Ebola or Ebola virus disease (EVD) is a highly contagious disease caused by the Ebola virus. The Ebola virus is an enveloped single-stranded RNA virus belonging to the genera of Filoviruses. There are six species of Ebola virus, out of which the Zaire Ebola virus has caused the most devastating Ebola virus disease resulting in multi-organ failure and homeostatic imbalance in infected patients. The Ebola virus disease occurs in both primates and humans. In humans, it is caused by four Ebola virus species, namely Zaire virus, Sudan virus, Taï Forest virus, and Bundibugyo virus. It can infect people of all ages (from infants to the elderly). EVD was earlier known as Ebola hemorrhagic fever or EHF, but in 2014 it was renamed EVD as it is not just a febrile illness. The transmission of EVD is both zoonotic (animals to humans) and anthroponotic (humans to humans). In zoonotic transmission, humans become infected by physical contact with infected animals or meat. Human-to-human transmission can occur via contact with blood and/or body fluids from infected humans. Ebola virus can be transmitted through the skin even without bruises or cuts, body fluids, or fomites. In Western Africa, the Ebola virus disease sporadic outbreaks in the recent decade were a global public health threat. According to WHO-reported statistics, around 40% of gross mortality due to EVD was recorded in December 2013.

Symptoms

The symptoms of Ebola virus disease become apparent rapidly between 2 to 21 days of infection. The Ebola infection usually may become noticeable within 3 weeks. The infected patients are not contagious until apparent symptoms begin to manifest. The major early symptoms of EVD are fever, muscle pain, fatigue, sore throat, and headache. Subsequent symptoms include vomiting, diarrhea, rash, symptoms of impaired kidney and liver function, low platelet count as well as both internal and external bleeding. EVD begins typically as a febrile illness of a non-specific nature followed by gastrointestinal symptoms such as abdominal pain and diarrhea. In patients with high viral loads, with a dysregulated immune response, the disease progresses to complicated fatal multiple organ dysfunction syndromes. Whereas the patients usually with lower viral loads, have a lesser magnitude of disease severity and progression, as well as organ dysfunction.

Diagnosis

Laboratory-based diagnosis proves to be of utmost importance for the confirmation of EVD. The laboratory diagnosis has a huge role to play in rapid response to outbreaks. There are three ways of detecting the Ebola virus in suspected patients. These include serologic tests that evaluate host antibodies generated against the virus, antigen-based tests that detect viral proteins, and molecular tests that detect viral RNA sequences. However, to date, none of the tests have proven to demonstrate the ability to detect the Ebola virus before the onset of symptoms in patients. Serologic detection of antibodies was done by IFAT or indirect immunofluorescence antibody testing earlier, but currently, IgG/IgM antibody detection is done by ELISAs or enzyme-linked immunosorbent assays. The use of a rapid antigen detection test is further recommended under field settings. The advantage is early detection using antigen-based methods as detectable antigen exists in nearly all EVD patients by the third day of illness. In addition, sophisticated molecular detection techniques such as conventional reverse-transcriptase polymerase chain reaction or RT-PCR, as well as real-time reverse transcription-PCR techniques have now gained much popularity and efficiency regarding sensitivity and specificity. Real-time RT-PCR performed on blood samples has turned out to be the standard testing method for diagnosis of acute cases of EVD in the setting of an outbreak, while real-time RT-PCR on saliva samples has turned out to be the standard for postmortem testing.

Management

Supportive care for an infected person includes rehydration with oral or intravenous fluids as well as treatment with symptomatic therapy. Patient isolation and proper care of both patients and caregivers are of utmost priority. Good outbreak control measures depend on the implementation of a regimen of interventions; involving case management, contact tracing, and surveillance, along with a good laboratory service, safe burials, and social mobilization. Two monoclonal antibodies namely Inmazeb and Ebanga were approved in both children and adults for the treatment of Ebola virus infection, especially Zaire Ebola virus species by the US Food and Drug Administration (FDA) in late 2020. In addition, vaccines are always the protective gear for any infectious diseases. In late 2020, the vaccine Ervebo was approved by the US FDA and World Health Organization for use in persons of 18 years or older in gaining protection against the Zaire Ebola virus. Another set of two vaccines namely Zabdeno and Mvabea were granted and recommended marketing authorization by the European Medicines Agency in May 2020. Due to the extent of mortality and affected health workers in the past episodes of EVD outbreaks, concerns from all corners of the world have been raised to investigate extensively on precautionary measures, early diagnostics, and therapeutics for the disease. There is a potential arena of treatments regarding blood products, immune therapies, and drug therapies, which are currently being evaluated and this area needs to be addressed on an immediate basis in the future.