Acanthocheilonema viteae: vaccination of jirds with irradiation-attenuated stage-3 larvae and with exported larval antigens

Jirds (Meriones unguiculatus) were immunized with irradiated (35 krad) stage-3 larvae (L3) of Acanthocheilonema viteae. The induced resistance against homologous challenge infection and the antibody response of the animals were studied. Immunization with 3, 2, or 1 dose of 50 irradiated L3 induced approximately 90% resistance. Immunization with a single dose of only 5 irradiated L3 resulted in 60.8% protection while immunization with a single dose of 25 L3 induced 94.1% protection. The protection induced with 3 doses of 50 irradiated L3 did not decrease significantly during a period of 6 months. Sera of a proportion, but not all resistant jirds, contained antibodies against the surface of vector derived L3 as defined by IFAT. No surface antigens of microfilariae or adult worms were recognized by the sera. Vaccinated animals had antibody responses against antigens in the inner organs of L3 and in the cuticle and reproductive organs of adult worms as shown by IFAT. Immunoblotting with SDS-PAGE-separated L3 antigens and L3-CSN revealed that all sera contained antibodies against two exported antigens of 205 and 68 kDa, and against a nonexported antigen of 18 kDa. The 205-kDa antigen easily degraded into fragments of 165, 140, 125, and 105 kDa which were recognized by resistant jird sera. Various antigens of adult worms, but relatively few antigens of microfilariae, were also recognized. To test the relevance of exported antigens of L3 to resistance, jirds were immunized with L3-CSN together with a mild adjuvant. This immunization induced 67.7% resistance against challenge infection and sera of the immunized animals recognized the 205- and 68-kDa antigens of L3.     

Studies of stage-specific immunity against Trichostrongylus colubriformis in sheep: immunization by normal and truncated infections.

Sheep immunized with multiple normal infections of 30,000 Trichostrongylus colubriformis larvae (T.c. L3) suppressed the fecundity, establishment and survival of adoptively transferred adult worms, showing that these parasites were susceptible to the effects of host immunity. When sheep were immunized by four 'truncated' larval infections of 4, 7 or 10 days' (d) duration with 10(5) T.c. L3, animals given 4 x 4d infections were susceptible to challenge, whereas sheep given 4 x 7d and 4 x 10d infections were significantly protected. A serial analysis of the rejection of T. colubriformis from nine sheep given 5 x 7d infections revealed that the challenge larval infection given intraduodenally was expelled within 3 days after challenge (DAC). However, another five of these sheep only rejected around 50% of transferred adult worms by 21 DAC when compared with control animals. The results indicate that stage-specific antigens produced by early L3 and L4 stages of T. colubriformis effectively immunize sheep against a larval challenge but appear less reliably protective against adult worms.     

Humoral immune response and antigenemia in sheep experimentally infected with Schistosoma bovis. Cross-reactivity with Fasciola hepatica antigens.

Circulating antigen level, IgG antibody response to worm antigens and to excretory/secretory products (ES), and specificity to Fasciola hepatica antigens were determined in 6 Schistosoma bovis-infected sheep at weekly intervals for 15 wk. A noninfected control group was included. An enzyme-linked immunosorbent assay (ELISA) sandwich and a double-antibody ELISA test was used for antibody and antigen detection, respectively. The infection induced an early and relatively low IgG response to adult worm extract. This response was significantly elevated by 3 wk postinfection (PI), reached its maximum level at 9 wk PI, and was followed by a subsequent decrease. The response to ES antigens was slightly higher than that to adult worms, although the response started later, at 8 wk PI, and remained at its maximum level until 15 wk. A remarkable level of cross-reactivity was observed when adult F. hepatica extract was used. However, a low degree of cross-reactivity was found with ES antigen. The ELISA for circulating antigens was performed at weekly intervals for 8 wk. Antigens were detected as early as the first week of infection, although differences were statistically significant from week 5 onward. The highest values were observed at 7 week PI.     

