Acquired immunity to Toxocara canis infection in mice

Acquired immunity develops against Toxocara canis infection in mice, and NIH mice are more immunoresponsive than CD1 mice. Twice infected NIH female mice showed 27% reduction in the total larval recoveries compared with non-sensitized controls. Twice-infected NIH male, and CD1 (both sexes) mice showed a negligible reduction in the total recoveries, though a significant (P less than 0.05) number of larvae were retained in the liver compared with the non-sensitized controls. All twice-infected mice showed a significant reduction in the number of larvae recovered from the brain compared with once-infected mice. Vaccination using ultraviolet irradiated embryonated eggs gave the best protection against reinfection. Excretory/secretory antigen afforded less protection, whilst whole adult worm vaccine and whole L2 culture vaccine gave no protection. Vaccinated mice had a higher 'free:penetrating ratio' of larvae in their intestine than similarly challenged but non-vaccinated mice. When the ileum was examined histologically 9 h post-infection, an inflammatory reaction was seen around the penetrating larvae in the sensitized and vaccinated mice but not in untreated controls, suggesting a role played by the intestine in the resistance against T. canis infection in mice.     

Orbital cellulitis associated with Toxocara canis in a dog

Reports of Toxocara canis ocular larva migrans are uncommon in animals, with only a few cases reported. Most reports involve larval migration into the retina and choroid, with parasitic invasion of the orbit reported only in experimental studies. This is the first clinical case of Toxocara canis infection in the retrobulbar region of a 10-year-old, cross-bred male dog presenting with unilateral orbital cellulitis. Ophthalmic signs included protrusion of the nictitating membrane, chemosis, exophthalmos and hypertropia. The parasite was diagnosed by histologic and parasitologic examination of orbital tissues, which were removed during enucleation.     

Larval development of Toxocara canis in dogs

The parasitic roundworm Toxocara canis is present in dog populations all over the world. Due to its zoonotic potential, this roundworm is of special interest not only for veterinarians, but also for medical practitioners. In the present review, current knowledge of infection routes and the subsequent development of larvae within the canine host is summarised. Furthermore, information about the clinical, pathological, enzymatic, haematological and histopathological changes was collected, giving a broad overview of current knowledge of the infection. Although the data collected over the years give an idea of what happens during the larval development of T. canis, many questions remain open. Nevertheless, it is important that we continue our efforts to further understand the biology of this versatile and compelling parasite and try to improve and optimise strategies to prevent the infection in dogs and thereby to protect humans from this infection.     

Transplanted infections with Toxocara canis as a model for the effectiveness testing of anthelmintics

Patent infections of adult dogs with Toxocara canis induced by transplantation of immature, intestinal stages were examined for their suitability for testing of anthelmintics. Each of 5 dogs were infected four times by transplantation of 80 immature, intestinal stages of Toxocara canis. The dogs were treated with various anthelmintics of well established efficacy (pyrantel, nitroscanate, mebendazole, piperazine) 20 dpi. All anthelmintics tested showed the same efficacy as had been assessed earlier by treatment of dogs infected prenatally with Toxocara canis.     

Seroprevalence of Toxocara canis in sheep in Wales

Antibody levels to Toxocara canis L2 excretory/secretory antigens were examined by ELISA in 400 serum samples from sheep in Powys and Gwent, Wales. A positive OD value was set at the mean +/-3S.D. of 45 control samples. Seroprevalence increased with age. Seven percent and 13% of 6-month-old sheep showed positive OD values as did 16% of 10-month-old, 27% and 31% of 15-month-old and 47% of cull ewes. Analysis of variance showed a significant increase in ELISA OD values among the seropositive sheep with increasing age of sheep.     

Behavior and pathogenicity of larva of Toxocara canis Werner 1782 (Anisakidae) in the mouse

To evaluate the interdependence between pathological changes and the level of infection the behaviour of Toxocara canis larvae in the host, the course of the disease as well as quality and quantity of histological changes were investigated after experimental infection with 1,000, 500, 250, and 125 larvae respectively. The main places where the larvae of Toxocara canis were found at any time after infection were musculature and brain. Regardless of the level of infection the absolute and relative number of larvae in the brain increased linearly, and parallel decreased in musculature. After the 60th day post infection the mice infected with 1,000 larvae showed compulsive movements, disturbance of equilibrium and paralysis of the hindlegs. The mice infected with 500 larvae showed similar symptoms 30 to 40 days later. Mice with weaker infections only showed slight disturbances of the general condition at the end of the trials. In the brain of all animals infected with larvae of Toxocara canis inflammatory reactions were found. Severe destructive changes in the nervous substance together with clinical symptoms were seen only in higher infected mice.     

