A Plague on Both Your Houses

The plague –nothing conjures up death quite like that word -after all, the bubonic plague wiped out half of Europe in the 14th century. But there have been others of its ilk –and all probably caused by the Yersinia pestis bacterium. Although the yet-unnamed infectious agent was identified in the 1890ies by the bacteriologist Alexandre Yersin -working at the time in the Pasteur Institute on plague samples from an outbreak in Hong Kong- the name was initially misattributed… Never work for somebody really famous when you discover something important. Personally, I preferred its previous name of Pasteurella pestis because that’s the name I was first taught and I liked the alliteration. But never mind.

The plague has three different presentations, depending upon the organs infected: bubonic plague, from infection of the lymphatic system and localized as buboes (swellings of infected lymph nodes which may become necrotic and turn black in their attempt to defend the body); pneumonic plague –infection of the lungs, presumably from aerosolized droplets from coughing or the like; and the rarest and likely most fatal of the three, septicaemic plague, which is an infection of the blood stream. All are carried by fleas, which are carried by rats, which then carry them to us.

Although we tend to associate the word ‘plague’ with the infamous ‘Black Death’ of European fame -not least because of the shock value of its name, I suspect- there have been several plagues throughout history. The first was originally thought to have been as early as 430 BCE in Athens, but a study published in the journal Cell in 2015 suggests that it began long before that –about 5,353 years before, actually. But perhaps a more assimilable article that outlines the background is found in a BBC news report, also in 2015: http://www.bbc.com/news/health-34603116

‘Samples taken from the teeth of seven bodies contained traces of the bacterial infection in the Bronze Age. They also showed it had, at the time, been unable to cause the bubonic form of plague or spread through fleas – abilities it evolved later.’ You have to love this kind of information, eh?

‘In its early days, it could cause only septicaemic or pneumonic plague – which is nearly always deadly and would have been passed on by coughing. By analysing the bacterium’s genetic code through history, the researchers estimate it took until 1000 BC for plague to evolve into its more familiar form. One mutation – acquiring the ymt gene – allowed the bacterium to survive inside the hostile environment of a flea’s gut. […]Developing a separate gene, called pla, allowed the infection to penetrate different tissues and cause bubonic plague.’

But all things change, don’t they? Things fall apart; the centre cannot hold, in the unforgettable words of Yeats. And yet why would a pathogen evolve to destroy the very hosts on which it depends? Why burn the hotel…?

I suppose an easy explanation might be that of a game in which each side –host/pathogen- continually attempts to outsmart the other. More virulence in the invader leads to more defensive mechanisms in the invaded –things as overt as quarantine or antibiotics, to the more subtle, but hopefully preventative development of immune resources by vaccination or over the longer term, adaptation of endogenous immune defenses: survival of the fittest.

But for me, the intriguingly unanswered question still remains: why kill your host? Why not coexist as, say, a parasite –or even a commensal- in the gut, or create a chronic condition that might weaken the owners, but not eliminate them? Of course, some pathogens are just evolutionary dead-ends – fireworks that illuminate the sky briefly and then disappear as suddenly as they appeared, or maybe finally settle into a desk-job and plod along just under the radar. But I suppose even germs want some time on the pedestal, though. Nothing ventured, nothing gained… Ecological opportunities beg for exploitation –leave a window unlocked, and something will find it.

Of course there are other ways of making a living: attack and retreat to fight again… While not strictly analogous, I am reminded of the Champawat tiger of Nepal (and later in the Kumaon district of India) in the late 19th century. She used to attack suddenly and then disappear before anybody could do anything about her. True, she was finally shot, but not before she’d managed to kill almost 450 people in different locations and instilled fear of her return for years. Fear is like that –especially fear of what Donald Rumsfeld (a once upon a time U.S. secretary of Defence, remember?) oxymoronically called the ‘known unknowns’.

The plague has managed a similar trick over the centuries, flaring up in one region, only to hide, then reappear in a totally different region later –often much later. ‘The most recent plague epidemics have been reported in India during the first half of the 20th century, and in Vietnam during wartime in the 1960s and 1970s. Plague is now commonly found in sub-Saharan Africa and Madagascar, areas which now account for over 95% of reported cases (Stenseth, 2008)’ [https://www.cdc.gov/plague/history/index.html]

But, even those of us living in North America are not entirely safe -remember that Hong Kong plague that Yersin was studying in the 1890ies? A ship from there arrived in San Francisco in the summer of 1899 with plague found among some stowaways, two of whom escaped and drowned in the Bay. An epidemic of plague hit San Francisco nine months later. Whether it was from them or from rats that swam ashore, is not known, but the disease has been with us ever since.

http://www.livescience.com/51792-plague-united-states.html  ‘Plague cases occur sporadically in the United States — between 1970 and 2012, an average of seven plague cases occurred yearly […] But plague cases don’t show up everywhere. Rather, most occur in rural areas in western states […] the CDC says. One reason why cases of plague are restricted to the West is that the rodent populations there carry the disease […] “Prairie dogs are one of the major rodent species that serves as a reservoir for plague, and they tend to be west of the 100th meridian” in the United States. For this reason, this line of longitude is sometimes referred to as the “plague line”.’

What, will the line stretch out to th’ crack of doom? asks Macbeth. I suspect that he would have found it fascinating that any of us would think we might be immune from history. And yet, despite all its bad press and the terrifying epithet of ‘Black Death’, plague cases in North America are rare. They can occur when people visit rural areas, says, Dr. Adalja, an infectious disease specialist at the University of Pittsburgh’s Center for Health Security, although ‘people are more likely to be infected with tick-borne illnesses such as Lyme disease, than plague.’

