Quannen is careful to distinguish between fact, hypotheses, and supposition when laying out these compelling stories. The reader is never left struggling to separate what is known from what are educated guesses. He is nimble with the science as he distinguishes spillover—“the moment when a pathogen passes from one species as host to another” from emergence—“where the spillover bug thrives and spreads within the new host.” He has a special talent for describing somewhat dry scientific concepts with memorable analogies—for example: “screening for antibodies is distinct from isolating virus just as a footprint is distinct from a shoe.”
His substantial text (500+ pages) covers many but not all of the zoonoses that now make up 60 percent of all human infectious diseases. Included are illnesses that have killed millions such as Spanish Flu, AIDS, and Bubonic Plague as well as unique and quirky diseases like Ebola, Hendra, and Nipah that have spilled over, killed, and then retreated.
Even with your knowledge about the diseases covered, you will likely learn something new and valuable, as I did. I was on the clinical service at the National Cancer Institute during the early days of the AIDS epidemic where we cared for patients before the nature of the disease was well understood. At the NCI, I was well aware of what Quammen describes as “the ratatouille of molecular biology and personal politics left out in the sun to ferment.” I was also knowledgeable about the early history of AIDS in gay men and in hemophiliacs and knew of the Canadian Flight attendant known as patient zero in And the Band Played On.
But I knew less about the scientific exploration to trace the origins of the disease. AIDS, Quammen explains, is an old illness initiated by “a bloody interaction between one chimpanzee and one human in southeastern Cameroon about 1908.” He lays out the probable history of persistence followed by slow progression of the disease in Central Africa. Acceleration likely was facilitated by altered human demographics, widespread reuse of needles for medical purposes, and changing social mores. This altered dynamics culminated in the worldwide epidemic we now face.
Almost every disease explored in Spillover has a natural history full of surprise and counterintuitive implications. Malaria, another killer of millions, is generally not thought of as a zoonosis because the four malarial types infect only humans, and mosquitoes act as a vector, not as a reservoir host. However, P. knowlesi a close relative of P. falciparum, is endemic in Malaysian Macaques and is capable of reproducing in all kinds of primates. If forms of malarial parasites exist in animal reservoirs and are capable of evolving into human pathogens, then the prospects for malaria irradiation are remote indeed.
In contrast to zoonoses that have killed millions, Ebola has killed only something more than 1,500 people thus far, but has received enormous attention because of its mortality rate of 60 to 75 percent, its sudden and mysterious appearance and disappearance, and its still-unknown reservoir, which may or may not be bats.
However, Quammen points out that the virus has several competitive disadvantages: It occurs in remote areas without dense populations. It kills quickly and symptoms appear shortly after infection, so isolation strategies can be utilized successfully.
Nipah, another zoonosis about which I knew nothing, illustrates many characteristics of these remarkable illnesses. Nipah is an RNA virus that leaps from bats to pigs to humans. It appeared in 1998 in Malaysia in pig handlers and was lethal in about 40 percent of infected patients. Pigs act as an amplifier host of the virus, and the initial outbreak was quelled by exterminating 1.1 million pigs. However, subsequent research established that the true reservoir was fruit bats. The same illness reappeared in 2001 in Bangladesh, a Muslim country without many pigs. It was ultimately traced to the consumption of raw date palm sap that had been contaminated with bat guano. The ultimate solution proved to be a 10 cent cover over the clay pots used to collect the sap rather than outlawing the consumption of date palm sap.
Quammen uses certain spillover diseases to illustrate the difficulties of disease control. SARS, a coronovirus with a reservoir in bats and an amplifier host in Palm Civets, spread to humans after wild animal consumption in China. It was propelled to a global epidemic through the worldwide airplane travel now routine in modern society.
Lyme disease, largely a product of our population encroachment on natural woodlands, is a bacterial disease with a complex natural history generally misunderstood by the public. The primary reservoirs are mice, shrews, and chipmunks, with the black legged tick rather than the deer tick as the primary vector. So Quammen states, “Forget about the deer abundance. White tailed deer are involved in Lyme but almost as a trace element—a catalyst.”
Deer function primarily as a site where adult ticks mate. Thus he says “A White-tailed deer in the woods during November is like a teeming singles bar in downtown Manhattan on Friday night, crowded with lubricious seekers.” In my view, that's a wonderful example of Quammen as a scientific interpreter and a literary artist.
Spillover ends with a discussion of the potential for an NBO (Next Big One). He suggests that it will be a zoonosis and is likely to be an RNA virus because of its constant mutability. The reservoir may well be a host with worldwide distribution like that of migratory birds in Flu epidemics. It is likely to have easy human-to-human passage by aerosol spread and will likely have a latent infectious period before clinical illness or lethality.
That seems consistent with a pandemic like Spanish flu or SARS but not so much like AIDS. Indeed if the natural history of AIDS is an alternative model for the next NBO then it may already exist in the world population limping along with a reproduction rate of about 1.0, persisting but not accelerating until the ideal circumstances present themselves: A disquieting but plausible thought.
This is a superb book. It's scientifically balanced, artfully written, entertainingly crafted, and very thought provoking. It will inform you, surprise you, and along the way, if you are anything like me, teach you a lot of medicine.
2012, W.W. NORTON & COMPANY, 592 PAGES, ISBN: 0393066800
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