The Pandemic Playbook
Blog Layout
DRC Ebola Outbreak 2019 Blog 4 Pandemic Potential of Ebola virus and Emerging Infectious Diseases in the 21st Century
I. MEDICAL ISSUES OF THE DRC EBOLA VIRUS OUTBREAK OF SUMMER 2019
4. Pandemic Potential of Ebola virus and Emerging Infectious Diseases in the 21st Century
EIDs comprise a wide variety of microbes and parasites that have a variety of transmission methods. While some hold the opinion that EIDs like Ebola virus do not easily infect humans, other experts hold the opposite view. This important question will be answered by dividing it into 2 smaller issues. Can EIDs like Ebola virus easily infect humans by person-to-person contact? Even with access to 21st-century technology, how safe are distant nations from EID pandemics?
Over the past 50 years, the view that Ebola virus and some EIDs were not very infectious was reasonable considering the data (24). However, recent data and reviews by experts conclude that Ebola virus and other EIDs are both infectious and lethal. To answer the questions of EID infection capacity and global travel, we must distinguish between the mid-20th century’s sparsely populated environments in which many modern EIDs were discovered and the 21st century’s megacities and rapid transportation systems, into which EIDs have penetrated (1).
From their discovery and over 50 years of observation, EIDs like Ebola virus only threatened the regions from which they came, which were usually heavily forested and sparsely populated. In those early days poor regional transportation prohibited people infected by EIDs from carrying the infectious agent to other regions. Early observations of outbreaks of Ebola virus and other EIDs showed a poor ability of the diseases to transfer serially among people (25-27). Person-to-person transmission may have been low because a microbe is not highly infectious. Another reason for non-sustained transmission could be that there were few people available to infect, called burnout. Burnout occurs when an epidemic cannot spread further by person-to-person or another transmission mode because there are too few people nearby to infect, while those who were previously infected and recovered are resistant to reinfection by this microbe.
However, a lack of people to infect, as in small villages where many dangerous EIDs were discovered, does not tell us if a microbe is very contagious. Another type of poorly transmitted EID is a microbe that is only infectious in the late stage of a patient’s illness. Here, the patient will be ill for days and only becomes infectious near the end of the symptoms caused by the EID-driven illness or upon death from the infection. In that case exposure and transmission to others is limited to a small time window late in the infection cycle.
Fear is a chief reason for the poor transmission of lethal EIDs. Once serial transmission of a lethal EID kills many people, communities recognize that the illness causing this outbreak is not like other diseases that cause fever, headaches and body pain. Fear of infection and death breeds community avoidance for those who have this type of disease. Without more hosts to infect, the transmission cycle breaks and the outbreak stops.
Some RNA virus EIDs, including the Ebola virus, fit into the latter 3 categories of ‘poorly infectious microbes’. Ebola virus and other EIDs were discovered in small villages or towns which limited the spread of infection. Only during late symptoms are infectious virus particles shed from the infected person, the disease carrier. When local populations realize that caretakers of EID cases die they avoid these caretakers and others who contacted Ebola patients. Ebola virus’s infectious capabilities are understood when analyzing Ebola virus and EID outbreaks in 21st-century urban settings. In urban environments, it is possible to distinguish between a microbe like rabies virus which can only infect people bitten by a rabid animal, and an acutely communicable disease which is rapidly transmitted in an urban environment.
Dr. Peter Salama is a medical epidemiologist with decades of experience and is the WHO’s Deputy Director-General of Emergency Preparedness and Response. One of his responsibilities is coordinating with partners to oversee the WHO’s tasks of eradicating EID outbreaks, including this Ebola virus outbreak in the DRC. In a recent interview addressing the DRC Ebola outbreak of 2018-2019, Dr. Salama reported that it has become very difficult to control EID outbreaks which have reached large cities. His observations show that when person-to-person transmission occurs in a large city, the reproductive number (the average number of new infections from a single person) of EIDs can increase up to between 2 and 4 people. Using this and recent Ebola virus outbreaks as prime examples, he specifically notes that our prior understanding of EID transmission—believing that EID microbes are naturally poorly infectious—is false. Dr. Salama commented that another ominous discovery in recent years is that EIDs occur more often in conflict zones, and as a result, make the work of ending EID epidemics more complex (22).
Next this discussion on EIDs shifts from the capacity to infect humans to their ability to spread globally. Over the 7,000 years of human maritime travel, respiratory microbes like measles, smallpox and the influenza virus have crossed continents, generating epidemics and pandemics. During this time non-respiratory microbes have also invaded distant continents, far from their primeval endemic habitats (28-29).
Within the EID definition, many re-emerging infectious diseases are returning as healthcare systems deteriorate. Some celebrated historical non-respiratory diseases and their transmission modes are: yellow fever virus and malaria (Plasmodium falciparum), transmitted by vector-borne mosquito bites; pneumonic or bubonic plague bacterium (Yersinia pestis), initially transmitted through rodent-to-flea-to-human bites; poliovirus and cholera (Vibrio cholera), initially transmitted by drinking fecal contaminated water or objects; and gonorrhea (Neisseria gonorrhea), a sexually transmitted disease.
Therefore, non-respiratory EID microbes have also been successful world travelers without modern transportation methods. Just as many invasive life forms have done in the past, new parasitic diseases colonize megacities in underdeveloped nations, where food and shelter are provided by their human hosts, often far from countervailing public health infrastructures and amidst the squalor of the poor. EIDs are both lethal and very infectious. And just as hundreds of other invasive species and microbes were scattered to new continents by traveling humans, EIDs have no natural or biological barriers which inhibit their successful colonization of the earth.
Copyright © 2019 Na’eem A. Abdullah All Rights Reserved
Morning fog on the African river Sangha. Congo. Sergey Uryadnikov Photographer/ Shutterstock Photos.
Many emerging infectious diseases originate in tropical ecosystems. See About Page - Sangha River.
PLEASE NOTE: 1. Please post Comments that are directly related to this field. 2. This site is Not Linked to Facebook. Thank you.