Filoviridae
Filoviridae is a family of non-segmented, negative-sense RNA viruses characterized by their filamentous structure. The most notable genera within this family are the Ebola virus and the Marburg virus, both known for causing severe hemorrhagic fevers in humans and other primates. First identified in the late 1960s, these viruses are transmitted primarily through direct contact with infected bodily fluids. The natural habitats of these viruses include regions in Central and West Africa, where outbreaks have been linked to specific animal reservoirs, notably fruit bats, which may carry the viruses asymptomatically.
Filoviridae viruses exhibit high pathogenicity, with mortality rates reaching up to 90%, even in the presence of advanced medical care. This extreme virulence, coupled with their potential for human-to-human transmission, makes them a significant concern for public health. Stringent quarantine measures are necessary to prevent outbreaks, and effective vaccines have been developed, although identifying the viral reservoirs remains crucial for minimizing future infections. Recent therapeutic advancements have shown promise, with the FDA approving specific treatments for the Ebola virus, highlighting ongoing efforts to combat these deadly pathogens.
Filoviridae
- TRANSMISSION ROUTE: Direct contact
Definition
The Filoviridae is a family of non-segmented, negative-sense, ribonucleic acid (RNA) viruses, distinguished from other members of the order Mononegavirales by having filamentous virus particles. The two best-known genera, the Ebola virus and Marburg virus, cause virulent hemorrhagic fevers in humans and other primates.
Natural Habitat and Features
The natural habitat of the Ebola virus and the Marburg virus, whose existence was unknown before 1967, has been the subject of much speculation and intense investigation. The first human cases of Marburg infection occurred in Germany but resulted from exposure to primates imported from Central Africa, where sporadic direct transmission to humans also occurs. Loci of Ebola are found in Zaire, the southern Sudan, and the Côte d'Ivoire in West Africa. Outbreaks have also occurred in Guinea, Liberia, and Sierra Leone. Another species of Ebola, not pathogenic to humans, causes outbreaks in monkeys in the Philippines.
Extensive serological testing of likely reservoir species in affected areas has pinpointed a common fruit bat, Rousettus aegyptiacus, as a carrier for Marburg. Fruit bats are strongly suspected in Ebola. They have been confirmed as carriers of two other emergent lethal viral illnesses in the Mononegavirales order: nipah virus infection (Southeast Asia) and hendra virus infection (Australia). In fruit bats, these viruses are either asymptomatic or cause mild illnesses.
Negative-strand RNA viruses, having penetrated a cell, serve as templates for positive strands of RNA that co-opt the cellular machinery of the cell to synthesize viral proteins. Transcription begins at a promoter site and may stop at boundaries between genes, producing positive strands coding only for certain proteins. As infection proceeds, the transcription process ignores gene boundaries and produces complete positive copies, which, in turn, serve as templates for the entire virus genome. Genome and proteins self-assemble into virions that bud off from the host cell membrane. Viruses of this type have high mutation rates because of an absence of proofreading ability in the enzyme that governs viral synthesis.
Pathogenicity and Clinical Significance
Members of the Filoviridae cause some of the most virulent viral illnesses known, with mortality rates of up to 90 percent, even in modern hospital settings. This virulence, coupled with moderate infectivity and the potential for human-to-human transmission, make Ebola and Marburg viruses matters of utmost concern for epidemiologists. These viruses are considered class-four hot pathogens. Their equally devastating effect on nonhuman primates constitutes a grave threat to rare species in Central Africa. An ongoing epidemic among lowland gorillas may lead these animals to extinction.
Aside from the Marburg virus in fruit bats, no active zoonosis attributed to Filoviridae in mammals other than primates has been identified, despite extensive searching. However, paleoviruses representing infections with genetically similar viruses occur in rodents and insectivores, and in bats in Central Africa. A paleovirus is a genetic marker, either a portion of the virus incorporated into host deoxyribonucleic acid (DNA) or genes encoding for specific resistance, which has been passed through geologic time and can be used to trace the infection history of entire lineages of animals.
The extreme pathogenicity of Ebola and Marburg viruses dictate stringent quarantine measures and extreme care in the protection of researchers and medical and veterinary personnel to prevent their coming in contact with the pathogen. Since the outbreaks in Marburg and in a primate facility in Reston, screening and quarantine procedures for the legal movement of primates used for research have become much more rigorous, but illegal trade in monkeys from the Eastern Hemisphere remains a concern. No endemic infections attributable to Filoviridae are known from the Western Hemisphere or outside the tropics.
Identification of an active case of either disease warrants immediate isolation of the infected person in a hospital setting. In this setting, intensive care can be provided with minimal contact with healthcare providers, recent contacts can be traced and isolated for observation, and the source of the infection can possibly be identified. Although two effective vaccines for Ebola have been developed—Ervebo, and Zabdeno and Mvabea—identifying the animal reservoir still remains vital as an avenue for modifying human behavior to minimize exposure.
Drug Susceptibility
Several drugs have shown promise in treating the Ebola virus, and some progress has also been made on the Marburg virus. The United States Food and Drug Administration (FDA) has approved Inmazeb and Ebanga for treating the Zaire Ebola virus. Antiviral agents must be specific to the genomes and replication strategies of negative-sense single-strand RNA viruses. However, some broad-spectrum antivirals, such as remdesivir, have shown potential in treating Ebola and Marburg. Remdesivir has also shown promise in being effective against Mononegavirales.
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