Plerocercoid Infection Research Articles

Subtle transcriptomic response of Eurasian perch (Perca fluviatilis) associated with Triaenophorus nodulosus plerocercoid infection

Determining the physiological effects of parasites and characterizing genes involved in host responses to infections are essential to improving our understanding of host-parasite interactions and their ecological and evolutionary consequences. This task, however, is complicated by high diversity and complex life histories of many parasite species. The use of transcriptomics in the context of wild-caught specimens can help ameliorate this by providing both qualitative and quantitative information on gene expression patterns in response to parasites in specific host organs and tissues. Here, we evaluated the physiological impact of the widespread parasite, the pike tapeworm (Triaenophorus nodulosus), on its second intermediate host, the Eurasian perch (Perca fluviatilis). We used an RNAseq approach to analyse gene expression in the liver, the target organ of T. nodulosus plerocercoids, and spleen which is one of the main immune organs in teleost fishes. We compared perch collected from multiple lakes consisting of individuals with (n = 8) and without (n = 6) T. nodulosus plerocercoids in the liver. Results revealed a small number of differentially expressed genes (DEGs, adjusted p-value ≤0.05) in both spleen (n = 22) and liver (n = 10). DEGs in spleen consisted of mostly upregulated immune related genes (e.g., JUN, SIK1, THSB1), while those in the liver were often linked to metabolic functions (e.g., FABP1, CADM4, CDAB). However, Gene Ontology (GO) analysis showed lack of functional enrichment among DEGs. This study demonstrates that Eurasian perch displays a subtle response at a gene expression level to T. nodulosus plerocercoid infection. Given that plerocercoids are low-metabolic activity transmission stages, our results suggest that moderate T. nodulosus plerocercoid infection most likely does not provoke an extensive host immune response and have relatively low physiological costs for the host. Our findings illustrate that not all conspicuous infections have severe effects on host gene regulation.

Development of helminthiasis pest holes of anthropogenic origin during transformation of water bodies, example of Krasnoyarskoye storage reservoir

Man-made impoundment-induced transformation of river biota leads to profound and irreversible changes in the hydrological regime, the structure of communities of all groups of aquatic organisms, from phytoplankton to fish and their parasites. The transformation of river communities following impoundment is accompanied by intensive eutrophication. Due to this fact, the role of zooplankton in the fish diet grows, and stable foci of helminthiases form. One typical example is the fish and human diphyllobothriasis caused by cestodes Dibothriocephalus latus (Linnaeus, 1758) Luhe, 1899 (syn. Diphyllobothrium latum ). The conditions in which the diphyllobothriasis pesthole has originated and developed are considered using the regulation of the Yenisei River and creation of Krasnoyarskoye storage reservoir as the example. D. latus plerocercoids were found in three species from the reservoir: perch, ruffe and pike, acting as second intermediate hosts, the primary role belonging to the perch, and to a smaller degree to the ruffe. Perch of both younger (2 +, 3+, 4+ years) and older age groups (5+ and older) are infected with plerocercoids due to the prevalence of plankton in their diet. A zonal pattern was observed in the plerocercoid infection in perch. The highest prevalence and mean abundance of helminthes were recorded from the fish living in the upper reaches, where habitats with shallow bays prevail; the infection rate in perch from in the middle and lower parts of the reservoir was somewhat lower.

