Definition of Trichinosis…(a picture of Trichinosis)
Trichinosis is an excruciatingly painful disease that is among the most dreaded of human afflictions. It can result in death when infection is heavy--although fewer than 2 percent of all reported cases are fatal. 
This disease is caused by very tiny parasitic worms called trichinae (Trichinella spiralis). It is not catching. People get trichinosis when they eat raw or undercooked meat that contains trichinae. 
The threadlike worms spend most of their lives curled up inside a protective capsule or cyst in muscle tissue. When the meat is eaten, the digestive juices in the stomach free these encysted worms or larvae from their capsules. They then pass into the small intestine where they develop into mature males and females in about 2 days. After mating, the females give birth to large numbers of young (called larvae), starting about the sixth day after infection. One female will give birth to between 1,000 and 1,500 larvae. These microscopic young worms penetrate the lining of the intestines, pass into the lymphatic system or the blood, and are carried to the heart. From there they are carried throughout the body by the circulating blood. They have an attraction for muscular tissue, so they invade the striated (voluntary) muscles of the body. They grow there for about 3 weeks, then coil up tightly, and in about 30 days develop a protective capsule--to complete the cycle (fig. 1). 
The worms can remain in this encysted form for many years--ready to infect any mammal that might eat the muscle tissue. 
Trichinae are about 1/250 of an inch long when they are born. When they reach the muscle tissue, they grow to a length of 1/25 inch, coiling up in a cyst about 1/50 inch long. When they develop into adult males and females in the intestine, they are about 1/8 and 1/6 inch long, respectively.
 

Human Symptoms… 
The disease caused by trichinae occurs during the time the larvae are being produced and encysting in the muscle tissue. In many light infections, the host is never aware of the condition. However, once infection is established, evidence of this infection--in the form of the encysted larvae--will persist until the muscle tissue is destroyed. 
The number of live trichinae in the meat that is eaten usually determines the seriousness of the disease. Eating moderate amounts of lightly infected raw or imperfectly cooked meat may produce no illness or only slight illness. But eating even small quantities of undercooked or raw meat that contains large numbers of trichinae may produce a painful and serious case of trichinosis. 
If the initial infection is relatively heavy, a person may have an upset stomach, vomiting, diarrhea, and other symptoms within 24 to 48 hours. However, these symptoms are often absent. 
The symptoms characteristically associated with trichinosis occur during the period of migration and encystment. This starts about a week after infection and may continue for a month or more. When thousands of young trichinae travel through the body at one time, the person may have muscular pain, rising fever, headache, and prostration. When the larvae reach the muscles, other symptoms develop. These include swelling of the face and other parts of the body, sore eyes, hemorrhages, fever, and difficult breathing. Stiffness of the muscles may occur in severe infections. Some patients may have symptoms of heart disease or symptoms of brain disorder, such as delirium or coma.

Who gets trichinosis? 
Anyone who eats undercooked meat of infected animals can develop trichinosis. Pork products are implicated more often than other meats. 

How Trichinosis spreads . . .
Trichinosis occurs when warm-blooded mammals eat raw or insufficiently cooked flesh that contains trichinae. The most common source of human trichinosis is pork, although outbreaks have been traced to the meat of wild boar, and bear and walrus meat, among others. 
Pigs commonly get trichinosis by eating infected meat scraps in raw garbage (or garbage that has not been properly cooked), by eating the carcasses of infected wildlife, or by eating infected offal. Pigs may also get trichinosis if they eat feces passed by other pigs (or other animals) containing trichinae, but this is not a common method of spread. 
The importance of wildlife as a reservoir of trichinae is not known, since there are no accurate incidence figures. However, trichinae have been found in a number of different animals, including rats, mice, dogs, cats, foxes, raccoons, skunks, squirrels, bears, and wolves. Trichinae have also been found in wild boars, whales, walrus, seals, and polar bears. 
The chain of infection is perpetuated in nature by carnivorous animals feeding on each other, and by cannibalism (in the case of rats, for instance). Swine enter this chain when they are allowed to eat the carcasses of wild animals that are infected with trichinae. In the past, rats have been accused of being an important reservoir of infection for swine, but current information indicates that this method of spread may have been overemphasized. Nevertheless, strict rodent control would eliminate a possible source of infection for swine. 
Much information still remains to be gathered to determine the role of wildlife and other possible sources of infection in perpetuating the disease in swine.
 
