Ebola Hemorrhagic Fever (EHF) is an acute hemorrhagic infectious disease caused by the Ebola virus (Ebolavirus). People are infected mainly through contact with 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 now prevalent mainly in Uganda, Congo, Gabon, Sudan, Côte d’Ivoire, South Africa, Guinea, Liberia, Sierra Leone and other African countries.
I. Disease overview
(A) Pathogenesis.
Ebola virus belongs to the filoviridae family (Filiviridae), 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, Bendibugio, Taï Forest and Leston 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 has 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. 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
Ebola-infected humans and non-human primates 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, Fulvous pre-shoulder fruit bats and small collared fruit bats, but their mode of circulation in nature is not known.
2. Transmission routes
Contact transmission is the most important route of transmission of the disease. It can be transmitted through contact with various body fluids, secretions, excreta and their contaminants from patients and infected animals.
Patients can maintain high levels of virus in their blood after infection, and health care workers are susceptible to infection without strict protective measures during treatment, care of patients, or disposal of patients’ bodies. Intra-hospital transmission is an important factor contributing to Ebola hemorrhagic fever outbreaks and epidemics.
According to the literature, the virus can be isolated from the semen of Ebola hemorrhagic fever patients, 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 alert and well protected.
3. Population susceptibility and season of onset
Humans are generally susceptible to Ebola virus. The incidence is mainly in adults, which is related to exposure or exposure to more opportunities. There is no information to suggest that there is a difference in incidence between the sexes.
No significant seasonality in the onset of Ebola hemorrhagic fever has been found.
(iii) Clinical presentation.
The incubation period of the disease is 2-21 days, usually 5-12 days. The incubation period has not been found to be infectious.
Patients have an acute onset with high fever, chills, extreme malaise, headache, myalgia, sore throat, conjunctival congestion and relatively slow pulse. This may be followed by nausea, vomiting, abdominal pain, diarrhea, mucus stools or bloody stools, and a skin rash.
Severely ill patients may have altered mental status, such as drowsiness and delirium. The patient may also show different degrees of bleeding, including bleeding from the nose, mouth, conjunctiva, gastrointestinal tract, vagina, skin or hemoptysis, hematuria, etc. Hypotension and shock may occur. It can be complicated by myocarditis, pneumonia and other multi-organ damage.
(D) Pathological features.
The main pathological changes are hemorrhage of the skin, mucous membranes 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.
II. Diagnosis, treatment and reporting
The early clinical symptoms of Ebola hemorrhagic fever are not specific, and care should be taken to differentiate it from other viral hemorrhagic fevers such as Lassa fever, yellow fever, Marburg hemorrhagic fever, Crimean-Congo hemorrhagic fever, and renal syndrome hemorrhagic fever. Definitive diagnosis relies mainly on laboratory tests. There is no specific treatment for Ebola hemorrhagic fever, but mainly symptomatic and supportive treatment, see the “Ebola hemorrhagic fever treatment plan”.
When medical institutions at all levels find suspected or confirmed cases of Ebola hemorrhagic fever that meet the case definition, they should make a direct report through the national disease surveillance information reporting system within 2 hours, and select “Ebola hemorrhagic fever” in the category of “other infectious diseases”. “. Report public health emergencies or related information in accordance with the requirements of the “National Public Health Emergencies Related Information Reporting Management (Trial)”.
III. Laboratory tests
(A) pathogenetic testing.
1, viral antigen detection: as Ebola hemorrhagic fever has high titer viraemia, ELISA and other methods can be used to detect viral antigens in blood specimens. Generally within 2-3 weeks after the onset of the disease, virus-specific antigens can be detected in the patient’s blood specimens. Immunofluorescence and immunohistochemistry can be used to detect viral antigens in animal and suspected case autopsy specimens.
2. Nucleic acid detection: RT-PCR and other nucleic acid amplification methods are used for detection. Viral nucleic acid can generally be detected in blood specimens from patients within 2 weeks after the onset of the disease, with a high detection rate in specimens within 1 week after the onset of the disease.
