All About Ebola

Ebola epidemics have spread through parts of Africa since 1976. The most recent outbreak started in 2018, and was to be declared over in April this year (2020). Unfortunately, days before the announcement of the end of the epidemic, 3 new patients were diagnosed with Ebola virus and succumbed to the disease (Yeung, 2020). This article will give an overview of Ebola and address the history, microbiology, transmission, presentation, and treatment of the disease. It will also briefly discuss the newly developed vaccine to prevent the infection.

The first case of Ebola was diagnosed in the Democratic Republic of Congo (DRC) in Africa in 1976. This initial outbreak had a total of 319 cases with a 90% mortality rate (Smith, 2006). A timeline of significant outbreaks in Africa is provided below.

 (Preston, 2020)

Ebola is an RNA virus that is alleged to have originated in fruit bats (WHO, 2016). The virus belongs to the family of Filoviruses, which are closely related in genome to paramyxoviruses (such as measles and mumps), parainfluenza virus and respiratory syncytial virus (Preston, 2012). Currently there are 5 subtypes of Ebola virus:

- Zaire

- Sudan

- Bundibugyo

- Tai forest

- Reston

With Reston being the only type unable to cause disease in humans.

The Ebola virus has a small genome, consisting of 19 000 base pairs, which encode for a mere 7 proteins (Smith, 2006). From the related literature, it appears that the most functionally important viral protein is the glycoprotein, of which there are 2 types. The first is the envelope glycoprotein, a structural protein that allows the virus to bind to the host cell in order to enter and replicate. The second type is the secreted glycoprotein. This form suppresses the immune system and results in the body being unable to clear the virus. The secreted form is also cytotoxic and causes cell rounding and apoptosis (Smith, 2006).

The Ebola virus is transmitted in 5 main ways:

- 1) Contact with infected fruit bats, through their saliva, faeces, or blood;

- 2) Contact with bodily fluid of infected chimpanzees;

- 3) Human-to-human transmission by direct contact with infected person or with items contaminated with infected bodily fluids;

- 4) Sexual transmission – the virus may remain in semen for up to 12 months following Ebola virus infection;

- 5) Transplacental to from mother-to-foetus (Smith, 2006; Preston, 2012).

The incubation period before the onset of symptoms is reported as 5 – 21 days according to the WHO (2016). The wide range is due the period being dependent on the route of exposure and the amount of virus the patient has come into contact with. For example, a patient exposed to a large amount of infected bodily fluid with a high viral load will have a much shorter incubation period. The convalescence period is lengthy and can be as long as 82 days (Smith, 2006).

The initial presentation of the disease includes the following symptoms:

- Fever

- Headache

- Abdominal pain

- Nausea

- Fatigue

- General illness

- Malaise

With progression of the disease the following is experienced:

- Severe sore throat

- Jaundice

- Vomiting

- Anorexia

- Black diarrhoea

- Mask-like face and depersonalization

On approximately day 5 of the disease the patient may experience a short-lived rash that peels. Following this there may be coagulation disorders, multiple organ failure (due to blood clotting, liquefaction and necrosis), and haemorrhage (Smith, 2006;WHO, 2016). In the terminal phase of the disease, patients may bleed into their lungs, stomach and intestines, and under their skin. Parts of their intestines may be sloughed off and vomited, causing a black vomit consisting of arterial blood, virus, and tissue. This vomit is highly contagious (Preston, 2012).

There are 2 prominent pathological processes that result in death of patients from Ebola: haemorrhage and disseminated intravascular coagulopathy (DIC). This occurs as the Ebola virus infects many different cells resulting in the release of chemicals, including cytokines, chemokines, and histamine. This results in fever, tissue swelling, and increased vascular permeability leading to a significant drop in blood pressure and, ultimately, shock. The endothelial damage also causes a cascade of blood clotting, which leads to consumption of factors and platelets resulting in haemorrhage (Smith, 2006). Ebola attacks connective tissue with a particular aggressiveness, multiplying inside the cells and liquefying the tissue. This leads to a maculopapular rash, which may cause spontaneous tears in the skin and result in haemorrhage between the skin and underlying tissues (Preston, 2012).

The diagnostic tests for Ebola include:

- Indirect fluorescence assay

- Enzyme-linked immunosorbent assay (ELISA)

- Real-time polymerase chain reaction (RT-PCR)

- Serum neutralization test

- Electron microscopy

- Cell culture isolation

- Antigen-capture detection test (WHO, 2016)

The gold standard test for a current Ebola infection is the RT-PCR and for past infection is an antibody test such as an ELISA (CDC, 2020).

There is currently no approved treatment for Ebola infection. The mainstay of patient care is ensuring the maintenance of adequate hydration by administering fluids and electrolytes (WHO, 2016). Attempts were made in the DRC to give a passive transfer of immunoglobulin from convalescent patients to those in early stages of disease, however the effectiveness was inconclusive (Smith, 2006). A new treatment is currently being experimented with and is in the form of a lipid nanoparticle – TKM-130803 siRNA, however results shown in a study done by Scott et al. (2020) were not promising.

Although no treatment for Ebola is available, there is a newly developed vaccine. This is named the rVSV-ZEBOV (trade name Ervebo) and was approved by the U.S Food and Drug Administration (FDA) on the 19 December 2019 (CDC, 2020). It has already resulted in the eradication of Ebola from Guinea in 2019 and is currently licensed in 4 African countries: DRC, Burundi, Ghana, and Zambia (WHO, 2020). There is promise that vaccination will result in the eradication of the virus from these countries as well.

References

Cdc.gov. 2020. Diagnosis | Ebola (Ebola Virus Disease) | CDC. [online] Available at: <https://www.cdc.gov/vhf/ebola/diagnosis/index.html> [Accessed 16 April 2020].

Cdc.gov. 2020. Prevention And Vaccine | Ebola (Ebola Virus Disease) | CDC. [online] Available at: <https://www.cdc.gov/vhf/ebola/prevention/index.html> [Accessed 16 April 2020].

Preston, R., 2012. Hot Zone. New York: Random House US.

Preston, R., 2020. Ebola Timeline. [online] HOT ZONE. Available at: <https://hotzoneebola.weebly.com/ebola-timeline.html> [Accessed 16 April 2020].

Scott, J., Sharma, R., Meredith, L., Dunning, J., Moore, C., Sahr, F., Ward, S., Goodfellow, I. and Horby, P., 2020. Pharmacokinetics Of TKM-130803 In Sierra Leonean Patients With Ebola Virus Disease: Plasma Concentrations Exceed Target Levels, With Drug Accumulation In The Most Severe Patients. [online] ScienceDirect. Available at: <https://www.sciencedirect.com/science/article/pii/S2352396419308163> [Accessed 16 April 2020].

Smith, T., 2006. Ebola. Philadelphia: Chelsea House Publishers.

WHO. 2016. Ebola Microbiology. [video] Available at: <https://www.youtube.com/watch?v=030mne4kSew> [Accessed 16 April 2020].

Who.int. 2020. Four Countries In The African Region License Vaccine In Milestone For Ebola Prevention. [online] Available at: <https://www.who.int/news-room/detail/14-02-2020-four-countries-in-the-african-region-license-vaccine-in-milestone-for-ebola-prevention> [Accessed 16 April 2020].

Yeung, P., 2020. Three New Ebola Cases Detected In Democratic Republic Of The Congo. [online] New Scientist. Available at: <https://www.newscientist.com/article/2240430-three-new-ebola-cases-detected-in-democratic-republic-of-the-congo/> [Accessed 16 April 2020].