[Three cases of visceral larva migrans due to ingestion of raw chicken or cow liver]

Brain food: rethinking food-borne toxocariasis

Human toxocariasis is a neglected tropical disease, which is actually global in distribution and has a significant impact on global public health. The infection can lead to several serious conditions in humans, including allergic, ophthalmic and neurological disorders such as epilepsy. It is caused by the common roundworm species Toxocara canis and Toxocara cati, with humans becoming accidentally infected via the ingestion of eggs or larvae. Toxocara eggs are deposited on the ground when infected dogs, cats and foxes defecate, with the eggs contaminating crops, grazing pastures, and subsequently food animals. However, transmission of Toxocara to humans via food consumption has received relatively little attention in the literature. To establish the risks that contaminated food poses to the public, a renewed research focus is required. This review discusses what is currently known about food-borne Toxocara transmission, highlighting the gaps in our understanding that require further attention, and outlining some potential preventative strategies which could be employed to safeguard consumer health.

Parasitological and molecular study of Toxocara spp. in Lumbericus terrestricus earthworms

Soil-associated invertebrates which are coprophagic are capable of acting as paratenic hosts for Toxocara species larvae eggs. The aim of the present study was to assess the role of Lumbricus terrestris earthworms as potential intermediate host for Toxocara species. A total of 240 earthworms were collected from the public places in four areas of Karaj, Alborz Province, Iran. The subjects of the study were digested to detect Toxocara species using microscopy and molecular analyses. Toxocara larvae and larval eggs were recovered from 1.7% (4/240) of the sampled earthworms. The recovery rate in Shah'Abbasi and Talaghani regions in the studied areas was higher than that of the other regions. In the mentioned area, 8.3% (4/48) of earthworms were revealed to be positive for Toxocara species by microscopic observation and only one was confirmed to be positive for Toxocara canis by polymerase chain reaction (PCR). This is the first molecular report of Toxocara canis infective larvae in Lumbricus terrestris earthworms that could be demonstrated in common environment.

Molecular characterization of Toxocara spp. eggs isolated from public parks and playgrounds in Shiraz, Iran

Human toxocariasis, a worldwide parasitic disease, is caused by the larval stage of intestinal nematodes of dogs and cats, namely Toxocara canis and Toxocara cati. Human infection occurs by the accidental ingestion of embryonated eggs present in the soil, vegetables or on other contaminated surfaces, as well as via consumption of uncooked paratenic hosts, such as bird meat and giblets. The objective of this study was to evaluate the contamination of soil in public parks and playgrounds in Shiraz using microscopy and molecular methods. A total of 150 soil samples were collected from public parks and playgrounds in various areas of Shiraz, southern Iran. The samples were treated with saturated zinc sulphate solution, and Toxocara spp. eggs were detected by microscopic observation followed by nested polymerase chain reaction (PCR). To differentiate T. canis and T. cati eggs from each other, PCR restriction fragment length polymorphism (RFLP) of the internal transcribed spacer (ITS)-rDNA region by SalI endonuclease enzyme was used. PCR-sequencing was performed to confirm the results of the PCR-RFLP method. Based on the flotation results of the 150 soil samples, six (4%) were found to be positive for Toxocara spp. eggs, whereas nested-PCR showed 24 samples to be positive (16%). Based on the PCR-RFLP method and the sequence of the ITS-rDNA region, a total of 23 out of 24 isolates were confirmed as T. cati and one out of 24 as T. canis. The results showed a higher number of soil samples to be positive for Toxocara by the molecular method than microscopy, and higher T. cati infection in soil samples, which could have an important role in human infection with toxocariasis in this region.

