Human toxocariasis

Who Let the Dogs Out? Unmasking the Neglected: A Semi-Systematic Review on the Enduring Impact of Toxocariasis, a Prevalent Zoonotic Infection

Toxocariasis remains an important neglected parasitic infection representing one of the most common zoonotic infections caused by the parasite Toxocara canis or, less frequently, by Toxocara cati. The epidemiology of the disease is complex due to its transmission route by accidental ingestion of embryonated Toxocara eggs or larvae from tissues from domestic or wild paratenic hosts. Even though the World Health Organization and Centers for Disease Control classified toxocariasis amongst the top six parasitic infections of priority to public health, global epidemiological data regarding the relationship between seropositivity and toxocariasis is limited. Although the vast majority of the infected individuals remain asymptomatic or experience a mild disease, the infection is associated with important health and socioeconomic consequences, particularly in underprivileged, tropical, and subtropical areas. Toxocariasis is a disease with multiple clinical presentations, which are classified into five distinct forms: the classical visceral larva migrans, ocular toxocariasis, common toxocariasis, covert toxocariasis, and cerebral toxocariasis or neurotoxocariasis. Anthelmintic agents, for example, albendazole or mebendazole, are the recommended treatment, whereas a combination with topical or systemic corticosteroids for specific forms is suggested. Prevention strategies include educational programs, behavioral and hygienic changes, enhancement of the role of veterinarians, and anthelmintic regimens to control active infections.

Fatal visceral larva migrans from Toxocara catis infection of the heart and liver in a child

We discuss the pathophysiology and epidemiology of Toxocara catis infection complicated by visceral larval migrans . We describe a previously healthy 19-month-old white male child found dead in bed by his mother. He had what was thought to be an upper respiratory infection for several days.The child had eosinophilic hepatitis and myocarditis complicating visceral larval migrans due to Toxocara catis infection from the family cat. We discuss the pathologic and clinical aspects of visceral larval migrans due to of Toxocara catis infection.

Toxocara Seroprevalence and Risk Factor Analysis in Four Communities of the Wiwa, an Indigenous Tribe in Colombia

The life of the indigenous Wiwa tribe in northeast Colombia is characterized by lacking access to clean drinking water and sanitary installations. Furthermore, free-roaming domestic animals and use of yucca and/or manioc as a primary food source favor the transmission of soil-transmitted helminths, e.g., Toxocara canis and Toxocara cati, the roundworms of dogs and cats. Infection may result in the clinical picture of toxocarosis, one of the most common zoonotic helminthoses worldwide. To estimate the Toxocara seroprevalence in four different villages of the Wiwa community, serum samples from 483 inhabitants were analyzed for anti-Toxocara-antibodies. Overall, 79.3% (383/483) of analyzed samples were seropositive. Statistically significant differences were observed between the four villages, as well as age groups (adults > adolescents > children), while sex had no effect. The high seropositivity rate demonstrates the risk of zoonotic roundworm infections and potential clinical disease in vulnerable indigenous inhabitants.

Sero-Epidemiology of Toxocara Canis Infection in Children Attending Four Selected Health Facilities in the Central Region of Ghana

OBJECTIVE

The study determined the seroprevalence of Toxocara canis infection among children attending four selected health facilities in the Central Region of Ghana.

DESIGN

Cross-sectional study.

METHOD

Sera from 566 children aged 1-15 years attending four selected health facilities in the Central Region of Ghana between July and September 2012 was used in a Toxocara excretory-secretory antigen-based ELISA to detect serum IgG. A short questionnaire was designed to obtain data on respondents as to age, gender, educational level, locality of residence, habits of washing of fruits, vegetable and hands before eating, keeping of pet (dogs or cats), and history of playing with soil and pets. Clinical information was also collected. Associations between sero-positivity and age group, gender, risk factors, educational level and other variables were determined by Chi square test.

