Succinate dehydrogenase and fumarate reductase activity in Aspiculuris tetraptera and Ascaris suum and the effect of the anthelmintics cambendazole,thiabendazole, and levamisole

Comley John C. W. and Wright Spdenis J. 1981. Succinate dehydrogenase and fumarate reductase activity in Aspiculuris tetraptera and Ascaris suum and the effect of the anthelmintics cambendazole, thiabendazole, and levamisole. International Journal for Parasitology11: 79–84. Succinate dehydrogenase and fumarate reductase activities from a particulate fraction of A. tetraptera and a soluble extract of A. suum have been determined using spectrophotometric methods. Fumarate reductase activity in A. suum could only be detected anaerobically. Succinate dehydrogenase activity from A. suum was partially characterized and shown to exist in several multimolecular forms (isoenzymes). The in vitro effect of the anthelmintics cambendazole, thiabendazole and levamisole on succinate dehydrogenase and fumarate reductase activity from the above nematodes are described. Significant inhibition of fumarate reductase activity of both nematodes was only achieved using 5 mM levamisole and 1 mM thiabendazole. After in vivo anthelmintic treatment of A. tetraptera only thiabendazole significantly inhibited fumarate reductase. It is suggested that the succinate dehydro-ogenase-fumarate reductase complex in these nematodes is unlikely to be the primary site chemotherapeutic attack for any of the anthelmintics tested.     

Zoonotic and non-zoonotic helminths in black rats of rain-fed and irrigated areas of Swat,Khyber Pakhtunkhwa,Pakistan

Present study was conducted to get information on helminth parasites of zoonotic importance among the black rats of district Swat, Pakistan. Two hundred and sixty nine rats were captured from agricultural ecosystem of the district using live captured traps from 2011 to 2013. Captured rats were anesthetized and surveyed for the presence of ectoparasites, then were carefully dissected for investigation of endoparsites. Helminth parasites of 8 species were identified. Presence of parasite was noticed in 23.7% of sampled rats. The infection rates of sampled rats was given in order of their infectivity as Syphacia obvelata 13(4.83%), Aspiculuris tetraptera 13(4.83%), Heterakis spumosa 12 (4.46%), Hymenolepis spp. 9(3.34%), H.diminuta 8(2.97%), Hymenolepis fusa 4(1.48%), Lutziella microacetabularae 4(1.48%) and Lutziella spp. 1 (0.37%). No significant difference (P < 0.4289) was found in prevalence of parasites among areas, crops, crop stages and sex of the host while adult rats were found more infected than sub-adults. S. obvelata and A. tetraptera were the most common species of helminths while Lutziella sp., 1 (0.37%) was found only in one host. Rattus rattus (the black rat) was regarded as the host of helminth parasites of zoonotic importance, therefore the hidden health hazards of this rodent species needed to be considered to prevent infectivity of humans. Current study was concluded that Rattus rattus harbored a wide variety of helminth parasites which shows a hidden risk to inhabitants of the region. Monitoring rats’ population in settle areas and educating the local community about the risk of rat borne parasitic diseases transmission through rats appears to be absolutely essential.     

Comparison of rapid expulsion of Trichinella spiralis in mice and rats

Alizadeh H. and Wakelin D. 1982. Comparison of rapid expulsion of Trichinella spiralis in mice and rats. International Journal for Parasitology12: 65–73. Primary infections of Tricliinella spiralis in both NIH mice and Wistar rats resulted in increased levels of mucosal mast cells and goblet cells. In mice the numbers of both cell types rose sharply before worm expulsion (days 8–10), remained at an increased level for a short time and declined quickly, reaching control levels on day 14 for goblet cells and between days 28 and 35 for mast cells. In contrast, in rats, the numbers of goblet cells and mast cells increased during worm expulsion and remained above control levels for a prolonged period. Challenge infections given shortly after expulsion of a primary infection (day 14) were expelled rapidly, worm loss being virtually complete with 24 h. In mice this response to challenge was short-lived and persisted only until day 16 after primary infection. After this time, challenge worms were expelled more slowly after infection. In rats the rapid expulsion response was expressed for at least 7 weeks after primary infection. Mice and rats showed differences in the conditions of infection necessary to prime for rapid expulsion, mice requiring larger and longer duration primary infections, but the expression of the response appeared to be similar in both species. In mice it was shown that rapid expulsion of T. spiralis was a response evoked specifically by prior infection with this species; infections with other intestinal nematodes had no effect. Similarly, the effect upon challenge infection was also specific to T. spiralis. The rapidity with which challenge infections are expelled suggests that either the specific inflammatory changes generated during primary infection result in an environment that is unsuitable for establishment of subsequent infections or that challenge infections provide a stimulus that can provoke an almost instantaneous response in the primed intestine. The relationship of the observed cellular changes to such mechanisms is discussed.     

