and CD4 T cells have both unique and redundant roles in control of the virus that differ based on the immunocompetence of the infected mice. MCMV encodes major histocompatibility complex (MHC) class I immune evasion genes that can have an impact in vitro, but their role in infection of immunocompetent mice has been difficult to identify. This review addresses the evidence for their in vivo function and suggests why they may be evolutionarily conserved.

The Widespread Evolutionary Significance of Viruses

In the last 30 years, the study of virus evolution has undergone a transformation. Originally concerned with disease and its emergence, virus evolution had not been well integrated into the general study of evolution. This chapter reviews the developments that have brought us to this new appreciation for the general significance of virus evolution to all life. We now know that viruses numerically dominate all habitats of life, especially the oceans. Theoretical developments in the 1970s regarding quasispecies, error rates, and error thresholds have yielded many practical insights into virus–host dynamics. The human diseases of HIV-1 and hepatitis C virus cannot be understood without this evolutionary framework. Yet recent developments with poliovirus demonstrate that viral fitness can be the result of a consortia, not one fittest type, a basic Darwinian concept in evolutionary biology. Darwinian principles do apply to viruses, such as with Fisher population genetics, but other features, such as reticulated and quasispecies-based evolution distinguish virus evolution from classical studies. The available phylogenetic tools have greatly aided our analysis of virus evolution, but these methods struggle to characterize the role of virus populations. Missing from many of these considerations has been the major role played by persisting viruses in stable virus evolution and disease emergence. In many cases, extreme stability is seen with persisting RNA viruses. Indeed, examples are known in which it is the persistently infected host that has better survival. We have also recently come to appreciate the vast diversity of phage (DNA viruses) of prokaryotes as a system that evolves by genetic exchanges across vast populations (Chapter 10). This has been proposed to be the “big bang” of biological evolution. In the large DNA viruses of aquatic microbes we see surprisingly large, complex and diverse viruses. With both prokaryotic and eukaryotic DNA viruses, recombination is the main engine of virus evolution, and virus host co-evolution is common, although not uniform. Viral emergence appears to be an unending phenomenon and we can currently witness a selective sweep by retroviruses that infect and become endogenized in koala bears.

Prospects for virally vectored immunocontraception in the control of wild house mice (Mus domesticus)

The wild house mouse (Mus domesticus) is not native to Australia and was introduced from Europe with early settlement. It undergoes periodic population explosions or plagues, which place significant economic and social burdens on agricultural communities. Present control mechanisms rely on improvements to farm hygiene and the use of rodenticides. This review covers over a decade of work on the use of virally vectored immunocontraception (VVIC) as an adjunct method of controlling mouse populations. Two viral vectors, ectromelia virus (ECTV) and murine cytomegalovirus (MCMV) have been tested as potential VVIC vectors: MCMV has been the most widely studied vector because it is endemic to Australia; ECTV less so because its use would have required the introduction of a new pathogen into the Australian environment. Issues such as efficacy, antigen choice, resistance, transmission, species specificity and safety of VVIC are discussed. In broad terms, both vectors when expressing murine zona pellucida 3 (mZP3) induced long-term infertility in most directly inoculated female mice. Whereas innate and acquired resistance to MCMV may be a barrier to VVIC, the most significant barrier appears to be the attenuation seen in MCMV-based vectors. This attenuation is likely to prevent sufficient transmission for broad-scale use. Should this issue be overcome, VVIC has the potential to contribute to the control of house mouse populations in Australia.

Mixed infection with multiple strains of murine cytomegalovirus occurs following simultaneous or sequential infection of immunocompetent mice

