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.

Pneumocystis carinii causes a distinctive interstitial pneumonia in immunocompetent laboratory rats that had been attributed to "rat respiratory virus".

A prevalent and distinctive infectious interstitial pneumonia (IIP) of immunocompetent laboratory rats was suspected to be caused by a putative virus, termed rat respiratory virus, but this was never substantiated. To study this disease, 2 isolators were independently populated with rats from colonies with endemic disease, which was perpetuated by the regular addition of naive rats. After Pneumocystis was demonstrated by histopathology and polymerase chain reaction (PCR) in the lungs of rats from both isolators and an earlier bedding transmission study, the relationship between Pneumocystis and IIP was explored further by analyzing specimens from 3 contact transmission experiments, diagnostic submissions, and barrier room breeding colonies, including 1 with and 49 without IIP. Quantitative (q) PCR and immunofluorescence assay only detected Pneumocystis infection and serum antibodies in rats from experiments or colonies in which IIP was diagnosed by histopathology. In immunocompetent hosts, the Pneumocystis concentration in lungs corresponded to the severity and prevalence of IIP; seroconversion occurred when IIP developed and was followed by the concurrent clearance of Pneumocystis from lungs and resolution of disease. Experimentally infected immunodeficient RNU rats, by contrast, did not seroconvert to Pneumocystis or recover from infection. qPCR found Pneumocystis at significantly higher concentrations and much more often in lungs than in bronchial and nasal washes and failed to detect Pneumocystis in oral swabs. The sequences of a mitochondrial ribosomal large-subunit gene region for Pneumocystis from 11 distinct IIP sources were all identical to that of P. carinii. These data provide substantial evidence that P. carinii causes IIP in immunocompetent rats.

Of mice and microflora: considerations for genetically engineered mice.

The phenotype of genetically engineered mice is a combination of both genetic and environmental factors that include the microflora of the mouse. The impact a particular microbe has on a mouse reflects the host-microbe interaction within the context of the mouse genotype and environment. Although often considered a confounding variable, many host-microbe interactions have resulted in the generation of novel model systems and characterization of new microbial agents. Microbes associated with overt disease in mice have been the historical focus of the laboratory animal medical and pathology community and literature. The advent of genetic engineering and the complex of mouse models have revealed previously unknown or disregarded agents that now oblige the attention of the biomedical research community. The purpose of this article is to describe and illustrate how phenotypes can be affected by microflora by focusing on the infectious diseases present in genetically engineered mouse (GEM) colonies of our collective institutions and by reviewing important agents that are rarely seen in most research facilities today. The goal is to introduce the concept of the role of microflora on phenotypes and in translational research using GEM models.

Immunological variation between inbred laboratory mouse strains: points to consider in phenotyping genetically immunomodified mice.

Inbred laboratory mouse strains are highly divergent in their immune response patterns as a result of genetic mutations and polymorphisms. The generation of genetically engineered mice (GEM) has, in the past, used embryonic stem (ES) cells for gene targeting from various 129 substrains followed by backcrossing into more fecund mouse strains. Although common inbred mice are considered "immune competent," many have variations in their immune system-some of which have been described-that may affect the phenotype. Recognition of these immune variations among commonly used inbred mouse strains is essential for the accurate interpretation of expected phenotypes or those that may arise unexpectedly. In GEM developed to study specific components of the immune system, accurate evaluation of immune responses must take into consideration not only the gene of interest but also how the background strain and microbial milieu contribute to the manifestation of findings in these mice. This article discusses points to consider regarding immunological differences between the common inbred laboratory mouse strains, particularly in their use as background strains in GEM.

Histopathology of naturally transmitted "rat respiratory virus": progression of lesions and proposed diagnostic criteria.

Rat respiratory virus (RRV) is the working name for a novel respiratory pathogen of laboratory rats in North America, Europe, and Asia. Although the agent has not been definitively identified, evidence supports a viral etiology. Because no serologic or molecular assays for RRV are available, diagnosis depends on histopathologic evaluation of the lung. We introduced 104 Wistar Han rats, free of known pathogens and of RRV-associated lesions, into a rat production colony positive for RRV-type lesions, but free of other histologic, serologic, or microbiologic evidence of infectious disease. Lungs of 8 of the naïve rats were examined grossly and microscopically each week, weeks 0-13. Irregular gray-white lesions suggestive of interstitial pneumonia were grossly evident from weeks 6 through 13. Primary histopathologic evaluation of all lungs by one pathologist found multifocal, lymphohistiocytic interstitial pneumonia or prominent perivascular lymphoid cuffing from weeks 5 through 13. Based on results of the initial evaluation, diagnostic criteria for RRV infection (i.e., changes seen only after exposure to the RRV-positive colony) were tentatively selected and used by 2 other pathologists to classify each lung as RRV positive, RRV equivocal, or RRV negative. The secondary evaluation found 95% concordance in RRV diagnosis between pathologists, and correlated well with the initial evaluation, thus confirming the consistency of the criteria. These data show that RRV-naïve rats introduced into an RRV-endemic colony develop equivocal microscopic lesions of RRV by 5 weeks of exposure, and positive diagnostic lesions by 7 weeks. Interstitial pneumonia becomes grossly evident after 6 weeks of exposure.