Experimental life cycle of Lagochilascaris major leiper, 1910 (Nematoda: Ascarididae) in cats (Felis domesticus)

The life cycle of Lagochilascaris major was studied using eggs collected from a natural clinical case in a domestic cat. Twenty-seven white mice (Mus musculaus), 5 hamsters (Mesocricetus auratus), and 1 vesper mouse (Calomys callosus) were orally inoculated with 800-1,300 embryonated eggs. When examined from 73 to 246 days postinoculation (PI), encysted third-stage larvae were seen in skeletal muscles and less frequently in connective tissue, liver, and lungs. Twenty-two of the 23 cats orally inoculated with 40-430 encysted larvae from these rodents, and necropsied from 1 hr to 185 days PI, became infected. Third-stage larvae were located in the stomach, esophagus, and oropharynx from 1 to 24 hr PI. At 48 hr, larvae, from mainly the fourth stage, were only found, unilaterally or bilaterally, inside a "sac" in the region of the semilunar fold of the palatine tonsil at the base of the tongue. Adult worms were found in this location from 10 to 175 days PI. No fistulated abscess to the outside medium was found. Adult worms were also found in the middle ears of 2 cats showing purulent otitis. Eggs in the ear secretion were under different stages of development. Eggs in feces were first observed on days 14 and 15 PI, and 1 cat shed them until 178 days PI. Six infected cats were treated with fenbendazole at 50 mg/kg of body weight for 3 consecutive days, eliminating all the parasites present in the tonsils. The drug was not effective against the parasites present in the middle ear. No stage of the parasite was found in the tissues of 5 cats given 4,000-5,200 eggs orally and examined after 19 and 50 days PI. This indicates that the life cycle of L. major requires an obligate paratenic host and is characterized by heteroxenic cycle.     

Shared carbohydrate epitopes on distinct surface and secreted antigens of the parasitic nematode Toxocara canis

The nematode parasite Toxocara canis is found in all dog populations and poses a poorly defined health hazard to humans. We have studied excretory-secretory antigen (ES) and surface antigens of the infective larval stage which is tissue-invasive in mammalian hosts. Antigens were probed with a panel of eight monoclonal antibodies raised in mice to whole ES. Six of eight antibodies reacted with periodate-sensitive carbohydrate epitopes on ES molecules, and the remaining two (Tcn-3 and Tcn-6) recognized either peptide or periodate-resistant sugar determinants. By immunoprecipitation and immunoblotting, the anti-carbohydrate monoclonals each reacted with several distinct ES molecules, known from previously published work to possess contrasting biochemical properties. Tcn-3 and -6 were directed predominantly against 32,000 and 120,000 m.w. molecules, respectively. Iodinated surface antigens of similar m.w. were precipitated by each antibody after detergent solubilization, but only two clones (Tcn-2 and -8) were able to bind exposed sites on the epicuticle of intact Toxocara larvae. Significantly, these antibodies do not bind to newly hatched larvae, and their target antigens are poorly expressed until the second day of in vitro cultivation. The specificities of the monoclonals were further studied by cold antibody inhibition of radiolabeled monoclonal binding, and by a matrix of two-site binding assays. These data show that Tcn-2, -4, -5, and -8 recognize a related group of repetitive carbohydrate epitopes, whereas Tcn-1, -6, and -7 bind discrete determinants on the same molecules. These studies are being continued to define further the structure of antigenic Toxocara carbohydrates and to compare the diagnostic utility of carbohydrate and peptide antigens.     

Brugia malayi: patterns of expression of surface-associated antigens.

