Effect of egg dosage and host genotype on liver trapping in murine larval toxocariasis

In this study we examined the effect of various initial sensitizing doses of infective Toxocara canis eggs and the effect of murine host genotype on the level of trapping of larvae in the liver after larval challenge. In the initial experiments, C57BL/6J mice were infected with a sensitization dose of 5, 25, 75, 125, or 250 infective T. canis eggs on day 0 postinfection (PI). On day 28 PI all mice were challenged with 500 infective eggs. On days 7, 14, and 21 postchallenge (PC) larval numbers within individual livers were determined. Trapping of larvae was observed in mice receiving a sensitization dose of 25 or more eggs. At 7 and 14 days PC the level of trapping increased with sensitization egg dose up to a dose of 125 eggs. At 21 days PC the level of trapping reached a plateau at a sensitization dose of 75 eggs. The peak level of larval trapping was observed on day 7 and day 14 PC following sensitization doses of 125 and 250 eggs, respectively. In the subsequent experiments, mice of various strains and H-2 haplotypes were inoculated with an initial sensitization dose of 125 eggs and a challenge dose of 500 eggs on day 0 and day 28 PI, respectively. Larval trapping within the liver was determined on day 14 PC. C57BL/6J mice trapped significantly more larvae than DBA/2J mice (P less than 0.01); all other strains trapped larvae at a lower, but statistically similar, level to the C57BL6/J mice.(ABSTRACT TRUNCATED AT 250 WORDS)     

Experimental heteroxenous cycle of Lagochilascaris minor Leiper, 1909 (Nematoda: Ascarididae) in white mice and in cats.

Reports of natural infections of sylvatic carnivores by adult worms of species similar to Lagochilascaris minor in the Neotropical region led to attempts to establish experimental cycles in laboratory mice and in cats. Also, larval development was seen in the skeletal muscle of an agouti (Dasyprocta leporina) infected per os with incubated eggs of the parasite obtained from a human case. In cats, adult worms develop and fertile eggs are expelled in the feces; in mice, larval stages of the parasite develop, and are encapsulate in the skeletal muscle, and in the adipose and subcutaneous connective tissue. From our observations, we conclude that the larva infective for the mouse is the early 3rd stage, while for the final host the infective form is the later 3rd stage. A single moult was seen in the mouse, giving rise to a small population of 4th stage larvae, long after the initial infection.     

Comparative efficacy of ivermectin and levamisole for reduction of migrating and encapsulated larvae of Baylisascaris transfuga in mice

The comparative efficacy of 2 anthelmintics (ivermectin and levamisole) against Baylisascaris transfuga migrating and encapsulated larvae was studied in mice. A total of 60 BALB/c mice inoculated each with about 1,000 embryonated B. transfuga eggs were equally divided into 6 groups (A-F) randomly. Mice of groups A and B were treated with ivermectin and levamisole, respectively, on day 3 post-infection (PI). Mice of groups A-C were killed on day 13 PI. Similarly, groups D and E were treated with ivermectin and levamisole, respectively, on day 14 PI, and all mice of groups D-F were treated on day 24 PI. The groups C and F were controls. Microexamination was conducted to count the larvae recovering from each mouse. The percentages of reduction in the number of migrating larvae recovered from group A (ivermectin) and B (levamisole) were 88.3% and 81.1%, respectively. In addition, the reduction in encapsulated larvae counts achieved by ivermectin (group D) and levamisole (group E) was 75.0% and 49.2%, respectively. The results suggested that, to a certain extent, both anthelmintics appeared to be more effective against migrating larvae than encapsulated larvae. However, in the incipient stage of infection, ivermectin may be more competent than levamisole as a larvicidal drug for B. transfuga.     

Kinetics of liver trapping of infective larvae in murine toxocariasis

Mice sensitized by prior infection with Toxocara canis eggs trap many larvae of a challenge infection within the liver. In this study the distribution of challenge larvae in sensitized mice was examined to determine the earliest onset of liver trapping and to establish if the previously described phenomenon truly represented larval trapping. In all experiments, C57BL/6J mice were infected with a sensitization dose of 125 infective T. canis eggs on day 0 postinfection (PI) and challenged with 500 infective eggs on day 28 PI. In the initial experiments, larval numbers were determined within the intestinal contents, intestinal wall, mesenteric tissues, liver, lungs, skeletal muscle, and brain of each mouse on days 0.5, 1, 2, 3, 5, and 6 postchallenge (PC). Migration patterns were similar among the test and control groups except the peak of larval numbers in the liver, seen at 1 day PC in control mice, was delayed until 3 days PC in the test group. Larval trapping occurred within the liver of test mice at least by day 5 PC. In subsequent experiments, larval numbers were determined within the liver, skeletal muscle, brain of each mouse, and within the eyes of each mouse group at 4, 8, 12, and 16 wk PC. Larval numbers within the liver of test mice were similar both at 5 days PC and 16 wk PC, implying that larvae were trapped in this organ rather than delayed in their migration to other body sites. Liver trapping did not protect the eyes or brain of sensitized mice from larval migration, nor did it result in larval killing.     

