Human Toxocarosis Research Articles

Differential serodiagnostics of Toxocara canis and Toxocara cati – is it possible?

One of the most common zoonotic helminth infections is caused by species in the genus Toxocara, particularly Toxocara canis and T. cati (Syn. T. mystax). However, their relative contribution to toxocarosis in humans remains largely unknown because causative larvae are seldom recovered and uncertainties regarding the validity of existing serological assays. In this study, we used sera from a pig model experimentally infected with T. canis and T. cati to evaluate whether a Western blot could discriminate between the two species. No proteins were observed that could be used as a diagnostic tool. In addition, a heterogenic protein pattern between individual hosts was found, which was most pronounced in the T. cati-infected pigs. There is therefore an urgent need to optimize and validate current methods or develop new species-specific serological methods in order to implement appropriate control measures.

Seroprevalence of human Toxocara infections in the Roma and non-Roma populations of Eastern Slovakia: a cross-sectional study.

Socioeconomic conditions and health of the Roma population, the most numerous minority in Europe, are worse than that of the non-Roma population. Information about the occurrence of human toxocarosis and other parasitic diseases in the Roma population is scarce or completely missing. The aim of this study was to map the seroprevalence of toxocarosis in the population living in segregated Roma settlements and to compare the data with the occurrence of antibodies in the non-Roma population of Eastern Slovakia. The seropositivity to Toxocara in 429 examined Roma inhabitants of segregated settlements reached 22·1%, while only 4/394 samples of the non-Roma population were found to be positive (odds ratio 27·7, P<0·0001). Headache, muscle pain, influenza-like symptoms and diarrhoea occurred significantly more often in seropositive persons than in seronegative individuals. In the Roma population positivity was not influenced by gender, level of education and poverty, but age, lack of sanitary facilities and heating with wood significantly increased the risk of infection. It can be assumed that besides the high prevalence of toxocarosis, other parasitic diseases and communicable diseases will also be more prevalent in the Roma population living in segregated settlements.

Risk of human toxocarosis in Poland due to Toxocara infection of dogs and cats.

The purpose of this paper was to present the current data on the risk of toxocarosis in humans in Poland and to give an overview of the clinical and diagnostic aspects of the disease. The number of reported clinical cases of Toxocara infection in children in Poland in medical literature has increased recently. The results of field surveys aimed to evaluate the soil contamination with geohelminth eggs conducted during the last few years showed that Toxocara is the most common zoonotic agent in urban public sites and in rural settlements. The questionnaire revealed rural inhabitants' low awareness of zoonotic parasite threats to humans. In particular parents should be advised as to what proper preventive measures to undertake to eliminate the toxocarosis risk factors for children in rural environment. Prevention of initial environment contamination with Toxocara canis and T. cati eggs, which includes proper treatment regimes to eliminate patent infections in dogs and cats and preventing pets from defecating in public areas and private households is vital. To provide the public with suitably presented information as well as pet owners with uniform recommendations, a close collaboration between veterinary and public health professionals is crucial.

Effect of low temperatures on the infectivity of Toxocara cati larvae parasitized in mouse tissues

Abstract The infectivity of Toxocara cati larvae in mouse tissues, following storage at 4 °C and −25 °C, was measured using a bioassay in mice. Tissues of donor mice infected with 30-day-old T. cati larvae were stored at 4 °C for 7 and 14 days, and at −25 °C for 24 hours, then tissue larvae were inoculated into recipient mice (n = 6/group). After 15 days, larval burden in recipient mice was assessed by digestion. In the control group, a mean of 42.0 % of the inoculated larvae were established in mice. Storage of tissues at 4 °C for 7 and 14 days did not affect larval infectivity; means of 43.5 % and 37.4 % of inoculated larvae, respectively, were established in mice. Larvae exposed to −25 °C for 24 hours did not establish in mice, except for one larva recovered from a single mouse. These results may support the potential of tissue larvae in livestock animals as a causative agent of human toxocarosis.

