Animal models for viral haemorrhagic fever

Viral haemorrhagic fever can be caused by one of a diverse group of viruses that come from four different families of RNA viruses. Disease severity can vary from mild self-limiting febrile illness to severe disease characterized by high fever, high-level viraemia, increased vascular permeability that can progress to shock, multi-organ failure and death. Despite the urgent need, effective treatments and preventative vaccines are currently lacking for the majority of these viruses. A number of factors preclude the effective study of these diseases in humans including the high virulence of the agents involved, the sporadic nature of outbreaks of these viruses, which are typically in geographically isolated areas with underserviced diagnostic capabilities, and the requirements for high level bio-containment. As a result, animal models that accurately mimic human disease are essential for advancing our understanding of the pathogenesis of viral haemorrhagic fevers. Moreover, animal models for viral haemorrhagic fevers are necessary to test vaccines and therapeutic intervention strategies. Here, we present an overview of the animal models that have been established for each of the haemorrhagic fever viruses and identify which aspects of human disease are modelled. Furthermore, we discuss how experimental design considerations, such as choice of species and virus strain as well as route and dose of inoculation, have an influence on animal model development. We also bring attention to some of the pitfalls that need to be avoided when extrapolating results from animal models.     

Detection and identification of dengue-1 virus in clinical samples by a nested-PCR followed by restriction enzyme digestion of amplicons

Dengue viruses cause a disease with clinical findings ranging from asymptomatic infections to severe manifestations, characterised by haemorrhage and shock and known as dengue haemorrhagic fever/dengue shock syndrome. Since this fever and syndrome usually results from sequential infections by distinct dengue serotypes, rapid detection and identification of dengue viruses circulating in endemic areas are important to implement control measures, and ultimately to avoid secondary infections that could result in dengue haemorrhagic fever/dengue shock syndrome. A nested-PCR was developed followed by restriction enzyme (Kpn I) digestion of the amplicons to differentiate dengue-1 from dengue-2. Seventy-five IgM-containing samples collected from 2 to 17 days after the beginning of the symptoms were examined. These samples were submitted to nested-PCR amplification, the amplicons were digested with Kpn I, and the results compared to virus isolation in C6/36 cells and to results obtained by the standard PCR. Out of 75 tested samples, virus was isolated from 2 (2.6%), 17 (22.7%) were positive by the regular PCR protocol, and 58 (77.3%) were positive by nested-PCR. All of the amplicons digested by Kpn I identified dengue-1 virus as the infecting strain. These results indicate that the nested-PCR provided a high yield of dengue genome amplification even in the presence of IgM antibodies, and restriction enzyme digestion defined rapidly the circulating serotype. Therefore, the combination of these techniques may be useful to rapidly identify dengue viruses in countries where dengue-1 and dengue-2 circulates, and this approach can also be applied to the other two serotypes.     

Tick-Borne Viruses of North America

The global incidence of tick-borne infectious diseases has increased since the beginning of the 21st century. The expansion of tick populations into new geographic locations and a variety of anthropogenic and natural factors are all drivers of the increase. In addition to the establishment of known tick-borne pathogens in new areas, several novel agents, including many viruses, have also emerged. At present in North America, there are five tick-borne viruses that are known to cause human disease: deer tick virus, Powassan virus, Colorado tick fever virus, Heartland virus, and Bourbon virus. Although uncommon causes of disease, these viruses pose formidable threats to the health of individuals residing in regions of endemicity, especially since there are currently no medical countermeasures available to combat them. This review focuses on the basic biology, ecology, epidemiology, transmission, clinical presentation, diagnosis, treatment, and prevention of these North American tick-borne arboviruses.     

