What is Ebola virus disease and should I be worried?

A very deadly outbreak of Ebola virus disease (EVD) has occurred in West Africa affecting the countries of Guinea, Sierra Leone, and Liberia.  It has infected approximately 1200 people and killed about 700 of them. What makes this disease so scary is that the fatality rate is very high historically from 50-90% of infected people die.

EVD first appeared in 1976 in Zaire where it killed about 300 people. Since then it has reappeared sporadically in various African countries, but the death toll has been relatively light -- less than 2000 altogether over the past 40 years not including this year. In Figure 1, you can see that the current outbreak in West Africa is the worst by far on record.

Figure 1. EVD cases by year (chart from Vox.com [link]).

EVD is caused by the Ebola virus, which is a virus whose genome is a linear, single-stranded, negative-sense piece of RNA. Ebola virus can infect a wide range of cells but its most important targets are the immune cell macrophages and monocytes, which results in a powerful inflammatory response as well as disruption of immune system functioning, producing the high fever and the inability of the body to get rid of the virus. A second important target are endothelial cells (e.g. cells that line the blood vessels), and disruption of blood vessel integrity leads to massive bleeding (EV causes "hemorrhagic fever"). Once inside of a cell the virus makes more copies of itself, and eventually the progeny bust out killing the infected cell [ref1].

The onset of symptoms after infection is rapid from 2 to 21 days. According to the World Health Organization (WHO), the illness is characterized "by the sudden onset of fever, intense weakness, muscle pain, headache and sore throat. This is followed by vomiting, diarrhoea, rash, impaired kidney and liver function, and in some cases, both internal and external bleeding. Laboratory findings include low white blood cell and platelet counts and elevated liver enzymes."

One complicating issue has been that EBV early symptoms resemble those of other diseases such as malaria, typhoid fever, or even flu which are much more common. However, now there are direct tests for Ebola virus proteins and/or antibodies against EV which can confirm the diagnosis. As the patient's condition worsens, death may arise caused by the shock from loss of blood volume or from the complications caused by excessive blood clotting as the body tries to cope with the blood leakage [ref2].

EVD transmission requires direct contact with blood or bodily fluids of an infected person and has not been observed via aerosol transmission. The last point is very important because the absence of aerosol transmission (e.g. sneezing, coughing) makes EVD much less transmissible. On the other hand, poor confinement techniques in hospitals in the affected areas such as reuse of needles and syringes and inadequate protective clothing (gloves and surgical masks) has contributed to its spread. Overall there has not been any large EVD epidemics because of the high fatality rate, rapid death, low transmissibility, and occurrence in isolated areas.

The persistence of the disease in Africa is likely due to its presence in another animal species endemic to Africa i.e. fruit bats. EV has been found in fruit bats and it is known that some people in Africa eat fruit bats.

Unfortunately no treatment exists that eradicates Ebola virus yet. Instead the patient's symptoms are treated which involves replenishing fluids, maintaining blood pressure, transfusing blood, and treating secondary infections. One of the bigger complications is caused by the excessive (and conflicting) bleeding and clotting. At times during the treatment a patient may receive procoagulants (to stop bleeding), while at other times she may receive anticoagulants (to stop clotting) [ref3].

Why aren't there better treatments? Sarah Kliff at Vox.com has an interesting article on one reason why no EVD vaccines exist today:

Bausch says that the obstacle to developing an Ebola vaccine isn't the science; researchers have actually made really great strides in figuring out how to fight back against Ebola and the Marburg virus, a similar disease.

"We now have a couple of different vaccine platforms that have shown to be protective with non-human primates," says Bausch, who has received awards for his work containing disease outbreaks in Uganda. He is currently stationed in Lima, Peru, as the director of the emerging infections department of Naval Medical Research Unit 6.

The problem, instead, is the economics of drug development. Pharmaceutical companies have little incentive to pour research and development dollars into curing a disease that surfaces sporadically in low-income, African countries. They aren't likely to see a large pay-off at the end — and could stand to lose money.

Another promising treatment would be to inject patients with antisera (antibodies) against Ebola virus produced by someone or something else (instead of making one's own anti-EV antibodies which could be stimulated by a vaccine). Indeed one source of antisera is from patients who have recovered from the disease. Another source would be from horses or goats or monkeys exposed to the virus; preliminary results have been encouraging. It is possible such antisera is used on an experimental basis during the current outbreak.

Should I be worried? Unless you live in Western Africa, the answer is a resounding no.

Yesterday, an American doctor infected by EVD in Liberia while treating patients was flown to Emory hospital in Atlanta. Special precautions were made to handle his admission (i.e. special isolation unit). Again EV is not highly contagious because transmission requires direct contact with bodily fluids that contain the virus. A modern hospital taking the proper precautions would make the threat of spread negligible.

Yet not everyone agreed with the CDC decision to transport the two infected Americans back to the U.S. where they can receive the best care modern medicine can offer:

Figure 2. Evidently Donald Trump is an expert in infectious disease.

It is obvious that Donald Trump is not an expert in infectious disease and intentionally or not is inciting fear and misunderstanding. This type of fear-mongering is very disappointing. Should we listen to Trump or the words of an expert?

There is no cure for the Ebola virus ravaging West Africa, and it kills most of those it infects. But when Bruce Ribner got the call that two Americans stricken with Ebola were headed to his hospital, he did not hesitate.

"I said, 'Hey, we've been practicing for this for 12 years,'" he said.

Ribner is an infectious disease specialist who oversees the isolation ward at Emory University Hospital, which is designed to house people suffering from highly lethal illnesses that could decimate a population if not contained.

Finally for some perspective, approximately 1.6 million people died of AIDS last year and almost 40 million people have died in total, which makes it a much greater danger to the typical person.

In closing, one consequence of this deadly Ebola virus outbreak is that it has focused attention on finding better treatments. Hopefully, the publicity lends momentum to efforts to develop a vaccine or effective antisera or some other cure so that Ebola virus disease will disappear as a scourge to humans like smallpox or plague. I am optimistic that effective treatments will be found soon.