Characterization of somatic antigens of adult Toxocara canis by western blotting

Aim: The objective of this study was characterize the somatic soluble antigens of adult Toxocara canis (Tc-SA) by western blotting. Materials and Methods: T. canis worms were collected from the naturally infected pups after deworming. The somatic antigen was prepared as per standard procedure with slight modification. These antigens were separated using Sodium dodecyl sulphate-electrophoresis (SDS-PAGE). The specific reactivity of the Tc-SA proteins was checked against the serum of naturally infected dogs as well with the hyperimmune serum raised in the rabbit by western blotting. Results: On SDS-PAGE recovered proteins ranged in size from 44 to 300 kDa. The immuno-reactivity of the naturally infected dog sera with the Tc-SA antigens showed 12 prominent immunoreactive bands of distinct sizes at 28.61, 32.60, 38.10, 43.04, 49.99, 67.57, 73.22, 105.77, 144.74, 161.11, 177.84 and 196.31 kDa. The immuno-reactivity of the hyper immune serum raised in rabbits against Tc-SA antigens was observed with 10 prominent bands of distinct sizes at 17.11, 24.15, 34.83, 43.46, 52.47, 55.89, 67.57, 70, 74.60 and 105.6 kDa. Conclusions: Common antigens band were observed at 67 and 105 kDa. These antigens merit further evaluation as candidate for use in diagnosis of toxocarosis in humans and adult dogs.

Factors affecting disease manifestation of toxocarosis in humans: Genetics and environment

Toxocara canis is regarded as the main cause of human toxocarosis but the relative contribution of T. cati is probably underestimated; serological and other diagnostic methods used in most studies of this zoonotic disease do not distinguish between the two parasites. The definitive hosts for T. canis are caniidae. Pups generally have higher infection rates than adult animals and are a major source of eggs in the environment. Humans usually acquire T. canis infection by accidental ingestion of embryonated eggs or encapsulated larvae from the environment or contaminated food, such infections may lead to visceral larva migrans (VLM), ocular larva migrans (OLM) or covert toxocarosis (CT). Although a mixed Th1- and Th2-mediated immunological response, particularly with high levels of IgE and eosinophilia is observed, the underlying mechanisms of molecular and immunopathogenesis for the development of the symptomatic syndromes of VLM, OLM, or of asymptomatic CT are largely unclear. Studies have indicated that immunological defences against various infectious diseases may be highly influenced by complex interactions of environmental and host genetic factors e.g. MHC class I and II, also known as human leucocyte antigen (HLA). Toxocara spp. infections are associated with a polarized CD4+ Th2 response with high IgE levels and eosinophilia, mediated mainly by HLA class II molecules. Associations have been made between HLA class II and pathological severity and host genetic effects on exposure to infection. Recent research suggests Foxp3+ CD4+CD25+-expressing T regulatory (Treg) cells play a role in regulation of the immunopathology of granulomas in experimental toxocaral granulomatous hepatitis and in enhanced expression of TGF-β1, which is an important factor for the local survival and function of Treg observed during T. canis invasion in the mouse small intestine, liver, muscle, and brain. Since the potential susceptibility loci HLA class II molecules, are considered involved in the regulation of a Th2-dominant immunity which is highly controlled by Foxp3+ CD4+CD25+ Treg cells by stimulation through TGF-β1, which thus provides a beneficial environment to T. canis larvae but severe injuries to local organs. However, TGF-β1 variant Leu10Pro known to be involved in disease severity warrants further elucidation as this too may have a role in the severity of human toxocarosis. Exploration of TGF-β1 polymorphism, Foxp3+ CD4+CD25+ Treg cells, and MHC polymorphisms may allow insight into the contribution made by environmental and genetic factors in influencing disease syndrome type and severity in humans with toxocarosis.

Veterinary and public health aspects of Toxocara spp

Pet dogs and cats can play an important role in the transmission of zoonotic nematodes such as Toxocara canis and Toxocara cati, by excreting eggs directly into the human environment, without the involvement of vectors or intermediate hosts. Human toxocarosis remains a hazard despite the availability of highly effective anthelmintics for dogs and cats. A good understanding of the biology and epidemiology of these parasites, and the risk factors that lead to their transmission to humans is required for effective prevention strategies. In this respect, the maintenance of high quality continuing education for veterinarians and the provision of suitably presented information to pet owners are of priority importance. A closer collaboration between veterinary and public health professionals within the ‘One Health’ concept is also required.

Tolerance to low temperatures of Toxocara cati larvae in chicken muscle tissue

Infectivity of Toxocara cati larvae in muscle tissue of chickens after storage at 4°C and −25°C was assessed in a mouse bioassay to provide information on the risk of meat-borne toxocarosis. Muscle tissue samples of 30-day old T. cati infections were stored at 4°C for 14 and 28 days and at −25°C for 12, 24 and 48h, whereafter, larvae were released by digestion. For each experimental group, the released larvae were inoculated in six mice. After 15 days, mice were euthanized and larval burden was assessed by digestion. In the control group (no storage of the infected chicken meat), 47.9% of the inoculated larvae established in mice, whereas storage of meat at 4°C for 14 days or 28 days reduced the recovery to 24.1% or 3.3%, respectively. Muscle larvae exposed to −25°C for 12, 24 or 48h did not establish in the mice. The observation that larvae retain infective after refrigeration at exposure in 4°C for 28 days, emphasize the zoonotic potential of poultry meat as a causative agent of human toxocarosis.

