In 1967 many cases died because of a disease outbreak manifest by fever and hemorrhage in central Africa , Democratic Republic of the Congo near Ebola river . Also there was another outbreak in South Sudan (850km away from the first outbreak location).
The 2 outbreaks were caused by two genetically different viruses: Zaire ebolavirus and Sudan ebolavirus. That means the 2 events are not related and came from different sources.
Ebola occurs sporadically in unpredictable outbreaks, In between outbreaks Ebola remains hidden in a non-human reservoir (probably Bats).
2014 Ebola outbreak one of the largest in history and first in west Africa , there was 10,114 cases and 4,912 deaths. controlling of this outbreak was challenging because of limited health care and limited supplies and ability to tract contacts.
Ebola virus is a single stranded RNA, encased a lipid envelop, it is member of Ebolavirus genus in the filoviridea family of viruses.
there is 5 species of Ebolavirus named by region:
- Zaire virus
- Sudan virus
- Ivory coast
- Bundibugyo virus
- Reston virus
Diffrent subtypes have different severities , but the first 4 strains (in bold) are lethal to humans.
Origin and Transmission of Ebola virus :
The natural reservoir of Ebola virus remains unconfirmed, but it’s believed that the virus is zoonotic from bats and nonhuman primates (chimpanzees, apes, monkeys) . Transmission from infected animal to human occurs by direct contact with blood, body fluid and tissues of infected animals or by consumption of wild animal meat “bush meat”.
Human to human transmission occurs by direct contact with blood, body fluid (urine, feces,vomit,sweat) and tissues of Ebola patient. Indirect transmission occurs by touching contaminated object ( needles and fomites).
Ebola virus is not readily transmitted through airborne routes or ingestion. But the nosocomial transmission is possible in health care providers ( doctors and nurses ) but has not occurred in actual outbreak settings . *
Pathogenesis of Ebola virus :
When the virus enters the body via infected blood or body fluids , it enter the cells and start replicating in monocytes , macrophages and dendretic cells which help in transmitting the virus to the whole body via lymphatic system.
After infection, the Virus forms Glycoprotein called Ebola virus Glycoprotein , which help in binding of the virus and Macrophages/ neutrophils, Dendritic cells, and Endothelial cells of blood vessels.
Ebola virus uses Ebola virus Glycoprotein to invade Macrophage and Neutrophil, then inhibit early steps of their activation. This inactivation allows the virus to evade immune system, colonize the host cells, and begin to replicate in large number. Macrophages infected with Ebola virus produce different cytokines and nitric oxide (NO) . Breakdown products of necrotic cells also stimulate the release of the same cytokines .
These cytokines are responsible for the fever, malaise, vasodilatation, increased vascular permeability, hypotension, and shock of ebola virus disease .
Hepatocellular necrosis lead to dysregulation of clotting factors and coagulopathy. Adrenocortical necrosis lead to hypotension and impaired steroid synthesis.
Ebola virus incubation period :
Incubation period is the duration between first exposure to the virus and when the sign and symptom of disease caused by the virus first appear.
Ebola virus incubation period is usually 2 to 21 days, the reported median incubation period is 8 to 10 days.
presentation of Ebola:
Ebola causes viral hemorrhagic fever with sudden onset of nonspecific symptoms:
- Nausea, vomiting and diarrhea
After 5 to 7 days patients develop diffuse erythematous, nonpruritic maculopapular rash on the the face, neck, trunk, and arms .
Gastrointestinal sign and symptoms may lead to severe fluid loss, dehydration, hypotension, and shock .
Severe form of Ebola disease can present with hemorrhagic and multi-organ dysfunction symptoms . Hemorrhagic symptoms include blood in the stool , petechiae, ecchymoses, oozing from venipuncture sites, and/or mucosal bleeding .
Directly prior to death, patient may experience tachypnea, hypotention, anuria , hiccups and coma.
fatality rate can range from 40% to 90% .
Ebola has a very similar presentation to many other diseases, like Any viral hemorrhagic fever ( Marburg virus , lassa virus , Dengue fever , yellow fever ) and other condition such as : Malaria, Typhoid fever, Meningococcemia, Influenza and enterohemorrhagic E.coli.
Travel and contact history is the most essential component of diagnosing Ebola.
It is extremely improbable that an individual with symptoms and sign of Ebola actually has Ebola, unless one of the following occurred within the preceding 21-25 days:
- Travel through an area currently affected by an Ebola epidemic.
- Direct physical contact with bats, rodent or primates in an area where Ebola is thought to be endemic.
- Direct physical contact with a patient actively suffering from Ebola.
Diagnosis is confirmed by detecting Ebola RNA sequences in blood using reverse transcriptase polymerase chain reaction (RT-PCR). this test is believed to be highly sensitive and specific when performed between day 3 and 10 after symptoms onset.
Antibody testing can also be performed , to either:
- Investigate a diagnosis in a patient with a high pretest probability but negative RT-PCR
- Diagnosis a case outside of the day 3-10 window.
- Identify prior Ebola exposure in a patient now recovered.
Ebola patient have laboratory findings in common :
- Abnormal hematocrit
- Transaminase elevations
- Prothrombin (PT) and partial thromboplastin times (PTT) can be prolonged
- Proteinuria, elevated blood urea nitrogen and creatinine
- hyponatremia, hypokalemia, hyperkalemia, hypomagnesemia, and hypocalcemia
Ebola Treatment :
Standard of care is supportive treatment (e.g. IV fluid, conventional transfusions, vasopressors, correction of electrolytes abnormalities).
All more specific forms of treatment are best considered experimental :
- Antibody preparation
by transfusion of whole blood or plasma from people who survived infection or by injection of Monoclonal antibodies (e.g. ZMapp)
e.g. brincidofovir, favipiravir, BCX4430, TKM-Ebola
Ebola Prevention :
On December 19, 2019 Ebola vaccine rVSV-ZEBOV ( Ervebo ) was approved by FDA as a safe vaccine against the Zaire ebolavirus species of ebolavirus. https://www.niaid.nih.gov/diseases-conditions/ebola-vaccines
Infection prevention precautions are important even after vaccination by strict quarantine of individuals with suspected or confirmed Ebola , contact tracing , close monitoring for symptoms in any individual who has been potentially exposed to Ebola and proper use of personal protective equipment (PPE) by healthcare workers.
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