Spillover (about pandemic diseases/much on Ebola)

Author: David Quammen
Publisher: W. W. Norton & Company, New York, NY


Spillover is the term used to describe the transmission of a virus from a host to humans. Among numerous other diseases it has a large amount of good information about AIDS and Ebola. The number of diseases will, or should, alarm any sane person. Considering the events unfolding around us it seems very timely. This was published in 2012 so the information is fairly up to date.

The number of disease control centers and research centers and researchers that exist to trace and study these diseases is large and often a surprise to most. Not only are there numerous national and international agencies many universities have research groups and the cooperation and amount of information shared and studied is constant and is measured in volumes. Research papers written by one will be read by another and by tying them together their combined efforts have prevented many tragedies. A clue here and a clue there.

The book is about zoonoses. A zoonosis is a pathogen that does as the book title reflects it spills over from a nonhuman animal host population to the human population. On page 21 the author says about the word zoonosis: “It’s a word of the future, destined for heavy use in the 21st century”. Current events have proven him 100% accurate. This book is a must read and a book that should be in every library both public and private. It answers many of the questions asked about Ebola and AIDS. By reading it a person will have a grasp on the problems we face from a pandemic disease and by understanding we may be able to prevent what is now an inevitable disaster from Ebola or an as yet unknown virus.

The author also says on page 21: “Ebola is a zoonosis. So is bubonic plague. So was the so-called Spanish influenza of 1918 – 1919, which had its ultimate source in a wild aquatic bird and, after passing through some combination of domesticated animals (a duck in southern China, a sow in Iowa?) emerged to kill as many as 50 million people before receding into obscurity. All of the human influenzas are zoonoses. So are monkeypox, bovine tuberculosis, Lyme disease, West Nile fever, Marburg virus disease, rabies, hantavirus pulmonary syndrome, anthrax, Lassa fever, Rift Valley fever, ocular larva migrans, scrub typhus, Bolivian hemorrhagic fever, Kyasanur forest disease, and a strange new affliction called Nipah encephalitis, which has killed pigs and pig farmers in Malaysia. Each of them reflects the action of a pathogen that can cross into people from other animals. AIDS is a disease of zoonotic origin caused by a virus that, having reached humans through just a few accidental events in western and central Africa, now passes human-to-human by the millions. This form of inter-species leap is common, not rare; about 60% of all human infectious diseases currently known either cross routinely or have recently crossed between other animals and us.”

The animals that carry these diseases are called “reservoir hosts” and include, but are not limited to, chimpanzees, bats, birds, camels, cattle, fowl, deer, gorillas, cats, dogs, goats, foxes, pigs, horses, rabbits, mice, rats, monkeys and sheep to name a few. They can infect humans from various sources such as passing from the hosts via mosquitoes, fleas and ticks. They can also be spread from bites from animals, coming in contact with their feces or urine, eating fruit that has come in contact with the animals, coming in contact with their blood or by eating the meat of an infected animal if one has an open sore in their mouth. Some viruses can be airborne also. Depending on the disease humans can infect other humans by several ways including sexual intercourse, blood to blood contact and other contact with other bodily fluids.

It goes into the history of many diseases mainly focusing on diseases of the present. The one presently on everyone’s mind is Ebola first recorded case of was in Africa in 1976. There are 4 major strains of Ebola. Ebola often has a higher mortality rate than the Bubonic Plague that hit Europe in the 14th century. (Bubonic plague had a mortality rate upwards of 50%. When the bubonic plague finally subsided the estimates of human losses in various areas were estimated to be between 35% to 60% of the population. It is believed overall about 50% died.

