Taeniasis and Taeniarhynchosis

TAENIIDOSES, diseases caused by the mature stages of parasitic worms belonging to the family Taeniidae (see Cestodes) and parasitizing the small intestine of certain mammals. In humans, 2 types of T. occur: taeniasis and taeniarhynchosis. 1. The causative agent of taeniasis is the pork tapeworm, or armed tapeworm (Taenia solium, 1758), which reaches 2 m in length and is characterized by the following features. The head is equipped, in addition to four suckers, with a rostellum with 22-28 hooks of 2 different sizes (Fig. 1), with the large ones (0.16-0.18 mm) alternating with the small ones (0.11-0.14 mm), forming a crown of hooks. Hermaphroditic proglottids (Fig. 2) are characterized by an additional (3rd) lobe located between the longitudinal axis of the proglottid (along which the trunk of the developing uterus is laid down) and the vagina. Mature proglottids of the pork tapeworm are characterized by the number of branches of the main uterine trunk (7-10) and their coarse configuration. The oncosphere (see Cestodes) is most often spherical; its dimensions are 0.031-0.030 mm. The shell of the oncosphere is thick, radially striated, and has 3 pairs of hooks. Man is the only definitive host of the pork tapeworm, and therefore the only source of environmental contamination with its proglottids and oncospheres, which are scattered by man together with excrement. Intermediate hosts are the pig (obligate host) and, more rarely, man, dog, cat, camel, wild

Figure 1. Head of Taenia solium from above; four suckers and hooks are visible.

Figure 2. Hermaphroditic proglottid of Taenia solium; 1-ovary (3 lobes); 2-vitelline gland; 3-testes; 4-developing uterus.

boar (facultative hosts). The oncosphere swallowed by the intermediate host is freed from its radially striated shell, penetrates the intestinal wall with the help of its hooks, enters the bloodstream, and via the circulatory system can be carried to various organs and tissues of the intermediate host. 2 1/2-4 months after infection, larvae, so-called bladder worms, or cysticerci (Cysticercus cellulosae), form in the pig's body, localizing predominantly in the intermuscular connective tissue, and also often in the central nervous system. 2. The causative agent of taeniarhynchosis is the beef tapeworm, or unarmed tapeworm (Taeniarhynchus saginatus, Goeze, 1782, syn. Taenia saginata, T. mediacanellata). This parasite reaches 10 m in length and occasionally even more. The head of the parasite, besides suckers, is usually equipped with a rudimentary rostellum, but chitinous armament is absent (Figs. 3 and 4). The ovary has only 2 lobes. In mature proglottids (Figs. 5 and 6), the uterus has 18-30 lateral branches from the central trunk, which, in contrast to the uterine branches of the pork tapeworm, are very delicate and closely spaced. The oncosphere is 0.03-0.04x0.02-0.03, often spherical, and practically indistinguishable from the oncosphere of the pork tapeworm (Fig. 7). The definitive host is man. The intermediate host is cattle, in the intermuscular connective tissue of which a bladder worm, or cysticercus (Cysticercus bovis), forms 3-6 months after the ingestion of the oncosphere. Both of the above-described parasites are cosmopolitans; both taeniasis and taeniarhynchosis can be encountered everywhere where pork or beef is consumed. In various regions of the USSR, accurately diagnosed cases of taeniasis usually do not exceed tenths of a percent. In the central regions of the USSR, in the Donbas, in the Far East, and in some other regions, the prevalence of taeniarhynchosis, although somewhat higher than that of taeniasis, is also insignificant. Man becomes infected with taeniasis from raw or under-

Figure 3. Head of Taeniarhynchus saginatus from above; 4 suckers; no hooks.