Ultrastructure of the intestinal cells of Aspiculuris tetraptera after in vivo treatment of mice with mebendazole and thiabendazole

Ultrastructural changes in the intestinal cells of female Aspiculuris tetraptera following in vivo treatment with mebendazole or thiabendazole are described. Major changes included a marked reduction in the luminal microbial flora and the appearance of large numbers of autophagic vesicles in the cytoplasm of the intestinal cells. Some mebendazole-treated nematodes were more severely affected, with a complete loss of cellular integrity and a collapse of the intestinal lumen. The possible role of the intestinal cell microtubules in inducing these anthelmintic effects is discussed.     

Kinetics of primary and secondary infections with Strongyloides ratti in mice

Dawkins H. J. S. and Grove D. I. 1981 Kinetics of primary and secondary infections with Strongyloides ratti in mice. International journal for Parasitology11: 89–96. The kinetics of infection with S. ratti were quantitated in normal and previously exposed C57B1 /6 mice. In primary infections, larvae penetrated the skin rapidly and were seen in peak numbers 12 h after infection. By 24 h after infection, larval numbers had declined appreciably and there was a slow decrease in numbers thereafter. Larvae were first observed in the lungs at 24 h and maximal recovery occurred at 48 h. It is thought that larval migration through the lungs is rapid. Worms were first seen in the intestines two days after infection. Maximum numbers were seen on the fifth day and worm expulsion was complete by day 10. Two moults took place in the small intestine during days 3 and 4 after infection. Rhabditiform larvae were first noted on the fourth day after infection. Mice exposed to S. ratti four weeks previously had significantly less larvae in the skin 4 and 12 h after infection but by 24 h there was no difference when compared with mice with primary infections. Peak recovery of larvae from the lungs occurred 24 h after infection; significantly less larvae were recovered on days 2 and 3 when compared with normal mice. There was a marked reduction in the adult worm burden in the gut; the number of worms recovered was less than one fifth of that seen in primary infections. Those worms which did mature were less fecund and were expelled from the intestines within 7 days of infection. It is suggested that in previously exposed animals, the migration of larvae from the skin is hastened, many of these larvae are destroyed in the lungs and that expulsion of worms which do mature in the intestines is accelerated.     

Immune expulsion of the nematode Aspiculuris tetraptera from mice given primary and challenge infections.

The distribution of larval Aspiculuris tetraptera was studied in 4-week-old male and female CFLP mice. Whereas on days 10–12 the larvae were entirely confined to the anterior third of the colon, by day 14 larvae could be found throughout the colon. After day 17 the larvae were again restricted to the anterior colon. This change in distribution was co-incident with a loss of a large proportion of the worm burden, which occurred more consistently in female than in male mice.The degree of acquired immunity stimulated by various immunizing regimens was assessed by the survival of a challenge infection in experimental and control mice. It was found that a high level of immunity was achieved by exposure to a 19-day primary infection, a 36-day low-level infection and also by three 6-day infections, in each of which the larvae were removed by piperazine treatment immediately after the crypt phase.     

Effects of mebendazole and levamisole on tetrathyridia of Mesocestoides corti in the mouse

Bennet E.-M., Behm C.A. and Bryant C. 1978. Effects of mebendazole and levamisole on tetrathyridia of Mesocestoides corti in the mouse. International Journal for Parasitology8: 463–466. Mebendazole, but not levamisole, administered to mice carrying artificial infections of 50 tetrathyridia of Mesocestoides corti, was effective in killing the parasites. However, simultaneous administration of mebendazole and levamisole was still more effective. Treatment with levamisole before infection had no additional effect.Injection of mice with dead larvae offered some protection against a subsequent challenge with 50 live larvae; however, levamisole did not then improve the anthelmintic efficacy of mebendazole. In mice rendered immunoincompetent by radiation mebendazole was less effective than in non-irradiated controls and levamisole again did not enhance the effect of mebendazole. It is concluded that anthelmintic efficacy of mebendazole depends on its anthelmintic activity supplemented by the host's immune response; and that levamisole stimulates the latter.     