Patterns of expression of surface-associated antigens were analyzed in the filarial nematode Brugia malayi immediately prior, and during development in the vertebrate host. Two surface-associated protein molecules, i.e., accessible to surface radioiodination and soluble in aqueous buffers, were investigated: Mrs 29-30,000 and 16,000, both of which are antigenic in infected animals. The Mr 29-30,000 glycoprotein is expressed in a surface-associated manner by adult worms and by fourth-stage larvae, but is not detectable in preparasitic third-stage larvae. The 16,000 component, which appears not to be glycosylated, is surface-associated in adult worms and fourth-stage larvae. In contrast to the 29-30,000 glycoprotein, the 16,000 protein is also expressed both by pre- and postparastic third-stage larvae. However, it becomes surface-associated only after infection. Thus, immediately prior, and during development within the vertebrate host, B. malayi displays at least two different patterns of expression of surface-associated antigens: (i) de novo, intiated either immediately after infection (phase specific) or during genesis of the fourth-stage larva (stage specific); (ii) continuous, but with phase-dependent surface exposure of previously cryptic antigens, during the transition from intermediate to definitive host.     

Effect of flubendazole on the number of first-stage larvae of Angiostrongylus cantonensis released in the faeces of treated rats

The effect of flubendazole orally administered at 10 mg/kg/day for 5 consecutive days (the 11th, 20th or 40th post-infection) on the number of first-stage larvae (L1) of Angiostrongylus cantonensis released in the faeces of rats each infected with 40 third-stage larvae was determined. Faecal examination for 5 months, the period from medication to dissection of rats, showed that L1 release ceased in all the rats of medicated groups by about 1 week after the termination of dosing and resumed 1-2 months later in 86% of the rats which were dissected at the end of experiments with the recovery of adult worms of both sexes. Throughout the period of 5 months, about 2-4 x 10(4) L1/gram of fresh faeces was recorded in non-medicated control groups. There was a 38-79% reduction in adult worms at the dissection. Microscopic examination of the uteri of the remaining adult worms and lung tissues of rats confirmed no normal egg production in the adult worms from rats of medicated groups, except the rats with the resumption of faecal L1 release.     

Trichinella spiralis: murine strain variation in response to monoclonally defined, protective, nonstage-specific antigens

Nine hybridoma cell lines secreting monoclonal antibodies (mAbs) against Trichinella spiralis muscle larvae (ML) excretory/secretory antigens (ESA) were developed. Two mAbs, 6-D8-E3 (6D8) and 6-B1-G10 (6B1), were studied in detail. Western blot analysis using ML ESA showed that 6D8 recognized 35- and 40-kDa constituents whereas 6B1 identified a doublet of 33 kDa. However, Western blots of SDS-PAGE of crude ML homogenate showed that 6D8 identified proteins of approximately 35 and 43-60 kDa, whereas 6B1 recognized bands of 42-50 kDa. These results indicated substantial apparent MW differences between secreted and nonsecreted proteins recognized by both mAbs. Neither 6D8 nor 6B1 reacted with adult worm ESA, but both recognized antigens in aqueous extracts of homogenates of whole adult worms. Competitive inhibition experiments using ML ESA as a target demonstrated that the antigen epitopes recognized by monoclonals 6D8, 6B1, a rat mAb, 9D4, and a 37-kDa antigen previously defined were noncross-reactive. MAbs 6D8, 6B1, and 9D4 were used to isolate proteins possessing target determinants by affinity chromatography from crude ML homogenates. Each mAb isolated distinct protein species as determined by SDS-PAGE (6B1, approximately 42 kDa; 6D8, approximately 28, 37, and 61 kDa; 9D4, approximately 29, 33, 38-57, 80, and 86 kDa). NFS mice responded in a dose-dependent manner to affinity-purified antigens and were 25-fold more effective (by weight of antigen) than either C3Heb/Fe(C3H) or B10.BR mice. Immunization of mice with 6D8, 6B1, or 9D4 antigens induced strong protection against a subsequent challenge infection in NFS mice as indicated by accelerated intestinal adult worm expulsion, reduced fecundity of the female worms, and reduction of ML burden. Affinity-isolated antigens stimulated in vitro proliferation of spleen and MLN cells from immune mice; however, the mitogenic response to these antigens barely varied among NFS, C3H, and B10.BR strains.     