3.Virus isolation: Blood specimens were collected from patients in the acute febrile phase, and virus was isolated and cultured using Vero, Hela and other cells, and the virus isolation rate of blood specimens within 1 week of onset was generally high.
(B) Serological testing.
According to the literature, specific IgM antibodies can be detected from the sera of patients as early as 2 days after the onset of the disease, and IgM antibodies can be maintained for several months. Ig G antibodies can be detected 7-10 days after the onset of disease and can be maintained for several years. In most patients, antibodies appear 10-14 days after the onset of disease, but in some severe cases, antibodies are never detected. A positive IgM antibody or a 4-fold or more elevated IgG antibody titer in two blood specimens separated by 1 week or more is diagnostic.
Serum-specific IgM antibodies are mostly detected by IgM capture ELISA; serum-specific IgG antibodies are mostly detected by ELISA, immunofluorescence and other methods.
IV. Preventive and control measures
At present, there is no vaccine to prevent Ebola hemorrhagic fever, isolation and control of the source of infection and strengthen personal protection is the key measures to prevent and control Ebola hemorrhagic fever.
(A) case and contact management.
Once a suspected case is found, strict isolation measures should be taken to control the source of infection and prevent the spread of the epidemic.
Close contacts are those who may come into contact with the patient’s blood, secretions, excretions, etc., after the onset of the disease, such as those who accompany, treat, transfer patients and dispose of the body. Close contacts are tracked and medically observed. The period of medical observation is 21 days from the date of last exposure. Once clinical symptoms such as fever, malaise and sore throat appear during medical observation, isolation should be carried out immediately and specimens should be collected for testing.
After the death of a patient, the handling and transfer of the body should be minimized. The corpse should be disinfected and wrapped with sealed leak-proof items and promptly incinerated or disposed of according to relevant regulations. When an autopsy is required, it should be performed in accordance with the “Regulations for Autopsy Examination of Patients with Infectious Diseases or Suspected Infectious Diseases”.
(B) Infection control in hospitals.
Do a good job of infection control in the hospital in accordance with the requirements of the “Hospital Infection Management Code”.
1. Strengthen personal protection.
On the basis of standard protection, contact protection and respiratory protection should be done.
2. Strict disinfection of patients’ secretions, excretions and their contaminated items.
Patient’s secretions and excretions need to be strictly disinfected and can be treated by chemical methods; infectious medical dirt (contaminated needles, syringes, etc.) can be treated by incineration or high-pressure steam disinfection.
Human skin exposed to suspected Ebola hemorrhagic fever patient’s body fluids, secretions or excretions, should be immediately washed thoroughly with water or soapy water, or disinfected with 0.5% iodophor disinfectant, 75% alcohol chlorhexidine wipe, use water or soapy water to thoroughly clean; mucous membranes should be rinsed with large amounts of water or 0.05% iodophor.
3, strengthen laboratory biosafety.
All experimental activities involving Ebola virus should be carried out in strict accordance with the relevant provisions of China’s laboratory biosafety.
Specimens should be collected for personal protection. Specimens should be placed in accordance with the ICAO Class A packaging and transport materials, in accordance with the “highly pathogenic microorganisms that can infect humans (virulent) strains or samples transport management regulations” requirements for transport to laboratories with Ebola virus-related experimental activities.
Laboratories conducting relevant experimental activities should have the appropriate biosafety level and experimental activities qualification. The corresponding experimental activities required biosafety laboratory level should be in line with the provisions of the “List of pathogenic microorganisms transmitted on earth”, virus culture in the BSL-4 laboratory, animal infection experiments in the ABSL-4 laboratory, the operation of uncultured infectious material in the BSL-3 laboratory, the operation of inactivated material in the BSL-2 laboratory, the operation of non-infectious material in the BSL-1 laboratory.
4.Epidemiological investigation
It mainly includes investigating the activity history of the case during the onset of the disease, searching for close contacts and co-exposed persons, and searching for the source of infection.
5.Public awareness and education, good risk communication
Actively publicize the prevention and treatment of Ebola hemorrhagic fever and raise public awareness of self-protection. Respond to social concerns in a timely manner.