Smoking Ears and Screaming Teeth - Trevor Norton (2010)

A Diet of Worms

‘The loathsome parasite is both an exquisite example of adaptation to environment and ethically revolting.’ – The Bishop of Birmingham

Far less beautiful things than flakes of fugu lurk within us. It is said that if all the tissues of a human body should magically vanish, the form of the person would still be clearly discernible from the distribution of their parasites. We are a walking menagerie of horrors. Parasites can infest every organ of our body from the lungs and heart to the eye and brain. None of our secret places is safe from habitation – there are even tiny worms that inhabit our eyelashes.

Most of our internal lodgers do little harm – after all, it is not in a tenant’s best interest to demolish the boarding house. But that doesn’t make them desirable. There are differences of opinion even among biologists. When Marlene Zuk, an American zoologist, was asked to name her favourite parasite, she chose a worm that takes over the brain and body of an unlucky grasshopper and becomes so large that it bursts open the insect to emerge. Clearly she had not sought the grasshopper’s opinion. The curator of parasitic worms at the British Museum plumped for his giant pickled tapeworm. On the other hand, Jack Haldane wrote, ‘Did God who made the lamb make thee? The same question applies to the tapeworm and … would clearly postulate a creator whose sense of values would not commend him to the admiration of society.’

For most people the tapeworm occupies the more repellent end of the spectrum. It’s a long, flat alien found in the human gut where it can become a long-term resident. One man harboured the same tapeworm for thirty-five years, and the biggest specimen ever to be ‘passed’ by a human had clearly been inside him for a while as it was thirty-nine metres long.

It has a pin head with suckers and thornlike hooks to anchor itself in the wall of the host’s intestine. The head manufactures a succession of broad, flat segments until there may be as many as a thousand. Production never stops and five to ten segments are shed from the ‘tail end’ every day. Each contains 100,000 eggs. The host has inadvertently become the egg depositor for a battery-reared flatworm that he feeds on a continuous slurry of pre-digested food.

In 1855 Dr Küchenmeister tried to resolve the question of whether humans acquired their flatworms through poor hygiene and ingesting the eggs that they (or others) had deposited, or from pigs that had swallowed the eggs, which encyst as ‘bladderworms’ in the hog’s muscles. There could be as many as 3,000 bladderworms in half a kilo of pork.

If Küchenmeister was to attract volunteers to test the possibilities, he thought it might be wiser not to mention that bladderworms, once swallowed, can lodge in the liver, muscles and eye (causing blindness), or in the brain – resulting in epilepsy or insanity. Fortunately he was acquainted with the Duke of Saxe-Coburg who offered doomed convicts for his experiments. Küchenmeister served one condemned man bladderworms in blood sausage and soup. The prisoner complained that the soup was cold, not appreciating that hot soup might kill the worms and ruin the experiment. After his execution a postmortem revealed ten tiny tapeworms in his gut. Surprisingly, this inspired a volunteer to swig lukewarm milk laced with bladderworms. Three months later, to Küchenmeister’s delight, the volunteer began to pass tapeworm segments. This test was repeated with a similar result on several more volunteers, but the final proof came from another convict whom Küchenmeister infected via worm-spiked sausage spread on a bread roll. When the convict was executed four months later, his gut was found to contain several full-grown tapeworms. Clearly humans could be infected from undercooked contaminated meat.

In many countries tapeworms have been deliberately disadvantaged by the population not eating sacred cows or unclean pigs. With better hygiene and food inspection tapeworms have virtually died out in western countries, but our liking for very rare steak keeps a few in business.

It was common practice to carry out dangerous experiments on convicts even into the twentieth century. They were considered the dross of humanity, who were generously being given an opportunity to perform a small service for society. There was, of course, no requirement to ask their permission. What is surprising is that Küchenmeister also persuaded willing volunteers to take part, for at that time there was no reliably effective treatment to rid the body of tapeworms.