Trichinella spiralis: Delayed rejection in mice concurrently infected with Nematospiroides dubius

The immune response of mice to the nematode Trichinella spiral's was markedly altered when the infection was superimposed upon an existing infection with Nematospiroides dubius. The expulsion of a primary infection of T. spiralis was delayed in such mice, and the worms persisted for at least 4 weeks longer than they did in control mice. The degree to which expulsion was suppressed was related to the number of N. dubius present. It would appear that both adult and larval stages of N. dubius can exert a suppressive effect, since the expulsion of T. spiralis was affected within days of a super-imposed (i.e., larval) N. dubius infection. When adult N. dubius were removed from mice 4 days before infection with T. spiralis, the mice expelled the latter parasite within the normal time, indicating that recovery from the suppressive effects of concurrent infection occurred rapidly. Concurrent infection with N. dubius appeared to affect both the afferent and efferent arms of the immune response to T. spiralis, since sensitization by, and memory of, prior infection were impaired and the expression of acquired immunity was inferior to that of controls.     

Trichuris suis and Oesophagostomum dentatum Show Different Sensitivity and Accumulation of Fenbendazole,Albendazole and Levamisole In Vitro

Background

The single-dose benzimidazoles used against Trichuris trichiura infections in humans are not satisfactory. Likewise, the benzimidazole, fenbendazole, has varied efficacy against Trichuris suis whereas Oesophagostomum dentatum is highly sensitive to the drug. The reasons for low treatment efficacy of Trichuris spp. infections are not known.

Methodology

We studied the effect of fenbendazole, albendazole and levamisole on the motility of T. suis and O. dentatum and measured concentrations of the parent drug compounds and metabolites of the benzimidazoles within worms in vitro. The motility and concentrations of drug compounds within worms were compared between species and the maximum specific binding capacity (B_max) of T. suis and O. dentatum towards the benzimidazoles was estimated. Comparisons of drug uptake in living and killed worms were made for both species.

Principal findings

The motility of T. suis was generally less decreased than the motility of O. dentatum when incubated in benzimidazoles, but was more decreased when incubated in levamisole. The B_max were significantly lower for T. suis (106.6, and 612.7 pmol/mg dry worm tissue) than O. dentatum (395.2, 958.1 pmol/mg dry worm tissue) when incubated for 72 hours in fenbendazole and albendazole respectively. The total drug concentrations (pmol/mg dry worm tissue) were significantly lower within T. suis than O. dentatum whether killed or alive when incubated in all tested drugs (except in living worms exposed to fenbendazole). Relatively high proportions of the anthelmintic inactive metabolite fenbendazole sulphone was measured within T. suis (6–17.2%) as compared to O. dentatum (0.8–0.9%).

Conclusion/Significance

The general lower sensitivity of T. suis towards BZs in vitro seems to be related to a lower drug uptake. Furthermore, the relatively high occurrence of fenbendazole sulphone suggests a higher detoxifying capacity of T. suis as compared to O. dentatum.     

The effect of levamisole and levamisole + vitamin C on oxidative damage in rats naturally infected with Syphacia muris

This study was performed to determine the effects of levamisole and levamisole + vitamin C against Syphacia muris naturally infection in rats and to detect its effect on the oxidative parameters in blood and tissues of host. For this purpose, natural infection was diagnosed using the cellophane tape method on the perianal region of rats. Infected rats (total 18) were divided into three groups. On the other hand six without helminth rats were used in this study as negative control group. Group 2 was given an orally levamisole HCl treatment with gastric gavage at a dose level of 20 mg/kg body weight in distilled water, every alternate day. Group 3 was given levamisole HCl via gastric gavage at a dose level of 20 mg/kg and vitamin C was given 1 g/L added to the drinking water. All the treatments continued for a period of 7 days. As a result; levamisole administered to rats at dose of 20 mg/kg orally 98.34% was found to be effective against adult S. muris in the rats. In addition to levamisole + vitamin C is effective to alleviate the oxidative damage in rats infected with S. muris.     