RESULTS

The overall sero-prevalence was 53.5% (n=566). Age, educational level and hospital visited were significantly associated with sero-positivity (p< 0.05). Children with history of playing with soil (χ(2)=9.03, p=0.003), pet-keeping (χ(2)=14.77, p=0.001) and not washing hands with soap before eating (χ(2)=5.82, p=0.016) were significantly associated with sero-positivity.

CONCLUSION

The sero-prevalence of T. canis infection in children in the study was high. The children should be educated to desist from risk factors such as playing with soil and pets and be encouraged to ensure proper personal hygiene.

Proteinases in excretory-secretory products of Toxocara canis second-stage larvae: zymography and modeling insights

Components released in excretory-secretory products of Toxocara canis larvae (TES) include phosphatidylethanolamine-binding proteins (TES26), mucins (TES120, MUC2-5), and C-type lectins (TES32, TES70) and their biochemical, immunological, and diagnostic properties have been extensively studied albeit proteinase activities towards physiological substrates are almost unknown. Proteolytic activities in TES samples were first analyzed by gel electrophoresis with gelatin as substrate. Major activities of ~400, 120, and 32 kDa in TES were relatively similar over a broad pH range (5.5–9.0) and all these were of the serine-type as leupeptin abolished gelatinolysis. Further, the ~400 kDa component degraded all physiological substrates tested (laminin, fibronectin, albumin, and goat IgG) and the 120 kDa component degraded albumin and goat IgG while proteinases of lower MW (45, 32, and 26 kDa) only degraded laminin and fibronectin, preferentially at alkaline pH (9.0). By protein modeling approaches using the known sequences of TES components, only TES26 and MUC4 displayed folding patterns significantly related to reference serine proteinases. These data suggest that most of serine proteinase activities secreted in vitro by infective larvae of T. canis have intriguing nature but otherwise help the parasite to affect multiple components of somatic organs and bodily fluids within the infected host.

Toxocara canis myelitis: clinical features, magnetic resonance imaging (MRI) findings, and treatment outcome in 17 patients

Toxocara myelitis is a rare disease. Few cases have been reported in the literature. Patients present with myelopathy, occasional eosinophilia in blood and cerebrospinal fluid (CSF), with abnormal signals on magnetic resonance imaging (MRI). In the current study we report 17 cases of isolated Toxocara myelitis from a single tertiary referral center in Lebanon, with description of the clinical presentation, laboratory data, MRI findings, and response to antihelminthic treatment. Clinical and laboratory data were collected for 17 patients who presented with evidence of spinal cord disease. The clinical presentation included sensory, motor, and autonomic dysfunction, predominantly in the lower extremities. Patients exhibited a subacute or chronic course; this was either slowly progressive or remitting-relapsing with mild to moderate disability. The patients underwent extensive blood and CSF workup as well as MRI of the spinal cord and brain. Only 2 patients had a high eosinophil count in the CSF, although blood eosinophilia was seen in 6 patients. All patients tested positive for Toxocara canis antibodies in the blood and CSF. MRI of the spinal cord revealed a single characteristic lesion in the spinal cord with fusiform enlargement that was isointense on T1-weighted images and hyperintense on T2-weighted images. Nodular enhancement was seen after gadolinium injection. Treatment with albendazole, with or without steroids, resulted in marked neurologic improvement and normalization of the MRI in all patients.The finding of a single inflammatory MRI lesion in the spinal cord with positive Toxocara canis serology in the blood and CSF in cases of subacute or chronic myelitis suggests the diagnosis of Toxocara myelitis, irrespective of the presence of eosinophilia. Antihelminthic treatment is associated with a good outcome.

