Excepcionalmente el ser humano puede infectarse. Esto quiere decir que los sexos se encuentran separados. Es decir, hay individuos de sexo femenino e individuos de sexo masculino. Se reproducen mediante huevos, dentro de los cuales se forman las larvas. Durante su desarrollo embrionario, se observan las tres capas germinativas: endodermo, mesodermo y ectodermo. Ejemplares adultos masculinos y femeninos.
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Resources Causal Agents Toxocariasis in humans is caused by infection with larvae of Toxocara spp. Confirmed zoonotic species include the dog roundworm T. It is not known whether other closely-related Toxocara species can infect humans e. Life Cycle View Larger Toxocara spp.
Unembryonated eggs are shed in the feces of the definitive host canids: T. Eggs embryonate over a period of 1 to 4 weeks in the environment and become infective, containing third-stage L3 larvae. Following ingestion by a definitive host , the infective eggs hatch and larvae penetrate the gut wall. In younger dogs T. In older dogs, patent egg-producing infections can also occur, but larvae more commonly become arrested in tissues.
Arrested larvae are reactivated in female dogs during late gestation and may infect pups by the transplacental major and transmammary minor routes in whose small intestine adult worms become established. In cats, T. Toxocara spp. Eggs ingested by suitable paratenic hosts hatch and larvae penetrate the gut wall and migrate into various tissues where they encyst. The life cycle is completed when definitive hosts consume larvae within paratenic host tissue , and the larvae develop into adult worms in the small intestine.
After ingestion, the eggs hatch and larvae penetrate the intestinal wall and are carried by the circulation to a variety of tissues liver, heart, lungs, brain, muscle, eyes. While the larvae do not undergo any further development in these sites, they can cause local reactions and mechanical damage that causes clinical toxocariasis. Hosts Toxocara canis infects essentially all wild and domestic canids; patent infections are more prevalent among puppies than older dogs.
Paratenic host ranges for both species encompass numerous species of mammals and birds. Livestock are important paratenic hosts; some human cases have been linked to consumption of undercooked beef, lamb, chicken, and duck meat particularly liver.
Cockroaches and earthworms have been experimentally infected, and could possibly serve as paratenic or transport hosts. Geographic Distribution Toxocara canis and T. While common globally, prevalence in both animals and people is highest in developing countries. In developed countries, more infections are detected among persons in lower socioeconomic strata.
Clinical Presentation The main clinical presentations of toxocariasis are visceral larva migrans VLM and ocular larva migrans OLM , although most infections are asymptomatic. In VLM, which occurs mostly in preschool children, the larvae invade multiple tissues commonly liver, lung, skeletal muscle, occasionally heart and cause various nonspecific symptoms e. Migration to the central nervous system neurotoxocariasis or neural larva migrans NLM is uncommon and can cause eosinophilic meningoencephalitis.
Death can occur in instances of severe cardiac, pulmonary, or neurologic involvement. Involvement is typically unilateral affecting one eye and associated visual impairment usually presents with uveitis, retinitis, or endophthalmitis; permanent visual damage or blindness can occur.
Associated larval granulomas have in some cases have been misdiagnosed as retinoblastoma. OLM most often occurs in older children or young adults, who uncommonly have visceral manifestations. Toxocara sp. Eggs are not clinically diagnostic for human cases as humans are incapable of harboring adult worms that pass eggs. Humans are paratenic hosts for Toxocara spp.
Toxocara eggs are golden in color, spherical to slightly pear shaped, thick-shelled, and have a pitted surface. The size range for different species varies slightly; T. Figure A: Toxocara sp. The worm was never identified, but the egg size is most consistent with T. Figure B: Toxocara sp. Figure C: Toxocara sp. Toxocara canis larva hatching. Figure A: Toxocara canis larva beginning to hatch. Figure B: T. Figure C: T. Adult Toxocara sp.
Adult Toxocara spp. They also possess large, spear-shaped cervical alae, which are broader in T. Figure A: Toxocara canis adult male and female. Figure B: Close-up of the anterior end of Toxocara canis, showing the three lips characteristic of ascarid worms. Figure C: Close-up of the anterior end of Toxocara cati, showing the three lips characteristic of ascarid worms. Figure E: Close-up of the posterior end of T.
Figure F: Close-up of the posterior end of Toxocara sp. In tissue, Toxocara spp. Two large excretory columns are present and single-pointed lateral alae are conspicuous along most of the body length. Figure A: Cross-section of Toxocara sp. Figure B: Longitudinal section of a Toxocara sp. Figure C: Longitudinal section of a Toxocara sp. Figure D. Toxocara canis longitudinal section arrow in the liver of an infected monkey.
Note the prominent granulomatous reaction and host infiltrate around the larva 20x magnification. Figure E: Cross-section of a larva of T. Laboratory Diagnosis Diagnosis of toxocariasis relies mostly on indirect means, particularly serology, since larvae are trapped in tissues and not readily detected morphologically.
While visualization of larvae in histologic sections provides unequivocal diagnosis, the probability of capturing a larva in a small biopsy specimen is low.
Since the larvae do not develop into adults in humans, a stool examination would not detect any Toxocara eggs. Antibody Detection Antibody detection tests are the only means of confirmation of a clinical diagnosis of visceral larva migrans VLM and ocular larva migrans OLM , clinical syndromes associated with Toxocara infections.
The currently recommended serologic test for toxocariasis is enzyme immunoassay EIA with larval stage antigens extracted from embryonated eggs or released in vitro by cultured third-stage larvae. The latter, Toxocara excretory-secretory TES antigens, are preferable to larval extracts because they are convenient to produce and an absorption-purification step is not required for obtaining maximum specificity. Further confirmation of serologic diagnosis of OLM can be obtained by testing aqueous or vitreous humor samples for antibodies.
Special considerations: The assay detects infections caused by both T. Evaluation of the true sensitivity and specificity of serologic tests for toxocariasis in human populations is not possible because of the lack of feasible parasitological methods to detect migrating Toxocara larvae in tissue. These inherent problems result in underestimations of sensitivity and specificity.
When interpreting serologic findings, clinicians must be aware that a measurable titer does not necessarily indicate current clinical Toxocara infection.
In most human populations, a small number of those tested have positive EIA titers that apparently reflect the prevalence of asymptomatic toxocariasis, or past infections that have since been cleared.
Paired serum samples demonstrating a significant rise in antibody level over time may be useful to confirm active infection. Suggested Readings Moreira, G. Human toxocariasis: current advances in diagnostics, treatment, and interventions. Trends in Parasitology, 30 9 , pp. Fillaux, J. Laboratory diagnosis of human toxocariasis.
Veterinary Parasitology, 4 , pp. Fisher, M. Toxocara cati: an underestimated zoonotic agent. Trends in Parasitology, 19 4 , pp. DPDx is an educational resource designed for health professionals and laboratory scientists. For an overview including prevention, control, and treatment visit www. Page last reviewed: July 9,
No son raros los accesos rabiformes. Puede presentarse diarrea intermitente. Encubierta TE. Estos huevos no son embrionados y por lo tanto no son infectivos.
Toxocara canis: características, morfología, síntomas de infección