Trichinella spiralis: Characterization and strain distribution of rapid expulsion in inbred mice

Appropriately immunized mice display a response that is biologically equivalent to rat rapid expulsion. Only two inbred strains ($\text{NFR}\text{N}\text{and}\text{NFS}\text{N}$ derived from NIH Swiss mice) have been shown to respond in this manner. Mice of the $\text{Balb}\text{c}$, CBA, $\text{A}\text{He}$, C₃H, SJL, or C₅₇Bl strains are “nonresponders” which require approximately twice as much intestinal exposure (in days) to Trichinella spiralis to elicit a response half as effective. Genetically, the responder is dominant, autosomal, and does not appear to be linked to the MHC. The characteristics of mouse and rat rapid expulsion of T. spiralis are not identical but share these features: initial rejection within 24 hr of challenge; a rejection efficiency >90%, from 1 to 5 weeks after the primary; induction of response does not require exposure to the complete infection; rapid expulsion is immunologically specific for preadults; adult worms are resistant. While a genetic basis for responsiveness exists in mice there is, as yet, no evidence for genetic control in rats. In both mice and rats, rapid expulsion is distinguished from the intestinal hyperreactivity associated with rejection of the primary infection by the kinetics and amplitude of the rejection of transplanted adult worms.     

Vaccination against the nematode Trichostrongylus colubriformis. III. Some observations on factors influencing immunity to infection in vaccinated guinea-pigs

Rothwell T. L. W. 1978. Vaccination against the nematode Trichostrongylus colubriformis. III. Some observations on factors influencing immunity to infection in vaccinated guineapigs. International Journal for Parasitology8: 33–37. Guinea-pigs were protected against infection with T. colubriformis when soluble material extracted from fourth-stage larvae was administered by the subcutaneous, intradermal, intraperitoneal and intraduodenal but not oral routes. The level of immunity following vaccination by the various effective routes was similar. Mature animals were found to respond significantly better to vaccination than immature animals. Significant immunity was present 10 days after vaccination but higher levels were found after 20 and 40 days. A single dose of vaccine was as effective as three divided doses. Finally, it was found that the adjuvant aluminium hydroxide gel, but not B. pertussis vaccine or levamisole improved the level of immunity to infection which followed vaccination.     

Further studies on the uptake of tritiated nucleic acid precursors by Babesia spp. of cattle and mice

Irvin A. D. and Young E. R. 1979. Further studies on the uptake of tritiated nucleic acid precursors by Babesia spp. of cattle and mice. International Journal for Parasitology9: 109–114. An in vitro culture technique developed earlier was used to study the metabolism of nucleic acid precursors by Babesia microti and B. rodhaini of mice and by B. divergens and B. major of cattle. [³H]Hypoxanthine was readily incorporated by all species of parasite, and the presence of leucocytes did not affect this uptake. When parasites were maintained in culture their ability to incorporate [³H]hypoxanthine fell rapidly after 24 h, but when B. major was maintained at 4°C its subsequent ability to incorporate [³H]hypoxanthine persisted for at least 3 days. This finding could be of practical value in assessing infectivity of stored blood in vitro.On autoradiography, [³H]hypoxanthine appeared to be incorporated into both DNA and RNA of parasites. Salvage pathways for purine metabolism appeared to be important in all species of Babesia whereas for pyrimidine metabolism salvage pathways were more important for murine babesias and the de novo pathway more important for bovine species. This difference may relate to different permeabilities of bovine and murine erythrocyte membranes or may be a more fundamental species difference.     

Effect of supplementing sheep diets with macroalgae species on in vivo nutrient digestibility,rumen fermentation and blood amino acid profile