Four abundant novel transcript genes from Toxocara canis with unrelated coding sequences share untranslated region tracts implicated in the control of gene expression

The Toxocara canis "abundant novel transcripts" (ant) are four highly expressed products, constituting >18% of ESTs from the infective stage of this widely prevalent nematode parasite. Using 5' RACE, we determined full-length sequences for each ant gene, between 1.8 and 2.8kb. The four genes (termed ant-3, -5, -30 and -34), share no coding sequence similarity, although their 3'UTRs (untranslated regions) are homologous. Predicted ANT-5 and ANT-30 proteins show distant similarity to RNA regulatory proteins, RNA-dependent RNA polymerase and DEAH-box helicase, respectively. Surprisingly, ant-3 appears to be bi-cistronic, encoding two ORFs (ANT-3.1 and -3.2), each with a predicted N-terminal signal sequence. Antibodies raised to recombinant proteins did not react with native parasite products, indicating that protein expression did not accord with transcript abundance. However, antibody reactivity to two gene products (ANT-3.1 and ANT-34) was present in patient sera, suggesting that these proteins are synthesized later in infection. To test whether 3'UTRs may regulate expression, the ant-34 3'UTR sequence was inserted adjacent to enhanced green fluorescent protein (EGFP) for transformation of Caenorhabditis elegans. The ant-34 3'UTR greatly reduced EGFP expression, inhibiting both transcription and translation. We identified a tract in this UTR with significant sequence complementarity to the C. elegans micro-RNA lin-4. While infective stage parasites stockpile high levels of the ant transcripts, we suggest that translation is repressed, possibly by a mechanism involving 3' UTR motifs shared by the four genes.

Prolactin evokes lactational transmission of larvae in mice infected with Toxocara canis

We investigated the trans-lactational maternal-neonatal transmission of Toxocara canis larvae in mice, with particular interest in the role of prolactin in their migration to the mammary gland. Two female mice were infected with 300 T. canis eggs soon after delivery of 27 offspring. After 1 week of breast-feeding, seven larvae were recovered from 4 of 13 offspring. After 2 weeks of lactation, 101 larvae were recovered from all the remaining offspring. Daily prolactin administration (5 microg) was performed 2 weeks before T. canis infection and continued until 2 weeks after infection in six non-pregnant female mice, which resulted in larval accumulation in the mammary gland. Furthermore, prolactin administration in female mice that had been infected with T. canis 4 weeks prior to prolactin treatment induced migration of larvae into the mammary gland. These findings suggest that prolactin is a promoting factor contributing to lactational transmission of T. canis larvae in mice.

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.

Eosinophilic pleocytosis and myelitis related to Toxocara canis infection

Toxocara canis causes the visceral larva migrans syndrome in which central nervous involvement is rare. We report the case of a 40-year-old woman presenting with a subacute weakness of the right leg and dysaesthesiae in the right Th8-Th10 dermatomas. Spinal magnetic resonance imaging examination showed abnormal hyperintensity within the spinal cord. Cerebrospinal fluid analysis revealed eosinophilic pleocytosis. Antibody titres to Toxocara canis were higher in the cerebrospinal fluid than in the serum. Treatment using mebendazole led to a complete clinical recovery, normalization of cerebrospinal fluid parameters and improvement in spinal magnetic resonance imaging abnormalities.

Cloning and characterisation of a prohibitin gene from infective larvae of the parasitic nematode Toxocara canis

Infective larvae of the parasitic nematode Toxocara canis express an mRNA (Tc-pro-1) encoding a predicted protein that shares significant homology with prohibitin, a protein involved in inhibition of cell proliferation - The closest homologues of Tc-pro-1 include an expressed sequence tag (EST) from Caenorhabditis elegans and Drosophila L2Cc, a protein thought to be essential for larval development and moulting. Other homologues include prohibitin from rat and human and an EST from Saccharomyces cerevisiae. Parasite life cycles generally include periods of developmental arrest, which in the larvae of T. canis may persist for many years without loss of metabolic activity. This report of the first full-length gene encoding prohibitin from a parasitic nematode raises interesting suggestions about the potential role of prohibitin in diapause and in the regulation of moulting in development.

