Insights into the Pathogenesis of Viral Haemorrhagic Fever Based on Virus Tropism and Tissue Lesions of Natural Rift Valley Fever

Rift Valley fever phlebovirus (RVFV) infects humans and a wide range of ungulates and historically has caused devastating epidemics in Africa and the Arabian Peninsula. Lesions of naturally infected cases of Rift Valley fever (RVF) have only been described in detail in sheep with a few reports concerning cattle and humans. The most frequently observed lesion in both ruminants and humans is randomly distributed necrosis, particularly in the liver. Lesions supportive of vascular endothelial injury are also present and include mild hydropericardium, hydrothorax and ascites; marked pulmonary congestion and oedema; lymph node congestion and oedema; and haemorrhages in many tissues. Although a complete understanding of RVF pathogenesis is still lacking, antigen-presenting cells in the skin are likely the early targets of the virus. Following suppression of type I IFN production and necrosis of dermal cells, RVFV spreads systemically, resulting in infection and necrosis of other cells in a variety of organs. Failure of both the innate and adaptive immune responses to control infection is exacerbated by apoptosis of lymphocytes. An excessive pro-inflammatory cytokine and chemokine response leads to microcirculatory dysfunction. Additionally, impairment of the coagulation system results in widespread haemorrhages. Fatal outcomes result from multiorgan failure, oedema in many organs (including the lungs and brain), hypotension, and circulatory shock. Here, we summarize current understanding of RVF cellular tropism as informed by lesions caused by natural infections. We specifically examine how extant knowledge informs current understanding regarding pathogenesis of the haemorrhagic fever form of RVF, identifying opportunities for future research.

The role of platelets in the pathogenesis of viral hemorrhagic fevers

Viral hemorrhagic fevers (VHF) are acute zoonotic diseases that, early on, seem to cause platelet destruction or dysfunction. Here we present the four major ways viruses affect platelet development and function and new evidence of molecular factors that are preferentially induced by the more pathogenic members of the families Flaviviridae, Bunyaviridae, Arenaviridae, and Filoviridae. A systematic search was performed through the main medical electronic databases using as parameters all current findings concerning platelets in VHF. Additionally, the review contains information from conference proceedings.

Infections of the developing world

Access to critical care is rapidly growing in areas of the world where it was previously nonexistent and where infectious diseases often comprise the largest disease burden. Additionally, with crowding, mass migrations, and air travel, infectious diseases previously geographically confined are quickly spread across the planet, often in shorter time frames than disease incubation periods. Hence, critical care practitioners must be familiar with infectious diseases previously confined to the developing world. This article reviews selected tropical diseases that are seen in diverse locales and often require critical care services.

[Actual vitamin and main foodstuffs consumption by recovered patients suffered from hemorrhagic fever with renal syndrome]

Actual consumption of vitamins A, E, beta-carotene, ascorbic acid, thiamin, pyridoxine and main foodstuffs by recovered patients suffered from hemorrhagic fever with renal syndrome has been given. Frequency analysis of foodstuffs consumption was used to study actual nourishment of recovered patients. Surplus consumption of fat mainly due to the use of saturated fatty acids, deficiency of poly unsaturated fatty acids, surplus sugar consumption and predominance of proteins of animal origin over proteins of vegetable origin in ration has been revealed. Deficiency of water soluble vitamins equals to 41,6-78,7% of all examined patients, deficiency of fat water soluble vitamins is lower (21,4-38,3%).

[Strokes caused by infection in the tropics]

INTRODUCTION

Almost three out of every four people in the world who suffer a fatal stroke live in developing countries. A number of different tropical diseases may appear in Europe in the coming years as a consequence of the demographic change that is being brought about by migratory flows. We review the main infectious causes of strokes in the tropics.

DEVELOPMENT

There are estimated to be 500 million cases of malaria every year. Cerebral malaria can cause cerebral oedema, diffuse or focal compromise of the subcortical white matter and cortical, cerebellar and pontine infarctions. Chagas disease is an independent risk factor for stroke in South America. At least 20 million people have the chronic form of Chagas disease. The main prognostic factors for Chagas-related stroke are the presence of apical aneurysms, arrhythmia and heart failure. Vascular complications of neurocysticercosis include transient ischemic attacks, ischemic strokes due to angiitis and intracranial haemorrhages. The frequency of cerebral infarction associated with neurocysticercosis varies between 2% and 12%. Gnathostomiasis is a cause of subarachnoid haemorrhage in south-east Asia. Other less common causes of stroke are viral haemorrhagic fevers due to arenavirus and flavivirus.

