What is Ebola?
- Ebola virus disease (also called Ebola hemorrhagic disease) is an infectious and fatal disease caused by a deadly virus called the Ebola virus commonly affecting humans and primates (such as monkeys, gorillas, chimpanzees).
- Ebola virus first appeared simultaneously in two regions in 1976 in Africa
- Nzara region in Sudan
- Yambuku region in Democratic Republic of Congo, near Ebola river
- Ebola virus is also called a hemorrhagic disease because the bleeding occurs during the course of its illness.
Epidemiology
- It is a deadly virus that can kill in a short period of time.
- This virus is enveloped, non-segmented, filamentous with negative-strand RNA virus.
- They belong to the order: Mononegavirales, and family: Filoviridae.
- Genus: Ebola Virus (named after the Ebola River in Africa where it was first found).
- Natural host are fruit bats of pteropodidae family
- Incubation period: 2-21 days. Patient is not contagious during the incubation period.
- It is considered to be an animal-borne (vector-borne) virus. Primarily sources being in bats, monkeys, chimpanzees, apes, etc.
- It needs a host to survive
Geographic spread
The Ebola Virus outbreak primarily occurred in remote villages of Central and West Africa near tropical rainforests and it has also spread to cities of Africa too. Ebola virus is identified in the countries of Africa such as
- Sudan
- Uganda
- Democratic Republic of Congo
- Ivory Coast
- Gabon
- Guinea
- Liberia
- Sierra Leone
- Nigeria
- Senegal
Besides, it also affected
- Philippines and People’s Republic China (Reston ebolavirus species)
Outbreak history
The first outbreak occurred in the Democratic Republic of Congo (formerly known as Zaire) in 1976.
The largest and most complex on-going outbreak is occurring in West African countries started in March 2014, these include-
- Guinea
- Liberia
- Sierra Leone
- Nigeria
- Senegal
None of the previous outbreak has developed into a pandemic
High-risk groups are
- Forest dwellers
- Bushmeat hunters
- Health workers
- Relatives of infected patients
- Lab technicians
- Corpse handlers
- Funeral attendees
Species of Ebola
- Reston ebolavirus was first discovered in Reston, USA.
- Zaire
- Sudan
- Tai
- Bundibugyo
- Bombali
- Ebola, Zaire, Sudan, and Tai viruses are known to cause disease in humans.
- Reston virus found in the Philippines and People’s Republic of China can affect humans, but no significant illness, disease manifestations, or deaths have been found so far. It is found to cause illness in nonhuman primates and pigs.
- Bombali virus was recently identified in bats
- Zaire ebolavirus is the deadliest of them all and responsible for the largest outbreak
Structure of the virus
Length- about 19 kb
Genes are arranged linearly coding for seven structural proteins:
- Nucleoprotein (NP)
- Polymerase cofactor (VP35, VP40)
- GP
- Transcription activator (VP30, VP24) and
- RNA polymerase (L)
- GP (transmembrane protein) is responsible for receptor binding and membrane fusion
Mode of transmission
- Animal to human transmission-
- Ebola was introduced in the human population through close contact with the blood, secretions, or other body fluids of infected wild animals such as fruit bats, nonhuman primates (apes, monkeys, etc. )
- Consumption of raw meat
- Human to Human transmission-
Direct contact (through skin cut or mucous membrane) with
- Blood or body fluids of a sick person (saliva, urine, feces, vomit, semen)
- Objects which are contaminated with infected body fluids
- Infected wild animals
- Unsterilized needles
- Sexual contact with an infected person (via semen). It was found that the Ebola virus can be isolated from seminal fluid for 82 days after the onset of symptoms
Ebola virus is not an airborne virus and does not spread by air droplets/aerosols
Pathophysiology
- Target cells of the virus: Endothelial cells, mononuclear phagocytes, hepatocytes
- After infection, a secretory glycoprotein known as the Ebola virus glycoprotein is synthesized
- The Ebola virus glycoprotein (GP) forms a complex which binds the virus to the endothelial cells lining the blood vessels. Thus, it interferes with the signaling of the neutrophils and allows the virus to evade the immune system by inhibiting the activation of the neutrophils.
