Trophoblast Deportation to the Lungs of Cotton Rats (Sigmodon hispidus)

Cotton rats (Sigmodon hispidus) have been used to study a variety of infectious agents, particularly human respiratory viral pathogens. During the course of comprehensive pathologic evaluations of aging breeders from our breeding colony, 6 of 22 (27%) female cotton rats had histologic evidence, limited to the lungs, of embolized cells that were confirmed to be trophoblastic in origin by HSD3B1 immunoreactivity. When pulmonary trophoblast emboli were numerous, they usually were associated with additional histologic findings in the lungs, including pulmonary edema and hemorrhage, endothelial hypertrophy, fibrinoid vascular necrosis, and abundant alveolar macrophages containing fresh fibrin and hemolyzing erythrocytes. Of the 6 cotton rats with pulmonary trophoblast emboli, 5 (83%) were at 8 to 18 d of the 27-d gestation period, with the greatest number of emboli per lung present between days 10 through 14. The remaining cotton rat had a focal pulmonary trophoblast embolus and was not pregnant but had delivered a litter 3 mo previously. Three other cotton rats in either the early or late stages of gestation showed no histologic evidence of pulmonary trophoblast deportation. This report is the first to document pulmonary trophoblast emboli in cotton rats. This finding suggests that cotton rats may be an alternative animal model for the study of normal and aberrant trophoblast deportation in routine pregnancies and gestational pathologic conditions in women.Abbreviations: HSD3B1, hydroxyl-C-5-steroid dehydrogenaseCotton rats (Sigmodon hispidus) are a relevant animal model for the study of human respiratory²³ viral pathogens, with increasing usage by academic and industrial institutions. The hemochorial placentation in Sigmodontinae²² is similar to that of humans and several laboratory animal species including mice, rats, hamsters, rabbits, guinea pigs, chinchillas, and nonhuman primates.^{10,20,40,42,44,49} In these species, one or more layers of analogous trophoblast types comprise the interhemal barrier between maternal and fetal blood supplies. Placental trophoblasts perform a number of critical functions during gestation, including mediation of uterine implantation and invasion, nutrient exchange, regulation of maternal blood flow, and hormone production.^{1,19,26-28,35,38,46,47}As a consequence of their inherent invasiveness, placental trophoblasts migrate into maternal uterine blood vessels, after which syncytiotrophoblasts (syncytial knots) are normally deported daily to the lungs in humans.^2,3,17 Deportation increases with frequency as gestation progresses,^3,4 with gestational pathologic conditions such as preeclampsia and eclampsia,^2,3,18,36 and after cesarean sections⁵⁰ and abortions.⁴⁸ The current thinking is that these syncytial knots undergo programmed cell death and apoptotic shedding during routine pregnancy, in contrast to conditions like preeclampsia and eclampsia, during which aberrant intervillous hemodynamics resulting in hypoxia favor necrosis and associated inflammation.^18,25,29,30 In addition, spontaneous trophoblast emboli have been documented in the lungs and a few other tissues, including uterus, adrenal gland, spleen, and liver of chinchillas,^6,11,52 hamsters,^7,41 and porcupines.²⁴ Experimentally, trophoblast invasion has been further studied in mice^8,9 and hamsters.⁵ To our knowledge, pulmonary trophoblast emboli in cotton rats have not previously been reported.Pairs of cotton rat breeders were maintained for the production of animals to be used in various studies investigating human respiratory viruses, including measles, respiratory syncytial, and parainfluenza viruses. During the course of comprehensive pathologic evaluations of aging breeders, 6 female cotton rats were incidentally found to have pulmonary trophoblast emboli. The purposes of the present case series were to characterize the embolized trophoblasts and associated pulmonary histopathology in these cotton rats and to correlate the incidence with gestational stage.     

Sugar preferences of "black rats", Rattus rattus L.

The choice of "black rats", Rattus rattus L ., for common sugars - sucrose, jaggery, glucose, fructose and lactose are described. In laboratory colonies, the sugars were preferred in the order glucose > sucrose > jaggery > fructose > lactose; but in another sequence - sucrose > jaggery > glucose > fructose > lactose, in the free living colonies. The discrepancy is accounted for by the characteristics of sugars which influence consummatory behaviour in the two situations.     

