Mutation of the fiber shaft heparan sulphate binding site of a 5/3 chimeric adenovirus reduces liver tropism

Natural tropism to the liver is a major obstacle in systemic delivery of adenoviruses in cancer gene therapy. Adenovirus binding to soluble coagulation factors and to cellular heparan sulphate proteoglycans via the fiber shaft KKTK domain are suggested to cause liver tropism. Serotype 5 adenovirus constructs with mutated KKTK regions exhibit liver detargeting, but they also transduce tumors less efficiently, possibly due to altered fiber conformation. We constructed Ad5/3lucS*, a 5/3 chimeric adenovirus with a mutated KKTK region. The fiber knob swap was hypothesized to facilitate tumor transduction. This construct was studied with or without additional coagulation factor ablation. Ad5/3lucS* exhibited significantly reduced transduction of human hepatic cells in vitro and mouse livers in vivo. Combination of coagulation factor ablation by warfarinization to Ad5/3lucS* seemed to further enhance liver detargeting. Cancer cell transduction by Ad5/3lucS* was retained in vitro. In vivo, viral particle accumulation in M4A4-LM3 xenograft tumors was comparable to controls, but Ad5/3lucS* transgene expression was nearly abolished. Coagulation factor ablation did not affect tumor transduction. These studies set the stage for further investigations into the effects of the KKTK mutation and coagulation factor ablation in the context of 5/3 serotype chimerism. Of note, the putative disconnect between tumor transduction and transgene expression could prove useful in further understanding of adenovirus biology.

Immune response is an important aspect of the antitumor effect produced by a CD40L-encoding oncolytic adenovirus

Oncolytic adenovirus is an attractive platform for immunotherapy because virus replication is highly immunogenic and not subject to tolerance. Although oncolysis releases tumor epitopes and provides costimulatory danger signals, arming the virus with immunostimulatory molecules can further improve efficacy. CD40 ligand (CD40L, CD154) induces apoptosis of tumor cells and triggers several immune mechanisms, including a T-helper type 1 (T(H)1) response, which leads to activation of cytotoxic T cells and reduction of immunosuppression. In this study, we constructed a novel oncolytic adenovirus, Ad5/3-hTERT-E1A-hCD40L, which features a chimeric Ad5/3 capsid for enhanced tumor transduction, a human telomerase reverse transcriptase (hTERT) promoter for tumor selectivity, and human CD40L for increased efficacy. Ad5/3-hTERT-E1A-hCD40L significantly inhibited tumor growth in vivo via oncolytic and apoptotic effects, and (Ad5/3-hTERT-E1A-hCD40L)-mediated oncolysis resulted in enhanced calreticulin exposure and HMGB1 and ATP release, which were suggestive of immunogenicity. In two syngeneic mouse models, murine CD40L induced recruitment and activation of antigen-presenting cells, leading to increased interleukin-12 production in splenocytes. This effect was associated with induction of the T(H)1 cytokines IFN-γ, RANTES, and TNF-α. Tumors treated with Ad5/3-CMV-mCD40L also displayed an enhanced presence of macrophages and cytotoxic CD8(+) T cells but not B cells. Together, our findings show that adenoviruses coding for CD40L mediate multiple antitumor effects including oncolysis, apoptosis, induction of T-cell responses, and upregulation of T(H)1 cytokines.

Macrophage metalloelastase (MME) as adjuvant for intra-tumoral injection of oncolytic adenovirus and its influence on metastases development

Oncolytic adenoviruses are a promising treatment alternative for many advanced cancers, including colorectal cancer. However, clinical trials have demonstrated that single-agent therapy in advanced tumor masses is rarely curative. Poor spreading of the virus through tumor tissue is one of the major issues limiting efficacy. As oncolytic viruses kill preferentially cancer cells, high extracellular matrix (ECM) content constitutes potential barriers for viral penetration within tumors. In this study, the ECM-degrading proteases relaxin, hyaluronidase, elastase and macrophage metalloelastase (MME) were tested for their antitumor efficacy alone and in combination with oncolytic adenovirus. MME improved the overall antitumor efficacy of oncolytic adenovirus in subcutaneous HCT116 xenografts. In a liver metastatic colorectal cancer model, intra-tumoral treatment of primary tumors from HT29 cells with MME monotherapy or with oncolytic adenovirus inhibited tumor growth. Combination therapy showed no increased mortality in comparison with either monotherapy alone. Contradictory results of effects of MME on tumorigenesis and metastasis formation have been reported in the literature. This study demonstrates for the first time in a metastatic animal model that MME, as a monotherapy or in combination with oncolytic virus, does not increase tumor invasiveness. Co-administration of MME and oncolytic adenovirus may be a suitable approach for further optimization aiming at clinical applications for metastatic colorectal cancer.