Sparganosis, Henan Province, Central China

To the Editor: Sparganosis is a parasitic zoonosis caused by invasion of the spargana, the plerocercoid larvae of various diphyllobothroid tapeworms belonging to the genus Spirometra (1). Although human sparganosis is cosmopolitan, it is most frequently found in eastern and southeastern Asia (2). During 1927–2009 in the People’s Republic of China, >1,000 cases in humans in 27 provinces were reported; most cases were in southern China, where human infections were mainly acquired by eating raw or insufficiently cooked meat of frogs and snakes or by placing frog or snake flesh on open wounds for treatment of skin ulcers or on eyes to treat inflammation (3,4). Sparganosis is rarely seen in central and northern China. Before 2006, only 3 imported cases from southern China had been reported in Henan Province in central China (5). However, since 2006 in Henan Province, 20 autochthonous cases caused by ingestion of live tadpoles have emerged. To assess the risk for human infection with sparganosis in this province and to strengthen public safety awareness, we investigated spargana infection in the animal hosts of Spirometra tapeworms. During July 2007–July 2010, wild frogs and frog tadpoles were collected from the cities of Shangqiu, Zhoukou, and Luohe in Henan Province. Necropsies identified plerocercoids in 11.93% (163/1,366) of tadpoles and in 26.58% (172/647) of frogs. By frog species, plerocercoids were found in 31.09% (111/357) of Rana limmocharis and 26.29% (61/232) of R. nigromaculata frogs, each significantly (p<0.05) more numerous in these species than in R. temporaria frogs (0/58). In addition, 177 wild frogs sold at markets in Luohe were also examined; plerocercoids were detected in 30.39% (31/102) of R. limmocharis and 28% (21/75) of R. nigromaculata frogs. Thus, in Henan Province, R. limmocharis and R. nigromaculata frogs are the main intermediate hosts of Spirometra tapeworms. No pathologic changes associated with the tapeworms were found in dissected tadpoles and frogs. We found 250 plerocercoids in tadpoles and 1,387 in frogs. Tadpoles contained 1–14 (mean 1.53) and frogs 1–87 (mean 6.85) tapeworms. In frogs, most plerocercoids were located in the muscles of hind legs and back; some were in the muscles of the abdominal wall and forelegs. Plerocercoids dissected from tadpole and frog tissues were wrinkled, whitish, and ribbon-shaped and continuously moved while in normal saline. Plerocercoids from tadpoles were 1–8 mm long and 0.2–0.5 mm wide; those from frogs were 1–13 cm long and 1–2.5 mm wide. Cyclops were collected from ponds and ditches by using a 425-µm mesh (no. 40) sieve and species were identified by microscopic appearance as Mesocyclops leuckarti (6,7). Procercoids were microscopically found in the hemocele of 3.53% (3/85) of cyclops; 3–5 worms per cyclop were found. Fecal examination of dogs and cats found Spirometra mansoni tapeworm eggs in 19.35% (6/31) of dogs and 33.33% (1/3) cats. In addition, a 3-month-old specific pathogen–free cat was orally inoculated with 33 plerocercoids from tadpoles, fecal samples were microscopically examined by sedimentation during 10–25 days postinfection (dpi), and the cat was euthanized and examined for adult worms. S. mansoni tapeworm eggs were found in the feces during 12–25 dpi, and 17 adult worms, 26–45 cm long, were recovered from the small intestines at 25 dpi; however, no plerocercoids were seen in the tissues. The adult worms were morphologically identified as S. mansoni according to the following features: scolex with 2 longitudinal grooves, mature and gravid proglottids with conspicuous uterus at the center of segments, spiral-shaped uterus (unlike the rosette-shaped uterus of Diphyllobothrium latum), and cirrus and vaginal pore with separate openings (8,9). Although in recent years in Henan Province wild frogs have been sold clandestinely at markets, persons in this province do not routinely eat raw frog meat or use raw meat as poultices. However, some villagers in Henan do believe that eating live tadpoles has a medicinal role for skin diseases and, thus, they contract sparganosis. Accordingly, the route of plerocercoid infection for humans in Henan Province differs from that in southern China. Because this disease is rare in central and northern China, sparganosis is often neglected and misdiagnosed. Our survey showed that in Henan Province, 11.93% of tadpoles are infected with plerocercoids and 3.53% of cyclops are infected with procercoids. Therefore, eating live tadpoles poses a high risk for plerocercoid infection and must be discouraged. In addition, drinking raw water containing cyclops also poses a slight risk for sparganosis.