Identification of abundantly expressed novel and conserved genes from the infective larval stage of Toxocara canis by an expressed sequence tag strategy

Larvae of Toxocara canis, a nematode parasite of dogs, infect humans, causing visceral and ocular larva migrans. In noncanid hosts, larvae neither grow nor differentiate but endure in a state of arrested development. Reasoning that parasite protein production is orientated to immune evasion, we undertook a random sequencing project from a larval cDNA library to characterize the most highly expressed transcripts. In all, 266 clones were sequenced, most from both 3' and 5' ends, and similarity searches against GenBank protein and dbEST nucleotide databases were conducted. Cluster analyses showed that 128 distinct gene products had been found, all but 3 of which represented newly identified genes. Ninety-five genes were represented by a single clone, but seven transcripts were present at high frequencies, each composing >2% of all clones sequenced. These high-abundance transcripts include a mucin and a C-type lectin, which are both major excretory-secretory antigens released by parasites. Four highly expressed novel gene transcripts, termed ant (abundant novel transcript) genes, were found. Together, these four genes comprised 18% of all cDNA clones isolated, but no similar sequences occur in the Caenorhabditis elegans genome. While the coding regions of the four genes are dissimilar, their 3' untranslated tracts have significant homology in nucleotide sequence. The discovery of these abundant, parasite-specific genes of newly identified lectins and mucins, as well as a range of conserved and novel proteins, provides defined candidates for future analysis of the molecular basis of immune evasion by T. canis.

Aspects of Toxocara epidemiology: human toxocarosis

Toxocarosis is the clinical disease in man caused by infection of zoonotic roundworms of dogs and cats, Toxocara canis and T. cati. In this review the mode of transmission to the human by oral ingestion of Toxocara eggs from the environment is discussed. T. cati seems to play a more important role than generally suggested. Direct contact with animals is not considered a potential risk because embryonation of excreted Toxocara ova requires a minimum of 2 weeks. For the same reason there is no relationship expected between infection and exposure to dogs and cats in the household. Children more frequently have clinical symptoms because of the closer contact with contaminated soil in yards and sandpits, the lack of hygiene, and because of eating dirt. Toxocara larval migration in the body can cause various clinical syndromes. Visceral larva migrans, ocular larva migrans, and covert toxocarosis are described. Serodiagnostic techniques are reliable tools to detect antibodies or antigens. Systemic treatment with anthelmintics is described but can result in hypersensitivity reactions caused by dying larvae. For ocular lesions, laser photocoagulation and corticosteroid therapy are described. Preventive measures consist of preventing contamination of the environment with Toxocara eggs and for education of pet owners and non-pet owners to increase awareness about potential zoonotic hazards. Veterinary practitioners, general practitioners, and public health agencies should therefore provide sufficient information and advice.

Aspects of Toxocara epidemiology: toxocarosis in dogs and cats

Toxocara canis and Toxocara cati are common roundworms of dogs and cats. In this review the life cycles of these parasites are described, including the various routes of transmission, such as transplacental, transmammary infection, and infection through paratenic hosts. The somatic and tracheal migration in the body of the hosts after infection with Toxocara eggs or larvae is discussed, with special reference to age resistance and differences between dog and cat. The clinical symptoms and pathology in adult and young dogs and cats are given. Diagnosis of patent infections can be obtained by fecal examination, and treatment consists of the use of anthelmintics. Control of the infection and disease is achieved by prevention of contamination of the environment, anthelmintic treatment strategy, and education. Special attention is given to the efficacy of anthelmintics against adult worms and against somatic larvae. It is concluded that education on the life cycles of the parasites, hygiene, and anthelmintic treatment schedules is required because of the zoonotic risks of Toxocara spp. Deworming of pregnant dogs and cats is not recommended.