Optimized mouse model for the imaging of tumor metastasis upon experimental therapy

Development of new cancer treatments focuses increasingly on the relation of cancer tissue with its microenvironment. A major obstacle for the development of new anti-cancer therapies has been the lack of relevant animal models that would reproduce all the events involved in disease progression from the early-stage primary tumor until the development of mature metastatic tissue. To this end, we have developed a readily imageable mouse model of colorectal cancer featuring highly reproducible formation of spontaneous liver metastases derived from intrasplenic primary tumors. We optimized several experimental variables, and found that the correct choice of cell line and the genetic background, as well as the age of the recipient mice, were critical for establishing a useful model system. Among a panel of colorectal cancer cell lines tested, the epithelial carcinoma HT29 line was found to be the most suitable in terms of producing homogeneous tumor growth and metastases. In our hands, SCID mice at the age of 125 days or older were the most suitable in supporting consistent HT29 tumor growth after splenic implantation followed by reproducible metastasis to the liver. A magnetic resonance imaging (MRI) protocol was optimized for use with this mouse model, and demonstrated to be a powerful method for analyzing the antitumor effects of an experimental therapy. Specifically, we used this system to with success to verify by MRI monitoring the efficacy of an intrasplenically administered oncolytic adenovirus therapy in reducing visceral tumor load and development of liver metastases. In summary, we have developed a highly optimized mouse model for liver metastasis of colorectal cancer, which allows detection of the tumor load at the whole body level and enables an accurate timing of therapeutic interventions to target different stages of cancer progression and metastatic development.

Induction of interferon pathways mediates in vivo resistance to oncolytic adenovirus

Oncolytic adenoviruses are an emerging experimental approach for treatment of tumors refractory to available modalities. Although preclinical results have been promising, and clinical safety has been excellent, it is also apparent that tumors can become virus resistant. The resistance mechanisms acquired by advanced tumors against conventional therapies are increasingly well understood, which has allowed development of countermeasures. To study this in the context of oncolytic adenovirus, we developed two in vivo models of acquired resistance, where initially sensitive tumors eventually gain resistance and relapse. These models were used to investigate the phenomenon on RNA and protein levels using two types of analysis of microarray data, quantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry. Interferon (IFN) signaling pathways were found upregulated and Myxovirus resistance protein A (MxA) expression was identified as a marker correlating with resistance, while transplantation experiments suggested a role for tumor stroma in maintaining resistance. Furthermore, pathway analysis suggested potential therapeutic targets in oncolytic adenovirus-resistant cells. Improved understanding of the antiviral phenotype causing tumor recurrence is of key importance in order to improve treatment of advanced tumors with oncolytic adenoviruses. Given the similarities between mechanisms of action, this finding might be relevant for other oncolytic viruses as well.

Integrin targeted oncolytic adenoviruses Ad5-D24-RGD and Ad5-RGD-D24-GMCSF for treatment of patients with advanced chemotherapy refractory solid tumors