Detection and identification of Diphyllobothrium nihonkaiense plerocercoids from wild Pacific salmon (Oncorhynchus spp.) in Japan

We investigated the risk of diphyllobothriasis from ingestion of wild Pacific salmon in Japan by surveying Diphyllobothrium plerocercoids in 182 salmon samples obtained from Japan. The plerocercoids were not detected in chum salmon (Oncorhynchus keta) (0/26), called Akizake in Japan, caught between September and November. However, the detection rate of plerocercoids in chum salmon, called Tokishirazu in Japan, caught between early April and June, was 51.1% (24/47) with an average of two plerocercoid larvae per fish. The detection rates of cherry salmon (Oncorhynchus masou) and pink salmon (Oncorhynchus gorbuscha) were 12.2% (10/82) and 18.5% (5/27), respectively, and the average number of plerocercoids per fish was 0.45 (37 larvae/82 fishes) and 0.22 larvae (6 larvae/27 fishes), respectively. Plerocercoids isolated from O. keta and O. masou were identified as Diphyllobothrium nihonkaiense on the basis of molecular analysis of the cox1 and nad3 genes. Moreover, four tapeworms (three from O. keta and one from O. masou) were obtained by infecting golden hamsters with plerocercoids. The morphological features of these tapeworms were similar to those of D. nihonkaiense isolated from humans. Therefore, we think that O. keta and not O. masou is the most important source of plerocercoid infections in Japan.

Evidence for negative impact of plerocercoid infection of Triaenophorus nodulosus on Perca fluviatilis L. stock in Upper Lake Constance, a water body undergoing rapid reoligotrophication

The macro‐pathological impact of plerocercoid infection of perch Perca fluviatilis livers was quantitatively determined by an index of liver lesion (ILL) in fish from Upper Lake Constance (ULC). These results were compared to the ILL values of perch from two other lakes. From February to November 1999, 2071 perch were examined from the three sites. Prevalence of infection in ULC was 13% in actively growing first year (0+ year) perch and 94% in older fish, whereas in the two lakes used for comparison the figures for 0+ year perch were 12 and 20%, and in older fish 62 and 60%, respectively. Infected livers from perch caught in ULC revealed significantly higher ILL values than those of fish from the other two lakes. Perch livers from ULC containing more than three Triaenophorus nodulosus larvae also showed significantly more serious pathological alterations than uninfected livers or those with normal infection levels of one to three T. nodulosus. In all three lakes, excluding heavily infected perch from ULC, 0+ year perch livers revealed little or no damage, whereas in livers of older perch pathological alterations were apparent. In addition, analysis of age and total length data showed that perch infected with one to three parasites in ULC grew significantly slower than uninfected ones, and severely infected perch (greater than three parasites) grew significantly slower than those with a normal parasite load. With respect to mass, growth of ULC fish suffering normal infection (49% of all adults) was reduced by 9% and in those with severe infections (45% of all adults) growth was 16% below expected at normal harvesting age.

Post-stocking perturbations in a population of subarctic whitefish, Coregonus lavaretus (L.): Effects on growth, condition and cestode infection

Lake Kilpisjarvi was stocked with a total number of 440 000 migratory and benthic whitefish fry during the period of 1959–1964. Thereafter, the Diphyllobothrium ditremum plerocercoid infection became a problem decreasing the feasibility and commercial exploitation of the whitefish stock. Since dense fish populations may cause stunting, all stockings in the study area were stopped in an attempt to enhance the fisheries. The aim of the present study was to explore the effect of the cessation of the stocking on the growth, condition, catches and D. ditremum infection of the whitefish population. A total of 1594 whitefish were sampled with benthic gill nets. Growth was estimated from length-at-age and mass–length relationship was estimated with a non-linear regression in 1982–1983, 1992–1993 and 1997. Parasite infection was studied in 1992–1993 and 1997. Growth and condition were poor in the beginning of the 1980s. In 1992–1993, the growth and condition of the fish improved as the numerical catch per unit effort decreased from 1982 to 1992. The mean catches of other fish species were low. There were no significant changes in whitefish growth or condition from 1992–1993 to 1997. From the 1970s to 1982–1983, during slow growth and poor condition of the fish, the median gillraker count was decreasing to 19 (min–max 14–26). In 1992–1993, the gillraker count had increased significantly to 23 (min–max 19–26). However, the improved growth and condition did not cause decrease in the D. ditremum burden. On the contrary, based on our own results and literature notes, the parasite abundance seems to increase during the observation period of 1964–1997.

