Category Archives: public health

Ebola’s Chain of Infection

Chain of Infection A chain of infection is a method for organizing the basic information needed to respond to an epidemic.  I’ve gathered the best information I’ve been able to find. As the current epidemic is analyzed, there is no doubt some of the recommendations and basic knowledge will change.

The Ebola Virus (EBOV)

img8The Ebola virus is a Filovirus, an enveloped RNA virus containing only eight genes. Three of the five ebola virus species are highly pathogenic to humans: Zaire ebolavirus (Case fatality rate (CFR) 70-90%), Sudan ebolavirus (CFR ~50%) and Bundibugyo ebolavirus (CFR 25%). The 2014 epidemic is caused by the  Zaire ebolavirus.

Ebola attaches to the host cell via glycoproteins that trigger absorption of the virus. Once inside the cell it uncoats and begins replicating the eight negative sense RNA genes (seven structural genes and one non-structural gene). It initially targets immune cells that respond to the site of infection; monocytes/macrophages carry it to lymph nodes and then the liver and spleen. It then spreads throughout the body producing a cytotoxic effect in all infected cells. Death occurs an average of 6-16 days after the onset of symptoms from multi-organ failure and hypotensive shock.

Symptoms present 2-21 days after infection and the patient is contagious from the onset of symptoms.  Symptoms include a fever, fatigue, headache, nausea and vomiting, abdominal pain, diarrhea, coughing, focal hemorrhaging of the skin and mucus membranes, skin rashes and disseminated intravascular coagulation (DIC). In the 2014 epidemic, abnormal bleeding has only occurred in 18% of cases and late in the disease process.

The Reservoir

Fruit bats in Africa are believed to be the primary reservoir. Transmission between bats and other animals is poorly understood.

ebola_ecology_800px

Portal of Exit

Ebola leaves its reservoir by contact with body fluids of an infected animal, often by bushmeat hunters. The spill-over is usually very small with the vast majority of human cases being caused by human to human transmission.

Transmission 

Transmission between humans occurs by contact of skin or mucus membranes with the body fluids of an infected person. Viral particles are found in all body fluids: blood, tears, saliva, sputum, breast milk,  diarrhea, vomit, urine, sweat and oil glands of the skin, and semen. Ebola can be found in semen three months after recovery from an infection but transmission by this route is poorly understood. Viral particles are found in other body fluids for 15 days or less after the onset of symptoms. It lasts the longest in convalescent semen and breast milk. All fluids from dead bodies are highly infectious.

All materials touched by the infected person, body fluids, medical waste, and used PPE must be discarded and destroyed as infectious medical waste. Non-disposable items like rubber boots, furniture, and building structures must be professionally decontaminated.

Ebola virus is a Biosafety Level 4 pathogen and a category A bioterrorism agent along with other viral hemorrhagic fevers.

Portal of Entry

Ebola enters the human body through breaks in the skin, including micro-abrasions and splashes on mucus membranes. Personal protective equipment (PPE) includes full body coverage including hood, mask or face shield, a tight fitting respirator, boots or shoe coverings, and double gloving. A buddy system should be used for dressing and disrobing. Removing PPE is a point of frequent contamination and should be done with help from another robed person.

Vulnerable populations

The most vulnerable populations for ebola are defined by their occupation. Care givers in medical facilities are at the highest risk because the viral titers reach the highest levels in fatal cases shortly before death. Mortuary and burial workers are also at high risk. The infectiousness of the bodies means that the usual burial practices can not be done in any setting or country. Home caregivers and decontamination workers would also be at a higher risk.

Information is lacking on survival vulnerabilities such as age, gender, pregnancy, or pre-existing conditions. More information on these aspects should be available in the post-epidemic analysis of the current epidemic.

 

References and further reading:

Martines, R. B., Ng, D. L., Greer, P. W., Rollin, P. E., & Zaki, S. R. (2014). Tissue and cellular tropism, pathology and pathogenesis of Ebola and Marburg Viruses. The Journal of Pathology, n/a–n/a. doi:10.1002/path.4456 [in press]

Chowell, G., & Nishiura, H. (2014). Transmission dynamics and control of Ebola virus disease (EVD): a review. BMC Medicine, 12(1), 196. doi:10.1186/s12916-014-0196-0

Toner, E., Adalja, A., & Inglesby, T. (2014). A Primer on Ebola for Clinicians. Disaster Medicine and Public Health Preparedness, 1–5. doi:10.1017/dmp.2014.115

Bausch, D. G., Towner, J. S., Dowell, S. F., Kaducu, F., Lukwiya, M., Sanchez, A., et al. (2007). Assessment of the Risk of Ebola Virus Transmission from Bodily Fluids and Fomites. Journal of Infectious Diseases, 196(s2), S142–S147. doi:10.1086/520545

CDC: Ebola Virus Disease portal

Reading in July

July 2014 reading 1

 

As I start working on my book project, I’m going to have less time to develop blog posts, so I thought I would share what I’m reading with you each month. This will also give me an incentive to keep blogging and reading! I’ll list the books I’ve read and the papers that I thought were particularly interesting.

Books

Papers

  • Squatriti, Paolo. “Offa’s Dyke Between Nature and Culture.” Environmental History, 2004, 37–56.
  • Squatriti, Paolo. “The Floods of 589 and Climate Change at the Beginning of the Middle Ages: an Italian Microhistory.” Speculum 85, no. 4 (November 18, 2010): 799–826. doi:10.1017/S0038713410002290.
  • Slavin, P. “Warfare and Ecological Destruction in Early Fourteenth-Century British Isles.” Environmental History 19, no. 3 (June 20, 2014): 528–50. doi:10.1093/envhis/emu033.

Biosecurity Failures Round-up

Like many of you, I’ve been watching and reading all the recent biosecurity lapses at our top labs with some dismay. This really isn’t something I normally would cover here on Contagions, but a comment from a reader reminded me that not everyone gets all the stories I’ve been tweeting (or retweeting) for the last few months. So here is a partial roundup in no particular order:

CIDRAP: Wholesale roster change coming for US biosecurity board

Superbug: The Leader of the Smallpox Eradication Effort Speaks About the Virus’ Rediscovery

Superbug: Virus in Found Tubes of Smallpox Is Viable

Superbug: Enhancing flu in the lab: Are accidents inevitable?

Found: Forgotten Vials of Smallpox | Science Blogs | WIRED

Exclusive: U.S. says government lab workers possibly exposed to anthrax

After Lapses,CDC Admits a Lax Culture at Labs | NYTimes

U.S. inspectors find further anthrax violations, mishandling http://www.reuters.com/article/2014/07/14/us-usa-anthrax-idUSKBN0FJ29X20140714

Transcript of CDC Press Conference on Recent Biosafety Incidents

On biosecurity at a local level: Out of the Lab & Into the Mouth These are getting to be yearly stories!

Meanwhile, elsewhere  Ebola (another category A bioterrorism agent) is raging unchecked in western Africa….

“How to Ignore a Plague” (Ebola) by Umaru Fofana

Ebola cases in West Africa reach 964, deaths top 600  http://www.cidrap.umn.edu/news-perspective/2014/07/ebola-cases-west-africa-reach-964-deaths-top-600

USAMRIID Providing Laboratory Support to Ebola Outbreak http://globalbiodefense.com/2014/07/15/usamriid-providing-laboratory-support-ebola-outbreak/#sthash.GxNfldMP.dpuf