CONCLUSIONS

Several diseases that are endemic in the tropics can be responsible for up to 10% of the cases of strokes in adults.

Emerging roles of tissue factor in viral hemorrhagic fever

Activation of coagulation by tissue factor (TF) is frequently observed in sepsis syndrome and is documented in certain viral hemorrhagic fevers. Coagulation protease complexes signal by activating the G-protein coupled, protease-activated receptors that regulate inflammation. Blockade of TF attenuates lethality in experimental models of Ebola virus infection but - similar to findings in bacterial sepsis - reduction of inflammation, rather than attenuation of coagulation, predicts survival of treated animals. Thus, targeting TF appears to aid the antiviral immune response in hemorrhagic fevers, and further studies are encouraged to define how TF-dependent signaling regulates immunity.

Molecular diagnostic techniques for use in response to bioterrorism

The use of micro-organisms as agents of biological warfare is considered inevitable for several reasons, including ease of production and dispersion, delayed onset of symptoms, ability to cause high rates of morbidity and mortality and difficulty in diagnosis. Therefore, the clinical presentation and pathogenesis of the organisms posing the highest threat (variola major, Bacillus anthracis, Yersinia pestis, Clostridium botulinum toxin, Francisella tularensis, filoviruses, arenaviruses and Brucella species), as well as the available diagnostic techniques and treatments for such infections, will be reviewed in this article. Due to the necessity of rapid identification and diagnosis, molecular techniques have been the ongoing focus of current research. Consequently, the molecular diagnostic techniques that have recently been developed for the diseases associated with these agents will be emphasized.

Endothelial cell function alteration after Junin virus infection

Hematologic involvement is the main feature of Argentine hemorrhagic fever (AHF), an endemo-epidemic disease caused by Junin virus (JV). Since endothelial dysfunction could play a role in AHF-altered hemostasis, we studied human umbilical vein endothelial cell (HUVEC) infection with a virulent (JVv) and a non-virulent (JVa) JV strain. Cells were infected by the two JV variants with no detectable apoptosis or cytopathic effect. Both viral variants up-regulated ICAM-1 and VCAM-1 levels, while von Willebrand factor (VWF) production was decreased. Prostacyclin (PGI2) release and decay accelerating factor (DAF) expression were greater in JVv- than in JVa-infected or control cells. Furthermore, nitric oxide (NO) production and endothelial nitric oxide synthase (eNOS) expression was only raised in JVv-infected supernatants. Significant NO and PGI2 values were also detected in AHF patient sera. These data demonstrate that endothelial cell responses are triggered subsequently by JV infection, suggesting that such alterations play a major role in the pathogenesis of AHF and perhaps in other viral-induced hemorrhagic diseases.

[Significant factors in the pathogenesis of hemorrhagic fevers]

<zakljucak> Patogeneza sindroma virusnih hemoragijskih groznica je slozena Virusi i njihovi antigeni, nadjeni u celijama vise organa, dovode do ostecenja celija i tkiva. Pored toga, vise cinilaca domacina je aktivno ukljuceno u nastanak bolesti. Medju njima su posebno znacajne endotelne celije za koje se smatra da zapocinju, a mononuklearne celije da direktnim delovanjem ili preko medijatora (citokina) dovrsavaju proces patogeneze. Kao posledica ove interakcije nastaje disfunkcija endotelnih celija u odrzavanju barijere izmedju vaskularnog i intersticijalnog prostora. Bolje poznavanje patogenetskih cinilaca sindroma virusnih hemoragijskih groznica moze doprineti poboljsanju lecenja obolelih.

Viral hemorrhagic fever--a vascular disease?

