Ebola and Marburg Viruses – Filoviruses

00:01 The filoviridae viruses.

00:04 The filoviridae are mid-sized viruses that contain a filamentus, enveloped, and helical capsid.

00:11 They are linear with a single-stranded, negative-sense RNA genome, which means that they must carry an RNA-dependent RNA polymerase.

00:20 The important species that we'll talk about today are the Ebola virus, very recognizable from the colored photo micrograph on the right, and a related virus, the Marburg virus seen here.

00:33 The Ebola and the Marburg viruses have the same mechanism of transmission.

00:38 And this slide offered by the CDC, sort of, shows the typical collection of factors which ultimately, wind up in the humans being secondarily infected.

00:51 This starts with transmission between bats and other animals in the local area, typically the jungle, and these include other primates, small duiker, elk, etc., and so forth.

01:04 And between these animals, there's an ongoing cycle until an accidental exposure to humans occurs.

01:12 Rarely is this a bite from one those animals or exposure to urine, although that can happen.

01:19 More often, it is the human ingesting bushmeat or meat made from one of these animals that itself is infected with or contaminated with the Ebola or Marburg virus.

01:31 So, we say that it's monkey-human or human-human transmission, but it could be any of the animals in the jungle that happens to have been contaminated with or colonized with the virus, and then the human is the accidental host.

01:47 What happens in terms of pathogenesis? The target cells for both of these viruses are primarily endothelial cells, the cells lining the blood vessels.

01:57 But in addition, phagocytes and hepatocytes are secondarily infected.

02:02 Once the infection occurs, then the release or the synthesis and release of the viral glycoprotein causes extensive toxic damage to all these tissues.

02:13 So, liver, lymph nodes, blood vessels, spleen, lungs, you name it.

02:18 And, of course, because there's an endothelial target, the overall effect is to have hemorrhagic disease causing failure in all those organ sites.

02:30 In addition, as this is occurring, then, of course, there's a cytokine storm, which is sort of like adding insult to injury. It adds an inflammatory picture causing yet still disruption of blood vessels, vascular leak, etc.

02:46 So, let's look at what the clinical diseases are related to this, and they're sort of umbrella diagnosed as African hemorrhagic fever.

02:55 The Ebola virus and Marburg virus both cause this. They're almost indistinguishable.

03:01 The only change is the location in Africa where one typically sees these.

03:07 So, you are probably familiar with a fairly recent outbreak in 2014, 2015 in West Africa that would be Ebola virus.

03:16 The Marburg virus more recently has been found in Uganda.

03:21 So both of these, African hemorrhagic fever, the incubation is up to 21 days.

03:27 And in terms of risk exposure, 14-21 days is the most typical time for onset of disease after exposure.

03:35 The clinical components of a hemorrhagic disease start with a flu-like illness, just like many other, the very nasty infections that we've talked about.

03:45 So, fevers, malaise, headaches, some coughing, nausea, vomiting, diarrhea, even a rash, a maculopapular rash.

03:55 And as the disease progresses, the fever becomes higher, the patient has more malaise, and they start to develop diffuse myalgias -- muscle pains.

04:05 An interesting finding from the West Africa Ebola outbreak was that about 15% to 20% of the patients presented with hiccups, irritation of the diaphragm causing hiccups.

04:18 So that plus flu-like illness plus exposure to an endemic part of Africa for a virus should suggest the possible diagnosis coming up.

04:29 Ultimately, over a period of 1 week or so, patients with the initial presentation progress to extensive hemorrhage.

04:37 And depending on how much virus they got and where the target was, the hemorrhage occurred related to those sites.

04:45 Principally, it was gastrointestinal hemorrhage, so extensive hematemesis, hematochezia -- bloody stools -- absolutely disseminated intravascular coagulopathy with DIC, edema, hypovolemic shock, bloody conjunctivae, you name it.

05:02 The mortality in these situations up to 90%.

05:06 Without support, 100%.

05:09 Even with medical support, the mortality rate remained at 50%.

05:13 There's really not much that one could do during the course of the illness.

05:18 Diagnosis currently by RT or reverse transcriptase PCR.

05:23 And treatment is with supportive care and, of course, strict isolation using the approach of clean to dirty with personal protective equipment, the PPE, the so-called space suits that everybody remembers from the news.

05:39 So, these 2 viruses constitute a very nasty chapter in viral medicine with a very high mortality rate and, of course, significant impact on people because of the high degree of contagiousness, especially human-human transmission.

05:55 So Ebola and Marburg viruses, the filoviruses, beware.