Hepatotrophic activity in mouse serum infected with plerocercoids ofSpirometra erinacei

To investigate the mechanism by which liver weight increases during plerocercoid infections as well as the possible existence of a hepatocyte-growth-factor (HGF)-like substance in the serum of mice infected with Spirometra erinacei plerocercoids, liver DNA synthesis was measured in vivo and in vitro. Infection with S. erinacei plerocercoids significantly stimulated DNA synthesis in mouse parenchymal hepatocytes prior to the increase in liver weight, at least partly by stimulating the induction of the salvage pathways of pyrimidine biosynthesis. Furthermore, infected mouse serum directly stimulated DNA synthesis in cultured mouse parenchymal hepatocytes. These results suggest that an HGF-like substance is present in the serum of mice infected with S. erinacei plerocercoids.

The immune response of wild rainbow trout, Salmo gairdneri Richardson, to naturally acquired plerocercoid infections of Diphyllobothrium dendriticum (Nitzsch, 1824) and D. ditremum (Creplin, 1825)

Natural infections of rainbow trout with two species ofDiphyllobothrium result in a host inflammatory response encapsulating the plerocercoid. The encapsulating cyst, observed by light and electron microscopy, comprises leucocytes, fibroblasts and collagenous connective tissue and is infiltrated with a blood vascular network. An indirect immunofluorescence technique and enzyme‐linked immunosorbant assay (ELISA) have shown that specific antibodies are elicited by the fish host to these Diphyllobothrium spp. These antibodies have been semi‐quantitatively measured by ELISA and correlated with worm burdens in individual fish.

Effect of infection with Spirometra erinacei plerocercoid on thyroid hormone in mice.

Young, male ICR mice were given tap water or distilled water containing 200 mg/l propylthiouracil (PTU) and were then infected with 10 plerocercoids of Spirometra erinacei to investigate the effect of plerocercoid infection on thyroid hormone in their hosts. Plerocercoid infection stimulated growth in PTU-induced hypothyroid mice as if they had never received PTU treatment: there were increases in weight in the liver, skeletal muscle, and spleen, as well as enhancement of the head and body length, in spite of a greater decrease in serum T4 levels than was observed in PTU-treated controls. Furthermore, the intact mice infected with plerocercoids showed a decrease in serum T4 levels as well as in the concentration of T4-binding globulin. These observations suggest that the growth stimulation and the decrease in concentrations of serum T4 and T4-binding globulin associated with plerocercoid infection in mice probably resulted from secretion of a growth hormone-like substance produced by plerocercoids of S. erinacei.

Carbohydrate metabolism in intact golden hamsters infected with plerocercoids of Spirometra erinacei (Cestoda: Diphyllobothriidae).

This study was performed to investigate the mechanism involved in a decrease in the serum glucose of golden hamsters infected with plerocercoids of Spirometra erinacei. The concentration of glucagon, the activity of glucose-6-phosphatase in the liver, and the in vivo incorporation of 2-deoxy-D-[1,2-3H]glucose into various organs increased in plerocercoid-infected hamsters compared with controls. Furthermore, the serum from the plerocercoid-infected hamsters enhanced the in vitro incorporation of [U-14C]glucose into adipose tissues, compared with control serum. The serum levels of immunoreactive insulin and somatomedin associated with nonsuppressible insulin-like activity in experimental animals, however, were not significantly different from those in controls. Therefore, we conclude that the decrease in serum glucose associated with plerocercoid infection is not the result of a decrease in gluconeogenesis, but the result of an increased utilization of glucose in the peripheral tissues.

