The Etiology of Visceral Larva Migrans: I. Diagnostic Morphology of Infective Second-Stage Toxocara Larvae

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Abstract
The structure and behavior of 2nd- stage T. canis and T. cati larvae in rodents are described. T. canis in the mouse is morphologically identical with T. canis recovered from human infection. The length of both spp. of Toxocara from the embryonated egg, from experimental infections in mice, and of T. canis from one human autopsy varied around 400[mu]. In tissue sections the maximum diameter of T. canis is approximately 20[mu], and of T. cati 16/u[mu]. The smaller diameter of T. cati served as the only distinguishing character. The diagnosis of Toxocara larvae in tissue sections can be made on the basis of transverse sections at the mid-gut level. In most cases specific identification requires only measurement of greatest diameter and recognition of single lateral alae and excretory column - mid-gut relationships. The application of these findings has permitted the identification of T. canis larvae in obscure nematode infections of man described in earlier publications.