 
 

Incidence in Humans …
Probably many people who have trichinae in their muscles are completely unaware of it--because these "guests," present in such small quantities, do not cause any symptoms, or the symptoms are so slight the patient recovers without the disease being diagnosed. 
Yet once infected, a person carried the encysted trichinae for life. Thus, older people--with greater chance for exposure--are more likely to have trichinae in their muscles than younger people. 
The incidence of trichinosis in humans in the United States has been falling steadily since 1953. The latest information (1968) indicates that 4 to 5 percent of the population carry trichinae in their bodies. 
Various studies carried out during the 1930's and early 1940's showed a much higher incidence--about 16 percent of the human population was apparently infected with the disease at that time. Thus, there has been about a 70-percent reduction of trichinosis during the past 25 years. 
The most recent study also shows a definite age-incidence relationship, with younger persons much less likely to be infected. The preponderance of calcified cysts also tends to indicate that only a few of the infections are of recent origin. 
This decrease in human incidence is supported by figures from the U.S. Public Health Service on the number of cases of human trichinosis. From 1960 to 1967, there was an average of 180 cases of trichinosis reported yearly. In contrast, the average for the preceding 10 years was 287 cases per year. 

What can be done to prevent the spread of trichinosis? 
The best prevention is to make sure that pork products are properly cooked. The desirable temperature is at least 150°F. Storing infected meat in a freezer with a temperature no higher than -13°F for 10 days will also destroy the parasite. 
 
 
 

What are the treatments?
Mebendazole is the treatment of choice. 
If the infection has caused severe heart, lung or central nervous system problems, steroids such as prednisone may be used. 

What are the side effects of the treatments? 
Sometimes mebendazole causes diarrhea and stomach upset. 

What happens after treatment?
Most symptoms disappear by about the third month, although vague muscular pains and tiredness may persist for months. 

How is the infection monitored?
Most people with trichinosis recover fully with treatment. 
 

Clinical Diagnosis 
Diagnosis of trichinosis in man is often difficult because symptoms usually don't occur until about a week after trichinous meat is eaten. Furthermore, clinical signs of the disease may be absent in the early stages, and those noted in the later stages often simulate other diseases. 
The early gastrointestinal symptoms--when they do occur--are often not recognized in the individual patient. Trichinosis in many instances is not suspected until one doctor has examined several patients having a common history of sickness following the eating of raw or insufficiently cooked pork or pork products. 
Thus, when trichinosis occurs in epidemic form it is likely to be correctly diagnosed, but isolated infections--especially if they are mild--are often not recognized. 
One of the best and earliest signs of trichinosis in many is an eosinophilia (increased numbers of a certain type of which blood cell in the blood). This is especially so with an eosinophilia rising over a period of several days--often to heights of 40 to 80 percent of the white blood cells. 
Certain other laboratory and biological tests are available for diagnosis, but their usefulness is limited because they are usually negative early in the course of the disease and may become negative in long-standing infections. These tests include the intradermal test, the complement-fixation test, the precipitin test (including the agar-diffusion test), several flocculation tests such as the bentonite, latex, and charcoal-card tests, and a fluorescent antibody test. All depend on the interaction between an antigen made from the tissues of the parasite (or its metabolic processes) and a specific antibody formed in the tissues of the host as a result of the infection. 
Definitive diagnosis of trichinosis must still be based on the actual demonstrations of the larvae in muscle tissues. 

