Trichinella spiralis: acquired immunity in swine

The ability of domestic pigs to develop protective immunity to Trichinella spiralis in response to inoculation with different doses of muscle larvae was assessed. Adult worms developing from the inoculations of 112, 500, and 10,000 larvae were expelled from the intestine about 6 weeks after inoculation. Inoculation with 25,000 larvae, however, resulted in more rapid intestinal worms expulsion, indicating that gut expulsion is dose dependent. Secondary expulsion also tended to be dependent upon primary infection level. Pigs initially inoculated with 500 to 10,000 larvae expelled the challenge infection of adult worms after 22 to 25 days; in contrast, infection by inoculation of only 112 larvae failed to induce significant enchanced gut expulsion of the challenge infection intestinal worms. However, all primary infection levels, including inoculation with 112 larvae, induced nearly absolute resistance to the muscle establishment of larvae from challenge adult worms. The fecundity of female worms recovered from immune pigs was reduced 75% in comparison to controls. These results show that, in contrast to some host species, very rapid gut expulsion does not occur in domestic swine. Yet, immune responses at the gut level are important, perhaps responsible for much of the inhibition reflected as reduction in the establishment of muscle larvae.     

The effects of x-radiation on Taenia pisiformis.

Following the exposure of eggs of T. pisiformis to X-radiation at doses of 10,000, 20,000 and 30,000 rads, hatching and activation in vitro were unaffected. Growth of larvae both in vitro and in vivo was reduced and many irradiated larvae were overcome by the host inflammatory reaction during intra-hepatic development. A negative correlation was established between the log₁₀ number of cysticerci in the abdominal cavities of rabbits 42 days after infection and the radiation dose. Significant abnormalities were induced in the morphology of rostellar hooks of cysticerci following irradiation of eggs although adult cestodes which developed from cysticerci derived from irradiated eggs were normal. Cysticerci exposed to 5000 and 10,000 rads of X-radiation developed to adult worms when fed to dogs but abnormalities were found, principally in the testes, ovaries and vitellaria; segmentation and the genital ducts were affected to a lesser extent.     

Acquired resistance to migrating larvae of Ascaris suum in young pigs by repeated drug-abbreviated infections

Cross-bred 3- and 8-wk-old pigs were used to test whether drug-abbreviated infections with Ascaris suum can stimulate acquired resistance to challenge. During the immunization period, both age groups of animals were infected with increasing numbers of A. suum eggs (500, 1,000, 2,000, 5,000, 10,000, and 20,000) at 7-day intervals while the pigs were receiving pyrantel tartrate in the feed. Two days after the last infective dose, animals were placed on unmedicated feed for 8 days and then challenged with 10,000 eggs. All pigs were killed 7 days after challenge, and milk spots on the livers and larvae recovered from the lungs were counted. Larval recoveries from lungs of the immunized animals were significantly smaller than those from the unimmunized animals in both age groups, suggesting that the pigs were capable of acquiring strong resistance to parasitic infections. In immunized animals, challenge infection did not contribute significantly to milk spot formation. The number of milk spots was significantly greater in the older animals, indicating that milk spot formation may be age related.     

Studies of stage-specific immunity against Trichostrongylus colubriformis in sheep: immunization with adult parasites.

Merino sheep immunized by the adoptive transfer of adult T. colubriformis for 8 weeks were significantly protected against a challenge infection of 20,000 larvae. Two additional groups of sheep received a primary infection of 9000 adult worms which were allowed to persist for 14 weeks before one group was drenched. When both groups were challenged 10 days later with 30,000 larvae, serial necropsies of these and naive sheep revealed that worm rejection did not occur until 7-10 days after challenge. By comparison with the rapid rejection of larval challenges from sheep immunized with normal primary infections, the results suggest that the antigens which elicited rejection in these experiments are stage-specific and were only present or synthesized in sufficient quantities when parasites had developed for 1 week.     