Guiding dengue vaccine development using knowledge gained from the success of the yellow fever vaccine

Flaviviruses comprise approximately 70 closely related RNA viruses. These include several mosquito-borne pathogens, such as yellow fever virus (YFV), dengue virus (DENV), and Japanese encephalitis virus (JEV), which can cause significant human diseases and thus are of great medical importance. Vaccines against both YFV and JEV have been used successfully in humans for decades; however, the development of a DENV vaccine has encountered considerable obstacles. Here, we review the protective immune responses elicited by the vaccine against YFV to provide some insights into the development of a protective DENV vaccine.     

Development of a consensus microarray method for identification of some highly pathogenic viruses

Some highly pathogenic viruses, such as Chikungunya virus, Japanese encephalitis virus, Yellow fever virus, Dengue virus, Hanta virus, SARS‐CoV, and H5N1 avian influenza virus can cause severe infectious diseases. However, the consensus method for detecting these viruses has not been well established. A rapid and sensitive microarray approach for detection of these viruses and a panel of specific probes covering nine genera and 16 virus species were designed. 70‐mer oligonucleotides were used at the genus level and 50‐mer oligonucleotides were at the species level, respectively. To decrease the interference of the host genome in hybridization, the consensus genus primers were designed and used to reverse transcribe only virus genome. The synthesis of the second strand was carried out with a random primer sequence (5′‐GTTTCCCAGTAGGTCTCNNNNNNNN‐3′). The amplified products were labeled and processed for microarray analyses. This microarray‐based method used the highly conserved consensus primers to synthesize specifically the virus cDNA and could identify effectively Chikungunya virus, Japanese encephalitis virus, Yellow fever virus, Dengue virus, Tick borne encephalitis virus, and H5N1 avian influenza virus. Using this method, one unknown virus isolated from pig brain in Shanxi Province, China was identified. This method may have an important potential application for the diagnosis of virus infection. J. Med. Virol. 81:1945–1950, 2009. © 2009 Wiley‐Liss, Inc.     

Non-human viruses developed as therapeutic agent for use in humans

Viruses usually infect a restricted set of host species, and only in rare cases does productive infection occur outside the natural host range. Infection of a new host species can manifest as a distinct disease. In this respect, the use of non-human viruses in clinical therapy may be a cause for concern. It could provide the opportunity for the viruses to adapt to the new host and be transferred to the recipient's relatives or medical caretakers, or even to the normal host species. Such environmental impact is evidently undesirable. To forecast future clinical use of non-human viruses, a literature study was performed to identify the viruses that are being considered for application as therapeutic agents for use in humans. Twenty-seven non-human virus species were identified that are in (pre)clinical development, mainly as oncolytic agents. For risk management, it is essential that the potential environmental consequences are assessed before initiating clinical use, even if the virus is not formally classified as a genetically modified organism. To aid such assessment, each of these viruses was classified in one of five relative environmental risk categories, ranging from "Negligible" to "Very High". Canary pox virus and the Autographa californica baculovirus were assigned a "Negligible" classification, and Seneca Valley virus, murine leukemia virus, and Maraba virus to the "High" category. A complicating factor in the classification is the scarcity of publicly available information on key aspects of virus biology in some species. In such cases the relative environmental risk score was increased as a precaution.     

Pathogenesis of puumala and other hantavirus infections

Hantaviruses are rodent/insectivore-borne negative-stranded RNA viruses which belong to the Bunyaviridae family. They do not cause any symptomatic disease in their adult carrier rodents, but in humans they are aetiologic agents of haemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS), both associated with a significant mortality. In cell culture hantaviruses do not cause cytopathic effects and the mechanisms of disease in man are not well understood. Increased capillary permeability is a central phenomenon in the pathogenesis of hantavirus infections. Although the viruses have in vivo a predilection for endothelial cells, it is presumed that inflammatory mediators of the host immune response play a significant role in the capillary leak that may produce abrupt hypotension and shock in severely ill patients. Mediators released by activated macrophages including NO and TNF-α are considered important. The pathogenesis of renal failure in HFRS also awaits to be resolved. This review summarises what is known about these phenomena and discusses also the molecular basis of the putative virulence factors of hantaviruses. Finally, the genetic predisposition and HLA association with severe Puumala virus infection will be discussed. © 1998 John Wiley & Sons, Ltd.     