The safety of oncolytic viruses for treatment of cancer has been shown in clinical trials while antitumor efficacy has often remained modest. As expression of the coxsackie-adenovirus receptor may be variable in advanced tumors, we developed Ad5-D24-RGD, a p16/Rb pathway selective oncolytic adenovirus featuring RGD-4C modification of the fiber. This allows viral entry through alpha-v-beta integrins frequently highly expressed in advanced tumors. Advanced tumors are often immunosuppressive which results in lack of tumor eradication despite abnormal epitopes being present. Granulocyte-macrophage colony stimulating factor (GMCSF) is a potent activator of immune system with established antitumor properties. To stimulate antitumor immunity and break tumor associated immunotolerance, we constructed Ad5-RGD-D24-GMCSF, featuring GMCSF controlled by the adenoviral E3 promoter. Preliminary safety of Ad5-D24-RGD and Ad5-RGD-D24-GMCSF for treatment of human cancer was established. Treatments with Ad5-D24-RGD (N = 9) and Ad5-RGD-D24-GMCSF (N = 7) were well tolerated. Typical side effects were grade 1-2 fatigue, fever and injection site pain. 77% (10/13) of evaluable patients showed virus in circulation for at least 2 weeks. In 3 out of 6 evaluable patients, disease previously progressing stabilized after a single treatment with Ad5-RGD-D24-GMCSF. In addition, 2/3 patients had stabilization or reduction in tumor marker levels. All patients treated with Ad5-D24-RGD showed disease progression in radiological analysis, although 3/6 had temporary reduction or stabilization of marker levels. Induction of tumor and adenovirus specific immunity was demonstrated with ELISPOT in Ad5-RGD-D24-GMCSF treated patients. RGD modified oncolytic adenoviruses with or without GMCSF seem safe for further clinical development.

Immunological effects of low-dose cyclophosphamide in cancer patients treated with oncolytic adenovirus

Patients with advanced solid tumors refractory to and progressing after conventional therapies were treated with three different regimens of low-dose cyclophosphamide (CP) in combination with oncolytic adenovirus. CP was given with oral metronomic dosing (50 mg/day, N = 21), intravenously (single 1,000 mg dose, N = 7) or both (N = 7). Virus was injected intratumorally. Controls (N = 8) received virus without CP. Treatments were well tolerated and safe regardless of schedule. Antibody formation and virus replication were not affected by CP. Metronomic CP (oral and oral + intravenous schedules) decreased regulatory T cells (T(regs)) without compromising induction of antitumor or antiviral T-cell responses. Oncolytic adenovirus given together with metronomic CP increased cytotoxic T cells and induced Th1 type immunity on a systemic level in most patients. All CP regimens resulted in higher rates of disease control than virus only (all P < 0.0001) and the best progression-free (PFS) and overall survival (OS) was seen in the oral + intravenous group. One year PFS and OS were 53 and 42% (P = 0.0016 and P < 0.02 versus virus only), respectively, both which are unusually high for chemotherapy refractory patients. We conclude that low-dose CP results in immunological effects appealing for oncolytic virotherapy. While these first-in-human data suggest good safety, intriguing efficacy and extended survival, the results should be confirmed in a randomized trial.

Human adenovirus replication in immunocompetent Syrian hamsters can be attenuated with chlorpromazine or cidofovir

BACKGROUND

Adenoviruses can cause severe toxicity in children and in immunocompromised adults, and therefore a means to abrogate replication would be useful. With regard to cancer treatment, replication competent oncolytic adenoviruses have been safe in humans, although their efficacy has been variable. Therefore, more effective agents are now entering clinical testing and, consequently, replication-associated side effects remain a concern. Preclinical analysis of replication related toxicity has been hampered by a lack of permissive models. Therefore, it has been difficult to study modulation of human adenovirus replication in immune competent animals.

METHODS

We investigated four different hamster carcinoma cell lines for transduction and cell killing potency in vitro and in vivo. Gene transfer was assessed using replication-deficient adenoviruses expressing luciferase. Cell killing was studied in vitro and in vivo using an oncolytic adenovirus that kills tumor cells by viral replication. After the most promising animal model had been selected, abrogation of virus replication was assessed in vitro and in vivo using a TCID(50) assay.

RESULTS

The results obtained suggest wild-type adenovirus replication in all four tested Syrian hamster cell lines and also normal organs. Virus replication could be abrogated with chlorpromazine, cidofovir and cytosine arabinoside, and the effect occurred subsequent to nuclear delivery of the viral genome. Attenuation of virus replication also was seen in vivo both in tumors and the liver.

CONCLUSIONS

Syrian hamsters may comprise a valuable immune competent model for evaluating anti-adenoviral drugs. Furthermore, chlorpromazine or cidofovir might be useful in case of adenovirus replication-associated symptoms in humans.