Samples, sample selection, and statistics: living with uncertainty.

The author explains how to determine how many animals in a population need to be sampled when monitoring for pathogens. He concludes that even with perfect testing programs, there is always a chance that an infected animal will be missed.

Ringtail in suckling Munich Wistar Fromter rats: a histopathologic study.

Ringtail is a pathologic condition of the tail of rats and other rodents that is traditionally attributed to low environmental humidity, although dietary deficiencies, genetic susceptibility, environmental temperature, and degree of hydration of the animal also have been suggested as possible causes. To the authors' knowledge, a detailed histopathologic study that may serve to shed light on the etiopathogenesis of this disease has not yet been published. We describe the histologic findings of ringtail observed in 12 suckling Munich Wistar Fromter (MWF) rats from two litters. Epidermal hyperplasia characterized by orthokeratotic and parakeratotic hyperkeratosis and acanthosis was observed in all affected rats. Numerous often dilated vessels were present in the dermis of tails that appeared of red/brown color at gross examination. In severe cases, the dilated vascular structures were thrombotic and accompanied by dermal hemorrhages and focal coagulative necrosis of the overlying epidermis. These findings suggest that epidermal acanthosis and hyperkeratosis are the main and primary events in the development of ringtail. To clarify the cause of this disease, future studies should be focused on the numerous factors that can induce such epidermal changes.

Hyperkeratosis in athymic nude mice caused by a coryneform bacterium: microbiology, transmission, clinical signs, and pathology.

The purpose of this study was to characterize a spontaneous disease condition causing hyperkeratosis in nude mice and to explore the etiologic role of a particular species of coryneform bacteria in this disease, colloquially known as "scaly skin disease." The study was divided into two parts. In the first phase, a series of inoculation experiments was conducted with a field isolate of the coryneform species used to study the clinical and histopathologic development of the disease syndrome. Athymic nude mice (4 to 5 weeks old) were inoculated on the skin of the back with a suspension of a pure culture of the coryneform bacterium that had been isolated from a field case. The culture was applied with a sterile cotton swab in concentrations varying from 6.1 x 10(4)/ml to 5.0 x 10(7)/ml. All inoculated mice became persistently infected throughout the 33 days of the experiment. Clinically evident hyperkeratosis in inoculated animals developed more frequently in mice housed in a microisolator cage than in a semi-rigid isolator and more frequently in mice inoculated with higher numbers of organisms. In all animals in which hyperkeratosis developed, it was first noted on day 7 after inoculation. The second series of experiments was designed to determine the success of various housing methods in excluding the infection, mechanisms of transmission, susceptibility of other stocks and strains of mice to the organism, and whether the other strains might serve as a source of the organism. Results of the study in various strains indicated that both immunocompetent and immunodeficient mice, whether glabrous or hirsute, could be infected with the organism, but only glabrous animals developed hyperkeratosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Resuscitation from hypovolemia in swine with intraosseous infusion of a saturated salt-dextran solution.

Prehospital fluid resuscitation of traumatic injury is limited by difficulty in delivering large volumes of fluid in the field and time delays associated with gaining vascular access. We addressed these limitations in 14 anesthetized swine by evaluating a highly efficient volume expander, a near-saturated salt-dextran solution (SSD) administered through a new device, which gains vascular access via intraosseous (IO) infusion into the sternal bone marrow. After a steady-state baseline was achieved, all animals were hemorrhaged to 45 mm Hg for one hour. Half of the hemorrhaged animals were infused intraosseously with either normal saline (NS) or SSD until cardiac output was restored to the baseline value. No further infusion was given and animals were monitored for 2 hours. Both regimens were able to restore cardiac output to the baseline value, but only 1.3 +/- 0.1 mL/kg of SSD was required vs. 31.6 +/- 6.3 mL/kg for NS. In addition, cardiac output was better sustained after 2 hours with SSD than with NS. No deleterious effects of IO infusion of SSD were observed. From the improvement in cardiovascular variables and the lack of significant sternal or pulmonary pathologic perturbations, these data suggest that IO infusion of SSD can effectively treat hypovolemia and may allow field treatment when logistic considerations make conventional resuscitation impractical.