The syndrome of "viral hemorrhagic fever" in man caused by certain viruses, such as Ebola, Lassa, Dengue, and Crimean-Congo hemorrhagic fever viruses, is often associated with a shock syndrome of undetermined pathogenesis. However, the vascular system, particularly the vascular endothelium, seems to be directly and indirectly targeted by all these viruses. Here we briefly summarize the current knowledge on Marburg and Ebola virus infections, the prototype viral hemorrhagic fever agents, and formulate a working hypothesis for the pathogenesis of viral hemorrhagic fever. Infections with filoviruses show lethality up to 89% and in severe cases lead to a shock syndrome associated with hypotension, coagulation disorders and an imbalance of fluid distribution between the intravascular and extravascular tissue space. The primary target cells for filoviruses are mononuclear phagocytotic cells which are activated upon infection and release certain cytokines and chemokines. These mediators indirectly target the endothelium and are thought to play a key role in the pathogenesis of filoviral hemorrhagic fever. In addition, direct infection and subsequent destruction of endothelial cells might contribute to the pathogenesis. Filoviruses, particularly Ebola virus, encode nonstructural glycoproteins which are released from infected host cells. Their function as potential determinants in pathogenicity remains to be investigated.

Bioterrorism and catastrophe response: a quick-reference guide to resources

BACKGROUND

Dentists' responses to catastrophe have been redefined by bioterrorism. Informed response requires accurate information about agents and diseases that have the potential to be used as weapons.

METHODS

The authors reviewed information about the most probable bioterrorist weapons (those from the Center for Disease Control and Prevention's Category A) from the World Wide Web and print journals and distilled it into a resource list that is current, relevant to dentistry and noncommercial. The Web sites cited include those sponsored by federal agencies, academic institutions and professional organizations. The articles cited include those published in English within the last six years in refereed journals that are available in most higher education institutions.

RESULTS

The authors present the information in a table that provides a quick-reference guide to resources describing agents and diseases with the greatest potential for use as weapons: anthrax, botulism, plague, smallpox, tularemia and viral hemorrhagic fevers. This article presents Web site and journal citations for background and patient-oriented information (fact sheets), signs and symptoms, and prophylactic measures and treatment for each of the agents and diseases. The table facilitates quick access to this information, especially in an emergency. This article also points out guidelines for response should a suspected attack occur.

CONCLUSIONS

Armed with information about biological weapons, dentists can provide faster diagnosis, inform their patients about risks, prophylaxis or treatment and rethink their own role in terrorism response.

CLINICAL IMPLICATIONS

Fast, accurate diagnosis limits the spread of exceptionally contagious diseases. Providing accurate information to patients minimizes misinformation and the associated public fear and panic that, unchecked, could overwhelm health care systems.

Hemorrhagic fever occurs after intravenous, but not after intragastric, inoculation of rhesus macaques with lymphocytic choriomeningitis virus

Arenaviruses can cause hemorrhagic fever and death in primates and guinea pigs, but these viruses are not highly pathogenic for most rodent carriers. In the United States, arenaviruses precipitated outbreaks of hepatitis in captive monkeys, and they present an emerging health threat in the tropical areas of Africa and South America. We describe infection of rhesus macaques with the prototype arenavirus, lymphocytic choriomeningitis virus (LCMV), using the WE strain that has been known to cause both encephalopathy and multifocal hemorrhage. Five macaques were inoculated: two by the intravenous (i.v.) and three by the intragastric (i.g.) route. Whereas the two i.v.-inoculated monkeys developed signs and lesions consistent with fatal hemorrhagic fever, the i.g.-inoculated monkeys had an attenuated infection with no disease. Pathological signs of the primate i.v. infection differ significantly from guinea pig arenavirus infections and make this a superior model for human viral hemorrhagic disease.

Threats in bioterrorism. I: CDC category A agents

Although once considered unlikely, bioterrorism is now a reality in the United States since the anthrax cases began appearing in the fall of 2001. Intelligence sources indicate there are many countries and terrorist organizations that either possess biological weapons or are attempting to procure them. In the future it is likely that we will experience additional acts of bioterrorism. The CDC category A agents represent our greatest challenge because they have the potential to cause grave harm to the medical and public health systems of a given population. Thus, it is imperative that plans be developed now to deal with the consequences of an intentional release of any one or more of these pathogens.

Role of the endothelium in viral hemorrhagic fevers

OBJECTIVE

To describe endothelial participation in the pathogenesis of viral hemorrhagic fevers and certain other acute infectious diseases.