Lipid metabolism in golden hamsters infected with plerocercoids of Spirometra erinacei (Cestoda: Pseudophyllidea).

Golden hamsters infected with Spirometra erinacei plerocercoids develop a hypertriglyceridaemia characterized by an increase in very low-density lipoprotein. Acyl-CoA synthetase activity, the rate of fatty acid synthesis in the liver and triglyceride production studies showed that the activation and synthesis of fatty acid and production of triglyceride in plerocercoid-infected hamsters were not significantly different from the controls. Lipase activity in post-heparin plasma was found to be suppressed in plerocercoid-infected golden hamsters. The presence of plerocercoids also resulted in a significant reduction in serum thyroxine, but the hypertriglyceridaemia associated with plerocercoid infection was not reversed by injecting the infected hamsters with 2 micrograms/day doses of L-thyroxine. The levels of serum immunoreactive insulin in plerocercoid-infected hamsters were not significantly different from the controls. We conclude that the hypertriglyceridaemia, associated with plerocercoid infection in hamsters, results predominantly from a suppression of triglyceride degradation, and that the suppression of lipase activity is probably not the result of hypothyroidism or the lack of insulin, but the result of secretion of growth hormone-like substances.

Some Biochemical Effects of the Growth Hormone Analogue Produced by Plerocercoids of the Tapeworm Spirometra mansonoides on Carbohydrate Metabolism of Adipose Tissue from Normal, Diabetic, and Hypophysectomized Rats

Plerocercoids of Spirometra mansonoides produce a functional analogue of mammalian growth hormone (GH). Plerocercoid growth factor (PGF) mimics the growth-promoting actions of GH, but has not been shown to duplicate all of the actions reported for GH. The purpose of this study was to determine the effects of plerocercoid infection (chronic PGF treatment) on glucose metabolism of adipose tissue and to compare the effects to those elicited by insulin and GH in intact, diabetic, and hypophysectomized male rats. Groups of rats were constantly exposed to PGF (via plerocercoid infection) or injected twice daily with bovine GH, insulin, or saline for 10 days. Basal oxidation rates of [U-14C]glucose to 14CO2 in adipose tissue segments were measured in vitro immediately after tissue removal. Other aliquots of adipose tissue were preincubated in hormone-free medium for 3 hr prior to testing the ability of the tissue to respond to insulin or human GH (hGH) added in vitro. Adipose tissue from PGF-treated intact and hypophysectomized rats had significantly elevated basal glucose oxidation rates, and the tissue was sensitive to further stimulation by insulin or hGH. The results obtained with intact and hypophysectomized rats were essentially the same, indicating that the effects of PGF were not due to suppression of endogenous GH. The basal glucose oxidation rate in adipose tissue from diabetic rats was stimulated (P less than 0.01) by PGF, but the tissue was not sensitive to insulin added in vitro. Furthermore, PGF had no effect on body growth or blood glucose concentrations of diabetic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Lesion induction by the plerocercoid Lacistorhynchus tenuis (Cestoda) and wound healing in the striped bass Morone saxatilis (Walbaum)

San Francisco Bay‐Delta striped bass, Morone saxatilis (Walbaum), form open lesions in response to a plerocercoid infection of Lacistorhynchus tenuis (Van Beneden, 1858) (Cestoda: Trypanorhyncha). Laboratory infection experiments showed that striped bass can be infected with the plerocercoids by ingesting infected copepods. Histological sections indicated that a cellular host response was mounted early in the infection period, and that despite the leucocytic infiltration the parasites continued to develop. However, at 3 months post‐infection some of the plerocercoids began to degenerate, and lesions formed at this time and 14 months post‐infection. Open lesions in adult striped bass collected from the field took 2 months to heal and were detectable for at least 22 months. Regeneration of the muscle tissue did not occur although the wound completely healed externally.