Having hungry internal residents stealing your food after you’d eaten it was believed to make you thinner. Victorians marketed ‘tapeworm tablets’ for figure-conscious ladies. The logic behind this was that the poor were thin and most of them had parasites. When I was a child, any lad with a hearty appetite attracted the ‘amusing’ comment, ‘You must have worms.’ Parasite-induced anorexia is now a well-known phenomenon, but it’s not attributed to the theft of digested food. Appetite can be suppressed by natural chemicals such as cytokines acting on the brain. Parasitic infection stimulates several responses in the host, including cytokine production, which induces a decline in appetite and consequent loss of weight.

Tapeworms are relatively benign as internal parasites go, but some people are hypersensitive to their presence and suffer nervous disturbance or may even die. The biggest tapeworm to infest humans comes from eating raw fish and the Japanese take a weekly tablet to purge their innards of recent recruits.

A variety of parasites jostle to occupy the human gut. The most common is the large roundworm, which is estimated to infect over 1,000 million people. It resembles a pallid earthworm and can reach forty centimetres in length. In contrast to the relatively languid tapeworm, the agile roundworm is forever stretching, coiling and twisting. It may be present in vast numbers: 5,000 have been found in a single person. They form writhing tangles that can completely block the bowel or the ducts from the gall bladder and pancreas, causing intense pain.

Each female roundworm sheds 200,000 eggs which exit with the host’s motions. If personal hygiene is not meticulous, a few eggs may be swallowed to sustain the infestation. These eggs hatch in the intestine and the small juveniles embark on an extraordinary odyssey around the host’s body. They bore through the gut wall and then into a blood vessel to be carried to various organs in the body, including the heart, where they lodge to cause problems later. Those reaching the lungs burrow through into the air passages to be coughed up into the mouth and swallowed again. On entering the intestine for the second time they stay to grow and flourish. This grand tour of the body damages all the membranes that the creatures pass through and in pigs they frequently cause the deaths of large numbers of young animals from porcine pneumonia.

It’s probable that the occasional coughing up of a roundworm caused momentary social embarrassment and also gave rise to legendary accounts of snakes living in the human stomach. There are vivid descriptions of vipers being vomited up, sometimes augmented by a reflux of lizards, frogs, toads and even mice, cats and dogs.

The biology of roundworms was worked out without resorting to self-experiment, but not without risk. Parasitologists take great care to avoid becoming infected, although a colleague of mine once shared a laboratory with someone studying large roundworms. She washed her hands scrupulously after handling the worms, but as she was in a wheelchair she first had to wheel herself over to the sink and then wheel herself back to the bench. Many researchers reacted to some of the substances exuded by the worms and suffered severe allergic reactions such as dermatitis and asthma. Despite this, most of them persevered with their research but some were completely prostrated by any contact with the worms.

Blood flukes are flatworms and are much smaller than the large roundworm but more dangerous. The male has a sucker to attach to the host’s flesh. The female lives permanently embraced in a fold along the length of the male’s body.

In 1908 Dr Claude Barlow became interested in flukes. As a missionary in rural China he discovered that half the patients he treated were suffering from fluke infections and in some villages every resident carried the parasites. He was so concerned that he took a year-long sabbatical at the London School of Tropical Medicine to learn about parasites.

Returning to China, Barlow realised that the locals were probably reinfecting themselves by using their faeces as fertiliser on the land. He found fluke larvae commonly on water chestnuts, a staple food that the Chinese peeled with their teeth, swallowing the larvae in the process. He wondered whether the adult flukes might also be a source of infection, so he swallowed some taken from an infected patient. Unsurprisingly, it was ‘a nauseating experience’, even though he did it in the dark so he couldn’t see what he was putting in his mouth. Barlow then observed what emerged from his other end, but found nothing remotely parasitical. He assumed that the flukes had been destroyed by his digestive enzymes so, on his second attempt, he took bicarbonate of soda to counteract this, followed by flukes and then a more conventional dinner. After three more attempts he was overjoyed to see that he was passing fluke eggs. He continued to do so for a year before getting rid of the parasites with drugs.