Resuscitation of hypovolemia in pigs using near saturated sodium chloride solution in dextran.

A 7.5% sodium chloride/6% Dextran solution (HSD) is effective for restoration of cardiovascular function after hemorrhagic shock. In the present experiments, we tested the usefulness and side effects of a 25% NaCl/24% Dextran solution (SSD), compared to HSD and 0.9% NaCl (NS). After 1 hr of baseline observation, 21 anesthetized pigs were submitted to hemorrhagic shock, maintaining a mean arterial pressure of 45 mmHg for 60 min. Continuous intravenous infusion of one of the solutions was then initiated and the infusion rate adjusted to restore and maintain cardiac output at baseline levels for 2 hr. The NS group required 121 +/- 22 ml/kg to achieve full resuscitation, while the HSD and SSD groups required 6.3 +/- 1.3 and 1.7 +/- 0.2 ml/kg, respectively. We conclude that SSD infusions were exceedingly effective at restoring cardiovascular function in volumes equal to only 10% of bled volume, but were associated with transient hemolysis and peripheral vein inflammation.

Comparison of intraosseous and intravenous delivery of hypertonic saline/dextran in anesthetized, euvolemic pigs.

STUDY OBJECTIVES: With renewed interest in intraosseous (IO) infusion, the present study examined if sternal IO infusion provided vascular entry of 7.5% NaCl/6% dextran-70 (HSD) as efficiently as IV infusion. DESIGN, SETTING, TYPE OF PARTICIPANTS, INTERVENTIONS: Twelve anesthetized pigs were catheterized for measurement of cardiovascular parameters. Six pigs were given a 4-mL/kg IO infusion of HSD under pressure over two to six minutes; each pig was paired with another that had been given HSD IV over the same time course. Rapid arterial blood sampling was used to evaluate vascular entry of NaCl and dextran with monitoring continued for two hours after infusion. MEASUREMENTS AND MAIN RESULTS: Complete vascular entry of infused sodium and dextran was generally complete within one minute after infusion in all experiments. Increases in mean arterial pressure, cardiac output, and other cardiovascular parameters were indistinguishable between IO and IV infusions. Plasma volume expansion was about 20% above baseline in both groups of pigs. Histologic examination showed minimum pathology to the sternum and no significant pulmonary complications. CONCLUSION: 1O vascular delivery of HSD is a viable alternative in emergency scenarios in which vascular access is compromised.

Suppression by traumatic brain injury of spontaneous hemodynamic recovery from hemorrhagic shock in rats.

The effects of brain trauma on cardiovascular and endocrine responses to hemorrhage were investigated. Forty anesthetized rats were randomly assigned to one of four groups of 10 rats each: a control group (Group C): a group with induction of hemorrhage at 16.2 ml/kg/10 min (Group H); a group with fluid-percussion brain injury at a peak pressure of 1.7 atm and an impulse duration of 25 msec (Group T); and a group receiving hemorrhagic shock following brain trauma (Group TH). Group C and T rats showed no significant alterations in cardiovascular function. At the end of hemorrhage there were no significant differences between Groups TH and H in the nadirs of mean arterial blood pressure (MABP) (mean values +/- standard error of the mean: 42 +/- 2 vs. 40 +/- 4 mm Hg) and stroke volume index (SVI) (0.61 +/- 0.11 vs. 0.66 +/- 0.10 ml/bt/kg); however, 1 hour post-hemorrhage recovery was blunted in Group TH compared to Group H (MABP 56 +/- 4 vs. 65 +/- 3 mm Hg; cardiac index 182 +/- 15 vs. 220 +/- 15 ml/min/kg; and SVI 0.71 +/- 0.06 vs. 0.81 +/- 0.06 ml/bt/kg). Since the two groups showed no significant differences in heart rate, preload (central venous pressure), and afterload (systemic vascular resistance), the reduced cardiac index recovery in Group TH is believed due to the attenuation of cardiac contractile performance. The Group TH preparation potentiated hormonal responses to hemorrhage with significantly higher epinephrine and aldosterone levels than in Group H. Brain trauma enhanced the norepinephrine response to hemorrhage, even at an injury level that by itself did not result in an increase in this hormone. Group TH rats also had significantly lower blood pH and HCO3 levels. The data suggest that brain trauma suppresses MABP and cardiac index recovery after hemorrhage mainly by inhibiting cardiac contractile performance, probably due to high catecholamine levels and severe metabolic acidosis.

Immediate hypertensive response to fluid percussion brain injury may be related to intracerebral hemorrhage and hypothalamic damage.