Optic neuritis in cerebral toxocariasis

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Toxocariasis simulating hepatic recurrence in a patient with Wilms' tumor

We report the case of a 3-year-old girl with stage I Wilms' tumor of favorable histology. During the course of chemotherapy 5 months post-diagnosis, an abdominal ultrasonogram revealed hypoechoic areas consistent with hepatic tumor recurrence. A liver biopsy performed to rule out recurrence of the malignancy was suggestive of toxocariasis and the diagnosis was confirmed by serologic testing. Although the patient had few classic signs of visceral larva migrans, her eosinophilia and family social history should have suggested this possibility. This case demonstrates that hepatic toxocariasis should be considered in evaluating hepatic hypoechoic lesions in a child, even when features typical of the disease are absent.

Diagnosis of human toxocariasis by antigen capture enzyme linked immunosorbent assay

AIMS

To evaluate an antigen capture enzyme linked immunosorbent assay (ELISA) which detects a carbohydrate epitope on the excretory-secretory (ES) antigens of Toxocara canis in clinical practice.

METHODS

Serum specimens from healthy adults, patients with acute visceral larva migrans, ocular and inactive toxocariasis, and with other helminth infections were examined by two site antigen capture ELISA.

RESULTS

Over half of the patients (19/28) with acute toxocariasis had a positive result in contrast to a small proportion of those with inactive disease (1/10) or ocular infection (2/7). False positive reactions, however, were found in 25% of the patients with serologically confirmed schistosomiasis and filariasis.

CONCLUSIONS

This assay is useful in confirming the diagnosis of acute visceral larva migrans but could not be used alone in diagnosis because of false positive reactions in patients with other helminth infections.

Toxocara antibodies in patients with visceral or ocular disorder in Slovenia

The incidence of Toxocara antibodies was determined in 319 sera from patients suspected of having Toxocara infection. Serological responses were compared with clinical manifestations and age of the patients. A seropositive reaction was found in 24% of the patients. Highly positive results (OD 0.510-1.000 and OD > 1.000) by ELISA were obtained significantly more frequently in younger patients than in older ones (p < 0.005). The percentage of seropositive patients with visceral disorder was found to decrease with age, whereas the proportion of seropositive patients with ocular disorder increased with age. Serologically confirmed Toxocara infection in Slovenia alerted us to the fact that this health issue should be given due attention in the future.

Surface associated glycoproteins from Toxocara canis larval parasites

The surface of infective larvae of Toxocara canis, the dog ascarid nematode, reveals relatively few exposed surface proteins which can be recovered in soluble form. The major components identified by surface labelling have molecular weights of 32, 55, 70 and 120 kilodaltons (kDa), and are all significantly glycosylated. All are recognised by the immune response in definitive (canine) and paratenic (murine or human) hosts. Expression of these antigens on the parasite surface begins after the larvae hatch from infective ova in vitro, and presumably in vivo. Each of these molecules may also be found in the set of secreted (ES) glycoconjugates released by larval parasites cultivated in vitro, and currently available biochemical and functional data on the surface/secreted ES glycoproteins are presented. Analysis with monoclonal antibodies (MAbs) confirms the identity of surface and ES molecules, and these MAbs show differing patterns of binding to the epicuticle, the cuticular matrix and to the oral orifice. Alternative mechanisms for antigen synthesis, insertion into the cuticle and export from the parasite are discussed.

Toxocara canis: proteolytic enzymes secreted by the infective larvae in vitro

Second-stage larvae of the dog nematode Toxocara canis are infective to man and cause the syndromes of visceral larva migrans and ocular toxocariasis. Larvae cultured in vitro secrete proteases which degrade components of a model of extracellular matrix and basement membranes. These enzymes have been characterized using a variety of techniques. Multiple enzyme activities were demonstrated by substrate gel electrophoresis, associated with proteins of molecular weights of 120 and 32 kDa. The enzyme activity was inhibited both in substrate gels and in a radiogelatin microplate assay by phenylmethylsulfonyl fluoride. Optimal activity occurred at pH 9, with minor activities apparent at pH 5 and 7; the relationship between these proteolytic activities is currently under investigation.