A contribution to the study of acute schistosomiasis (an experimental trial)

In an attempt to establish an experimental model of acute schistosomiasis, sequential histological changes were investigated in the skin, lung, liver and spleen of mice infected with 30 or 100 cercariae of Schistosoma mansoni according to four sets of experiments: single infection, repeated infections, unisexual infection and infection in mice born from infected mothers. Animals were killed every other day from exposure up to 50 days after infection. Only mild, isolated, focal inflammatory changes were found before the appearance of mature eggs in the liver, even when repeated infections were made. Severe changes of reactive hepatitis and splenitis appeared suddenly when the first mature eggs were deposited, around the 37th to 42nd day after infection. The mature eggs induced lytic and coagulative necrosis of hepatocytes around them which was soon followed by dense infiltration of eosinophils. So, mature egg-induced lesions appeared as the major factors in the pathogenesis of acute schistosomiasis in mice. Mice born from infected mothers were apparently able to rapidly modulate the egg-lesions, forming early fibrotic granulomas. The murine model of acute schistosomiasis appeared adequate for the study of pathology and pathogenesis of acute schistosomiasis.     

Observations on Toxocara pteropodis infections in mice

Infection in mice with Toxocara pteropodis was investigated. In mice fed infective eggs, third-stage larvae hatched out and penetrated the mucosa, predominantly that of the lower intestine. They travelled via the portal vein to the liver, where they remained at least 14 months. They grew in length from 430 +/- 15 micron, at three days post infection (p.i.), to 600 +/- 50 micron, at six to nine weeks p.i., after which time growth ceased. Blood eosinophilia appeared at 28 days p.i., and eosinophil levels continued to rise gradually beyond this time. In female mice the larvae did not migrate from the liver in response to pregnancy or lactation. When infective eggs were inoculated subcutaneously or intra-peritoneally, larvae hatched out and ultimately appeared in the liver in larger numbers than seen with oral infections.     

Larval migration in oral and parenteral Toxocara pteropodis infections and a comparison with T. canis dispersal in the flying fox, Pteropus poliocephalus

When eggs of T. pteropodis were fed in large doses to juveniles of a definitive host, Pteropus poliocephalus, larvae hatched throughout the gastrointestinal tract. The majority penetrated the mucosa of the distal half of the intestine, to reach the liver via the portal circulation. A few entered the lymphatics to eventually reach the liver by passing through the lungs and migrating tracheally or continuing in the systemic circulation. Patent infections did not develop. Eggs inoculated subcutaneously also hatched and larvae again reached the liver, travelling via the circulation through the lungs and often other tissues; again, some underwent tracheal migration. Infective larvae of T. canis, identical in size with T. pteropodis, passed through the liver and lungs and dispersed mainly to skeletal muscles, but with time gradually accumulated in the brain. These findings indicate that Toxocara larval distribution is not primarily influenced by larval dimensions but reflects goal-directed behaviour.     

Effects of irradiation on the biology of the infective larvae of Toxocara canis in the mouse

Mice were infected with either 2,000 normal or irradiated embryonated eggs of Toxocara canis and the number of larvae in their livers, lungs, brains, and carcasses investigated at 5, 20, and 33 days of infection. Mortality of mice infected with normal eggs was 33% between day 4 and 8 postinfection but there was no mortality among mice infected with irradiated eggs. Irradiation with 60, 90, or 150 kr of X-rays inhibited the migration of larvae from the livers and lungs and their accumulation in brain and carcass in proportion to the irradiation dose. By day 33 of infection, the ratio of larvae in liver and lungs to larvae in brain and carcass was 0.16 in normal mice, 0.42 in 60-kr mice, 0.98 in 90-kr mice, and 23.3 in 150-kr mice. Irradiated larvae, particularly those migrating through the peritoneal cavity, died faster than normal larvae until day 20. Irradiation favored survival after day 20. By days 20 and 33 postinfection the total parasite load was 29% and 8%, respectively, of the administered dose in control mice, 18% and 12% in 60-kr mice, 8% and 4% in 90-kr mice, and 0.9% and 0.3% in 150-kr mice. Irradiation of infective T. canis larvae, then, reduces their pathogenicity, inhibits their migration from liver and lungs, kills some of the parasites during the first 3 weeks of infection, but favors their late survival in the host.     

