Part of Kuban's Paluxy website
Among the serious problems young-earth creationists face is explaining the survival of scores of human-specific diseases, and how Noah and his family managed to survive while being infected with them all. Many diseases and parasites can survive only for short periods of time outside a human host. Among these are measles, smallpox, polio, typhus, hepatitis, sexually transmitted diseases such as gonorrhea, chlamydia, HPV, and trichomoniasis, and syphilis. Many other diseases can only survive in humans and insect vectors with short life spans. In order to survive the Flood year, all such diseases must have inflicted one or more of the eight people on the Ark. Many if not most of the animals aboard the ark also would have had to be infected with multiple diseases, in order to explain how such diseases survived (Isaac, 1998).
Strict creationist Johnathan Sarfati dismisses these problems with some questionable proposals. He states that "...germs were probably more robust in the past, and have only fairly recently lost the ability to survive in different hosts or independently." However, if diseases were more "robust" in the past, one might expect them to cause even more severe symptoms than they do now. He also presents no evidence for the idea that they could infect different hosts. Even if this were true, it does not solve the problem. All this would do is swap one host for another for each such disease, still leaving each animal with many diseases, since only a pair (or seven pairs for unclean animals) of each animal "kind" was taken aboard the ark.
Sarfati also argues that "even now many germs can survive in insect vectors or corpses, or in the dried or frozen state, or be carried by a host without causing disease." He does not explain where dry or frozen conditions would be found during a violent global flood. His comments also neglect the fact that diseases and parasites that survive in insect hosts generally only do so for short periods of time--generally far shorter than a year. Many depend on living human hosts for survival. Although some do not cause serious illness, many others do. Finally, Sarfati suggests that loss of disease resistance "is consistent with the general degeneration of life since the Fall." However, Noah was many generations from the Fall, and Sarfati's proposal also requires that many diseases that cause severe illness or death in humans today would have caused no serious harm to Noah and his family, but again Sarfati presents no evidence for this.
In order to appreciate the magnitude of the problem, consider that even if we set aside all human-specific bacteria and viruses, there are scores of human-specific parasites that also cause illness or disease, including various protozoans, fungi, yeasts, insects, and helminths (parasitic worms). There are over 100 types of helminths alone, including roundworms, hookworms, whipworms and pinworms. They produce symptoms ranging from constipation and stomach bloating to anemia, asthma, diarrhea, fatigue, joint pain, limb swelling, rashes, and malnutrition.
Even if ignoring the question of how the clean-living Noah and his family managed to get infected with all of these parasites and scores of diseases (including sexually transmitted ones), the question is how they either the humans or the diseases survived. Many human-specific diseases often cause severe illness or death, even acting alone. Many also weaken the immune system, making the victims even less able to tolerate other infections. Thus, it is difficult to imagine how the ark family survived the Flood year, let alone managed to feed and care for tens of thousands of animals (many very sick animals, no less). Of course, YECs can propose that God miraculously protected the ark passengers from the effects of all these diseases. However, inventing such ad hoc extra-Biblical miracles (Isaac, 1998) seems to invalidate YEC claims that a global Flood is scientifically sound and consistent.
There is another interesting aspect of this issue. As noted by Mark Isaac (1998), many host-specific diseases which don't kill their host are usually soon eliminated by the host's immune system. So if Noah had a functioning immune system (and Sarfati suggests it would have been better than that of modern humans), many diseases would have been erraticated before the end of the flood year. Even if a disease like measles skipped from passenger to passenger, well before the end of the Flood year the disease would have gone extinct. Yet its still here, along with many other short-duration diseases.
In order to survive, many extant disease agents and parasites must have infected Noah and his family during the Flood year. This presents two serious problems for advocates of a recent global flood: 1. How Noah and his family survived so many diseases and infections, and 2. How many short-lived diseases survived the Flood year.
Jonathan Sarfati, 1997. How did all the animals fit on Noah's Ark? frame left First published: Creation 19(2):16-19. March 1997. Web version a: http://www.answersingenesis.org/creation/v19/i2/animals.asp