Insulin-like effects of fatty acid synthesis in liver of hamsters infected with plerocercoids of the tapeworm, Spirometra mansonoides.

Elevated serum lipids are associated with infections of laboratory rodents with plerocercoids of Spirometra mansonoides. The effect of infection with these larval tapeworms on triglyceride degradation and hepatic de novo fatty acid synthesis was investigated in Syrian hamsters. Serum lipoprotein electrophoresis revealed a consistent elevation in very low density lipoproteins in the infected animals. Lipoprotein lipase activity was enhanced in the infected animals. After seven days of plerocercoid infection the activity of acetyl-CoA carboxylase (E.C. 6.4.1.2) was significantly elevated after 6, 12 and 18 hours of fasting. Fatty acid synthetase was significantly increased after 0, 6, 12, 18 and 24 hours of fasting. Therefore, a chronic insulin-like activity on lipid metabolism of hamsters is associated with plerocercoid infection.

Biological effects ofSpirometra erinacei plerocercoids in several species of rodents

Observations were made of the biological effects on infection with plerocercoids of Spirometra erinacei on normal female Snell mice, male chinese hamsters, golden hamsters, normal and hypox rats. Plerocercoid infection caused the strongest growth-promoting effect on normal Snell mice. In mice, this effect appears to be independent of strain. Chinese hamsters infected with these larvae showed similar growth. The infected normal rats and golden hamsters, however, showed a weight increase in the skeletal muscle only, while the hypox rats exhibited no effect at all. The elevation in the concentration of serum triglyceride was observed in all the animals investigated except for rats. Golden hamsters, in particular, exhibited a marked increase in the concentration of serum free fatty acids and total cholesterol. There was close correlation between the concentrations of serum triglyceride and free fatty acids, and the regression coefficient of the resulting linear regression equation for the experimentals was higher than that for the controls. This suggests that serum triglyceride results from an increased concentration of serum free fatty acids derived from stimulated lipolysis. The total cholesterol concentration in the serum decreased in chinese hamsters infected with larvae. The serum glucose concentration increased in normal Snell mice but decreased in chinese and golden hamsters. No difference in glycerol and free fatty acid concentration was observed in infected animals except for golden hamsters.

Spirometra mansonoides: effects of plerocercoid infection on glycogen deposition in rats.

The effects of infection with plerocercoids of Spirometra mansonoides on tissue glycogen deposition of rats was determined. Hypophysectomized rats infected for two days had higher liver glycogen concentrations than controls and this effect was greatest after one week. Elevated liver glycogen associated with plerocercoid infection was observed in fed animals both at the beginning and at the end of the light period as well as after an overnight fast. Glycogen phosphorylase (1,4 alpha D glucan: orthophosphate alpha glucosyltransferase EC 2.4.1.1.) was inhibited but glucose-6-phosphatase (EC 3.1.3.9) was unaffected in the livers of infected hypophysectomized rats. While this effect is similar to actions of both growth hormone and insulin, plerocercoid infection had no influence on glycogen of cardiac or skeletal muscle at any time. Plerocercoid infection had no effect on the glycogen concentration of any tissue of intact rats.

The Lipogenic Effect of the Growth Factor Produced by Plerocercoids of the Tapeworm, Spirometra mansonoides, Is Not the Result of Hypothyroidism

Plerocercoid larvae of the tapeworm, Spirometra mansonoides produce a growth hormone-like factor that stimulates body growth of a variety of normal and hormone-deficient animals. Plerocercoid infection (15 per hamster) stimulated an increase in body weight, and markedly suppressed pituitary weight and growth hormone (GH) concentrations of serum and pituitaries of Syrian hamsters. The suppression of serum GH persisted for at least 4 mo after the initiation of infection. The presence of plerocercoids also resulted in a significant reduction (30-50%) in serum thyroxine (T4). The pronounced lipogenic effect associated with plerocercoid infection was not reversed by injection of the infected hamsters with high (10 or 20 micrograms/day) or low (1 or 2 micrograms/day) doses of L-thyroxine. These results suggest that the plerocercoid growth factor may function in a manner similar to high levels of endogenous GH by activating the feedback system that inhibits pituitary secretion of both GH and TSH. Whereas hypothyroidism may be associated with hyperlipidemia the resultant hypothyroid state induced by plerocercoid infection does not explain the hypertriglyceridemia and hypercholesterolemia which were a consistent observation in plerocercoid-infected hamsters.