As with human cytomegalovirus (HCMV) infection of humans, murine CMV (MCMV) infection is widespread in its natural host, the house mouse Mus domesticus, and may consist of mixed infection with different CMV isolates. The incidence and mechanisms by which mixed infection occurs in free-living mice are unknown. This study used two approaches to determine whether mixed infection with MCMV could be established in laboratory mice. The first utilized two naturally occurring MCMV strains, N1 and G4, into which the lacZ gene was inserted by homologous recombination. The lacZ gene was used to track recombinant and parental viruses in simultaneously coinfected mice. In the second approach, a real-time quantitative PCR (qPCR) assay was used to detect viral immediate-early 1 (ie1) gene sequences in mice successively coinfected with G4 and then with the K181 MCMV strain. In both systems, mixed infection was detected in the salivary glands and lungs of experimentally infected mice. MCMV-specific antibody in sera and G4 IE1-specific cytotoxic lymphocyte responses in the spleens of twice-infected mice did not prevent reinfection. Finally, the prevalence of mixed infection in free-living mice trapped in four Australian locations was investigated using real-time qPCR to detect ie1 DNA sequences of N1, G4 and K181. Mixed infection with MCMVs containing the G4 and K181 ie1 sequences was detected in the salivary glands of 34·2 % of trapped mice. The observations that mixed infections are common in free-living M. domesticus and are acquired by immunocompetent mice through simultaneous or successive infections are important for vaccine development.

Development of multiplex PCRs for detection of common viral pathogens and agents of congenital infections

Potential causes of congenital infection include Toxoplasma gondii and viruses such as cytomegalovirus (CMV), enterovirus, hepatitis C virus, herpes simplex virus types 1 and 2 (HSV-1 and -2), human herpesvirus types 6, 7, and 8, lymphocytic choriomeningitis virus, parvovirus, rubella virus, and varicella-zoster virus. Testing for each of these agents using nucleic acid tests is time consuming and the availability of clinical samples such as amniotic fluid or neonatal blood is often limited. The aim of this study was to develop multiplex PCRs (mPCRs) for detection of DNA and RNA agents in the investigation of congenital infection and an mPCR for the viruses most commonly requested in a diagnostic virology laboratory (CMV, Epstein-Barr virus, enterovirus, HSV-1, HSV-2, and varicella-zoster virus). The assays were assessed using known pathogen-positive tissues (cultures, placentae, plasma, and amniotic fluid) and limits of detection were determined for all the agents studied using serial dilutions of plasmid targets. Nested PCR was performed as the most sensitive assay currently available, and detection of the amplicons using hybridization to labeled probes and enzyme-linked immunosorbent assay detection was incorporated into three of the four assays. This allowed detection of 10 to 10(2) copies of each agent in the samples processed. In several patients, an unexpected infection was diagnosed, including a case of encephalitis where HSV was the initial clinical suspicion but CMV was detected. In the majority of these cases the alternative agent could be confirmed using reference culture, serology, or fluorescence methods and was of relevance to clinical care of the patient. The methods described here provide useful techniques for diagnosing congenital infections and a paradigm for assessment of new multiplex PCRs for use in the diagnostic laboratory.

Is there an association ofPneumocystisinfection with the presence of arena-, hanta-, and poxvirus antibodies in wild mice and shrews in Finland?

As part of studies on the nature of the endemic virus infections in natural rodent hosts, the possible association of cyst forms ofPneumocystisspp. with the presence of hanta-, cowpox-, and arenavirus antibodies in wild mice (Apodemus flavicollis,N=105;Apodemus agrarius,N=63;Micromys minutus,N=50) and the common shrew (Sorex araneus,N=101) was studied in south-central Finland. One hantavirus (Saaremaa virus, SAAV) seropositiveA. agrarius, and 2 cowpoxvirus (CPXV) seropositiveS. araneuswere detected, and antibodies against an arenavirus (Lymphocytic choriomeningitis virus, LCMV) were found in all 3 mouse species but not in shrews. Cyst forms ofPneumocystisspp. were detected in all species exceptA. agrarius. There was no significant association between virus antibodies (LCMV in mice, and CPXV in shrews) and cyst forms ofPneumocystisin any of the species. Concurrent presence of virus antibodies (LCMV) and cyst forms ofPneumocystiswere detected only in 1M. minutus. In conclusion, we found no evidence of any association betweenPneumocystisand antibodies to any of the viruses tested.

Kin interactions and changing social structure during a population outbreak of feral house mice

Populations of feral house mice (Mus domesticus L.) in Australia undergo multiannual fluctuations in density, and these outbreaks may be partly driven by some change in behavioural self-regulation. In other vertebrate populations with multiannual fluctuations, changes in kin structure have been proposed as a causal mechanism for changes in spacing behaviour, which consequently result in density fluctuations. We tested the predictions of two alternative conceptual models based on kin selection in a population of house mice during such an outbreak. Both published models (Charnov & Finerty 1980; Lambin & Krebs 1991) propose that the level of relatedness between interacting individuals affects their behavioural response and that this changes with population density, though the nature of this relationship differs between the two models. Neither of the models was consistent with all observed changes in relatedness between interacting female mice; however, our results suggested that changes in kin structure still have potential for explaining why mouse outbreaks begin. Therefore, we have developed a variant of one of these conceptual models suggesting that the maintenance of female kin groups through the preceding winter significantly improves recruitment during the subsequent breeding season, and is therefore necessary for mouse outbreaks. We provide six testable predictions to falsify this hypothesis.