Immune response against protozoal and nematodal infection in mice with underlying Schistosoma mansoni infection

Schistosoma mansoni infection induces T helper (Th) 2-dominant immune response in mice not only to S. mansoni itself but also to other coexisting antigens. In the present study, we challenged S. mansoni-infected mice with the intestinal nematode, Strongyloides venezuelensis, and the intracellular protozoa, Leishmania major to see whether such Th2-dominant immune responses alter susceptibility of the host to other concomitant parasitic infections. The recovery of S. venezuelensis adult worms from the small intestine was significantly decreased by S. mansoni infection, and the protection to S. venezuelensis appeared to act on migrating larvae. Antibodies elicited by S. mansoni infection showed cross-binding to third-stage larvae antigen of S. venezuelensis. On the other hand, S. mansoni infection did not affect the outcome of L. major infection in both susceptible BALB/c and resistant C57BL/6 mice. Popliteal lymph node cells of BALB/c mice expressed mRNA for interleukin (IL)-10 rather than IL-4, regardless of S. mansoni infection, and those of C57BL/6 mice expressed IFN-gamma mRNA upon L. major antigen stimulation, even in S. mansoni-infected mice. Our findings suggest that Th2-dominant immune response induced by S. mansoni protects mice from intestinal helminthic infections, whereas they do not always modulate protozoal infections.     

Antigens of Amblyomma americanum ticks recognized by repeatedly infested sheep

Sera were taken from 3 sheep that had been infested 5 times with Amblyomma americanum and that exhibited manifestations of humoral depression to homologous antigens and anti-tick resistance. Proteins extracted from the intestine or salivary glands of unfed ticks or salivary glands from partially (3-day) fed ticks were analyzed by polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate-PAGE. Antigens recognized by the sheep in the same materials before and after each infestation were analyzed by western blots. The sheep responded to 44 antigens. Nine to 23 antigens were recognized by the preinfestation sera and the sera of 2 gnotobiotic sheep. Four antigens (34,000, 36,500, 38,000, and 115,000 MW) were revealed conspicuously by the serum of the first infestation but very weakly or not at all by the sera of the third infestation onward. Two antigens (35,500 and 29,000 MW) from fed salivary glands were revealed only by sera taken after manifestations of resistance had appeared. These antigens may be responsible for anti-tick protection. The 29,900 MW antigen was present also in salivary extracts of Boophilus microplus.     

Further observations on the development of Gongylonema pulchrum in rabbits

Third-stage larvae of Gongylonema pulchrum from naturally infected dung beetles were inoculated orally into 24 rabbits. Worm recovery ranged from 54 to 91% (mean = 67.5%) during the period from 24 hr to 52 wk postinoculation (PI). Two hours PI, the larvae entered the mucosa at the junction of the stomach and esophagus and migrated upward. Early development occurred primarily in pharyngeal mucosa, tongue, and buccal mucosa. The third molt took place 11 days PI and the final molt at 36 days PI. Male worms reached sexual maturity at 7 wk PI and females at 9 wk PI. Adult worms were found mainly in the esophagus but also occurred in the tongue and the wall of the oral cavity after 30 wk PI. Embryonated eggs appeared in the feces of 3 rabbits inoculated with 50 or 100 larvae on days 72-81 PI. Morphologically, the cuticle in young fourth-stage larvae exhibited bosses on the anterior portion on day 11 PI, and the left spicule length : total body length exhibited no remarkable change between 9 and 52 wk PI. The latter finding confirms the utility of the ratio for identification of the nematode.     

Brugia pahangi: production of a monoclonal antibody reactive with the surface of infective larvae.