Contamination of dog hair with eggs of Toxocara canis

Toxocara canis, the common intestinal nematode of dogs and foxes, is the parasite responsible for human toxocarosis. It has recently been shown that dogs may harbour eggs of the parasite in their fur. To further investigate this claim a population of 100 stray dogs was examined to establish the prevalence and intensity of adult toxocaral worm infection in the intestines and eggs harboured in the hair. A novel method of washing the eggs from the hair was used. Sixty-seven percent of dogs were found to have T. canis eggs on their hair with a mean egg retrieval of nearly 584 eggs per gram from positive dogs. The age of the dog was found to be the only significant factor to influence the prevalence and intensity of eggs, with 95% of all the eggs recovered found on puppies. Thirty-nine percent of dogs were found to have adult T. canis worms in their intestine, although a significantly higher percentage of puppies (80%) were infected with worms than adults (22.5%). Puppies also had more worms per infection than adults and have a strong positive correlation between egg and worms numbers whereas adults did not. These studies show that stray dogs, particularly puppies, potentially harbour considerable numbers of eggs on their hair, at densities far higher than those reported in the soil or the general environment.     

Variations in innate resistance to experimental Toxocara canis infection in two strains of mice

Strain-, sex- and age-based resistance of mice to Toxocara canis infection was demonstrated. Infection doses of similar numbers resulted in significantly (P less than 0.05) greater worm establishment in CD1 mice than in NIH mice, as well as a greater heterogeneity of responses between individuals. Male mice had significantly (P less than 0.05) fewer larvae in the brain and more larvae in the liver than female mice, when mice of greater than or equal to 3 months old were used. Appreciably more larvae were retained in the liver of male CD1 mice than in NIH mice. Orchidectomized mice had higher levels of brain infestation and a lower larval recovery from the liver compared with intact male mice. Infections in young mice of both strains showed more diversity in establishment and migration pattern between individuals than in older mice. Despite these differences in distribution of larvae and in the numbers recovered from experimental infections, the acute and chronic clinical signs observed in the two strains were very similar.     

Toxocara canis: proteinases in perivitelline fluid from hatching eggs

Developing larvae of Toxocara canis may secrete several kinds of enzymes within the egg perivitelline fluid (EPF) prior to and during hatching. In particular, proteinases in EPF could play a role in larval emergence within the host gastrointestinal lumen but its presence and nature is unknown. In this work, proteolytic activities in hatching fluid of T. canis were identified and analysed by substrate gel electrophoresis at different pH values and by using type specific protease inhibitors. Three bands of 91, 68 and 38 kDa showed gelatinolytic activity and all proteinase activity from EPF was of the aspartic-type since it was inhibited by pepstatin A. Interestingly, a significantly higher proteolytic activity was observed at acidic pH (< or =5.5). These data suggest that T. canis developmentally secretes and accumulates in EPF aspartic proteinases with a pH-dependent activity that might help the parasite to take advantage of conditions in the host gastrointestinal microenvironment where egg hatching is induced and executed.     

犬弓首蛔虫TcCPG1的表达及其与几丁质的结合特性

为探讨犬弓首蛔虫（Toxocara canis,T.canis）软骨素蛋白多糖TcCPG1的表达特征及其与几丁质的结合方式,为犬弓首蛔虫软骨素蛋白多糖的功能研究提供依据,笔者克隆T.canis软骨素蛋白多糖1基因（Tc-cpg-1）并原核表达重组蛋白TcCPG1,采用镍柱亲和层析技术对重组蛋白进行纯化,并与几丁质进行结合试验;采用实时荧光定量PCR（quantitative real-time polymerase chain reaction,qRT-PCR）进行Tc-cpg-1基因的转录水平的性别和组织差异表达分析。结果显示：Tc-cpg-1基因编码区（coding sequence,CDS）的长度为1 251 bp,共编码417个氨基酸;SDS-PAGE电泳结果显示重组蛋白TcCPG1以包涵体形式存在,相对分子质量大小约为70 ku;对表达条件进行优化后,以0.8 mmol·L^-1 IPTG于16℃诱导14 h时可获得大量目的蛋白;利用镍柱亲和层析纯化可以获得具有较高纯度的目的蛋白,与几丁质进行结合试验,验证了重组蛋白TcCPG1能够与几丁质结合;通过qRT-PCR对Tc-cpg-1基因转录水平的组织差异性进行分析,发现Tc-cpg-1在雌虫中高量表达,尤其在雌虫的生殖组织中表达量最高,表明Tc-cpg-1可能参与了T.canis雌虫的生殖过程,推测TcCPG1可能通过与卵壳中几丁质的相互作用从而影响T.canis的胚胎和生殖发育过程。     