Evaluation of pyrantel-tartrate abbreviated Ascaris suum infections for the development of resistance in young pigs against migrating larvae

Crossbred young pigs were used to test whether abbreviated infections with eggs of Ascaris suum can stimulate the acquisition of resistance to challenge. Weanling pigs from an Ascaris-free colony were kept free of A. suum until they were divided into groups at the age of 7-8 weeks. The experimental animals received pyrantel tartrate during the period when they were being exposed to increasing numbers of infective A. suum eggs and challenged 10 days after the last infective dose. Liver milk-spot counts and larval recoveries from the lungs indicated that the strongest resistance was acquired by the animals that received the drug continuously for 6 weeks while being exposed to six weekly infective egg doses. The data do not suggest any drug-related suppression of the resistance response to A. suum infection.     

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.     

Scanning electron microscopy of the lip denticiles of Ascaris suum adults of known ages.

Purebred Hampshire pigs, farrowed and maintained under conditions precluding extraneous helminth infection, were exposed to a single dose of 10,000 Ascaris suum infective eggs. The pigs were killed at intervals of 28, 41, 55, 86, 115, 145, 175, and 206 days after infection. At necropsy, no gross lesions were found in the lungs or livers of infected pigs. The worms were recovered from the small intestine, identified, counted, and fixed. The heads were excised, critical point dried, mounted en face, and examined by scanning electron microscopy. Worms 28 to 115 days old had unworn denticles that were triangular when viewed laterally but blunt when viewed tangentially. Wearing of the denticles was observed first with 145-day-old worms; wearing increased with age both in numbers of denticles affected and in degree of wear so that by 206 days after inoculation, almost all denticles in the center of the lip were worn. Worn denticles appear truncated when viewed from any angle. The denticles outside the central area were not affected by wear. The size of the denticles varies not only between specimens of the same age, but also on each specimen. However, average denticle size is directly related to the size and, accordingly, to the age of the worm. External to each denticle is a corresponding depression that we have called the denticular groove. One 28-day-old specimen had some extra denticles aligned irregularly along the lip; this irregularity gave the appearance of a double row. The denticles of the two subventral lips are similar to those of the dorsal and are equally affected by wear. There was no detectable difference in denticles of male and female worms. Since wear can now be specifically correlated with age, we conclude that the denticles are functional and become worn through use. Consequently, adult A. suum may be an even more injurious pathogen than heretofore supposed.     

Single and multiple worm infections of Echinostoma caproni (Trematoda) in the golden hamster

Six of 10 hamsters fed a single metacercarial cyst of Echinostoma caproni (single-worm infections) and 13 of 19 hamsters fed either 2 or 5 cysts (multiple-worm infections) were infected with adult echinostomes at necropsy 22 days post-infection. Considerable histopathological changes to the small intestine occurred in hamsters carrying single-worm infections. There were no differences in either mean length, width or wet weight of echinostomes in single- versus multiple-worm infections. The mean number of eggs/worm from single-worm infections (525) was significantly greater than that from multiple-worm infections (288). The average percentage of fully developed miracidia/worm from single worms (94%) was similar to that from worms in multiple infections (92-95%). Single worms of E. caproni were capable of self-fertilization and production of viable eggs. Miracidia derived from single worms were as capable of infecting laboratory-reared Biomphalaria glabrata and producing patent rediae as were those from multiple infections.     

