This morning’s death in Texas of Mr. Thomas Eric Duncan, marks the first death (ever) from Ebola in America. Mr. Duncan, a Liberian man who had traveled to Texas to visit family, was the first person to be diagnosed with the disease while in the U.S. and became the first person to die of the disease in the U.S. Before widespread panic sets in, let’s look at the facts.
How contagious is Ebola?
Hopefully, the CDC’s optimism is called for in that the congation-effect of Ebola all comes down to something called “R0.”
The reproduction number, or “R nought,” is a mathematical term that tells you how contagious an infectious disease is. Specifically, it’s the number of people who catch the disease from one sick person, on average, in an outbreak.*
Take, for example, measles. The virus is one of the most contagious diseases known to man. It’s R0 sits around 18. That means each person with the measles spreads it to 18 people, on average, when nobody is vaccinated. (When everyone is vaccinated, the R0 drops to essentially zero for measles).
At the other end of the spectrum are viruses like HIV and hepatitis C. Their R0s tend to fall somewhere between 2 and 4. They’re still big problems, but they spread much more slowly than the measles.
And that brings us back to Ebola. Despite its nasty reputation, the virus’s R0 really isn’t that impressive. It typically sits around 1.5 to 2.0.
Even in the current epidemic in West Africa, where the virus has been out of control, each person who has gotten sick has spread Ebola to only about two others, on average.Why is that?
Many factors contribute to the R0, such as how long you’re infectious** and how many virus particles are needed to make another person sick.
But in Ebola’s case, the mode of transmission probably helps keep its R0 low. Ebola isn’t spread through the air, like the measles or flu. It requires close contact with some bodily fluid, such as blood or vomit, containing the virus.
Now at this point, you’re probably thinking, “OK. But an R0 of 2 is nothing to brush off.” You’re right. R0 of 2 means one person infects two people, who then infect four people, then eight, 16, 32 — the numbers go up fast.
But that isn’t likely to happen in a place with a good public health system, a first world country because people with Ebola aren’t contagious until they show symptoms.
Ebola virus disease
- Ebola virus disease (EVD), formerly known as Ebola haemorrhagic fever, is a severe, often fatal illness in humans.
- The virus is transmitted to people from wild animals and spreads in the human population through human-to-human transmission.
- The average EVD case fatality rate is around 50%. Case fatality rates have varied from 25% to 90% in past outbreaks.
- The first EVD outbreaks occurred in remote villages in Central Africa, near tropical rainforests, but the most recent outbreak in west Africa has involved major urban as well as rural areas.
- Community engagement is key to successfully controlling outbreaks. Good outbreak control relies on applying a package of interventions, namely case management, surveillance and contact tracing, a good laboratory service, safe burials and social mobilisation.
- Early supportive care with rehydration, symptomatic treatment improves survival. There is as yet no licensed treatment proven to neutralise the virus but a range of blood, immunological and drug therapies are under development.
- There are currently no licensed Ebola vaccines but 2 potential candidates are undergoing evaluation.
The Ebola virus causes an acute, serious illness which is often fatal if untreated. Ebola virus disease (EVD) first appeared in 1976 in 2 simultaneous outbreaks, one in Nzara, Sudan, and the other in Yambuku, Democratic Republic of Congo. The latter occurred in a village near the Ebola River, from which the disease takes its name.
The current outbreak in west Africa, (first cases notified in March 2014), is the largest and most complex Ebola outbreak since the Ebola virus was first discovered in 1976. There have been more cases and deaths in this outbreak than all others combined. It has also spread between countries starting in Guinea then spreading across land borders to Sierra Leone and Liberia, by air (via travelers.
The most severely affected countries, Guinea, Sierra Leone and Liberia have very weak health systems, lacking human and infrastructural resources, having only recently emerged from long periods of conflict and instability. On August 8, the WHO Director-General declared this outbreak a Public Health Emergency of International Concern.
A separate, unrelated Ebola outbreak began in Boende, Equateur, an isolated part of the Democratic Republic of Congo.
At the time of this article, a second case of Ebola is suspected in Texas. A sheriff’s deputy, said to have served the warrant (for physical possession of the victim) to Mr. Duncan’s home prior to his death, is now under watch for the deadly virus. We will keep you posted.
BNI Operatives: Street smart; info savvy.
As always, stay safe.
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