犬弓首蛔虫ITS1基因的克隆及序列分析

通过对国内5个犬弓首蛔虫株(T.canis)即GD株、CQ株、YN株、HN株和GZ株的rDNA的内转录间隔区Ⅰ(ITS1)序列进行PCR扩增、克隆、测序和序列分析,旨在确定ITS1是否可作为T.canis分子分类的遗传标记。结果显示:GD株、CQ株、YN株、HN株和GZ株的ITS1序列基本一致,仅GD株有2个碱基的差异,HN株和GY株分别有1个碱基的差异;与GenBank中登录的T.canis(序列号为AB110024、AB110026)的ITS1序列同源性高达98.9%～99.4%。结果表明ITS1可作为分子标记用于T.canis与其它蛔虫的种间鉴定,但不适合用于T.canis种内遗传变异的研究,为进一步的分子遗传学和分子诊断学研究奠定基础。     

Experimental Toxocara canis infection in cynomolgus macaques (Macaca fascicularis)

Visceral larva migrans was produced in 16 cynomolgus macaques (Macaca fascicularis) experimentally inoculated with 45,000 embryonated eggs of Toxocara canis as a single bolus or in 3 divided doses. The hematologic and serologic changes were similar to those observed in children with visceral Toxocara infection. Neurologic signs developed in 3 animals and were characterized by ataxia and nystagmus. Growth rates were diminished in inoculated animals when compared with the rates in noninoculated controls. Diagnostic antibody titers as measured by enzyme-linked immunosorbent assay were noted in all inoculated macaques by the 4th week, and these titers persisted during the 7-month period of observation. Antibody to Toxocara was not detected in the aqueous or vitreous humors. Lesions comprised severe granulomatous hepatitis and encephalomyelitis. Intraocular lesions associated with larval migration were not observed.     

Immunity to Toxocara vitulorum repeated infections in a rabbit model.

Eleven rabbits were infected with 10 embryonated eggs of Toxocara vitulorum per g body weight on Days 0, 35 and 72. Embryonated eggs and larvae were enumerated in feces on Days 1-3 after each infection. Two rabbits were killed and larvae were enumerated in small intestine, liver, lungs, skeletal muscles, heart, kidney, brain, eye, uterus, and mammary glands on Days 5, 15, 30, 65 and 101. Serum was obtained on Days 0, 5, 15, 30, 42, 50, 65, 78, 86 and 101 to perform enzyme-linked immunosorbent assays (ELISAs) and Western blots against an extract of embryonated eggs. Between 4 and 10% of the administered parasites, almost all embryonated eggs, were found in the feces after the first or second infection, but 32% (27% of them larvae) after the third. Yields of tissue parasites were 4.1% of the administered dose on Day 5, 2% on Day 15, and 0.8% on Day 30 of the first infection, 0.1% on Day 30 of the second infection, and 0.06% on Day 30 of the third. Larvae were found only in liver, lungs and muscle, including heart. Larva content declined steadily in liver and lungs from Day 5 to 30 of the first infection, was absent in the liver at Day 30 of the second, and in both organs at Day 30 of the third. Muscle larva content increased from Day 15 to 30 of the first infection, and persisted throughout the third infection. Production of IgM antibody was minimal, IgG and the sum of IgMGA antibodies increased slightly or moderately after the first and second infections, but dramatically after the third. Western blots revealed the first antigens (12) by Day 15 of the first infection. Their total number increased with time and number of infections, but some antigens disappeared, whereas new antigens appeared in the course of the observations. Four antigens (32,500-41,000 mol.wt.) may be related to protection. Comparison of the Western blot patterns of two rabbits showed differences in the antigens, recognizable for each rabbit.     

Experimental infection of Japanese quail with Toxocara canis larvae through earthworms

The migration and distribution of Toxocara canis larvae in the tissues of earthworms exposed to 5 x 10(5) infective eggs in soil, as well as the reinfectivity of the larvae in Japanese quail fed with three earthworms, were studied. The average number of larvae recovered from an earthworm gradually declined from 9 +/- 3.21 to 4.5 +/- 2.00 at 4-16 days. No larvae were recovered at Day 20. When compared between three portions of the earthworms' body, the middle part showed the greatest recovery in comparison with the anterior and posterior parts. At necropsy, the average larval burden of quail at 15 days post-infection was 6 +/- 3.60 in the liver and no larvae were recovered from other tissues. The role of the earthworm in relation to paratenism is discussed.