White spots of the liver in pigs experimentally infected with Ascaris suum

To make clear the relationship between Ascaris suum infection and the appearance of white spot lesions on the surface of the liver in pigs, three groups of pigs were inoculated orally with embryonated A. suum eggs and observed clinicopathologically. Group A of three pigs were inoculated 21 times with 100 eggs each of the nematode, group B of three pigs 4 times with 50,000 eggs each for 10 weeks, and group C of two pigs 2 times with 50,000 eggs each at a one-week interval. All the pigs were sacrificed at the same time 1 week after the final inoculation. Such signs of the nematode infection as dyspnea, coughing and fever appeared in all the pigs of groups B and C seven days after inoculation to continue for several days. In addition, peripheral blood eosinophilia was recorded in these animals 7 or 14 days after inoculation. At autopsy, mesh-worked white spots, some compact and others lymphonodular, were observed on the surface of the liver in all the pigs of the three groups. Main white spots were mesh-worked and lymphonodular in the pigs of group A. They were severe and compact in group B. Therefore, they were rough to the touch. In group C mesh-worked white spots fused with one another and covered the surface of the liver. These white spot lesions observed were morphologically very similar to those found in the field conditions. Complement-fixating antibodies reacting to adult A. suum antigen were detected only in sera from the pigs of group B. Moreover, antibodies involved in the intradermal reaction of immediate type were found in the pigs of groups A and B.     

Brugia pahangi: granulomatous lesion development in jirds following single and multiple infections

The development of adult worm burdens and microfilaremias were determined in jirds which received 2, 3, or 4 subcutaneous inoculations of 50 Brugia pahangi infective larvae. Parasite burdens in multiply inoculated jirds were compared to those in four different groups of jirds which received single inoculations of 50 infective larvae. One of each of these singly inoculated groups was infected on the same day that one of the inoculations was given to the multiply infected jirds. Thus, the duration of the infections in the four groups of jirds receiving one inoculation was 54, 118, 189, and 254 days. The development of lymphatic lesions and granulomatous hypersensitivity to B. pahangi antigen was assessed in all jirds at necropsy. The percentage recoveries of adult worms and their locations did not differ in the singly inoculated jirds with infections of different durations. A protective resistance to reinfection, as measured by adult worm recovery in multiply infected jirds, did not occur. The lymphatic lesion scores and numbers of intralymphatic thrombi was greatest in singly inoculated jirds examined 54 days after infection. Pulmonary granuloma areas around adult filarial antigen coated beads embolized in the lungs of jirds 3 days prior to necropsy were also greatest in singly inoculated jirds examined 54 days after infection. Using criteria of lesion scores and lymph thrombi numbers to assess lymphatic lesion severity, a decrease in lesion severity as well as pulmonary granuloma size around antigen coupled beads was seen by 118 days after infection in singly inoculated jirds.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of crowding on adults of Philophthalmus gralli (Trematoda) grown in chickens

Chickens were infected with six, 10, 30, 50, or 100 metacercariae of Philophthalmus gralli per eye and the adults were harvested 9, 14, 21, 35, and 50 days later. The worms recovered were measured and assessed for maturity. Significantly more adults from infections of six and 10 metacercariae per eye were recovered than from infections of 100 per eye. When metacercariae were placed in one eye, over one-fourth of the resulting adults were found in the opposite eye. Worms recovered from groups of zero to 10 were significantly longer than those in groups of 41 to 50 and 51 to 60 at all ages sampled. The normal movement of worms from the conjunctival sac to the outside of the nictitating membrane was hindered by crowding; when more than 10 were present, some worms developed in the sac to mature adults. Worms in all groups produced eggs in which miracidia developed at the same rate.     

Elucidation of Schistosoma japonicum population dynamics in pigs using PCR-based identification of individuals representing distinct cohorts

