CHAPTER VII

ANIMAL PARASITES

Not only pathogenic bacteria but certain kinds of animal parasites sometimes enter the human body in or upon articles of food. One of the most important of these is the parasite causing trichiniasis.

TRICHINIASIS

Trichiniasis or trichinosis is a disease characterized by fever, muscular pains, an enormous increase in the eosinophil blood corpuscles, and other more or less well-defined symptoms; at the onset it is sometimes mistaken by physicians for typhoid fever. The responsible parasite is a roundworm (_Trichinella spiralis_, formerly known as _Trichina_) which is swallowed while in its encysted larval stage in raw or imperfectly cooked pork.[90] The cysts or envelopes in which the parasites live are dissolved by the digestive fluids and the young larvae which are liberated develop in the small intestine to the adult worm, usually within two days. The young embryos, which are produced in great numbers by the mature worms, gain entrance to the lymph channels and blood stream, and after about ten days begin to invade the muscles--a procedure which gives rise to many of the most characteristic symptoms of the infection. It is estimated that in severe cases as many as fifty million embryos may enter the circulation. The parasites finally quiet down and become encysted in the muscle tissue and the symptoms, as a rule, gradually subside. Ingestion of a large number of parasites at one time often results fatally, the mortality from trichiniasis being on the average somewhat over 5 per cent and rising in some outbreaks to a much higher figure (30 per cent). On the other hand, many infections are so light as to pa.s.s unnoticed. Williams[91] found _Trichinella_ embryos present in 5.4 per cent of the bodies of persons dying from other causes. Such findings are considered to indicate that occasional slight _Trichinella_ infections even in the United States are quite common. This might indeed be expected from the frequent occurrence of infection in swine, about 6 per cent of these animals being found to harbor the parasite.

[Ill.u.s.tration: FIG. 7.--Trichinae encysted in intercostal muscle of pig.

(About 351.) (After Neumann and Mayer.)]

The specific symptoms (such as the muscular pain) of trichiniasis may be due in part to mechanical damage of the muscle tissue, but it is also probable that they are partly due to toxic products exuded by the worms and partly to the introduction of alien protein material--the protein of the worm--into the tissues. Secondary bacterial infection is also a possibility, but there is little evidence to prove that this is an important factor in most cases of trichiniasis. The various stages observed in the progress of the disease are plainly connected with the different phases of the worm's development--the initial localization in the intestines, the invasion of the muscles, and the final encystment.

Swine become infected with this parasite by eating sc.r.a.ps of infected meat, or the offal of their own kind, or by eating infected rats. The rat, through its cannibalistic propensities, becomes infected frequently, and is one of the chief factors in the wide dissemination of the disease. Human infection is practically accidental and self-limited; biologically speaking, man as a host does not enter into the calculations of the parasite.

Treatment of established trichiniasis infection is palliative, not truly remedial. The parasites, once inside the body, cannot be materially affected by the administration of any drug. While cure of trichiniasis is thus difficult, if not impossible, prevention is very simple. The thorough cooking of all food is sufficient to preclude infection. This relatively simple means of destroying the larvae is a more certain as well as less expensive method of preventing infection than is the laborious microscopic examination of the tissues of every slaughtered hog. In Germany between 1881 and 1898 over 32 per cent of 6,329 cases of trichinosis that were investigated were traced to meat that had been microscopically examined and pa.s.sed as free from trichinae.[92] On the other hand, thorough cooking removes all possibility of danger.

TENIASIS

Various tapeworm or cestode infections are contracted by eating meat containing the parasite. Particular species of tapeworm usually infest the flesh of specific hosts, as _Tenia saginata_ in the beef and _Tenia solium_ in the hog. The dwarf tapeworm, _Hymenolepis nana_, develops in rats, and the human infections with this parasite occasionally observed are probably caused by contamination of food by these animals.

[Ill.u.s.tration: FIG. 8.--_Cysticercus cellulosae_ in pig's tongue. (After Neumann and Mayer.)]

Sometimes the existence of the tapeworm in man is restricted to the alimentary tract and the symptoms vary from trivial to severe, but sometimes (_Tenia solium_) the larval stage of the tapeworm invades the tissues and becomes encysted in various organs (brain, eye, etc.), where, as in the case of cerebral infection, it may result fatally. The encysted larva of _Tenia solium_ was at one time regarded as an independent animal species and named _Cysticercus cellulosae_. The condition known as "measly pork" is produced by the occurrence of this encysted parasite.

