Ebola hemorrhagic fever is an acute hemorrhagic infectious disease caused by Ebola virus. It is mainly contracted through contact with blood, body fluids, secretions and excretions of patients or infected animals, and the clinical manifestations are mainly sudden onset of fever, hemorrhage and multi-organ damage. Ebola hemorrhagic fever has a high mortality rate of 50%-90%. The disease was first discovered in Africa in 1976 and is prevalent mainly in Uganda, Congo, Gabon, Sudan, Côte d’Ivoire, South Africa, Guinea, Liberia, Sierra Leone, Nigeria and other African countries.
(I) Pathogenesis
Ebola virus belongs to the filovirus family, which is a single-stranded negative-stranded RNA virus without segmentation. The virus is long filamentous body, can be rod-shaped, filamentous, “L” shape and other forms. The virus has a lipid envelope with brush-like protrusions, mainly composed of viral glycoproteins. The Ebola virus genome is an unsegmented negative-stranded RNA of 18.9 kb in size, encoding 7 structural proteins and 1 non-structural protein.
Ebola virus can proliferate in human, monkey, guinea pig and other mammalian cells, and is sensitive to cells such as Vero and Hela.
Ebola virus can be classified into Zaire, Sudan, Taï Forest, Leston and Bendiboujou types. All four subtypes can cause disease in humans after infection, except for the Leston type, which is not pathogenic to humans. The nucleotide composition of the genomes of different subtypes varies greatly, but the genomes of viruses of the same subtype are relatively stable.
Ebola virus is moderately resistant to heat, and there is no significant change in infectivity after 1 month of storage at room temperature and 4°C. It takes 1 hour to inactivate the virus at 60°C and 5 minutes to inactivate it at 100°C. The virus is sensitive to ultraviolet light, γ-rays, formaldehyde, hypochlorous acid, phenols and other disinfectants and lipid solvents.
(B) epidemiological characteristics
1.Infectious source and host animal
Patients and primates infected with Ebola virus are the infectious source of the disease.
The natural hosts of Ebola virus are thought to be fruit bats of the family Foxbatidae, especially Hammerhead fruit bats, Fusiformes ex-shoulder fruit bats and small collared fruit bats, but their circulation in nature is not yet known.
2. Transmission routes
Contact transmission is the most important route of transmission of the disease. It can be transmitted through contact with blood, body fluids, secretions, excreta and contaminants of patients and infected animals.
The risk of infection in general business activities, travel, social interactions and general workplace is low. Patients can maintain high levels of the virus in their blood after infection. Health care workers, patients’ families or other close contacts are susceptible to infection without strict protective measures during treatment, care of patients or disposal of patients’ bodies.
According to the literature, the virus can be isolated in the semen of patients with Ebola hemorrhagic fever, so the possibility of sexual transmission exists. Some animal experiments have shown that Ebola virus can be transmitted through aerosols. Although it has not been confirmed that cases of sexual transmission and airborne transmission have occurred, but should be alerted and well protected.
3.Population susceptibility
Humans are generally susceptible to Ebola virus. The incidence of disease is mainly concentrated in adults, which is related to exposure or exposure to more opportunities. There is no data to suggest that there is a difference in incidence between the sexes.
(C) Clinical manifestations
The incubation period of the disease is 2-21 days, usually 8-10 days. The incubation period has not been found to be infectious.
Patients have an acute onset with fever and rapid progression to high fever with malaise, headache, myalgia, sore throat, etc.; nausea, vomiting, abdominal pain, diarrhea, rash, etc. may also occur. The disease may enter the extreme stage after the 3rd-4th day, with persistent high fever, increased symptoms of infection and gastrointestinal symptoms, and different degrees of bleeding, including skin and mucous membrane bleeding, vomiting blood, hemoptysis, blood in the stool, hematuria, etc.; in severe cases, there may be impaired consciousness, shock and multi-organ involvement, and most of them die of bleeding and multi-organ dysfunction within 2 weeks after the onset of the disease.
(D) Pathological characteristics
The main pathological changes are hemorrhage of skin, mucous membrane and organs, and focal necrosis can be seen in multiple organs. Point and focal necrosis of hepatocytes is a typical feature of the disease, and small inclusion bodies and apoptotic vesicles are seen.