Category Archives: Geography

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

Illustrations of the 1896-1897 Influenza Epidemic in Paris

1890 Influenza cartoon (Source: National Library of Medicine)
1897 Influenza cartoon (Source: National Library of Medicine)

This image has been used here at Contagions in various cropped versions as the header and avatar for several years now. I found a couple more related illustrations that are worth sharing and put the illustration in better context. This is an emergency tent hospital erected to handle the epidemic of 1897.  It certainly looks different from the outside as you can see below.

outside
Source: National Library of Medicine
c05532
Source: National Library of Medicine

Based on the date of this newspaper header (12 Jan 1897), this must be illustrations of a lesser known epidemic in 1896-1897 that occurred between the pandemic of 1890 (Russian flu) and that of 1900.

Another view of the scene in the usual header here.

C05532 crop

Reading in August

august

Just a little update on my reading in August. I’ve been jumping around a bit reading on the history of malaria and wetlands.  Lots of interesting bits and pieces!

Books

  • John Aberth. An Environmental History of the Middle Ages: The Crucible of Nature, 2013.
  • Gregory of Tours (d. 594): Glory of the Confessors 
  • Gregory of Tours (d. 594): The Life of the Fathers
    • Looking at what diseases people are seeking cures for primarily at the shrines of the saints.
  • William McNeill, Plagues and Peoples. 1976.
    • I reread this book about every ten years, so I’m working my way through it over lunch at work at the present. Odd to reread a book I first read in the late 1980s as a student.  Its surprising how well it holds up, but it is now out of date in biology, history and anthropology. It really can’t be used to represent modern views on either infectious disease biology or history. We really need a new, updated edition!  Just to give a few examples, HIV hadn’t even been identified in 1976 (as McNeill mentions in the preface of the 1998 edition) and antibiotic resistance and ‘(re)emerging infectious diseases’ were not considered critical problems (although both had begun to appear).
  • Robert Sallares, Malaria and Rome: A History of Malaria in Ancient Italy. 2002 (in progress)
 Standout Papers – (more or less in order they were read)
  • Couser, J. (2010). The Changing Fortunes of Early Medieval Bavaria to 907 ad. History Compass, 8(4), 330–344. doi:10.1111/j.1478-0542.2009.00671.x
  • King, G., & Henderson, C. (2013). Living cheek by jowl: The pathoecology of medieval York. Quaternary International, xxx, 1–12. doi:10.1016/j.quaint.2013.07.032
  • Förster, F., Großmann, R., Hinz, M., Iwe, K., Kinkel, H., Larsen, A., et al. (2013). Towards mutual understanding within interdisciplinary palaeoenvironmental research: An exemplary analysis of the term landscape. Quaternary International, 312(C), 4–11. doi:10.1016/j.quaint.2013.07.045
  • Rippon, S. (2009). ‘Uncommonly rich and fertile’ or “not very salubrious?” The Perception and Value of Wetland Landscapes. Landscapes, 10(1), 39–60.
  • Bankoff, G. (2013). The“English Lowlands” and the North Sea Basin System: A History of Shared Risk. Environment and History, 19(1), 3–37.
  • Justin T. Noetzel. Monster, Demon, Warrior: St Guthlac and the Cultural Landscape of the Anglo-Saxon Fens. Comitatus: A Journal of Medieval and Renaissance Studies, Volume 45, 2014, pp. 105-131.
  • O’Sullivan, L., Jardine, A., Cook, A., & Weinstein, P. (2008). Deforestation, mosquitoes, and ancient Rome: Lessons for today. BioScience, 58(8), 756–760.