In vivo and in vitro distribution of type 5 and fiber-modified oncolytic adenoviruses in human blood compartments

BACKGROUND

Successful tumor targeting of systemically administered oncolytic adenoviruses may be hindered by interactions with blood components.

MATERIALS AND METHODS

Blood distribution of oncolytic adenoviruses featuring type 5 adenovirus fiber, 5/3 capsid chimerism, or RGD-4C in the fiber knob was investigated in vitro and in patients with refractory solid tumors.

RESULTS

Virus titers and prevalence in serum of patients increased over the first post-treatment week, suggesting replication. Detection of low virus loads was more sensitive in blood clots than in serum, although viral levels > 500 viral particles/mL did not differ significantly between both sample types. While adenovirus bound to erythrocytes, platelets, granulocytes, and peripheral blood mononuclear cells in vitro, the virus was mainly detectable in erythrocytes and granulocytes in cancer patients. Taken together with a temporary post-treatment decrease in thrombocyte counts, platelet activation by adenovirus and subsequent clearance seem likely to occur in humans. Fiber modifications had limited observed effect on virus distribution in blood cell compartments. Neutrophils, monocytes and cytotoxic T lymphocytes were the major leukocyte subpopulations interacting with adenoviruses.

CONCLUSION

Serum and blood clots are relevant to estimate oncolytic adenovirus replication. Insight into viral interactions with blood cells may contribute to the development of new strategies for tumor delivery.

Safety of glucocorticoids in cancer patients treated with oncolytic adenoviruses

Oncolytic adenoviruses are an emerging treatment option for advanced and refractory cancer. Such patients are often treated with corticosteroids to ameliorate tumor associated symptoms. Thus, it is important to evaluate whether safety is affected by immunosuppression possibly induced by corticosteroids. Concurrent low-dose cyclophosphamide, appealing for its immunomodulatory effects, could also impact safety. In a retrospective case-control study, we evaluated the effect of systemic corticosteroid use in cancer patients receiving oncolytic virotherapy. Four treatment groups were identified: (1) oncolytic adenovirus with oral glucocorticoids, (2) virus alone, (3) virus with glucocorticoids and cyclophosphamide and (4) virus with cyclophosphamide. Adverse events, neutralizing antibody titers, viral DNA in circulation and tumor responses were evaluated. The most common adverse effects were grade 1-2 fatigue, nausea, fever and abdominal pain. Common asymptomatic findings included self-limiting grade 1-3 hyponatremia and aspartate aminotransferase increase. Safety was good and no significant differences were observed between the groups. All patients had an increase in neutralizing antibody titers post-treatment, and no trends for differences between groups were observed. There were fewer post-treatment virus genomes circulating in patients receiving glucocorticoids when compared to their control groups. Overall, glucocorticoid use in cancer patients receiving oncolytic adenovirus, with or without low-dose cyclophosphamide, seems safe.

Defects in innate immunity render breast cancer initiating cells permissive to oncolytic adenovirus

Background

Cancer stem cells/initiating cells (CSC/CIC), are thought to exist as a small population in malignant tissues. They are resistant to conventional cancer treatments and possibly underlie post-treatment relapse. The CIC population can be targeted with capsid modified oncolytic adenoviruses.

Methodology/Principal Findings

We studied the mechanisms of innate immunity to oncolytic adenovirus Ad5/3-Delta24 in conventional treatment resistant non-CIC breast cancer cells, breast cancer CD44⁺/CD24^−/low CIC population and normal breast tissue CD44⁺/CD24^−/low stem cells. We compared virus recognition by pattern recognition receptors for adenovirus, Toll-like receptors (TLR) 2 and 9 and virus induced type I interferon (IFN) response regulation in these cell types. We show TLR mediated virus recognition in these non-immune cell types. Normal tissue stem cells have intact type I IFN signaling. Furthermore, TLR9 and TLR2 reside constantly in recognition sites, implying constant activation. In contrast, breast cancer CD44⁺/CD24^−/low CIC have dysregulated innate immune responses featuring dysfunctional virus recognition caused by impaired trafficking of TLR9 and cofactor MyD88 and the absence of TLR2, having a deleterious impact on TLR pattern recognition receptor signaling. Furthermore, the CIC have increased inhibitory signaling via the suppressor of cytokine signaling/Tyro3/Axl/Mer receptor tyrosine kinase (SOCS/TAM) pathway. These defects in contribute to dysfunctional induction of type I IFN response in CIC and therefore permissivity to oncolytic adenovirus.