The occurrence of Toxocara species in naturally infected broiler chickens revealed by molecular approaches

Consuming raw and undercooked meat is known to enhance the risk of human toxocariasis because Toxocara species have a wide range of paratenic hosts, including chickens. The aim of this study was to identify species of Toxocara in naturally infected broiler chickens using molecular approaches. A polymerase chain reaction (PCR) method was used for the differentiation of Toxocara canis and Toxocara cati larvae recovered from tissues and organs, and identified by microscopic observations. Thirty-three 35- to 47-day-old broiler chickens were used for examination of Toxocara larvae. The duodenum, liver, lungs, heart, kidneys, skeletal muscles and brain of each chicken were examined using the pepsin method, and DNA from each tissue was extracted as the template for PCR assay. The findings revealed that 5 of 33 (15.2%) broiler chickens were infected with Toxocara larvae. Larvae were recovered from the liver (n = 19), duodenum (n = 8), skeletal muscles (n = 8) and brain (n = 2) of broiler chickens naturally infected with Toxocara spp. The results showed that the frequencies of the species in the chickens were T. canis larvae (n = 5, 83.3%) and T. cati larvae (n = 1, 16.7%). Our data from the present study demonstrated the importance of broiler chickens as a paratenic host for the parasite's life cycle in the environment. The implementation of DNA amplification as a routine diagnostic technique is a specific and alternative method for identification of Toxocara larvae, and allowed the observation of specific species under field conditions within the locations where broiler chickens are typically raised and exposed to Toxocara spp. eggs or larvae.

Knowledge gaps in the epidemiology of Toxocara: the enigma remains

Toxocara species infect a wide range of companion, domestic and wild animals as definitive and paratenic hosts, via multiple routes of transmission, producing long-lived tissue-inhabiting larvae and resistant eggs that can survive in the external environment. Therefore Toxocara and the disease it causes in humans, toxocariasis, represents an ideal aetiological agent for the development of the one health approach. However, despite increasing awareness of the public health significance of toxocariasis, gaps in our understanding of certain key aspects of the parasite's biology and epidemiology remain. These gaps hinder our ability to integrate research effort within the veterinary, medical and environmental disciplines. This review will highlight key deficits in our understanding of nine dimensions of Toxocara epidemiology and discuss a potential scenario to develop a more integrated, one health approach to improve our understanding of the prevention and control of this complex and cryptic zoonosis.

Neurotoxocarosis: marked preference of Toxocara canis for the cerebrum and T. cati for the cerebellum in the paratenic model host mouse

Background

Infective larvae of the worldwide occurring zoonotic roundworm T. canis exhibit a marked affinity to the nervous tissues of paratenic hosts. In humans, most cases of neurotoxocarosis are considered to be caused by larvae of T. canis as T. cati larvae have rarely been found in the CNS in previous studies. However, direct comparison of studies is difficult as larval migration depends on a variety of factors including mouse strains and inoculation doses. Therefore, the present study aims to provide a direct comparison of both roundworm species in mice as a model for paratenic hosts with specific focus on the CNS during the acute and chronic phase of disease to provide a basis for further studies dealing with neurotoxocarosis.

Methods

C57Bl/6J mice were infected with 2000 embryonated T. canis and T. cati eggs, respectively as well as Balb/c mice infected with T. cati eggs only. On 8 time points post infection, organs were removed and microscopically examined for respective larvae. Special focus was put on the CNS, including analysis of larval distribution in the cerebrum and cerebellum, right and left hemisphere as well as eyes and spinal cord. Additionally, brains of all infection groups as well as uninfected controls were examined histopathologically to characterize neurostructural damage.

Results

Significant differences in larval distribution were observed between and within the infection groups during the course of infection. As expected, significantly higher recovery rates of T. canis than T. cati larvae were determined in the brain. Surprisingly, significantly more T. canis larvae could be found in cerebra of infected mice whereas T. cati larvae were mainly located in the cerebellum. Structural damage in brain tissue could be observed in all infection groups, being more severe in brains of T. canis infected mice.

Conclusions

The data obtained provides an extensive characterization of migrational routes of T. canis and T. cati in the paratenic host mouse in direct comparison. Even though to a lesser extent, structural damage in the brain was also caused by T. cati larvae and therefore, the potential as pathogenic agents should not be underestimated.

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.

Hepatic lesions caused by migrating larvae of Ascaris suum in chickens

Group A consisted of chickens infected with a single dose of Ascaris suum and group B of chickens infected with two successive doses. At days 1, 3, 7, 14 and 21 after the first or second infection dose, six chickens from each group were sacrificed. In both groups, larvae were recovered from the livers on days 1, 3, and 7 and lungs on days 3 and 7. No larvae were detected in chickens on day 14. Clear white lesions were noticed only on the livers from chickens of group B at day 7 but had disappeared at day 14. A comparison with group B showed mild histological changes that developed relative to the livers from group A.

