Effect of mechanical ventilation versus spontaneous breathing on abdominal edema and inflammation in ARDS: an experimental porcine model.

BACKGROUND: Mechanical ventilation (MV), compared to spontaneous breathing (SB), has been found to increase abdominal edema and inflammation in experimental sepsis. Our hypothesis was that in primary acute respiratory distress syndrome (ARDS) MV would enhance inflammation and edema in the abdomen. METHODS: Thirteen piglets were randomized into two groups (SB and MV) after the induction of ARDS by lung lavage and 1 h of injurious ventilation. 1. SB: continuous positive airway pressure 15 cmH2O, fraction of inspired oxygen (FIO2) 0.5 and respiratory rate (RR) maintained at about 40 cycles min- 1 by titrating remifentanil infusion. 2. MV: volume control, tidal volume 6 ml kg- 1, positive end-expiratory pressure 15 cmH2O, RR 40 cycles min- 1, FIO2 0.5. MAIN OUTCOMES: abdominal edema, assessed by tissues histopathology and wet-dry weight; abdominal inflammation, assessed by cytokine concentration in tissues, blood and ascites, and tissue histopathology. RESULTS: The groups did not show significant differences in hemodynamic or respiratory parameters. Moreover, edema and inflammation in the abdominal organs were similar. However, blood IL6 increased in the MV group in all vascular beds (p < 0.001). In addition, TNFα ratio in blood increased through the lungs in MV group (+ 26% ± 3) but decreased in the SB group (- 17% ± 3). CONCLUSIONS: There were no differences between the MV and SB group for abdominal edema or inflammation. However, the systemic increase in IL6 and the TNFα increase through the lungs suggest that MV, in this model, was harmful to the lungs.

Abdominal organ perfusion and inflammation in experimental sepsis: a magnetic resonance imaging study.

Diffusion-weighted magnetic resonance imaging (DW-MRI) uses water as contrast and enables the study of perfusion in many organs simultaneously in situ. We used DW-MRI in a hypodynamic sepsis model, comparing abdominal organ perfusion with global hemodynamic measurements and inflammation. Sixteen anesthetized piglets were randomized into 3 groups: 2 intervention (sepsis) groups: HighMAP (mean arterial pressure, MAP > 65 mmHg) and LowMAP (MAP between 50 and 60 mmHg), and a Healthy Control group (HC). Sepsis was obtained with endotoxin and the desired MAP maintained with norepinephrine. After 6 h, DW-MRI was performed. Acute inflammation was assessed with IL-6 and TNFα in abdominal organs, ascites, and blood and by histology of intestine (duodenum). Perfusion of abdominal organs was reduced in the LowMAP group compared with the HighMAP group and HC. Liver perfusion was still reduced by 25% in the HighMAP group compared with HC. Intestinal perfusion did not differ significantly between the intervention groups. Cytokine concentrations were generally higher in the LowMAP group but did not correlate with global hemodynamics. However, cytokines correlated with regional perfusion and, for liver and intestine, also with intra-abdominal pressure. Histopathology of intestine worsened with decreasing perfusion. In conclusion, although a low MAP (≤60 mmHg) indicated impeded abdominal perfusion in experimental sepsis, it did not predict inflammation, nor did other global measures of circulation. Decreased abdominal perfusion partially predicted inflammation but intestine, occupying most of the abdomen, and liver were also affected by intra-abdominal pressure. NEW & NOTEWORTHY The study increases the knowledge of abdominal perfusion during sepsis. We used diffusion weighted imaging to assess perfusion simultaneously and noninvasively in different abdominal organs. The technique has not been used in a sepsis model before. Cytokine concentrations were measured in different abdominal organs and vascular beds and related to regional perfusion. Decreased abdominal perfusion, but not global measures of circulation, predicted inflammation. Intestine, occupying most of the abdomen, and liver were also affected by intra-abdominal pressure.