- Viral replication takes place in large number and colonizes the host cells
- The virus is also carried throughout the entire body (such as lymph nodes, liver, lungs, spleen, etc. ) resulting in extensive tissue damage. The virus affects almost every tissue of the body except the bones and muscles.
- The virus triggers the release of pro-inflammatory cytokines resulting in clot impairment thus creating blood clots.
- Blood clots go towards the organs (such as lungs, eyeballs, etc.) causing both internal and external bleeding.
- The virus resides in the immunologically privileged sites of the body such as the testes, the interior of the eye, placenta, central nervous system, cerebrospinal fluid and thus is shielded from the body’s immune system.
- The disease could progress to multi-organ failure, septic shock, and eventually death within 6-10 days.
Clinical features of Ebola virus disease
Symptoms appear anytime between 2-21 days, commonly between 8-10 days.
The patient only becomes contagious once he/she begins to show symptoms
Lab findings
- Low white cell count
- Low platelets
- Elevated liver enzymes
Diagnosis
Initial diagnosis is difficult since the early symptoms are nonspecific to Ebola infection.
Sample collection for Ebola virus disease
- The specimen should be taken only after the onset of symptoms.
- It takes up to 3 days after the onset of symptoms for the virus to reach detectable levels.
- A minimum of 4 ml blood should be taken for sample testing.
- Sample from an infected person is highly contagious and it should be transported with caution, in a leak-proof container.
- In case of a post-mortem diagnosis, tissue samples must be taken from the liver, spleen, bone marrow, kidney, lungs, etc.
Differential diagnosis
- Dengue
- Malaria
- Typhoid fever
- Shigellosis
- Cholera
- Leptospirosis
- Rickettsiosis
- Relapsing fever
Management
Conservative managements are done to improve the condition of the patients and improve survival-
- Rehydration with an oral solution or intravenous fluid containing electrolytes
- Maintenance of blood pressure
- Proper oxygenation
- Pain control with analgesics
- Nutritional support
- Treating secondary bacterial infections
- Severely ill patients need intensive care support
Medicines for Ebola virus disease
Prognosis
- Poor prognosis due to High fatal rate (fatality rate 80-90%).
- Morbidity and mortality rates are very high and they vary (20-90%) with the different strains of ebola virus.
- The most lethal Ebola virus subtype is the Zaire Ebola virus (mortality rate as high as 88%).
Prevention
- Avoid contact with infected patients
- Wearing gloves during hospital procedures
- Wash hands frequently
- Isolating the infected individuals
- Practice nurse barrier techniques
- Proper sterilization and disposal of equipment (such as needles, syringes, etc.)
- Use of Personal Protection Equipments (PPE) for health workers
- Safe disposal of the dead bodies
- Screening of travelers from affected countries in airports, seaports, etc.
- Quarantine and observation of suspected cases for 21 days from exposure
- Avoid eating bushmeat (meat of wild animals) and undercooked meat
Vaccination
- The first approved vaccine against ebolavirus is rVSV-ZEBOV (called Ervebo™).
- It was first approved by the U.S. Food and Drug Administration (FDA) on December 19, 2019.
- Dose- Single dose is proved to be safe and effective against the Zaire ebolavirus species.
- It is recommended for individuals above 18 years of age (except pregnant and breastfeeding women).
Bioterrorism
Research and experiments have shown that the Ebola virus can be used as a biological weapon, although the Ebola virus is unstable when removed from a human/animal host making it unlikely for weaponization.
Conclusion
- Ebola virus disease is an extremely virulent and a newly emerging deadly infection
- It has the ability to cause high casualty with large outbreaks
- Raising awareness of the risk factors of Ebola virus infection and preventive measures can help individuals to reduce human infections and deaths
