Aspects of the morphology, life cycle and epidemiology of Toxocara species and Toxascaris Leonina

[摘要] English: The present study has provided detailed and comprehensive information on the morphological aspects, life cycle, and epidemiology of Toxocara canis, Toxocara cati and Toxascaris leonina. The overall results of the study results are briefly summarized as follows:1. In the morphological studies of these parasites, it has been observed that there are gross morphological similarities in the developmental stages of T. canis, T. cati and T. leonina. However, closer and detailed observations have revealed that the various developmental stages differ from one another in their fine morphological features. The observed morphological differences were:a. Eggs of T. canis and T. cati look very similar under the light microscope, in some eggs it seems that the surface pits and ridges of T. canis are larger and coarser than in the eggs of T. cati. However, unlike the eggs of Toxocara spp., eggs of T. leonina have no surface pits and ridges but are smoother on the surface.b. Second-stage larvae of T. canis recovered from the eggs and from the infected tissues of mice were stumpy and vigorously motile. The larval stages from both sources were similar in their morphological features and had comparable size measurements indicating that larval stages did not undergo development in the paratenic host. Like the larvae of T. canis, second-stage larva of T. cati recovered from the eggs and from the infected tissues of mice were stumpy and vigorously motile. The larval stages from both sources were similar in their morphological features and had comparable size measurements. The second-stage larvae of T. canis recovered from eggs or from tissues of mice had a greater width than the comparable second-stage larvae of T. cati. Unlike the larval stages recovered from the embryonated eggs of T. leonina, larvae recovered from infected tissues of mice were longer and wider and had more distinct morphological features. This indicated that larval stages recovered from the tissues of infected mice had probably undergone development to third-stage larvae.c. Adults T. canis, T. cati and T. leonina resemble each other in their gross morphological features, but also differ in their detailed and fine structural features. The major differences were on the shape of cervical alae, the presence or absence of an esophageal ventriculus, the position of the vulva in the female worms, as well as the number and arrangement of papillae on the tail of the male worms.d. Precloacal median papilla were recorded and described in males of T. canis and T. cati. Previous researchers did not describe the presence of these structures in male Toxocara spp. worms. In the present study, a female T. canis worm with a length of 27.5 cm was recovered from an infected dog and it was larger than any recorded in the literature.2. In the study of the modes of transmission of ascarids, it has been observed that transplacental transmission of T. canis occurred in mice infected during but not before pregnancy. Transmammary transmission of T. canis and T. cati larvae had also occurred in mice infected prior to or during pregnancy. However, unlike in T. canis and T. cati, had neither transplacental nor transmammary transmission occurred in T. leonina. Larval stages were recovered from most tissues and organs of infected mice, and the larvae gradually accumulated in various extraintestinal tissues for the three ascarid species and especially in the brain of mice infected with T. canis.3. The study on T. leonina transmission to the definitive hosts through experimentally infected mice as paratenic host, has indicated that dogs can be infected by ingesting infected tissues of mice that were infected with T. leonina infective eggs originally obtained from dogs. However, in cats this was not possible and it has been suggested that cats may not be the proper definitive host for T. leonina originating from dogs.4. In an epidemiological survey of Toxocara spp. T. leonina, and other intestinal helminths of dogs and cats in Jimma, Southwestern Ethiopia, it was shown that the overall prevalence rates for parasitic infection were 60.78% in faecal samples of dogs from the environment, 78.60% in faecal samples of dogs taken from the rectum, 66.23% in faecal samples of cats and 33.38% in soil samples were recorded. Parasite species identified were Toxocara canis, T. cati, Toxascaris leonina, hookworms, Spirocerca lupi, Trichuris vulpis, taeniids, Ascaris species and Strongyloides species. A relatively high mean egg count of 15.25 was observed for T. canis in dog faecal droppings collected from the environment. The potential of these parasites as a cause of zoonotic infections, ways of prevention of infection and control measures were discussed.

[发布机构] University of the Free State