A hunting club in Iowa got an unpleasant Christmas surprise several years ago when its members shot more than 100 deer to make special smoked Christmas sausages. Soon after the gifts were distributed to friends and family, 67 people who had eaten the sausage complained of excruciating muscle pain, weakness and fever. The diagnosis: trichinosis.
The Iowans, it turned out, had thrown in a bit of ground pork with the venison. And the pork was infected with the larvae of the tiny roundworm Trichinello spiralis, which causes trichinosis.
The Christmas episode was unusual because of the number of people affected, but the disease itself is not rare. "We get that kind of outbreak all the time," said Dr. Peter Schantz , assistant chief of the branch at the Centers for Disease Control in Atlanta that studies worms.
The CDC estimates that there are 150,000 to 300,000 new cases of trichinosis, several of them fatal, each year in this country. Many cases are never diagnosed, and the agency estimates that about 4 percent of Americans carry trichinosis larvae in their muscles.
Although many people are under the impression that meat inspectors look for such things as trichinosis larvae in pork, there are no federal laws requiring them to do so. Of all the states, only Illinois requires trichinosis inspections.
Until now, the available tests for trichinosis in meat have been expensive and slow. But after a 35-year, $10 million effort, the U.S. Department of Agriculture has developed a new test that may make trichinosis detection in meat easy and inexpensive. The test may also pick up human trichinosis, which until now has lacked a good diagnostic test.
The new test is called ELISA, for enzyme-linked immunosorbant assay, and it makes use of the fact that the blood of animals with trichinosis infections contains specific proteins secreted by the worms. The ELISA test can detect those worm proteins in a blood sample taken at slaughter. According to Dickson Despommier, a biochemist at Columbia University who helped develop ELISA, the test costs only a few cents per animal tested and seems to be completely reliable.
Congress would have to pass a new law to require use of the test on pork produced in the United States. In the past, mandatory testing has been rejected because of the cost and because consumers of pork can avoid the disease by cooking the meat to an internal temperature of 170 degrees, which kills the larvae.
Pork producers, however, have indicated an interest in voluntarily using the ELISA test because of its low cost and because it would open new markets for their meat. Most other countries, aware that U.S. pork frequently contains trichinosis, will not import fresh American pork. The National Pork Producers Council estimates that the export market would increase by one third and the domestic market by 2 percent if U.S. pork could be guaranteed trichinosis-free.
Pork producers, USDA officials and representatives of the scientific community will meet in Washington on March 21 to review USDA's work on the new test and to explore the prospects for putting it into widespread use.
Trichinosis occurs when a person eats meat containing live trichinosis larvae. The larvae burrow into the lining of the small intestine, molt a few times, then mate and produce new larvae. These larvae are carried through the bloodstream to the muscles, where they squirm around for a few weeks, causing weakness and pain, and then enclose themselves in cysts, where they live peacefully for years, causing no more symptoms. Eventually the larvae die, but the cysts remain permanently.
The disease can be fatal if the larvae infest the heart or brain. The larvae don't form cysts there, but they irritate the tissue.
The only treatment is to give one of two drugs, mebenzadole or thiabenzadole, both of which kill the worms in the intestine but neither of which works on the worms in the the rest of the body.
Although the CDC estimates that nearly 80 percent of all trichinosis cases in this country arise from pork, pigs are not the only animals to carry trichinosis. It can be present in the flesh of any animal that eats meat. Rodents frequently have the disease, and in fact many pigs get trichinosis when they kill and eat infected rats. The disease has even been transmitted through horse meat, in an incident in which horses were found to have eaten an infected rat in their grain.
Trichinosis is an ancient disease, dating back at least to 1200 B.C., according to trichinosis historian William C. Campbell of the Merck Institute of Therapeutic Research in Rahway, N.J. An Egyptian weaver living near the Nile River at that time was recently discovered to have trichinosis cysts in his mummified muscles. But the disease itself was not recognized until 1859.
As Campbell tells the story, a servant living on a farm in Germany became ill after preparing the meats for the Christmas meal. After two weeks, she was taken to the hospital at Dresden, where hospital pathologist Albert von Zenker diagnosed her as having typhoid. The woman lay curled up in bed, her muscles hurting so much that she could barely move. Fifteen days after she entered the hospital, she died. Zenker, in the course of his autopsy, crushed a bit of her muscle tissue and looked at it under a microscope. To his immense surprise, he saw dozens of tiny worms wriggling about. He looked at other bits of muscle tissue. More worms.
Zenker made the connection between the worms and the woman's disease, Campbell said. Zenker and his colleagues showed that they could transmit the disease to a dog, a rabbit and a pig by feeding them the woman's flesh. Then he traveled to the farm where the woman had worked and discovered that the entire staff had become ill in January. The man who butchered the pigs had developed muscle pains so severe that he was confined to bed for three weeks, barely able to move his arms, legs or neck.
Finally, Zenker examined some sausage and ham from a pig killed on the farm Dec. 21 and saw that they were riddled with trichinosis larvae. The trail of the disease was established.
Once trichinosis was recognized, Europeans began documenting outbreak after outbreak, according to Campbell. In Germany alone, there were 8,491 cases between 1860 and 1880. European countries passed laws requiring that all pork be inspected for the presence of trichinosis larvae, and the United States, for a brief period around the turn of the century, also inspected pork that was to be exported. The U.S. stopped, Campbell said, because the process was viewed as too expensive, particularly after the Europeans passed strict import regulations to keep U.S. pork from flooding their markets.
The European method of inspecting pork at that time was to look at it under microscopes -- a procedure so time-consuming and labor-intensive that when it was used in the United States in 1894 it added 16 cents a pound to the price of pork, Campbell said. The Germans at that time had 100,000 pork inspectors, which is as many men as were in the U.S. Army, and spent more on inspections than the entire budget of the U.S. Department of Agriculture.
Eventually, a second method of inspecting pork was developed, which involved breaking down the muscle tissue with an enzyme and then looking to see if any worms were released. That method, too, was slow and expensive. Nonetheless, both enzymes and microscopic examination method are still used in the Common Market countries, which all require inspection of pork for trichinosis.
Work leading to the ELISA test has been under way since around 1950, and the Agriculture department now believes it has found a method not only cheaper than the older methods but also more reliable, according to Despommier. He said the ELISA test detects larvae in concentrations as small as 1 per 100 grams of pork. In contrast, the microscopic evaluation detects 1 larva per 50 grams of pork, and the enzyme method detects 1 larva per gram of pork.
The Agriculture department has tested ELISA by looking at the serum of 1,300 Puerto Rican pigs. There is no trichinosis in Puerto Rico, so all of the pigs should have tested negative. They did.
Then they tested pigs that they had purposely infected with trichinosis. All tested positive.
Next the department sent samples of pig blood serum to four laboratories, without telling the labs which pigs had trichinosis and which did not. The labs made no mistakes in picking out the trichinosis-infected pigs.
Despommier said there is no reason the ELISA test could not be expanded to detect other diseases in meat. One reason the United States has no laws requiring meat inspectors to look for diseases such as trichinosis; brucellosis, a bacterial infection of cattle; or salmonellosis, a bacterial infection that is common in chickens, is that there were no good testing systems available. Now, he said, "we can develop tests for all of these diseases."