Clonorchosis

CLONORCHOSIS, clonorchosis, a helminthic disease of the liver in humans and carnivorous mammals, caused by the parasitization in the bile ducts of the trematode Clonorchis sinensis (Figs. 1 and 2) (Cobbold; 1875) [syn.: Cl. endemicus (Baelz; 1883), Distoma sinensis (Cobbold; 1875), Distoma spathulatum (Leuckart; 1876), Opisthorchis sinensis (Morgan; 1927)]. The parasite is flat, delicate, translucent, and lanceolate in shape. Body length is 12–20 mm with a width of 3–4 mm. There are two suckers; the oral one is larger than the ventral one. The branched testes are located one

Figure 1. Clonorchis sinensis.

behind the other in the very posterior part of the body; in front of the testes lies the ovary and the seminal receptacle. The middle third of the body length is occupied by the coils of the uterus, along the sides of which are scattered vitelline glands, having the character of delicate, grape-like follicles. The genital openings open directly anterior to the ventral sucker. The eggs, equipped with an operculum at one pole and a delicate protrusion of the shell at the opposite one, reach a length of 0.028–0.030 mm with a width of 0.016–0.017 mm. — Biology: Clonorchis is characterized by a double change of intermediate hosts. The eggs are excreted with feces into the external environment, mature, after which a miracidium hatches in a moist environment, selecting as its first intermediate host mollusks of the species Melania libertina, Melania hongkongensis, and Bythinia striatula. In the body of the mollusks, the parasite undergoes parthenogenetic reproduction. The second intermediate hosts are cyprinid fish Pseudorasbora parva and Carassius auratus (goldfish), in the bodies of which metacercariae are formed. When eaten in an insufficiently cooked form, these fish infect humans, dogs, cats, and pigs, which are the definitive hosts for Clonorchis. This parasite is widely distributed in China, Japan, and Korea. Within the borders of the USSR, Clonorchis was discovered for the first time in 1928 in the Far Eastern Territory, predominantly among the national minorities of the north (Golds, Gilyaks, etc.), as well as in domestic carnivores: cats and dogs. In the same year, Witte discovered Clonorchis in the gallbladder of a Chinese person autopsied in Khabarovsk. The small ethnic groups of the north were found to be infected with clonorchosis in the amount of 6.2% (Skryabin, Podyapolskaya, and Shults; 1929). With intensive infection, the patient exhibits an enlarged liver and jaundice; the walls of the bile ducts thicken, their lumen expands sharply, and the glandular tissue undergoes atrophy. In more severe cases, diarrhea with blood, progressive emaciation, and frequent nosebleeds are observed; cachexia develops, which can lead to a fatal outcome. The disease can take on a protracted character with alternating periods of improvement (in winter) and deterioration (in summer). In a whole series of cases, in the presence of clonorchosis of the liver, primary cancerous tumors were observed. Oldt (1927) points out that with clonorchosis, liver cancer occurs in 1.14% (out of 287 cases), while in individuals free from clonorchosis infestation, liver cancer was detected in 0.35% (out of 1,461 cases). For diagnosis, it is necessary to examine the feces or duodenal juice for Clonorchis eggs. — Therapy is poorly developed. Injections of emetine intravenously or subcutaneously are recommended, with the course of treatment being conducted over approximately 3 weeks. — Prophylaxis: individual prophylaxis comes down to abstaining from eating undercooked fish; public prophylaxis should consist of protecting water bodies from contamination with human and carnivore feces and broad sanitary education of the population with an explanation of the parasite's development cycle, from which two rules follow: consume fish after thorough boiling or frying and do not feed raw fish to cats and dogs. Figure 2. Egg of Cl. sinensis.