Parasitic disease

“ Moreover, in recent years the massive migration of people from the south countries, where parasitic diseases are common, towards developed countries fueled that many parasitic infections are now reemerging and generating new health problems at a global level. ”

“ In the meantime, as parasitic growth was extraordinary, and as every endothelial cell was crowded with parasites seen in no other disease, it forced itself upon their belief, and they were justified in assuming, that they must be causative. ”

“ It has now been discovered that a great number of human diseases are caused by microscopic parasites, which are spoken of in a general way by the name invented by the great Pasteur, viz. "microbes." Wool-sorter's disease, Eastern relapsing fever, lock-jaw, glanders, leprosy, phthisis, diphtheria, cholera, Oriental plague, typhoid fever, Malta fever, septic poisoning and gangrene have been shown to be caused each by a peculiar species of the excessively minute parasitic vegetables known as bacteria (or Schizophyta) . ”

“ Nothing is more important for us to recognize than that our diseases are contracted from neighboring subjects just in proportion as we are closely associated with them. From our fellowmen we contract, as everyone knows, a large number of diseases, either by direct contact or by means of the air that surrounds us. From the earth we get hook-worms and other animal parasites, either by coming directly in contact with it or through eating uncooked fruits and vegetables. From water we get typhoid fever, dysentery, cholera, and many other parasitic diseases. ”

“ From the facts here given it will be seen that the individual's susceptibility to disease produced by parasitic bacteria will depend upon his habits of cleanliness, his care in handling infectious material, or care in cleansing the hands after such handling, upon his habit of eating food cooked or raw, and upon the condition of his skin and mucous membranes, since any kind of bruises will increase susceptibility. ”

“ Other Protozoan Diseases.—Many other diseases of man are probably caused by parasitic protozoans. Dysentery of one kind appears to be caused by the presence of an amœba-like animal in the digestive tract which comes usually through an impure water supply. Smallpox, rabies, and possibly other diseases are caused by protozoans. Smallpox, which was once the most dreaded disease known to man, because of its spread in epidemics, has been conquered by vaccination, of which we shall learn more later. ”

“ Loathsome contagious diseases include those whose presence excites abhorrence in others, and which are essentially chronic, such as favus, ringworm of the scalp, parasitic fungus diseases, Madura foot, leprosy and venereal disease. Dangerous contagious diseases are such as trachoma, filariasis, hookworm infection, amœbic dysentery, and endemic hematuria. ”

“ The last few years of the nineteenth and the first few years of the present century are marked in the annals of medicine by a great increase in our knowledge of certain parasitic diseases, and, above all, in our knowledge of the agency by which the parasites causing the diseases are conveyed from host to host. ”

“ The knowledge about parasitic diseases at different levels, such as life cycles, structures, molecular biology, development of new drugs and vaccines, and its ability to escape or modulate different mechanisms of defense of its hosts, is essential to better development of therapies and diagnostics. This special issue addresses many of such issues. We have divided the special issue in two blocks, the first dealing with protozoan parasites and the second one dealing with different helminth infections. ”

“ This treatise is not professional, that is to say, it does not concern itself with therapeutics or the curative treatment of parasitic affections; yet it introduces and helps to solve many questions relating to epidemics, endemics, and epizoötics due to parasites. The medical man who only looks at the phenomena of parasitism as displayed within the human territory must of necessity acquire a cramped, narrow, and distorted conception of the rôle played by parasites in the production of disease. ”

“ There are numerous diseases of men and animals that are demonstrably the products of parasitic life, and such diseases may take the most terrible epidemic forms, as in the case of the silkworms of France, referred to at an earlier part of this article. Now it is in the highest degree important to know whether the parasites in question are spontaneously developed, or whether they have been wafted from without to those afflicted with the disease. The means of prevention, if not of cure, would be widely different in the two cases. ”

“ This cycle of development may continue for an indefinite time, and there may be such a rapid increase in the parasites as to bring about the death of the individual; but with him the parasite would also perish, for there would be no way of extending the infection and providing a new crop. The disease has been transmitted by injecting the infected blood into a normal individual. ”

“ The scope of this topic could be immense, as there are hundreds of parasitic species that infect humans, and also because parasitic infections are considered as one of the leading causes of high morbidity and mortality in underdeveloped countries, mainly in children and the elderly, affecting the physical and intellectual capabilities of such population and resulting in high expenses in treatment and rehabilitation. ”

“ The knowledge of the causation of disease by bacterial and protozoic parasites is a thing which has come into existence, under our very eyes and hands, within the last fifty years. The parasite, and much of its nature and history, has been discovered in the case of splenic fever, leprosy, phthisis, diphtheria, typhoid fever, glanders, cholera, plague, lock-jaw, gangrene, septic poisoning (of wounds) , puerperal fever, malaria, sleeping sickness, and some other diseases which are fatal to man. ”

“ An obligate parasite can develop only within a living host; while a facultative parasite can, according to circumstances, lead either a parasitic or saprophytic form of existence. The fact that certain contagia are completely, and others only partially, parasitic brings out important differences in their life-history. Thus, so far as we know, the contagia of scarlet fever, measles, small-pox and hydrophobia do not multiply outside the body. Hence there is a reasonable prospect of annihilating them by measures of disinfection and isolation. The position of diphtheria is doubtful. ”

“ What makes the discovery epochal is the fact that it dropped a brand-new idea into the medical ranks—an idea destined, in the long-run, to prove itself a veritable bomb—the idea, namely, that a minute and quite unsuspected animal parasite may be the cause of a well-known, widely prevalent, and important human disease. ”

