Filoviruses: Ebola virus and Marburg virus

These pathogens of diseases that occur as hemorrhagic fevers were described relatively recently and have been little studied. They are classified in a separate family, Filoviridae, with a single genus, Filovirus. The viruses are filamentous or cylindrical in shape and sometimes resemble rhabdoviruses in appearance. Their genome is also represented by RNA. Although the appearance and cytoplasmic inclusions in infected cells slightly resemble those of rabies, the structure of Marburg and Ebola viruses differs from the rhabdoviruses to which they were previously classified, and has no antigen relationship with them or with any other known virus.

Marburg and Ebola viruses are similar in many ways in terms of morphological features and sizes. They are straight (Ebola virus) or twisted in various ways threads (Marburg virus - spiral, in the form of the number 6, V-shaped); their ends are rounded. Sometimes there are forms with thread-like branches. The outer diameter of the virions is 70-100 nm, the average length is 665 nm, but in electron microscopic preparations there are particles up to 1400 nm long (Ebola virus).

The Ebola virus genome is represented by one molecule of single-stranded negative RNA with a molecular weight of 4.0-4.2 MDa. In the center of the virion there is a strand with a diameter of 20 nm, which forms the basis of the cylindrical helical ribonucleoprotein of the virus with a diameter of 30 nm. Between the ribonucleoprotein and the virion membrane there is an intermediate layer with a thickness of 3.3 nm. The virion has an outer lipoprotein membrane with a thickness of 20-30 nm, on the surface of which at a distance of 10 nm from each other there are spikes with a length of 7-10 nm. The virion, as well as the Marburg virus, contains 7 structural proteins.

In the patient's material, Marburg and Ebola viruses are quite resistant to heating. In blood and plasma, they are inactivated at a temperature of 60 °C for 30 minutes, in a 10% suspension of the liver of sick monkeys - at 56 °C for 1 hour, under the influence of UV rays - for 1-2 minutes. In a liver suspension, under the influence of acetone, methanol or formalin, they are inactivated within 1 hour. They are sensitive to the action of fat solvents - ethanol, chloroform and sodium deoxycholate. They are well preserved at -70 °C, in lyophilized form (more than 1 year is the observation period).

Marburg and Ebola viruses differ in antigenic properties. Convalescent serum and immune serum of guinea pigs react differently with these viruses. In-depth studies of antigenic relationships between Marburg and Ebola viruses have confirmed their differences. Their antigens can be detected using immunofluorescence, complement fixation and neutralization reactions in guinea pigs. Ebola virus has 2 known serovariants - Sudanese and Zaire. The viruses reproduce well in monkey cell cultures, are pathogenic for guinea pigs and in experiments cause a disease in various monkey species, the pathogenesis and clinical picture of which resemble the disease in humans.

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Marburg fever

Marburg virus was first detected in 1967 during an outbreak of hemorrhagic fever in Yugoslavia and Germany among people who had been in contact with monkeys from Uganda (31 cases). The virus is also transmitted by direct contact from sick to healthy people. The disease is endemic in the countries of East and South Africa (South Africa, Kenya, Zimbabwe). Cases of the disease are also possible in other countries upon entry of persons in the incubation period, which is 3-9 days. The onset of the disease is acute: prostration and severe fever (sometimes two-wave type) quickly occur. In the first days, the virus is detected in the blood, urine and nasopharyngeal discharge. Later, a rash appears, vesicles on the soft palate, turning into ulcers. The liver is damaged, renal failure develops, sometimes mental and nervous disorders. Duration of the disease is up to 2 weeks, recovery - up to 3-4 weeks. During this period, drowsiness, adynamia, and hair loss are observed. Mortality is 30-50%. In men who have recovered from the disease, the virus remains in the sperm for up to 3 months.

Ebola fever

The Ebola virus (named after a river in Zaire) was first isolated in 1976 in Sudan and Zaire during an outbreak of severe hemorrhagic fever. Over 500 people fell ill, 350 of whom died. In subsequent years, sporadic cases of the disease were registered in the same region. Antibodies to the virus have been found in residents of Central African countries. Natural foci of the virus have not been identified. It is assumed that the disease is a zoonotic disease (the reservoir of the virus is wild rodents or bats). The assumption is based on the periodic appearance of the disease as a result of infection in the jungle, but the incidence ceases before it reaches epidemic levels. Mostly adults fall ill, they become a source of infection for others in the family and in the hospital. The disease is transmitted through close contact with patients, especially with blood or secretions containing blood, as well as with sputum and sperm. Therefore, airborne (especially among medical workers) or sexual transmission is not excluded. The incubation period is 3-16 days. The onset of the disease is acute: severe headache, fever, myalgia, nausea, chest pain. Then a rash appears, profuse diarrhea with blood, leading to dehydration; bleeding develops. Recovery is slow. Mortality is up to 90%.

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Diagnostics

Early diagnostics of Marburg and Ebola fevers consists of detecting the virus or its antigens in the blood, urine, hemorrhagic exudate during infection of monkey cell cultures or using neutralization reactions, complement fixation, IFM, RIF, etc. In later stages of the disease and during the convalescence period, the diagnostic sign is the detection of complement-fixing (from the 2nd-3rd week) or virus-neutralizing antibodies.

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Treatment

Symptomatic treatment consists of maintaining water-salt balance, kidney and liver function, and combating hemorrhagic syndrome. Convalescent plasma transfusions have a very good effect, especially in combination with interferon administration.

Prevention

Identified patients are isolated. Exceptional precautions should be taken to prevent medical personnel from coming into contact with blood, saliva, sputum, and urine of patients (work with personal protective equipment). If Marburg and Ebola viruses were once transmitted to people through contact with an unknown reservoir, it is possible that they could adapt to direct transmission from person to person, as a result of which these severe infections could be introduced from natural foci to regions where natural hosts do not exist. WHO recommendations have been developed to prevent the import of infection with monkeys and other animals to non-endemic countries.

Specific prevention

Vaccines for the prevention of Ebola fever have been developed in the United States and Russia.