Pseudoparasites

Pseudoparasites, or false parasites, are free-living forms which, having accidentally entered the human or animal organism, live in it for some time in the position of parasites, biologically not being such. Thus, the habitation of a free-living organism in the human body is a random phenomenon and uncharacteristic for the corresponding species. At the same time, the parasitic lifestyle of true parasites is a species trait for them. Pseudoparasites can be external and internal. As external ones, one can note the larvae of the house fly (Musca domestica), the blowfly (Lucilia), etc., when they develop in wounds or ulcers of the body, where eggs were laid by the females of these insects. Normally, the larvae of the named flies live in manure, decomposing organic substances, and in carrion. Developing on a living body, they erode tissues and can be the cause of the death of the weakened host. At the same time, the larvae of the Wohlfahrtia fly are true parasites, since the tissues of a living organism serve as the only place of their habitation. Pseudoparasites can also be such free-living arthropods as myriapods. In the human intestine, Geophilus electricus, Chaetechelyne vesuviana, Himantarium Gervaisi, Scutigera coleoptrata, Julus terrestris, and other myriapods have been found. In the nasal cavity and in adjacent sinuses, various species of Geophilus and Lithobius were sometimes encountered. The presence of such pseudoparasites manifests itself in various painful disorders of the intestine or headaches, dizziness, neuralgias, etc. Remarkable cases of finding live adult dung beetles Onthophagus bifasciatus in the human intestine in India can possibly be explained by their crawling into the intestine through the anus. Often, live fly larvae are discovered in the human intestine, entering there with food (with salted fish, vegetables, meat, etc.); such are the larvae of the cheese fly (Piophila casei), the flesh fly (Sarcophaga carnaria), the lesser house fly (Homalomyia canicularis), and others. Among other animals, mites of the family Tyroglyphidae, slugs, and some protozoa (Chlamydophrys stercorea, etc.) have been detected in the intestine. One should distinguish actual pseudoparasites from imaginary ones. The former were actually on or in the human body, while the latter entered the examined material (vomit, feces, urine, etc.) from the outside and are mistakenly taken for animals that exited the human body. Sometimes patients intentionally mislead the doctor, claiming that certain animals (e.g., an earthworm, etc.) exited their intestine or with vomit. An erroneous conclusion can also be made involuntarily, since some animals can enter feces or vomit masses after they have already been passed (such are various protozoa: ciliates, rhizopods, fly larvae, non-parasitic nematodes, etc.). To avoid errors, an accurate anamnesis and precautions when collecting excrement for diagnostic examination (dry and clean dishes, protection from dust, flies, etc.) are necessary. The erroneous recognition of extraneous organisms as pseudoparasites can lead the doctor to a false judgment about the causes of the observed disease. Pseudoparasites should be distinguished from guest parasites (see). The ability of free-living animals to pseudoparasitism explains to us one of the paths of the phylogenetic development of true parasitism. Thus, insect larvae (e.g., flies), usually found in food products (meat, vegetables, etc.) and having many chances to enter the stomach and intestine of some animal together with food and withstand the action of its digestive juices, can, under a pseudoparasitic lifestyle, gain chances for survival and, in the order of natural selection, turn into true parasites. Pseudoparasites must also be distinguished from homeoparasites (see Parasites).