Fourteen years later Barlow feasted on flatworms once again. At the time he was working in Cairo. A pathologist had claimed that Egypt would never be an important country until the flukes draining the people’s energy were controlled. He was referring to blood flukes that give rise to schistosomiasis or ‘big belly’. It was the second-most common disease in the world and it still affects 200 million people. The parasites can survive in the human body for ten or even thirty years, but are often fatal to their hosts long before that.

Like many parasites the blood fluke has a complicated life history. It spends part of its existence inside freshwater snails. Paddling in contaminated paddy fields or washing in a stream is sufficient to become infected. In 1944 there was concern that Allied troops fighting abroad and having contracted schistosomiasis would bring it back home when they were demobbed. A senior medic declared that: ‘The establishment of schistosomiasis in North America is a serious possibility.’ Barlow wondered whether the snails back home would be susceptible to infection by blood flukes and would therefore provide the essential second host. He tried to import American snails into Egypt for his experiments, but most of them died in transit. If the snails couldn’t be brought to the flukes, the parasites would have to be taken to the snails. The container in which they were shipped was Barlow himself. Although more expensive than postage, this method would not require an import licence.

The head of the US Navy’s Preventative Medicine Unit thought it was far too risky. Blood flukes cause severe dysentery, anaemia and emaciation. They produce so many eggs that thousands or even millions of flukes remain in the host’s body, causing widespread inflammation that stops the flow of blood to vital organs such as the bladder, liver, lungs and heart. They are lethal.

This didn’t discourage Barlow. Over three weeks he dosed himself four times and also infected a baboon called Billy (after Herr Bilharz who had first described schistosomiasis). Three weeks later Barlow and Billy took a plane to the United States. During the flight Billy escaped and terrified the passengers.

Barlow was already having sweats and dizzy spells, and his appetite had gone. It would get much worse. Three months later his scrotum began exuding serum. Under the microscope the eggs of the flukes were visible. It was known that a parasite’s eggs emerged in the host’s urine or faeces, but not through the skin. To find the parents of the eggs, Barlow had a piece of skin the size of a luggage label cut from his body. The incision went as deep as the fat layer beneath. He stoically refused a local anaesthetic in case it disturbed the parasites. The biopsy revealed adult blood flukes in the skin. After the operation he refused a taxi and walked across town to the station.

Barlow was now suffering severe night sweats and began to pass blood. He had almost more pain than he could endure, and great bladder distress. He got little sleep because he had to urinate every twenty minutes. His condition got progressively worse. After being confined to bed for three weeks, his temperature soared to 40° C. He realised it was a close call and was relieved to still be alive.

His morale was not helped when Billy the baboon, who had become a dear companion, died of schistosomiasis. Yet he continued his ordeal even though he was passing 12,000 eggs per day and had blood in his urine the whole time.

Eventually Barlow agreed to start a course of drugs to clear the infection. He returned to work in Cairo but got no better, so he sought treatment at an Egyptian hospital specialising in parasitic infections. He was injected with antimony, which is so toxic that if it leaks from the injected vein the limb may have to be amputated. Even if it is confined to the circulatory system it can cause acute vascular collapse or dangerously erratic heart rhythms. It damaged Barlow’s heart. What’s more, the treatment was ‘filthy’. He began to vomit and felt nauseous all the time. But it worked. Eighteen long, miserable months after he had deliberately infected himself, he stopped passing eggs.

All this suffering left Claude Barlow too weak to carry out the experiments on snails that had been the purpose of his ordeal. Instead, a colleague tried to infect American snails with the flukes, but failed.

In the late nineteenth century there was a Europe-wide epidemic of miners and construction workers dying from ‘miner’s anaemia’. In 1881 an army of labourers dispersed after constructing the nine-mile-long St Gotthard tunnel through the Alps. They spread the disease from the tin mines of Cornwall in the north to the sulphur mines of Sicily in the south. All the victims were found to be infested with hookworms.