“ In certain cases the chronic disease represents really a series of acute onsets; thus in the case of the parasites there may be periods of complete quiescence of infection but not recovery, the parasites remaining in the body and attacking when the defences of the body are in some way weakened. ”

“ The worms which inhabit the intestines have a sharp biting mouth by which they fasten themselves to the mucous membrane and devour the blood. The most prominent symptom of the disease is anæmia, or loss of blood, due not only to the direct eating of the parasite, but to bleeding from the small wounds caused by its bite. Large numbers of eggs are produced by the parasite which are passed out with the feces, which becomes the only infectious material. In a city provided with water-closets and a system of sewerage there would be no means of extension of infection. ”

“ Cause.—The parasite, which lives in the blood and tissues, is known, but its exact method of transmission to man is still in the realm of uncertainty.
Symptoms.—The disease begins in an indefinite manner and then assumes the form of a continued fever, associated with enlargement of the spleen and liver and progressive emaciation. Bleeding from the nose is not uncommon, and in Europeans the peculiar earthy-grey colour of the skin is very striking. The disease lasts for months and even years and is very frequently fatal. ”

“ It is evident that just as the parasite has his weapons of offence and defence so has the host, otherwise there would be no recovery from infectious diseases. Although many of the infectious diseases have a high mortality, which in rare instances reaches one hundred per cent, the majority do recover. In certain cases the recovery is attended by immunity, the individual being protected to a greater or less degree from a recurrence of the same disease. The immunity is never absolute ”

“ It was found that the life cycles of these parasites ran parallel with the clinical cycle of malarial disease. It was found that when the parasite had arrived at maturity the apyretic interval in an ague was about to conclude, and that when the parasite had arrived at the sporulating stage the patient had entered on the shivering stage of his fever. During that and the succeeding hot and sweating stage the spores had entered the red blood corpuscles, and when the parasite had ensconced itself in the red blood corpuscle and begun to grow, the fever had come to an end. ”

“ Having found a suspected parasite in the blood or flesh of a patient, we can not accuse the parasite with certainty of being the cause of the disease, unless we can separate it entirely from the fluids and cells of the diseased body without depriving it of its virulence. In some cases it is not easy, if possible, to cultivate the parasite outside of the body; in other instances it can be readily accomplished. Of course, all such attempts require scrupulous care to prevent contamination from other germs that might accidentally be introduced into the same soil. ”

“ Effect of Parasitism on the Parasite.—The usual effect of parasitism on the parasitic organism is that the various organs necessary for a free life tend to degenerate, whilst there is a multiplication and development of organs of adhesion, by means of which the parasite maintains its hold on its host. There is further an immense increase in the powers of reproduction, which may take the form of an increase in the number of fertilised eggs produced, or the parasite may at some time of its life reproduce asexually, by budding, or fission, or parthenogetically. ”

“ Now it is quite evident that if in any way we can kill the parasites as they exist in man, we not only cure the individual man of malarial fever, but at the same time prevent his being a means of infection for other men who have not yet acquired the disease. ”

“ The effect of damage in producing chronic disease may not appear at once, for the great power of adaptation of organs and the exercise of reserve force may for a time render the damage imperceptible; when, however, age or the supervention of further injury diminishes the power of adaptation the condition of disease becomes evident. Chronic disease may be caused by parasites when the relation between host and parasite is not in high degree inimical, as in tuberculosis, gonorrhoea, syphilis, most of the trypanosome diseases and the diseases produced by the higher parasites. ”

“ It is, of course, easy to believe that an extensive parasitism and destruction of the corpuscles would be disastrous to the health of the individual, and the severity of the disease will depend upon the extent of the parasitism. Corresponding to this life history of the organism, the disease malaria is commonly characterized by a decided intermittency, periods of chill and fever alternating with periods of intermission in which these symptoms are abated. ”

“ The larval and adult stages of endoparasites become similarly specialized, and although there are many cases in which the parasites that excite a disease in one kind of animal are able to infect animals of different species, the general tendency is in the direction of absolute limitation of one parasite, and indeed one stage of one parasite to one kind of host. The series of events seems to be a gradual progression from temporary or occasional parasitism to obligatory parasitism and to a further restriction of the obligatory parasite to a particular kind of host. ”

“ The most important of these are anthrax, glanders, tuberculosis, infectious pleuro-pneumonia, swine plague, hog cholera, hog erysipelas, and fowl cholera. All of these have been proved to be due to bacterial parasites, the morphological and biological characters of which are now well known. The infectious agent and usual mode of infection being known in any given disease, we have a scientific basis for measures of prophylaxis. These naturally include the destruction of the specific micro-organism to which the disease is due wherever it may be found. ”

“ Already it has been demonstrated that several of the infectious diseases are caused by specific parasitic bacteria, and it is more than probable that investigations now in progress will lead to further discoveries rendering preventable and controllable many diseases which occasion much human suffering and contribute largely to mortality. ”

“ There are, however, other organisms called [3] parasites, which can exist in living tissues of animals or vegetables. The organisms at whose expense the parasites live are called their hosts. Parasites not only contribute nothing to their hosts, but generally harm them by producing poisonous substances or depriving them of food. Some parasites are able to lead a saprophytic existence also, but as a rule they live at the expense of animal or plant life. Pathogenic, or disease-producing, germs belong to the group of parasites. ”