Ebola Virus Disease; a closer look
On 17 July 2019, the WHO declared the ebola virus disease (EVD) outbreak in the Democratic Republic of Congo a public health emergency of international concern. With health authorities struggling to contain the country’s deadly outbreak where more than 1,650 people have died since it began nearly one year ago, we spoke with Doctor Mike Catton, Deputy Director at The Peter Doherty Institute for Infection and Immunity in Melbourne to learn more about this severe, and often fatal, haemorrhagic disease.
“EVD is a rare but severe, often fatal illness in humans. Popular media often use ‘ebola’ interchangeably, referring to both a disease and a virus. However, EVD is caused by ebola viruses, of which there are five species. Since 1976 when ebola viruses were first discovered, human outbreaks have been caused by two of these species: Zaire ebola virus and Sudan ebola virus, and have occurred in sub-Saharan Africa. There have never been cases of EVD in Australasia.
“It is understood that ebola viruses are ancient viruses which have infected mammals such as bats for millions of years. Occasionally ebola virus spreads into larger animals such as primates, and from time to time there is onward spread into humans which may then cause outbreaks. It is spread in the human population through human-to-human transmission. Overall death rates are about 50% for Sudan EVD, and 80% for Zaire EVD.”
EVD is not an airborne infection, it is transmitted in humans though close and direct contact with infected bodily fluids, the most infectious being blood, faeces and vomit. It can also be transmitted indirectly, via contact with previously contaminated surfaces and objects, however this risk is low. The incubation period for EVD is from 2 to 21 days, and a person infected with ebola cannot spread the disease until they develop symptoms.
“Ebola disease tends to go through three phases. The onset of symptoms is sudden, but for the first few days these are non-specific symptoms of high fever, weakness, lethargy and muscle aches. This is followed by about a week of gastrointestinal symptoms such as nausea, vomiting and diarrhoea, which can be mild or severe. The survivors begin to recover at this point, but many patients progress to shock and failure of multiple organs. Uncommonly, abnormal bleeding such as gastrointestinal bleeding, haemorrhages in the eye, oral bleeding or leakage of blood into the skin can feature at this stage. However, this bleeding is more common in the movies than in real life. Death is common amongst patients that progress to shock,” said Dr Catton.
EVD is often difficult to clinically distinguish from other infectious diseases such as malaria, typhoid fever and meningitis. There are a number of diagnostic methods to confirm that symptoms are caused by Ebola virus infection, and it is strongly recommended that diagnostic tests which have undergone an independent and international evaluation be considered for use.
“These days, molecular testing for ebola virus genetic material is done using blood samples or swabs. This is called real-time polymerase chain reaction (RT-PCR) and is the standard testing approach for EVD. It is very accurate, very quick, taking only a few hours, and can be done even in quite spartan field laboratories set up at the site of outbreaks in Africa. Biocontainment laboratory facilities and/or equipment is used to keep the scientist safe during this step.
“Amplifying and detecting the ebola virus gene target from this genetic material is done on automated RT-PCR analysers and the results are visually displayed with computer software. The RT-PCR analysers can be made relatively small and portable, which allows for field use,” said Dr Catton.
There is still no fully validated treatment or vaccine for EVD, however early supportive care, with rehydration with oral and intravenous fluids and symptomatic treatment, improves survival. However, there have been exciting advances in recent years in terms of treatment for EVD including blood treatments, immune therapies and drug therapies.
“Early data on the effectiveness of some experimental antiviral drugs, and of cocktails of synthetic antibodies in treating EVD have shown promising results. There is also promising data on experimental ebola virus vaccines, and these have been used in field trials during recent outbreaks,” said Dr Catton.
Since the outbreak of EVD was declared in DRC in August 2018, a ring vaccination strategy has been implemented in North Kivu and Ituri provinces. In May 2019, the WHO reported that, since the outbreak began, more than 111,000 people in DRC have been vaccinated with an experimental vaccine called rVSV-ZEBOV-GP.
The unlicensed rVSV-ZEBOV-GP vaccine consists of an animal virus called vesicular stomatitis virus (VSV), which has been genetically engineered to contain a protein from the Zaire ebola virus, and therefore provokes an immune response to the ebola virus. Preliminary results released by the WHO confirm high efficacy of the vaccine against ebola, and a reduction in overall case fatality rates.
Despite this encouraging early data on rVSV-ZEBOV-GP, the outbreak of EVD in DRC has worsened recently due to violent attacks against aid workers and a communication break down between communities and response workers. In May 2019, the WHO’s Strategic Advisory Group of Experts released new guidelines to address these concerns.
The threat of an EVD outbreak in Australia is low. If a traveller has recently returned from a trip to an ebola virus high risk area, and presents either at the border, or to their doctor with symptoms consistent with EVD, then they are likely to be tested for the disease by an expert public health laboratory using RT-PCR.
Testing can be done accurately and fast in Australia. The national reference laboratory for African haemorrhagic fevers like EVD is the Doherty Institute, Melbourne. At this laboratory, testing is available around the clock, or support will be provided to the local laboratory as required.
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This article appeared in the July 2019 Edition of ePathWay which is an online magazine produced by the Royal College of Pathologists of Australasia (http://www.rcpa.edu.au/Library/Publications/ePathway).
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