The study reported here investigated the interactions of successive infections and acquired resistance of pigs to challenge infections of Schistosoma japonicum. Two morphologically indistinguishable geographical isolates from China (from Anhui and Zhejiang provinces) were used for the infections. The worms of the two isolates were distinguishable by PCR-linked restriction fragment length polymorphism analysis of the nicotinamide adenine dinucleotide phosphate dehydrogenase I gene of the mitochondrial genome. Thirty-two pigs divided into seven groups were used in the experiment. Two groups received a single infection by either the Anhui or the Zhejiang isolate. In Challenge Groups 1, 4, 6, 8 and 12, a primary infection of the Zhejiang isolate was followed by a challenge infection with the Anhui isolate at week 1, 4, 6, 8 or 12 after the primary infection. In this way it was possible to determine whether worms recovered by perfusion originated from the primary or the challenge infection. Only the challenge infection at week 1 resulted in a higher worm burden when compared with a single primary infection with the Zhejiang isolate. The results showed that challenge worms were able to establish, and that the proportion of worms originating from challenge infection increased at the later challenge infections, however without an increase in the total number of worms. In addition, mixed pairs of the two isolates were found in all challenge-infected groups. The results indicate that pigs are able to mount a partial resistance against re-infection with S. japonicum by 4 weeks after a primary infection, but that worms of the challenge infections eventually replace the primary infection. The finding of mixed pairs of the two isolates indicates that worms of S. japonicum are either polygamous or able to wait in solitude for up to 12 weeks for a partner.     

Elucidation of Schistosoma japonicum population dynamics in pigs using PCR-based identification of individuals representing distinct cohorts

The study reported here investigated the interactions of successive infections and acquired resistance of pigs to challenge infections of Schistosoma japonicum. Two morphologically indistinguishable geographical isolates from China (from Anhui and Zhejiang provinces) were used for the infections. The worms of the two isolates were distinguishable by PCR-linked restriction fragment length polymorphism analysis of the nicotinamide adenine dinucleotide phosphate dehydrogenase I gene of the mitochondrial genome. Thirty-two pigs divided into seven groups were used in the experiment. Two groups received a single infection by either the Anhui or the Zhejiang isolate. In Challenge Groups 1, 4, 6, 8 and 12, a primary infection of the Zhejiang isolate was followed by a challenge infection with the Anhui isolate at week 1, 4, 6, 8 or 12 after the primary infection. In this way it was possible to determine whether worms recovered by perfusion originated from the primary or the challenge infection. Only the challenge infection at week 1 resulted in a higher worm burden when compared with a single primary infection with the Zhejiang isolate. The results showed that challenge worms were able to establish, and that the proportion of worms originating from challenge infection increased at the later challenge infections, however without an increase in the total number of worms. In addition, mixed pairs of the two isolates were found in all challenge-infected groups. The results indicate that pigs are able to mount a partial resistance against re-infection with S. japonicum by 4 weeks after a primary infection, but that worms of the challenge infections eventually replace the primary infection. The finding of mixed pairs of the two isolates indicates that worms of S. japonicum are either polygamous or able to wait in solitude for up to 12 weeks for a partner.     

Further studies on Capillaria philippinensis: development of the parasite in the Mongolian gerbil

Capillaria philippinensis larvae from the digestive tract of a Northern Luzon freshwater fish (Hypselotris bipartita) experimentally exposed to embryonated eggs, were given by stomach tube to Mongolian gerbils (Meriones unguiculatus). The larvae developed into adults within 10 to 11 days and female worms produced larvae within 13 to 14 days. These larvae developed into second generation adults by days 22 to 24 and the second generation females produced eggs that were present in the feces of the animal on the average 26 days after infection. Most females were oviparous but a few larviparous females were always present. The gerbils died on an average of 46 days after infection, with the highest numbers of worms recovered between days 36 and 46. All stages of the parasite were generally found at necropsy. Gerbils developed patent infections after receiving 2 or 3 laeval from fish, and 852 to 5,353 worms were recovered at necropsy. These studies show that autoinfection in an integral part of the life cycle of C. philippinensis, both initially and in maintaining the infection. The natural transmission of the parasite was demonstrated when H. bipartita from a lagoon in the endemic area were fed to gerbils and 3 became infected. The parasite can also be maintained in the laboratory by transfer of worms by stomach tube from the small intestines of an infected gerbil to a clean gerbil.     