Liver involvement in dengue viral infections

Dengue fever is the commonest viral haemorrhagic fever worldwide and is a leading cause of morbidity and mortality in the tropics. Dengue viral infections are frequently associated with varying degrees of liver injury. Liver injury is more severe in dengue haemorrhagic fever or severe dengue. We review the current knowledge on liver involvement following dengue viral infections and explore the links between clinical manifestations, pathogenesis, and their impact on management     

Modulation of immune responses in the central nervous system by Zika virus,West Nile virus,and dengue virus

Arthropod-borne viruses (arboviruses) pose significant threats to global public health by causing a spectrum of diseases ranging from mild febrile illnesses to severe neurological complications. Understanding the intricate interplay between arboviruses and the immune system within the central nervous system is crucial for developing effective strategies to combat these infections and mitigate their neurological sequelae. This review comprehensively explores the mechanisms by which arboviruses such as Zika virus, West Nile virus, and Dengue virus manipulate immune responses within the CNS, leading to diverse clinical manifestations.     

Circoviruses: Immunosuppressive threats to avian species: A review

Circoviruses are small, non-enveloped, icosahedral viruses that are unique among animal viruses in having circular, single-stranded DNA genomes. Their genomes are also the smallest possessed by animal viruses. The circovirus family currently comprises three members, chicken anaemia virus, porcine circovirus, and psittacine beak and feather disease virus, with pigeon circovirus being classified as a tentative member. Infections with each of the four circoviruses are associated with potentially fatal diseases in which virus-induced damage to lymphoid tissue and immunosuppression are common features. Experience with other animal virus families suggests that additional animal species will be infected by, as yet undiscovered, circoviruses and that these may display similar tissue tropism and disease-causing potential. Recent reports describing the association of circovirus-like viruses with immunodeficiency-related diseases of geese and southern black-backed gulls suggest that circovirus infections of avian species may be more common than previously recognized, and prompt the question of whether novel circoviruses infect poultry to cause clinical and/or subclinical diseases that may be economically important. This review has three purposes. First, it is designed to summarize the currently available information about the classified circoviruses and viruses that are regarded as circovirus-like. Second, it aims to alert the readership to the possibility that other avian species, including commercial poultry, may be infected with novel circoviruses. Finally, possible methods for discovering novel circoviruses and for controlling infections by such viruses are suggested.     

Receptor use by the Whitewater Arroyo virus glycoprotein

Whitewater Arroyo virus (WWAV) is a North American New World arenavirus, first isolated from rats in New Mexico in 1993, and tentatively associated with three human fatalities in California in 1999-2000. However, it remains unclear whether WWAV was the cause of these, or any other, human infections. One important characteristic of viruses that influences pathogenic potential is the choice of cellular receptor and the corresponding tropism of the virus. In the arenaviruses, these properties are determined largely by the viral glycoprotein (GP). We have previously noted for the New World clade B arenaviruses, which include four severe human pathogens, that the ability to cause human disease correlates with the ability of the GP to use the human transferrin receptor 1 (hTfR1) to enter cells. In addition, pseudotyped retroviral vectors displaying the GPs from pathogenic clade B viruses transduced a range of cell lines in vitro that were distinct from those that could be transduced by non-pathogenic clade B viruses. WWAV was initially classified as a New World clade A virus, based on sequence analysis of its nucleoprotein gene. However, more extensive analyses have revealed that WWAV and the other North American arenaviruses are probably recombinant clade A/B viruses, and that the WWAV GP is more closely related to the clade B GPs. Based on this finding, we sought to understand more about the possible pathogenic potential of WWAV by determining whether its clade B-like GP exhibited the characteristics of a pathogenic or non-pathogenic clade B virus. Our studies found that WWAV GP did not use hTfR1 for entry, and that its overall in vitro tropism was most similar to the GPs from the non-pathogenic clade B viruses. Although many viral factors in addition to GP receptor use and tropism determine whether a virus is able to cause disease in humans, our analysis of the WWAV GP does not support the idea that WWAV is a human pathogen.     