Toxocara cati larvae persist and retain high infectivity in muscles of experimentally infected chickens

The distribution of Toxocara cati larvae in the organs of chickens (n=31), experimentally inoculated with 3000 embryonated eggs, was examined 1, 2, 3, 7, 29, 86 and 175–176days post-infection (dpi), and the infectivity of recovered larvae was evaluated by bioassay in mice. The duodenum, liver, lungs, heart, brain, pectoral muscles (white meat), and hindlimb muscles (red meat) of the chickens were HCl–pepsin digested for larval recovery. Larvae were recovered from all chickens [mean=220.4±114.9 (SD)], and although no decrease of total larval recovery was observed over time, predilection sites changed: liver (92.6% of larval recovery) at 1 dpi; lungs (77.3%) and liver (20.9%) at 2 dpi; lungs (80.8%), muscles (9.4%), and liver (8.5%) at 3 dpi; muscles (52.0%) and lungs (45.6%) at 7 dpi, whereafter most larvae were recovered from muscles: 29 dpi (99.5%), 86 dpi (99.3%) and 175–176 dpi (99.6%). In the bioassay, 52.9% of larvae from 175 to 176days old infections in chickens established in mice, which demonstrates that T. cati larvae retain infective in the muscles of chickens for half a year. These results highlight the zoonotic potential of poultry meat as a causative agent of human toxocarosis.

Diagnóstico de la toxocarosis humana

Human toxocarosis is an important parasitic zoonosis caused by larval stages of Toxocara species, the roundworms from dogs and cats. Larval migration through different soft tissues in the human generates several clinical entities in the patient, such as visceral larva migrans, ocular toxocarosis, and neurotoxocarosis. Definitive diagnosis by histopathological methods is very difficult or almost impossible and, nowadays, the diagnosis is usually made by clinical signs/symptoms, epidemiological background of the patient and the use of hematological and immunological tests which finally help to confirm the clinical suspicion of the illness. The purpose of this paper was to update the available knowledge on the use of different tools for both the diagnosis and following up of human toxocarosis.

Syndrome de détresse respiratoire aiguë secondaire à une infection àToxocara cati

Human toxocarosis is a helminthozoonosis due to the migration of toxocara species larvae throughout the human body. Lung manifestations vary and range from asymptomatic infection to severe disease. Dry cough and chest discomfort are the most common respiratory symptoms. Clinical manifestations include a transient form of Loeffler's syndrome or an eosinophilic pneumonia. We report a case of bilateral pneumonia in an 80 year old caucasian man who developed very rapidly an acute respiratory distress syndrome, with a PaO2/FiO2 ratio of 55, requiring mechanical ventilation and adrenergic support. There was an increased eosinophilia in both blood and bronchoalveolar lavage fluid. Positive toxocara serology and the clinical picture confirmed the diagnosis of the "visceral larva migrans" syndrome. Intravenous corticosteroid therapy produced a rapid rise in PaO2/FiO2 before the administration of specific treatment. A few cases of acute pneumonia requiring mechanical ventilation due to toxocara have been published but this is, to our knowledge, is the first reported case of ARDS with multi-organ failure.

Wild carnivores as source of zoonotic helminths in north-eastern Italy

Abstract Two hundreds and sixty red foxes, eighteen badgers and eight stone martens from north-eastern Italy were examined for zoonotic parasites by SCT, with particular attention to Trichinella sp. and Echinococcus multilocularis. No adult worms of E. multilocularis were observed in the intestine of red foxes or mustelids. Out of 223 fox faecal samples analysed by a commercial CA-ELISA, 5.8 % was positive to Echinococcus coproantigens. Trichinella sp. was detected by digestion of muscle in 1.2 % of examined foxes (2/172), but not in mustelids (0/11). Toxocara canis, responsible for human toxocarosis, resulted to be common in fox population (48.5 %). This parasite was found both in young (53.3 % of cubs and 61.9 % of sub-adults) and in adult animals (42.7 %). Other zoonotic parasites as Uncinaria stenocephala (52.3 %) and Trichuris vulpis (0.4 %) were detected in fox populations.

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.