Histopathologic changes and larval recovery of Toxocara cati in experimentally infected chickens

This study was made to determine the distribution pattern of Toxocara cati larvae in chickens as a paratenic host and its potential zoonotic risk by consuming infected chickens. Two groups of chickens were fed with 1,000 and 3,000 embryonated eggs of T. cati. The chickens were necropsied 3, 7, 14, and 21 days postinfection. The liver, lungs, kidneys, spleen, small intestine, and half of all the striated muscles were digested for larval recovery. Squash method was used for brain. Larvae were recovered from the liver and brain of infected chickens with 1,000 embryonated eggs. Samples of these tissues were prepared for histopathologic studies. Experimental chickens exhibited hemorrhages in the liver, lungs, and kidneys on all days postinfections (dpi). White spots on the liver surfaces that showed necrotic foci, infiltration of eosinophils, and a few lymphocytes around necrotic areas were seen on 14 and 21 dpi. Remains of larvae were present in the liver on 14 dpi. Pathologic findings showed that larvae migrated in different organs of chickens. We suggest that chickens could be paratenic hosts, and human infection with T. cati might occur after consumption of raw or undercooked meat of infected chicken with T. cati.

Toxocariasis in Japan

Toxocariasis has long been considered a parasitic disease affecting pet owners and children who often play in sandboxes at public parks. Recent cases of this animal-borne infection, however, indicate that its clinical manifestations and etiologies are changing. In this article, we will describe the critical characteristic features of toxocariasis alongside the contributions of Japanese researchers to a better understanding of the disease.

Establishment and migration pattern of Toxocara canis larvae in chickens

Migrations of Toxocara canis larvae were observed in experimentally infected chickens. Three groups of three chickens were inoculated orally with T. canis eggs. Within each group, individual chickens received either 5,000, 10,000, or 20,000 eggs. A group of infected chickens was then necropsied at either 1, 3 or 6 days post infection (dpi). The entire duodenum, spleen, liver, heart, lungs, right inner pectoral muscle, and brain were subjected to pepsin digestion for larval recovery. Larvae were predominantly (>87%) recovered from the liver and lungs, and only a few larvae were seen in other organs or tissues in all chickens, with the exception of the duodenum at 1 dpi of chickens inoculated with 20,000 eggs. The percentage of total larval recovery varied widely among chickens (range: 0.4-16.7%). Similar numbers of larvae were distributed in the liver and lungs at 1 dpi. Subsequently, more larvae were found in the lungs than the liver at 3 dpi, whereas the larval distributions in the liver and lungs were reversed at 6 dpi. These observations suggest that T. canis larvae can migrate by a hepatopulmonary route in the chicken, and reinforces the possibility that chickens harboring migrating T. canis larvae may pose a zoonotic risk, especially if the liver is consumed.

A retrospective study of ocular toxocariasis in Japan: correlation with antibody prevalence and ophthalmological findings of patients with uveitis

To classify the clinical characteristic of ocular toxocariasis in Japan, the prevalence of antibodies to Toxocara antigens was examined in patients with uveitis of unknown aetiology. From 1982 to 1993, serum specimens of 383 cases and intraocular fluid samples of 22 cases were serologically screened for Toxocara infection with five immunodiagnostic tests. Fifty-five sera and 11 intravitreous fluid samples were estimated to have significantly high antibody levels against larval excretory-secretory (ES) antigens of T. canis. Eight cases were positive in both serum and vitreous fluid, and three were positive only in the vitreous fluid. Among the 58 antibody positive samples, 20 cases were omitted due to a lack of detailed description of ocular findings. The remaining 38 cases are described in this study. Of these 38 cases, 34 (89%) were older than 20 years of age. Ocular lesions were located in the posterior fundus in 11 cases, in the peripheral fundus in 18 cases, and in both areas in seven cases. Of the eight cases in which papillary oedema or redness was observed, chorioretinal lesions were also present in seven of them. Tractional retinal detachment was present in five cases. These observations suggest that ocular toxocariasis in Japan has a different clinical profile compared with those in the other countries, and indicate a need for revised classification of ocular toxocariasis.