Our idea here is to develop appropriate tests for identifying whether or not, say, a highly specific protein known to be present in the capsular covering of certain pathogenic viruses is in a given fossil specimen. That¿s the antigen we will then probe for using custom-designed antibodies. If we come up with a positive, that the protein is there, then we have narrowed our search enormously, down to that set of viruses known to manufacture the protein of interest. That gives us a clue as to what genes we should then look for in primer design for use in PCR experiments. If we get corroboration back, in the form of an expected sequence, then we know that this particular pathogen or kind of pathogen was present in that mammoth at whatever time it lived. That¿s not a demonstration of hyperdisease, clearly. That¿s only saying that you can in fact retrieve genetic information on "fossil" exogenous viruses. But that would be an astounding breakthrough for our work, because once we know how to conduct the proper experiment in the first case, the procedure can be generalized to all cases.
Another possible approach is using electron microscopy. This seems very primitive, sort of harkening back to a different age. But for us, identification is everything. If we could get an initial impression of what kinds of pathogens are present in a fossil, then we could go to more sensitive modern techniques to learn a lot more about them. In the particular case of mammoths, our idea is that if we could get vascular tissues, which occur on the inside of well-preserved bones, we could search for organized particles by a process of filtration. A number of viruses have organized capsules that are morphologically distinctive and diagnostic. If we can identify such viruses in filtrates examined microscopically, then we¿ve got something else we can use to establish whether this or that particular pathogen is present. The test then becomes to see whether we can complete the hat trick by fishing out a sequence for it using PCR.
SA: Are you looking at samples from mammoths from a particular area?
Image: CLARE FLEMMING
RM: We¿re in all of these cases trying to find individuals that were possibly parts of one or more "terminal populations." This is another one of the very hard things that we have to do. The logic of our argument is such that it has to be accepted that the killer pathogens were not present in the population until they were introduced. Once introduced, their effect was so massive that the population and thereafter the species died out in its entirety. If we¿re talking about extremely lethal, acute infections, then once the panzootic gets started species will presumably have to disappear very quickly¿perhaps in a few tens to a few hundreds of years. The difficulty paleontologically is to find those specimens from terminal populations. It¿s really very difficult to do because you have no idea necessarily where to look. So we¿re doing the best that we can, and what that means in the case of mammoths is going to northern Asia and radiocarbon-dating as many young-looking specimens as we can¿and we have had some success in this already. One of the places we¿ve worked in, for example, is Wrangel Island, which is where mammoths survived up until about 4,000 years ago. That¿s clearly a terminal population case. Another is the Taimyr Peninsula, which is where the youngest radiocarbon dates for continental Asia have come from. It looks like that was some kind of refugium for mammoths¿they survived there up until about 10,000 years ago.
SA: Are you envisioning a single disease or a suite of diseases wreaking all this havoc?