NEJM on Ebola

The New England Journal of Medicine has an Editorial criticizing the quarantines in NJ and other states.

Health care professionals treating patients with this illness have learned that transmission arises from contact with bodily fluids of a person who is symptomatic — that is, has a fever, vomiting, diarrhea, and malaise. We have very strong reason to believe that transmission occurs when the viral load in bodily fluids is high, on the order of millions of virions per microliter. This recognition has led to the dictum that an asymptomatic person is not contagious; field experience in West Africa has shown that conclusion to be valid. Therefore, an asymptomatic health care worker returning from treating patients with Ebola, even if he or she were infected, would not be contagious.

In the same issue, there is an article: Clinical Illness and Outcomes in Patients with Ebola in Sierra Leone. Take a look at the supplementary material. Figure S8 shows temperature and heart rate for fatal and non fatal cases

Panels B, C,E and F represent cases with a normal temperature-pulse association.

All of these are infected. One of the three was a fatal. Table S5 shows symptoms. 11/36 did not present fever. We don’t see if they presented other symptoms but, from the legend:

Eight fatal subjects and one nonfatal subject showed no reported symptoms on the case notification form and were excluded from these results.

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From Schieffelin et al. (2014) Clinical Illness and Outcomes in Patients with Ebola in Sierra Leone NEJM DOI: 10.1056/NEJMoa1411680 Figure S7

Perhaps people can die of Ebola without being viremic to the level needed for infect others? I also wonder if they really meant “millions per microliter” or “millions per milliliter”. The former is 109/milliliter. Figure S7 shows viral loads in fatal and nonfatal patients, and it does look like Ebola in serum can reach that level, but two of the fatal cases are well below that. Other sources have claimed that the number of particles needed for an infection is on the order of 1-10. Even at 106/ml,a microliter would be 1000 particles. When people are exposed to infected bodily fluids, are the volumes involved in the picoliter range?

Update: the ID50 is on the order of 1-10 for animal models, but in mice the sensitivity depends on the route of introduction.

The LD50 of mouse-adapted EBO-Z virus inoculated into the peritoneal cavity was ~1 virion. Mice were resistant to large doses of the same virus inoculated subcutaneously, intradermally, or intramuscularly.