36 Comments

The news is full of reports of an outbreak of Ebola in the west African country of Guinea. Ebola is one of a group of related viruses which cause viral haemorrhagic fever. There is no vaccine or treatment for these viruses. So far reports are that there have been at least 80 cases with 59 deaths.

Here’s a little FAQ for those of you wanting to know more about these amazing and terrifying viruses.

1. What is Ebola?

Ebola is one of two members of the Filoviridae family of single-stranded RNA viruses. The other member is Marburg. There are five types of Ebola virus, named after where outbreaks first appeared, and which differ in their mortality rates:
(i) Zaire ebolavirus (ZEBOV) – most frequent cause of outbreaks (last in the Democratic Republic of Congo 2008) and highest mortality rate (47-100%)
(ii) Sudan ebolavirus (SEBOV) – mortality rate of 42-65%, last outbreak in 2012 in Uganda
(iii) Reston ebolavirus (REBOV) – Discovered in 1989 when there was an outbreak of disease in laboratory macaques in Reston, Virginia, USA. Has since been found in nonhuman primates in Pennsylvania, Texas and Italy. Did not cause disease in exposed human laboratory workers*
(iv) Côte d’Ivoire ebolavirus (CIEBOV) (or Tai ebolavirus) – killed chimpanzees in Tai national park in 1994, only human case was in one of the scientists performing the necropsies on the infected chimps but they recovered
(v) Bundibugyo ebolavirus – two outbreaks to date (2007 in Uganda and 2012 in the Democratic Republic of Congo), mortality rate of 34-50%

2. How is Ebola transmitted?

The primary mode of transmission of Ebola is unknown. Bats are thought to be the most likely reservoir (1). Some people have caught Ebola from contact with or by eating infected bushmeat. Secondary spread occurs through direct contact with infected patients, their body fluids or remains, so family members, hospital workers and those burying the dead are at greatest risk. The incubation period for infection ranges from 2 to 21 days (mean 4-9 days).

An interesting paper was published in the journal Scientific Reports in 2012 in which piglets were inoculated oronasally with Zaire ebolavirus (2). The piglets had a high temperature and rapid breathing for a few days but soon recovered. But they were infectious, spreading the virus through the air to macaques who developed symptoms of Ebola infection and had to be euthanised.

3. What’s the largest recorded Ebola outbreak?

The biggest outbreak to date was in Uganda in 2000, when 425 people were infected with Sudan ebolavirus – 224 died. Ebola is a little like the great white shark of the virus world. Before this current outbreak, there had only been 2317 clinical cases and 1671 confirmed deaths in the last 50 years (3), a negligible number compared to many other infectious diseases.

4. Do people with viral haemmorrhagic fever really bleed out of every orifice before they die?

The name viral haemorrhagic fever is a bit of a misnomer. In less than 10% of Ebola cases, patients will experience bleeding from their mucous membranes, including those in the nose, gums, gastrointestinal tract and vagina. Death occurs by multiple organ failure. Most frequently infected people will have a fever with chills, malaise, joint and muscle pain. They also may have a rash. Other symptoms include nausea, diarrhoea, vomiting, stomach pains, throat and chest pain, a cough. From there patients experience severe headaches and confusion which can progress to delirium and coma.

5. Why is this such a big story?

With the exception of the dead chimps and the scientist who recovered in the Ivory Coast, Ebola has never been reported from west Africa; the majority of outbreaks have been in central Africa. What has alarmed many is that the cases have moved from forest communities to the capital city, Conakry. The capital has a port and airports and, with an estimated population of 2 million, will be difficult to quarantine should the need arise.

6. Can survivors continue to shed virus?

Yes. Survivors from an outbreak in 1995 in the Democratic Republic of the Congo which killed 244 of the 315 people infected, were followed for several months afterwards. Researchers tested their tears, sweat, faeces, urine, saliva, semen, and vaginal secretions. For semen, 4 of the 5 convalescents tested had at least 1 specimen that tested positive for Ebola genetic material. The latest semen sample was obtained over 3 months after the onset of infection (4). There were no cases of transmission from those individuals with positive semen samples.

* Go read Richard Preston’s book The Hot Zone, which is all about the outbreak in Reston.

Reference:
1. Leroy EM, Kumulungui B, Pourrut X, Rouquet P, Hassanin A, Yaba P, Délicat A, Paweska JT, Gonzalez JP, Swanepoel R (2005). Fruit bats as reservoirs of Ebola virus. Nature. 2005 Dec 1;438(7068):575-6.
2. Weingartl HM, Embury-Hyatt C, Nfon C, Leung A, Smith G, Kobinger G (2012). Transmission of Ebola virus from pigs to non-human primates. Sci Rep. 2012;2:811. doi: 10.1038/srep00811. Epub 2012 Nov 15.
3. Leroy EM, Gonzalez JP, Baize S (2011) Clin Microbiol Infect. 17(7):964-76. doi: 10.1111/j.1469-0691.2011.03535.x
4. Rowe A1, Bertolli J, Khan AS, Mukunu R, Muyembe-Tamfum JJ, Bressler D, Williams AJ, Peters CJ, Rodriguez L, Feldmann H, Nichol ST, Rollin PE, Ksiazek TG (1999). Clinical, virologic, and immunologic follow-up of convalescent Ebola hemorrhagic fever patients and their household contacts, Kikwit, Democratic Republic of the Congo. Commission de Lutte contre les Epidémies à Kikwit. J Infect Dis. 1999 Feb;179 Suppl 1:S28-35.