Mouse mast cell protease-6 and MHC are involved in the development of experimental asthma.

Allergic asthma is a complex disease with a strong genetic component where mast cells play a major role by the release of proinflammatory mediators. In the mouse, mast cell protease-6 (mMCP-6) closely resembles the human version of mast cell tryptase, ß-tryptase. The gene that encodes mMCP-6, Tpsb2, resides close by the H-2 complex (MHC gene) on chromosome 17. Thus, when the original mMCP-6 knockout mice were backcrossed to the BALB/c strain, these mice were carrying the 129/Sv haplotype of MHC (mMCP-6(-/-)/H-2bc). Further backcrossing yielded mMCP-6(-/-) mice with the BALB/c MHC locus. BALB/c mice were compared with mMCP-6(-/-) and mMCP-6(-/-)/H-2bc mice in a mouse model of experimental asthma. Although OVA-sensitized and challenged wild type mice displayed a striking airway hyperresponsiveness (AHR), mMCP-6(-/-) mice had less AHR that was comparable with that of mMCP-6(-/-)/H-2bc mice, suggesting that mMCP-6 is required for a full-blown AHR. The mMCP-6(-/-)/H-2bc mice had strikingly reduced lung inflammation, IgE responses, and Th2 cell responses upon sensitization and challenge, whereas the mMCP-6(-/-) mice responded similarly to the wild type mice but with a minor decrease in bronchoalveolar lavage eosinophils. These findings suggest that inflammatory Th2 responses are highly dependent on the MHC-haplotype and that they can develop essentially independently of mMCP-6, whereas mMCP-6 plays a key role in the development of AHR.

CD11c+ cells are required for antigen-induced increase of mast cells in the lung.

Patients with allergic asthma have more lung mast cells, which likely worsens the symptoms. In experimental asthma, CD11c(+) cells have to be present during the challenge phase for several features of allergic inflammation to occur. Whether CD11c(+) cells play a role for Ag-induced increases of lung mast cells is unknown. In this study, we used diphtheria toxin treatment of sensitized CD11c-diphtheria toxin receptor transgenic mice to deplete CD11c(+) cells. We demonstrate that recruitment of mast cell progenitors to the lung is substantially reduced when CD11c(+) cells are depleted during the challenge phase. This correlated with an impaired induction of endothelial VCAM-1 and led to a significantly reduced number of mature mast cells 1 wk after challenge. Collectively, these data suggest that Ag challenge stimulates CD11c(+) cells to produce cytokines and/or chemokines required for VCAM-1 upregulation on the lung endothelium, which in turn is crucial for the Ag-induced mast cell progenitor recruitment and the increase in mast cell numbers.

Mouse development is not obviously affected by the absence of dermatan sulfate epimerase 2 in spite of a modified brain dermatan sulfate composition.

Dermatan sulfate epimerase 2 (DS-epi2), together with its homolog DS-epi1, transform glucuronic acid into iduronic acid in DS polysaccharide chains. Iduronic acid gives DS increased chain flexibility and promotes protein binding. DS-epi2 is ubiquitously expressed and is the predominant epimerase in the brain. Here, we report the generation and initial characterization of DS-epi2 null mice. DS-epi2-deficient mice showed no anatomical, histological or morphological abnormalities. The body weights and lengths of mutated and wild-type littermates were indistinguishable. They were fertile and had a normal lifespan. Chondroitin sulfate (CS)/DS isolated from the newborn mutated mouse brains had a 38% reduction in iduronic acid compared with wild-type littermates, and compositional analysis revealed a decrease in 4-O-sulfate and an increase in 6-O-sulfate containing structures. Despite the reduction in iduronic acid, the adult DS-epi2-/- brain showed normal extracellular matrix features by immunohistological stainings. We conclude that DS-epi1 compensates in vivo for the loss of DS-epi2. These results extend previous findings of the functional redundancy of brain extracellular matrix components.

