The Moving Castle of Ebola 伊波拉之移動城堡

Having looked at the various human ebola outbreaks in the past forty years, the next question is how do they move from one place to another, and what happens during those quiescent period?

To understand the first question, we first look at the life cycle of ebolavirus.  Though not yet fully understood, the virus primarily survives in fruit bats of the Pteropodidae family.
They cause infection to wild animals and mammals like apes only occasionally.  Infection in human occurs primarily because of human animal contact followed by human to human spread.  The following graph from CDC summarizes such transmission routes.

Ecology of Ebolavirus. CDC, US.            (http://www.cdc.gov/vhf/ebola/resources/virus-ecology.html)

This suggests that, even in the absence of reported human infection, the virus exists, probably widely in the fruit bat family.

Natural host fruit bat of Ebolavirus. UNC website. (http://news.unchealthcare.org/news/2014/june/dispatch-from-guinea-containing-ebola)

The World Health Organization has put together the geographical locations of where serological evidence, such as the detection of antibodies in serum suggesting prior infection, to ebolavirus.  As from the health map obtained from the WHO website, apart from those countries with known ebola outbreaks in central and western africa, there are evidence to show infection has occurred in other parts of Africa such as Medagasgar and in South East Asia.  This coincides the areas within which the ebola host fruit bats are found.  Of note is that the fruit bat is also found as far as the east coast of Australia.

Distribution of the natural host fruit bat of ebola virus and areas with known evidence of human or animal infections. WHO website.

The map also showed that the Reston ebolavirus, so far considered not causing human diseases, have caused infections in animals in Mainland China as well as all over the United States, the latter through importation of infected Monkeys rather than due to the presence of natural host.  Such evidence suggested that, during the period of apparent quiescent, infection still occurs in various areas where the natural hosts are found without causing devastating human outbreaks.

Photo credit:
University of North Carolina News Room on Ebola hemorrhagic fever.
http://news.unchealthcare.org/news/2014/june/dispatch-from-guinea-containing-ebola