So-called hydatid disease is due to the cystic growth produced by the larva of a species of tapeworm (_Echinococcus_) inhabiting the intestine of the dog. Human infection may be caused by contaminated food as well as more directly by hands soiled with petting infected dogs. Several varieties of tapeworms infesting fish, especially certain fresh-water species, may be introduced into the human body in raw or partly cooked fish.

Methods for the prevention of tapeworm infection include the destruction of the larvae by heat--that is, the thorough cooking of all meat and fish--and the minimization of close contact with those animals, such as the dog and cat, that are likely to harbor parasites. Cleanliness in the preparation and serving of food, and attention to hand-washing before meals, and especially after touching pet animals, are necessary corollaries.

UNCINARIASIS

Hookworm infection (uncinariasis, ankylostomiasis) is commonly caused by infection through the skin of the feet, but the possibility of mouth infection cannot be disregarded, and in regions where hookworm disease exists methods of guarding against food contamination should be practiced, as well as other precautions. Billings and Hickey[93] believe that hookworm disease is contracted by unconscious coprophagy (from raw vegetables) much more frequently than is generally supposed.

OTHER PARASITES

A number of other parasitic worms (e.g., _Strongyloides_, _Ascaris_ or eelworm, and _Oxyuria_ or pinworm) may conceivably enter the human body in contaminated food, and while, as in hookworm disease, other modes of infection are probably more important, the liability to occasional infection by uncooked food must not be overlooked.

[Ill.u.s.tration: FIG. 9.--_Lamblia intestinalis._ (After Neumann and Mayer.)]

Various forms of dysentery or diarrhea have been attributed to infection with _Giardia (Lamblia) intestinalis_. Observations made by Fantham and Porter[94] upon cases contracted in Gallipoli and Flanders have given support to this view. Strains of this parasite of human origin have been shown to be pathogenic for mice and kittens. It is considered possible that these animals may act as reservoirs of infection and spread the disease by contamination of human food.

FOOTNOTES:

[90] The consumption of raw sausage made with pig meat is particularly likely to give rise to trichiniasis.

[91] _Jour. Med. Research_, VI (1901), 64.

[92] Edelmann, Mohler, and Eichhorn, _Meat Hygiene_, 1916, p. 182.

[93] _Jour. Amer. Med. a.s.soc._, LXVII (1916), 1908.

[94] _Brit. Med. Jour._, II (1916), 139.

CHAPTER VIII

POISONOUS PRODUCTS FORMED IN FOOD BY BACTERIA AND OTHER MICRO-ORGANISMS

In close relation to the cases of infection with animal or plant parasites which have been discussed, there are certain well-established instances of poisoning by substances that have been generated in food while it is still outside of the body. This is the common type of food poisoning in popular estimation, but in point of fact the proved cases of this cla.s.s are much less frequent than the instances of true infection with bacteria of the _paratyphoid-enteritidis_ group (chapter vi). Thus far the best-known examples of poisoning by the products of micro-organisms are botulism and ergotism.

ERGOTISM

Ergotism or ergot poisoning is due to the use of rye that has become diseased through the attack of a fungus, _Claviceps purpurea_. It occurred frequently in the Middle Ages when in times of famine the ergot or spurred rye (O.Fr. _argot_, "a c.o.c.k's spur") was often used in default of better food. In Limoges in 922 it is said that forty thousand persons perished from this cause. Improvement in the facilities for transportation of food into regions where crops have failed, and the use of special methods for separating the diseased grain from the wholesome have greatly reduced the prevalence of ergotism. In Western Europe poisoning from this cause has practically ceased, although Hirsch recorded some twenty-eight outbreaks in the nineteenth century; in parts of Russia the disease is said still to occur in years of bad harvest.[95]

The poison ergot itself has long been used as a drug in obstetrics, but its composition is complex and is still not completely understood.

Several const.i.tuents of ergot have been extracted, and these have been shown to possess different physiological effects.[96] The symptoms observed in the outbreaks of ergotism of mediaeval times are not wholly reproduced experimentally by the drug and are thought to have been in part due to the semi-starvation engendered by the use of rye from which the nutritious portions had been largely removed by the growth of the fungus.

