Efficacy of mebendazole and albendazole against Trichinella spiralis in mice

Changes in the sensitivity of Trichinella spiralis to anthelmintic treatment during the first 3 days of infection in mice were studied. Oral administration of either mebendazole or albendazole at 6.25 mh/kg 2 hr after exposure to infection eliminated 95-100% of the worms as determined at necropsy on day 7 postinoculation. Beyond the first day of infection the sensitivity of the parasite to benzimidazole therapy was much reduced and an oral dose of 50 mg/kg was only partially but significantly active against the adult worms. Despite decline in drug sensitivity during the enteral phase, gavage administration of either mebendazole or albendazole at 50 mg/kg for 5 consecutive days during the invasive phase of infection significantly reduced (96 and 67%, respectively) the number of larvae subsequently recovered from host musculature on day 45 postinoculation.     

Trichinella spiralis: major histocompatibility complex-associated elimination of encysted muscle larvae in swine

A heretofore undescribed host-mediated reactivity against encapsulated muscle larvae (ML) of the nematode Trichinella spiralis is reported. Inbred miniature swine (NIH minipigs) of three independent SLA phenotypes, which received a primary oral dose of 300 T. spiralis ML, successfully resisted a secondary infection of 10,000 ML; however, only pigs of the SLAa/a phenotype exhibited an unusual and highly significant reduction in the numbers of encysted ML from the primary infection (P less than 0.0003). This initial anti-encysted ML reactivity was confirmed in subsequent trials by comparing the prechallenge ML burdens with the reduced ML numbers in primary-infected aa pigs after challenge. Analyses of inbred strains of mice, selected for major histocompatibility type and for resistance or susceptibility to infection with T. spiralis, showed no such anti-encysted ML response. Because elimination of encysted T. spiralis ML had been accomplished previously only through selected drug regimens, our demonstration of a nonpharmacological, host-mediated reactivity against this stage of the parasite in swine highlights the importance of MHC genes in regulating disease resistance in a livestock species.     

Trichinella spiralis: phospholipase in challenged mice and rats

Mice challenged with 400 larvae of T. spiralis showed greatly elevated phospholipase levels in tissues of the small intestine from 5 to 29 days after infection, after which the levels returned to those of the uninfected controls. Related to these rises in enzyme levels were greatly increased numbers of eosinophils in the bone marrow. Increases strikingly above those in the controls were noted from 8 to 20 days after infection. In rats challenged with 3000 larvae, the enzyme levels were elevated from 4 to 18 days, and the eosinophils were increased during the same periods. A working hypothesis is proposed to explain these phenomena.     

In vitro stress response to elevated temperature, hydrogen peroxide and mebendazole in Trichinella spiralis muscle larvae

Three stimuli, elevated temperature, hydrogen peroxide and mebendazole, were compared for their ability to induce heat-shock responses in Trichinella spiralis muscle larvae (L1). In vitro effectiveness of each 'stressor' was evaluated by viability score, protein content and levels of hsp90, hsp70 and hsp60. Detection of the respective heat-shock proteins was done by Western blotting and the heat-shock proteins and quantitation of the immunoblots by image analysis. Exposure of L1 to elevated temperature (e.g. 45 degrees C, 2 h) had no measurable effect. However, exposure to hydrogen peroxide resulted in the induction of constitutive and higher mol. wt heat-shock proteins. In these experiments, heat-shock protein induction correlated strongly with other damage parameters, including loss of viability and increased mortality. Larvae stored in the presence of mebendazole showed no signs of damage. These data indicate that when L1 suffer damage through the action of stimuli, enhancement of heat-shock protein production and damage suffered are causally related.     

Studies on anthelmintic effects of flubendazole and mebendazole on the rat lungworm Angiostrongylus cantonensis in mice and rats

Flubendazole and mebendazole given orally at 10 mg/kg/day 5-7 days post-infection (total 30 mg/kg) were found to eliminate 93-100% of Angiostrongylus cantonensis larvae in mice and rats. No significant difference was observed between the effects of the 2 drugs. The effectiveness of the drugs decreased with the increase in days post-infection on which medication was administered. It was found possible to treat A. cantonensis adults in rats by administering flubendazole or mebendazole at 10 mg/kg/day for 10 consecutive days. The drugs exhibited better anthelmintic efficacy in a divided dosing regimen than in a single dosing regimen.     

Trichinella spiralis: vascular recirculation and organ retention of newborn larvae in rats

The recirculation of Trichinella spiralis newborn larvae was studied in inbred AO rats. Newborn larvae collected after in vitro incubation of adult T. spiralis worms for 2 or 24 hr were injected into rats through the tail vein or hepatic portal vein. Blood samples from the femoral vein, hepatic portal vein, and abdominal aorta were collected at intervals from 1 min to 24 hr after larval injection. Newborn larvae of both ages (24 hr or 2 hr old) persisted in femoral vein blood for less than or equal to 5 hr after injection, but they could be detected in portal vein blood by 24 hr after injection. The injection of larvae into a tail vein or the portal vein did not influence the pattern of larval circulation, although there was a 1-5 min delay in newborn larval appearance time after injection into the portal vein. Transcapillary migration through tissue and back to the circulation was evident in the appearance of newborn larvae in the thoracic duct lymph up to 24 (occasionally 48) hr after tail vein injection of newborn larvae. During the course of a natural primary infection, no evidence for trapping of larvae in the mesenteric lymph node could be found despite direct larval migration through this organ. Injected newborn larvae were retained in the lungs, and small numbers could be recovered 24 hr after intravenous injection. We conclude that a proportion of newborn larvae recirculates within the vasculature for several hours; a smaller population extravasates but can reenter the circulatory system via the lymphatics. Furthermore, some newborn larvae are found in organs rich in capillaries up to 24 hr after their entry into the blood.     