Immunological Aspects Associated with Suppression of Hormone Levels in Rats Infected with Plerocercoids of Spirometra mansonoides (Cestoda)

The effect of the plerocercoid larvae of Spirometra mansonoides on hormone levels and the immune system of intact and hypophysectomized (Hx) rats was studied. Intact rats exhibited a decrease in serum growth hormone (GH) and thyroxine (T4) concentrations and a suppression of the humoral immune response 2 wk postinfection. At 4 and 9 wk postinfection, hormone concentrations and the humoral immune response returned to normal levels in the rats. When rats were infected with plerocercoids and then received daily injections for 2 wk of either GH or T4, the immune response returned to normal in the T4-injected, but not the GH-injected animals. Plerocercoid infection had no effect on the humoral immune response of Hx rats. The results of the present study suggest that PGF may act via an endocrine pathway to suppress the host's immune response enabling the parasite's survival in this host.

Comparison of the Effects of the Growth Factor Produced by Spirometra mansonoides and Growth Hormone in Diabetic-Hypophysectomized Rats: Lipid Composition

Growth and development of the thymus is dependent on secretions from the anterior pituitary, presumably growth hormone. Diabetes mellitus is known to reduce immunological competence. These studies compare the effects of bovine growth hormone (bGH) and the growth factor produced by plerocercoid larvae of the tapeworm, Spirometra mansonoides, on metabolism of lymphoid tissue, thymus and spleen, in hypophysectomized rats made diabetic with a single intraperitoneal injection of alloxan. Whereas the control diabetic-hypophysectomized rats gradually lost weight throughout the experimental period, both bGH and plerocercoid infection caused significant weight gains during the experimental period. The diabetic-hypophysectomized rats treated with bGH had significantly heavier thymuses and spleens than controls. Plerocercoid infection also caused significant increases in thymus weights. Both bGH and plerocercoids stimulated the metabolic activity of thymocytes isolated from treated rats and tested for their ability to incorporate 3H-thymidine into DNA in vitro. Thus, these growth factors have similar effects on the lymphoid tissue of diabetic-hypophysectomized rats which are apparently independent of normal insulin levels. Whether this anabolic effect is direct or mediated by somatomedin remains to be determined.

A Lipogenic Effect in Intact Male Hamsters Infected with Plerocercoids of the Tapeworm, Spirometra mansonoides

Plerocercoids of the tapeworm, Spirometra mansonoides, produce a potent growth stimulating substance which is active in several species of mammals. While most of the actions of the plerocercoid growth factor (PGF) are similar to those of growth hormone (GH), lipid metabolism is one area where their actions are not alike. This report demonstrates that plerocercoid infection not only stimulates growth of intact male hamsters but is lipogenic as well. The lipogenic effects of plerocercoid infection were demonstrated by increases in epididymal fat pad weights, serum triglycerides, cholesterol, and total lipid. The livers of the plerocercoid-infected hamsters also had more cholesterol and more lipid phosphorus than controls. Incorporation studies using [2-14C]acetate showed that infected hamsters incorporated significantly higher levels of the radionuclide in their livers and serum after 1 hr than the controls. The lipogenic effect of plerocercoid infection is distinctly unlike the reported lipolytic action of GH and the lack of any stimulation of [2-14C]acetate incorporation into the epididymal fat pads is unlike the reported acute actions of insulin as well.