Solutions from History

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October 2014
Ivan Obolensky

Infectious diseases are not new, nor are they a byproduct of our technologically advanced societies. As western economies and cultures have expanded into remote areas, new pathogens have made themselves known to us. Sometimes the contact has been relatively benign, but at other times quite the opposite.

Between 1951 and 1955 almost 2,500 US soldiers suffered from a viral hemorrhagic disease called Seoul Hantaan; 121 died. This was the first Western experience of a new class of disease called viral hemorrhagic fevers (VHFs). At the time the cause was not identified, and it was not until 1970 that the viral agent, the Hantaan Virus, was isolated.

Army doctors treating the disease found that the chances of recovery were increased provided there was careful monitoring and control of liquids and electrolyte levels. The virus caused the patient’s capillaries, the smallest blood vessels in the body, to leak fluids and proteins both externally and internally affecting the chemical balance in vital organs such as the kidneys, liver, and heart. The organs would cease functioning before the immune system could respond leading to convulsions, shock, and then death. Bleeding from the eyes, ears, and other orifices was another disturbing symptom but was a non-life threatening aspect of the virus’s presentation.

In the 1960s another VHF outbreak occurred in a remote part of Bolivia. The virus in this case was carried by a species of mice which spread the disease through its urine. When the huts of the indigenous people were swept each morning prior to breakfast, dust soaked with this mouse urine (which contained the virus) would then become airborne and spread the disease to sleeping family members.

As in all VHFs, humans were not the natural host. VHFs depend on the local rodent population such as mice, rats, bats, or other similar small mammals for replication and survival.1

In the past outbreaks have been remote and the viral agents were named after the specific locations where the outbreak occurred. Ebola, for instance, is named after the Ebola River in the northern part of the Democratic Republic of the Congo where the first reported VHF outbreak of the Ebola virus occurred.

Ticks, mosquitoes, and other arthropods can also be carriers of the disease after they have come in contact with the natural virus reservoir.

VHFs and the viruses that cause them have been in existence for centuries but due to the host species’ often distant locations as well as language barriers, lack of knowledge of this type of disease has prevented widespread familiarity in the West.

Since the 1960s, several types of VHFs have made their appearance with Ebola being the most well known by the general public.

VHFs are caused by the viruses of four separate viral families: arenaviruses, bunyaviruses, filoviruses and flaviviruses and have been isolated with difficulty and only within the last half century due to their extremely small size.

The VHF families have several common characteristics.2

They are all RNA viruses.

RNA viruses use RNA (Ribonucleic Acid) as its genetic material rather than DNA (Deoxyribonucleic Acid).

RNA is similar in composition to the double-stranded DNA molecule that carries genetic information in humans but is usually found as a single-stranded molecule.

RNA is also more unstable than DNA and more prone to mutations because it lacks the proofreading elements of DNA that reduce bad copies. This can be helpful for the virus as it can change significantly making elimination by immune systems harder but also making virus classification difficult.

In the human cells, Messenger RNA transmits information it copies from the DNA to sites that manufacture the amino acids that make proteins and enzymes. These are the catalysts that help sustain metabolic processes that aid in cell regulation.

VHF-producing viruses depend on specific species for survival. When humans come in contact with these hosts, they can become infected and in some cases, as in Ebola, the virus can survive when passed to humans.

Outbreaks of VHF have been sporadic and isolated to specific regions. There is no cure or drug treatment in most cases other than the regimen developed by the US Army mentioned above (hydration and electrolyte management).3

The Ebola virus is a Filovirus. There are five known strains depending on where it was discovered. The specific natural reservoir is unknown but following the pattern of other VHFs, it is likely a small mammal. The virus incubates for 2 to 21 days. Symptom onset is rapid and includes fever, joint and muscle pain, headache, sore throat and weakness followed by vomiting and diarrhea. It is not known at this time why some people recover and others do not although the management of fluids and electrolytes improves the chance of survival but is not foolproof. The Ebola-Zaire virus had a 73.61% mortality rate when it first emerged in 1976.4

Human-to-human transmission is through contact with infected body fluids. Although it is not an airborne virus like influenza, or SARs, sneezing and coughing can turn virus-containing body fluids into an aerosol and spread the disease. The Ebola virus can survive on surfaces in the open air but not for very long: several hours in darkness and longer in cold temperatures. At 4 °C (39.2 °F) it can last for 50 days.

It is susceptible to eradication outside the body using household bleach solutions but strict infection controls must be practiced to prevent spreading to medical workers.5

Epidemiologists use the mathematical model called SIR (Susceptible Infected Recovered Model) to estimate the rate at which the diseases spread through a population. One number that comes out of this analysis is the reproductive number or R number (R0). If the number of those recovering but who are infectious is larger than number of those with new infections, the outbreak will die out. In this case R0 is less than one. With R0 greater than one, more people are being infected than are recovering which means the outbreak is growing. 6

Estimates of R0 for Ebola range from 1.83 (1995) in the Congo to 1.34 in Uganda (2000). KCBS in Los Angeles recently reported R0 for the current Ebola outbreak at 2 which means that 2 people are infected for everyone who has the disease. 7 Based on past outbreaks after medical intervention, the R0 dropped to .3 or .4 which means medical procedures that include proper protocols and quarantine can control its spread provided they are followed.8

This is not the first time that disease on a widespread scale has threatened human populations.