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.     

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.     

Ascaris suum: protective immunity in pigs immunized with products from eggs and larvae

Parasite products were collected at three distinct phases of development of Ascaris suum, and their immunogenicity was determined after injection into rabbits and pigs. Products were derived from (1) the hatching fluid of infective eggs; (2) the conditioned medium of 2nd-stage larvae that developed to 3rd stage in vitro in defined medium; and (3) the conditioned medium of 3rd-stage larvae that developed to 4th stage in vitro in defined medium. Protein profiles from these three preparations, separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, were less complex than that of extracts from homogenized A. suum larvae. Hyperimmune rabbit antiserum raised against either egg products, 2nd- to 3rd-stage larval excretory-secretory products, or 3rd- to 4th-stage larval excretory-secretory products showed strong homologous reactions after immunoelectrophoresis, but relatively weak cross-reactions with the other preparations. A combined enteral immunization of pigs with egg products and parenteral immunization with the 2nd- to 3rd-stage larval excretory-secretory products, and 3rd- to 4th-stage larval excretory-secretory products induced antibody to each preparation and significant protective immunity to a challenge exposure with 10,000 A. suum eggs. However, a marked pathological response to larvae migrating in the liver after challenge exposure was also induced.     

Mouse strain difference in visceral larva migrans of Toxocara canis

The mode of larval migration (visceral larva migrans) in Toxocara canis infection was compared for BALB/c, C57BL/6, C3H/He, DBA/2, NC and BALB/c nude mice following oral infection with 400 eggs. The mean recovery of larvae from the liver on day 2 post infection (PI) was not different in terms of the strain, age or sex of the mice. The number of larvae recovered from the liver decreased in all strains on days 6, 12 and 21 PI, but the mean for BALB/c and (NC X BALB/c) F1 mice was significantly higher than that for C567BL/6, NC and BALB/c nude mice, unless the total number of larvae in the carcasses on day 21 PI was the same among those strains including athymic nude mice. The mean recovery of larvae from the liver on day 6 PI increased with age in both NC and BALB/c mice, although no sex difference was observed. From these results, it is emphasized that the age and strain of animals should be properly selected for animal experimentation with T. canis infection.     

Alternative migration routes of Ascaris suum in the pig

Experiments were conducted to investigate possible alternative routes of extraintestinal migration of Ascaris suum larvae in the pig. Pigs were infected with A. suum via injection of newly hatched larvae into cecal veins (i.v.), into cecal lymph nodes (LN), or intraperitoneally (i.p.), and control animals were inoculated orally with infective eggs (p.o.). Two pigs per inoculation route were necropsied on days 1, 4, and 13 postinoculation. The numbers of liver lesions and the percentage of larvae recovered was considerably greater in pigs inoculated i.v. or p.o. on each necropsy day. However, irrespective of inoculation route, at least a proportion of larvae passed through the livers and were able to complete migration to the small intestine by day 13. The results indicate that larval penetration of the intestinal wall is not necessary for liver-lung migration and that passage through the liver may be favorable for migrating A. suum larvae, although a delayed arrival in the small intestine cannot be ruled out for larvae following alternative routes.     

Manifestations of resistance to Haemonchus contortus in sheep: Worm populations and abomasal changes in sheep superinfected with 1,000,000 larvae of H. contortus

The super-infecting dose produced a marked rise in gastric pH in all sheep from the 3rd day after administration of larvae. Expulsion of the existing population of adult worms may have begun on the 4th day but was still only completed in 3/6 sheep on the 5th day. The larvae caused extensive damage in the individual glands which they parasitised. Very few of the 10⁶ larvae survived for 27 days and only in 1/8 sheep had they developed beyond early 4th stage at 27 days. Extensive histological changes were seen in the fundic mucosa beginning as early as 2 days after the superinfection. While the pH change preceded expulsion of the adults and was consistent in its timing, the timing of the expulsion was irregular. This throws doubt on the hypothesis that the change in physico-chemical conditions produced by the superinfecting larvae is the only cause of the expulsion of the adult worms.     