The book explains the conditions that increase the odds of contact with the hosts such as overpopulation and deforestation. As the human population grows the contact with animals hosts increase thus increasing the chances of more spillovers occurring. The disease needs to continue infecting one person after another in order to be a pandemic. If it infects a person and the person does not have contact with others that are susceptible it dies out or reaches what is called a dead end. It is believed that unknown numbers of diseases did this. When it takes hold in a human population the epidemic spreads and grows until the number of people infected or susceptible people reaches the maximum then it starts to decline. Of 1000 people in an area if 500 were infected and either survived or died from there on the epidemic is declining. It is increasing when the number of potential people susceptible to infection remains larger than the number that have survived or died. Because of the toll in suffering and losses both human and economic and the disruption caused it may not appear to be declining when in fact it is. If it continues through the 1000 and does not come in contact with another host, human or otherwise (it can go back to animals from humans acting in reverse) it dies out and goes no further. If it has an avenue of travel to another population it can become a pandemic. Throughout history it is possible for a small tribe or area to become infected and either dies out, recovers or has those not susceptible and the disease starts there and ends there having no way out. With the ability of masses of people to travel long distances in short periods of time the potential for the spread of disease is quite large and quite rapid. We are witnessing that with Ebola.

Gorillas are very susceptible to Ebola and researchers have found areas that at one time had a large population of gorillas to be virtually “gorilla free”. Ebola can go from one animal host to another before entering the human population. It is difficult to trace but the belief is the Ebola that is here in the present is not an old disease but fairly recent as a mutation of another. All viruses mutate and Ebola does so rather quickly. It is probable many people died of it but in areas where life is short, hard and early death is not uncommon death is often attributed to many other causes.

The author writes of dead end hosts and the possibility of Ebola and other zoonoses being around in large numbers but dying out before starting an epidemic: “Outbreaks have been contained and terminated; in each situation the viruses come to a dead end, leaving no offspring. Not the virus in total throughout its range, of course, but that lineage of virus, the one that has spilled over, betting everything on this gambit – it’s gone, kaput. It’s an evolutionary loser. It hasn’t caught hold to become an epidemic disease within human populations. It hasn’t caused a huge epidemic. Ebolaviruses, judged by experience so far, fit that pattern. Careful medical procedures (such as barrier nursing by the way of isolation wards, latex gloves, gowns, masks, and disposable needles and syringes) usually stop them. Sometimes simpler methods can bring a local spillover to a dead-end too. This has probably happened more times than we’ll ever know.. Advisory: if your husband catches and Ebolavirus, give him food and water and love and maybe prayers but keep your distance, wait patiently, hope for the best – and, if he dies, don’t clean out his bowels by hand. Better to step back, blow a kiss, and burn the hut.”

The author also has a large portion devoted to AIDS. It has been traced to the area where they felt it emerged and some plausible theories as to how it got into the human population and spread. At one time a Canadian flight attendant was deemed to be patient zero, in other words the first in the Western hemisphere to have it. It has been determined that it has been around longer. There are HIV and SIV categories and subcategories. The S stands for simian which denotes monkey. They have found evidence that it was around in Zaire, the Democratic Republic of the Congo, in 1959. After years of research they found samples from that area that had been in storage for decades in a laboratory/research center in Africa.

They have ultimately traced it to a section of Cameroon in 1908 give or take a degree of error. The area was remote and contact was minimal. As was discussed with Ebola it often died out before passing from one person to the next, reaching what was the dead end. They have traced it to a species of monkey living in that area. A person could have gotten it by butchering a monkey and getting blood in a cut or eating raw meat and having a cut or sore in his mouth. As the population grew and more and more contact was made it began to slowly filter out. One thing that they believe hastened its spread was between 1921 and 1959 the authorities treated many of the tropical diseases with injections. This was before the disposable syringe and the number of shots given was so high the proper sterilization of needles was not possible. They were also costly and had to be reused over and over. Between 1917 and 1919 a French doctor treated 5347 sleeping sickness cases with only 6 syringes. Infect one prostitute and the spread would quicken. Think of how many may have been infected.

With the increasing numbers of cases and growing concern about Ebola and the spread of AIDS at such a rate this book is a must. It is a thick book but don’t let it intimidate you or discourage you. It is so interesting it is a fast read.