Hymenolepis nana: Maturation in an immunosuppressed unnatural rat host

When eggs of the dwarf tapeworm Hymenolepis nana, cycled exclusively and directly through mice for more than 10 years, were inoculated into previously uninfected inbred Fischer (F344) strain rats, they failed to mature in the rat intestinal lumen. Eggs of H. nana inoculated into the rat developed normally into cysticercoids (cysts) in the intestinal tissue, but thereafter failed to mature in the lumen except when the host was treated with cortisone acetate from the day of cyst maturation. The Fischer rat initially given eggs of H. nana became completely immune to egg challenge within 2 days of egg inoculation; no cysts derived from challenge eggs were found in the immunized rat. Immunosuppression, assessed by the success of cyst recovery in the tissue 4 days after egg challenge, had no promotive effect on the recovery of adult worms derived from eggs initially inoculated. Rats initially given eggs and immunosuppressed by cyclophosphamide or antithymocyte serum did not harbor any adult worms. Cortisone acetate treatment which was sufficient for eggs inoculated to mature (a total of 75 or even 200 mg, from Day 5 of egg inoculation) had no effects of immunosuppression, whereas cortisone acetate treatment which was sufficient for immunosuppression (a total of 150 mg from Day -2, two days prior to the initial egg inoculation) induced some adult formation as well. In addition, when mouse-derived cysts were inoculated into the rat instead of eggs, they also failed completely to mature even when the rat was treated with cyclophosphamide or antithimocyte serum. However, when the rat was treated with cortisone acetate from the day of cyst inoculation, the cysts developed into adult worms. Therefore, these results indicate that the Fischer rat clearly differs in its susceptibility to the tissue phase of egg inoculation and to the lumen phase of cyst inoculation of H. nana, and strongly suggest that the failure of maturation of H. nana in the unnatural host Fischer rat is not attributed to innate and/ or acquired immunity of the rat but to other nonimmunological mechanisms.     

Embryonation and Infectivity of Ascaris suum Eggs. A Comparison of Eggs Collected from Worm Uteri with Eggs Isolated from Pig Faeces

Ascaris suum eggs were collected from pig faeces or dissected from worms obtained from the same pigs. Eggs from the two sources were allowed to embryonate in 0.1 N H2SO4, in 1 % buffered formalin or in tap water. The embryonation of the sulphuric acid and water cultures occurred at the same speed, while the formalin cultures developed slightly more slowly. By experimental inoculation of helminthfree pigs and subsequent counting of white spots in the livers and larvae in the lungs day 7 p. i., the infectivity of eggs dissected from worm uteri and embryonated in sulphuric acid (a normal laboratory procedure) was compared with that of eggs collected from faeces and embryonated in water (i.e. more naturally developed eggs). The results suggest that the two types of eggs were equally infective. For this reason the common practice of using Ascaris eggs dissected from worms for experimental infections might be acceptable.     

Dipetalonema viteae: primary, secondary and tertiary infections in hamsters.

Hamsters were given primary infections of 100, 200, and 300 D. viteae larvae and groups killed at various intervals after infection. In addition, hamsters were sequentially infected with 100, 200, and 300 larvae and groups killed at 100 or 75 days after the secondary and tertiary infection, respectively. Blood microfilariae were detected on Day 60 following a primary infection, reached a maximum on Day 75, declined to low levels by Day 105, and were negative on Day 120. No microfilariae reappeared in the blood of hamsters given secondary or tertiary infections.Between 20–30% of the infecting larval dose had reached the adult stage by Days 75 or 100 postinfection in hamsters given primary, secondary, or tertiary infections. There was no evidence of arrested larval development in hamsters receiving a second or third challenge infection. Almost half of the tertiary infection hamsters developed subcutaneous nodules and their numbers varied greatly among individual animals. The nodules variously contained living worms, pus, and fragmented worms, or pus only. Hamsters given primary infections of 100, 200, or 300 larvae and killed 375 days after infection had no subcutaneous nodules; however, hamsters given the 200 and 300 larval infections were seen to have dead worms in the subcutaneous tissues. No stunting of adult worms was noted and all female worms had uteri packed with microfilariae.     