The antisecretory peptide AF-16 may modulate tissue edema but not inflammation in experimental peritonitis induced sepsis.

Sepsis is a life-threatening condition due to a dysregulated immunological response to infection. Apart from source control and broad-spectrum antibiotics, management is based on fluid resuscitation and vasoactive drugs. Fluid resuscitation implicates the risk of volume overload, which in turn is associated with longer stay in intensive care, prolonged use of mechanical ventilation and increased mortality. Antisecretory factor (AF), an endogenous protein, is detectable in most tissues and in plasma. The biologically active site of the protein is located in an 8-peptide sequence, contained in a synthetic 16-peptide fragment, named AF-16. The protein as well as the peptide AF-16 has multiple modulatory effects on abnormal fluid transport and edema formation/resolution as well as in a variety of inflammatory conditions. Apart from its' anti-secretory and anti-inflammatory characteristics, AF is an inhibitor of capillary leakage in intestine. It is not known whether the protein AF or the peptide AF-16 can ameliorate symptoms in sepsis. We hypothesized that AF-16 decreases the degree of hemodynamic instability, the need of fluid resuscitation, vasopressor dose and tissue edema in fecal peritonitis. To test the hypothesis, we induced peritonitis and sepsis by injecting autologous fecal solution into abdominal cavity of anesthetized pigs, and randomized (in a blind manner) the animals to intervention (AF-16, n = 8) or control (saline, n = 8) group. After the onset of hemodynamic instability (defined as mean arterial pressure < 60 mmHg maintained for > 5 minutes), intervention with AF-16 (20 mg/kg (50 mg/ml) in 0.9% saline) intravenously (only the vehicle in the control group) and a protocolized resuscitation was started. We recorded respiratory and hemodynamic parameters hourly for twenty hours or until the animal died and collected post mortem tissue samples at the end of the experiment. No differences between the groups were observed regarding hemodynamics, overall fluid balance, lung mechanics, gas exchange or histology. However, liver wet-to-dry ratio remained lower in AF-16 treated animals as compared to controls, 3.1 ± 0.4, (2.7-3.5, 95% CI, n = 8) vs 4.0 ± 0.6 (3.4-4.5, 95% CI, n = 8), p = 0.006, respectively. Bearing in mind the limited sample size, this experimental pilot study suggests that AF-16 may inhibit sepsis induced liver edema in peritonitis-sepsis.

Does the antisecretory peptide AF-16 reduce lung oedema in experimental ARDS?

Background: Acute respiratory distress syndrome (ARDS) is an acute inflammatory condition with pulmonary capillary leakage and lung oedema formation. There is currently no pharmacologic treatment for the condition. The antisecretory peptide AF-16 reduces oedema in experimental traumatic brain injury. In this study, we tested AF-16 in an experimental porcine model of ARDS.Methods: Under surgical anaesthesia 12 piglets were subjected to lung lavage followed by 2 hours of injurious ventilation. Every hour for 4 hours, measurements of extravascular lung water (EVLW), mechanics of the respiratory system, and hemodynamics were obtained.Results: There was a statistically significant (p = 0.006, two-way ANOVA) reduction of EVLW in the AF-16 group compared with controls. However, this was not mirrored in any improvement in the wet-to-dry ratio of lung tissue samples, histology, inflammatory markers, lung mechanics, or gas exchange.Conclusions: This pilot study suggests that AF-16 might improve oedema resolution as indicated by a reduction in EVLW in experimental ARDS.

Mycotic proventriculitis in gray partridges (Perdix perdix) on two game bird farms.