Les helminthes transmissibles des carnivores domestiques à l’homme : évaluation des risques et stratégies de prévention

A wide range of parasites can infect carnivorous pets. Some are more significant than others, owing to their prevalence, their pathogenicity for animal hosts, or their capacity to cause human disease. This article focuses on roundworms (Toxocara spp.) and tapeworms (Echinococcus spp.), which are emerging public health hazards in France. When humans ingest infective Toxocara eggs, the eggs hatch and release larvae that can migrate anywhere in the body, causing a disease called visceral larva migrans. Common target organs are the eyes, brain, liver, and lungs, with a risk of permanent visual, neurological and other tissue damage. Epidemiological studies have identified geophagy and pet dogs (particularly puppies) as the principal risk factors for human toxocarosis. Childrens' play habits and their attraction to pets put them at a higher risk for infection than adults. Eggs of the dog tapeworm Echinococcus granulosus hatch and release embryos that migrate to various organs and form voluminous cysts, causing a disease called cystic echinococcosis. Human alveolar echinococcosis is caused by the larval stage of the fox tapeworm Echinococcus multilocularis, which usually develops in the liver. Larval growth is slow, resulting in an asymptomatic phase of several years before diagnosis. Left untreated, the condition may be lethal. In central and eastern European areas where Echinococcus multilocularis is endemic, dogs that have access to rodents should be considered as potential hazards for humans. Rational measures for preventing animal and human infection include pet owner education and regular deworming of dogs and cats. Education of pet owners should focus on prevention, and will include personal hygiene, clearing up pet feces regularly to reduce environmental contamination, and minimizing exposure of children to potentially contaminated environments. Because puppies, kittens, pregnant and nursing animals and hunting dogs are at the highest risk of roundworm or tapeworm infection--and are therefore responsible for most environmental contamination and human disease--antihelminthic treatments are most effective when they are initiated early and target these animal populations. Various guidelines for the treatment and control of parasitic infections in carnivorous pets have been proposed in the United States (by the Centers for Disease Control and Prevention, and the Companion Animal Parasitology Council) and in Europe (by the European Scientific Counsel Companion Animal Parasitology). In France a non profit organization (CEPHA, Comité d'Experts en Parasitologie Humaine et Animale) was recently created to participate in the prevention of parasitic zoonoses associated with companion animals.

Role of dogs in contamination of urban environment with causes of parasitic zoonoses

Dogs belong to the group of animals that were the first to be domesticated. They live in cohabitation with humans and share their environment much more intimately than any other animal specie. The close contact between strays and pets, on the one side, and the pollution of urban areas with the feces of these animals, on the other, close the chain of infection with parasites, which jeopardizes also human health in the final link of that chain. Dogs are carriers and the true hosts to large numbers of species of zoonotic parasites - Cryptosporidium parvum, Giardia lamblia, Echinoccocus granulosus, Dipyllidium caninum, Toxocara canis, Ancylostomidae spp. and others, whose eggs or other developmental forms they eliminate into the environment through feces. The increase in the number of cases of toxocarosis in humans (syndrome of visceral larvae migrans), ancylostomosis (cutanea larvae migrans), hydatidosis, toxoplasmosis, or cryptosporidiosis are the best indicators of these relations. In order to resolve this problem, it is necessary to conduct systematic investigations of their parasitic fauna with the maximum cooperation of the animal owners, compulsory health education of the population in the area of the diseases that are transferred from animals to humans, and, certainly, carrying out the dehelminthization of dogs.

Circulation of Toxocara spp. in suburban and rural ecosystems in the Slovak Republic

Toxocara spp., the common roundworms of domestic and wild animals, are the causative agents of larval toxocarosis in humans. The migration of Toxocara larvae in men causes clinical syndrome, called larva migrans visceralis or larva migrans ocularis. The objective of the present work was to investigate the prevalence of toxocarosis in dogs, red foxes ( Vulpes vulpes), and small mammals in the Slovak Republic. T. canis infection was diagnosed in 16.6% out of 145 dogs examined. Young animals showed significantly higher positivity (50.0%) than adults (12.4%). Coprological investigation of 310 red foxes showed 8.1% prevalence of T. canis, with higher occurrence in animals from rural conditions (8.6%) than from suburban environment (5.6%). Out of 710 small mammals examined, anti- Toxocara antibodies were detected in 7.7% of the animals. The most frequently seropositive species was Apodemus agrarius (15.9%). Seropositivity of small mammals from suburban localities was higher (10%) compared with rural areas (5.8%), with adult animals exhibiting higher seropositivity (8.0%) than subadults (6.8%). Our results have confirmed the importance of dogs, red foxes and small mammals in circulation of this serious helminthozoonosis in suburban and rural ecosystems.

Population dynamics of Toxocara canis in pigs receiving a single or multiple infection.