Uhmm, I’d be careful with squirrels in California, though…












Ever since I was a little knicker I had a dog, or a cat, or both. It was part of growing up –playing with the dog in the park, avoiding the cat’s claws as it grabbed for the piece of wool dangling temptingly in front of it. And then there were the times sitting curled up in the dog house just to see what it was like to live there, or sharing my ice cream cone with it because it looked hungry. Being licked in the face was also easier than washing before dinner… Memories, no doubt aggrandized with time, but nonetheless part of the mythology of childhood. My childhood; my mythology.

But I had somehow assumed that it was just a part of la Belle Époque for people of my age; something that the younger generations had long since abandoned for fear of contagion or changing perceptions of what a child should be allowed to do -or want to do. We live in a much more heterogeneous, sanitary society than we used to: a cultural melange that often accords animals a different role in our lives. Whether this is an advancement or merely a change in outlook didn’t much concern me: I’ve already had my past, lived my childhood.

But several months ago I happened upon a review article in the Canadian Medical Association Journal http://www.cmaj.ca/content/187/10/736.full on ‘Reducing the risk of pet-associated zoonotic infections’ and it got me thinking about my pregnant patients and their unintended risks. Of course, every health care provider –every woman, it seems- knows about not cleaning out the kitty litter in pregnancy (Toxoplasmosis) –and even avoiding the other end of the cat (Cat-scratch disease: gram-negative bacterial infections)- and yes, or the perils of eating some types of raw fish sushi too frequently (Mercury contamination). These all seem to be part of a societal mythos to which we are so often exposed, that one almost wonders if there is a gene that the placenta activates whose sole job is to send avoidance signals to the pregnant brain.

And yet the article outlined many more diseases that animals can transmit to humans (zoonoses) that are more quietly under the radar –multidrug-resistant bacteria as an increasingly worrisome emerging threat, for example. So, in the interests of patient safety, I thought it incumbent upon me to add animals to my list of questions. There was no spot for them on the prenatal form, so I kind of slipped it in under ‘other’. Along with ‘occasionally’, I find that ‘other’ is one of the more important categories of words that I like to use.

One woman, Lorraine, seemed to find the questions objectionable however. It was almost as if she felt I was accusing her of uncleanliness, or maybe petophilia, or something.

“I’ve never owned a cat, doctor,” she said with a bit of a huff in her voice. “I’ve always thought they were dirty animals,” she added, as if to justify her vehemence. “They eat vermin when you’re not around.”

“Sometimes that’s a good thing,” I said, hoping to calm her down a little.

She pinned me to my seat with needles from her eyes. She obviously resented the inference of suboptimal conditions where she lived. I left it lying fallow.

“We do have a dog, however –my husband insists on having one,” she admitted with a little reluctant shrug, obviously wary of my reaction. “But it is only allowed on the rug in the kitchen –far away from the food preparation area- and it sleeps in the garage.” She stared out the window behind me, this time avoiding my eyes. “And he takes it to the vet all the time for its vaccinations and flea medication. Costs him a fortune, what with the price vets charge nowadays.” Her eyes flitted around the room, obviously tallying the cost of the pictures on the wall, and even the knickknacks on a little oak table that patients had given me. Obstetricians were clearly not immune to price-gouging –although in Canada with our healthcare system, the extortion was presumable aimed at the government.

Then she waxed reflective. “I had a dog when I was young, though. Boots was his name and he used to follow me to school –I lived in a small town with not much traffic,” she was quick to explain, lest I think she was careless about its safety. “We used to share everything, I remember.” She risked a quick, guilty glance at my face to see if she had transgressed, even at that age.

“And then I got parasites –cryptosporidium­. My mother made me memorize the word; she says I got it from being licked in the face by Boots. I remember I had terrible diarrhea and cramps, but I also remember her telling me that there was no treatment for it and that because of what I let the dog do, I was going to have parasites for the rest of my life… She had a drinking problem at the time, though, so she soon forgot about it… I didn’t.” She sighed somewhat theatrically and continued. “After that initial attack of diarrhea I never had the problem again, so like about so many other things, maybe she was wrong about that.”

I nodded reassuringly. “People with intact immune systems seem to be able to restrain it –keep it in check. And besides, how certain were they of the diagnosis back then?”

She shrugged. “It was just something my mother told me…”

A sudden look of panic attacked her face. “The immune system is dampened in pregnancy isn’t it?” But before I could explain what that meant, her eyes opened like she’d seen a ghost. “Am I going to give it to my baby?”

The answer, of course, is probably not –especially if the condition is not active during the pregnancy- but using a ‘probably’ would only inflame her anxiety. I find when there is a heightened level of concern that actually looking it up on the computer as they sit and watch, is very reassuring: I am then au courant. So I Googled the Center for Disease Control website for ‘infections in pregnancy’ (http://www.cdc.gov/ncbddd/disasters/infections.html) and printed it out for her. It wasn’t much, but it seemed to help. It didn’t do anything to foster a more tolerant attitude towards dogs, however…

That night, as I sat reading in the living room in front of a crackling fire and my own dog lay dreaming near the fireplace, I got to thinking about my own life with dogs. Was I at risk? But then, when I stirred in my chair and one of his eyes opened and stared at me curiously, I realized it didn’t really matter. The risk was worth it.

Umm, I did wash my hands this time after he wandered over and licked them, however; but I think he was just telling me not to worry about him