Conclusions/Significance

CICs may underlie the incurable nature of relapsed or metastatic cancers and are therefore an important target regarding diagnostic and prognostic aspects as well as treatment of the disease. This study addresses the mechanisms of innate infection immunity in stem cells deepening the understanding of stem cell biology and may benefit not only virotherapy but also immunotherapy in general.

Adenoviruses with an αvβ integrin targeting moiety in the fiber shaft or the HI-loop increase tumor specificity without compromising antitumor efficacy in magnetic resonance imaging of colorectal cancer metastases

Background

Colorectal cancer is often a deadly disease and cannot be cured at metastatic stage. Oncolytic adenoviruses have been considered as a new therapeutic option for treatment of refractory disseminated cancers, including colorectal cancer. The safety data has been excellent but tumor transduction and antitumor efficacy especially in systemic administration needs to be improved.

Methods

Here, the utility of αvβ integrin targeting moiety Arg-Gly-Asp (RGD) in the Lys-Lys-Thr-Lys (KKTK) domain of the fiber shaft or in the HI-loop of adenovirus serotype 5 for increased tumor targeting and antitumor efficacy was evaluated. To this end, novel spleen-to-liver metastatic colorectal cancer mouse model was used and the antitumor efficacy was evaluated with magnetic resonance imaging (MRI).

Results

Both modifications (RGD in the HI-loop or in the fiber shaft) increased gene transfer efficacy in colorectal cancer cell lines and improved tumor-to-normal ratio in systemic administration of the vector.

Conclusions

Antitumor potency was not compromised with RGD modified viruses suggesting increased safety profile and tumor specificity.

Oncolytic adenovirus coding for granulocyte macrophage colony-stimulating factor induces antitumoral immunity in cancer patients

Granulocyte macrophage colony-stimulating factor (GMCSF) can mediate antitumor effects by recruiting natural killer cells and by induction of tumor-specific cytotoxic T-cells through antigen-presenting cells. Oncolytic tumor cell-killing can produce a potent costimulatory danger signal and release of tumor epitopes for antigen-presenting cell sampling. Therefore, an oncolytic adenovirus coding for GMCSF was engineered and shown to induce tumor-specific immunity in an immunocompetent syngeneic hamster model. Subsequently, 20 patients with advanced solid tumors refractory to standard therapies were treated with Ad5-D24-GMCSF. Of the 16 radiologically evaluable patients, 2 had complete responses, 1 had a minor response, and 5 had disease stabilization. Responses were frequently seen in injected and noninjected tumors. Treatment was well tolerated and resulted in the induction of both tumor-specific and virus-specific immunity as measured by ELISPOT and pentamer analysis. This is the first time that oncolytic virus-mediated antitumor immunity has been shown in humans. Ad5-D24-GMCSF is promising for further clinical testing.

Prolonged systemic circulation of chimeric oncolytic adenovirus Ad5/3-Cox2L-D24 in patients with metastatic and refractory solid tumors

Eighteen patients with refractory and progressive solid tumors were treated with a single round of triple modified oncolytic adenovirus (Ad5/3-Cox2L-D24). Ad5/3-Cox2L-D24 is the first non-Coxsackie-adenovirus receptor-binding oncolytic adenovirus used in humans. Grades 1-2 flu-like symptoms, fever, and fatigue were seen in most patients, whereas transaminitis or thrombocytopenia were seen in some. Non-hematological grades 3-5 side effects were seen in one patient with grade 3 ileus. Treatment resulted in high neutralizing antibody titers within 3 weeks. Virus appeared in serum 2-4 days after treatment in 83% of patients and persisted for up to 5 weeks. One out of five radiologically evaluable patients had partial response (PR), one had minor response (MR), and three had progressive disease (PD). Two patients scored as PD had a decrease in tumor density. Tumor reductions not measurable with Response Evaluation Criteria In Solid Tumors (RECIST) were seen in a further four patients. PR, MR, stable disease, and PD were seen in 12, 23.5, 35, and 29.5% of tumor markers analyzed, respectively (N=17). Ad5/3-Cox2L-D24 appears safe for treatment of cancer in humans and extended virus circulation results from a single treatment. Objective evidence of anti-tumor activity was seen in 11/18 (61%) of patients. Clinical trials are needed to extend these findings.

