Day 18: Amplifier
A side effect of Quammen's book is that I have learned a lot about zoonotic diseases in the last fourteen days. For example, I learned that a spillover is a contained event, while the emergence of a disease is a developing process. That is an important distinction bestowing precision to the language.
A vector does not cause the disease, it carries and transmits a pathogen in the process of getting something from another organism (blood for example). A reservoir host is an organism unencumbered by a pathogen and keeps it alive during times in which there is no active infection. An amplifier host allows the pathogen to reproduce in large quantities. Neither the reservoir host nor the amplifier host gain anything from the spillover. Actually gorillas and chimpanzees get sick and die when they become amplifier hosts for ebola virus.
In Contagion's last sequence (which chronologically occurs at the beginning of the story but has been placed at the end to conceal the spillover which causes the disease and holds the key to subsequent events), we see that a displaced fruit bat perches on the beams of a building housing domestic pigs. After the bat drops the fruit, presumably tainted with pathogens found on the bat's saliva, a pig eats it. The fruit bat is the reservoir host, the pig is the amplifier host. The now abundant pathogen transfers from the pig's mouth into the chef's hands by direct contact. As the chef is asked to meet one of the guests in the restaurant, Beth (Gwyneth Paltrow), he wipes his hands on his apron but does not wash them. In the next scene the chef and Beth are holding hands. That's how Beth becomes the index case (what people now might refer to as patient zero) of an emergent zoonosis caused by a spillover event. The fortuitous circumstances are ultimately generated by humans, who in their greed and unethical treatment of the planet and its creatures, become the primus movens (a first uncaused cause) of the pandemic.
In the first chapter of Quammen's book, the reader is faced with the description of a mysterious illness afflicting a mare called Drama Series. The pregnant mare quickly became ill, and despite the best efforts of the trainer and one of the stable hands, Drama Series died and, eventually, so did all the other horses at the stable as well as her trainer (the stable hand was infected and became ill, but survived). A new virus was identified as the culprit. It came to be known as Hendra virus and Drama Series was the index case. Quammen explains that the horse acted as amplifier host, and tells the story of the hunt for the reservoir host, which turned out to be the flying fox. Although a significant percentage of flying foxes (almost 50%) test positive for Hendra virus, people who handle them do not get infected. The amplifier host is necessary for human infection to occur, while horses get infected from flying foxes droppings or saliva.
In the 1995 film, Outbreak, a monkey appears to be the amplifier host for the fictional and deadly Motaba virus which mutates from aerosolized (like the SARS-CoV-2, the virus behind COVID-19) to airborne transmission. In airborne transmission no direct contact is necessary for the infection to occur. Outbreak is much less interested in presenting a possible scenario than Contagion is. This might have something to do with the wider access to information we have today. The public might still enjoy dramatic and scary stories, but their believability matters more than ever before.
Were it not for the pandemic, I would know next to nothing about any of these things. I'm not the only one. As we watched Robbie Keough (Rene Russo) and her colleagues arriving in Cedar Creek to assess the outbreak, all dressed in yellow scrubs and a kind of round cap which, to my non-trained eye, appeared to be something you might want to wear in an operating room to protect patients, Tessa exclaimed: "Good thing they have covered their hair!"
She later searched to see whether Cinema Sins had made an Outbreak video and remarked on that fact. Regrettably they hadn't which is to say our work is never done and we have new life goals.
Canada cases 11,284
World cases 1,016,128
World deaths 53,146
World recoveries 211,409