Containing the international spread of Ebola
People who recover tend to improve six to eleven days into the illness. In the current outbreak, this happens around 45 percent of the time (1,848 cases and 1,013 deaths as of 9 August), which is higher than previous outbreaks.
For the other 55 percent of cases, however, the organs and blood clotting system of the body shut down as an irreversible decline sets in, leading to death.
The infectiousness of Ebola virus
In infections such as influenza, cases may be infectious to other people before they feel unwell. People with Ebola virus infection, on the other hand, are only infectious after becoming sick. This makes it just a little easier for health authorities to limit transmission.
In the current outbreak in West Africa, human-to-human transmission is responsible for the ongoing epidemic. Contact with infected body fluids through broken skin or mucous membranes (e.g., the eyes and mouth) can transmit the virus to others. This even applies to dead bodies, which makes funerals potentially dangerous.
No definite human-to-human transmission has been demonstrated through breathing, unlike infections such as measles, chicken pox, and influenza. But a study in animals suggested that the Zaire strain of Ebola virus could be transmitted from pigs to monkeys through air. The significance of this for human-to-human transmission isn’t clear.
International response
With one billion people travelling overseas each year, it’s never been easier for an infection in one part of the world to reach another.
The WHO last week announced that the Ebola outbreak met the conditions for a “public health emergency of international concern” and recommended countries with Ebola check everyone leaving the country for possible infection. This is called “exit screening” and involves measures such as questionnaires, information sheets and measuring the temperature with thermal scanners.
In countries that don’t have Ebola, the WHO stated there should be “no general ban on international travel or trade” to those countries with Ebola.
It also recommended all countries have the capacity to identify and deal with travelers coming back with a fever from a nation with Ebola. This is called “entry screening” and often involves the same strategies used in the “exit screening”.
During the SARS outbreak, however, both exit and entry screening strategies failed to detect many cases. The virus spread from Asia to various parts of the world, especially to Canada.
There may not have been many cases of SARS among travelers to explain its limited detection on airport screening. But there were other possibilities too that can be applied to Ebola virus as well as SARS. Some infected people may be in the incubation period so they genuinely aren’t sick at the time of the trip.
Alternatively, some people might be sick but would not declare their illness for fear of quarantine. They may have evaded the thermal scanners by taking medication to hide their fever. Others with the illness may naturally not have had a fever at the time of thermal scanning.
But despite the limited detection rate of the airport screening process during the SARS outbreak, it was still thought to be a useful way to educate incoming travelers about what to do and where to go if they became sick.
Sanjaya Senanayake is Associate Professor of Medicine, Infectious Diseases Physician at Australian National University. This story is published courtesy of The Conversation (under Creative Commons-Attribution/No derivatives).