Trichinella spiralis: nonspecific resistance and immunity to newborn larvae in inbred mice

The implantation and development of intravenously injected Trichinella spiralis newborn larvae were examined in different strains of inbred mice by determining muscle larvae burden. This was compared to the numbers of muscle larvae that established after a natural infection during which a quantitative assessment of intestinal newborn larvae production was made. In most inbred strains of mice, newborn larvae do not all successfully implant in muscle. Mice of the DBA/1 strain are the most resistant to successful implantation, and C3H mice are the most permissive. This pattern is evident in the strains studied whether newborn larvae are injected intravenously or are produced by intestinal adults. Thus, after a natural infection, 100% of intestinally produced newborn larvae implanted in C3H mice, whereas in NFR 68% and DBA/1 mice 62% successfully matured in muscle. Immunity to newborn larvae could be demonstrated as early as 10 days after exposure to this stage of the life cycle. This immunity was protective against a complete challenge infection given 9 days after newborn larvae had been injected intravenously. Protection against newborn larvae was identical in male and female mice or in mice from 1 to 9 months of age. We conclude that there are two mechanisms by which mice impair newborn larvae establishment or development in muscle. The first appears to be nonimmunological (non-specific resistance), and the second is immunological. Genetically determined variation in strain-specific expression is apparent with both mechanisms. In strains displaying high intrinsic "resistance" (DBA/1), this process is likely to account for most of the 38% reduction in newborn larvae establishment in a primary infection. However, immunity against newborn larvae develops quickly enough to have a significant effect on migratory larvae in primary infections where adults persist in the intestine (e.g., the B10 congenic mice), or when high adult worm burdens delay adult worm rejection. Muscle larvae burden, therefore, reflects systemic nonspecific resistance to newborn larvae as well as immunological processes that occur in the intestine and systemically.     

Trichinella spiralis: migration of larvae in the rat

Counts were made of Trichinella spiralis “migratory” larvae recovered from blood, abdominal cavity, lungs, liver, kidneys, and thoracic duct lymph of male albino rats from 4–15 days postinoculation. From these data, the pathways the larvae utilized to travel from the small intestine to skeletal muscle were determined. Approximately 70% of the encysted muscle larvae were accounted for by the lymph-blood circulatory system pathway. The data indicate that the other 30% probably migrated by way of both (a) the hepatic portal circulatory system to the heart and then to the general circulation and skeletal muscle; and (b) the abdominal cavity and/or abdominal fluids to skeletal muscle.     

Comparison of cholinesterase activities in the excretion-secretion products of Trichinella pseudospiralis and Trichinella spiralis muscle larvae

The presence of cholinesterases (ChE) is reported in T. pseudospiralis excretion-secretion products (ESP) by spectrophotometric method, using acetylthiocholine (ATCI) and butyrilthiocholine (BTCI) as substrates. By inhibition assays, we found that T. pseudospiralis release both acetyl- and butiryl-cholinesterases (AchE and BchE, respectively). The sedimentation coefficientes of these enzymes were determined by sucrose density gradient. We studied the in vivo ChE secretion by immunoblot assays using AchE from Electrophorus (electric eel) and sera from normal or infected mice with T. pseudospiralis or T. spiralis. The presence of anti-AchE antibodies was only demonstrated in the sera from T. pseudospiralis infected mice. Moreover the in vivo secretion was corroborated by the high difference determinate between the ChE activity of the immuno complexes from T. pseudospiralis infected sera and the immunocomplexes from T. spiralis infected sera as well as normal sera. Finally, we analyzed the effect of the organophosphate Neguvón (metrifonate) on the ChE activity from the T. pseudospiralis ESP. The drug inhibits in part this activity. Moreover Neguvón (metrifonate) showed a high activity against the T. pseudospiralis viability.     

Muscle fiber selectivity of Trichinella spiralis and Trichinella pseudospiralis (1983)

The biceps, semimembranosus, biceps femoris, and soleus muscles of female Rockland Wistar mice infected with either 1,000 Trichinella spiralis or 1,000 Trichinella pseudospiralis larvae were removed on days 12, 14, 16, and 18 post-infection (PI), sectioned and stained histochemically for their myosin ATPase activity. Light microscopic examination of the sections revealed that larvae of T. spiralis invade only the slow twitch muscle fibers, and those of T. pseudospiralis invade both the fast twitch and the slow twitch fibers. In sections obtained from mice infected with either parasite and killed on days 16 and 18 PI, identification of the majority of the infected fibers as fast twitch or slow twitch was not possible due to pathological modification of infected fibers.