Multiple Cryptosporidium genotypes detected in wild black rats (Rattus rattus) from northern Australia

As part of a broader investigation into the potential role of black rats (Rattus rattus) as disease vectors into native small mammal populations of northern Australia, blood and faecal samples from wild black rats were screened by molecular methods, for piroplasms (Babesia and Theileria), trypanosomes and the enteric parasite Cryptosporidium. While piroplasms and trypanosomes were not detected in the blood of these animals, the overall prevalence of Cryptosporidium 18S rDNA in faecal samples was 8.2% (7/85). Co-occurrence of multiple genotypes was observed in 57.1% of the infected individuals (4/7); cloning and re-sequencing resulted in 14 sequences which broadly grouped with Cryptosporidium sp. rat-genotypes II and III. A novel rat-derived Cryptosporidium sp. genotype at the actin locus was also obtained from five animals. The relatively low infection rate detected, and the epidemiological data on cryptosporidiosis, do not conclusively support a current threat to native Australian mammals from black rats carrying Cryptosporidium. However, this observation is based on sampling limited isolates, in limited regions. Further studies, also including sampling of native mammals, are required on larger sample sizes and from wider geographic areas, to determine the significance of these findings, including the public health importance of Cryptosporidium spp. from rodents.     

Strongyloidiasis in cotton rats (Sigmodon hispidus) from central Oklahoma

Thirty-one of 40 cotton rats (Sigmodon hispidus) collected from central Oklahoma were infected with Strongyloides sp. (78% prevalence). Larvae of Strongyloides sp. (rhabditiform or filariform) were not demonstrable in intestinal contents and scrapings. Female nematodes recovered from intestinal contents and scrapings had morphological similarities with Strongyloides sigmodontis. Cotton rats infected with Strongyloides sp. were indistinguishable clinically from non-infected hosts. Infected animals had no significant gross lesions, but the presence of Strongyloides sp. in the intestinal mucosa was associated with villus atrophy and mild to moderate infiltration of the lamina propria by lymphocytes, plasma cells and occasional eosinophils. Other organs or tissues examined were free from lesions induced by Strongyloides sp.     

Frugivory by introduced black rats (Rattus rattus) promotes dispersal of invasive plant seeds

Oceanic islands have been colonized by numerous non-native and invasive plants and animals. An understanding of the degree to which introduced rats (Rattus spp.) may be spreading or destroying seeds of invasive plants can improve our knowledge of plant-animal interactions, and assist efforts to control invasive species. Feeding trials in which fruits and seeds were offered to wild-caught rats were used to assess the effects of the most common rat, the black rat (R. rattus), on 25 of the most problematic invasive plant species in the Hawaiian Islands. Rats ate pericarps (fruit tissues) and seeds of most species, and the impacts on these plants ranged from potential dispersal of small-seeded (≤1.5 mm length) species via gut passage (e.g., Clidemia hirta, Buddleia asiatica, Ficus microcarpa, Miconia calvescens, Rubus rosifolius) to predation where <15% of the seeds survived (e.g., Bischofia javanica, Casuarina equisetifolia, Prosopis pallida, Setaria palmifolia). Rats consumed proportionally more seed mass of the smaller fruits and seeds than the larger ones, but fruit and seed size did not predict seed survival following rat interactions. Although invasive rat control efforts focus on native species protection, non-native plant species, especially those with small seeds that may pass internally through rats, also deserve rat control in order to help limit the spread of such seeds. Black rats may be facilitating the spread of many of the most problematic invasive plants through frugivory and seed dispersal in Hawaii and in other ecosystems where rats and plants have been introduced.     

Developmental Plasticity of Postweanling Cotton Rats (Sigmodon hispidus) as an Adaptation to Nutritionally Stochastic Environments

Elucidating interrelationships between rate of growth and sexual maturation in unpredictable or stochastic environments could increase our understanding of life-history strategies of small mammals. It has been hypothesized that species living in environments where food availability is unpredictable might become sexually mature at smaller sizes and channel excess energy into reproduction rather than into compensatory growth. We explored this hypothesis in female cotton rats (Sigmodon hispidus) by feeding variable levels of dietary protein during early postweanling development (14–45days of age) and monitoring compensatory growth and fitness after nutritional rehabilitation (45–100days of age). Growth was optimum in females fed diets containing 16% protein, with minimal requirements estimated to be 12%. Females fed diets containing <12% protein exhibited suppressed development, including delayed puberty. However, these nulliparous females demonstrated compensatory growth during the early period of nutritional rehabilitation, regardless of the severity of previous restrictions in protein. No long-lasting fitness consequences from postweanling nutritional restrictions were apparent as we observed no difference in date of conception, body mass of dams at parturition, litter size, or rate of growth of neonates. We offer a possible adaptive explanation for this observed plasticity in growth and development. This revised version was published online in July 2006 with corrections to the Cover Date.     