The population dynamics of Toxocara canis in pigs, and their immune response to a primary and a challenge infection, were studied by parasitological, haematological and serological parameters. Seventy pigs were divided into 4 groups; 35 pigs received a primary infection (group A), 15 pigs received both a primary and a challenge infection (group B), 15 pigs received the challenge infection only (group C), and 5 pigs served as helminth-free controls (group NC). A dose of 50,000 eggs was administered for the primary infection (day 0) and a dose of 10,000 eggs was given for the challenge infection (day 28). On days 7, 14, 21 and 28 p.i., 5 pigs of group A, and on days 35, 42 and 49 p.i., 5 pigs from each of groups A, B and C were necropsied. Numbers of recovered larvae varied widely among the 5 pigs of each group on all days of necropsy. Toxocara canis larvae were recovered predominantly from the lungs; migration of larvae to other organs or tissues from the lungs was restricted. In group A, the larval burden in the lungs peaked on day 14 p.i., and the larval densities decreased significantly over time. Thereafter, the majority of larvae were recovered from the lungs until the end of the experiment (day 49 p.i.). A few larvae were found in the muscles and brain until day 42 p.i., and 2 larvae were found in the eyes of 2 pigs on day 35 p.i. There was little evidence of protective immunity to a challenge infection in this experiment. The eosinophil levels tended not to increase in pigs receiving a challenge infection, in contrast to the challenge control pigs. The fact that T. canis larvae migrate and persist in the tissues of pigs for more than 1 month suggests a zoonotic risk in infected pigs. The relevance of these data to the population biology and immunology of porcine and human toxocarosis is discussed.

A survey on environmental contamination of suburban parks and playgrounds in Harare, Zimbabwe, with canine helminths of zoonotic significance.

In an attempt to assess the possible risk to humans of soil-transmitted canine helminths of of zoonotic significance, 161 faecal samples and 81 soil samples were collected from 6 public parks and playgrounds in Harare between March and June 1998 and examined for nematode ova. Of the 161 faecal samples collected, 17.4% were positive for Ancylostoma sp. ova and 5.6% were positive for T. canis ova. No other nematode species ova were found. Over 50% of the faecal samples positive for Ancylostoma sp. ova were 'moist', and this suggests that the moisture content of faeces contributes to the development and survival of this parasite in the environment. Only 3 of the 81 soil samples collected were positive for T. canis. The low levels of contamination of public playgrounds and parks with T. canis ova suggests that environmental contamination might not be important in the aetiology of human toxocarosis in Harare.

Seroprevalence of Toxocara infection in middle-class and disadvantaged children in northern Spain (Gipuzkoa, Basque Country).

The prevalence of human toxocarosis in disadvantaged socioeconomic population in Europe is unknown. In Gipuzkoa the seroprevalence in middle-class children 2- to 5-years-old, and 6- to 16-year-olds, was zero (n = 135) and 4.4% (n = 320), respectively. In contrast, among socially and economically disadvantaged children the figures were 37% (n = 27) and 65.7% (n = 64). This high prevalence obliges us to consider toxocarosis as a public health problem.

Immunodiagnosis of toxocarosis in humans: evaluation of a new enzyme-linked immunosorbent assay kit

Excretory/secretory (E/S) antigen derived from second-stage larvae of Toxocara canis maintained in defined medium in vitro has been well established worldwide for the immunodiagnosis of human toxocarosis by enzyme-linked immunosorbent assay. Such an enzyme-linked immunosorbent assay, based on the detection of human anti-T. canis (E/S antigen) serum immunoglobulin G, has recently been commercialized by Biokema-Affinity Products (Crissier-Lausanne, Switzerland). This commercial test kit was evaluated with regard to its application in a routine diagnostic laboratory and the reliability of the results. Of 78 patients with suspected clinical toxocarosis, 71 had anti-T. canis antibodies (positive serological result) corresponding to a diagnostic sensitivity of 91%; 14% of serum samples (n = 199) from patients with protozoan or with helminthic infections also showed positive reactions mainly related to infections with Trichinella, Strongyloides, and Fasciola species. An epidemiological study with 1,000 serum samples from randomly selected healthy blood donors and children in Switzerland demonstrated a seroprevalence of 2.7%. The test kit under evaluation had an overall diagnostic sensitivity of 91% and a relative specificity of 86%, the latter being related to some protozoan and helminthic infections. Because of the scarcity of such infections, potential cross-reactivity does not play a major role under the conditions found in the middle part of Europe. In conclusion, the application of the test kit provided for use in this study can be recommended for routine diagnostic use.