Fluid percussion brain injury is associated with an immediate rise in mean arterial pressure (MAP). However, the cerebral morphologic basis for this response is still not clear. Thirty-four anesthetized rats were injured using a lateral craniotomy preparation. In 19 rats, impact level was set at 1.73 +/- 0.04 atm, and impact duration was kept at 25 msec to examine the relationship between postinjury hypertensive response and cerebral lesions. MAP was monitored for 1 hour after impact. Fluid percussion produced an increase in MAP from 99 +/- 3 to 134 +/- 4 mm Hg (p less than 0.001), with an increment range of -2 to 87 mm Hg (36 +/- 5 mm Hg) or 0 to 96% increase. The MAP peak occurred at 15 +/- 2 seconds and then rapidly returned to the preimpact level. Histopathological findings, principally hemorrhage, were graded and ranked from 1 to 19 according to relative severity and hypothalamic involvement. There was a significant correlation between MAP rise and the injury ranking (r = 0.52, p = 0.02). No appreciable damage was observed in the brainstem caudal to the diencephalon. Fifteen rats were subjected to higher injury levels. The overall impact magnitude ranged from 1.3 to 3.5 atm. A linear relationship was found between impact magnitude (X, atm) and increment in MAP (Y, mm Hg) (Y = 28.1*X - 14.0, r = 0.62, p less than 0.001). Our study indicates that the immediate postinjury hypertensive response is closely correlated with the impact magnitude and may be related to intracerebral hemorrhage and hypothalamic damage but not necessarily to caudal brainstem damage.

Renal responses to graded hemorrhage in conscious pig.

We developed a conscious pig model with a chronically instrumented kidney to measure renal blood flow (RBF), glomerular filtration rate (GFR), and excretory functions during hemorrhage. Seven to 10 days before experimentation, pigs were splenectomized, arterial and venous catheters were implanted, an ultrasonic flow probe was placed on the renal artery, and a pyelostomy was performed for nonocclusively placing a ureteral catheter. Measurements were taken before hemorrhage, and at hemorrhage volumes of 7, 14, 21, and 28 ml/kg (equivalent to 10.5, 21, 31, and 42% of the estimated blood volume), or at corresponding time points for controls. RBF was decreased by 30% when 21% of the blood (14 mg/kg) was removed, before arterial pressure, GFR, or urine flow or excretion was changed. At volumes of hemorrhage greater than 14 ml/kg, there were progressive decreases in RBF, GFR, urine flow rate, osmotic and electrolyte excretion, and arterial pressure. Thus pigs, like humans, respond to hypovolemia with an early redistribution of blood flow away from the kidney.

Morphologic alterations in rat retina after hypervolemic infusion of cross-linked hemoglobin.

Hypervolemic infusion in rats of bis (3,5-dibromosalicyl) fumarate cross-linked hemoglobin (DBBF-Hb) to 40-60% of blood volume produced histologic lesions in retina which were not observed in rats similarly infused with human serum albumin or lactated Ringer's solution. Rats treated with 40% DBBF-Hb, exhibited intermittent zones of dense retinal pigmented epithelium while 60% DBBF-Hb animals exhibited severe inner retinal edema and retinal pigmented epithelium vacuolization, large focal zones of photoreceptor outer segment disruption and in one animal, subretinal hemorrhage. Light microscopic immunocytochemical evaluation of retinas with antibodies directed to human hemoglobin and albumin, showed the presence of both hemoglobin and albumin in this tissue. Transmission electron microscopy of the lesions demonstrated vacuolated retinal pigmented epithelial cells and large areas of focal photoreceptor outer segment disruption. We conclude that hypervolemic infusion disrupts the blood retinal barrier and that although both DBBF Hb and albumin cross, only hemoglobin produced damage in the retina.

Morphologic effects of hypervolemic administration of DBBF hemoglobin in the rat.

Conscious rats were given either 14 g/dl bis(3,5-dibromosalicyl) fumarate cross-linked hemoglobin (DBBF-Hb) in lactated Ringer's (LR) as an intravenous bolus (40, 50, or 60% of blood volume), 12.5 g/dl human serum albumin (HSA) in LR as a control for oncotic effects, or LR as a control for injection volume. The high dose HSA and DBBF-Hb rats experienced pulmonary edema after injection; one rat in each of these groups died soon after dosing. Rats were killed after 48 hours for histopathology. Only the 60% HSA and the 50% and 60% DBBF-Hb rats had treatment-related lesions. In the liver, randomly distributed mononuclear cell aggregates occasionally surrounded a necrotic hepatocyte. Liver lesions in 60% DBBF-Hb rats were the largest and most numerous, but in all groups were qualitatively similar. Hearts from HSA and DBBF-Hb rats had similar mild inflammatory lesions. We conclude that bolus administration of DBBF-Hb causes morphologic lesions in rats only at volumes sufficient to cause pulmonary edema. Hepatic and cardiac changes with high volumes of DBBF-Hb resembled those in rats given a corresponding bolus of HSA, suggesting that vascular overload with a hyperoncotic solution, rather than cytotoxicity of DBBF-Hb, caused the injury.