The History of Trichinosis . . . 
In the early 1800's, several human anatomists referred to minute, calcified particles found in the muscles of man during anatomical dissections. However, it remained for James Paget, a 21-year-old medical student at St Bartholomew's Hospital in London, to first identify and describe the parasite. 
On February 2, 1835, Paget observed certain little specks in the muscles of a 50-year-old Italian man who had died of tuberculosis. The first-year student's curiosity led him to borrow a microscope from Robert Brown, botanist at the British Museum, and under its lens he found that each of these specks consisted of a minute, coiled worm encased in a cyst. Paget turned his material over to his professor, Sir Richard Owen, who presented a paper on the subject later that month in which he named the parasite. 
A Philadelphia physician, Joseph Leidy, became the first person to observe the encysted trichinae in pork. This occurred in October 1846. Twenty years later, he recalled the circumstances of this observation. While eating a slice of pork, he noticed some minute specks that reminded him of the trichinae spots he had seen in the muscles of a human subject only a few days previously. He saved the rest of the ham slice, and later, on examining it under the microscope, found it to be full of Trichinella spiralis. However, the parasites were all dead from the heat of the cooking. From this, Dr. Leidy correctly deduced that there was no danger of infection if meat was thoroughly cooked. 
Two German scientists--Rudolf Leuckart, an outstanding zoologist and parasitologist, and Rudolph Virchow, the father of modern pathology--conducted animal experiments during the 1850's demonstrating the development and animal-to-animal transmission of trichinae. But at this point, most medical workers regarded trichinae as merely zoological and medical curiosities--as fairly harmless "guests" of man. 
It was not until early in 1860 that trichinae were exposed as pathogenic agents able to produce severe illness and death. In January of that year, Friedrich A. von Zenker, a physician in Dresden, Germany, studied the case of a 20-year-old servant girl who entered the municipal hospital 5 weeks after becoming sick at Christmastime. She died 2 weeks later, supposedly of typhoid fever. However, the course of her illness was not characteristic of typhoid. Zenker carefully recorded all of the now generally recognized symptoms of trichinosis. 
Zenker was familiar with trichinae, but there is no evidence that he suspected these parasites as a cause of the girl's death until he was in the midst of an autopsy. He then discovered, on microscopic examination of the muscles of her arm, "dozens of trichinae, lying free in the muscle, either coiled or extended and exhibiting the plainest signs of life." Later Zenker also found sexually mature worms in the girl's intestines. 
It is to Zenker's credit that he did not stop with this remarkable discovery. Instead, he went on to make an equally brilliant record as an epidemiologist by tracing, step by step, the circumstances that led to the servant girl's illness and death. In his investigation, he found that her illness had been shared by others, for several persons in the same household had become sick but had recovered. 
Zenker visited this household and, from the girl's employer, found that she was in the habit of testing and nibbling all the food she prepared. Apparently she had eaten raw sausage from the meat of a pig killed for the Christmas holidays. Four days later she became sick. The victim's employer and his wife also became ill with similar, but less severe, symptoms. The butcher, too, had eaten some of the pork raw--as was customary among butchers in Germany--and he developed a rather severe case of trichinosis, which was diagnosed as gout. 
Fortunately, some of the sausage and a ham were still available. Zenker examined this meat under a microscope and found that it, too, was heavily infected. 
The Dresden physician sent portions of the muscles of the young woman to Virchow and Leuckart, which led to further investigations. It was not long before these scientists demonstrated the complete cycle of development of this parasite. 
The news of Zenker's discovery spread rapidly. Once the disease was recognized,there were numerous reports from different towns of quite large outbreaks of human trichinosis. This knowledge, quite naturally, caused great public uneasiness and alarm. Two epidemics in the province of Saxony, in particular, exerted a profound influence on the medical and public health authorities of Germany. 
The first was in 1863, in Hettstadt, a town of about 4,000 people, where 158 persons contracted trichinosis and 27 of them died. Two years later, in 1865, a second major epidemic occurred in Hedersleben--a town half that size. There, 337 persons fell ill after eating raw or insufficiently cooked pork, and 101 died. During the 20 years from 1860 to 1880, a total of 8,491 cases of trichinosis were registered, with a mortality rate of around 6 percent. 
The first approach to the problem was the thorough cooking of all pork. This is perhaps the simplest method of preventing trichinosis--and one of the most effective. Public education campaigns urging this measure were attempted in Germany and other areas. However, they failed to overcome the fondness of Germans and Middle Europeans, generally, for raw pork--especially sausage and raw spiced ham. 