Monoclonal antibodies against infective third-stage larvae (L3) of Brugia pahangi were generated from mice immunized with L3 antigens. The monoclonal antibodies were L3 stage-specific or stage-nonspecific. A BpG1 monoclonal antibody (IgG1 subclass) showing L3 stage-specificity was examined in detail. BpG1 recognized the surface of B. pahangi L3 and also reacted with the surface of Brugia malayi L3 but not with the surface of filarial worms of other genera, such as Acanthocheilonema viteae and Litomosoides carinii. BpG1 promoted cellular adhesion to the surface of B. pahangi L3. BpG1 bound on living L3 was shed but the shedding rate was relatively slow. The surface antigen recognized by BpG1 had a molecular weight of 58 kDa. It was stable to heat and periodate treatments but sensitive to trypsin digestion and was released from living L3 by SDS but not by Triton X-100 or CTAB. Preincubation of L3 with BpG1 significantly reduced the recovery rate of worms compared with the preincubation with a monoclonal antibody (IgG1 subclass) against the inner tissues of B. pahangi L3 or control supernatant of P3U1 myeloma cells. This result suggests that the antigen containing the BpG1 epitope may be one of the targets of a protective immune response against Brugia infection.     

Experimental infection of Dirofilaria immitis in raccoon dogs

Canine heartworm (Dirofilaria immitis) is a nematode that naturally parasitizes in the pulmonary arteries and the right ventricle of domestic dogs (Canis familiaris) as final hosts. Japanese raccoon dogs (Nyctereutes procyonoides viverrinus) also are known to be susceptible to infection by the parasite. However, prevalence of this infection among free-ranging raccoon dogs is low and so is the worm burden. To examine the susceptibility of the raccoon dog to D. immitis infection, 3 raccoon dogs and 2 beagles were inoculated 4 times with 25 third-stage larvae (L3s) of D. immitis at 3-wk intervals. Worms were recovered from 2 raccoon dogs and both domestic dogs. The average percentage of recovery (2.3%) of the raccoon dogs was almost 10 times lower (24.5%) than that of the domestic dogs, but there was no significant difference in the body length of worms recovered from 2 types of hosts. To examine microfilaremia, 2 raccoon dogs were infected with 100 L3s. Microfilaremia was observed for 180 days postinoculation (PI) but disappeared at about 300 days PI. The raccoon dog was mildly susceptible to infection with D. immitis, but surviving worms developed and matured normally.     

Screening of murine monoclonal antibodies against living schistosomula of Schistosoma mansoni by radioimmunoassay

A radioimmunoassay was developed to screen supernatants of murine monoclonal antibodies against surface antigens of living schistosomula of Schistosoma mansoni. Of 196 clones screened, 10% bound schistosomula. Of these, 74% bound only schistosomula. The remaining molecules also reacted with soluble adult worm antigens and soluble egg antigens as determined by enzyme-linked immunosorbent assay. Immunoblot analysis demonstrated that monoclonal antibody 204-3E4 reacted with a 68 kDa protein, a glycoprotein that induces substantial resistance against S. mansoni infection. Recognition of an 18 kDa antigen by 204-3F1 antibody was stage-specific with the antigen being expressed in cercariae, 3- and 24-h-old parasites but not 4-day, lung stage or adult worms. Monoclonal antibody 204-4E3 reacted with purified S. mansoni paramyosin. These data indicate that radioimmunoassay using living schistosomula is a rapid alternative method to identify murine hybridomas that secrete antibodies which react with surface antigens of S. mansoni.     

Echinococcus multilocularis coproantigen detection by enzyme-linked immunosorbent assay in fox, dog, and cat populations

A sandwich enzyme-linked immunosorbent assay (ELISA) for the detection of Echinococcus multilocularis coproantigens (EM-ELISA) was developed with polyclonal rabbit (solid phase) and chicken egg (catching) antibodies that were directed against E. multilocularis coproantigens and somatic worm antigens, respectively. In experimentally infected dogs and cats, coproantigens were first detectable 6-17 days postinfection (PI) in samples of 8 dogs (worm burdens at necropsy: 6,330-43,200) and from 11 days PI onward in samples of 5 cats infected with 20-6,833 worms. After anthelmintic treatment of 4 dogs and 5 cats at day 20 PI, coproantigen excretion disappeared within 3-5 days. The sensitivity of the ELISA was 83.6% in 55 foxes infected with 4-60,000 E. multilocularis, but reached 93.3% in the 45 foxes harboring more than 20 worms. The EM-ELISA was used in surveys of "normal" dog and cat populations in Switzerland. Among 660 dogs and 263 cats, 5 dogs and 2 cats exhibited a positive reaction. In 2 of these dogs (0.30%) and 1 cat (0.38%), intestinal E. multilocularis infections were confirmed by necropsy, polymerase chain reaction PCR, or both. The specificites of the ELISA in these groups were found to be 99.5% and 99.6%, respectively, if positive ELISA results that could not be confirmed by other methods were classified as "false positive" reactions.     

