Sunday, 31 August 2014

Ebola: Blood, sweat and tears...

This post follows up the recent one on convalescent semen being able to harbour infectious Ebola virus (EBOV; although I am not aware of any infection resulting from this route of transmission there has been at least one report for Marburg virus [4]).

I thought I'd give the same treatment to tears and sweat which are also fluids intermittently listed as possible sources of EBOV infection for humans. Some examples of the scientific literature which support the risk messaging, follow.

Blood...

I think we are all pretty clear that the blood of an advanced case of Ebola virus disease (EVD) is heavily laden with virus and is the most serious of the risk factors for acquiring infection by an ebolavirus.

Viral loads (amount of virus in the sample) in blood can be above 106-108 plaque forming units or copies (pfu; a measure of infectious virus present using a lab test that measure the impact of virus on infected cells; copies measure viral genome and cannot prove infectious virus is present) per millilitre of blood in acute phase disease patients and non-human primates.[5,6]

Sweat...

There is not a lot on sweat containing signs of an ebolavirus.
  • Bausch and colleagues found no trace of EBOV in a single acute sweat sample.[1]
  • Jaax and colleagues found that in experimentally infected non-human primates (NHPs; rhesus macaques), that connective tissues next to hair follicles and sweat glands in the skin as well as the cells lining ducts of glands in the skin were sometimes positive for EBOV antigens (proteins).[2]
  • Davis and colleagues infected NHPs (African green monkeys) and found signs of EBOV antigens in the cells lining the sweat gland ducts and in cells in the connective tissues next to hair follicles, but no virus particles by electron microscopy.[3]
  • Zaki and colleagues found heavy signs of EBOV antigens (proteins) in the tissues around the sweat glands, but rarely also within sweat glands and ducts.[8] No virus particles were seen in the sweat glands or ducts when examined by electron microscopy.
Tears...

There is also very little I have found on this one.

  • Bausch and colleagues found EBOV RNA in tears from 1 sample, but no infectious virus could be isolated.[1]
  • Jaax and colleagues found some signs of virus in macrophages in the ciliary body of the eye of experimentally infected NHPs
Spit...
  • Bausch and colleagues found infectious EBOV in 1 of 12 acute saliva samples (from 10 patients; none from 4 convalescent samples) and EBOV RNA in 8 of 12 (67%) of acute samples (none from convalescent samples).[1] RT-PCR positivity was significantly associated with fatal outcome.
  • Formenty and colleagues found EBOV antigens and EBOV RNA in oral fluids from fatal cases and those who survived infection.[7]
References...
  1. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2395567/pdf/bullwho00439-0113.pdf
  2. http://www.ncbi.nlm.nih.gov/pubmed/8712894
  3. http://www.ncbi.nlm.nih.gov/pubmed/9278608
  4. http://link.springer.com/article/10.1007/BF01734141
  5. http://www.sciencemag.org/content/suppl/2014/08/27/science.1259657.DC1/Gire.SM.pdf
  6. http://www.nature.com/nature/journal/vnfv/ncurrent/pdf/nature13777.pdf
  7. http://www.ncbi.nlm.nih.gov/pubmed/16652308
  8. http://www.ncbi.nlm.nih.gov/pubmed/9988163