DATA EXTRACTION AND SYNTHESIS

Survey of published literature on viral hemorrhagic fevers interpreted in light of observations in patients and research on those diseases.

CONCLUSIONS

Endothelial involvement is an extremely important factor in the clinical syndrome termed viral hemorrhagic fever. Endothelial dysfunction is important in the genesis of bleeding, which is not universal and is commonly seen only in the presence of thrombocytopenia or severe platelet dysfunction. The pathogenesis of endothelial dysfunction varies in the different diseases. In some situations, direct endothelial infection is important in increased vascular permeability, changes in the procoagulant vs. anticoagulant balance, or cytokine production. In all the viral hemorrhagic fevers studied to date, cytokine induction is an important factor and also acts on the endothelium. Poor myocardial contractility is a very important issue in viral hemorrhagic fever and is not caused by direct viral infection of the heart; it is increasingly being recognized that these patients present with low cardiac output and high peripheral resistance and that they respond poorly to fluid infusion. The clinical findings in viral hemorrhagic fever differ from those in the sepsis syndrome and should be studied and interpreted separately; this approach will sharpen therapeutic approaches and could shed light on the problems of sepsis in general.

[Cerebrovascular disease in the tropics]

OBJECTIVES

To review the clinical manifestations, diagnosis, and therapy of diseases causing cerebrovascular disease (CVD) in the tropics.

DEVELOPMENT

Most prevalent conditions causing CVD in the tropics include: sickle cell disease, Takayasu s arteritis, cysticercosis, infective endocarditis, Chagas disease, viral hemorrhagic fevers, gnathostomiasis, leptospirosis, snake bites, cerebral malaria, puerperal venous thrombosis, and tuberculosis. These conditions may cause cerebral infarcts or hemorrhages, and in most instances are related to either vascular damage secondary to angiitis or hemorrhagic diathesis with bleeding in other organs. In some patients, the severity of the neurological picture makes impossible to identify an specific stroke syndrome and cerebrovascular complications are only recognized on neuroimaging studies or autopsy.

CONCLUSIONS

There is a group of tropical infectious and non infectious diseases that may cause cerebral infarcts or hemorrhages. Prompt diagnosis and therapy are needed to reduce the severity or brain damage and to avoid recurrent strokes.

Hemorrhagic fever virus-induced changes in hemostasis and vascular biology

Viral hemorrhagic fever (VHF) denotes a virus-induced acute febrile, hemorrhagic disease reported from wide areas of the world. Hemorrhagic fever (HF) viruses are encapsulated, single-stranded RNA viruses that are associated with insect or rodent vectors whose interaction with humans defines the mode of disease transmission. There are 14 HF viruses, which belong to four viral families: Arenaviridae, Bunyaviridae, Filoviridae and Flaviviridae. This review presents, in order, the following aspects of VHF: (1) epidemiology, (2) anomalies of platelets and coagulation factors, (3) vasculopathy, (4) animal models of VHFs, (5) pathogenic mechanisms, and (6) treatment and future studies. HF viruses produce the manifestations of VHFs either by direct effects on cellular functions or by activation of immune and inflammatory pathways. In Lassa fever, Rift Valley fever and Crimean-Congo HF, the main feature of fatal illness appears to be impaired/delayed cellular immunity, which leads to unchecked viremia. However, in HF with renal syndrome and dengue HF, the immune response plays an active role in disease pathogenesis. The interplay of hemostasis, immune response, and inflammation is very complex. Molecular biologic techniques and the use of animal models have helped to unravel some of these interactions.

Venezuelan hemorrhagic fever: clinical and epidemiological studies of 165 cases

Epidemiological and clinical data are presented on 165 cases of Venezuelan hemorrhagic fever (VHF), a newly emerging viral zoonosis caused by Guanarito virus (of the family Arenaviridae). The disease is endemic in a relatively circumscribed area of central Venezuela. Since its first recognition in 1989, the incidence of VHF has peaked each year between November and January, during the period of major agricultural activity in the region of endemicity. The majority of cases have involved male agricultural workers. Principal symptoms among the patients with VHF included fever, malaise, headache, arthralgia, sore throat, vomiting, abdominal pain, diarrhea, convulsions, and a variety of hemorrhagic manifestations. The majority of patients also had leukopenia and thrombocytopenia. The overall fatality rate among the 165 cases was 33.3%, despite hospitalization and vigorous supportive care.

Centers for Disease Control and Prevention (CDC). Update: outbreak of Ebola viral hemorrhagic fever--Zaire, 1995

As of June 25, public health authorities have identified 296 persons with viral hemorrhagic fever (VHF) attributable to documented or suspected Ebola virus infection in an outbreak in the city of Kikwit and the surrounding Bandundu region of Zaire (1,2); 79% of the cases have been fatal, and 90 (32%) of 283 cases in persons for whom occupation was known occurred in health-care workers. This report summarizes characteristics of persons with VHF from an initial description of cases and preliminary findings of an assessment of risk factors for transmission.

[Experimental Ebola fever in Macaca mulatta]

Aerogenic infection of M. rhesus with Ebola virus causes in them a disease similar in the principal clinical and virological parameters a grave form of Ebola fever in humans, as it is described in literature. Rapid development of symptoms of total intoxication in the presence of fever, hemorrhagic diathesis, and high viremia are indicative of the infection severity in monkeys.

Virologic investigation of a case of suspected haemorrhagic fever

After travelling in subSaharan Africa, an area known for sporadic cases of Marburg virus infection, a young Swedish man presented with a classical picture of severe viral haemorrhagic fever complicated by disseminated intravascular coagulation and septicaemia. Serum samples examined by electron microscopy revealed particles of a size compatible with filovirions. Indirect fluorescent antibody tests indicated transient seroconversion to Marburg virus. In lymphocyte transformation assays of cells isolated from the patient 11 months after the onset of acute disease, Marburg viral antigen was able to stimulate lymphocyte proliferation 3.9-fold; however, exhaustive attempts to isolate virus from acute phase blood cultured in vitro or in vivo from guinea pigs and monkeys failed. Data suggest that this patient may have been infected with a filovirus. This case demonstrates the difficulties that may occur in laboratory diagnosis of viral haemorrhagic fevers.

Haemostatic derangements associated with arenavirus infection in the guinea-pig: radioimmunoassay of fibrinopeptide A to assess thrombin action in infected animals

Pichinde virus infection of inbred guinea-pigs is a model for arenaviral infections in humans. Infected animals experience reduced levels of multiple coagulation factors caused by either consumption coagulopathy or impaired factor synthesis. A radioimmunoassay (RIA) of guinea-pig fibrinopeptide A (gFPA) has been developed to measure the degree of thrombin action in vivo. gFPA was synthesized via the solid-phase method and conjugated to bovine serum albumin (BSA). A double antibody RIA was established employing goat anti-rabbit IgG to precipitate the primary complex composed of either 125I-5-Tyr-gFPA or 125I-12-Tyr-gFPA and rabbit anti-gFPA-BSA. The cross-reaching material was removed by mixing the plasma with 3 vol of ethanol. The supernatant was filtered through a hollow fibre apparatus by centrifugation. Plasma gFPA immunoreactivities of outbred guinea-pigs averaged 6.56 ng/ml. The gFPA-RIA was validated by determining the quantity of gFPA released from thrombin-degraded fibrinogen. A transient elevation of gFPA levels was detected in Pichinde-infected animals by the gFPA-RIA using 125I-12-Tyr-gFPA as a tracer. The pathogenic mechanism by which the increased gFPA levels may lead to the lethality of Pichinde virus infection remains to be elucidated. It is possible that the coagulopathy triggers changes in immune and inflammatory pathways that induces high cytokine concentrations, with deleterious effects on organs such as the heart and lungs.

Pathophysiology of shock and hemorrhage in a fulminating viral infection (Ebola)

Eleven rhesus monkeys were monitored intensively during experimental infection with Ebola virus. Prominent neutrophilia with left shift and lymphopenia were the earliest abnormalities and were statistically significant by day 4 (P less than .02 and P less than .01, respectively). By day 4 falls in platelet counts were not statistically significant, whereas in vitro platelet aggregation was markedly depressed, progressing rapidly to complete failure by the time of maximum illness. Intraplatelet protein studies suggested this event was the result of in vivo activation and degranulation. Coagulation cascade defects were mainly in the intrinsic system and were surprisingly mild, with no evidence of selective consumption or production deficit of factor VII or VIII. When the possibility of indirectly mediated damage to endothelium possibly by a nonspecific immune response was examined, weight loss was less severe in drug-treated monkeys, and all had detectable plasma prostacyclin metabolites, but there was no improvement in survival.

