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Ecology of plague in Africa: response of indigenous wild rodents to experimental plague infection.

The Mastomys natalensis species complex, subdivided into genetically distinct species having diploid chromosome numbers 2n = 32 and 2n = 36, is a reservoir for several zoonoses including Lassa fever and plague. This report describes a study to determine whether these sibling species and three other rodent species have different potential as reservoirs for plague. It was found that M. natalensis (2n = 32) was significantly more resistant to experimental plague infection (50% survived inoculation with 120 000 Yersinia pseudotuberculosis subsp. pestis) than was M. coucha (2n = 36) (none of which survived doses of 190 Y. pseudotuberculosis subsp.pestis). In descending order of resistance were M. natalensis, Aethomys chrysophilus, M. coucha, Tatera leucogaster and A. namaquensis. No A. namaquensis survived inoculation of 10 or more plague bacilli.Previous reports on susceptibility to plague or other infections, which were based exclusively on findings in the universally distributed laboratory-bred Mastomys, are thus not necessarily applicable to the M. natalensis species as a whole but probably only to M. coucha. The Y. pseudotuberculosis subsp. pestis fraction-1 passive haemagglutination test appeared to be relatively insensitive in that only 5 out of 47 animals surviving experimental plague infection showed specific antibodies 6 weeks after challenge.The geographic distribution of human plague in southern Africa corresponds closely with that of the plague-susceptible species, M. coucha, while the resistant species, M. natalensis, predominates in areas where human plague has not been recorded. The role of A. namaquensis in the ecology of plague needs to be carefully studied and its possible importance in plague research should be investigated further.

Africa↗

[Acute and chronic Lassa virus infection of Vero cells].

Acute and persistent infections of Vero cells with a cloned Lassa virus were studied. After acute infection at a multiplicity of 2 PFU/cell the latent period was 12-16 hrs and the maximum yield of virus particles in the growth medium was obtained 28-32 hours postinfection. A persistently infected cell line was established by inoculating Vero cells with the cloned Lassa virus followed by subcultivation of the infected cells. The infected cells underwent 36 passages. Lassa virus production by the infected cells followed a cyclic pattern varying from 10(2) to 10(5) PFU/ml. Neither the plating efficiency of the virus nor its growth curves changes at 35 degrees C and 39 degrees C. The replication of the cloned virus in infected cells (superinfection) was markedly depressed in comparison to that of normal Vero cells infected with Lassa virus. The role of defective interfering particles in the establishment of persistent infection is discussed.

Defective Viruses↗

Controlling the exotic diseases: 1. Isolation facilities.

The exotic diseases are highly virulent transmissible conditions that include Lassa fever, some viral hemorrhagic fevers, smallpox and plague. Any of these diseases could be brought into or diagnosed in Canada as the result of natural or laboratory acquired infection. The patients must be isolated until the presumptive diagnosis is proved. High-security isolation is necessary and needs to be backed up by high-security laboratory services. In Canada facilities for high-security isolation are generally not available; therefore, hospitals must preplan and be ready to effect the best possible isolation under the existing conditions. The plan should address construction, ventilation, filtration, temperature and humidity, together with protective measures for staff and careful handling of laboratory specimens. Materials the patient has contacted and areas or vehicles he or she has been in will have to be decontaminated, and appropriate, safe disposal of corpses must be considered.

Canada↗

The inbreeding of the Y and the Z strains of Praomys natalensis with special reference to the laboratory uses of the Mastomys.

The Y and the Z strains of Praomys natalensis (Mastomys) are being sucessfully inbred, as far as is known for the first time. Spontaneous tumours of the glandular stomach have been found to develop in these rodents. Evidence is provided of the great potential of the laboratory Mastomys for use in medical research on cancer, plague, bilhaziasis, and more recently in the research on the Lassa fever virus.

Animals↗

[Serological evidence of Lassa virus circulation in the Republic of Guinea].

Seroepidemiological investigations in Guinea were carried out to estimate the areas of Lassa virus circulation. The recombinant protein of Lassa virus nucleocapsid was used as the antigen to analyse blood sera by ELISA. In some regions, from 30 to 54.9% of the population had antibodies to Lassa virus, but in others only 6-7%.

Adolescent↗

[The dynamics of the formation of IgG subclasses in Balb/c and CBA mice infected with the LCM, Lassa and Mopeia viruses and their role in diagnosis].

