Birds of a Feather, Kill Together
Posted in Uncategorized on March 17th, 2003 by Bigwig – Comments OffGiven the ubiquitous coverage and discussion of the Middle East, I thought we could relax and talk about a less stressful subject tonight, say….deadly hemorrhagic fevers. Like Ebola, for instance. That feels relaxing to me. Does it feel relaxing to you?
I thought so.
A new theory that groups Ebola in with a family of avian retroviruses on the basis of its physical appearance and history has prompted an expedition to the Congo in hopes of finally discovering the elusive host of the virus.
Birds were implicated as a possible host to the deadly virus by David Sanders and Scott Jeffers at Purdue University, Indiana, and Anthony Sanchez, at the US Centers of Disease Control in Atlanta, Georgia, who showed in December that there are strong structural similarities between Ebola and some bird retroviruses.
“The biochemistry of entry of Ebola [into a cell] is really similar to bird retroviruses. It is clear that they have a common ancestor.” Sanders told New Scientist.”We suggest the possibility that the current natural reservoir is a bird host – it’s consistent with Ebola’s epidemiology.”
The central African rift valley separates the ranges of bird species into distinct western and eastern groupings. Ebola outbreaks occur in central and western Africa but not in the east – consistent with being confined to the bird populations on one side of the rift valley.
Most human cases of Ebola are the result of a hunter who has eaten infected bushmeat, the flesh of either gorillas or chimpanzees. The hunter then comes down with the virus and passes it along to those in close contact with him, both before and after his death. The main, and possibly only, transmission route of the virus among primates and humans (yes, redundant, I know) is through contact with the fluids or flesh of an infected person. What is not known is how the virus infects the primates the hunter ate to begin with, though obviously it can also be spread by close contact among the members of a specific primate population as easily as it can be among a comparable human group.
The distinct disadvantage that researchers have been at in tracing the disease reservoir has been that it’s nigh on impossible to observe a primate group at the level of detail necessary to even develop a theory about the transmission route. A researcher would not only have to catalog all the daily food items eaten over the course of several months if not years to even have a chance of observing a infected chimp, but also somehow account for all the insects the primates came in contact with over the same period.
If the bird theory holds, then the most likely vector of transmission is bird feces, most likely ingested along with leaves or vegetation. The avian host would probably not be a common species, or one that gorillas and chimps come into regular contact with, as the primates in the specific area that Ebola is found in would either have died out or become immune to the virus over time. So, a rare to uncommon forest species, as it certainly has to share the same ecosystem in order to pass along the virus. Or, if Ebola outbreaks are seasonal, which is as yet undetermined, then possibly a migratory species might be to blame. That would be bad news for the researchers, as the host species would have already passed through the area.
The argument against a migratory species being the Ebola is that the virus should be present over the entire migratory route, and there just aren’t many avian species that migrate over that short an area. If the Ebola host is a bird, it’s probably a resident species for central and western sub-Saharan Africa, not one that moves in and out of the area. It would also be one not normally used as a food source by the natives, (else the connection between birds and Ebola would have been made earlier) and consequently a species that not much is known about. For other reasons, it would also be nice if the species frequented caves as well as forests.
There actually is a avian family that fits all of those requirements, the Rockfowls, or Picathartidae, which inhabit the requisite habitat (caves and forests) and overall range, are uncommon to rare and about whom very little is known.
There’s no guarantee that either of the species in the Picathartidae family is the Ebola reservoir, but given the relative congruence of what is known about those avians with what is known and theorized about Ebola, researchers would be extremely remiss if they didn’t try very hard to capture a Rockfowl sample.
But, just in case, you heard it here first.