BOTULISM

The best established case of poisoning by means of bacterial products taken in with the food is the serious malady known somewhat inappropriately as botulism (botulus, sausage).[97] This kind of food poisoning, which has a characteristic set of symptoms, seems to have been first recognized and described in 1820 by the German poet and medical writer Justinus Kerner. In two articles (1820-22) he enumerates 174 cases with 71 deaths occurring in Wurttemberg between 1793 and 1822 and apparently in most cases connected with the use of insufficiently smoked sausage. Mayer[98] tabulates about 600 additional cases observed in various parts of Germany down to the end of 1908, the total mortality in the 800 cases being about 25 per cent. In France botulism is said to be very rare.[99] In Great Britain Savage[100] declares that he has been unable to trace the occurrence of a single outbreak. In the United States several instances of botulism poisoning are on record (Sheppard,[101] 1907, 3 cases, 3 deaths, canned pork and beans; Peck,[102] 1910, 12 cases, 11 deaths; Wilbur and Ophuls,[103] 1914, canned string beans, 12 cases, 1 death; Frost,[104] 1915, 3 cases, 3 deaths). Professor Stiles[105] has given a graphic description of his own attack of probable botulism due in all likelihood to minced chicken.

[Ill.u.s.tration: FIG. 10.--_Claviceps purpurea:_ 1, ergot on rye-gra.s.s; 2, ergot on rye; 3, section of a portion of the conidial form of fruit, 300; 4, a sclerotium or ergot; 5, head of ascigerous form of fruit; 6, an ascus, 300; 7, a single spore, 300. (After Ma.s.see, _Plant Diseases_, by courtesy of the Macmillan Company.)]

_Symptoms._--The description of a case seen by Wilbur and Ophuls,[106]

is so typical that it may be cited:

Girl, aged 23, Tuesday evening, Nov. 23, 1913, ate the dinner including the canned string beans of the light green color together with a little rare roast beef. The following day she felt perfectly normal except that at 10:00 in the evening the eyes felt strained after some sewing. Thursday morning, thirty-six hours after the meal, when the patient awoke, the eyes were out of focus, appet.i.te was not good, and she felt very tired. At night she had still no appet.i.te, was nauseated, and vomited the noon meal apparently undigested. Friday morning, two and one-half days after the meal, the eyes were worse, objects being seen double on quick movement, and it was noticed that they had a tendency to be crossed. A peculiar mistiness of vision was also complained of. She was in bed until late in the afternoon, when she visited Dr. Black. She had had some disturbance in swallowing previous to this time and stated that it felt as if "something came up from below" that interfered with deglut.i.tion. The fourth day she remained in bed, was much constipated, and noticed a marked decrease in the amount of urine voided. There was at no time pain except for occasional mild abdominal cramps, no headache, subnormal temperature, and a normal pulse. The fourth and fifth days the breathing became difficult at times and swallowing was almost impossible. The patient complained of a dry throat with annoying thirst. The sixth day there were periods of a sense of suffocation with a vague feeling of unrest and as if there might be difficulty in getting the next breath. The upper lids had begun to droop. The voice was nasal. When the attempt was made to swallow liquids they pa.s.sed back through the nose. The patient felt markedly weak.

Physical examination at this time showed ptosis of both upper eyelids, dilatation of the right pupil, sluggish reaction to light of both pupils, apparent paralysis of the internal rectus of the left eye, normal retina, inability to raise the head, control apparently having been lost of the muscles of the neck, inability to swallow, absence of taste. The tongue was heavily coated and the throat was covered with a viscid whitish mucus clinging to the mucous membrane. The soft palate could be raised but was sluggish, particularly on the right side. The exudate on the right tonsil was so marked that it resembled somewhat a diphtheritic membrane. The seventh day there was some change in the condition; occasional periods occurred when swallowing was more effective, and there was less tendency to strangle. On the eleventh day there was some improvement of the eyes, still strangling on swallowing, sensation of taste was keener, and the general condition improved. The twelfth day the patient was able to move her head, but was unable to lift it except when she took hold of the braids of her hair, and pulled the head forward. The eyes could be opened slightly, speech was less nasal and more distinct, and improvement in swallowing was marked.

At the end of two weeks the patient was able to take soft diet freely, and at four weeks she was up in a chair for a couple of hours complaining only of general weakness and inability to use her eyes. At the end of five weeks she was able to leave the hospital and return to her home and later to resume her regular work.

In all cases the nervous system is strikingly affected in this form of food poisoning. Dizziness, double vision, difficulty in chewing and swallowing, and other symptoms of nervous involvement occur with varying intensity and may persist for a long time after the first signs of the attack. Temperature, pulse, and respiration remain practically normal.

In contrast with the traditional type of food poisoning gastro-intestinal symptoms may be slight or altogether lacking. Freedom from abdominal pain is usually noted; diarrhea is the exception and constipation the rule; vomiting sometimes occurs, but may be absent. In the cases described by Sheppard there was "an entire absence of the usual gastro-intestinal symptoms from first to last, no pain or sensory disturbance and no elevation of temperature." The visual disturbances are very characteristic. Stiles relates his own experiences as follows: