Snail Fever—Is Its End in Sight?
BY AWAKE! CORRESPONDENT IN NIGERIA
DESPITE stunning developments in the fields of medicine and science, humankind is unable to straighten out many of its age-old problems. This has been true of efforts to subdue snail fever.
Seemingly, all the means are available to do the job. Doctors understand the life cycle of the parasite involved. The disease is easily diagnosed. Effective drugs are available to cure it. Governmental leaders are eager to promote efforts to prevent it. Yet, the end is not in sight for this disease that plagues millions of people in Africa, Asia, the Caribbean, the Middle East, and South America.
Snail fever (also called bilharziasis or schistosomiasis) has plagued man for millenniums. Calcified eggs found in Egyptian mummies furnish proof that the disease afflicted Egyptians in the days of the pharaohs. Thirty centuries later, the same disease continues to plague Egypt, sapping the health of millions of residents of that country. In some villages of the Nile Delta, 9 out of every 10 persons have been infected.
Egypt is just one of the 74 or more countries where snail fever is endemic. Worldwide, according to World Health Organization (WHO) figures, 200 million people are infected with the disease. Of the 20 million chronic sufferers, about 200,000 die each year. Among tropical parasitic diseases, snail fever is said to rank second only to malaria in terms of people it afflicts and the social and economic damage it causes.
Life Cycle of the Parasite
Understanding snail fever, and thus knowing how to prevent and cure it, means understanding the parasite that causes it. A key point is this: To survive and prosper from generation to generation, this parasite requires two hosts, two living creatures inside which it can feed and develop. One is a mammal, such as a human; the other is a freshwater snail.
This is what happens. When a person infected with the parasite urinates or defecates into the water of a pond, a lake, a stream, or a river, he releases parasite eggs—possibly up to a million eggs a day. These eggs are too small to be seen without the aid of a microscope. When the eggs make contact with water, they hatch, freeing the parasites. The parasites use tiny hairs on their bodies to swim to a freshwater snail, which they penetrate. Inside the snail, they multiply for the next four to seven weeks.
When they leave the snail, they have only 48 hours to find and enter a human or other mammal. Otherwise, they will die. Upon reaching such a host who has come into the water, the parasite bores through the skin and enters the bloodstream. This may cause the person some itching, though often he has no clue that an invasion has taken place. Inside the bloodstream, the parasite makes its way to the blood vessels of the bladder or the intestines, depending on the species of parasite. Within weeks the parasites grow into adult male and female worms up to one inch [25 mm] in length. After mating, the female begins to release eggs into the bloodstream of the host, thus completing the cycle.
About half the eggs leave the body of the host in the feces (in intestinal snail fever) or in the urine (in urinary snail fever). The rest of the eggs remain in the body and damage important organs. As the disease progresses, the victim may develop fever, abdominal swelling, and internal bleeding. Eventually the disease can lead to bladder cancer or failure of the liver or the kidneys. Some victims become sterile or paralyzed. Others die.
Solutions and Problems
To prevent the spread of the disease, at least four things can be done. If any one of these measures were applied universally, the disease would be wiped out.
A first measure is to eliminate the snails in the water sources. Snails are vital to the development of the parasite. No snails, no snail fever.
The main effort has been to produce a poison that is strong enough to kill snails but will not pollute the environment. In the 1960’s and 1970’s, attempts to eradicate snails succeeded in killing all life in vast stretches of water. Efforts have been made at Egypt’s Theodor Bilharz Research Institute to find a molluscicide (an agent that kills snails) that does not harm other forms of life. Dr. Aly Zein El Abdeen, president of the institute, notes regarding such an agent: “It’s going to be thrown in the water, which is used for crops, is drunk by people and by animals, and where fish live, so we have to be dead sure that none of these are affected.”
A second measure is to kill the parasites in humans. Until the mid-1970’s, treatment involved drugs that caused many side effects and complications. Often, treatment required a series of painful injections. Some complained that the cure was worse than the disease! Since then, new drugs, such as praziquantel, have been developed that are effective against snail fever, and these can be taken by mouth.
Though these drugs have proved successful in field projects in Africa and South America, a major problem for many countries has been the cost. WHO lamented in 1991: “The endemic countries are unable to proceed with large-scale [snail fever] control programmes because of the high cost of the treatment; the hard currency costs of the drug itself are usually more than the total per capita budget of most African ministries of health.”
Even where the drugs are made available at no cost to the patient, many people do not go for treatment. Why? One reason is that the death rate from the disease is relatively low, so some people do not consider it a serious problem. Another reason is that people do not always recognize the symptoms of the disease. In some parts of Africa, blood in the urine (a primary symptom of the disease) is so common that it is considered a normal part of growing to maturity.
A third measure is to keep the eggs out of the water systems. If latrines were built to prevent contamination of local streams and ponds and if everyone used them, the danger of getting snail fever could be reduced.
Global studies show significant decreases in the disease after piped water supplies and latrines are installed, but these provisions do not guarantee prevention. “It takes only one person to defecate in the canal to perpetuate the cycle,” observes scientist Alan Fenwick, who has researched snail fever for over 20 years. There is also the risk of broken sewage pipes leaking infected excreta into water sources.
A fourth measure is to keep people out of water that is contaminated by the parasite. This too is not as easy as it may appear. In many lands lakes, streams, and rivers that supply drinking water are used for bathing, irrigating crops, and washing clothes, as well. Fishermen come in contact with water daily. And in the intense heat of the tropics, to children a body of water can be an irresistible swimming pool.
What Hope for the Future?
There is no doubt that sincere people and organizations are working diligently to fight snail fever and that tremendous progress has been made. Researchers are even working to develop a vaccine against it.
Nevertheless, the prospects of eradicating the disease look remote. States Dr. M. Larivière in the French medical journal La Revue du Praticien: “Despite the successes . . . , the disease is far from disappearing.” Though prevention and cure can be a reality for individuals, a universal solution to the problem of snail fever may not be found until God’s new world is here. The Bible promises that there “no resident will say: ‘I am sick.’”—Isaiah 33:24.
[Picture on page 15]
When they enter polluted waters, humans can become infected with parasites that cause snail fever