, , ,

A year ago on November 22, 2014, I posted “How many days for Ebola to become symptomatic and infective?” That post included a chart of infectivity going from a single Ebola virus to ten billion, with a doubling time of eighteen hours.

“This chart presents an estimate for how long it takes Ebola to become symptomatic, given various levels of the number of viruses entering the body. The virus’s doubling time is about eighteen hours; thus if a single Ebola virus entered the body, at that rate it takes about thirteen days before the first fever strikes. A person infected with a large number of viruses, because they touched some virus-laden bodily fluids and then touched their own eyes, nose, mouth or open skin irritation, would display symptoms in only four days.”


That opening paragraph admits the numbers on the graph are not exact, and are estimates based on the rate of development of the disease once it was in a medical setting where blood samples taken from Ebola victims could be used to measure the viral load in the patients at various levels of severity.

Ebola chart for timing progression of symptoms and contagion

Time in days for Ebola to manifest symptoms and become infectious.

This last few months I have read and reread several times Missing Microbes by Martin J. Blaser, MD, and on page 252 in Notes about page 190, he writes an astonishing paragraph:

In their initial experiments, Marjorie Bohnhoff and her colleagues showed that the dose of Salmonella required to infect half of the exposed mice went from about 100,000 bacterial cells to 3, following a one-day exposure to the antibiotic streptomycin (M Bohnhoff et all., “Effect of Streptomycin on susceptibility of intestinal tract to experimental Salmonella infection, ” Proceedings of the Society for Experimental Biology  and Medicine 86 [1954]: 132-37.) In later studies, the team extended the work, showing that penicillin was just as effective as streptomycin, that they could enhance susceptibility of mice to a Staphylococcus species that was incapable of colonizing by itself, and that injecting the antibiotic into tissues had no effect, thus implicating the normal gut bacteria in the protective effect and their depletion by antibiotics in promoting infections. (M. Bohnhoff and C. P. Miller. “Enhanced susceptibility to Salmonella infection in streptomycin-treated mice,” Journal of Infectious Diseases III [1962]: 117-27.) These and further observations are more than fifty years old, but they have been largely forgotten.

What I was searching for was some firm figures on how many bacteria it took to cause an infection in a normal mammal, in this case mice, not humans. They published that it took 100,000, thus on the chart above comes in at day 12. If my chart were accurate the initial infections would more likely have taken place on day 8 or 9, or perhaps my chart is accurate and the initial infection took only 2,000 to 5,000 viruses. The chart above may be a reasonable guide to the infectivity of Ebola.

What appalled me in the quote above was the alarming increase in susceptibility to new infections of a mammal given an antibiotic. This effect wasn’t too much of a problem in 1962 because viruses had not yet developed immunity to the various antibiotics, and if someone caught a second disease they just gave them another course of antibiotics and usually that worked. Unfortunately some diseases have now developed some immunity to these medical treatments, and Clostridium difficile  C. diff — is now infecting thousands of people who take antibiotics to cure some other disease. Other pathogens are already becoming immune to antibiotics and will thrive in a human body that has had its natural viral fighting ability compromised by antibiotics.

Humanity has now entered a time when antibiotics are our deadly enemy.