Hemorrhagic fevers, with special reference to recent outbreaks in southern Africa

In considering the diagnosis of a patient admitted to the Johannesburg Hospital, suffering from an illness characterized by high fever and complicated by a hemorrhagic state from which he died, a list of possible causes of his illness was drawn up. This list included the arthropodborne viral infections prevalent in southern Africa, namely, chikungunya fever, Sindbis fever, West Nile fever, yellow fever, and Rift Valley fever; viral infections associated with rodents, such as Lassa fever; the viral infection associated with monkeys, Marburg virus disease; the rickettsial infections; tick-bite fever (the variety of spotted fever of tick typhus occurring in southern Africa) and Q fever; the bacterial infections, especially the coccal infections, plague septicemia, and meningococcal, staphylococcal, and streptococcal septicemia; and the blood protozoal infections malaria and trypanosomiasis. In addition, rubella, Gasser's syndrome, Henoch-Schönlein purpura, and viperine snakebite were briefly described in this review. All of these conditions may be complicated by the development of a hemorrhagic state. The circulation of large numbers of infecting organisms, by they viruses, rickettsiae, bacteria, or protozoa, may initiate the coagulation cascade, the formation of fibrin and its deposition in the finer blood vessels, and the aggregation and entanglement of platelets resulting in marked thrombocytopenia and bleeding. This bleeding tendency is greatly aggravated when the infection specifically involves the parenchymal cells of the liver; such a condition results in defective formation of coagulation factors such as prothrombin. The proper care of patients in whom a hemorrhagic state has developed requires urgent and accurate diagnosis followed by immediate and appropriate treatment that will combat the infection and alleviate the hemorrhagic state and liver disorder. If the hemorrhagic state is due to one of the dangerous infectious fevers, adequate protection of the medical, nursing, and laboratory staff concerned is also vital.

[Recent Lassa, Marbourg and Ebola viruses in African tropical viruses. I. Semiology--physiopathology--diagnosis--treatment (author's transl)]

Three new viruses have been identified in Africa during the present decade. They may cause sporadic cases or limited outbreaks, and they are probably endemic in areas which are still ill-defined. Severe forms of infection lead to the haemorrhagic syndrome or to hypovolemic shock, the physiopathology of which is being studied. The case-fatality ratio of severe cases is between 30 and 85 per cent. Nosocomial outbreaks have been observed, but they can be avoided if appropriate barrier nursing measures are carried out for the treatment of patients or adequate protection measures for sampling and examination of laboratory specimens. As such cases may be transferred outside the endemic zone, this implies that countries receiving travellers from Africa should have hospitals with specialized units for strict isolation and treatment of these patients.

Pathogenetic mechanisms in dengue haemorrhagic fever: Report of an international collaborative study*

In a study of 55 persons with dengue haemorrhagic fever-36 of whom showed the dengue shock syndrome-clinical, haematological, virological, and serological changes were correlated with serial measurements of complement components and immunopathological studies. Viruses dengue-1 or dengue-2 were isolated from the sera of 9 patients. Serological responses indicative of secondary dengue virus infections were observed in 53 patients; 2 (infants) had primary infections. During the acute phase of the disease, dengue antibody titres rose logarithmically. Marked depression of complement components, especially C3, was observed. Activation of both the classical and alternative complement pathways was demonstrated, with depression of both C4 and C3 proactivator levels in most instances, although in some cases it appeared that one mechanism was involved to a greater extent than the other. The level of depression of C3 was correlated with the severity of the disease. Relatively stable transferrin levels indicated that depletion of complement proteins was not primarily due to extravasation. Fibrinogen levels were depressed and fibrinogen split products were found in the plasma. The accumulated data provide further evidence of the central role that activated complement components play in the pathogenesis of dengue haemorrhagic fever.