I just love oysters. Today they are seen as a luxury food. But did you know that in Victorian times oysters were a poor man’s food? Servants were fed on oysters several times a week and there were sometimes howls of protest at repetitious “economies”!
In the 19th century, oysters were plentiful and cheap; and were sold on almost every street corner in London. The lower class used oysters as a substitute for expensive beef in stews and soups. One of the most popular Victorian dishes with the lower class was oyster pie!
Did you know entire human civilizations have thrived off this small, tasty bivalve? Massive piles of oyster shells (e.g., middens) have been found on every large landmass on Earth, and evidence of oyster consumption has been dated to almost two hundred million years ago.1
Claire Panosian Dunavan, professor of medicine and infectious diseases at the David Geffen School of Medicine at UCLA and a past-president of the American Society of Tropical Medicine and Hygiene, loves oysters too. Oysters Rockefeller, yes. Steamed oysters with ginger and scallions. And best of all: raw, briny oysters with a dash of Tabasco, lemon juice, or a delicate mignonette.
But she’s giving them up!
I haven’t been “bitten” by an oyster since 1986 (one “got” me and I ended up throwing up for 2 days!) But some people have been “got” by oysters. In the late 1980s there was a study linking oyster intake, intestinal symptoms, and Vibrio stool cultures in roughly 500 doctors and scientists visiting New Orleans. Yes, those who ate oysters—both raw and cooked—suffered more diarrhea than those who abstained. But so what? More than half of the subjects who were found to have non-cholera Vibrio bacteria in their stool never became ill.
Then, in 1995, the FDA approved the first-ever Hepatitis A vaccine. “What a boon,” says professor Dunavan. “Especially for people who loved filter-feeding bivalves like oysters, mussels, scallops, and clams, as well as many others at risk for Hepatitis A’s harshest blows (think citrine conjunctivae, hemorrhage, encephalopathy), which were all too common in my early-career days.”2
But she’s worried about Vibrios, a nasty bacterial strain. I had my dose in 2006 when I volunteered to help in Sri Lanka, after the tsunami. Conditions were appalling. I got cholera bad! (Vibrio cholerae). I nearly died but kept myself alive drinking the plane dry of chardonnay on the 23-hour flight back home! I think it worked partly as a bactericidal but death from cholera happens within hours, due to rapid dehydration due to diarrhea. Since wine is 88% water, I attribute my survival to that! Haha!
Cholera has been with us since ancient times, of course. Over the centuries, millions have died (and still do in poorer unhygienic countries) . Medical history was made when physician John Snow figured out that the London cholera epidemic of 1854 was being caused by the water pump in Broad Street (Golden Square). He had the pump shut off (they removed the handle!) and the epidemic, which killed over 600 people, came rapidly to an end.3
It was an important step in epidemiology. Incidentally, the actual pump is still there today, in the Soho district, as a memorial.
Anyway, back to oysters! Or rather back to the cousins of cholera. Vibrios are motile, comma-shaped bacteria that live in brackish coastal water and sometimes contaminate oysters. Although Vibrio cholerae is the clan’s most infamous species, one of the deadliest bacteria on Earth today is Vibrio fulnificus. It can kill you in less than a day! And it happens to be here in the USA.
It is easily picked up by walking along the sea shore. If you happen to have a tiny skin crack or cut in your foot look out! V. fulnificus can penetrate through a miniscule skin breach and the results of an infection can be disastrous. The mortality rate is at least 18%.
If you are sick with liver disease or other afflictions, you are especially vulnerable. At the very least you could end up with profound sepsis and necrotic, blistering wounds for which you could need skin grafts.
Yet, if your overall health is compromised, did your doctor warn you not to eat raw seafood? Of course not.
Now we have a new kid on the block: Vibrio parahaemolyticus. Although less lethal than V. vulnificus, this species also causes gastroenteritis, wound infections, and sepsis mediated by a heat-stable toxin found in human pathogenic strains. It is found in oysters and clams, etc. as far north as British Columbia.
A recent report from Australia about oyster-related V. parahaemolyticus infections in 268 people with a median age of 52: in this outbreak, many sufferers were on drugs that reduce gastric acid — a timely reminder that hypochlorhydria (which increases with age even in unmedicated people) predisposes us not just to infections due to Vibrios but other gastrointestinal pathogens as well.
Climate Change
In the eastern United States, the incidence of V. vulnificus infection has increased more than 8-fold from 1988 to 2018, with case numbers projected to double by 2100. In recent years, similar trends have been noted with respect to V. parahaemolyticus and cholera.1
The spread of Vibrio pathogens has been blamed on warmer ocean waters; at least by lazy thinkers. I’m not a fan of global warming, although “climate change” cannot be denied.
But just blaming warming oceans is to overlook a very important extra factor in play: sewage!
Fecal contamination of the oceans (and vomit) is dramatically on the rise, due to increased populations as a whole, plus faulty septic systems or wastewater treatment plants, as well as boaters and beach-goers dumping directly into the water.
My own favorite oystery (is that a word?) in France was closed down for months last year, due to fecal contamination (Arcachon).
One can expect these problems to get worse, as human populations continue to grow relentlessly.
Can anything be done? The industry puts its hopes (me too!) in rapid post-harvest cooling and other modern strategies, such as depuration, thermal processing, freezing, irradiation, high-hydrostatic pressure, and high-salinity relaying. We will just have to see.
Professor Dunavan has announced she’s giving up raw oysters. Me? I’ll continue to take my chance, as here in a French market stall…
Finally: a note about cholera vaccine. If you had one you will remember the very “heavy arm” after-effect! In years past one had to have a certificate of cholera vaccination before being allowed on a plane. But protection only lasts about 6 months. In the 1970s the WHO stopped recommending it.
To be honest, I had completely forgotten about it when I went to Sri Lanka, an omission that might have cost me my life.
Prof. Keith
References:
- https://simplyoysters.com/oyster-history
- https://www.medpagetoday.com/opinion/parasites-and-plagues/114376
- [Case Studies in Public Health. 2018 Mar 30:77–99. doi: 10.1016/B978-0-12-804571-8.00017-2]