Systemic adenoviral gene delivery to orthotopic murine breast tumors with ablation of coagulation factors, thrombocytes and Kupffer cells

BACKGROUND

Rapid clearance of adenoviruses from blood by macrophage lineage cells of the liver and spleen, and binding to platelets, hinder their successful systemic use for cancer gene therapy. Vitamin K dependent coagulation factors are important mediators for the adenovirus liver tropism. Here we aim to determine the effects of coagulation factor, thrombocyte and liver macrophage (Kupffer cell) ablation on biodistribution of serotype 5 adenoviruses in mice with orthotopic breast tumors.

METHODS

Prior to intravenous injection of adenoviruses, mice bearing orthotopic breast tumors were pretreated with warfarin to inhibit vitamin K dependent coagulation factor synthesis, an anti-platelet antibody causing thrombocytopenia or an inhibitor of the Kupffer cell scavenger receptor or their combination. Virus availability in blood after injection was determined from blood samples and transgene expression in tissues analyzed 72 hours afterwards with In Vivo Imaging and luciferase assays.

RESULTS

Warfarin pretreatment reduced gene delivery to liver, spleen and lung. Kupffer cell ablation increased persistence of adenoviruses in blood but didn't affect biodistribution significantly. Depletion of Kupffer cells combined with thrombocytopenia doubled the systemic gene delivery of 5/3 chimeric adenovirus to tumors (p < 0.05). Triple ablation of platelets, Kupffer cells and coagulation factors increased the tumor to liver ratio of systemic adenovirus gene delivery by 81% (p < 0.05).

CONCLUSIONS

Depletion of coagulation factors can reduce transduction of liver, spleen and lung. Kupffer cell depletion is the most feasible method of increasing amount adenovirus in systemic blood flow and in combination with ablation of thrombocytes can increase the transduction of adenovirus to tumors.

Characterization of divergent and atypical canine coronaviruses from Sweden

Field canine coronaviruses (CCVs) identified during a series of outbreaks of gastroenteritis in Swedish dogs were subjected to genetic analysis involving the open reading frame 1b (ORF1b) and the membrane (M) and spike (S) protein genes. Four field viruses originating from the Stockholm region presented identical sequences and segregated separately from other CCVs characterized so far and from GOT/05, the variant recovered in Western Sweden. A recombinant origin of the fifth virus identified in the Stockholm region is suggested. In addition, the five viruses originating from the same geographical area displayed atypical 5′ S gene sequences.

SYBR Green real-time reverse transcription-polymerase chain reaction assay for the generic detection of coronaviruses

Coronaviruses are etiologic agents of respiratory and enteric diseases in humans and in animals. In this study, a one-step real-time reverse transcription-polymerase chain reaction (RT-PCR) assay based on SYBR Green chemistry and degenerate primers was developed for the generic detection of coronaviruses. The primers, designed in the open reading frame 1b, enabled the detection of 32 animal coronaviruses including strains of canine coronavirus, feline coronavirus, transmissible gastroenteritis virus (TGEV), bovine coronavirus (BCoV), murine hepatitis virus (MHV) and infectious bronchitis virus (IBV). A specific amplification was also observed with the human coronaviruses (HCoV) HCoV-NL63, HCoV-OC43, HCoV-229E and severe acute respiratory syndrome coronavirus (SARS-CoV). The real-time RT-PCR detected down to 10 cRNA copies from TGEV, BCoV, SARS-CoV and IBV. In addition, the assay exhibited a high sensitivity and specificity on clinical samples from different animal species. The developed assay represents a potential tool for laboratory diagnostics and for detecting still uncharacterized coronaviruses.