Echinococcus multilocularis: responses to infection in cotton rats (Sigmodon hispidus)

Various aspects of the responses of cotton rats to intraperitoneal infections with Echinococcus multilocularis were examined to determine if they could be related to the progress of the infection. At 14 weeks post-infection, infected animals had enlarged spleens; there was a slight decrease in packed cell volume, but no reticulocytosis. The number of all four types of leukocytes in the peripheral blood (lymphocytes, monocytes, neutrophils and eosinophils) increased during the course of the infection. In the peritoneal fluid, the numbers of neutrophils increased, monocytes and basophils decreased, and lymphocytes and eosinophils remained unchanged. Antibodies to E. multilocularis were detected in the serum of infected cotton rats as early as 2 weeks post-infection. The mean levels of transaminases (SGOT and SGPT) in the serum of infected animals were higher than in controls, and 5'-nucleotidase levels were elevated in heavily infected animals. There were no differences in responses between male and female animals. Comparison with results previously obtained suggest that both the outcome of the infection, and responses to it, may be under host control.     

Fatal Caryospora bigenetica (Apicomplexa: Eimeriidae) infections in cotton rats, Sigmodon hispidus

Four groups of cotton rats, Sigmodon hispidus, were shown to be suitable secondary hosts for the viperid coccidium, Caryospora bigenetica, following oral inoculation of a mixture of oocysts and sporocysts. Swelling of the face, ears, and scrota and hemorrhagic ears were the predominant clinical signs and some cotton rats died in 3 of 4 experiments. Developmental stages of C. bigenetica were found in connective tissue components of the ear, nose, cheeks, anal skin, scrotum, and penile sheath of all cotton rats in which these tissues were examined. Additionally, developmental stages of C. bigenetica were found in connective tissue components of the following tissues examined from some cotton rats: tongue, lung, testicle, epididymis, rectum, base of the tail, footpad, and bone marrow. The present study shows that C. bigenetica can be pathogenic for cotton rats and demonstrates many new anatomic sites for developmental stages of this parasite in the secondary host.     

Environmental Influences on Mass Dynamics of the Cotton Rat (Sigmodon hispidus) Thymus Gland

The influence of season on thymus gland mass was examined relative to captivity, gender, and age in 921 cotton rats (Sigmodon hispidus) from free-ranging and laboratory populations. Age-related involution of the thymus gland was evident in free-ranging males and females and captive females. A distinct seasonal cycle in thymus mass dynamics was apparent among adult cotton rats. Mass of the thymus gland was greatest from late fall to early winter before declining 2-4 fold during spring. Thymus gland mass remained low through spring and summer in adult cotton rats when reproductive activity was maximum. No seasonal cycle in thymus mass was apparent among juveniles. Possible involvement of sex hormones in regulating thymus size is discussed.     

Black rats (Rattus rattus) from medieval Mertola (Baixo Alentejo, Portugal)

This paper is about the analysis and interpretation of micromammal samples from archaeological sites while reporting on a black rat assemblage from XIII^th century Muslim levels in the city of Mertola. Questions concerning skeletal representation, size plus age estimations and bone fragmentation are discussed from a taphonomic standpoint. It is concluded that the tendency to interpret rodent accumulations in anthropic sites as evidence of preybird activities might be an oversimplification in need of substantial revision.     

Karyotypes and serum transferrin patterns of hybrids between Asian and Oceanian black rats,Rattus rattus

Karyotypes and serum transferrin patterns were examined in Asian and Oceanian black rats (R. rattus). Japanese R. r. tanezumi and Malayan R. r. diardii had 2n=42, but Australian and New Guinea R. r. rattus showed 2n=38 chromosomes. F₁ hybrids between Japanese and Australian rats and Malayan and New Guinea rats had 2n=40 chromosomes which consists of the two genomes of both parents. Although various matings between the F₁ hybrids were made, only one F₂ male rat with 2n=39 chromosomes was obtained. The F₁ hybrids seem to be semisterile. Parental transferrin phenotypes were TfR in Japanese rats and TfCD in Oceanian rats. F₁ hybrids examined showed TfRD in both male and female and one F₂ hybrid had TfR type transferrin. Based on the above investigations, it is suggested that Asian and Oceanian black rats are geographically isolated and evolved different chromosomal and serum transferrin characteristics, but the sexual isolation of the two groups is incomplete at the present time.Contribution No. 826 from the National Institute of Genetics, Japan. Supported by a grant-in-aid from the Ministry of Education of Japan (Scientific Expedition in 1968, No. 8801 in 1969 and No. 9001 in 1970).     