Proventriculitis and chronic respiratory disease were diagnosed in two flocks of gray partridges (Perdix perdix) on unrelated Swedish game bird farms. Affected birds showed loss of condition, respiratory signs, and flock mortality rates of 50 and 98%, respectively. The proventricular lesions were associated closely with fungal organisms that were microscopically indistinguishable from the ascomycetous yeast Macrorhabdus ornithogaster (former provisional name "megabacterium"). At necropsy, the proventriculi were swollen and hyperemic, and viscous mucus adhered to the mucosa. Proventricular hemorrhages were commonly detected, and one bird had proventricular rupture and peritonitis. Microscopically, mild to severe subacute to chronic lymphoplasmacytic proventriculitis, microabscesses, necrosis, epithelial metaplasia, disrupted koilin, ulcers, and hemorrhages were observed. Transmission electron microscopy of the proventricular microorganisms revealed a membrane-bound nucleus, vacuoles, ribosomes, microtubules in parallel arrays, and a two-layered cell wall but no mitochondria. Scanning electron microscopy of the proventricular epithelium demonstrated masses of organisms with occasional constrictions in parallel arrangement. Many of the birds also suffered from concurrent respiratory bacterial infections and/or gastrointestinal candidiasis. The clinical course and gross and microscopic proventricular lesions were similar to those described in psittacine and passerine pet birds colonized by M. ornithogaster-like microorganisms but differed from published case reports and experimental infections of chickens in which the clinical signs and lesions have been considerably milder. The findings presented in this paper suggest that mycotic proventriculitis, presumably associated with M. ornithogaster, may be a serious but possibly opportunistic, although unusual, disease problem in gray partridges on game farms.

An activating mutation in the PDGF receptor-beta causes abnormal morphology in the mouse placenta.

An oncogenic D842V mutation in the platelet-derived growth factor (PDGF) alpha-receptor (Pdgfra) has recently been described in patients with gastrointestinal stromal tumors. In order to test if the same mutation would confer oncogenic properties to the homologous PDGF beta-receptor (Pdgfrb), the corresponding aspartic acid residue at position 849 of Pdgfrb was changed into valine (D849V) using a knock-in strategy. This mutation turned out to be dominantly lethal and caused death even in chimeras (from 345 transferred chimeric blastocysts, no living coat chimeras were detected). Experiments employing mouse embryonic fibroblasts (MEFs) indicated hyperactivity of the mutant receptor. The mutant receptor was phosphorylated in a ligand-independent manner and, in contrast to wild-type MEFs, mutant cells proliferated even in the absence of ligand. Knockout experiments have previously indicated a role for Pdgfrb in placental development. We therefore analyzed wild-type and Pdgfrb D849V chimeric placentas from different gestational stages. No differences were detected at embryonic days 11.5 and 13.5 (n=4). At embryonic day 17.5, however, chimeric placentas (n=3/4) displayed abnormalities both in the labyrinth and in the chorionic plate. The changes included hyper-proliferation of alpha-smooth muscle actin and platelet/endothelial cell adhesion molecule-1 positive cells in the labyrinth and cells in the chorionic plate. In addition, the fetal blood vessel compartment of the labyrinth was completely disorganized.

Epidemiologic investigation of an outbreak of goose parvovirus infection in Sweden.

An outbreak of goose parvovirus (GPV) infection on a Swedish goose farm in the spring of 2004 increased the mortality rates from 2% in the early unaffected hatches to 90% and 99% respectively in the two hatches following virus introduction and 40% in goslings hatched later in the same breeding season. In this paper we describe the clinical observations, diagnostic procedures, and epidemiologic investigation carried out to elucidate the source of the infection. The diagnosis was confirmed by serology, virus isolation, and sequence analysis of a 493-bp-long fragment of the VP1 gene. Phylogenetically the causative virus was closely related to pathogenic GPV strains isolated in 2003 and 2004 from Poland and the United Kingdom, respectively. The Swedish isolate exhibited less homology with pathogenic strains from Hungary and Asia and with attenuated vaccine strains. The epidemiologic investigation showed that the virus was first introduced to a contract farm (farm A) and then was transferred with newly hatched goslings to the farm that had submitted the birds for necropsy (index farm). The exact time and source of the virus introduction to farm A could not be determined with absolute certainty. Possible sources of the infection included backyard goose eggs that had been delivered to farm A for subcontract incubation and hatching, wild geese that frequented the flock of breeding geese on pasture on farm A, and a clutch of Canada goose eggs (Branta canadensis) that had been produced by wild geese and was hatched in the same machine as the eggs produced by farm A.