Induction of lymphatic lesions by Brugia pahangi in jirds with large and small preexisting homologous intraperitoneal infections

The effect of intraperitoneal (i.p.) infections induced by inoculations of 30 or 150 Brugia pahangi third-stage larvae (L3) on the development of infections and lymphatic lesions induced by subsequent homologous subcutaneous (s.c.) inoculations were compared in the present study. Lymphatic lesion severity, as judged by the numbers of lymph thrombi present, and lymphatic lesion scores were significantly reduced in both groups of jirds with existing i.p. infections. The numbers of adult worms that developed, locations of these worms, and the subsequent microfilaremias did not differ significantly between groups. All jirds with i.p. infections developed similar antibody titers to crude somatic adult antigen as measured by ELISA. These levels did not change following s.c. infections. Immediate and delayed footpad swelling responses were also similar in all groups. Results of these experiments support and extend previous studies indicating that i.p. infections of B. pahangi induce a hyporesponsive state in jirds to subsequent s.c. infections without significantly affecting the subsequent parasite burden. This effect appears to be independent of the numbers of L3 inoculated i.p. prior to lymphatic-induced infection. Circulating antibody titers and footpad swelling responses to B. pahangi antigen were not reduced in jirds with the hyporesponsive lymphatic inflammatory response and do not correlate with this condition.     

In vitro and in vivo studies on the bioactivity of a ginger (Zingiber officinale) extract towards adult schistosomes and their egg production

The bioactivity of an ethyl acetate extract of ginger (Zingiber officinale) towards Schistosoma mansoni adult pairs, both cultured in vitro and in vivo in laboratory mice, was investigated by monitoring worm mortality and fecundity. In vitro, a concentration of 200 mg l(-1) of extract killed almost all worms within 24 h. Male worms seemed more susceptible than female under these conditions. Cumulative egg output of surviving worm pairs in vitro was considerably reduced when exposed to the extract. For example, after 4 days of exposure to 50 mg l(-1), cumulative egg output was only 0.38 eggs per worm pair compared with 36.35 for untreated worms. In vivo efficacy of the extract was tested by oral and subcutaneous delivery of 150 mg kg(-1) followed by assessment of worm survival and fecundity. Neither delivery route produced any significant reduction in worm numbers compared with untreated controls. Worm fecundity was assessed in vivo by cumulative egg counts per liver at 55 days post infection with mice treated subcutaneously. Such infections showed egg levels in the liver of about 2000 eggs per worm pair in 55 days, in both treated and control mice, with no significant difference between the two groups. To ensure that density-dependent effects did not confound this analysis, a separate experiment demonstrated no such influence on egg output per worm pair, at intensities between 1 and 23 worms per mouse.     

In vivo and in vitro egg production by Nematospiroides dubius during primary and challenge infections in resistant and susceptible strains of mice

Experiments were conducted to examine adult worm burdens, fecal egg output, and in vitro fecundity of Nematospiroides dubius in resistant LAF1 and susceptible CBA mice 12, 15, 18, and 21 days following primary and challenge infections. A strong correlation was obtained on the number of eggs produced by worms cultured in vitro and the egg production as assessed by fecal egg count. Worm counts, fecal egg counts, and in vitro fecundity were similar on all days studied following a primary infection in both mouse strains. However, after challenge infection, LAF1 mice showed lower worm burdens, fecal egg output, and in vitro egg production when compared to CBA mice. Although the egg production of surviving female worms from immune LAF1 mice was decreased, it never fell below a threshold of 100 eggs/day. The reduced fecundity may be a manifestation of a general anti-worm response rather than responses directed specifically at worm reproduction.