HO BOY! PREPARE FOR A SCHLOCKFEST!!!
This is certainly a challenging question. The exact details regarding every known human pathogen may never be known.
Straw-man. Doh. FOCUS!
However, some concepts are worth exploring. The issue should always be considered in the light of the large body of biblical and scientific evidence that there was such a Flood, and so we need to look at possible mechanisms to explain how these diseases did survive the Flood.
By crikey, these people suck! Imagine me saying this: "The issue of Elvis' reincarnation in Tennessee as a young girl should always be considered in the light of the large body of literary evidence, i.e. "Forty Days In Vegas,", and scientific evidence, i.e. the stains on a napkin in a diner downtown." Talk about your ridiculous presupposition!
The following suggestions should suffice to show that even if we exclude any miraculous intervention, there are potential answers which between them are probably adequate to cover the organisms concerned. In addition, there may be aspects which have not even been thought of yet.
So, what they're saying is, even if they don't have all the answers, on average, they have enough of them to sort of make their point. No real scientist would ever get away with such poppycock, but I digress...imagine me saying: "Even excluding miraculous intervention, there are potential answers which between them are probably adequate to cover the reincarnation of Elvis, according to the Bible". Feh.
(2) Mutational 'Horizontal Evolution'
This is likely to be relevant for viruses in particular. Random changes (for example, mutations) have never been shown to generate significant amounts of new teleonomic (functional, project-oriented) information. Thus they do not create a new organism, or cause any true (uphill) 'evolution'. However, it only takes an informationally insignificant accidental change in the protein coat of a virus to vary the way it is recognized by an immune system and cause a major shift in infectivity.3 Thus, a harmless green monkey virus may begin causing serious illness in humans.
Notice how these people carelessly forget the fact that we've only been studying genetic information for, like, 50 years, DUDE! We're talking processes which happened over aeons!
Furthermore, the declining lifespans of humans after the Flood may indicate an overall degeneration, such that Noah's family may have had a lot more host immunity to diseases which now cannot be asymptomatically carried.
Notice how there is zero physical evidence for this assertion. Show me the money, baby! Since these people are so heavily set against genetic change of any kind in living forms, how can they suddenly support the viewpoint of our bodies gradually degrading to a fixed level which is now maintained by the vast majority of all human civilization? Was there some magical point where we stopped degrading? Why do the cavemen we find frozen in mountain ranges have pretty much the same DNA as us? They certainly didn't look like they live for centuries! God!
Some disease organisms today can be carried in one part of the body, but cause disease if in another (for example, the yeast which causes vaginal 'thrush' is usually carried harmlessly in the intestine.) Also, some organisms only cause disease when there is a reduction in the population of beneficial germs, for instance in the intestine. The effectiveness of this way of a person being protected from an organism they were carrying by means of a flourishing population of healthy 'good' germs may well have decreased after the Flood. The disharmony between man and his environment may have worsened as extinction of some plant species led to dietary restrictions.
So let me get this straight - they're saying that after a global flood, which would have farked up almost every fish in the oceans (unless God magically made the rain salty enough, thereby dooming every fresh-water fish in existence to a painful death too), humans' DNA began to degrade, and this, combined with a poorer diet because there were fewer plant species around (and for this sudden die-back there is no evidence whatsoever, esp. not in light of research conducted on the dietary habits of ancient civilization...you know, that stuff that they have PHYSICAL proof for in museums...), the viruses were suddenly given a more friendly environment to propogate in. Doh.
Today, we know that some disease organisms (for example, the malarial parasite) are carried in, for example, mosquitoes. This raises other questions. Were flying insects part of the 'creeping things' which were all sent on board the Ark, or did they have their own 'arks' outside, such as huge rafts of matted, floating vegetation? Could the viruses survive within biting insect populations for long enough considering these insects' life-spans? It should be remembered that not all humans would have perished in the first few weeks of the Flood. Many may have survived for some time, at first on high ground, then on makeshift rafts.
There are enough viruses that would DEFINITELY NOT be found in insects to refute this little piece of reasoning quite nicely. For instance, viruses which cannot survive outside humans, that only infected humans living, in, say, the Amazon Basin, a place Noah could never have known about, let alone visited.
This could apply especially to those dying in the late stages of the Flood, becoming bloated and floating to shore later. This seems conceivable for some moulds and bacteria ? even some viruses have been known to last for decades.7 Of course, organisms then have to have an opportunity to again infect a living person.
OK, I guess we can give them this one - despite the fact that many viruses require specific temperatures to survive (e.g. HIV), and because all the sharks and other scavengers would've been dead from saline shock. And it seems that these geniuses don't know the difference between HIV and AIDS. No surprises there!
Though some viruses die readily when dry, others survive long periods in the dried state. For example, rabies virus in bat droppings can dry out to become airborne dust, which has infected cave explorers. How does anything stay dry in a worldwide Flood? Some of the floating clumps mentioned earlier may have had dry interior portions ? also, some parts of the Ark itself would have provided a dry enough environment.
OH God, I can't believe these people thought of this. No comment!
The whole matter of apparent catastrophic snap-freezing of some mammoths in the Arctic circle is controversial as regards whether it was associated with the Flood or a post-Flood event, but it brings to mind the fact that many disease organisms survive well when frozen. In general, the Flood event was probably a warm one, but insufficient modelling has been done to establish what conditions could have been possible at the poles.
Yeah, exactly. It's really funny how all those Arctic ice cores don't seem to have anything even remotely resembling a worldwide flood recorded in them. Those cores go back millions of years, and from the look of them, the snowfall's been pretty damn steady for a while now.
None of the possibilities discussed above is presented as an answer adequate by itself for all the different types of disease organisms. Taken together, however, they demonstrate that the common anti-creationist 'betcha-can't-answer' jeer about a sickly family staggering off the Ark laden with every disease known to man is a caricature which does not do justice to the known facts. Further research and thought on the subject is encouraged.
Yeah, that's exactly what these guys should do, methinks.