In this study, a brown macroalgae species, Saccharina latissima, processed to increase its protein concentration, and a red macroalgae species, Porphyra spp., were used to evaluate their in vivo digestibility, rumen fermentation and blood amino acid concentrations. Four castrated rams were used, whose diets were supplemented with a protein-rich fraction of S. latissima, a commercial Porphyra spp. and soybean meal (SBM). Our results show that the protein digestibility of a diet with S. latissima extract was lower (0.55) than those with Porphyra spp. (0.64) and SBM (0.66). In spite of the higher nitrogen (N) intake of diets containing Porphyra spp. and SBM (20.9 and 19.8 g N/day, respectively) than that with S. latissima (18.6 g N/day), the ratio of N excreted in faeces to total N intake was significantly higher in the diet with S. latissima than those with Porphyra spp. and SBM. This reflects that the utilization of protein in S. latissima was impaired, possibly due to reduced microbial activity. The latter statement is corroborated by lower volatile fatty acid composition (25.6, 54.8 and 100 mmol/l for S. latissima, Porphyra spp. and SBM, respectively) and a non-significant tendency for lower ammonia concentration observed in diets with S. latissima and Porphyra spp. compared to SBM. It is important to note that the S. latissima used in this trial was rinsed during processing to remove salt. This process potentially also removes other water-soluble compounds, such as free amino acids, and may have increased the relative fraction of protein resistant to rumen degradation and intestinal absorption. Furthermore, the phlorotannins present in macroalgae may have formed complexes with protein and fibre, further limiting their degradability in rumen and absorption in small intestines. We recommend that further studies explore the extent to which processing of macroalgae affects its nutritive properties and rumen degradability, in addition to studies to measure the intestinal absorption of these macroalgae species.     

The occurrence of the second moult of Ascaris lumbricoides and Ascaris suum

Maung M. 1978. The occurrence of the second moult of Ascaris lumbricoides and Ascaris suum. International Journal for Parasitology 8: 371–378. Eggs of Ascaris lumbricoides and A. suum were cultured at 28°C and observed daily. Larvae were released by pressure, by artificial hatching with CO₂, and by natural hatching after infection of laboratory mice. The early stages of development in the egg were observed to comprise two moults, one occurring immediately after the other. Both moults were initiated within the egg, but the time of completion of the second moult varied considerably, and in some instances was not completed until the larvae reached the liver of experimentally infected animals.     

Protection against Mesocestoides corti infection in mice treated with zymosan or Salmonella enteritidis 11RX

Toye P. G. and Jenkin C. R. 1982. Protection against Mesocestoides corti infection in mice treated with zymosan or Salmonella enteritidis 11RX. International Journal for Parasitology12: 399–402. Zymosan and Salmonella enteritidis 11RX were found to partially protect mice against infection with the cestode Mesocestoides corti. Thus, mice previously infected with S. enteritidis 11RX contained fewer parasites in the peritoneal cavity compared to normal mice. Mice pretreated with zymosan contained fewer parasites in the peritoneal cavity and in the liver compared to normal mice and this protection was enhanced by the passive transfer of serum from mice chronically infected with M. corti. Examination of mice in the initial stages of infection revealed that the administration of zymosan led to an alteration in parasite location from the peritoneal cavity to the liver.     

Histopathological appearances in primary and secondary infections with Strongyloides ratti in mice

Dawkins H. J. S., Muir G. M. & Grove D. I. 1981. Histopathological appearances in primary and secondary infections with Strongyloides ratti in mice. International Journal for Parasitology11: 97–103. The histological appearances of the skin, lungs and small intestines of mice with primary and secondary infections with S. ratti are described. When the skins of mice with a primary infection were examined, larvae were seen scattered throughout the dermis. An inflammatory reaction of neutrophils and eosinophils was first noted around larvae 12 h after infection. By 48 h, mononuclear cells were prominent. The intensity of the inflammatory reaction gradually increased to a maximum on the fifth day and the larvae were destroyed. Very few larvae were seen in the lungs; those observed were located in the alveolar spaces and were not surrounded by an inflammatory infiltrate. Worms in the small intestines were found mostly in the crypts of Leiberkuhn, and were probably located within the epithelial layer; there was no significant villous atrophy or cellular infiltration. Marked differences were found in the tissues of mice with secondary infections. In the skin, oedema and neutrophils and eosinophils were seen around worms as early as 2 h after infection. By 24 h after infection, there was a mixed inflammatory infiltrate and worms were undergoing disintegration. Larvae in the lungs were surrounded by polymorphonuclear and mononuclear cells 48 h and 72 h after infection and the engulfed larvae were undergoing lysis. Only a few worms were seen in the intestines of mice with a secondary infection; the histological appearances were similar to that found in animals with primary infections. It is suggested that the rapid development of an oedematous reaction in the skins of immune mice may facilitate the entry of larvae into the bloodstream and that inflammatory cells destroy many larvae in the lungs of immune mice.     