Effects of social environment on sexual maturation in female cotton rats (Sigmodon hispidus)

Age at sexual maturation among female cotton rats was measured in a variety of intraspecific social environments. Two experiments were conducted. In Experiment I, female cotton rats attained vaginal perforation and first estrus at younger ages and lighter body masses when paired from weaning with a conspecific juvenile male than when caged alone. In Experiment II, these findings were replicated and extended. Females housed with juvenile males matured at the youngest ages, while those housed alone matured at the oldest ages. Females housed with adult males matured at intermediate ages. Presence of a second juvenile female during maturation was significantly associated with early vaginal opening but not with early first estrus. The results of this study are discussed in context of similar social environmental effects on female sexual maturation that have been identified in other rodent species.     

Leishmania tropica in the black rat (Rattus rattus): persistence and transmission from asymptomatic host to sand fly vector Phlebotomus sergenti

Black rats (Rattus rattus) receiving Leishmania tropica injected intradermally into the ear were studied for the persistence of parasites and infectivity to natural sand fly vector. The mammalian host, the parasite, and the vector all originated from the endemic focus of Urfa, Turkey. Rats did not develop lesions or any apparent signs of disease, although at the site of inoculation they harboured live parasites capable of infecting sand flies. The number of L. tropica amastigotes detected in the inoculated ear by quantitative real-time PCR ranged from 5 x 10(3) to 10(6). Parasite DNA was also present in the tail and contralateral ear, sites distant from inoculation. After feeding on the ears of asymptomatic rats, Phlebotomus sergenti became infected with L. tropica. The average infection rate was 2.9%, and rats were infective for sand flies even 24 months post infection. The infectivity of the vertebrate host for insect vector was therefore not linked to the symptomatic stage of the infection. Such lack of correlation between clinical symptoms and infectivity to sand flies was reported previously for Leishmania infantum, the agent of visceral leishmaniasis; for species causing cutaneous leishmaniasis, however, this is the first evidence of transmission from a host without any visible cutaneous changes. If confirmed in the field, transmission from the asymptomatic host would be of great epidemiological significance.     

Neurohistological observations on the kidney of Rattus rattus rufescens (Indian black rat) as revealed by cholinesterase technique.

The intrinsic innervation of the kidney in Rattus rattus rufescens (Indian black rat) has been studied by cholinesterase technique, under various temperatures, incubation periods and different pH values. The percentage of myelinated nerves was rather high in the medulla region, whereas the non-myelinated nerves dominated in association with the uriniferous tubules and their branches, glomerulus and renal vein in the cortex region. Periarterial AChE-positive ganglia were recorded in the medulla region. The perivenous and periglomerulus plexuses were formed by the non-myelinated nerves and their branches.     

Salmonella ochiogu: experimental infection of laboratory rats (Rattus rattus)

Oral infection of experimental rats with 10(8) colony forming units of Salmonella ochiogu resulted in clinical salmonellosis in 42 of 98 (43%) rats and a carrier state in 56 of 98 (57%). Infection was characterized by septicaemia, pneumonia and loss of condition. Organisms were shed in faeces on the first day after infection and cultures of most visceral organs revealed good systemic dissemination of the serotype, which was pathogenic to experimental rats.     

Acute and Chronic Airway Disease After Human Respiratory Syncytial Virus Infection in Cotton Rats (Sigmodon hispidus)