Occurrence of Helicobacter species other than H. hepaticus in laboratory mice and rats in Sweden.

The aim of this study was to determine which Helicobacter species other than H. hepaticus colonize laboratory mice and rats in Sweden. We analyzed 63 intestinal samples from mice and 42 intestinal samples from rats by partial 16S rDNA sequence analysis. Previously these samples had been found positive for Helicobacter species but negative for H. hepaticus in a polymerase chain reaction screening assay at the National Veterinary Institute in Sweden. H. ganmani, H. typhlonius, H. rodentium, an uncharacterized Helicobacter species ('hamster B'), and a possibly novel species were detected in mice. The possibly novel species was most closely related to H. apodemus strain YMRC 000216 (98.3% sequence similarity). Two different Helicobacter species were detected in rats: H. ganmani and H. rodentium. H. ganmani colonization of rats has not previously been reported.

Feasibility of (68)Ga-labeled Siglec-9 peptide for the imaging of acute lung inflammation: a pilot study in a porcine model of acute respiratory distress syndrome.

There is an unmet need for noninvasive, specific and quantitative imaging of inherent inflammatory activity. Vascular adhesion protein-1 (VAP-1) translocates to the luminal surface of endothelial cells upon inflammatory challenge. We hypothesized that in a porcine model of acute respiratory distress syndrome (ARDS), positron emission tomography (PET) with sialic acid-binding immunoglobulin-like lectin 9 (Siglec-9) based imaging agent targeting VAP-1 would allow quantification of regional pulmonary inflammation. ARDS was induced by lung lavages and injurious mechanical ventilation. Hemodynamics, respiratory system compliance (Crs) and blood gases were monitored. Dynamic examination using [(15)O]water PET-CT (10 min) was followed by dynamic (90 min) and whole-body examination using VAP-1 targeting (68)Ga-labeled 1,4,7,10-tetraaza cyclododecane-1,4,7-tris-acetic acid-10-ethylene glycol-conjugated Siglec-9 motif peptide ([(68)Ga]Ga-DOTA-Siglec-9). The animals received an anti-VAP-1 antibody for post-mortem immunohistochemistry assay of VAP-1 receptors. Tissue samples were collected post-mortem for the radioactivity uptake, histology and immunohistochemistry assessment. Marked reduction of oxygenation and Crs, and higher degree of inflammation were observed in ARDS animals. [(68)Ga]Ga-DOTA-Siglec-9 PET showed significant uptake in lungs, kidneys and urinary bladder. Normalization of the net uptake rate (Ki) for the tissue perfusion resulted in 4-fold higher uptake rate of [(68)Ga]Ga-DOTA-Siglec-9 in the ARDS lungs. Immunohistochemistry showed positive VAP-1 signal in the injured lungs. Detection of pulmonary inflammation associated with a porcine model of ARDS was possible with [(68)Ga]Ga-DOTA-Siglec-9 PET when using kinetic modeling and normalization for tissue perfusion.

Dermatan Sulfate-Free Mice Display Embryological Defects and Are Neonatal Lethal Despite Normal Lymphoid and Non-Lymphoid Organogenesis.