Developmental and age-related changes in proteins in the female reproductive tract of Heligmosomoides polygyrus (Nematoda)

Proteins in the female reproductive tract of Heligmosomoides polygyrus at days 8, 16, 35, 90, and 140 postinfection (PI) were examined using polyacrylamide gel electrophoresis. Sixteen-day-old and 140-day-old worms also were examined histochemically. Egg production of these worms was assessed for each age group. In analyzing proteins using electrophoresis, the reproductive tracts were separated into 3 sections: the tip, or anteriormost part of tract, containing oogonia; the middle region, containing developing oocytes; and the posterior region, containing the uterus with fertilized eggs. Three major reproductive tract proteins were identified as having molecular weights of greater than 140 kDa, 115 kDa, and 82 kDa. These were found in all parts of the reproductive tract from worms of all ages except those at 8 days PI (which are too young to produce eggs) and are believed to be yolk proteins. Four low molecular weight proteins (L1-4) are believed to be nucleoproteins. L4 was absent from the posterior section of the reproductive tracts and L3 was limited to the posterior sections and may be associated with sperm stored in the uterus. Of 5 high molecular weight proteins the second heaviest, designated H2, appeared to be relatively more concentrated in the posterior sections of the reproductive tract. An 85-kDa protein was limited to the tip and middle sections of reproductive tracts. Histochemical tests on sectioned H. polygyrus showed strong positive reactions for protein in cytoplasmic granules in developing oocytes and in eggs of younger worms (16 days) but a reduced reaction in older worms (140 days). Strains for collagen showed a slight positive reaction in and between developing oocytes and a strong reaction in the egg shells. Stains for nucleoproteins particularly reacted with sperm stored in the uterus, and slightly reacted with fertilized eggs and the nucleoli of the intestinal and ovarian epithelium. Egg production by H. polygyrus increased to 123 eggs/female/day by 16 days PI but declined from 121 eggs/female/day at 35 days PI to 64 eggs/female/day in worms 140 days old. Electrophoresis indicated no loss in the different types of proteins in the reproductive tract of older worms, but histochemistry and protein content assays suggest that older worms that produce fewer eggs contain a relatively smaller amount of protein in the female reproductive tract.     

Detection of anti-parelaphostrongylus tenuis antibodies in experimentally infected and free-ranging moose (Alces alces)

Confirming Parelaphostrongylus tenuis infection in moose (Alces alces) and other susceptible hosts is difficult. An enzyme-linked immunosorbent assay (ELISA) was developed using the excretory-secretory (ES) products of third-stage P. tenuis larvae (ES-ELISA) and the test applied to serum samples obtained from seven moose calves (5-9.5 mo old) given infective larvae (L3) in doses approximating those likely to be received in nature (3-30 L3). Anti-P. tenuis immunoglobulin G antibodies were detected in all seven inoculated moose during the course of infection until the termination of experiment 61-243 days post-inoculation (DPI). Five animals tested between 16-25 DPI had significant antibody levels, while a sixth animal did not test positive until 46 DPI. The seventh animal was not tested until 199 DPI. Antibody levels remained elevated in all five animals that harbored adult worms at the termination of the experiment. Whereas, antibody levels showed a gradual decline in the two remaining animals, presumably because of death of worms, and antibodies were undetected in one animal at the time of necropsy. The other animal displayed an anamnestic increase in antibody level following a challenge inoculation of infective larvae. Terminal and peak optical density (OD) values detected by ES-ELISA strongly correlated with inoculation dose (r = 0.98, P = 0.02 and r = 0.95, P = 0.04, respectively) among animals harboring adult worms (n = 4) but not significantly with the number of worms recovered postmortem (peak OD, r = 0.82, P = 0.18; terminal OD, r = 0.93, P = 0.07). Unlike the ES products, use of somatic antigens of the adult worm in ELISA did not provide satisfactory results. Antibodies to P. tenuis were detectable by ES-ELISA in two of 21 free-ranging moose from an enzootic area but not from any of 23 animals from a non-enzootic area. The ES-ELISA appears to be a useful test for assessing exposure of moose to P. tenuis.     