Infection with respiratory syncytial virus (RSV) generally presents as a mild, upper airway disease in human patients but may cause severe lower airway disease in the very young and very old. Progress toward understanding the mechanisms of RSV pathogenesis has been hampered by a lack of relevant rodent models. Mice, the species most commonly used in RSV research, are resistant to upper respiratory infection and do not recapitulate the pattern of virus spread in the human host. To address the need for better rodent models of RSV infection, we have characterized the acute and chronic pathology of RSV infection of a relatively permissive host, cotton rats (Sigmodon hispidus). We demonstrate that virus delivered to the upper airway results in widespread RSV replication in the ciliated respiratory epithelial cells of the nasal cavity and, to a lesser extent, of the lung. Although acute inflammation is relatively mild and rapidly eliminated after viral clearance, chronic, eosinophilic lung pathology persists. These data support the use of cotton rats as a robust rodent model of human RSV disease, including the association between RSV pneumonia and subsequent development of allergic asthma.Abbreviations: BAL, bronchoalveolar lavage; RSV, human respiratory syncytial virusHuman respiratory syncytial virus (RSV) is the primary cause of lower airway disease in infants and children worldwide.³⁹ Although generally limited to the upper airway, RSV infection can also manifest as bronchiolitis and pneumonia in young children and the elderly and has been implicated as a major cause of middle ear infections (otitis media).^3,55 In addition to the problems associated with acute illness, children who experience severe RSV disease in infancy are at increased risk for development of asthma and recurrent wheezing later in childhood.^35,53,56RSV is ubiquitous worldwide, with most children infected in infancy, and essentially all children are infected by 3 y of age.²⁰ Although reinfection throughout life has been documented, the true incidence of upper airway infection is difficult to quantify, given that treatment for such infections typically is not sought. In comparison, lower airway infection is more likely to come to medical attention, and it is currently estimated that at least 33.8 million episodes of RSV-induced acute pulmonary infection in children younger than 5 y occur yearly and that as many as 200,000 of those episodes are fatal.⁴⁰ Although supportive treatment for severe RSV disease is highly effective in infants, access to such treatment is generally only available in industrialized countries. More than 90% of fatal RSV cases occur in the developing world.⁴⁰Mice have been used extensively to study RSV infection, yet there are key limitations of the mouse model for the study of human RSV disease and immunity. The most important of these is the poor permissiveness of the mouse for human RSV. RSV replicates to a limited extent in the mouse lung, and large viral loads delivered in a relatively large volume are generally used with this model. Even with intranasal inoculation, primarily lower, and not upper, airway infection is achieved in WT mice. This scenario is unlike the human disease, in which the upper airway is the primary target of RSV replication.^24,25 Mice are essentially resistant to upper airway infection, with little to no virus detected in nasal washes evaluated by plaque assay, and only rare RSV-antigen–positive cells are detected by immunohistochemistry.^13,18,21 In addition to this altered route of entry, the pattern of lung infection is markedly divergent between humans and mice. In humans, RSV primarily infects ciliated bronchiolar epithelial cells and, to a much lesser extent, alveolar cells.³² In contrast, bronchiolar epithelial cells are infected only rarely in the mouse lung; instead RSV targets the pneumocytes.³⁷Unlike mice, cotton rats are susceptible to RSV infection of the upper airway, and the pattern of lower airway infection mirrors that seen in human patients. The cotton rat was established as a model of RSV infection more than 3 decades ago and has since emerged as the preferred rodent model in which to evaluate RSV therapeutics and vaccine candidates.^{19,23,33,41,49,57,60} In addition, as the availability of species-specific reagents has improved, cotton rats have become an increasingly useful model in which to study RSV pathogenesis.⁶ However, whereas the susceptibility of cotton rats to RSV infection has been established firmly, the pathology of RSV infection in this species has not yet been extensively characterized.Asthma clearly is a multifactorial disease, dependent on both genetic and environmental factors (see references 28 and 30 for recent reviews), and many studies have pointed to a role for respiratory virus infection in the induction of asthma. In one study,¹⁷ the combination of atopy and the presence of virus in nasal secretions synergistically increased the odds ratio for wheezing in children 25-fold, and another study²⁹ showed that repeated rhinovirus infections in the first 3 y of life increased by 26-fold the risk of developing asthma by the age of 6 y. This relationship is obviously a complex one, influenced both by the nature and the timing of the viral infection. Nonetheless, as many as 80% of acute asthma exacerbations in children and approximately 50% in adults are associated with viral infection.^33,42 The majority of these infections are attributed to rhinoviruses, but other respiratory viruses, including influenza virus, RSV, and coronaviruses, can provoke these attacks.^33,42 Beyond the exacerbation of established asthma, evidence that severe RSV disease in infancy is correlated with development of asthma and recurrent wheezing in later childhood is mounting. An association between lower airway RSV infection and subsequent development of recurrent wheezing and asthma was demonstrated more than 30 y ago,¹⁶ and several recent prospective studies have strengthened this correlation.^27,53In the current study, we expand upon existing knowledge of the cotton rat model of RSV infection by characterizing the spread of virus after droplet inhalation and the early and late inflammatory response to viral challenge. We confirm the observation that cotton rats are relatively permissive in regard to RSV infection as compared with mice, and we demonstrate that the infection of cotton rats, like that in the human host, is primarily an upper airway phenomenon. In addition, we show that primary RSV infection of the cotton rat lung, even at the low levels in this study, induces chronic changes consistent with those in cases of human allergic asthma. This finding is of interest because of the substantial literature associating early, severe respiratory infection with the development of asthma later in life. The studies of RSV infection in cotton rats that we describe here suggest that this species may be predisposed to atopy and that, long after virus clearance, changes associated with allergic inflammation persist in human hosts. Therefore, in addition to the usefulness of cotton rats for testing RSV treatments and vaccine candidates, we suggest that this species may serve as a model system for determining the involvement of virus infection in the development of allergic asthma.