History and Geography Antiquity

Although knowledge of the parasite causing trichinosis was first obtained in 1835, knowledge of the disease dates back to antiquity. Dietary laws prohibiting the eating of swine are thought to have been engendered by the observation that human illness sometimes followed the eating of such flesh. In 1940 Asa Chandler stated: "There can be little doubt that this worm, with the pork tapeworm as an accomplice, was responsible for the old Jewish law against the eating of pork." Historians have surmised that Muhammad recognized that certain epidemics could have been caused by ingestion of pork, and thus followed the example of Moses in prohibiting pork consumption.

Nineteenth Century

The first person to actually see trichinae was James Paget, a 21-year-old freshman medical student at St. Bartholomew's Hospital in London. In 1835 Paget noted a curious pathological condition in the cadaver of a middle-aged man that was brought in for study. The cadaver had "spicules of bone" in the muscles. They were so hard that they blunted the scalpel. Others had seen these gritty particles previously, but it was Paget who had natural history training and the intense desire to observe new things, and thus he was the first to note that the particle was a worm in its capsule. Paget did not have a microscope, but eventually secured the use of one from the botanist Robert Brown of the British Museum. Specimens of the worm were taken to Richard Owen, who was to become England's greatest comparative anatomist. Owen subsequently presented a paper on the worm at the Zoological Society, and gave the parasite its name. Owen's presentation at the Zoological Society occurred just 18 days after Paget's announcement.

Although Paget's discovery was overshadowed by the detailed and complete memoir by Owen, Paget retained his intense spirit of scientific inquiry and published many papers on medical subjects. Later, he became Sir James Paget, one of the most distinguished surgeons of his time.

Trichinae in animals other than humans were first noted in 1846. Joseph Leidy, a professor of anatomy working in Philadelphia, found the worms in the extensor muscles of the thigh of a hog. Leidy had previously seen trichinae in human bodies in a dissection room, and he could perceive no distinction in the worms from the two hosts. In 1850 Ernst Herbst, working in Gottingen, established that trichinae from meat eaten by an animal may invade its muscles. Herbst infected a badger with trichinous dog meat and then fed the infected badger meat to three dogs. All three dogs were infected at autopsy.

The significance of Herbst's experiments, as well as Leidy's observations, was not appreciated at the time because leading authorities believed that the trichinae from nonhumans were of a different species from those of humans. Herbst himself believed that trichinae were actually the larvae of filarial worms.

The problem of determining the life cycle of trichinae soon caught the attention of two of the leading researchers of their time, Rudolf Virchow of Berlin and Rudolph Leuckart of Giessen. Leuckart, in 1850, observed that the female intestinal trichinae are viviparous, but he believed that the trichinae were derived from the intestinal nematode Trichuris trichiura. Virchow, in 1859, fed encapsulated trichinae from a human to a dog, where the worms reached sexual maturity. Virchow refuted Leuck-art's claim that the trichinae were identical with Trichuris.

Verification of the life cycle of trichinae and the discovery of the pathogenesis of trichinous infections represent monumental contributions by Friedrich Albert Zenker in 1860. Zenker performed an autopsy on a 20-year-old servant girl in Dresden whose illness had been diagnosed as typhoid fever. He examined muscle fibers from the arm and was startled to see "dozens of trichinae, lying free in the muscle, either coiled or extended, and exhibiting the plainest signs of life." Other skeletal muscles examined were likewise inhabited by the worms. Upon examining intestinal contents, Zenker saw sexually mature worms. It was apparent to him that the parasite underwent its entire life cycle in one and the same host.

Zenker subsequently investigated the household in which the servant girl worked, and found the parasite in sausage that had been prepared just prior to the onset of the girl's illness. Furthermore, other members of the household who had eaten the meat had become seriously ill with the same symptoms as shown by the unfortunate servant girl.

Following the establishment of the details of the life cycle and pathogenesis of trichinae, several outbreaks of infection were recorded. Some 140 epidemics of trichinosis were noted in Europe between 1860 and 1877, in which 3,044 persons were known to have fallen ill and 231 to have died.

Beginning in 1863, examination of pork for trichinae was practiced in parts of Germany, and in 1879 a law was enacted in Prussia whereby all pork was required to be examined for trichinae. In this same year, ordinances were passed in Italy, Austria, and Hungary forbidding the importation of swine or pork products from the United States, and other countries followed with similar bans. Subsequently, the U.S. Department of Agriculture, although not providing for specific examination for trichinae, did specify methods for the processing of pork products that are customarily eaten raw. Such procedures will destroy the infectivity of any trichinae present. Public education, and heat treatment of the garbage used to feed hogs, have also helped to reduce the incidence of the disease in North America and Europe.

Donald E. Gilbertson

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