Botulism top suspect in swan deaths

BOTOX offers the illusion of eternal youth. This dream substance, when injected under the skin, smoothes out wrinkles and forehead lines.

Five million Botox treatments are given in the United States each year, making it the world’s most widely used cosmetic procedure. This strange substance has a dark side, as the swans in Cork Lough, if they weren’t mute, would tell us.

When an animal or a plant dies, there’s a wake. Bacteria, waiting in the wings, gorge themselves at a long-awaited feast. Their numbers mushroom in this time of plenty, but soon the oxygen supply runs out, putting a stop to the microbial gallop. The revellers, out of gas, heel over and die. Then it’s the turn of a new crop of mourners; the anaerobic bacteria. These, the most ancient life-form on the planet, live only in places were there’s no free oxygen. The stenches from rotten eggs and decomposing carcasses come courtesy of them.

One of their number goes by the glamorous name of Clostridium botulinum (pictured inset), a bacterium first discovered in contaminated meat. “Botulus” is the Latin for “sausage” and “botulism” is “sausage” poisoning. It’s not the organism itself that does the damage, but a toxin created by it. As the bug breaks down dead matter, it generates a bi-product, a poison so lethal that a tablespoon of it would be enough to kill the entire human race. Sold under the trade name Botox, this most toxic of substances attacks the nerves which control muscles. Paralysis begins with the face and eyes, then spreads to the limbs. If the respiratory muscles fail, the victim dies. The toxin can enter the body through a wound. Infants sometimes pick it up by swallowing honey, but the commonest culprit is contaminated, often tinned, food.

C. botulinum thrives in rubbish dumps, where scavenging gulls encounter it. In warm summers, avian botulism can reach epidemic proportions. Following complaints from pilots of bird-strikes at Dublin Airport, the herring gulls on Lambay were culled each summer from 1985 to 1987. A population of 44,000 was reduced to 10,000. Numbers were expected to recover, but they didn’t; an epidemic of botulism broke out. The gulls never returned to their former numbers; there were fewer than 4,000 gulls on Lambay in 1999. Herring gull numbers have declined throughout Ireland.

This can’t all be ascribed to botulism, but the disease is probably a major factor. Gulls may be the commonest victims, but they are not the only creatures at risk. “Limberneck” and “duck disease” are alternative names for the condition. Dabbling ducks absorb the toxin when sifting through mud in shallow ponds and drains.

Ducks are among the victims of a mysterious illness that has broken out at the Lough, Cork’s famous urban lake. Around 40 swans have died there during the last month and, as I write, testing is under way to determine the cause of the deaths. According to reports, avian flu has been ruled out and no toxic substances appear to be present in the water. Botulism is now the prime suspect.

The Lough, famously, produced the largest carp ever recorded in Ireland. Dead fish have been found there recently, suggesting that oxygen levels fall drastically at night. Algae release oxygen during the day, but take it in during the hours of darkness. But what could cause so severe an organic overload?

Warm, late-summer water carries less oxygen. Vast quantities of stale bread, deposited in the lake by an army of well-intentioned swan and duck feeders, adds to the shortage, as does discarded fishing bait and the droppings of the birds. The aerobic bacteria smother and can’t cope with the load of detritus. Cesspool conditions may develop at the bottom of the lake, a paradise for the likes of C. botulinum.

Although botulism has been recorded in European, American and Australian swans, these big vegetarians are far less likely to become victims than gulls or dabbling ducks. Indeed, swans are fairly tolerant of organic pollution.

They feed mostly on living plants and algae, not dead ones. Botulin toxin would have to be very pervasive for them to absorb it in lethal quantities.

The disease is usually fatal, but infected birds sometimes recover, if given plenty of clean water and allowed to rest undisturbed.