During the second pandemic (1350) better known as the Black Death, the handling of the crisis in Venice and Florence was given to a select group of the leading citizens who sat on special health commissions.

Their duties were the enforcement of existing sanitary laws such as the burial of those who died, the removal of infected persons to established locations, the interdiction of travelers from infected cities, and the isolation of the goods they brought with them.

The commissions established and dictated the procedures to be followed including the use of quarantine. Compliance was mandatory and force was used when necessary.

Quarantine in the strict sense of the word started in the Venetian colony of Ragusa (Dubrovnik) in 1377. All travelers and their goods entering into the colony were isolated for thirty days. The practice spread and began to target specifically goods and travelers from areas and ports known to be infected. In 1383 the city of Marseilles insisted on forty days from which the word quarantine, literally ‘forty days’, is derived. Venice built its own quarantine station in 1423 on an island in the lagoon and then another which became models for plague hospitals.9

For the first time organizational procedures, protocols, and governance rather than individual actions ensured the continued survival of the cities affected.

Plague continued to revisit Europe up until the 18th century with less and less virulence. Past procedures that had been effective were put back into practice and the spread of the disease subsided.

Gradually these procedures became less necessary possibly due to the weakening of each successive wave of infection.

By the 20th century, travel between countries became commonplace and with the rise of antibiotics formerly deadly diseases appeared defeated, lessening the need for controls strictly for health reasons.

From the above there are several key points that can be said about the current outbreak:

Control of Ebola as well as other VHFs requires rapid quarantine and strict medical protocols in order to reduce the Reproductive Number to a low value. Left alone, the mortality rate in a dense population could conceivably reach 79% based on simulations of a population of 22,000.10

Part of the difficulty in controlling the spread of the virus is that Ebola symptoms are similar to other diseases in their initial presentation making it hard for medical staff unfamiliar with it to diagnose it accurately. Further, it is likely that there will be many more initial false positives until a rapid accurate testing regimen can be provided.

News about Ebola and reports of infections can create an atmosphere of fear whereby those who have a potential infection would rather not subject themselves to quarantine.

The virus has not been able to be contained to its local areas and has spread to cities in Africa creating a large number of potential infections.

Quarantine has been the only proven method for handling any and all outbreaks of deadly infectious diseases as mentioned above although there has been some question about this in that the natural mutations that occur with virulent diseases may have also contributed to quarantine success.11

Modern air travel and porous borders can facilitate the spread of the infection. International protocols are at this time insufficient to lead to containment.

The good news, if this can considered as such, is that the R0 for Ebola (2) is significantly less than, say, measles (12-18) or smallpox (5-7) but is nearly as virulent as Influenza (2-3).12

It is a fact that given proper medical quarantining and intervention, the spread of the disease can be contained.

It is hoped that the draconian measures taken to combat plague in the past may not be needed now to combat VHFs such as Ebola. But it should be restated and emphasized that having organizational procedures, strict protocols, and positive coordinated governance were required to ensure containment previously and may be needed again.

 


 

  1. Garrett, L. (1994). The Coming Plague: Newly Emerging Diseases in a World Out of Balance. New York, NY: Farmer, Strauss, and Giroux
  2. N.A. (2014). Viral Hemorrhagic Fevers Fact Sheet, CDC. Retrieved October 12, 2014 from http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/Fact_Sheets/Viral_Hemorrhagic_Fevers_Fact_Sheet.pdf
  3. Crawford, D. (2011) Viruses, A Very Short Introduction. New York, NY: Oxford University Press
  4. Yarus, Z. (2012). A Mathematical Look at the Ebola Virus. Retrieved October 12, 2014 from http://home2.fvcc.edu/~dhicketh/DiffEqns/Spring2012Projects/Zach%20Yarus%20-Final%20Project/Final%20Diffy%20Q%20project.pdf
  5. (N.A.) (2014). Ebolavirus Pathogen Safety Data Sheet – Infectious Substances. Retrieved October 12, 2014 from http://www.phac-aspc.gc.ca/lab-bio/res/psds-ftss/ebola-eng.php
  6. N.A. (2014) Will the Ebola Outbreak Become an Epidemic: A Look into Epidemiological Models. Retrieved October 12, 2014 from https://foodforscientificthought.wordpress.com/2014/07/29/will-the-ebola-outbreak-become-an-epidemic-a-look-into-epidemiological-models/
  7. Chowell, G., Hengartner NW, Castillo-Chavez, C., Fenimore, PW, Hyman, JM, The basic reproductive number of Ebola and the effects of public health measures: the cases of Congo and Uganda. Retrieved on October 12, 2014 from http://www.ncbi.nlm.nih.gov/pubmed/15178190
  8. Legrand, J., Grais, R., Boelle, P., Valleron, A. Flahault, A. Understanding the Dynamics of Ebola epidemics. Retrieved on October 12, 2014 from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2870608/
  9. Slack, P. (2012). Plague, A Very Short Introduction. Gosport, GB: Oxford University Press.
  10. Yarus, op. cit.
  11. Slack, op. cit.
  12. N.A. (2014). Basic Reproductive Rate (R0). Retrieved on October 12, 2014 from http://practice.sph.umich.edu/micphp/epicentral/basic_reproduc_rate.php

 


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© 2014 Ivan Obolensky. All rights reserved. No part of this publication can be reproduced without the written permission from the author.

 

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