Infective larvae of Trichostrongylus calcaratus, T. axei, T. colubriformis, T. affinis, Obeliscoides cuniculi, and Longistriata noviberiae were unable to penetrate the intact skin of the rabbit and establish infection when precautions were taken to prevent the rabbit from ingesting larvae from the skin surface. With the exception of L. noviberiae, these trichostrongyloids also failed to penetrate rabbit skin in in vitro tests using larvae of Ancylostoma sp. as positive controls. The literature indicates that few species of trichostrongyloid parasites have the ability to penetrate the skin of the host and establish infection. Yokogawa (1922) found that Heligmosomum muris (= Nippostrongylus braziliensis) penetrated the skin of rats and established infections proportional to the number of larvae applied. Sarles (1930, 1932) and Stoll (1932) infected rabbits with Trichostrongylus calcaratus by placing the infective larvae on the skin. Schwartz and Alicata (1935) were able to infect white mice with Longistriata musculi by placing the infective larvae on the skin and allowing the water to evaporate. Gupta (1963) was able to establish percutaneous infection by placing larvae of Molineus barbatus on the skin of ferrets. Using the in vitro test, Gupta also found that the M. barbatus larvae penetrated mouse skin. At this laboratory, preliminary attempts by the present author to establish percutaneous infection with T. calcaratus larvae were unsuccessful. Consequently, controlled experiments were conducted to test the ability of T. calcaratus, T. axei, T. colubriformis, T. affinis, Obeliscoides cuniculi, and Longistriata noviberiae third-step larvae to penetrate the skin and establish infection in rabbits. MATERIALS AND METHODS Twelve experiments were conducted between 1962 and 1964 to determine if Trichostrongylus Received for publication 21 September 1964. calcaratus and other trichostrongyloid larvae could effect skin penetration and establish infection in domestic rabbits. In each of the tests, the controls were given oral inocula containing the same numbers of larvae administered to the test rabbits by subcutaneous injection or by direct application to the skin. The different methods of infection and exposure were as follows: (a) Oral infections were given by placing the rabbits on their backs and pipetting the larvae into the pharynx. ( b) Subcutaneous injections were made either on the abdomen or the back, after clipping the fur to a short stubble. The larvae, in 1 ml of water, were injected under the skin with a 5-ml syringe and a 20-gauge needle. (c) Skin applications of infective larvae were made on the abdomen or the back after clipping the fur as in (b). The length of skin exposure to infective larvae was altered in the various experiments, ranging from 15 to 75 min. In some test groups, coarse charcoal was added to the moist skin during the exposure period, assuming that traction (Spindler, 1933) might play a part in the penetration of the skin. In some groups, the skin was washed with 70% ethyl alcohol following the period of exposure. In seven of the experiments, a plaster cast was applied ar und the body to enclose the test area to prevent the rabbits from ingesting larvae from the surface of the skin. A plaster cast was also used with one group of rabbits given subcutaneous injections of Trichostrongylus calcaratus larvae. To apply the plaster cast following the exposure period, a 3 by 3 inch bandage was placed on the skin over the area of larval application, and cheesecloth was wrapped around the abdomen and thorax for padding. Strips of cheesecloth, impregnated with plaster of Paris and loosely rolled, were moistened in warm water and wrapped around the midregion and chest. Except for the front legs, the cast covered the entire body from the cervical to sacral vertebrae.
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Apr 30, 2018
Raquel Martins 
Open Access