Ontogeny of inflammatory cell responsiveness: superoxide anion generation by phorbol ester-stimulated fetal, neonatal, and adult bovine neutrophils.

Newborn calves, like human infants, are uniquely susceptible to bacterial infections. Part of this increased susceptibility may be related to defects in newborn polymorphonuclear leukocyte (PMN) defensive functions. It remains unclear whether reported deficits in newborn PMN function represent maturational disorders or are manifestations of some form of perinatal suppression phenomenon. We therefore compared the ability of bovine newborn PMNs (less than 24 h old), newborn PMNs (7-10 days of age), fetal PMNs (210-220 days gestational age), and adult PMNs to generate superoxide anion (O2-) as an indicator of respiratory burst activity. Citrated blood was collected, and PMNs were isolated to greater than 95% purity and 98% viability. O2- generation was measured as the superoxide dismutase-inhibitable (10 micrograms/ml) reduction of ferricytochrome c (2 mg/ml) after activation of PMNs with phorbol myristate acetate (PMA, 2 micrograms/ml) to directly stimulate protein kinase C. The reaction kinetics were measured (37 degrees C, 550 nm) using a spectrophotometer and chart recorder for continuous monitoring. O2- generation was measured for 5 min after the initial lag period and the total nanomoles of O2- generated calculated using the extinction coefficient for ferricytochrome c. Newborn PMNs (N = 10) generated significantly less O2- (5.7 +/- 0.8 nmol O2-/10(6) cells/5 min, P less than 0.01) than did adult PMNs (N = 14) (9.6 +/- 2.1 nmol O2-/10(6) cells/5 min) or fetal PMNs (N = 4) (10.7 +/- 0.7 nmol O2-/10(6) cells/5 min). PMNs from 7- to 10-day-old calves (N = 9) generated almost identical amounts of O2- as newborn PMNs (5.7 +/- 1.6 nmol O2-/10(6) cells/5 min). There was no difference in measured lag time period between newborn and adult PMNs, but fetal PMNs had significantly reduced (P less than 0.01) mean lag time. The data indicated that bovine newborn PMNs have a decreased ability to generate O2- in response to PMA stimulation, which persists for at least 7-10 days, and that this functional decrement may be a manifestation of some form of perinatal PMN suppression phenomenon rather than a developmental abnormality since fetal PMNs produced O2- as well as adult PMNs.

Exogenous methemoglobin as a cyanide antidote in rats.

The effects of the administration of methemoglobin (MetHb) prepared in vitro were evaluated in Sprague-Dawley rats given increasing doses of potassium cyanide (KCN). Median lethal dose (LD50) studies were conducted by giving intraperitoneal injections of KCN (in 0.3- to 0.5-ml volumes), then 2 min later administering intravenous (iv) doses of 1000, 1500, or 2500 mg/kg of MetHb through the tail vein. Control rats received an equivalent volume of saline. The resulting LD50 values for KCN were 7.4 +/- 1.1, 11.7 +/- 1.1, 13.9 +/- 1.0, and 14.2 +/- 1.0 mg/kg (mean +/- SD) for the control (no MetHb) and 1000-, 1500-, and 2500-mg/kg dose groups, respectively. Additional groups of rats were given 1000, 1500, or 2500 mg/kg MetHb and submitted for necropsy. The gross finding of darkened kidneys was present in both dose groups, but became consistent and more prominent in the 2500-mg/kg dose group. Evidence of pathologic changes was not present in other organs. Single-dose pharmacokinetic studies were conducted using iv doses of 1600 and 2500 mg/kg MetHb. The elimination half-life was similar in both doses (62.6 min), but the volume of distribution (95.3 +/- 7.2 and 126.3 +/- 5.2 ml/kg, mean +/- SE) and clearance (1.1 +/- 0.1 and 1.5 +/- 0.1 ml/min/kg) were significantly different (P less than 0.05) for the 1600- and 2500-mg/kg dose groups, respectively. From these data we conclude that although MetHb is cleared from the vascular system rapidly, it may be an effective and nontoxic antidote for doses of cyanide up to twice that of the control LD50.