Synthesis, in vitro and in vivo biological evaluation,COX-1/2 inhibition and molecular docking study of indole-N-acylhydrazone derivatives

The objective of this work was to obtain and evaluate anti-inflammatory in vitro, in vivo and in silico potential of novel indole-N-acylhydrazone derivatives. In total, 10 new compounds (3a–j) were synthesized in satisfactory yields, through a condensation reaction in a single synthesis step. In the lymphoproliferation assay, using mice splenocytes, 3a and 3b showed inhibition of lymphocyte proliferation of 62.7% (±3.5) and 50.7% (±2), respectively, while dexamethasone presented an inhibition of 74.6% (±2.4). Moreover, compound 3b induced higher Th2 cytokines production in mice splenocytes cultures. The results for COX inhibition assays showed that compound 3b is a selective COX-2 inhibitor, but with less potency when compared to celecoxib, and compound 3a not presented selectivity towards COX-2. The molecular docking results suggest compounds 3a and 3b interact with the active site of COX-2 in similar conformations, but not with the active site of COX-1, and this may be the main reason to the COX-2 selectivity of compound 3b. In vivo carrageenan-induced paw edema assays were adopted for the confirmation of the anti-inflammatory activity. Compound 3b showed better results in suppressing edema at all tested concentrations and was able to induce an edema inhibition of 100% after 5?h of carrageenan injection at the 30?mg?kg^?1 dosage, corroborating with the COX inhibition and lymphoproliferation results. I addition to our experimental results, in silico analysis suggest that compounds 3a and 3b present a well-balanced profile between pharmacodynamics and pharmacokinetics. Thus, our preliminary results revealed the potentiality of a new COX-2 selective derivative in the modulation of the inflammatory process.     

Antimicrobial terpenoids of Gossypium: Hemigossypol, 6-methoxyhemigossypol and 6-deoxyhemigossypol

The sesquiterpenoid aldehydes, hemigossypol (1a), 6-methoxyhemigossypol (1b), and 6-deoxyhemigossypol (1c), were isolated and identified from Verticillium-infected stele tissue of Gossypium barbadense. Structures were established by spectral (UV, IR, NMR, MS) evidence and chemical transformations. This is the first report of (1b) and (1c) in nature, and of NMR and m.p. data for crystalline pure (1a). Compound (1a) occurred in diseased stele tissues of all 21 Gossypium species examined and in the genera, Cienfuegosia, Gossypioides, Hampea, and Thespesia; it was absent in three Hibiscus spp. Compound (1b) occurred in the same taxa as (1a), except that it was absent in species of two cytogenetic groups (A and B genome) of Gossypium. Compound (1c) occurred in trace quantities, or was not detected, in most species; however, its distribution appeared to besimilar to that     

Trypanosoma musculi and Trichinella spirails: Concomitant infections and selection for resistance genotypes in mice

Trypanosoma musculi infections were given to mice of different strains before, at the same time, and after an infection with 400 Trichinella spiralis. Examined parameters of the host response to T. spiralis were worm rejection, antifecundity responses, development of immunological memory, and muscle larvae burden. After dual infection, each mouse strain showed characteristic effects on resistance to T. spiralis. This was due to a dynamic interaction between the genes controlling rejection of T. spiralis and those influencing T. musculi growth. C3H mice develop high trypanosome parasitemias. This impairs worm expulsion and the development of memory to T. spiralis when Trypanosoma infections take place on the same day or 7 days before. The C57B1/6 mouse develops low parasitemias and T. musculi infections on the same day, or 7 days before T. spiralis, delaying worm rejection only slightly despite the overall weak capacity of B6 mice to expel worms. NFR-strain mice are strong responders to T. spiralis and also develop low parasitemias. Trypanosome infections on the same day, or after T. spiralis, produce a delay in worm rejection; the former is comparable to C3H mice. However, NFR mice alone showed enhanced rejection of worm when T. musculi infections preceded T. spiralis by 7 days. An unusual feature of C3H mice was that T. musculi infections 7 days before T. spiralis increased antifecundity responses at the same time that worm expulsion was inhibited. Trypanosome infections can therefore modulate distinct antihelminth immune responses in different directions simultaneously. The different outcomes of dual infections compared with single infections provides another selective mechanism by which genetic polymorphisms can be established and maintained in the vertebrate host.