Effects of immunoactivity on Ascaris suum infection in mice]

The immune response to sheep red blood cell (sRBC) was monitored in the mice infected with Ascaris suum or Trichinella spiralis. The effects of the infection with T. spiralis or the injection with cyclophosphamide(CY) as an immunosuppression agent prior to challenge infection with the embryonated eggs of A. suum were monitored in mice by means of the level of infection with A. suum and cellular and humoral immune response to sRBC. Following the oral administration of 1,000 eggs of A. suum to mice, delayed-type hypersensitivity (DTH) and rosette-forming rate were gradually decreased and reached to the lowest levels at the 5th week and 6th week postinfection, respectively, and then returned to normal at the 10th week. The hemagglutinin(HA) and hemolysin(HE) titers were gradually elevated and reached to peak at the 3rd week postinfection, and then returned to normal level. The appearance ratios of the eosinophils and mast cells were in peak at the 4th week and the 2nd week postinfection, respectively. Meanwhile the harvest ratio of A. suum larvae from the liver and lungs was 21.97% at the 1st week postinfection. Following the oral administration of 300 T. spiralis infective larvae, DTH and rosette-forming rate were gradually decreased with the lapse of time and reached the lowest values in the 30th and 21st day of postinfection, and then slightly increased and transiently decreased in the 70th and 80th day of postinfection, respectively. HA and HE titers were the lowest in the 21st and 90th day, whereas the ratios of eosinophils and mast cells were the highest on the 40th and 14th day postinfection, respectively. Following the intraperitoneal injection of CY, the body weight, the spleen weight, DTH, rosette-forming ratio, HA and HE titers, the number of WBC and the ratio of the mast cell were predominantly decreased in the 5th day, and then returned to the same value of the 1st day postinjection. The ratio of eosinophils was gradually decreased following to advance of days. At the 1st, 5th and 10th days after intraperitoneal injection of CY of 400 mg/kg, a dose with 1,000 eggs of A. suum was administered orally to mice, and harvest rate of the larvae at the 7th day postadministration was 7.07% in the 1st day, 14.94% in the 5th day, 10.1% in the 10th day, 8.02% in control group. The effect of prior infection with infective larvae of T. spiralis upon immunological sequelae of a challenge infection of mice with embryonated eggs of A. suum in 30 or 70 days interval was checked.(ABSTRACT TRUNCATED AT 400 WORDS)     

小黑瓢虫对高氏瘤粉虱捕食作用的研究

在高氏瘤粉虱不同虫态共存的条件下,小黑标虫对高氏瘤粉虱各虫态的选择次序为卵＞1龄若虫＞2龄若虫＞3龄若虫＞4龄若虫和拟蛹,对卵的捕食率均最高,有明显的嗜好选择;小黑瓢虫幼虫捕食粉虱卵的数量,随着龄期的增长而递增,其中4龄幼虫的捕食量最大,4龄期捕食量平均为1565．42粒,占全幼虫期总食卵量的45．42％,整个幼虫期可捕食高氏瘤粉虱的卵数平均为3446．5粒。小黑瓢虫3龄幼虫对粉虱卵的捕食作用率在所给的猎物密度（1500粒／皿）条件下,随着自身密度的增加而降低。     

Development of Angiostrongylus cantonensis in the lung of Achatina fulica (author's transl)

Twenty-four Achatina fulica from Pai-sha of the Pescardores Islands, where no Angiostrogylus cantonensis has been found in A. fulica(4), were inoculated with the first stage larvae of A cantonensis. One snail was killed every day after 24 days following inoculation. The lung of each snail was separated and examined for larvae under microscope. The same lung was then digested with pepsin. The larvae recovered after pepsin digestion were examined for more detailed morphology. This study confirmed that the first stage larvae of A. cantonensis passed through the respiratory pore to the lung of A. fulica and developed into infectious form (3rd stage larvae) in the lung. The second and third stage larvae were found in the lung on the 7th and 17th day respectively after inoculation. Worm capsules were found in the lung on the 12th day after inoculation and the size of capsule was in proportion to the duration of the infection.     

