Filoviruses: Ebola and Marburg virus

These causative agents of diseases, proceeding according to the type of hemorrhagic fevers, have been described relatively recently and have been little studied. They are classified in a separate family Filoviridae with a single genus Filovirus. The viruses are threadlike or cylindrical in shape and sometimes resemble rhabdoviruses. Their genome is also represented by RNA. Although the appearance and cytoplasmic inclusions in infected cells slightly and resemble those in rabies, the Marburg and Ebola viruses are different in structure from the rhabdoviruses to which they were referred earlier and do not have an antigenic relationship with them or with any other known viruses .

According to morphological features and sizes, the Marburg and Ebola viruses are similar in many respects. These are direct (Ebola virus) or thread-twisted threads (the Marburg virus is spiral, in the form of a 6 digit, V-shaped); their ends are rounded. Sometimes forms with filiform branches occur. The outer diameter of the virions is 70-100 nm, the average length is 665 nm, but electron-microscopic preparations contain particles up to 1400 nm in length (Ebola virus).

The genome of the Ebola virus is represented by one single-stranded negative RNA molecule with a molecular mass of 4.0-4.2 MD. In the center of the virion is a 20-nm-diameter cord, which forms the basis of a cylindrical spiral ribonucleoproteide virus with a diameter of 30 nm. Between the ribonucleoprotein and the envelope of the virion is located an intermediate layer 3.3 nm thick. The virion has an external lipoprotein membrane 20-30 nm in thickness, on the surface of which at a distance of 10 nm spikes 7-10 nm long are located from each other. In the composition of the virion, as well as the Marburg virus, there are 7 structural proteins.

In the material from the patient, the Marburg and Ebola viruses are sufficiently resistant to heat. In blood and plasma, they are inactivated at a temperature of 60 ° C for 30 minutes, in a 10% suspension of the liver of monkey patients - at 56 ° C for 1 hour, under UV rays - for 1-2 minutes. In a suspension of the liver under the influence of acetone, methanol or formalin inactivated for 1 hour. Sensitive to the action of fat solvents - ethanol, chloroform and sodium deoxycholate. Well preserved at -70 ° C, in lyophilized form (more than 1 year - observation period).

The Marburg and Ebola viruses differ in antigenic properties. Serum of convalescent and immune sera of guinea pigs react differently with these viruses. In-depth studies of the antigenic relationship between the Marburg and Ebola viruses confirmed their differences. Their antigens can be detected with the help of immunofluorescence reactions, complement binding and neutralization on guinea pigs. Ebola virus has 2 serovariants - Sudanese and Zairian. Viruses multiply well in monkey cell cultures, are pathogenic for guinea pigs and in an experiment cause a disease in various species of monkeys, the pathogenesis and clinic of which resemble human disease.

[1], [2], [3], [4], [5], [6], [7], [8], [9],

Marburg fever

The Marburg virus was first discovered in 1967 during an outbreak of hemorrhagic fever in Yugoslavia and Germany among people who contacted the monkeys from Uganda (31 cases). The virus is transmitted and with direct contact from patients to healthy people. The disease is endemic for the countries of Eastern and Southern Africa (South Africa, Kenya, Zimbabwe). It is also possible cases of disease in other countries when entering persons who are in the incubation period, which is 3-9 days. The onset of the disease is acute: rapidly prostration occurs, a marked fever (sometimes of a two-wave type). In the early days, the virus is found in the blood, urine and the nasopharynx. Later, a rash appears, on the soft palate - vesicles, turning into sores. The liver is damaged, kidney failure, and sometimes mental and nervous disorders develop. Duration of the disease - up to 2 weeks, recovery - up to 3-4 weeks; during this period, there is drowsiness, adynamia, hair loss. Mortality - 30-50%. In ill men, the virus remains in the semen up to 3 months.

Ebola fever

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

[10], [11], [12], [13], [14], [15], [16], [17],

Diagnostics

Early diagnosis of Marburg and Ebola fevers consists in the detection of the virus or its antigens in blood, urine, hemorrhagic exudate when the culture of monkey cells is infected or by neutralization, complement fixation, IFN, RIF, etc. In later stages of the disease and during the reconvalescence, a sign is the detection of complement-binding (from the 2nd-3rd week) or virus-neutralizing antibodies.

[18], [19], [20], [21], [22], [23],

Treatment

Symptomatic treatment is to maintain water-salt balance, kidney and liver function, fight against hemorrhagic syndrome. A very good effect is the transfusion of plasma convalescents, especially in combination with the introduction of interferon.

Prevention

Identified patients are isolated. Exceptional precautions should be used to prevent contacts of medical personnel with blood, saliva, sputum, urine of patients (work with individual protective equipment). If once the Marburg and Ebola viruses were transferred to people on contact with an unknown reservoir, it is possible that they will be able to adapt to direct transmission from person to person, as a result of which these serious infections can infiltrate from natural foci into regions where natural hosts do not exist . WHO recommendations have been developed for the prevention of infection with monkeys and other animals in non-endemic countries.

Specific prevention

In the US and in Russia, vaccines have been developed to prevent Ebola fever.