Ebola

Well, the first patient to come down with Ebola in America has now led to the first person to contract Ebola in America.  Meanwhile, another 50 people are being monitored to see if they come down with the disease.  Great.  Just great.

The strain of the Ebola virus that is currently burning through much of west Africa, and has now been brought to both Europe and America, has a lethality rate of about 50%.  That is, one out of every two people who catch the virus end up dying from the infection.  The survivors, even though they are immune to reinfection, may have serious long term health problems from the disease.  It’s too early to tell how serious that will be.

Government pronouncements that Ebola was not going to come to this country were, of course, ridiculous.  The latency period of Ebola can be up to 21 days.  That is, from the time the virus gets into your system to the first symptoms appearing can be as little as two days, or as many as three weeks.  Airport screening protocols will not be effective at keeping out people who show no symptoms. 

So a rational person would assume that more infected people will cross our borders.  That’s the bad news.  The good news is that you are not infectious during the latency period.  You can only infect other people once you display symptoms.  After the onset of symptoms, starting with fever and sore throat, you stay infectious until one of two things happens: a) you get better, or b) your remains are cremated after you die.

How bad the US outbreak will be is based on a concept called the Basic Reproduction Number, or R0.  What R0 boils down to is the average number of new people infected by each person with the disease.  With the current outbreak in West Africa, R0 is running about 2.  Each new case ends up infecting two more.  This doesn’t sound so bad, until you realize that the number of patients is doubling about once a month.  So you start with one patient, who becomes two, who become four, who become eight, and so on.  This kind of pattern gets really scary after about ten doublings.

At two to the tenth power, 4096 people are currently infected.  With a periodicity of one month (figure average of 15 days of latency, followed by 15 days of infectiousness), at the end of one year, 16384 people have caught the virus in the last month.  One year later, over 16 million new cases come up at the two-year anniversary of the start of the outbreak.  Six months later, you get a billion new cases in the last month.  If R0 was to stay at 2, within three years half of the world’s population will be dead, and the survivors will all be immune.

On the other hand, if R0 can be kept below 1, than the outbreak dies off.  Given that the first patients to contract the disease in both the US and Europe are health care workers, presumably trained to follow anti-contamination protocols, I’m not as confident about the situation as the CDC’s pronouncements would have one believe.

So let’s review.  Lethal disease?  Check.  You can be infected, and still act normal for a time?  Check.  Death does not make you non-infectious, and indeed makes you more dangerous to the living than ever? Check.  So basically, we’re in the early days of the Zombie Apocalypse.