The epimerization of glucuronic acid into iduronic acid adds structural variability to chondroitin/dermatan sulfate polysaccharides. Iduronic acid-containing domains play essential roles in processes such as coagulation, chemokine and morphogen modulation, collagen maturation, and neurite sprouting. Therefore, we generated and characterized, for the first time, mice deficient in dermatan sulfate epimerase 1 and 2, two enzymes uniquely involved in dermatan sulfate biosynthesis. The resulting mice, termed DKO mice, were completely devoid of iduronic acid, and the resulting chondroitin sulfate chains were structurally different from the wild type chains, from which a different protein binding specificity can be expected. As a consequence, a vast majority of the DKO mice died perinatally, with greatly variable phenotypes at birth or late embryological stages such as umbilical hernia, exencephaly and a kinked tail. However, a minority of embryos were histologically unaffected, with apparently normal lung and bone/cartilage features. Interestingly, the binding of the chemokine CXCL13, an important modulator of lymphoid organogenesis, to mouse DKO embryonic fibroblasts was impaired. Nevertheless, the development of the secondary lymphoid organs, including the lymph nodes and spleen, was normal. Altogether, our results indicate an important role of dermatan sulfate in embryological development and perinatal survival.

Five month persistence of Helicobacter pylori infection in guinea pigs.

Seven Dunkin-Hartley guinea pigs were infected with the Sydney strain of H. pylori (SS1). Gastric histopathology was evaluated and serum antibody response to H. pylori cell-surface proteins was analysed by enzyme immunoassay (EIA) and immunoblot. Tissue and faecal samples from five control animals were analysed for the presence of naturally occurring Helicobacter spp. infection by culture and Helicobacter genus-specific PCR. The H. pylori infection persisted for 5 months, in most animals accompanied by a histologically severe antral gastritis, exhibiting focal degeneration and necrosis of gastric crypt epithelium. Increased numbers of mitotic figures were observed in the gastric epithelium, indicating a regenerative process. Infected animals displayed specific antibodies towards H. pylori cell-surface proteins in immunoblot, whereas EIA was of dubious value creating false-positive results. Serum complement C3 and cholesterol levels appeared to be elevated in infected animals. Helicobacter spp. infection was not detected in the control animals. The persistent infection, accompanied by severe gastritis and a prominent serum antibody response, and the apparent absence of a natural Helicobacter spp. infection makes the guinea pig model useful in H. pylori research.

Development and use of a simple polymerase chain reaction assay to screen for Helicobacter spp. and H. hepaticus in intestinal and fecal samples from laboratory mice.

A simple and sensitive duplex polymerase chain reaction (PCR) assay was developed for use in detection of Helicobacter species and H. hepaticus in laboratory mice. Bacteria were extracted and concentrated from fecal pellets and intestinal segments by use of buoyant density centrifugation. To improve quality assurance, an internal control (mimic) for detection of false-negative reactions was included. In addition, cartridges (Capillette) pre-filled with PCR reagents, were used to minimize the hands-on time required, thus reducing the risk of contamination with previously amplified material. Laboratory mice from Swedish animal houses sent to the National Veterinary Institute for health monitoring were found to have high prevalence of H. hepaticus.

Cross-protection of chicken immunoglobulin Y antibodies against H5N1 and H1N1 viruses passively administered in mice.

Influenza viruses remain a major threat to global health due to their ability to undergo change through antigenic drift and antigenic shift. We postulated that avian IgY antibodies represent a low-cost, effective, and well-tolerated approach that can easily be scaled up to produce enormous quantities of protective antibodies. These IgY antibodies can be administered passively in humans (orally and intranasally) and can be used quickly and safely to help in the fight against an influenza pandemic. In this study, we raised IgY antibodies against H1N1, H3N2, and H5N1 influenza viruses. We demonstrated that, using whole inactivated viruses alone and in combination to immunize hens, we were able to induce a high level of anti-influenza virus IgY in the sera and eggs, which lasted for at least 2 months after two immunizations. Furthermore, we found that by use of in vitro assays to test for the ability of IgY to inhibit hemagglutination (HI test) and virus infectivity (serum neutralization test), IgYs inhibited the homologous as well as in some cases heterologous clades and strains of viruses. Using an in vivo mouse model system, we found that, when administered intranasally 1 h prior to infection, IgY to H5N1 protected 100% of the mice against lethal challenge with H5N1. Of particular interest was the finding that IgY to H5N1 cross-protected against A/Puerto Rico/8/34 (H1N1) both in vitro and in vivo. Based on our results, we conclude that anti-influenza virus IgY can be used to help prevent influenza virus infection.