The intestinal hookworm is tiny, but it has vicious, hooked ‘teeth’ that bite into the gut wall so that it can suck blood from its host. One or two worms would do little damage but some miners contained thousands of them. With so many bloodthirsty inmates, no wonder the men became anaemic and died. An infected person passed uncountable numbers of eggs and it was assumed that others became infected by inadvertently swallowing some. But improved hygiene in mines failed to curb the disease.

Meanwhile, a parasitologist in Cairo called Arthur Looss was self-experimenting by swallowing an entirely different intestinal parasite. While eagerly searching through his stools he was surprised to find hookworm eggs. Having never socialised with miners, how had he acquired their worms? A few weeks earlier he had been giving hookworm eggs to experimental guinea pigs and a drop of the worm solution had fallen onto his hand. He kept his hands well away from his mouth and washed them thoroughly, yet he had become infected. To discover how, he deliberately put a solution of hookworms on the back of his hand. Within a minute or two the water on his hand was clear; hundreds of worms had vanished into his skin.

Looss made several unsuccessful attempts to clear the infection with thymol, a powerful disinfectant that irritates the kidneys. Some of the remedies on offer were worse than having worms. Thymol would be superseded by carbon tetrachloride, or dry-cleaning fluid as we now call it. Even in tiny doses it causes mental confusion, nausea and vomiting, followed later by necrosis of the liver leading to convulsions, respiratory failure and even death. Unfortunately for Looss, a safe and effective cure for hookworm was still twenty-seven years in the future.

Looss had initially become infected by chance, and now serendipity intervened again. A patient in a local hospital had to have his leg amputated, which was unfortunate for the patient but lucky for Looss. Immediately before the operation Looss splashed the leg with hookworm solution and later examined the detached limb. Dissection revealed that the worms had entered via the hair follicles, from which, given time, they would have migrated to the intestine.

Miners labouring underground often went barefoot, inviting infection from the millions of worms thriving in the damp dust underfoot. Merely getting them to wear shoes or even painting the soles of their feet with tar greatly reduced the rates of infection.

Hookworm is not confined to miners. In the Third World the majority of the population may go barefooted. It still infects 900 million people who have their energy sapped. Even in the southern states of the USA, the rural poor have long suffered from hookworm and, despite large eradication programmes, in some areas it is still said to infect fifteen per cent of children, retarding both their physical and mental development.

The tropics offer an even richer menu of parasites. In the nineteenth century the majority of explorers, soldiers and administrators who went to tropical West Africa never returned. Eighty-five per cent died or were ‘reduced to mental and physical wretchedness’. India was almost equally dangerous. For two months of the year a quarter of the entire population was incapacitated. The culprit was malaria.

Often the smaller the parasite, the worse its effects. Malaria is caused by a microscopic organism called Plasmodium. By 1898 the basic life history of the parasite was understood and the disease was known to be spread by particular types of mosquito. Unlike many internal parasites that produce eggs to be expelled, Plasmodium multiplies itself within the blood stream and the number of retained parasites increases exponentially. The blood becomes the parasites’ broth. They invade the red blood cells and if the cells are destroyed faster than the body can replenish them the consequences are dire. Even if the victim’s defences keep the infection in check some of the parasites sequester themselves in the body only to emerge again periodically, causing a relapse.

What was needed was a vaccine, but it was not until 1971 that a promising idea for one came along. David Clyde spent years in the tropics before becoming a researcher at the University of Maryland. He thought that irradiating malaria-carrying mosquitoes with just enough X-rays to weaken the parasites without killing the mosquito might be the first step towards producing a vaccine. The plan was to inject the now-benign parasites into a human and stimulate the body to produce antibodies against malaria.

For the tests, the hypodermics were mosquitoes and the guinea pigs were volunteer prisoners from penitentiaries. Clyde also became a volunteer because he thought it was essential to know exactly how a patient felt, and he would be able to describe any side effects far more accurately than the average convict.

He did far more experiments on himself in order to test whether the procedure would protect against different types of malaria. He became feverish and shivered uncontrollably, as well as vomiting, filling several hours with ‘absolute misery’. The bouts of fever returned every twelve hours until he cured the infection with drugs. He also ran tests to determine which strain of malaria produced the best vaccine. The technique was to fasten several cages to his arms, each containing several hundred infected but irradiated mosquitoes. He was bitten about 3,000 times which was very unpleasant. The next step was to see how effective the immunisation was by first being vaccinated, and then bitten by malarial mosquitoes. It worked: he didn’t develop malaria.