Remarkable findings concerning PBDEs in the terrestrial top-predator red fox (Vulpes vulpes)

In the present study, we have analyzed muscle, liver, and adipose tissue of 33 red foxes from Belgium for their content of polybrominated diphenyl ethers (PBDEs). Median sums of seven tri- to hepta-BDEs (BDE 28, BDE 47, BDE 99, BDE 100, BDE 153, BDE 154, and BDE 183) were 2.2, 2.4, and 3.4 ng/g lipid weight in adipose tissue, liver, and muscle, respectively. These levels were lower than those found in various species of voles and mice, the main prey species of the red fox. This is probably related to the high capacity of the foxes to metabolize and eliminate lower brominated congeners. BDE 209 generally dominated the PBDE congener profiles in the red fox samples. In samples containing BDE 209, this congener contributed, on the average, approximately 70% to the total PBDE content. BDE 209 was measured in concentrations as high as 760 ng/g lipid weight in the liver, but the detection frequency was not more than 40%. In animals with the highest BDE 209 levels, this congener was detected in muscle, liver, as well as in adipose tissue. Other abundant congeners were BDE 153 and BDE 47, which prevail in other terrestrial species. The particular PBDE congener profile observed in the red fox resembles that seen in grizzly bears from Canada, but differs from those previously reported for terrestrial avian species. Our data confirms unambiguously that BDE 209 does bioaccumulate in terrestrial top predators, such as the red fox.

Rodent host specificity of European hantaviruses: evidence of Puumala virus interspecific spillover

In order to investigate rodent host specificity of European hantaviruses, experimental infection of colonized and wild-trapped rodents was performed. In addition to the natural rodent reservoir, Clethrionomys glareolus, Puumala hantavirus (PUUV) could infect colonized Microtus agrestis and Lemmus sibiricus, but not Syrian hamsters or Balb/C mice. Neither C. glareolus, nor M. agrestis, could be readily infected by Tula hantavirus (TULV). Wild-trapped Apodemus flavicollis and A. agrarius, the natural reservoirs of Dobrava (DOBV) and Saaremaa (SAAV) hantaviruses, respectively, could both be infected by SAAV. NMRI mice could also be infected by SAAV, but with lower efficiency as compared to Apodemus mice. Balb/C and NMRI laboratory mice, but not C. glareolus, could be infected by DOBV. To our knowledge, this is the first time DOBV and SAAV have been shown to infect adult laboratory mice. Moreover, potential hantavirus spillover infections were investigated in wild-trapped rodents. In addition to the natural host C. glareolus, we also found M. arvalis and A. sylvaticus with a history of PUUV infection. We did not find any C. glareolus or A. sylvaticus infected with TULV, a hantavirus which is known to circulate in the same geographical regions of Belgium.

Behavioral, physiologic, and habitat influences on the dynamics of Puumala virus infection in bank voles (Clethrionomys glareolus)

Populations of bank voles (Clethrionomys glareolus) were monitored during a 4-year study in southern Belgium to assess the influence of agonistic behavior, reproductive status, mobility, and distribution of the rodents on the dynamics of Puumala virus (abbreviation: PUUV; genus: Hantavirus) infection. Concordance was high between data from serologic testing and results of viral RNA detection. Wounds resulting from biting or scratching were observed mainly in adult rodents. Hantavirus infection in adults was associated with wounds in the fall, i.e., at the end of the breeding season, but not in spring. In addition, sexually active animals were significantly more often wounded and positive for infection. Hantavirus infection was associated with higher mobility in juvenile and subadult males. Seroconversions observed 6 months apart also occurred more frequently in animals that had moved longer distances from their original capture point. During nonepidemic years, the distribution of infection was patchy, and positive foci were mainly located in dense ground vegetation.

Tula hantavirus in Belgium

European common voles (Microtus arvalis), captured in Belgium in 1999, were proven by molecular as well as by serological techniques to be infected with Tula hantavirus (TULV). This is the first evidence for the presence of TULV in this country. No indication of spill-over infections of Puumala virus, known to be highly endemic among bank voles (Clethrionomys glareolus) within the same geographical regions as the trapped TULV-infected common voles, was observed. Together with previous reports on the circulation of TULV in eastern/central Europe, this finding suggests a more wide-spread circulation of this hantavirus serotype throughout the continent.