Role of T cells, cytokines and antibody in dengue fever and dengue haemorrhagic fever

Dengue infections are a major cause of morbidity and mortality in the tropical and sub-tropical regions of the world. There is no vaccine for dengue and also there are no anti-viral drugs to treat the infection. Some patients, typically those experiencing a secondary infection with a different dengue serotype, may progress from an acute febrile disease to the more severe forms of disease, dengue haemorrhagic fever and dengue shock syndrome. Here we discuss the significant immunopathological component to severe disease and how T cells, cytokines and cross-reactive antibody combine to contribute to the progression to dengue haemorrhagic fever. These events are thought to lead to vascular leakage, the signature event in dengue haemorrhagic fever, and are addressed in this review by incorporating the concept of heterologous T cell immunity. The need for effective measures against dengue and dengue-related illness is clear. We propose that drugs against dengue virus, or the symptoms of severe dengue disease, are a viable goal.     

Clinical and laboratory findings in patients with oliguric and non-oliguric Hantavirus haemorrhagic fever with renal syndrome: an analysis of 128 patients

Patients with haemorrhagic fever with renal syndrome (HFRS) may present without significant oliguria. We compared different initial clinical symptoms and laboratory findings in patients who developed oliguric acute renal failure (ARF) with those in patients who did not develop oliguric ARF. Overall, 128 patients with serologically confirmed HFRS were hospitalized at the University Hospital for Infectious Disease, Zagreb, Croatia between January 1999 and December 2010. Clinical signs and laboratory findings were extracted from medical charts, and were assessed for their relationship to the development of oliguric ARF. Puumala virus infection was diagnosed in 101 (79%) patients, and Dobrava-Belgrade virus infection in 27 (21%). Oliguria or anuria developed in 30% of patients. We identified the following risk factors for the development of oliguria and anuria on multivariable analysis: conjunctival hyperaemia or bleeding (relative risk (RR) 1.84, 95% CI 1.09–3.10; p 0.023), diarrhoea (RR 1.45, 95% CI 1.07–1.97; p 0.017), serum sodium of ≤133 mM (RR 2.21, 95% CI 1.34–3.64; p 0.002), and dipstick protein value of >1.5 g/L (RR 1.59, 95% CI 1.09–2.33; p 0.016), as well as hiking in the forest (RR 1.92, 95% CI 1.13–3.26; p 0.016). Our findings may help physicians in the earlier identification of patients with a more severe form of HFRS caused by Puumala and Dobrava-Belgrade viruses. Particular attention should be given to findings such as conjunctival hyperaemia or bleeding, diarrhoea, a low serum sodium level, and proteinuria.     

Identification of two severe fever with thrombocytopenia syndrome virus strains originating from reassortment

Recently, a novel bunyavirus, severe fever with thrombocytopenia syndrome virus (SFTSV), was isolated in central China. The virus can cause multi-clinical symptoms: severe fever, thrombocytopenia, leukocytopenia, with a mortality rate of ∼10%. Several studies show that SFTSV could undergo rapid evolution via gene mutation and homologous recombination. However, as an important evolutionary force for segmented-genome viruses, reassortment has not been reported in SFTSV. In this study, we identified two SFTSV strains of which the S segment has different origin from M and L, suggesting that reassortment might be potential force driving rapid change of SFTSV. This result might shed new light on the evolutionary behavior of the novel virus.     