Predicting the effect of immunocontraceptive recombinant murine cytomegalovirus on population outbreaks of house mice (Mus musculus domesticus) in mallee wheatlands

Virally vectored immunocontraception using a modified murine cytomegalovirus (MCMV) is being developed for the control of house mice in Australia. In this paper, we develop disease–host models using a combination of laboratory and field data. We then combine these models with a model of a previous mouse population outbreak to explore the likely effectiveness of modified MCMV for controlling mice. Models of homogeneous mixing with and without vertical/pseudovertical transmission provided reasonable fits to field serological data collected during the onset and development of a mouse population outbreak in south-eastern Australia. Both models include the high transmission rate of MCMV suggested by the data. We found no strong support for non-linear contact rates or heterogeneous mixing. When applied to a past outbreak of mice both models gave similar results and suggested that immunocontraceptive MCMV could be effective at reducing agricultural damage to acceptable levels. Successful control was still possible when lags in the development of infertility of up to 10 weeks were added to the model, provided high levels of infertility were achieved. These lags were added because mice can become pregnant just before becoming infertile – the resultant litter would not emerge for 6–7 weeks. Trade-offs between two parameters that could be altered by engineering strains of MCMV – the level of infertility in infected mice and the virus transmission rate – were explored and suggest that a variety of parameter combinations could produce successful control. Our results are encouraging for the future development of virally vectored immunocontraception control of house mice, but future work will need to consider some of the assumptions of these single-strain models.

Is the prevalence of Taenia taeniaeformis in Microtus arvalis dependent on population density?

Populations of common voles Microtus arvalis were studied as hosts of the tapeworm Taenia taeniaeformis during a 14-yr survey. They were monitored in spring, summer, and autumn in a pastoral ecosystem in eastern France. A total of 7,574 voles were sampled during 2 multiannual population fluctuations. A third fluctuation was sampled during the increase phase only. Overall prevalence was lowest in summer (0.6%), increased by 3 times in autumn (1.5%) and a further 5 times in spring (7.8%). Analysis of prevalence, based on 7,384 voles, by multiple logistic regression revealed that extrinsic factors such as season and intrinsic factors such as host age and host density have a combined effect. In the longer term, host age and host density were positively associated with prevalence in summer. Host density was strongly associated with autumn prevalence. There was no association between the fluctuation phase and prevalence. The study shows that a long timescale (here a multiannual survey) is necessary to demonstrate the positive effect of host density on the prevalence of this indirectly transmitted parasite. The demonstration of this relationship depends on the rodents being intermediate rather than definitive hosts.

Can outbreaks of house mice in south-eastern Australia be predicted by weather models?

Outbreaks of house mice (Mus domesticus) occur irregularly in the wheat-growing areas of south-eastern Australia, and are thought to be driven by weather variability, particularly rainfall. If rainfall drives grass and seed production, and vegetation production drives mouse dynamics, we should achieve better predictability of mouse outbreaks by the use of plant-production data. On a broader scale, if climatic variability is affected by El Niño–Southern Oscillation (ENSO) events, large-scale weather variables might be associated with mouse outbreaks. We could not find any association of mouse outbreaks over the last century with any ENSO measurements or other large-scale weather variables, indicating that the causal change linking mouse numbers with weather variation is more complex than is commonly assumed. For the 1960–2002 period we were only partly successful in using variation in cereal production to predict outbreaks of mice in nine areas of Victoria and South Australia, and we got better predictability of outbreaks from rainfall data alone. We achieved 70% correct predictions for a qualitative model using rainfall and 58% for a quantitative model using rainfall and spring mouse numbers. Without the detailed specific mechanisms underlying mouse population dynamics, we may not be able to improve on these simple models that link rainfall to mouse outbreaks.