Immunity to Litomosoides carinii in Mastomys natalensis. II. Effects of chemotherapeutically abbreviated and postpatent primary infections on challenges with various stages of the parasite

Naive Mastomys natalensis, Litomosoides carinii-infected M. natalensis at a postpatent stage of the infection and L. carinii-infected M. natalensis treated chemotherapeutically with furazolidone (FUR), FUR and diethylcarbamazine (FUR/DEC) or amoscanate (AMOS) were challenged by either injection or implantation of 40 third stage larvae (L3, s.c.), 40 fourth stage larvae (L4, 16 days old, i.p.), 20 male and 20 female preadult worms (36 days old, i.p.), 12 adult female worms (i.p.) or 6 X 10(6) microfilariae/kg (i.v.). Microfilaraemia in animals challenged at a postpatent stage (independent of the kind of challenge), was either totally suppressed or at least greatly reduced. Necropsy of L3-challenged animals showed that neither the length of the worms nor their content of morphologically intact, intrauterine stages was affected. Infected, treated animals challenged with developing stages (L3, L4 and preadult worms) showed reduced levels of microfilaraemia (by up to 75%). Dissection of AMOS-treated, L3-challenged animals showed that both the developmental rate and the fertility of the worms were affected. Microfilaraemia was also reduced after implantation of adult worms into treated animals. This was independent of the interval between treatment and challenge (44-150 days) except in animals challenged 10 days after AMOS-treatment, which showed no difference from naive controls. However, infected, treated M. natalensis, cotton rats and gerbils did not develop immunity against intravenously injected blood microfilariae.     

Fate of developing larvae of Onchocerca lienalis and O. volvulus in micropore chambers implanted into laboratory hosts

Infective larvae of Onchocerca lienalis and O. volvulus implanted subcutaneously within micropore chambers into laboratory hosts moulted to the fourth stage (L4) and underwent limited development and growth. Similar recoveries of O. lienalis L4 larvae in the range of 33-66% were obtained from chambers implanted into CBA and BALB/c strains of mice, jirds, and the natural bovine host. A relatively constant proportion of larvae survived up to 24 days post implantation and thereafter recoveries declined, although some worms were still alive after 96 days. Recoveries of O. volvulus L4 larvae from chambers given to normal or T-cell deprived mice were equivalent to one another and to those obtained with O. lienalis. Moulting of O. lienalis in chambers was observed on days 3 and 5, in close accordance with the timing of the third moult in cattle following systemic infection. Moulting of O. volvulus occurred between days 3-6. Morphological changes in developing larvae included a small but significant increase in length, a transient increase in width, and early development of the spicular primordia and genital tube. L4 larvae of O. lienalis, but not those of O. volvulus, exhibited 3 distinct caudal papillae not present on infective larvae.     

Acquired immunity in rats against Angiostrongylus cantonensis infection

Acquired immunity against Angiostrongylus cantonensis was induced by immunizing rats with somatic antigens from fifth-stage larvae and adult worms and live third-stage larvae. Rats immunized twice had significantly fewer worms than rats immunized three times. Fewer worms were recovered from rats immunized with 200 live third-stage larvae than from any other groups. Rats immunized with somatic antigens had higher enzyme-linked immunosorbent assay (ELISA) antibody levels than rats immunized with live larvae. Rats immunized with live third-stage larvae of Angiostrongylus cantonensis were more strongly protected against challenge infections (62-92%) than rats immunized with antigens extracted from fifth-stage larvae (0-30%) and adult worms (11-24%).