Fatal acute intestinal pseudoobstruction in mice.

Here we describe the epizootiology and pathology of spontaneous, fatal acute intestinal pseudoobstruction that occurred in a mouse colony of 1000 breeding pairs, mainly of the C57Bl/6 strain and free from known pathogenic agents. Most of the mice affected were dams in the second week of lactation. At necropsy, segments of the small intestines were distended with fluid contents. Widespread apoptosis of the villus epithelium of the small intestine and superficial epithelial cells of the large intestine, associated with strong expression of active caspase 3, was a distinctive feature. Necrotic enterocytes, mucosal erosions, and acute mucosal inflammation were prominent in some mice, and morphologic signs of toxemia were generally present. No light microscopic neuronal changes were apparent in the gut, and no etiologic agents were identified. These results indicate that sudden activation of apoptosis in the trophically stimulated gut epithelium during peak lactation was instrumental for the fatal outcome of the condition, but the primary cause of the motility dysfunction of the bowel was not established.

Diabetes and myocarditis in voles and lemmings at cyclic peak densities--induced by Ljungan virus?

Although it is well-documented from theoretical studies that pathogens have the capacity to generate cycles, the occurrence and role of pathogens and disease have been poorly empirically studied in cyclic voles and lemmings. In screening for the occurrence of disease in cyclic vole and lemming populations, we found that a high proportion of live-trapped Clethrionomys glareolus, C. rufocanus, Microtus agrestis and Lemmus lemmus at high collective peak density, shortly before the decline, suffered from diabetes or myocarditis in northern Scandinavia. A high frequency of animals had abnormal blood glucose (BG) levels at the time of trapping (5-33%). In contrast, C. rufocanus individuals tested at a much lower overall density, and at an earlier stage relative to the decline in the following cycle, showed normal BG concentrations. However, a high proportion (43%) of a sample of these individuals kept in captivity developed clinical diabetes within five weeks, as determined by BG levels and a glucose tolerance test performed at that later time. A new picornavirus isolated from the rodents, Ljungan virus (LV), was assumed to cause the diseases, as LV-induced diabetes and myocarditis, as well as encephalitis and fetal deaths, were observed in laboratory mice. We hypothesize that LV infection significantly affects morbidity and mortality rates in the wild, either directly or indirectly, by predisposing the rodents to predation, and is at least involved in causing the regular, rapid population declines of these cyclic voles and lemmings. Increased stress at peak densities is thought to be an important trigger for the development of disease, as the occurrence of disease in laboratory mice has been found to be triggered by introducing stress to LV-infected animals.

Intrauterine death, fetal malformation, and delayed pregnancy in Ljungan virus-infected mice.

BACKGROUND: A picornavirus (Ljunganvirus [LV]) has recently been associated with disease during pregnancy in its natural rodent reservoir and in humans. A study of laboratory mice infected under controlled conditions was therefore undertaken. METHODS: CD-1 female mice were infected gestational day two and subjected to varying regimes of stress. RESULTS: LV infection in combination with stress resulted in uterine resorptions, malformations, and neonatal death. A short delay in time to first pregnancy and births was observed in pairs infected in utero. CONCLUSIONS: LV is found in different species of native animals in both Europe and the United States and human epidemiological evidence connects LV and human reproduction, while the observations here indicate that LV is responsible for reproductive problems in a laboratory mouse model. The current findings suggest that the hypothesis that LV also causes disease in pregnant women and their offspring deserves further study.