So other methods of prevention were considered. As early as 1863, the microscopic examination of pork for trichinae was practiced in some parts of Germany. Virchow advocated governmental inspection of pork for trichinae by means of the trichinoscope. The inspection consists of compressing a thin slice of meat between two plates of glass and examining the suspect tissue with a magnifying lens or the lower power of a microscope. 
In 1866, legislation calling for the trichinoscopic examination of all hogs slaughtered for food was adopted in many parts of Germany. By 1877, obligatory inspection of pork was begun in Prussia--the leading German State at that time--and other States of North Germany as well as the larger towns of South Germany soon followed. 
At this point, American swine had already gained the reputation of being heavily infected with trichinae. Around 1890, a French veterinarian, after stating the incidence of trichinae in various European countries, wrote: "These figures are greatly exceeded, however, by those of the pigs sent to Europe from the United States of America in such immense numbers, chiefly from the markets of Cincinnati and Chicago; this is demonstrated by the examinations made in different parts of Europe, and even in America." 
As indicated by this statement, the United States had developed a thriving pork export market in Europe by the latter part of the 19th century. Starting in 1872, exports of ham and bacon, in particular, jumped sharply, and within a decade were up to 15 times their previous levels. However, fears of trichinae-infected pork soon put a damper on that market. 
In 1879, an ordinance was passed by the Italian government forbidding the importation of swine or pork products from the United States. Similar laws prohibiting the importation of American pork were soon introduced in Portugal, Norway, Austria, and Hungary. In 1880, Bismarck signed a decree that prohibited the importation into Germany of American pork sausage and chopped meat and, in 1883, a decree excluding all American pork. In February 1881, France prohibited the importation of all American salted pork (although this interdiction was applied only intermittently during the next decade). 
As a result of these actions, bacon and ham exports from the United States dropped sharply--to about 60 percent of their previous level. In 1880, the year before the prohibitions went into effect, the United States sold 70 million pounds of pork to France and 43 million pounds to Germany. Exports to these countries fell to practically nothing. In the 10 years following 1881, American pork was shut out of nearly every market in continental Europe. 
In 1883, President Arthur appointed D.E. Salmon, later Chief of the Bureau of Animal Industry, to head a commission to investigate the situation. The commission reported first that infection wasn't nearly as high as alleged. Then they presented evidence to show that even if there was some infection, practically all the trichinae were destroyed by the salting process and the length of the trans-Atlantic voyage. Finally, they accused the Germans of incompetent inspections and pointed out that no German outbreaks of trichinosis could be traced to American pork. 
But, despite the protests, the markets remained closed. So Americans took action. 
In August 1890, the Congress of the United States passed a law providing for the inspection of meats for exportation. However, this referred primarily to the way in which they were packed and their condition at the time of shipment--rather than to the health of the animals at slaughter--and this did not satisfy the foreign requirements. 
So on March 3, 1891, Congress passed a much broader meat inspection act that provided for the microscopic examination--to show freedom from trichinae--of all slaughtered pork intended for export. Foreign representatives watched the work carried out under this law very carefully. In September 1891, the German decree of 1883 was repealed and American pork was permitted to enter under certificate. The German action was followed shortly by the removal of a similar prohibition by Denmark and later by Italy, France, and Austria. 
However, the lost market was not easy to regain--for a number of reasons. First, the ban had placed a "stigma" on American pork that was hard to erase. Second, trade arrangements that had been disrupted were slow in being set up again--our brands of meat were not longer familiar, commercial connections had been severed, and requirements for cuts and cures had changed. Third, the organization of a force of trained and equipped inspectors to examine the pork for trichinae could not be established overnight. 
Nevertheless, some 38 million pounds of pork were microscopically examined the first year, 22 million pounds of which went to countries requiring inspection (by 1893, Germany and France were the only European countries retaining this requirement). This amount of inspected pork for export grew until it reached a high of 120 million pounds in 1898. 
However, this growth was not without problems. The Yearbook of Agriculture for 1895 notes: "And notwithstanding the agrarian protectionists of Germany, who have instituted by unjust discriminations every possible impediment to the consumption of pork and beef from the United States in the Empire, 26,670,410 pounds of microscopically inspected hams, bacon, and other cured swine flesh were exported directly to that country, while France, which is intermittently discriminating against us, took 9,203,995 pounds of the same product; Denmark, 472,443; Spain, 4,752; and Italy, 3,630." 