Figure 4. Hermaphroditic proglottid of Taeniarhynchus saginatus: 1-ovary (2 lobes); 2-vitelline gland; 3-testes; 4-uterus in the very initial period of development.

cooked or fried measly pork (taeniasis) or beef (taeniarhynchosis). The pork and beef tapeworms attach in the uppermost segment of the small intestine, often in the duodenum, occurring in single specimens and, more rarely, in multitudes (up to several dozen in individual cases). - The pathological effect of the parasites consists mainly of two factors: 1) mechanical influence as a result of the fixation of the parasites to the intestinal mucosa by suckers,

Figure 5. Mature proglottid of Taenia solium with a developed uterus.

and, in the case of the pork tapeworm, by hooks, which leads to local circulatory disturbance and disruption of the integrity of the mucosa. The movement of the parasites, and in rarer cases, the blockage of the intestinal lumen by them, can also have a pathological effect. 2) On the other hand, as a result of the parasite's vital activity, substances are released that act toxically on the host's organism and cause chronic poisoning. Clinical manifestations in T. do not fit into the picture of a characteristic symptom complex on the basis of which an accurate diagnosis of the disease could be made. Most often, painful phenomena consist of a number of gastrointestinal tract disorders, often combined with various changes in the nervous system, and more rarely, in the hematopoietic organs. The range of these phenomena in different patients can be very wide-from complete health to severe illness, even with a fatal outcome in individual cases. Usually, one encounters symptoms of mild and moderate severity, such as: appetite disorders, nausea, vomiting, stool disorders, headaches, dizziness, sometimes to the point of fainting. Apathy, loss of ability to work, irritability, and sometimes pronounced symptoms of anemia are often observed. However, the characteristic picture of pernicious anemia is encountered much less frequently than in diphyllobothriasis. Taeniasis more often than taeniarhynchosis proceeds with weakly expressed painful phenomena, however, it is much more dangerous than taeniarhynchosis, as it can lead to cysticercosis (see Cysticercosis). One of the signs of the disease, characterizing primarily taeniarhynchosis, is the ability of mature proglottids, which have detached from the strobila of the parasite, to exit from the anus and crawl for some time along the thighs and other parts of the host's body.

The diagnosis of T. can be made on the basis of the structure of the proglottids or oncospheres excreted by the patient. Neither the clinical picture nor immunobiological reactions are specific. The absence of oncospheres in excrement does not give the right to deny the presence of parasites. It is possible to differentiate taeniasis from taeniarhynchosis only by mature or hermaphroditic proglottids and the scolex. Attempts to distinguish the beef tapeworm from the pork tapeworm on the basis of the structure of the oncosphere always lead to numerous errors due to the absence of sharp distinguishing features in the structure of the oncospheres. The prognosis for T. is in most cases favorable. The best therapeutic agent is male fern extract, which gives a good result in adults, while in children even a repeated course of treatment often remains ineffective. Figure 6. Mature proglottid of Taeniarhynchus saginatus with a developed uterus.

in children, however, even a repeated course of treatment often remains ineffective. For the treatment methodology, see Tapeworms. The prevention of T. must be carried out in two directions. 1. Protection of humans from the possibility of infection from measly meat. To this end, veterinary-sanitary control of beef and pork has been organized at slaughterhouses and meat inspection stations, with the subsequent destruction of the entire carcass in case of generalized cysticercosis or the release of conditionally fit meat (using boiling, salting, freezing). However, in addition to the indicated measures of public prevention, due to the imperfection of diagnostic methods for cysticercosis in its mild degrees and the insufficiency of veterinary-sanitary supervision, personal prevention is also necessary. The latter boils down to consuming beef and pork exclusively in a well-boiled and well-fried form. 2. Protection of cattle and pigs from infection with cysticercosis. To this end, broad sanitary education of the population is necessary, and in particular, an explanation of the perniciousness of the custom of scattering excrement everywhere, especially in barns, courtyards, on streets, and other places to which animals have access. It is necessary to achieve the construction of rational, enclosed latrines to which domestic animals, which could eat or scatter excrement and thus contaminate the surrounding soil with it and the elements contained in it, would not have access.