Sequence of the nucleocapsid protein gene of Machupo virus: close relationship with another South American pathogenic arenavirus,Junín

Summary The sequence of the nucleocapsid (N) protein of Machupo virus (causative agent of Bolivian haemorrhagic fever) has been determined, and used to infer a phylogenetic relationship to other arenaviruses. The relationship of the virus to Junín and Tacaribe viruses, together with previous demonstrations of antigenic similarity and cross-protection by heterologous viruses, suggest that vaccines developed against Argentine haemorrhagic fever might also be effective against the Bolivian disease.     

The senile dementias: a new model

Kuru and Creutzfeldt Jakob disease are fatal neurological disorders in humans that are transmissible to humans and other experimental animals. Largely because of their transmissibility the etiology of these diseases has been ascribed to infectious agents classified as "slow" or unconventional viruses. A related neurological disease in sheep called scrapie has also been ascribed to infection by slow viruses. Despite more than 20 years of intensive research no viruses or other infectious agents have ever been isolated or identified as the causative factors in these transmissible neurological diseases. The model presented below suggests that these "subacute spongiform virus encephalopathies" are not due to any infectious agent. Rather, I propose that they are caused by peptide hormones that may be transmitted from one individual to another in blood or other tissue. These hormones are postulated to activate genes in neurons whose proteins result in the observed pathology. It also is suggested that other non-transmissible human neurological diseases such as Alzheimer's disease may be due to endogenously produced peptide hormones that progressively activate genes responsible for the synthesis of amyloid proteins that are associated with neurological diseases.     

Enhancement of autoantibody pathogenicity by viral infections in mouse models of anemia and thrombocytopenia

Viral infections are involved in the pathogenesis of blood autoimmune diseases such as hemolytic anemia and thrombocytopenia. Although antigenic mimicry has been proposed as a major mechanism by which viruses could trigger the development of such diseases, it is not easy to understand how widely different viruses might induce these blood autoimmune diseases by this sole mechanism. In mice infected with lactate dehydrogenase-elevating virus (LDV), or mouse hepatitis virus, and treated with anti-erythrocyte or anti-platelet monoclonal autoantibodies at a dose insufficient to induce clinical disease by themselves, the infection sharply enhances the pathogenicity of autoantibodies, leading to severe anemia or thrombocytopenia. This effect is observed only with antibodies that induce disease through phagocytosis. Moreover, the phagocytic activity of macrophages from infected mice is increased and the enhancing effect of infection on autoantibody-mediated pathogenicity is strongly suppressed by treatment of mice with clodronate-containing liposomes. Finally, the disease induced by LDV after administration of autoantibodies is largely suppressed in animals deficient for gamma-interferon receptor. Together, these observations suggest that viruses may trigger autoantibody-mediated anemia or thrombocytopenia by activating macrophages through gamma-interferon production, a mechanism that may account for the pathogenic similarities of multiple infectious agents.     

Detection of Puumala and Rift Valley Fever virus by quantitative RT-PCR and virus viability tests in samples of blood dried and stored on filter paper

Haemorrhagic fever viruses cause emerging infections worldwide, and blood or serum is the main sample used for diagnosis. However, storage and transportation of such samples from remote areas to regional laboratories may be complicated and expensive. In this study, a novel approach was evaluated for the detection of Puumala hantavirus (PUUV) RNA and Rift Valley fever virus (RVFV) RNA. Whole-blood samples spiked with viable virus particles were tested in parallel with clinical samples from patients with acute haemorrhagic fever with renal syndrome (nephropathia epidemica). Individual blood samples were spotted on filter paper, dried, and used for RNA extraction at later time points. PUUV RNA was detected by RT-PCR after storage at room temperature for up to six weeks. In contrast, only low copy numbers of RVFV RNA were detected after 1-2 days even though viable RVFV was eluted from the dried filter papers after the same time. The use of filter paper to collect and store blood samples for PUUV RNA detection is therefore a simple and reliable procedure. This approach might facilitate sampling and analysis of other RNA viruses from human or animal sources and could be used for field studies in remote areas or in developing countries.