The German problem was centered around the fact that, although the action of September 1891 allowed American pork to enter the German Empire under certificate, no kingdom or local authority of the Empire was obliged to recognize the certificate as having any sanitary value. Thus, in May 1892, a Prussian circular was issued that called for the reinspection of American pork. Other local and State governments passed regulations requiring reinspection of American pork. 
This led to diplomatic difficulties between the two countries. In 1895, the Secretary of Agriculture even went so far as to hint at retaliation. In the Yearbook of Agriculture, Secretary J. Sterling Morton wrote as follows: "Reciprocal certification of the chemical purity of wines exported from those countries to the United States may some time be demanded from the German and French governments as a sanitary shield to American consumers, for certainly American meats are as wholesome as foreign wines." In 1897, the Department sent a special agricultural attache to Berlin. Charles Wardell Stiles spent nearly 2 years there investigating the charges made against American pork. 
Undoubtedly there was some basis for the German accusations. In the haste of reestablishing the trade, the requirements were not always fully understood, and some uninspected shipments were made that were not accompanied by certificates. Also, there is some evidence that uninspected pork was packed in boxes marked with the American inspection stamp and then shipped from Belgium and Holland into Germany. 
On the other hand, American records indicate that more than just sanitary reasons were involved in the German actions--that it was a political and economic questions as well. During this period, Bismarck embarked on a protectionist policy for German agriculture. The Yearbook of Agriculture of 1897 comments as follows: "We now find a serious obstacle . . . in the active hostility . . . toward our agricultural products by the agrarian population of certain European countries where we formerly possessed a profitable market. Yielding to pressure . . . the governments of these countries have in several instances sought to limit importation from the United States by the imposition of unwarranted restrictions." 
The special agricultural attache was more explicit several years later when he bitterly reported: "There appears to be a systematic attack upon American meats carried on by certain German newspapers and individuals. It is repeatedly asserted that our pork is dangerous . . . local regulations of alleged sanitary nature, but of a most exasperating character, are promulgated . . . butcher associations turn into amateur sanitary societies, and after discoursing at length upon the great dangers of 'Yankee' products and the unheard-of frauds practiced by men who are pictured as almost criminal, they incidentally mention that American competition (while furnishing meat to the working classes) is injuring their own trade." 
The difficulties were further complicated in 1898 by the discovery of a secret Prussian circular that instructed officials to withhold information from U.S. Consuls on conditions of health and disease in Prussia. In addition, new German fiscal regulations were put into effect some time later that, according to a 1905 report, "operated against our trade last year to the extent that shipments fell from about 15 million pounds in 1903 to 5 million pounds in 1904." 
Thus, when the Congress of the United States passed a new meat inspection act on June 30, 1906, the provisions for microscopic examinations of pork intended for export were omitted, and such inspections were discontinued. In his report for 1907, Secretary of Agriculture "Tama Jim" Wilson said, "Germany, while requiring our certificates of microscopic inspection, was not willing to accept them as conclusive, but reinspected all pork imported from the United States. As the inspection seemed to be of little or no benefit, but of considerable expense, it was stopped." 
Trichinoscopic inspection of pork remained important in many countries of Europe, however. Adoption of this system of protection depended, in large part, on the culinary habits of the people. 
In France, for instance, trichinosis was rarely seen because people prefer pork well cooked. In contrast, in Germany, where the people are fond of raw or semiraw pork products, trichinosis was widespread--8,491 cases (513 deaths) from 1860 to 1880 and 6,329 cases (318 deaths) from 1881 to 1898. Here trichinoscopic examination of pork was almost a necessity. 
A huge number of inspectors were employed to carry on this work. Some worked at this full time, while others such as physicians, druggists, and barbers did this inspection work on a part-time basis. The number of inspectors so employed was variously estimated at 18,581 in all of Germany in 1881, and as high as 28,224 in Prussia alone by 1899. It was pointed out that the latter figure was almost as large as the entire army of the United States before the Spanish-American War (28,238 officers and men in 1897). 
While the United States' problems with trichinosis at the turn of the century were never really resolved, they did lead to two developments important to today's agriculture. First, they were responsible in part for establishing a Federal meat inspection service. Second, the results of Stiles' work in Berlin in 1897 and 1898 led to the recommendation that agricultural attaches be sent to a number of different countries to represent U.S. agricultural interests. 
 
 
 

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