In 1986 David Clyde was honoured by the World Health Organisation for his efforts, but sadly the vaccine that relied on irradiated mosquitoes could not be scaled up sufficiently for mass inoculation. Subsequent attempts at producing a vaccine have also been disappointing. Plasmodium is a formidable opponent – it has an immense capacity to mutate when challenged by a new drug, and can hide in the body away from harm.

Until the late nineteenth century, outbreaks of ague (mostly malaria) were commonplace in Britain and the disease was endemic in the East Anglian marshes of southeast England. We still have several species of mosquito capable of transmitting malaria should they become infected, and exotic mosquitoes are now appearing in Europe. With global warming the climate is likely to attract such immigrant insects, but the scarcity of people and animals with malaria in Britain, and the prompt treatment of those who contract it, should keep us safe.

In the 1950s we thought that malaria could be wiped from the face of the Earth. Global deaths from the disease fell by ninety-five per cent in the wake of extensive mosquito-eradication programmes, and a third of the world’s population, living in previously malaria-stricken regions, are now free of the disease. But with the ban on the use of DDT for spraying inside houses malaria re-emerged. The mosquitoes soon became immune to other pesticides and in 2006 the World Health Organisation recommended the renewed use of DDT, despite concerns over its environmental effects. A billion-dollar grant from the health foundation of Bill and Melinda Gates has stimulated new initiatives, and a vaccine is in the pipeline. The results of the preliminary trials are promising. In the meantime malaria continues to kill a million people every year. Half the victims are children.

Not all parasites are the darkest of villains – some may even be beneficial. In the 1930s and 1940s patients suffering from syphilis-induced lunacy were deliberately given malaria. The infection was controlled with quinine and of 600 cases the mental state of almost half of them improved.

Parasites have cohabited with humans for millennia. Physiologically, we have usually come to a mutual understanding that allows both to thrive. Often infections in early life prepare the body’s immune system for future encounters. In developed countries, children raised in clean houses with no pets suffer more allergies and asthma than those who are brought up in less fastidious conditions. Even a parasite or two may be preferable. Twenty-four patients suffering with multiple sclerosis, half of whom had recently been diagnosed as having parasitic worms, were studied for five years. In those with worms the disease progressed more slowly and relapses were far less frequent than in the parasite-free group. Much larger-scale studies of Africans have indicated that people suffering with schistosomiasis rarely suffered from diabetes, rheumatoid arthritis or multiple sclerosis. These diseases, especially diabetes, are common and are increasing in developed countries. They are all autoimmune conditions in which the body’s defences attack its own tissues and organs.

Invading parasites are recognised as foreign bodies by regulatory immune cells, the ‘office managers’ of the body’s defence team. Their job is to marshal the host’s immune responses to repel boarders. Humans have always been parasitised, so the regulatory immune cells have been kept busy. Perhaps now, with our ‘old companions’ eliminated, the under-employed immune cells may go into overdrive and cause autoimmune diseases.

On the other hand, parasites may enable us to control some conditions. In the laboratory, extracts of blood flukes have enabled diabetes-prone mice to stay free of the disease. It raises the possibility of a similar drug for people, to combat the scourge of diabetes. A trial with patients suffering from inflammatory bowel disease indicated that regular dosing with parasitic whipworms eliminated the symptoms.

Inflammation and allergies are usually triggered by an excessive immune response. Whipworms, flukes and hookworms survive within us by damping down our immune response that should attack them. John Turton, working at a medical research laboratory in England, relieved his hay fever for two summers by deliberately infecting himself with hookworms. When he got rid of the parasites his allergy returned.

Summer-holiday preparations may never be the same again: suntan lotion, insect repellent, dose of hookworms …


A male blood fluke lovingly enfolds an unsuspecting female.