The dynamics of the induction of individual IgG subclasses in BALB/c and CBA mice and their role on the diagnostics of arenaviruses LCM, Lassa and Mopeia was studied. The study demonstrated that in solid-phase enzyme immunoassay (EIA) isotypes IgG2a and IgG2b to virus Mopeia could be used for the differentiation of virus Mopeia from viruses LCM and Lassa, and the antigen of virus Mopeia could be used for the preparation of diagnostic EIA systems not only to nonpathogenic virus Mopeia, but also to pathogenic viruses LCM and Lassa.

Animals↗

Stampidine prevents mortality in an experimental mouse model of viral hemorrhagic fever caused by lassa virus.

BACKGROUND: The potential use of microorganisms as agents of biological warfare (BW) is a growing concern. Lassa virus, a member of the Arenavirus class of Hemorrhagic fever (HF) viruses has emerged as a worldwide concern among public health officials. The purpose of the present study was to further elucidate the antiviral activity spectrum of stampidine, a novel nucleoside analog with potent anti-viral activity against the immunodeficiency viruses HIV-1, HIV-2, and FIV, by examining its effects on survival of mice challenged with Lassa virus. METHODS: We examined the therapeutic effect of Stampidine in CBA mice inoculated with intracerebral injections of the Josiah strain of Lassa virus. Mice were treated either with vehicle or nontoxic doses of stampidine administered intraperitoneally 24 hours prior to, 1 hour prior to, and 24 hours, 48 hours, 72 hours, and 96 hours after virus inoculation. RESULTS: The probability of survival following the Lassa challenge was significantly improved for stampidine treated mice (Kaplan Meier, Chi-squared = 11.7, df = 2, Log-Rank p-value = 0.003). CONCLUSION: Therefore, stampidine shows clinical potential as a new agent for treatment of viral hemorrhagic fevers caused by Lassa virus.

Animals↗

[Hemorrhagic (Marburg, Ebola, Lassa, and Bolivian) fevers: epidemiology, clinical pictures, and treatment].

The evaluation of the biological and epidemiological properties of Ebola, Marburg, Lassa, and Machupo viruses suggests that they are of social importance for health care authorities. The studies have created prerequisites to the development of reliable biosafety means against these pathogens. Particular emphasis is laid on the methods for infection diagnosis and on the studies to design specific protective agents--immunoglobulins and inactivated vaccines.

Animals↗

[Indirect immunoenzyme method for the laboratory diagnosis of Lassa and Ebola hemorrhagic fevers].

Conditions for performing solid-phase indirect enzyme-immunoassay (SPEIA) for the detection of Lassa and Ebola virus antigens and antibodies to them using horseradish peroxidase-labeled antispecific globulins were developed. The method is highly sensitive, specific, and reproducible. By this method, antigens of Lassa and Ebola viruses could be detected in tissue culture fluid of the infected cell cultures and in animal organ suspensions. Detection of antibodies to Lassa and Ebola viruses in human convalescent sera and in normal donors by means of SPEIA opens possibilities for its use in large-scale diagnostic and seroepidemiological surveys.

Animals↗

[Arenaviruses].

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Arenaviridae↗

[Marburg, Lassa and Ebola viral hemorrhagic fevers (author's transl)].

For each of these three fevers recently described, the authors report the history of their identification. The features of the three viruses, and the clinical aspects of the diseases they induce, are also indicated. The laboratory diagnosis is described. Practical indications are given for the transportation of the specimens to the only three high security laboratories in the world. The laboratory diagnosis is described. Some cautions are indicated handling and treating patients. It must be envisaged also to organize a four degrees quarantive cautions; compulsory for necropsies, burials, and occasionally for long distant transportations of patients are indicated.

Adult↗

The investigation of emerging and re-emerging viral diseases: a paradign.

Emerging virus infections are defined as previously nonthreatening viruses that can decimate new populations by finding fresh hosts and vectors--often with the help of humans who introduce new species into virgen environment, Several etiologic agents of these diseases, some of the interacting factors that contribute to their development and the role of molecular medicine in their understanding is discussed.

Ebolavirus↗

Hemorrhagic fever viruses.

This article reviews the epidemiology, pathophysiology, and clinical management of patients with suspected or confirmed viral hemorrhagic fever infection. The focus is on clinical management based on case series from naturally occuring outbreaks of viral hemorrhagic fever infection as well as imported cases of viral hemorrhagic fever encountered in industrialized nations. The potential risk of bioterrorism involving these agents is discussed as well as emergency department and critical care management of isolated cases or larger outbreaks. Important aspects of management, including recognition of infected patients, isolation and decontamination procedures, as well as available vaccines and therapies are emphasized.

Arenaviridae Infections↗