Endocrine interrelationship between the parasitoid Chelonus sp. and its host Trichoplusia ni

The egg-larval parasitoid Chelonus sp. induces the precocious onset of metamorphosis in the 4th (penultimate) stadium of its host Trichoplusia ni, emerges from the prepupa, and then feeds on it. Qualitative and quantitative changes in ecdysteroids and juvenile hormone were measured. Hemolymph of 3rd-to 4th-instar host larvae and the parasitoids they contained, as well as nonparasitized and parasitized eggs, were analyzed. In the host hemolymph a broad peak of ecdysteroids during molting into the 4th stadium and a continuous increase from day 2 (onset of precocious wandering) until day 4 (emergence of parasitoid) were observed; 20-hydroxyecdysone and 20,26-dihydroxyecdysone were predominant. The juvenile hormone titer fluctuated in the 3rd and early 4th stadium and fell to undetectable levels shortly before the precocious onset of wandering. The parasitoid's ecdysteroids started to increase on the molt to the 2nd instar (= early 4th instar of the host) and thereafter fluctuated on a high level, 20-hydroxyecdysone, 20,26-dihydroxy-ecdysone, and ecdysone being predominant. The juvenile hormone titer was high in late 1st-instar parasitoids, decreased to low levels at ecdysis into the 2nd instar, and increased again to high levels in the 2nd-instar larvae at the time when their shape changed from flat to cylindrical. After ecdysis to the 3rd instar the juvenile hormone titer fell. A comparison revealed that both ecdysteroids and juvenile hormone fluctuate independently in parasitoid and host at most stages, suggesting that the parasitoid produces its own hormones. The first data on ecdysteroids and juvenile hormones in the egg stage of a parasitoid/host system are reported. At the stage of eye pigmentation parasitized eggs contained more immunoreactive midpolar ecdysteroids than non-parasitized ones. 20-Hydroxyecdysone and 20,26-dihydroxyecdysone were the predominant ecdysteroids in both nonparasitized and parasitized eggs, but the latter contained several additional ecdysteroids which were not seen in nonparasitized eggs. The titer of juvenile hormone was similar in both. Shortly before hatching the ecdysteroids were low in parasitized and nonparasitized eggs, but the content of juvenile hormone was much higher in the former. At this stage the majority of parasitoids have already eclosed and teratocytes are released. The results of HPLC analysis indicated the presence of juvenile hormone III together with juvenile hormones I and II in parasitized eggs, but only juvenile hormones I and II in nonparasitized eggs.     

Evaluation of the co-agglutination test in diagnosis of experimental microsporidiosis

Microsporidiosis is an emerging and opportunistic infection associated with wide range of clinical syndromes in humans. Confirmation of the presence of microsporidia in different samples is laborious, costly and often difficult. The present study was designed to evaluate the utility of the Co-agglutination test (Co-A test) for detection of urinary, fecal and circulating microsporidial antigens in experimentally infected mice. One hundred and twenty male Swiss albino mice were divided into non infected control and infected experimental groups which were further subdivided into two equal subgroups; immunosuppressed and immunocompetent. Microsporidial spores were isolated from human stools and identified to be Encephalitozoon intestinalis by the molecular methods. They were used to infect each subgroup of mice, then their urine, stools and sera were collected at the 1st, 3rd, 5th, 7th and 9th days post-infection (PI). Co-A test, using prepared hyperimmune serum, was used to detect antigens in all samples collected. The cross reactivity of microsporidial hyperimmune sera with antigens of Cyclospora cyatenensis and Cryptosporidium parvum was investigated by Co-A test. The results showed that Co-A test was effective in detecting microsporidial antigen in stool of immunosuppressed infected mice from the 1st day PI, and in urine and serum from the 3rd day PI till the end of the study. In the immunocompetent subgroup, Co-A test detected microsporidial antigens in stool, serum and urine of mice from the 1st day, 3rd day and the 5th day PI, respectively till the end of the study, without cross reactivity with C. cyatenensis or C. parvum in both subgroups. Co-A test proved to be simple and suitable tool for detecting microsporidial antigen in different specimens and did not need sophisticated equipment. It is very practical under field or rural conditions and in poorly equipped clinical laboratories.     

Larval recovery of Toxocara canis in organs and tissues of experimentally infected Rattus norvegicus

The aim of this note was to record for the first time the recovery of Toxocara canis larvae from tissues and organs of Rattus norvegicus (Berkenhout, 1769), Wistar strain, until the 60th day after experimental infection. Rats were orally infected with embryonated T. canis eggs, killed on days 3, 5, 8, 10, 15, 30, and 60 after inoculation and larvae were recovered from liver, lungs, kidneys, brain, and carcass after acid digestion, showing a pattern of migration similar of that previously observed in mice.