[Hantavirus infection epidemiology in Belgium]

In Europe, Puumala (PUU) is a hantavirus responsible for a human disease called nephropathia epidemica and its natural reservoir is the red bank vole, (Clethrionomys glareolus). Although the population densities and the prevalence rates of infection were high in red bank voles in southern Belgium during the 1996 and 1999 epidemic years, the percentages of infected rodents were low in 1997 and 1998, when only a few positive sites were found. Antibodies against PUU virus were mainly detected in the red bank vole but also in the wood mouse (Apodemus sylvaticus) and the red fox (Vulpes vulpes). The analysis of genomic sequences has shown that the Belgian viruses and the German strain Erft constitute a genetic lineage well separated from the other European PUU strains.

Incidence of hantavirus infections in Belgium

Over the last two decades, and from the moment that serological detection was possible, human hantavirus infections have been documented in most European countries. This paper summarises the available data on hantavirus cases in Belgium. These data enable the demonstration of the existence of a 3-year epidemic cycle in Belgium, which is apparently linked to rodent population dynamics.

Genetic characterization of Puumala hantavirus strains from Belgium: evidence for a distinct phylogenetic lineage

Puumala hantavirus (PUUV) sequences were recovered from red bank voles (Clethrionomys glareolus) trapped between 1996 and 1998 in four localities of southern Belgium: Thuin, Montbliart, Momignies and Couvin. In addition, three PUUV isolates originating from bank voles trapped in the 1980s in southern (Montbliart) and northern (Turnhout) Belgium were genetically characterized. Analysis of the complete S and partial M segment sequences showed that the Belgian PUUV strains constitute a genetic lineage, distinct from other known PUUV lineages from Europe and Japan. This lineage also includes a wild strain (Cg-Erft) originating from a neighbouring area of Germany. Within the Belgian lineage, geographical clustering of genetic variants was observed. In the Montbliart site, the range of diversity between the most temporally distant strains (from 1986 and 1996-1998) was higher than between those from 1996 and 1998, suggesting slight genetic drift via accumulation of neutral or quasi-neutral substitutions with time.

Hantavirus infections

Hantaviruses are the causative agents of the zoonotic diseases known as haemorrhagic fever with renal syndrome (HFRS) in Europe and Asia, and hantavirus pulmonary syndrome (HPS) in the Americas. These pathogens are maintained in the wild by rodent reservoirs and are mainly transmitted via the aerosol route. The infection is chronic and apparently asymptomatic in host animals. Whilst HFRS is caused by Hantaan, Seoul, Dobrava and Puumala hantaviruses, HPS is associated with Sin Nombre-like viruses. Common clinical features of HFRS and HPS include fever, myalgia, thrombocytopenia, leukocytosis and a capillary leak syndrome associated with shock in most severe cases. Outbreaks of HFRS and HPS are generally observed during years with dense rodent populations resulting from favourable climatic and environmental conditions. Human activities, such as rodent trapping, farming, cleaning rodent-infested areas, construction work, camping and hunting, are also implicated in the occurrence of hantavirus disease. Prophylactic measures in endemic areas rely essentially on information campaigns and rodent control.

Spatial and temporal dynamics of Puumala hantavirus infection in red bank vole (Clethrionomys glareolus) populations in Belgium

Dynamics of hantavirus infection and population densities in rodents were investigated from 1996 to 1999 in southern Belgium. Evidence of Puumala infection was restricted to Clethrionomys glareolus. Although the serotype was not determined, antibodies against hantavirus were also found in eight Apodemus sylvaticus. In fall 1996, the seroprevalence in C. glareolus was high (20.1%, 37 of 184) and the infection was widely distributed in the area studied whereas a focal occurrence of positive rodents and lower seroprevalence rates were recorded in spring 1997 (14.3%, six of 42), fall 1997 (6. 6%, 11 of 166), spring 1998 (6.4%, three of 47) and fall 1998 (6.7%, 11 of 165). A pullulation of rodents was observed in spring 1999 and was associated with a markedly higher seroprevalence in C. glareolus (47.7%, 189 of 396). In all seasons, infection rates in adults were higher than in juveniles and subadults. No significant difference of prevalence was recorded between males and females. In two trapping sites, the temporary disappearance of positive animals after a crash in rodent populations suggests that a threshold in density is necessary for the maintenance of the enzootic cycle.